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Processed Modernity: Cooking Ingredients and the Materiality of Food

In this paper I examine the meanings and values articulated through the use of preserved and (ultra)processed foods in everyday cooking in Mérida, Yucatán. Most studies on the practices deployed in the kitchen have tended to focus on cooking instruments and appliances, as well as on the part played by cookbooks and other instruments in the reproduction of culinary knowl-edges and practices. In contrast, here I focus on the very ingredients used in by cooks, arguing that through their materiality and their aesthetics, cooking ingredients contribute to the objectification of local values. The choice of ingredients by one or another cook expresses values such as “modern” and cosmopolitan, and simultaneously support claims of “authenticity” and “tradition,” and thus are lived as constitutive of regional identity. The use of preserved and processed foods is a common practice in Yucatán’s domestic and restaurant kitchens, which, as elsewhere, has historical grounds. There have been in the city of Mérida, since the turn of the twentieth century, industrial plants making beer, cookies and crackers, vegetable oils, soda drinks, chili pepper sauces, and recados (different pastes of spices). More recently, local industries have begun to package local dishes to sell them frozen, canned or vacuum-packed in plastic containers. I argue that these ingredients are important in transforming the local taste of and for Yucatecan food, and that, as objects that receive and give meaning to regional culinary culture, they become an important locus for the discursive and praxis-based negotiations of local forms of “modernity.”

Introduction: the Routinization of Industrialized Foods
In October 2019 I visited a new store specialized in lamb cuts. Next to the counter where they keep the frozen meat, a small box displayed small packages (100 gr each) of vacuum packaged cochinita pibil and lechón en relleno negro. The former is a long-established dish in Yucatán, while the latter is a recent innovation on the recipe of lechón al horno. Each of these individually sized pouches contains a portion of a meal that correspond with "traditional" recipes for which recados exist. Both packages list only natural condiments and no artificial preservatives, color or flavor enhancers. Recados are a local combination of spices, herbs and flavoring and thickening ingredients (usually garlic and the juice of Seville oranges) used to convey the "correct" flavor of a meal, much like Oaxaca moles and Indian masalas. For example, lechón al horno (baked piglet) is supposed to be piglet baked in an oven -although piglets are difficult to acquire, and cooks are constrained to use pork meat. Cooks marinate the meat with the juice of Seville oranges, and a recado made grinding black peppercorns, garlic, salt, oregano and bay leaves. After marinating for several hours, they bake the meat along with some guano leaves (Thrinax radiata) for aroma. Cochinita pibil is pork cooked in a pit oven (locally called pib). Cooks previously marinate the meat for several hours with a paste made with the juice of Seville oranges, achiote (annatto), black pepper, cumin, nutmeg, onion, garlic, and depending on the cook, with ground allspice peppercorns, cinnamon, and cloves (see Rodriguez, 2015, pp. 58-59) 1 . After wrapping the meat with banana leaves cooks place it in the pit oven, covering it with branches and leaves, and bake it for eight or more hours. 2 1 Most, but not all the ingredients I have listed are found in Rodriguez's cookbook (2015). 2 Recipes may vary from cook to cook. Some may use or omit one of the ingredients, but still, the taste must be alike and recognizable. Sometimes variations are introduced because of fluctuations in access to ingredients. For example, despite its local importance and production, sometimes coriander seeds are not easy to find. Illustrating these variations, a cook in a small city in the northeast of Yucatán told me he uses small amounts of achiote in preparing lechon. Despite this unusual ingredient, he says his customers like it, and some have told him they prefer his rendition over other more "traditional" formulae. The company, named Maya Foods, began processing and vacuum packaging these dishes in small pouches. In a newspaper interview they stressed values associated with modern foods: they assure that their meat is hygienic, free of bacteria and other living microorganisms, and most important, they claim to have improved the process, making the meat more appealing (they point out that early attempts to can cochinita pibil by other companies turned the meat into a paste, instead of the texture of shredded meat -similar to pulled pork) (Progreso Hoy, Oct. 8, 2018. See also the Mayan Foods company's website at: https:/ /www.mayanfood.com.mx).
Variations in a few of the ingredients transform similar dishes into locally discernible ones. More often, cochinita is made with achiote, lechon is not. Allspice peppercorns in cochinita impart the aroma and flavors of cinnamon, nutmeg, and cloves, missing in lechon. Banana leaves and guano leaves also add different aromas; and baking the meat (in both cases pork and not piglet) in either a pit oven or a bakery oven result in different textures. In principle, the cook must use the "right" recado, otherwise his or her dish will taste differently of what all consumers expect. In this context, "lechon in relleno negro" is a new urban development. I have found people who say they like this new version, and suggested the best places to find it, but others have said to me that don't even consider tasting it, preferring the established, "traditional" style. 1 These differences in flavor, aroma, texture, color, are the result of using recados, well-known spice pastes that should make us pay attention to the materiality and meaning of edible ingredients, especially those of spices and condiments. I have found a similar response to different "innovations." For example, queso relleno (stuffed cheese) is the emptied shell of an Edam cheese stuffed with ground pork mixed with capers, saffron, chopped sweet green pimientos, onion and tomatoes, and ground allspice peppercorns. One restaurant introduced for lent days the same cheese stuffed with cazón (hogfish), and friends who tried it told me it was out of curiosity, they liked the taste, but prefer the "traditional" version. Although vacuum packing these meals in plastic pouches may seem an insignificant practice, it signals a small, but apparent incongruity: despite tacit references to a concern for "natural," "organic," and "traditional" ingredients, the portions of cochinita and lechon are sold in plastic pouches. This seems to be almost a trivial fact, except that it is precisely its apparent insignificance that heightens the routinization and the widespread everyday social acceptance of industrialized edible goods. If vacuum packaged meals in plastic seem ordinary and inconsequential, they coincide with other "trivial" practices that are indexical of the routine acceptance of industrialized food. For example, some five years ago, at a birthday party, I found that our hosts served fruit salad sprinkled with phosphorescent red and green salts. I was surprised, but younger guests explained to me that this is not a new practice. People at the table said to enjoy the citrussy flavor of the salt and the almost effervescent hotness of the chili pepper. For several decades prior to this party, a fruit salad (xek in Maya language) -made with green fruits such as mango, along with slices of bananas, pineapple, Valencia oranges, small San José oranges (Citrofortunella mitis), and jicama -has been served as a snack at parties. They were usually sprinkled with ground dry red chili peppers (chile de árbol, Capsicum annuum L.), salt and lime juice. Today, the dressing often includes chem-ical color and flavor enhancers as well as, very often, Monosodium Glutamate (MSG). Several brands are widely available to enhance the fruits' flavors. Many friends, both in Yucatán and in Mexico City have told me that they enjoy the flavors of these artificially colored and flavored salts.
Yucatán consumers have grown used to the flavor and texture of canned ingredients (Ayora-Diaz, 2014). Several local friends in Yucatán, including some who claim to be "foodies," have told me that they find no discernible difference between the flavor of freshly made refried and black beans stew, and the flavor of their canned versions: "they taste like the real ones" -although some have confessed that they need to "correct" them adding fried onions, fresh epazote leaves, and chicken stock cubes, rich in MSG. Consumers tend to see (and defend) canned, industrially processed goods as important relief in their busy contemporary life. Likewise, I have found many men and women who have praised industrially processed and ultraprocessed foods as means to save money and time in their everyday chores, especially so when they are single mothers or when they must fulfil their roles as wives, mothers, and in addition work outside their homes. They often defend their use of these canned and preserved ingredients and meals highlighting their convenience, hygiene, price, and ready availability. Thanks to these products they can, in a short time, put a whole meal together.
Drawing from the texts of classical economists, Robin Leidner (1993, p. 1) discusses the routinization of work in fast food chains. She argues that work is routinized by fragmenting tasks and making them repetitive. This production strategy leads to product uniformity, and this logic is subsequently transferred to the relationship between workers and service consumers, and then to consumers who, in general, come to accept this mode of interaction as "natural." In this chapter I am concerned with the routinization of flavors and taste as they are mediated by mechanisms of repetition and fragmentation that, as I have argued, lead to the "naturalization of taste" (Ayora-Diaz, 2012). This is a lasting global trend that has led to what Winson (2013) has called the industrial diet. Here I argue that these ingredients and meals are important elements for local material culture that contribute by constructing, but also in undoing regional identity. To support this argument, I stress the Yucatán people's appropriation and naturalization of modern values that support the consumption of industrialized ingredients and meals. In this sense, the favorable disposition toward processed and ultra-processed foods becomes "naturalized" through its repetitive consumption and the appropriation of corporate reasons (convenience, hygiene, price) that justify judging them with positive values (Shove, 2003).

The Materiality of Cooking
While usually classified as immaterial culture, cooking and food have a materiality that we need to recognize to better understand the material foundations of the relationship between cooking, eating and identity. In discussing the importance of social and cultural matters on material culture, Daniel Miller emphasized the importance of looking at the materiality of the world and, at the same time, warned against fetishizing it (Miller, 1998). In a later text, he suggested (2005, loc. 147) that "objects are important not because they are evident and physically constrain or enable, but often precisely because we do not 'see' them." Along those lines, Lemonnier (2012, pp. 11, 14) has argued that anthropologists must pay attention to mundane objects, because, despite their apparent ordinariness, they can, in some circumstances, and for specific groups, play an important part articulating practices, ideas, cultural values and social relations into meaningful things. For example, for most Mexicans corn tortilla is an everyday staple, but others (for example those using the Michoacan Paradigm, recognized by UNESCO, for nationalist purposes) see it as an object charged with symbolic, historic, cultural importance that needs to be defended. Miller (2010, pp. 6-7) also suggests that by looking at "stuff" (humans included), that is, at everyday objects and their relational and contextual meanings, we can acquire a deeper understanding both of persons and our social arrangements and aggregates. I believe this is the case in point for food production and consumption. Often, the production of meals is a hidden process in domestic and restaurant kitchens -although for some customers the spectacularization of cooking is perceived as an asset in some restaurants, and for some types of food (like the Japanese teppanyaki). However, often we do not see (or are uninterested in) what technologies are used to make our food, nor we witness the selection and use of ingredients -other than when watching TV shows. When we consume a meal, we tend to pay attention to its aesthetic qualities: colors, aroma, flavor, textures, or composition on the plate, but many people are unable to identify the ingredients in their meal. Because they are usually ground, fried, stewed, ingredients in sauces or stews, for example, may be concealed from our sight and we may like or dislike the flavors or aroma, but we are not aware, for example, of which ingredients were used to make it, nor of the instruments employed in their production; or whether, for example, before searing the steak in a high temperature oven or a coal grill, the chef precooked it in a sous vide. And yet, the technologies used in the kitchen are often an important locus for studies of the materiality of food.
The importance of these objects is reflected in many studies. For example, all 39 chapters in the volume Food and Material Culture (McWilliams, 2014) focus on the tools and instruments used for cooking, serving, or consuming meals. Even the two chapters on etiquette look at the way in which, and how, different utensils were used at the table (Riley, 2014;Sutton, 2014). These objects have been the focus of many publications on the material culture of domestic kitchens: How were they furnished? What appliances could be found at home in different historical periods? How was/is the gendered categorization of kitchen work related to the availability and everyday use of the appliances, instruments and utensils found in the kitchen and the table? Consequently, objects, instruments, and tools such as knives, pots, spoons, different types of ovens, fridges, tableware, receive privileged attention in seeking an understanding of how the meanings of these mundane objects is negotiated among different agents (Cockburn & Dilic, 1994;Freeman, 2004;Johnson & Lloyd, 2004;Miller, 2001;Pink, 2004). Similarly, in the volume Cooking Technology. Culinary Transformations in Mexico and Latin America (Ayora-Diaz, 2016), most authors examine the part played by different cooking instruments, tools, and appliances in shaping the meaning of the food cooked and shared in different contexts.
Although several chapters in the latter volume highlight the use of specific ingredients in making Mexican foods, only two chapters explicitly examine the part played by ingredients in the elaboration of meals (in addition to the use of different appliances). Ayora-Diaz (2016a) defines ingredients as a technology (because of their techno-scientific nature) and thus as meaningful material elements in meals (2016b). On her part, Pérez (2016) recognizes the importance in using different varieties of chili peppers to render and distinguish among different varieties of Oaxaca moles. In this context, I argue that the use of different ingredients as meaningful markers of the identity of a food, should make us examine, in addition to other technologies, the presence of different types of ingredients as part of the kitchen and of cooking material culture. Thus, during his examination of the transformation of food into waste, Evans (2014) was already pointing at the use of ingredients in the kitchenalthough he focused on the cultural construct of waste rather than on the meaning of ingredients themselves.
Ingredients, I argue, are an important part of the materiality of food that draws from and gives meaning to the everyday practices of cooking and food consumption, and are turned into a node in which cultural values, social practices and forms of cultural representation converge. "Natural" and "organic" ingredients are the product of agricultural and farming practices in which seeds are planted, grown, harvested, processed (dried, smoked, milled, salted, toasted); animals are inseminated, their offspring are fed, grown, and then, after killing them, processed cutting them in meaningful parts (sirloin, New York, etc.), processed (salted, smoked, dried, pickled, salted, etc.). Then they are placed in the local, regional, national, or international market, where place of origin may add or decrease their value (Parasecoli, 2017). Consumers buy them because they favor their appearance, flavor, aroma, and texture. Despite their everydayness, they are important material elements in our food, and they are marked by values (moral, economic, political, symbolic) ranging from local to global ones. The choice of ingredients for cooking, despite their apparent "mundane" existence, is instrumental in underlining the identification of subjects with different cultural "identities."

Ingredients for "Tradition" and Change
For over two decades I have been studying the cooking and gastronomy of Yucatán, a Mexican state in the eastern peninsula of the same name. As I have been arguing, it is the preference for certain ingredients and their combination that root the identity of regional food, and has become, along with other forms of cultural representation, an important element in the foundation of the (hegemonic) identity of the state (Ayora-Diaz & Vargas Cetina, 2010;Ayora-Diaz, 2010Vargas Cetina, 2017). While the taste of food may seem to have an abstract and immaterial existence, taste is derived from the use of material ingredients and from the use of cooking instruments that achieve meals with the preferred aesthetic set of properties. Thus in contrast to Mexican predilection for beef, Yucatecan cooks prefer (in order): pork, turkey and chicken, fish and seafood, and beef. Most iconic dishes from Yucatecan gastronomy are based on pork or use it along other meats. For example, turkey is stuffed with ground pork, both in its 'white' or 'black' sauce (relleno) versions. Puchero, a Sunday stew consumed during family gatherings, in its fancy version combines pork, chicken and beef along with seasonal vegetables, rice and pasta. Cochinita pibil and lechon al horno are available, every day, at street food stands and popular markets. Also, like in other Caribbean islands, and in the Mexican region of Veracruz, black lima beans are favored over other colors (the different colors are associated with different textures, aromas, and flavor). In Yucatán, among the most common spices we find combinations of annatto, all spice, black and white peppercorn, cinnamon, cloves, coriander seeds, and cumin; common herbs are bay leaves, chaya, cilantro, epazote, oregano, parsley, and thyme; garlic, red and white onions, and radish are often used in cooking or as garnish; chili peppers such as habanero, dry red (Capsicum annuum L.), max (C. annuum var. glabriusculum) and x'kat (C. Annuum I) are used to flavor stews and as side dishes; Key and Persian limes, limas (Citrus x limetta) and Seville oranges are common additions to garnish the food, and to marinate meats; avocado, cabbage, tomatoes, carrots, potatoes, sweet potatoes, chayotes (Sechium edule), and plantains can be added into stews or served as side dishes; and rice or noodles can be side dishes as well. Evidently, none of the listed ingredients is exclusive of Yucatecan cooking and gastronomy. What makes them part of the regional cuisine is the form in which they are assembled, their combinations, their aesthetic effects over the colors, aromas and flavors of the meal.
Based on this recognition I have moved from the notion of the "field" to the concept of "assemblage." The former, drawn from Bourdieu (1977), has spatial and temporal connotations that may that suggest that the 'gastronomic field' is unchanging and self-contained. While the concept has advantages in understanding how different social actors might work toward creating and establishing a welldefined gastronomic "tradition," in everyday life, cooking practices change all the time on account of the continued interaction among multiple culinary codes in local, translocal and global-local scales (Ayora-Diaz, 2020). In contrast, the concept of "assemblage" (de Landa, 2006(de Landa, , 2016, privileges what Manuel de Landa calls relations of exteriority. Here, these relations suggest that the components may be extracted or aggregated into any assemblage without losing their identity. Cumin is assembled with other ingredients in other Mexican regions, however, the specific way in which it is assembled with other ingredients in the Yucatán region supports the identity of Yucatecan food. When used in other cuisines is not seen as a "Yucatecan" ingredient. In addition, the gastronomy of Yucatán draws its taste from the use of multiple ingredients originated in Europe, the Middle East and Asia, but these ingredients, through time, have become localized during the creation of specific regional recipes and through local cultivation. Recipes adopted from elsewhere became adapted to Yucatecan taste. They have become part of the Yucatecan culinary and gastronomic assemblages. 1 In the same manner, some Yucatecan foods have detached from the Yucatán region, so that today it is possible to find them re-signified and reinterpreted in different locations. For example, once I ate a sandwich of cochinita pibil at the O'Hare Airport in Chicago at Rick Bayles' Tortas La Frontera, and although I found the food tasty, I found its flavor very different from the Yucatecan version of the meal. As Wilk (2019) argues, the US consumer perceives it as "Yucatecan," even though it does not meet local standards in its place of origin.
In this sense, spices, herbs, meats, instruments, appliances, and procedures, become movable parts of different assemblages, each with its own "identity," which at the same time are part of other, sometimes larger, assemblages. The mobility of people is usually accompanied by the mobility of cooking technologies and edible goods. As detachable parts of culinary assemblages, they become instrumental in the local, ethnic, and national transformation of cooking and eating practices. 1 I should note here that the theory of assemblages encompasses the concepts of territorialization, deterritorialization and re-territorialization. The first refers to those processes that make a practice, set of cultural values, a cuisine, co-extensive with a society and territory. The second designates the processes that question, challenge that co-extensiveness, for example, the fragmentation of cooking practices along ethnic, national, or regional codes that, multiplying within a territory lead to the weakening of the first processes. And the third refers to the efforts made by individuals, groups and/or institutions to reaffirm the co-extensiveness of a gastronomy and a "people." Despite what these terms suggest, their presence is not sequential but simultaneous, and they are multi-scalar (Ayora Diaz 2020).

Recados and the Culinary-Gastronomic Assemblage of Yucatan
Ingredients are key material objects employed to achieve the taste of Yucatecan food. The way they are put together during the preparation of a meal is very important to bring a recipe into existence as a locally recognizable and meaningful dish. The reproduction of taste is achieved through the transmission of culinary knowledge from one generation to the next, and from one neighbor to another. It is by sharing this knowledge that a culinary-gastronomic "tradition" becomes coextensive with an inhabited space. During the nineteenth century, literacy was uncommon, and this culinary knowledge was mostly based on the bodily imitation of practices and on the oral transmission of instructions. Still, historically, cookbooks have long been important in maintaining culinarygastronomic codes and culinary-gastronomic identities (Bower, 1997;Floyd & Forster, 2003). Spain granted independence to the peninsula of Yucatán in 1821 (Campos García, 2002). Only eleven years later, a Merida woman published a culinary guide (prontuario) in which she provided housewives with cooking guide (Aguirre, 1832). As most cooking texts of the time around the world, the instructions were very general, and unlike today's cookbooks, they were probably used as mnemonic devises dependent on the cooks' , their relatives' or their customers' experience and memory of taste. It was later, at the end of the nineteenth century, when the Yucatán elites were enjoying the benefits of the regional economic boom stemming from the henequen plantations, that new regional cookbooks emerged reflecting the newly acquired wealth, including recipes of meals from around the world. Recipes that today are recognizable as iconic within the Yucatecan gastronomic canon, were then in an inchoate stage. At the end of the nineteenth century, specific combinations of spices and condiments were prescribed to prepare recipes for regional meals. The assemblage of spices began to be codified, but they were not yet named recados. I propose that the taste of Yucatecan food is the product of an assemblage of multiple objects charged with local meanings. Aguirre's and later cookbooks are themselves material objects, sometimes in view of everybody, sometimes hidden in drawers in the kitchen. Women collect recipes in handwritten notebooks, sometimes copying their favorite recipes from friends' or relatives' cookbooks, sometimes inserting newspaper clippings between pages. The recipes in these notebooks include references (implicit) to the cookbooks they were borrowed from, but they list as well other material objects considered necessary to cook a meal correctly: types of pans, skillets, and other coking instruments. They advise on the use of open fires or ovens, on boiling or roasting or frying. Lastly, but more importantly, they list ingredients that the cook, domestic or professional must use to cook a specific meal. Today Yucatecan cookbooks can be seen moving away from general instructions regarding the use of ingredients for the domestic manufacture of recados. Recipes for recados, in turn, have changed from the simple provision of the list of ingredients, to their "modern" version in which the author prescribes exact measurements of the ingredients require to prepare them.
Yucatecan cooking employs several recados, and each is specific for one given dish. Hence, each recado results from the combination of different quantities of spices and other ingredients. For example, the recados required for cooking puchero, turkey in black stuffing, turkey in white stuffing, turkey in escabeche, pork pibil, baked piglet, ajiaco, and steaks, to name just a few of them, are different from each other. The use of each recado imparts on the meal the flavor, aromas, and colors Yucatecans associate with each recipe. Although I have examined several cookbooks published since the end of the nineteenth and beginning of the twentieth centuries, many are no longer available, and those that are, are those that were popular and widely used, leading to numerous reprints. Still, in two important cookbooks from the end of the nineteenth century, there is no mention of recados. However, the cooking instructions list the spices and condiments that today define the taste of iconic Yucatecan meals (Navarrete Arce, 1898; Rendón de García, 1889). It was until 1940 that the name recados appeared in two widely available cookbooks -at least at that time (Hernández Fajardo de Rodríguez, 1940;Ruz viuda de Baqueiro, 1940). 1 In the latter cookbooks, recados appear prescribing the assemblage of specific ingredients in precise proportions. Some recados may appear to be similar to others regarding the spices included, but they differ in proportions and on the addition of one or more spices, changing thus the aesthetics of the meal in which they are used. 1 These were self-published cookbooks. The authors and later their descendants published several reprints through the decades. However, by the time I began my research on the regional food of Yucatán, they had become difficult to find. The descendants of Hernández Fajardo told me that the recipes were too elaborate for today's rhythm of life, the demand had declined, and they decided not to reprint it anymore. The more recent cookbook by Will Rodriguez (2015) includes the recipes for eight different recados.
As an illustration, the following cooking instructions were written at different times for the same meal, relleno negro (turkey with black stuffing). There are coincidences and variations. But it was the 1940 cookbook that uses the term "recado," and provides two lists of these spice blends (one in each volume). Relleno negro, is the name given to turkey stuffed with ground or minced pork and boiled eggs. Today it can be found, every day, at restaurants, but it used to be the preferred meal at weddings and baptism ceremonies. It is one of the very few dishes in Yucatán cooking that may be spicy hot. In the following paragraphs I am quoting only the portions of recipes in which the ingredients are listed: RELLENO NEGRO DE VALLADOLID. [You] need to burn an almud [a variable measure. Between 1.75 and 5.68 liters] of chili peppers. Soak it in water for two days, changing the water periodically. After taking them from the water they should be ground very thick with a head of garlic, a large piece of achiote paste, ten or twelve oregano leaves, one spoon (soup spoon) of black pepper, and twelve allspice peppercorns. … (Rendón de García 1938García [1889, p. 94).
Gran relleno negro, de Valladolid. To obtain a good relleno, [you] must burn old chili bobo eight days in advance, three almudes, charring them but not like coal; as they are taken from the skillet they must be soaked in salted water, being careful to change the water four times a day and stirring them well with a sieve for the chilies to release their hotness … When it is ready to be served, it is strained and ground with enough achiote, one raw garlic head, and black peppercorns; adding half a cuarta [750 ml] of nixtamal to thicken the chili [sauce] … (Navarrete Arce, 2010Arce, [1910Arce, /1898, pp. 62-63).
RECADO DE CHILMOLE o RELLENO NEGRO 1 kg of dry red [colorado] chile 1 large Tabasco peppercorn [allspice] or two medium size ¼ teaspoon of cumin 1 full spoon of black pepper 1 and ½ spoons of achiote 1 raw head of garlic 5 or 6 oregano leaves The top and seeds of the red chili pepper are removed and [the chili] is charred sprinkling it with alcohol until it turns black, then it is soaked and ground with the recados and everything else; it is dissolved in water and strained … (Hernández F. de Rodríguez n.d. [1940], p. 35).
Like these, most recados combine spices that must be roasted and ground along with (usually) garlic and the juice of Seville oranges. It is the latter two that contribute to reach the consistency of a paste that domestic and restaurant cooks use in the proportions they have learned to reach the aromas and flavors locally expected from each meal. However, there have been progressive transformations in their manufacture that lead to changes in the relationship of local people to regional food and, as I discuss in the next section, to their effects on the expected taste of long-established recipes.

Processing Modernity: Recados and the Transformations of Taste
Recados are an important component for reproducing the taste of Yucatecan food. Iconic recipes are found all over the state, as well as in the neighboring states of Campeche and Quintana Roo. The meals obtained from these recipes have played an important part in the process of territorializing Yucatecan cooking and gastronomy. However, their repetition all over the region consists of a repetition with difference; that is, they are not a repetition of the same, of an identical taste. Ingredients are repeated in each locality, but somewhere cooks use a bit more, somewhere else they use a bit less of different ingredients, and yet cooks strive to maintain the overall structure of the dish. For example, when cooking turkey in black stuffing some family cooks and small handcraft producers of recados may include all the prescribed spices but may choose to burn chili peppers which are less sharp than those preestablished; others, in contrast, may chose habanero pepper to craft their recado, making it an extremely spicy meal. These are important variations, as each corresponds with the taste preferences of different consumers who, despite the differences in recado composition, are expecting to eat turkey in black stuffing. Hence, cooks choose where to buy their recados depending on the flavors they prefer. I have met, for example, people who willingly travel 160 km from Merida to Valladolid just to buy their favorite recados at the popular market, or within Merida, cooks who buy their recados at a market that is on the other end of the city because they do not like the recados in the market near their homes. 1 Recado handcrafters, both those who produce small quantities to sell in the market, and those who make them at home for domestic consumption, must be very careful in their attempts to "innovate," as they would not wish their recados or their food to be rejected or criticized by customers, relatives, and/or friends. Likewise, when making recados, the cook must be careful not to eliminate any ingredient at the base of a recipe. For example, the recado for escabeche de pavo (turkey stewed with pickling ingredients) must be made with salt, black pepper, white pepper, allspice, garlic, and the juice of Seville oranges. The elimination of any of these would produce a different flavor-aroma effect. Nonetheless, gradually, consumers are beginning to neglect some flavors. Some ten years ago, at the public market in Valladolid, I asked the woman selling recados for a small bag of recado de escabeche. She took a small plastic bag from a batch and handed it to me. Next I asked for a bag of recado for steaks. She took another bag from the same batch and handed it to me. When I pointed out that it was the same recado she nodded, 'yes, it is' . However, they are different spice blends. Recado for steaks 1 Making recados at home is not easy, and it is time consuming. Additionally, one must own the right appliances to make them. Achiote seeds are very hard, and they must be first soaked and then pulverized in a mortar, a grinding stone or an electric mill, and burning chili peppers induce fits of coughs within the house and among neighbors. Also, the quantities needed to make them and to prepare meals may well exceed the needs of a nuclear family.
should be a paste made from ground black pepper, salt, garlic and white vinegar. Although the two pastes look alike (dark greyish), their flavor and aroma are different from escabeche, as steak recado lacks allspice, cinnamon, and white pepper. This disregard for their differences has led to the recent creation and widespread consumption of "recado for everything." Both in popular markets (handcrafted), and in supermarkets (industrially processed) it is now possible to purchase recado para todo. Today, a cook's expertise and "hand" are judged partly based on her or his election of recados, and the place to buy them, or by the cook's disposition to make them at home. However, it is also very common to find domestic cooks who use industrially processed recados. If handcrafted ones kept the identity of a recipe while making room for family and local differences, industrially processed recados tend to homogenize the flavor of Yucatecan recipes. They are produced with the aid of large electric grinders, and each commercial brand must keep the rates of different spices fixed and controlled to ensure customers will remain faithful to their products. Also, they must ensure hygienic conditions. These industrially produced recados lead to the homogenization of taste and to the "naturalization" of taste preferences that change, gradually, over time. For example, sometimes I have wondered how in Valladolid consumers accept as "authentic" a rendition of Escabeche de pavo de Valladolid marketed by a local business that specializes in its production. I have found that this business' food resembles little the food as it is still prepared by some domestic cooks. 1 This acceptance, seems to me, stems from the generalized acceptance of industrially processed ingredients and meals. Most consumers cannot afford the time to replicate a recipe and thus adopt adapted recipes to their low income and contribute to routinize the acceptance of homogenized flavors.
There is today a widespread acceptance and adoption of industrially processed ingredients and meals, including recados. Industrialization in Yucatán began following the blueprint of the European industrial revolution, and the industrialization of food took off by the end of the nineteenth century -although the local diet had already incorporated different industrially processed ingredients (Negroe Sierra & Miranda Ojeda, 2007), and alcoholic beverages (Hernández Álvarez & Cámara Gutiérrez, 2019) imported from Europe and the United States. The industrialization of Yucatán began during the 1870s. Food ingredients and beverages became industrialized during the last part of the nineteenth and beginning of the twentieth century as chocolate, sugar, soda drinks, beer and pasta became industrially processed local products (Zayas Enríquez, 1908, pp. 312-313).
Though the first cookbooks where I found instructions for the manufacture of recados were from 1940 (the 7 th edition of Rendón de García, published in 1938, does not include recipes for recados), the first small processing industry, La Anita, began operating in 1913, twenty-seven years earlier, suggesting that even if they were later consigned into print, recados were in use decades earlier before their published appearance. In 1968, another company, El yucateco, launched its own line of regional recado pastes and condiments. Brands have since multiplied: La Carmita, Mi lindo Yucatán, and Del Mayab, recados are found in local markets. Some, like El yucateco and La Anita have expanded into chili sauces into which they add color and flavor enhancers, and food stabilizers. Although each small industry produces a range of recados, those of achiote, relleno negro/chilmole, and 'for everything,' are in greater demand. Most cooks I know indistinctly use one brand or another, and I have not found domestic cooks faithful to any specific brand. Depending on need and availability domestic cooks buy whichever one they find. 1 My mother, who was born and grew up in Valladolid followed a very elaborate recipe: she marinated the turkey with recado de escabeche and the juice of Seville oranges. Then she boiled the turkey but did not thoroughly cook it. After taking it from the broth, she would do a new marinade with the same recado and some white vinegar. Then proceeded to roast on coal whole garlic heads, white onions and xkat chili peppers. After shredding the meat by hand, she would put the meat, onions, garlic, and chili peppers back into the broth. Before serving the meal, she would take out the meat and reserved the broth to cook pasta elbows served as side dish. For garnish she sliced red onions and soaked them in the juice of Seville oranges along with bay leaves and allspice peppercorns. The flavors, aromas, look and textures of this food were significantly different from the boiled chicken that now locally passes as "escabeche." After all, for them, the replicability of the recipe using industrialized recados as time-saving devices, is more important than replicating flavors of the past.
The homogenization of Yucatecan flavor is partly recado-based and coincides with the explosion and fragmentation of the urban foodscape of Yucatán. If, as I have discussed (Ayora-Diaz, 2012), Yucatecan food was hegemonic in the region, since the 1970s there has been a multiplication of food choices: the food of other Mexican regions, from South America and the Caribbean, from Europe, Asia and of US food chains (hamburgers, pizzas, pulled pork, Chinese, sushi, and other fast foods) have relativized the value of Yucatecan taste. Currently, many teenagers and young adults prefer Chinese, Italian, and Japanese food, or hamburgers and fries, over Yucatecan meals. Thus, Yucatecan food, at least among young people, has been displaced as an anchor of regional identity. The nostalgia for flavors of the past is more important for older people. New restaurants are emerging where cooks seek to be recognized for their "innovations" on long established recipes. As one chef explained to me, "We are seeking to attract young customers who will then become more interested in Yucatecan food."

Conclusion: Processed Cooking and Identities
Meals are the material expression of the taste of Yucatán -that is, the taste favored by the inhabitants of the state. In their materiality they assemble historical, ethnic, cosmopolitan, and cultural images and representations. The most common appliances needed to prepare Yucatecan meals are basic and simple, and in urban kitchens I found aluminum and non-stick skillets, as well as pots, casseroles, griddles (comales), knifes, ladles and spoons, blenders, and gas and microwave ovens. Yet, it is the ingredients in the pantry and refrigerator that underscore cooking and eating preferences: onions, garlic, epazote, habanero pepper, oregano, black pepper, bay leaves, chaya, and cilantro are still common. In addition, one finds small boxes of recados industrially processed, bottles of habanero and Tabasco sauce, mayonnaise, canned tomatoes, canned beans, canned tuna, canned jalapeño peppers, and bottles sauces of pico de gallo (or salsa Mexicana), and green tomatillo sauce. Once, a lady my wife and I know was frustrated as she could not find a small jar or can of green sauce, and we told her: 'look, there is tomatillo, onion and garlic over there, why don't you make it?' She replied that she had no time and she just needed a small quantity. It is in this sense that that the ideology of modernity highlights convenience and price (certainly it is cheaper to buy a small can of sauce than to make it) in industrially processed food and ingredients. Despite revelations in newspapers and other media of the adulteration of dry leaves, ground spices, and tuna, for example, modern domestic cooks prefer to rely on canned ingredients. They are convenient, hygienic, last longer, and they are cheaper; one only needs to open a can or a bottle, and the ingredients are ready for enjoyment.
In Yucatán it is common, since the twentieth century, to find women working outside the home. As elsewhere, when women abandoned the kitchen, men did not take their place, neither they shared cooking responsibilities (of course, there are exceptions). As several women confided me in interviews, cooking has become for many a burden. Some said they do not like cooking, but they must do it because they feel responsible for feeding their husbands and children. Others have told me that they prefer to buy ready-made meals to avoid cooking. This spirit has been captured by a cookbook titled Cocina al chingadazo (Cooking in a whack) that recommends women to cook using many processed ingredients during weekdays, and suggest that, on weekends, it is the obligation of husbands to take their wife out for meals, as they have already cooked all weekdays (Arjona Martín, 2006). Using processed ingredients has become routinized, and they today part of the "modern" local diet, displacing its importance in the construction of regional Yucatecan identity.


provenance: AgriculturalAndFoodSciences,2022-2022-Agricultural And Food Sciences-2022.jsonl.gz.gz

text:
The intervening effect of l-Lysine on the gel properties of wheat gluten under microwave irradiation

Graphical abstract

Introduction
Wheat gluten (WG) is a kind of protein with unique characteristics in wheat flour, widely used in the field of food processing, such as noodles and bread (Hoehnel, Bez, Petersen, Amarowicz, Juskiewicz, Arendt, et al., 2020;Sun, Chen, Hou, Li, Qian, Zhang, et al., 2021). Gel properties are important functional characteristics of WG, protein gelation is a process in which denatured protein molecules aggregate to form an ordered protein network structure. The protein molecule is induced to unfold from the native state, thus the groups originally wrapped inside the molecular chain are gradually exposed. The stretched peptide chain is partially folded in different conformation, and the denatured protein aggregates to form macromolecules. Therefore, the three-dimensional network structure is constituted, which wraps water and other substances, and finally the gelation is formed (Bhattacharya & Jena, 2007;Tanger, Müller, Andlinger, & Kulozik, 2022;Xiao, Li, Liu, Peng, Wang, Wang, et al., 2020). All the dough-related flour products are related to the textural characteristics of WG. In the process of converting the water-wheat flour mixture into dough, WG is solvated with water. Moreover, under the action of directional shear force and heating, the disulfide bonds and secondary bonds (hydrogen bonds, hydrophobic bonds and ionic bonds) in polypeptide chains were broken and recombined to form ordered spatial network structure. WG protein built the backbone of the dough and formed three-dimensional gluten network through chemical interactions, thereby combining starch particles, fat and other ingredients stuck in the gluten network (Li, Zhu, Yadav, & Li, 2019). However, native WG consists of globular gliadin and glutenin, whose main secondary structures were β-sheet with high bond energy. The compact molecular structure and poor hydrophilicity of WG limit the improvement of its functional properties, especially the further improvement of gel properties. Moderate physical or chemical modifications are ways to develop WG protein gel potential during food processing.
In addition, the heating process is crucial to obtain WG gel with good quality, and discrepant quality of WG products might be obtained using different heating treatments. The traditional water bath (WB) heating method based on conduction, it has the problems of low energy efficiency and environmental pollution (Wang, Muhoza, Wang, Feng, Xia, & Zhang, 2019). Moreover, the thermal transmission from the outside to the inside of the traditional WB heating method reduced the gel properties of WG due to the slow conduction rate. As a green processing technology, microwave (MW) heating has the characteristics of high energy efficiency and pollution-free. Furthermore, MW directly affected the electrostatic interaction and positioning of charged groups in protein molecules, which interfered with the electric field distribution and electrostatic interaction in amino acid residues. The alternating electromagnetic field caused charge separation, thereby changing the secondary and tertiary structure of the protein (Dong, Wang, & Raghavan, 2021). MW heating has been widely used in many food processing fields, especially in changing protein gel quality. But the protein aggregation produced by the rapid heating of the MW causes the quality of the protein gel to deteriorate (Fu, Hayat, Li, Lin, Xu, & Wang, 2012). Because the WG protein molecules are in an enclosing state at the initial heated stage, it is difficult for MW to fulfill its function to unfold protein. Cao et al. found that when MW was used to replace the first stage (40 ℃ for 30 min) of the two-stage WB heating of surimi, the gel strength was significantly lower than that of the WB heating (Cao, Fan, Jiao, Huang, Zhao, Yan, et al., 2018). In addition, the action of the MW alternating electric field makes the molecular dipole moment oriented, which is inclined to cause amorphous aggregation of the protein, therefore, the formed gel appears to be harder rather than more elastic. Due to the special heating mode of MW, adding a dielectric substance into the system to control the state balance during the gelation is an effective approach to regulate and control ordered aggregation of WG under MW irradiation.
L-Lysine is a weakly alkaline amino acid, which can inhibit the disordered aggregation of protein. As a small molecule additive, L-Lysine is often used to improve the solubility and gelation characteristics of proteins in food systems. L-Lysine is the first limiting amino acid in WG, involved in the synthesis of various proteins such as skeletal muscle, enzymes, serum proteins, and peptide hormone. Additionally, L-Lysine significantly increased the solubility of myosin and the emulsifying stability of meat products (Li, Li, Zhu, Ning, Cai, & Zhou, 2019;Zhu, Ning, Li, Xu, Zheng, & Zhou, 2018). After adding L-Lysine, the electrochemical characteristics of the protein system in the MW field will change regularly with the concentration of L-Lysine, especially the conductivity of the system increased significantly (Cao, Li, Fan, Wang, Zhu, Huang, et al., 2021). However, Liao et al. studied the dielectric properties of lysine aqueous solution. The results demonstrated that the dielectric loss (ε") of the solution was unchanged with the increase of L-Lysine concentration (Liao, Raghavan, Wu, & Yaylayan, 2003). Generally, the addition of dielectric will enhance the dielectric loss of the system, and the dielectric properties will change with the increase of temperature (Feng, Xue, Li, Wang, Yang, & Xue, 2015). The aforementioned research proved that owing to the directional rearrangement produced by L-Lysine during the dipole polarization, L-Lysine can serve as a dielectric buffer in the alternating electromagnetic field of MW.
Therefore, the purpose of this research was to regulate the orderly aggregation of WG under the action of the MW field through the dielectric buffer effect of L-Lysine to enhance the quality characteristics of WG protein food. This work could be meaningful for food industry to have an insight into the molecular interaction of WG under the MW irradiation and provide a novel approach for the development of new applications of WG in the agricultural food industry.

Materials
Commercial WG flour was purchased from Anhui Ante Food Co., Ltd (Suzhou, Anhui, China) with a protein content of 77.35 ± 0.97% (The total protein contents were determined with a Kjeltec8400 (FOSS analytical instruments Co. Ltd, Denmark)) on a dry matter basis and 7.27 ± 0.04% moisture. L-Lysine was purchased from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China). Page Ruler Prestained Protein Ladder was purchased from Thermo Scientific (MA, USA). 5, 5-dimercapto-2, 2-dinitrobenzoic acid (DTNB) was purchased from Yuanye Biotechnology Co., Ltd (Shanghai, China). The 8-Anilino-1-naphthalenesulfonic acid hydrate ammonium salt (ANS) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd (Shanghai, China). All the other chemical reagents were of analytical grade unless otherwise specified.

Preparation of WG gels
WG was dispersed in deionized water to a concentration of 16% (w/ v) and L-Lysine (0%, 0.1%, 0.125%, 0.15%, 0.175% and 0.2%, w/w, referred to GB14880-2012) was added to WG dispersion. WB heating treatment: WG sample dispersion was incubated at 90 ℃ for 30 min in WB. The time-temperature history of the heating process was recorded by the thermocouple (Fig. S1). MW heating treatment: the fiber-optic probe attached to the computer MW solid-liquid phase synthesis/ extraction instrument (Model XH-200A, Xianghu, Beijing, China) was inserted into the WG dispersion, the temperature curve recorded from the WB heating was programmed to ensure an equivalent heating rate. The reactions were stopped by transferring the samples to the ice water for 30 min after heating. The prepared WG gels were stored at 4 • C (Wang, Liu, Luo, Li, Mu, Zhao, et al., 2019). Part of the protein gels was used to freeze-dry for subsequent testing.

Determination of gel strength
The gel strength of WG gels was measured by using TA.TOUCH Texture Analyzer equipped with a P/0.5 diameter probe (BosinTech, Shanghai, China). The parameters were set as follows: pretest speed 2.0 mm/s; post-test speed 2.0 mm/s; test speed 1.0 mm/s; trigger force 5.0 g; the samples were pierced to depth 10 mm and the maximum force of the sustained compression was defined as the gel strength value (g). The experiment was conducted in five replicates (Xiao, Liu, Wang, Jin, Guo, Liu, et al., 2020).

Determination of water holding capacity (WHC)
Slices with the mass of 2-3 g (M 1 ) were cut from the middle part of the prepared WG gels. The slices were then wrapped in filter paper in 50 mL centrifuge tube and centrifuged at 8000 g at 4 ℃ for 15 min in a CR22N centrifuge (Hitachi, Tokyo, Japan). The filter papers were removed and WG gels were weighted (M 2 ). Each experiment was repeated five times in parallel . The WHC was calculated as follows: (1)

Determination of chemical interactions
The reagents used to break certain types of bonds were as follows: 0.05 M NaCl (PA); 0.6 M NaCl (PB); 0.6 M NaCl + 1.5 M urea (PC); 0.6 M NaCl + 8 M urea (PD). It was the difference in protein concentration that indicated the existence of ionic bonds (difference between PB and PA), hydrogen bonds (difference between PC and PB), hydrophobic interactions (difference between PD and PC). The sample (0.3 g) was homogenized in a 5 mL reagent, and reacted at 4 ℃ for 1 h and then centrifuged at 5000 g for 15 min. The soluble protein content was determined by using the bicinchoninic acid protein assay kit (Beyotime, Shanghai, China) (Cao, Li, Luo, Mu, Zhong, Jiang, et al., 2017).

Determination of free sulfhydryl (SH) groups and disulfide bonds (S -S) content
Prepared protein solution: protein samples of 75 mg were dissolved in 1 mL Tris-Gly (0.086 M Tris, 0.09 M glycine and 0.004 M EDTA, pH 8.0), mixed with 4.7 g GuHCl, and diluted to 10 mL with Tris-Gly. To determine the free SH groups, the prepared protein solution of 1 mL was mixed with 4 mL urea-guanidine hydrochloride (8 M urea and 5 M GuHCl in Tris-Gly) and 50 μL of Ellman's reagent (4 mg/mL in Tris-Gly) and incubated for 30 min in dark condition. The absorbance of the solution was measured at 412 nm with a UV-2800A spectrophotometer (UNICO, WI, USA). To determine the total SH groups, the prepared protein solution of 1 mL was mixed with 4 mL urea-guanidine hydrochloride and 50 μL of 2-mercaptoethanol, then incubated at 25 • C for 1 h. Subsequently, trichloroacetic acid (12%, w/v) of 10 mL was added to the mixture and incubated at 25 • C for 1 h. The solutions were then centrifuged at 5000 g for 10 min. The process was repeated three times. The precipitate was dissolved in 10 mL urea-guanidine hydrochloride with 40 μL Ellman's reagent, the mixed solution was incubated for 30 min in dark condition, and then recorded the absorbance at 412 nm (Zhang, Chen, Liu, Mei, Yu, & Kan, 2020). The buffer solution without proteins was used as the blank control.
Where: 73.53 = 10 6 /(1.36 × 10 4 ), 1.36 × 10 4 was the extinction coefficient for Ellman's reagents/ (L/ (mol × cm)); A 412 was the absorbance value of the protein sample at 412 nm; C was the protein concentration (mg/mL); D was the dilution factor of the sample solution, where the free sulfhydryl groups dilution factor was 5.02 and the total sulfhydryl groups dilution factor was 10.

Determination of surface hydrophobicity (H 0 )
H 0 : The protein sample was dissolved in phosphate buffer solution (0.01 M, pH 7.0) to prepare a protein solution (0.5%, w/v) and centrifuged at 4000 g for 10 min. The concentrations of the supernatants were diluted to different concentrations (0.05-0.5 mg/mL). Different diluted sample solutions (4 mL) and 20 μL ANS solution (0.008 M) were mixed evenly, and the fluorescence intensity of the sample solutions was measured within 10 min at room temperature by using an RF-5301PC fluorescence spectrophotometer (Shimadzu, Tokyo, Japan). The excitation wavelength was 390 nm, the emission wavelength was 470 nm, and the scanning slit was set at 5 nm. H 0 was the initial slope of the fluorescence intensity relative to the protein concentration (Zhao, Wang, Hong, Liu, & Li, 2021).

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE)
The concentration of protein solution was adjusted to 1 mg/mL. The protein was solubilized in 0.0625 M Tris-HCl buffer (pH 6.8) containing SDS (2.3%) and glycerol (10%) and then heated for 10 min in boiling water. The sample solution was cooled at room temperature and centrifuged for 10 min at 8000 g. A sample of 10 μL was then loaded into the polyacrylamide gel (5% stacking gel, 12% separating gel). The gel was dyed with 0.1% (w/w) coomassie brilliant blue R-250 for 40 min. The gel was subsequently decolorized until the protein bands were clear (Wang, Luo, Zhong, Cai, Jiang, & Zheng, 2017).

Fourier transformed infrared spectroscopy analysis (FTIR)
The secondary structure of WG in the gels was measured by Nicolet iS50 Fourier Infrared Spectrometer (Thermo Nicolet Inc., Waltham, MA, USA). Powder sample (1 mg) was mixed with 99 mg of KBr was ground thoroughly and pressed into pellets. The spectra were recorded in the range of 400-4000 cm − 1 (He, Shi, Walid, Zhang, Ma, & Xue, 2015).

Determination of intrinsic fluorescence spectrum
The fluorescence intensity of the sample solution (0.5%, w/v) was measured by a fluorescence spectrophotometer. The excitation wavelength and emission wavelength were set to 280 nm and 290-450 nm respectively, and the slit width of the excitation wavelength and emission wavelength were 5 nm (Wu, Wu, Wang, Fan, Chen, Ma, et al., 2019).

Scanning electron microscopy analysis (SEM)
The processed WG gel samples were cut transversally into cube and lyophilized (Du, Dang, Khalifa, Du, Xu, & Li, 2020). Freeze-dried samples were mounted on a silver specimen holder and coated with gold. The microstructure was observed with an accelerating voltage of 10 kV by HITACHI SU8010 (Hitachi, Tokyo, Japan).

Statistical analysis
The data were expressed as means ± standard deviations (SD) of three replicates at least. The ANOVA significance of data was analyzed by SPSS Statistics 22 using analysis of Tukey's HSD, and the difference was significant (P < 0.05). All graphs were presented by Origin 9.1.

Gel properties analysis
The gel strength of protein gels is a considerable indicator of protein aggregation and food texture, and is directly related to the microstructure of the gel. The effect of L-Lysine addition on gel strength of heatinduced WG was shown in Fig. 1A. It could be seen from the figure that the gel strength of heat-induced WG gel was significantly improved through adding L-Lysine (P < 0.05), which suggested that L-Lysine could improve the texture properties of heat-induced gels. As the addition of L-Lysine increased from 0.1 % to 0.2 %, the gel strength increased subsequently, demonstrating that the addition of L-Lysine changed the internal structure of heat-induced WG gels, resulting in changes in textural properties. It was speculated that the reason was that protein molecules were rapidly arranged to form a stronger gel network structure under the action of L-Lysine. Besides, the gel strength of WG gels prepared by MW irradiation increased significantly than WB treatment (P < 0.05), when the addition of L-Lysine to 0.2%, the gel strength reached the maximum. There are two main explanations for the enhanced gel strength of amino acid in the MW field: ① The dielectric dissociated from L-Lysine enhanced MW heating induced protein aggregation; ② L-Lysine changed the pH of the system and the acid-base variation induced protein aggregation. Regarding the first explanation, L-Lysine is an alkaline amino acid with the side chain containing the proton-able amino group (-NH 2 ), which can dissociate charged ions and increase the conductivity in the system. The conductivity increased due to the temperature of the system increased (Fig. S2), and the addition of L-Lysine led to the weakening of steric hindrance and electrostatic repulsion between protein molecules. Therefore, under MW heating, the intense Brownian motion of protein molecules was enough to overcome the residual repulsive energy barrier between protein molecules, increasing the chance of effective collision and aggregation (Anema, 2019;Yanagida, Ueda, Murata, Esaki, & Ishii, 2007). Although this explanation focused on the MW thermal effect after amino acid dissociation, the MW electromagnetic effect was ignored, that could directly act on polar protein molecules. Even at the same temperature, the aggregation rate of protein heated by MW was faster. Compared with traditional conduction heating, when the energy absorption value was the same, MW can achieve higher degrees of crosslinking between protein molecules (Cao, Jiao, Fan, Huang, Zhao, Yan, et al., 2019). For the second explanation, alkaline amino acids could increase the hydration layer and net negative charge of the protein in the system, and the pH value of the mixed system gradually deviated from the isoelectric point of the protein (Fig. S3). Protein molecules were not easy to contact with each other under electrostatic interaction, and the action of the MW alternating electric field broke the balance of the system. Thus, the protein molecules were cross-linked and aggregated, so the gel strength was improved. To prove whether the change of pH is the key factor affecting the gel strength, NaOH was used to regulate the pH of the system to make it the same as the pH of adding L-Lysine. The gel strength of WG gels decreased (Fig. S4). A hydration layer was formed around the ions, which was difficult for the intervention of cations to react with proteins and the role of MW in the system was limited (Basse, Bosc, Saiter, Chan-Huot, Dupas, Maillard, et al., 2020). The influence on the aggregate formation of protein in the electromagnetic field was weakened, which proved that the change of pH value was not the key factor to improve WG gel quality. Based on the facultative ion of alkaline amino acids, we tried to explain the process of MW-induced protein aggregation regulated with L-Lysine by the dielectric buffer.
The electromagnetic field of the MW would make the charged groups of the protein directional rearrangement with L-Lysine addition. The alternating electric field of the MW altered the charge distribution of the protein, thereby destroying the electrostatic interaction between the protein-peptide chains and inducing the protein to form aggregates. Furthermore, L-Lysine could induce the unfolding of protein and hinder over-aggregation (Wang, Zhao, Zhang, Liu, Jauregi, & Huang, 2020). The positively charged side chain of L-Lysine band to WG residues through electrostatic interaction, which could promote the formation of network structure and enhance the stability of three-dimensional network structure. Then under the synergistic effect of L-Lysine and MW, the protein gel formed developed networks and improved the gel strength.
WHC is a physical parameter, indicating the proportion of total water in the gel network under certain external force. The greater the WHC, the stronger the water binding capacity of the gel. The effect of adding L-Lysine on the WHC of heat-induced WG proteins was depicted in Fig. 1B. It could be seen from the figure that the WHC of heat-induced WG gel was significantly improved through adding L-Lysine (P < 0.05), probably because L-Lysine promoted the partial unfolding of protein molecules and increased the exposure of polar amino acid side chains, which interacted more easily with water, thus increasing the WHC of WG gels. Similar results were observed by Fu et al. for L-Lysine enhanced the WHC of myosin gels (Fu, Zheng, Lei, Xu, & Zhou, 2017). Further, the addition of L-Lysine could change the pH and make WG deviate from the isoelectric point, thereby increasing the electrostatic repulsion between protein molecules and fully exposing the binding sites of water, which led to a rise in WHC. In Fig. 1B, the WHC of MW group was higher than WB group, similar to the research of Ji et al., the WHC of mixed surimi gel treated by MW was remarkably enhanced showed that MW promoted the interaction between protein molecules and made more water retention (Ji, Xue, Zhang, Li, & Xue, 2017). Adding L-Lysine in WG under alternating electric field changed the conformation of protein molecules and promoted the cross-linking of protein molecules, forming a denser and uniform gel network structure. The denser three-dimensional network structure could confine more water in the gel system and enhance the WHC of the gel.

Intermolecular interactions analysis
WG was a biomacromolecule with spatial structure composed of various amino acids connected to each other. The important intermolecular forces that maintaining the complex three-dimensional network structure and stability of gluten gels mainly included covalent bond (disulfide bond and peptide bond) and non-covalent bond (ion interaction, hydrogen bonding, hydrophobic interaction, etc.). Chemical interactions have an important impact on the structure and texture properties of WG gels.
The content of ionic bond, hydrogen bond and hydrophobic interaction in heat-induced WG protein after adding L-Lysine was shown in Fig. 2A,2B. The chemical forces in the heat-induced WG from strong to weak were hydrophobic interaction > hydrogen bond > ionic bond, and the contribution of hydrophobic interaction and hydrogen bond was much greater than that of ionic bond, suggesting that the main forces maintaining conformational stability in thermally induced WG gels were hydrophobic interactions and hydrogen bonds. Similar results were obtained by Wang et al. in their study of egg yolk gels (Wang, Zhang, Chi, & Chi, 2021). The content of ionic bonds was the lowest of the noncovalent bonds and had no significant difference in all the samples. This was mainly because L-Lysine has both positive and negative charges, so the charged environment of the whole matrix was basically in equilibrium under the action of heating. The content of hydrogen bonds and hydrophobic interactions of the gels was much higher than that of ionic bonds ( Fig. 2A, 2B). The hydrogen bonding content of thermally induced WG gels was reduced and hydrophobic interactions were enhanced by the addition of L-Lysine. This might have occurred because L-Lysine acted as a dielectric buffer during the thermally induced gels and the heating resulted in the hydrogen bonds being broken, leading to a reduction in hydrogen bonding content. However, some studies had reported that L-Lysine had a strong ability to form hydrogen bonds, which might enhance the hydrogen bonding of myosin gels (Fu, Zheng, Lei, Xu, & Zhou, 2017). Hydrogen bonds mainly existed between the side amide groups of glutamine amino acids which were abundant in the repeating domains of WG and were easy to interact with through hydrogen bonds. However, the addition of L-Lysine in WG resulted in a decrease in the hydrogen bonds content, probably caused by the nonthermal effect of MW. The WG protein molecules unfolded during the heating process, and the hydrophobic parts were exposed to the hydrophilic environment. To maintain the thermodynamic stability of the system, the hydrophobic interactions between adjacent protein molecules increased. Therefore, the addition of L-Lysine combined with MW enhanced the hydrophobic interactions between protein molecules. Non-polar amino acid residues tended to accumulate inside the molecule, minimizing the area in contact with water, which led to aggregation and the formation of a three-dimensional gel.
Disulfide bonds in proteins were one of the most functional groups. Cysteine in gluten protein formed disulfide bonds through thiol oxidation, which provided stable support for the tight structure of WG protein.
The presence of disulfide bonds also made the network structure more compact. In the WG network, disulfide bonds were present both inside and outside the amino acid side chains. Intramolecular disulfide bonds were mainly found in wheat gum protein monomers or wheat gum protein polymers, and intermolecular disulfide bonds were mainly found in wheat gum protein polymers (Kondov, Verma, & Wenzel, 2011). The effect of adding L-Lysine on thermally induced disulfide bonds in WG was shown in Fig. 2C. As could be seen from the graph, the addition of L-Lysine significantly increased disulfide bond content in heat-induced WG gels (P < 0.05), which indicated that the addition of L-Lysine would promote the expansion of wheat gluten protein molecules, and more sulfhydryl groups will be exposed on the surface or inside of the protein molecules. As a result, the exposed sulfhydryl groups crosslinked and formed more disulfide bonds. Disulfide bonds played a crucial role in the thermal aggregation of protein in the formation of the gel network. Zhang et al. found that L-Lysine affected the formation of disulfide bonds in myosin gel, enhancing the gel strength (Zhang, Wu, Jamali, Guo, & Peng, 2017). Similarly, the proteins would aggregate to form larger particles, the protein gel would become denser and the gel strength would increase. Moreover, the disulfide bonds content of WG treated by MW increased than WB (Fig. 2C), during the MW heating process, the protein molecules absorbed heat and then expanded, which loosen the structure of the protein. The free SH groups embedded in the molecule were exposed and formed disulfide bonds during the gelation. MW caused the change of protein conformation and the position of free SH, so it was easier to promote the formation of disulfide bonds. The rise of disulfide bonds content caused the protein to undergo more cross- linking during the thermal gelation process and increased the gel strength. It showed that the combined action of MW and L-Lysine has the potential to orderly crosslink WG molecules.

Hydrophobicity (H 0 ) analysis
H 0 of proteins can be used to evaluate changes in protein structure. When the hydrophobic amino acid residues inside the protein molecules are exposed, some non-polar amino acid side chains of the protein molecules associated with each other form hydrophobic regions due to the repulsion of water molecules, the protein-protein aggregates maintained by hydrophobic forces. The changes in the tertiary structure of the protein are analyzed by observing the changes in H 0 . Additionally, ANS was used as a highly efficient fluorescent probe capable of attaching to the non-polar ends (hydrophobic groups) of protein molecules, and the amount of hydrophobic groups on the surface of the molecule is represented by the amount of fluorescence intensity. In this study, changes in wheat gluten protein H 0 were characterized by detecting fluorescence intensity.
It could be seen from Fig. 2D that the addition of L-Lysine significantly increased the H 0 of the heat-induced WG gel (P < 0.05), indicating that the addition of L-Lysine had led to the expansion of the molecular structure of WG protein and the exposure of hydrophobic group. Guo et al. found that L-Lysine could increase the H 0 of porcine myosin. L-Lysine destroyed the protein structure, caused the exposure of aromatic acid, and led to the exposure of hydrophobic groups (Guo, Peng, Zhang, Liu, & Cui, 2015). However, with the same amount of L-Lysine added, the H 0 of the MW group was lower than that of the WB group. The addition of L-Lysine might bind to the charged residues on WG due to the electrostatic effect of MW, which destroyed the ionic bonds within molecules. As the protein disassociated and stretched, some hydrophobic groups embedded in the molecule were exposed and hence the H 0 increased. The H 0 of WG treated by MW irradiation increased due to the polarization of alternating electromagnetic fields. MW broke the balance between hydrophilic and hydrophobic substances, which led to the stretching of protein structure and exposed the hydrophobic groups initially inside the molecules. These results enhanced the hydrophobic groups' exposure to the surface, promoted the orderly aggregation of proteins within the MW field, and might affect the three-dimensional network structure of WG gels. However, the enhancement of H 0 changed the environment around the protein molecules, causing the protein molecules to self-aggregate, resulting in a decrease in H 0 . It could be seen from Fig. 2D that the increases in H 0 tend to balance, indicating that with the intervention of zwitterionic L-Lysine, it did act as a dielectric buffer in the MW field. The zwitterion of L-Lysine shielded the increasing H 0 so that the protein molecules were in a relatively stable and stretched state, which was conducive to the further orderly aggregation of protein molecules. The combined treatments were more effective in inducing the further unfolding of WG, which favored inhibiting the flocculation between protein molecules. The increase in H 0 reduced the WG gels' water fluidity and enhanced the WHC; it was proved that the MW synergistic effect of L-Lysine on the gel quality of the WG was improved.

SDS-PAGE electrophoresis analysis
Changes in WG subunits were investigated by using SDS-PAGE, as shown in Fig. 3. Electrophoretic bands could be divided into aggregates (130-200 kDa); HMW-GS (66-130 kDa); ω-Gliadin (39-55 kDa); LMW-GS (36-44 kDa); α/β (28-40 kDa); γ-Gliadin (38-42 kDa) and soluble peptide (<25 kDa) according to molecular weight (Zhao, Hou, Tian, Zhou, Yang, Wang, et al., 2020). It could be seen from the figure the basic subunit bands were visible clearly, which mean that the addition of L-Lysine with heating treatment would not change the molecular weight of WG subunits, the energy of chemical bonds was much higher than the quantum energy of heating. Proteins will form dimers, multimers, and even insoluble protein precipitates under many physical stimuli such as heat and high pressure. Compared with the WB group, a part of the protein aggregates with the larger molecular weight accumulated at the loading port in MW group. MW is a physical stimulus that is different from heat and pressure and has its peculiarities. Under the synergistic action of L-Lysine and MW, proteins cross-linked each other through disulfide bonds to form insoluble protein aggregates. At the same time, the depth of the other subunit bands decreased obviously, indicating that the formation of the WG gel network required the cross-linking of proteins of different molecular weights. WG aggregated irregularly under the action of the alternating electric fields. The binding of these aggregates was loose, and the intermolecular interactions were weak. During the electrophoresis process, some proteins were easily dissolved from the irregular aggregates. Therefore, the intensity of the high molecular polymer band at the upper end of the electrophoresis lane was lighter, and the width of the band was also narrower. With the addition of L-Lysine, the protein molecules formed ordered aggregation. In addition to the rapid temperature rise of materials, MW may also have a non-thermal effect. The polar groups in protein molecules were affected by electromagnetic waves, which promoted the formation of new hydrophobic bonds of protein molecules and cross-linking aggregation. The proteins of some small molecules participate in the formation of gel network by embedding or chimerism, subunit bands (10-15 kDa) of soluble peptide disappearance, so the subunit bands of high polymers were gradually deepened.
FTIR spectra of thermally induced WG gels treated with different concentrations of L-Lysine in the amide I region were displayed in Fig. 4. The peak patterns of all the samples remained basically unchanged, indicating that the WG molecules were able to maintain most of their helical structure under these treatment conditions. The content of α-helix decreased with the increase of L-Lysine while the content of β-sheet increased in the alternating electromagnetic field with L-Lysine. The superposition of the dipole moments of all peptide bonds that made up the α-helix, resulting in a strong directional dipole moment. The external electric field coupled with the directional dipole moment decreases the content of α-helix. Moreover, Li et al. found that L-Lysine could significantly reduce the α-helix content of myosin, while increasing the β-sheet content (Li, Li, Zhu, Ning, Cai, & Zhou, 2019). The increase in the β-sheet structure changed the protein-protein interaction and exposed the hydrophobic sites of the protein, which promoted protein network formation. Zhu et al. also reported that low α-helix and high β-sheet contents in the protein structure suggested a simultaneous increase in its flexibility and H 0 (Zhu, Fu, Wu, Qi, Teng, Wang, et al., 2020). MW is an electromagnetic wave with an alternating electric field that has a "tear" effect on polar protein molecules. Under the action of a high-frequency external electric field, the polarity orientation of the water was induced to change, causing the movement of protein molecules and mutual friction. The alternating electric field of MW directly acted on the charged groups and affected the microenvironment of WG, destroying the ordered structure in the secondary structure of the protein to form a disordered structure. While the addition of L-Lysine alleviated the fierce impact on WG in the MW field and promoted the orderly aggregation. In general, L-Lysine existed in a zwitterionic form [NH 3 + (CH 2 ) 4 CH-(NH 2 )COO − ], which could increase the hydration layer and negative charge of protein in the system and improve the stability of the system. Therefore, under the synergistic effect of the MW heating and L-Lysine, new molecular order crosslinks appeared within proteins and prompted the secondary structure of proteins to interconvert.

UV spectra analysis
WG had a UV absorption peak at about 275 nm, which was mainly caused by the π-π* transition of aromatic heterocycles such as tryptophan (Trp) and tyrosine (Tyr) on its peptide bonds. As shown in Fig. 5A,5B, an increase in UV absorption intensity of WG after adding L-Lysine in both treatments. L-Lysine promoted the unfolding and partial expansion of polypeptide chains in WG. Some amino acid residues originally in the hydrophobic environment of protein molecules might be exposed to the molecular surface due to the changes in protein spatial structure. With the increase of L-Lysine addition, the UV absorption intensity of the MW-treated WG was raised. The protein backbone directly absorbed MW energy in the alternating electric field. Water was a polar compound, in which the atoms with high electronegativity had electron repulsion pulling effect, resulting in uneven charge distribution and dipole moment formation. Moreover, the zwitterionic of L-Lysine played the role of dielectric buffer in the MW field due to directional rearrangement of polar molecules. Therefore, the polarization effect was increased under the condition of MW heating (Hu & Cross, 1995;Liu & Ma, 2016), and the effect on the unfolding of WG protein was enhanced. Hence, molecular mobility in the polar region of the protein was increase, the tertiary structure of the protein was loosened, and the spatial conformation of the protein molecule was changed. With the increase of L-Lysine addition, the maximum UV absorption peak of WG protein had a slight blue shift, showing that the increased the polarity of the microenvironment of protein molecules, caused by the distribution of the aromatic residues (Tyr, Trp, and phenylalanine (Phe)) was transferred to the surface of protein molecules (Qin, Luo, Cai, Zhong, Jiang, Zheng, et al., 2016). The intramolecular or intermolecular interactions with the action of L-Lysine lead to the regular aggregation of protein molecules under MW field.

Fluorescence spectra analysis
Aromatic amino acid residues (Try, Trp and Phe) could produce characteristic spectra to reflect changes in their microenvironment. For example, the endogenous fluorescence of Trp residues was very sensitive to changes in its microenvironment. Therefore, Trp residues were usually used to characterize the variation in the tertiary structure of the protein. The maximum emission wavelength of protein λ max indicates the polarity of the environment of amino acids in protein changes. The change of fluorescence intensity is determined by the exposure degree of fluorescent amino acids. Fig. 5C,5D showed that the addition of L-Lysine had no significant effect on the peak shape of the fluorescence spectrum of WG. The maximum fluorescence emission of Trp residues corresponding to WG protein λ max was around 343 nm. Generally, Trp residues in a polar environment if λ max > 330 nm (Zhang, Chen, Liu, Mei, Yu, & Kan, 2020). With the increase of L-Lysine addition, the maximum fluorescence intensity of all the samples was around 343 nm, showing that all Trp residues were present in the polar environment. With the addition of L-Lysine increased, the fluorescence intensity of WG strengthened, suggesting the microenvironment of Trp residues has changed. The unfolding of the WG led to the exposure of the internal hydrophobic groups, which indicated the enhancement of polar environment. The charge and mass of L-Lysine molecules were non-spherical symmetrically and the positive and negative charge centers were not coincident, so L-Lysine had the permanent dipole moment. The result of fluorescence intensity was also consistent with the UV absorption intensity, indicating the MW with L-Lysine altering the tertiary structure of the protein, causing more unfolding of the protein and the exposure of internal chromophores, thus increasing the fluorescence intensity. General amino acids had an average dipole moment of about 3.8 D, which was greater than that of water molecules (1.81 D). Moreover, each protein had a certain electric dipole moment, which was the target of the electromagnetic field. MW caused the dipole to rotate and quickly rearrange with the change of the interactive electric field, resulting in the change of the tertiary structure of the protein. The stretching protein molecules orderly aggregated and gradually cross-linked under the traction of electromagnetic field, and the gel properties of WG were improved accordingly.

Microstructure of WG gels
The microstructure is the basis of the gel strength and WHC of the protein gels. The SEM micrograph of WG gels without L-Lysine exhibited a discontinuous network (Fig. 6A) due to the compact structure of WG and the limited effect of MW on WG. The chambers of the gel simply by MW heating were larger and rougher, the texture structure was the irregular arrangement, and it appeared blocky. These might cause by the irregular aggregation of proteins produced by the intense electromagnetic oscillation of MW heating. The surface proteins of the MW-heated WG gels without L-Lysine addition were thick and filamentous, the chambers were small, and the texture structures were flat. Under the regulation of L-Lysine, a network structure with fine chambers was formed by the proteins orderly cross-linking, and with a more delicate and dense surface texture. MW heating could avoid forming clustered Fig. 6. SEM microstructure (×400) of wheat gluten gels. Wheat gluten gels treated by water bath (A-F) and microwave (a-f) treatment with L-Lysine addition at 0%, 0.1%, 0.125%, 0.15%, 0.175% and 0.2%, respectively. structures with the action of L-Lysine as a dielectric buffer in the alternating electric field (Wang, Jiao, Yan, Meng, Cao, Huang, et al., 2021). The addition of L-Lysine promoted the formation of disulfide bonds and the enhancement of hydrophobic interactions during gelation. With the increased intermolecular forces, the WG realized orderly cross-linking between protein molecules. Therefore, the network structure became denser and more even (Fig. 6A-F), which varied with the change of gel strength. The zwitterionic L-Lysine inhibited the disorder aggregation of WG and enhanced the solubility of the protein. The aggregation and solubility of protein could affect the formation of gelatin, thus altering the microstructure of the gels. L-Lysine influenced the charge distribution of WG and the microenvironment of the electromagnetic field. The polymerization rate of WG with charged groups was greater than the frequency of vibration and rotation, resulting in a denser WG gels network structure. These results were more favorable for the physical interception of water, thus the water in the gel network more difficult to escape, enhancing the WHC of the gel.

Conclusion
Compared to the non-L-Lysine addition in WG by MW treatment, L-Lysine improved the gel properties. The synergistic effect of the alternating electric field in MW and L-Lysine accelerated the protein molecular denaturation and unfolding. The unfolding of protein molecules caused the exposure of internal groups of protein, including hydrophobic residues. Therefore, the improvement of UV and fluorescence spectra intensity was enhanced. Moreover, zwitterionic L-Lysine reduced the damage of the secondary structure of the protein and the destruction to other intermolecular interactions due to polarization of electromagnetic coupling. The increase of β-sheet and disulfide bonds facilitated the formation of the protein gels network. Further microstructure showed the uniform network of WG proved that protein molecules can be regulated orderly in MW field with the dielectric buffering effect of L-Lysine. In conclusion, the method of MW and adding L-Lysine improved the functional properties in WG and provided a theoretical basis for further research in promoting the quality of WG based food in the agricultural industry.