6.3: Deep Fat Frying of Food
Ram Yamsaengsung
Department of Chemical Engineering
Faculty of Engineering
Prince of Songkla University
Hat Yai, Thailand
Bandhita Saibandith
Department of Biotechnology
Faculty of Agro-Industry
Kasetsart University
Chatuchak, Bangkok, Thailand
| Key Terms |
| Frying chemistry | Mass transfer | Frying technology |
| Heat transfer | Mass and material balance | Industrial continuous frying systems |
| Heat balance | Product drying rate | Vacuum frying systems |
Variables
Introduction
This chapter introduces the basic principles of frying and its relevance to the food industry. To illustrate its importance, various fried products from around the world are described, and the mechanisms, equipment, and chemistry of the frying process are discussed. The pros and cons of frying food are presented in the context of texture, appearance, taste, and acceptability.
Frying is a highly popular method of cooking and has been used for thousands of years. A few examples from around the world include noodles, egg rolls, and crispy taros in China; tempuras (battered fried meats and vegetables) in Japan; fish and chips in the United Kingdom; and fried pork legs in Germany. In Latin countries and Tex-Mex restaurants, fried foods include tortilla-based products, such as tacos, nachos, and quesadillas. Examples of other popular fried foods include French fries, onion rings, and fried chicken, along with fried desserts such as doughnuts and battered, fried candy bars.
Traditionally, there are two major types of fried foods: (1) deep-fat fried (deep fried), such as potato chips, French fries, and battered fried chicken; and (2) pan fried, such as pancakes, eggs, and stir-fried dishes. This chapter focuses on atmospheric and vacuum deep-fat frying systems.
Outcomes
After reading this chapter, you should be able to:
- • Describe various types of frying technology
- • Describe basic frying chemistry and the heat and mass transfer mechanisms that are involved in the manufacture of different types of fried products
- • Explain the advantages and disadvantages of the frying process
- • Analyze the frying process using fundamental equations and calculate rate of water removal and amount of heat required during frying
Concepts
Frying Technology
Frying is defined as the process of cooking and drying through contact with hot oil. It involves simultaneous heat and mass transfer. Frying technology is important to many sectors of the food industry from suppliers of oils and ingredients; to fast-food outlets and restaurants; to industrial producers of fully fried, par-fried, and snack food products; and finally to manufacturers of frying equipment. The amount of fried food and oil used at both the industrial and commercial levels is massive.
Deep-Fat Frying (Deep Frying)
The process of immersing food partially or completely in oil during part or all of the cooking period at atmospheric pressure (760 mm Hg or 101.3 kPa absolute) is called deep-fat frying or deep frying. The food is completely surrounded by the oil, which is a very efficient heat-transfer medium. In addition to cooking the food, frying oil produces a crispy texture in food such as potato chips, French fries, and battered fried chicken (Moreira et al., 1999). The resulting product is usually golden brown in color with an oil content ranging from 8 to 25%.
A typical deep-fat fryer consists of a chamber into which heated oil and a food product are placed. The speed and efficiency of the frying process depend on the temperature and the overall quality of the oil, in terms of degradation of triglycerides and changes in thermal and physical properties such as color and viscosity (Moreira et al., 1999). The frying temperature is usually between 160° and 190°C. Cooking oil (such as sunflower oil, canola oil, soybean oil, corn oil, peanut oil, and olive oil) not only acts as the heat transfer medium, but it also enters into the product, providing flavor; Table 6.3.1 lists the oil content of commonly deep-fat fried products.
In addition to frying at atmospheric pressure, food products can also be fried under a vacuum, where the pressure is reduced to about 60 mm Hg (8 kPa absolute). At this lower pressure, the boiling point of water is decreased to 41°C allowing for the frying oil temperature to be reduced to 90°–110°C. As a result, heat-sensitive products, such as fruits with a high sugar content (e.g., bananas, apples, jackfruits, durians, and pineapples) can be fried to a crisp. Furthermore, the fried products are able to maintain a fresh color and intense flavor, while the frying oil will have a longer life because of less contact with atmospheric oxygen.
| Product | Oil Content (%) |
|---|---|
|
Potato chips |
33–38 |
|
Tortilla chips |
23–30 |
|
Expanded snack products |
20–40 |
|
Roasted nuts |
5–6 |
|
French fries |
10–15 |
|
Doughnuts |
20–25 |
|
Frozen foods |
10–15 |
Chemistry of Frying
Sources of Oil Used in Frying
Oil seed crops are planted throughout the world to produce cooking oil. The seeds are washed and crushed before oil is removed using an extraction process. The oil is then refined to remove any unwanted taste, smell, color, or impurities. Some oils, such as virgin olive oil, walnut oil, and grapeseed oil, are pressed straight from the seed or fruit without further refining (EUFIC, 2014). Some other sources of frying oil include sunflower, canola, palm, and soybean.
Most vegetable oils are liquid at room temperature. When oils are heated, unsaturated fatty acids, which are the building blocks of triglycerides, are degraded. Monounsaturated-rich oils, such as olive oil or peanut oil, are more stable and can be re-used much more than polyunsaturated-rich oils like corn oil or soybean oil. For this reason, when deep-frying foods, it is important not to overheat the oil and to change it frequently.
Chemical Reactions
Many chemical reactions, including hydrolysis, isomerization, and pyrolysis, take place during frying and affect the quality and storage time of the oil. Several of these reactions lead to spoilage of the oil.
Hydrolysis is a chemical reaction in which a water molecule is inserted across a covalent bond and breaks the bond. Hydrolysis is the major chemical reaction that occurs during frying. As the food product is heated, water in the food evaporates and the water vapor diffuses into the oil. The water molecules cause hydrolysis in the oil, resulting in the formation of free fatty acids, reduction of the smoke point of the oil, and unpleasant flavors in both the oil and the food. The smoke point, or the burning point, of an oil or fat is the temperature at which it begins to produce a continuous bluish smoke that becomes clearly visible (AOCS, 2017). Baking powder also promotes hydrolysis of the oil (Moreira et al., 1999). Table 6.3.2 lists the smoke points of some common oils used in frying. For high temperature cooking (160–190°C), an oil with a low smoke point, such as unrefined sunflower oil and unrefined corn oil, may not be suitable.
| Cooking Oils and Fats | Smoke Point °C | Smoke Point °F | Cooking Oils and Fats | Smoke Point °C | Smoke Point °F |
|---|---|---|---|---|---|
|
Unrefined sunflower oil |
107°C |
225°F |
Grapeseed oil |
216°C |
420°F |
|
Unrefined corn oil |
160°C |
320°F |
Virgin olive oil |
216°C |
420°F |
|
Butter |
177°C |
350°F |
Sunflower oil |
227°C |
440°F |
|
Coconut oil |
177°C |
350°F |
Refined corn oil |
232°C |
450°F |
|
Vegetable shortening |
182°C |
360°F |
Palm oil |
232°C |
450°F |
|
Lard |
182°C |
370°F |
Extra light olive oil |
242°C |
468°F |
|
Refined canola oil |
204°C |
400°F |
Rice bran oil |
254°C |
490°F |
|
Sesame oil |
210°C |
410°F |
Avocado oil |
271°C |
520°F |
Isomerization (polymerization) is the process by which one molecule is transformed into another molecule that has exactly the same atoms but arranged differently. Isomerization occurs rapidly during standby and frying periods. The bonds in the triglycerides are rearranged, making the oil more unstable and more sensitive to oxidation.
Pyrolysis results in the extensive breakdown of the chemical structure of the oil resulting in the formation of compounds of lower molecular weight.
Fried foods may absorb many oxidative products, such as hydro-peroxide and aldehydes, that are produced during frying (Sikorski & Kolakowska, 2002), thus affecting the quality of oil.
Repeated frying (using the same oil several times) increases the viscosity and darkens the color of the cooking oil. If the physico-chemical properties of cooking oil deteriorate, the oil must be discarded because it can prove to be harmful for human consumption (Goswami et al., 2015; Rani et al., 2010; Choe et al., 2007). Antioxidants, such as Vitamin E, added during frying are extremely effective in decreasing the rate of lipid oxidation, while enzymes such as superoxide dismutase, catalase, and peroxidase are also beneficial. Nonetheless, Vitamin E effectiveness decreases with increasing temperature (Goswami et al., 2015).
Heat and Mass Transfer Processes During Frying
The frying process, whether atmospheric or vacuum frying, is quite complicated involving coupled heat and mass transfer through a porous medium (the food), crust formation, and product shrinkage and expansion. These mechanisms all contribute to the difficulties in predicting physical and structural appearance of the final product. Thus, an understanding of the frying mechanism and the heat and mass transport phenomena is useful for food processors in order to produce and develop new fried and vacuum fried snack foods to meet the demands of consumers.
Heat Transfer
During the frying process, both heat and mass transfer take place, with water leaving and oil entering the product (Figure 6.3.1). The heat transfer processes include radiation from the heat source to the fryer, conduction from the fryer outer wall to the inner surface, and from inner surface to oil. Once the oil is heated, heat energy is transferred by convection to the surface of the product. Due to the high temperature of frying (160–190°C), the convective heat transfer coefficient is much higher than air-drying processes. Finally, heat is conducted from the hotter surface to the colder center of the product, thus increasing its temperature.
Heat transfer during the frying process can be described using the three following simplifying assumptions (Equations 6.3.1–6.3.3) relating to convection, conduction, and sensible heat.
The first assumption is that heat is transferred from the oil to the product surface via convection:
\[ q=h\Delta T = hA(T_{s}-T_{\infty}) \]
where q = heat flux (J s −1 m −2 or W m −2 ) (due to convection, in this case)
h = convective heat transfer coefficient (W m −2 °C −1 )
A = surface area of product (m 2 )
∆ T = difference in temperature (°C) between the product surface temperature and the oil temperature = T s – T ∞
T s = product surface temperature (°C)
T ∞ = oil temperature (°C)
Table 6.3.3 lists ranges of values of the convective heat transfer coefficient ( h ) for several processes and media. Forced convection increases the heat transfer coefficient dramatically compared to free convection. At the same time, liquids have a much greater h value than gases, while a convection process with phase change can create a heat transfer coefficient as high as 2,500–100,000 W m −2 . Krokida et al. (2002) provide a good compilation of literature data on convective heat transfer coefficients in food processing operations and Alvis et al. (2009) is a good source for values of the coefficient in frying operations.
The second assumption is that heat is transferred from the product surface internally via conduction:
\[ q=hA\frac{\Delta T}{\Delta x} = kA\frac{(T_{1}-T_{2})}{\Delta x} \]
| Process | h (W m −2 K −1 ) |
|---|---|
| Free convection: | |
|
Gases (e.g., air) |
2–20 |
|
Liquids (e.g., water, oil) |
50–1000 |
| Forced convection: | |
|
Gases (e.g., air) |
25–300 |
|
Liquids (e.g., water, oil) |
100–40,000 |
| Convection with phase change: | |
|
Boiling or condensation |
2,500–100,000 |
where q = heat flux (J s −1 m −2 ) or (W m −2 ) (due to conduction in this case)
k = thermal conductivity (W m −1 °C −1 )
A = surface area of product (m 2 )
∆ T = T 1 – T 2 = difference in temperature between the inner and outer surface of the product (°C)
∆ x = thickness of product (m)
The third assumption is that the heat from the oil is also used as sensible heat (change in the temperature of the product without a change in phase) to increase the product temperature toward the oil temperature:
\[ Q=\Delta H = \dot{m}C_{p} \Delta T= \dot{m}C_{p}(T_{1}-T_{2}) \]
where Q = sensible heat (J s −1 )
∆ H = change in enthalpy (J)
\(\dot{m}\) = mass flow rate (kg s −1 )
C p = specific heat (kJ kg −1 °C −1 )
∆ T = T 1 – T 2 = change in temperature of the material without undergoing a phase change (°C)
Table 6.3.4 gives the specific heat of water, vegetable oil, and common materials. As shown, the specific heat of vegetable oil is less than half that of liquid water, indicating that much less energy is needed to raise the temperature of the same amount of material by 1°C.
| Material |
Specific Heat (
C
p
)
(kJ kg −1 °C −1 ) |
|---|---|
|
Liquid water |
4.18 |
|
Solid water (ice) |
2.11 |
|
Water vapor |
2.00 |
|
Vegetable oil |
2.00 |
|
Dry air |
1.01 |
Sensible heat from the oil increases the water temperature to its boiling point. The release of heat energy at the boiling point is known as the latent heat of vaporization, or the heat required to evaporate the water or change its phase from liquid to gas. The latent heat of vaporization cools the product region during evaporation, keeping the product temperature near the boiling point (until most of the water has been removed).
Heat Balance
The simplified heat balance equation is:
\[ \rho C_{p}\frac{dT}{dt}-div[k\nabla T] = Q_{\text{heatsource}}+h(T-T_{\infty}) \]
where ρ = density of product (kg m −3 )
C p = heat capacity of product (J kg −1 °C −1 )
div [ k ∇( T )] = conduction term = \(\frac{\partial}{\partial x}(k\frac{\partial T}{\partial x})+\frac{\partial}{\partial y}(k\frac{\partial T}{\partial y})+\frac{\partial}{\partial z}(k\frac{\partial T}{\partial z})\)
x = direction x (m)
y = direction y (m)
z = direction z (m)
k = thermal conductivity (W m −1 °C −1 )
Q heatsource = latent heat of evaporation term (J s −1 m −2 )
h = convective heat transfer coefficient (W m −2 °C −1 )
T ∞ = oil temperature at time t (°C)
T = product temperature at time t (°C)
t = time (s)
The simplified heat balance equation (Equation 6.3.4), consists of the heat accumulation term [ ρC p ( dT/dt )], the conduction term div [ k ∇( T )], the heat source term ( Q heatsource ) denoting the latent heat of vaporization, and the convection term, h(T oil – T) , at the boundary surface, respectively. The heat accumulation term represents the change in the enthalpy of the system as a function of time. This change accounts for the heating of the product (change in enthalpy) and the transfer of the heat from the heated product toward evaporating the water vapor from the product. The conduction term accounts for the transfer of the heat from the product surface toward the center of the material, while the convection term accounts for the transfer of heat from the oil to the product surface and is dependent on the heat transfer coefficient of the cooking oil (Yamsaengsung et al., 2008).
Mass Transfer
The mass transfer processes during frying include (Figure 6.3.1):
- 1. As the hot oil heats the product by conduction, the heat evaporates the water in the product when it reaches the water boiling temperature (Farkas et al., 1996).
- 2. As the water turns into vapor, it diffuses within the product and moves out of the product by convection.
- 3. Oil is driven into the product via capillary pressure (which is the pressure difference between two immiscible fluids in a thin tube), resulting from the interactions of forces between the fluids and the solid walls of the tube. Capillary pressure can serve as both an opposing force and a driving force for fluid transport (Moreira and Barrufet, 1998).
- 4. The final product is comprised of solids, water, air, and oil. In general, the product becomes more hygroscopic, i.e., readily attracts water from its surrounding, as frying proceeds. French fries are an excellent example of a product with a crispy surface or crust and a soft inner portion called crumb. In brief, after a specific time, the surface of the product becomes crispy, while the internal part of the product may retain a certain amount of moisture, leaving it with a softer texture.
Figure 6.3.2 depicts a typical non-hygroscopic material and a hygroscopic material (Figura and Teixeira, 2007). Each material consists of all three phases: gas, liquid water, and solid. One major difference is that in a hygroscopic material there is bound water. Bound water is defined as water that is bonded strongly to the inner surface of the pores of the materials (Yamsaengsung and Moreira, 2002) and very difficult to remove. In contrast, free water can be removed through capillary diffusion (Moreira et al., 1999) and convection flow from a pressure gradient. The bound water requires a longer drying and frying time to be removed. While more heat energy is required to remove this bound water, its removal leads to shrinkage of the material. Drying can also lead to shrinkage of the material, but frying can lead to additional puffing and expansion of the structure as the water vapor and gas expand during the later stages of the frying process (Yamsaengsung and Moreira, 2002).
Product Drying Rate
The percent moisture content of a food material can be expressed as wet basis (% w.b.) or dry basis (% d.b.) by mass. Percentage wet basis is commonly used in commercial applications while percentage dry basis is used in research reports.
The % w.b. is defined as:
\[ \%\ w.b.=(\frac{\text{water content (kg)}}{\text{total weight of product (kg)}}) \cdot100 \]
The % d.b. is defined as:
\[ \%\ d.b.=(\frac{\text{kg of water}}{\text{kg of dried food}}) \cdot100 \]
The drying rate of the product during the frying process is divided into constant and falling rate periods. During the constant rate period, water removal is fairly constant. During the falling rate period, the rate of water removal is drastically reduced. Each period is characterized by an averaged set of heat and mass transport parameters (Yamsaengsung, 2014). The moisture ratio ( MR ) is defined as:
\[ MR = \frac{MC_{t}-MC_{e}}{MC_{o}-MC_{e}} \]
where MR = moisture ratio
MC t = moisture content at frying time t (decimal d.b. or w.b.)
MC e = equilibrium moisture content; the moisture content of the product under equilibrium conditions at constant temperature and relative humidity (d.b. or w.b.)
MC 0 = moisture content at start of frying, time = 0 (d.b. or w.b.)
Figure 6.3.3 illustrates the constant rate and the falling rate periods of the MR during the frying process.
During the constant rate period, free water is removed as vapor via evaporation and diffusion from the product. Changes in the product surface as the crust forms are also taking place during this period. Typically, for crispy foods, the moisture content should be less than 5% w.b. During the falling rate period, a distinct crust region has been developed and bound water is being removed via vapor diffusion. The rate of oil absorption is proportional to the rate of moisture loss during the constant rate period, but is limited by the presence of the crust during the falling rate period. The development of crust and the increase in pressure inside the structure as the gas vapor expands with continuous heat absorption help to limit oil absorption, while causing the pores of the product to expand and the entire product to increase its thickness. This expansion is called puffing (Moreira et al., 1999).
In terms of mass transfer, the diffusion equation (Equation 6.3.8) may be written to account for the convective flow of liquid and vapor as (Moreira et al., 1999):
\[ \frac{dc}{dt}-div[D\cdot \nabla(c)]=\dot{V} \]
where \(\frac{dc}{dt}\) = change in concentration of component (liquid, vapor, or oil) (kg mol m −2 s −1 )
div [ D·∇(c) ] = convective flow = \(\frac{\partial}{\partial x}(k\frac{\partial T}{\partial x})+\frac{\partial}{\partial y}(k\frac{\partial T}{\partial y})+\frac{\partial}{\partial z}(k\frac{\partial T}{\partial z})\)
D = diffusion coefficient (m −2 s −1 )
c = concentration of component (liquid, vapor, or oil) (kg mol m −3 )
\(\dot{V}\)= rate of convective flow of liquid (kg mol m −2 s −1 )
When applied to each component, i.e., liquid, vapor, or oil, Equation 6.3.8 is used to quantify the removal of liquid water and vapor from the product and the absorption of oil by the product during the frying process, i.e., as a function of time. The rate of water removal is estimated using the diffusion coefficient, while the change in the concentration of the component (liquid, vapor, or oil) is estimated using experimental data as a function of frying time (Yamsaengsung, et. al., 2008).
The heat and mass transfer equations allow calculation of the energy consumption, the heat required for heating of the cooking oil and removal of water from the product during the frying process, the amount of water that is being removed during frying, and, in many cases, the amount of product that would be obtained at the end of the frying period.
Material (Mass) Balance
Equations 6.3.4 and 6.3.8 describe heat and mass transfer during frying in three dimensions. Solving them requires advanced numerical methods, which are beyond the scope of this chapter. This section presents a model using simplified material balance (mass balance) equations, which accounts for the change in mass of each component during the process.
Equation 6.3.9 states the concept of the material, or mass, balance in words:
\[ \{ \text{accumulation within the system} \}=\{\text{input through system boundaries} \} - \{\text{output through system boundaries} \} + \{\text{generation within the system} \} - \{\text{consumption within the system} \} \]
Accumulation refers to a change in mass (plus or minus) within the system with respect to time, whereas the input and output through the system boundaries refers to inputs and outputs of the system (Himmelblau, 1996). If considered over a time period for which the balance applies, Equation 6.3.9 is a differential equation (consider, for example, the mass balance of water in Figure 6.3.4). When formulated for an instant of time, Equation 6.3.9 becomes a differential equation:
\[ \frac{dm_{H_{2}O,within\ system}}{dt}=\dot{m}_{H_{2}O,in} - \dot{m}_{H_{2}O,out1} - \dot{m}_{H_{2}O,out2} \]
where m H2O is the mass of water and \(\dot{m}\) H2O is the mass flow rate of water (mass/time, kg/s). When evaluating a process that is under equilibrium, or steady-state, condition, the values of the variables within the system do not change with time, and the accumulation (change in mass within the system with respect to time) term in Equations 6.3.9 and 6.3.10 is zero.
To illustrate application of the mass balance, consider a frying operation to make potato chips (which are fried potato slices). For this example, 4 kg of peeled raw potato slices containing 83% water enter a fryer to make chips with 2% water and 30% oil. How many kg of water are evaporated from the product leaving the fryer, and how many kg of potato chips are produced in the process? The process is at steady state conditions.
The system is the fryer, and no accumulation, generation, or consumption occurs, since the process is steady state. Also, assume potatoes are made up of water and solids. The next step is to write the mass balance equations, total and for each component (% solids, % water), and solve for the unknowns.
The total mass balance of potato slices is:
in = out, as the time-dependent terms in Equation 6.3.10 are zero
R + oil (absorbed from fryer) = W + P
The total material entering the fryer is given as 4 kg peeled raw potato slices. Substituting R = 4 kg in the total mass balance, yields one equation with two unknowns:
4 kg + oil (absorbed from fryer) = W + P
Hence, a second equation is needed (basic material balances principle). The potatoes are composed of water and solids, hence, the terms in the total mass balance equation can be multiplied by the respective component percentages. The percent solids balance is:
4 kg (1 – 0.83) + 0 = W (0) + P (1 – 0.32)
0.68 = 0.68 P
P = 1 kg of potato chips produced
Percent water balance is:
4 kg (0.83) + 0 = W (1) + P (0.02)
3.32 = W + 0.02 P
3.32 = W + (0.02) 1 kg = W + 0.02
W = 3.3 kg of water removed
Percent oil balance:
4 kg (0) + oil = 3.3 kg(0) + 1 kg(0.3)
Thus, the mass of oil absorbed by the potatoes during frying is 0.3 kg.
The total material balance is 4 kg + 0.3 kg = 3.3 kg + 1 kg, or 4.3 = 4.3, which confirms the conservation of mass law.
Applications
In order to design and construct a productive and cost-effective frying system, product properties and characteristics, including size, shape, thickness, thermal conductivity, specific heat capacity, composition, and desired product attributes, such as color, texture (hardness, crispiness), smell, and flavor, all play a role and affect the frying time and temperature. Using equations for mass balance and heat transfer, the rate of water removal and a drying curve can be developed which can be used to predict the moisture loss and the product weight, which, in turn, affects the frying time and production capacity.
Industrial Continuous Deep-Fat Frying Systems
A typical continuous frying system consists of a fryer, a heat exchanger, an oil tank with a cooling system, a control panel, and a filter. Another common type of frying system consists of a combustor, an oil heat exchanger, and a fryer. In the combustor, a gas burner burns natural gas with fresh air and foul gas (vapors from the fryer) to produce combustion gases that flow through a heat exchanger to heat the frying oil that is re-circulated through the fryer. In many cases, exhaust gas recirculation is used to increase turbulence, provide combustor surface cooling, and reduce emissions. To reduce emissions and smells, vapors generated from the frying process are directed from the fryer to the combustor where they are incinerated (Wu et al., 2013).
Table 6.3.5 provides examples of mechanical specifications of some continuous frying systems and their throughputs, while Table 6.3.6 gives pricing and frying time of some systems.
| Model |
Dimensions
(mm) |
Effective Frying Space, length × width × height (mm) | Hp | Energy Consumption (kWh) | Edible Oil Capacity (L) | Production Capacity | |||
|---|---|---|---|---|---|---|---|---|---|
| length | width | height | Peanuts | Snacks | |||||
|
FRYIN-302-E |
3450 |
2350 |
1950 |
2600 × 820 × 700 |
3 |
232.44 |
440 |
480 kg/hr |
300 kg/hr |
|
FRYIN-402-E |
4950 |
2350 |
1950 |
4100 × 820 × 700 |
5 |
348.67 |
650 |
650 kg/hr |
550 kg/hr |
|
FRYIN-602-E |
6450 |
2450 |
2070 |
5890 × 820 × 700 |
7.5 |
464.89 |
850 |
Modified from https://www.tsunghsing.com.tw/en/product/oil_fryer-fryin_series.html
Vacuum Frying Systems
The vacuum frying process, first developed in the 1960s and early 1970s, provides several benefits compared to the traditional (atmospheric) frying process. It is now widely used to process fruits in Asian countries. The principle behind vacuum frying is that using reduced pressure (below 101.3 kPa), the boiling point of water can be reduced from 100°C to as low as 45°C and the cooking oil temperature can also be reduced to less than 100°C (compared to atmospheric frying at 170°–190°C). As a result, products with high sugar content, such as ripened fruits, can be fried without burning and caramelization. Common methods to improve vacuum-frying of fruits include immersion in high sugar solutions and osmotic dehydration (Fito, 1994; Shyu and Hwang, 2001).
| Machine Type | Products | Fuel Source/Power Consumption |
Capacity
(kg/hr) |
Frying Time
(min.) |
Cost, US$ |
|---|---|---|---|---|---|
|
Automatic continuous fried nuts processing line |
nuts, almond, cashew, peanuts, etc. |
diesel, LPG, gas, biofuel |
N/A |
N/A |
$143,145 |
|
Automatic snacks frying machine |
chips, meat, chicken, peanut |
electric/10 kW |
100–1,000 |
N/A |
$14,314 |
|
Continuous banana chips fryer machine |
chips, biscuit, donut, French fries, potato chips, banana chips, snacks |
electric/25 kW |
100–500 |
2–20 |
$25,766 |
|
Snack food fryer |
snack foods |
electric/25 kW |
100–500 |
1–10 |
$143,145 |
Modified from https://www.gracefoodmachinery.com/continuous-fryer-systems.html
Figure 6.3.6 shows a schematic of a vacuum fryer (Yamsaengsung, 2014). In addition to the features shown in Figure 6.3.6, a vacuum fryer must have a centrifuge to remove the oil content from the surface before the vacuum is broken. Table 6.3.7 provides a comparison of process operating conditions and applications for traditional and vacuum frying systems. The main components in the vacuum frying process are the vacuum fryer (8–10 mm thick wall and fryer cap), the condenser (for condensing water vapor), the water collector, and the vacuum pump (either rotary or liquid water ring type). However, the main drawbacks of vacuum frying are the high cost involved in purchasing the equipment and the more complicated process management. With the addition of a vacuum pump, a water condensing system, and much thicker fryer wall (8–10 mm vs. 1–2 mm), the cost of the vacuum fryer can be double the cost of an atmospheric fryer.
The benefits of vacuum frying include the ability to:
- • fry high sugar content products such as fresh fruits;
- • maintain original color, while adding intense flavor to the final product;
| Conditions/Attributes | Atmospheric Frying | Vacuum Frying |
|---|---|---|
|
Temperature |
160°–190°C |
90°–140°C |
|
Pressure (absolute) |
101.3 kPa |
3.115 kPa |
|
Convective heat transfer coefficient (h) |
−2 K −1 (80-120°C)[b] −2 K −1 (200-300°C)[b] |
217–258 W m −2 K −1 (120°–140°C)[c] 700–1600 W m −2 K −1 (140°C)[d] |
|
Oil absorption |
25–40% w.b. |
1–10% w.b. |
|
Oil usage life |
susceptible to lipid oxidation |
minimal lipid oxidation longer usage life |
|
High sugar content foods |
not possible |
possible |
|
Major composition |
high starch/ high protein |
high starch high protein high sugar |
|
Taste/texture |
bland to salty/crispy |
intense flavor/crispy |
|
Color |
intensity of color decreases |
intensity of color is maintained |
|
Investment cost |
low |
high |
[a] Yamsaengsung (2014); [b] Farinu and Baik (2007) at 160°–190°C; [c] Pandey and Moreira (2012) at 120°–140°C; [d] Mir-Bel et al. (2012) at 140°C.
- • reduce the amount of oil absorbed into the final product to as low as 1–3% depending on the machine (Garayo & Moreira, 2002); and
- • extend the life of cooking oil by reducing its exposure to oxygen (lipid oxidation) and using a lower cooking oil temperature.
Moreover, even though Garayo and Moreira (2002) found that potato chips fried under vacuum conditions (3.115 kPa and 144°C) had more volume shrinkage, their texture was slightly softer and they were lighter in color than potato chips fried under atmospheric conditions (165°C). Yamsaengung and Rungsee (2003) also found that, compared to atmospheric frying, vacuum fried potato chips retained a lighter color and had a more intense flavor.
Examples
Example \(\PageIndex{1}\)
Example 1: Material balances
Problem:
Determine how many kg of raw potato slices containing 80% water must enter a batch fryer to make 500 kg of potato chips (fried potato slices) with 2% water and 30% oil. Also calculate how many kg of water are evaporated and leave the fryer. The process is at steady state conditions.
Solution
Draw a schematic of the problem, enter the given data and identify the unknowns. Then, write down the material balance equations and solve for the unknowns.
The system is the fryer, and no accumulation, generation, or consumption occurs, that is, it is at steady state. Also assume potatoes are made up of water and solids.
The total material balance in the fryer is:
in = out
R + oil (in fryer) = W + P
R + oil = W + 500 kg
We have one equation and two unknowns, so we need another equation.
Percent solids balance:
R (1 – 0.80) + 0 = W (0) + 500 kg(1 – 0.32)
R = 1700 kg
R = 1700 kg of raw potato slices containing 80% water are required
Percent water balance is:
1700 kg(0.80) + 0 = W (1) + 500 kg(0.02)
1360 = W + 10
W = 1350 kg of water removed from potato slices in the frying process
Finally, determine the amount of oil in the fried chips by conducting a percent oil balance:
1700 kg(0) + oil = 1350 kg(0) + 500 kg(0.3)
oil = 150 kg
Total material balance:
1700 kg + 150 kg = 1350 kg + 500 kg
This example illustrates the use of material balances using food initial and final composition data to calculate the amount of raw material entering the fryer to manufacture a product with specific composition characteristics.
Example \(\PageIndex{2}\)
Example 2: Moisture content of fried chips
Problem:
During a batch frying process, the weight of 50 kg of raw, fresh peeled potato slices decreases to 15 kg after frying. Each fried chip contains 30% oil content. If the initial moisture content of the fresh peeled potato is 80% (w.b), determine the final moisture content (% w.b.) of the fried chips.
Solution
Draw a schematic of the problem, enter the given data and identify the unknowns. Then, write down the material balance equations and solve for the unknown moisture content of the fried chips, using the definition of percent wet basis.
The system is the fryer, and no accumulation, generation, or consumption occurs (steady state). Also assume potatoes are made up of water and solids.
The total material balance in the fryer is:
in = out
R + oil absorbed = W + P
From the problem statement, mass of P = 15 kg with 30% oil.
Using percent oil content, calculate how much oil (in kg) the chips contain:
0.30 × 15 kg = 4.5 kg of oil in fried chips
To figure the percent solids balance, note that in material balance applications in food engineering, the dry matter is constant. Hence, solids in = solids out.
From the raw materials with 80% water (and 20% solids), the dry matter (% solids) is:
50 kg × 0.2 = 10 kg
Calculate how much water (in kg) is in the chips:
chips = water + dry matter + oil
15 kg = kg H 2 O + 10 kg + 4.5 kg
kg H 2 O = 15 kg – 10 kg – 4.5 kg = 0.05 kg
Then, on a wet basis, the moisture content of the chips is (from Equation 6.3.5):
\( \%\ w.b. = \frac{\text{kg of water}}{\text{total of weight of product}} \times 100= \frac{0.05\ kg}{15\ kg}\times100=0.333\% \)
This example shows how the final moisture content of the fried product can be calculated. Its importance lies in the effect of moisture on the crispiness of fried foods. Typically, for crispy snacks, the moisture content should be less than 5% w.b., so this fried product is considered crispy.
Example \(\PageIndex{3}\)
Example 3: Drying curve
Problem:
The following data represent the change in weight of vacuum fried bananas (70% w.b. moisture content) as a function of frying time. Also assume the moisture content in % d.b. at equilibrium (at the end of frying) is 0.02 kg water/kg dry matter. Neglect the weight of the oil absorbed (% oil content = 0.0%) and plot the drying curve as a function of the frying time (moisture ratio vs. time).
|
Time
(min) |
Weight
(kg) |
Solids
(kg) |
H
2
O
(kg) |
|---|---|---|---|
|
0 |
10 |
3 |
7 |
|
1 |
8.4 |
3 |
5.4 |
|
2 |
7.2 |
3 |
4.2 |
|
3 |
6.3 |
3 |
3.3 |
|
4 |
5.4 |
3 |
2.4 |
|
6 |
4.6 |
3 |
1.6 |
|
8 |
4.1 |
3 |
1.1 |
|
10 |
3.65 |
3 |
0.65 |
|
12 |
3.4 |
3 |
0.4 |
|
14 |
3.35 |
3 |
0.35 |
|
16 |
3.3 |
3 |
0.3 |
Solution
Calculate moisture ratio using Equations 6.3.6 and 6.3.7:
\( \%\ d.b. = \frac{\text{kg of water}}{\text{total of weight of product}} \cdot 100 \) (Equation \(\PageIndex{6}\))
\( MR = \frac{MC_{t}-MC_{e}}{MC_{o}-MC_{e}} \)
For the banana with 70% w.b. moisture, the percent solids content is 1 – 0.7 = 0.3 or 30%. For an initial weight of 10 kg, the solids content is 0.3 × 10 kg = 3 kg (a constant throughout the process).
Determine moisture content in % dry basis using Equation 6.3.6 at each time t :
% d.b. = (total weight – weight of solids)/(weight of solids)
For example,
At t = 0 min MC 0 (t=0) = (10 kg – 3 kg)/(3 kg) = 2.33
At t = 1 min MC 1 (t=1) = (8.4 kg – 3 kg)/(3 kg) = 1.80
At t = 2 min MC 2 (t=2) = (7.2 kg – 3 kg)/(3 kg) = 1.40
Repeat the procedure for all times.
Next, determine MR using Equation 6.3.7. For example,
MR t = ( MC t – MC e )/( MC o – MC e )
At t = 0 min MR 0 = (2.33 – 0.02)/(2.33 – 0.02) = 1.00
At t = 1 min MR 1 = (1.80 – 0.02)/(2.33 – 0.02) = 0.77
At t = 2 min MR 2 = (1.40 – 0.02)/(2.33 – 0.02) = 0.60
Repeat the procedure for all times using table below.
|
Time
(min) |
Weight (kg) |
Solids
(kg) |
H
2
O
(kg) |
MC
(d.b.) |
MR |
|---|---|---|---|---|---|
|
0 |
10 |
3 |
7 |
2.33 |
1.00 |
|
1 |
8.4 |
3 |
5.4 |
1.80 |
0.77 |
|
2 |
7.2 |
3 |
4.2 |
1.40 |
0.60 |
|
3 |
6.3 |
3 |
3.3 |
1.10 |
0.47 |
|
4 |
5.4 |
3 |
2.4 |
0.80 |
0.34 |
|
6 |
4.6 |
3 |
1.6 |
0.53 |
0.22 |
|
8 |
4.1 |
3 |
1.1 |
0.37 |
0.15 |
|
10 |
3.65 |
3 |
0.65 |
0.22 |
0.09 |
|
12 |
3.4 |
3 |
0.4 |
0.13 |
0.05 |
|
14 |
3.35 |
3 |
0.35 |
0.12 |
0.04 |
|
16 |
3.3 |
3 |
0.3 |
0.10 |
0.03 |
Example \(\PageIndex{4}\)
Example 4: Production throughput of a continuous fryer
Problem:
At a potato chip factory, 1,000 kg of potatoes are fed into a continuous vacuum fryer per hour.
- (a) Assuming the initial moisture content of peeled potatoes is 80% (w.b.) and the final moisture content is 2% (w.b.), how much water is removed per hour?
- (b) How much (in kg) of oil is added to the potato chips per hour? Potato chips have 2% w.b. moisture content and 30% oil.
- (c) How many bags can be produced in one day if each bag contains 50 g of potato chips and the factory operates for 8 hours per day?
Solution
Draw a schematic of the problem, enter the given data and identify the unknowns. Then, write down the material balance equations and solve for the unknowns. Neglect oil content in product. This is a continuous process (material/time).
-
(a) Determine the amount of water removed from the raw potatoes,
R
, per hour.
Water in initial product:
1,000 kg/hr × 0.8 = 800 kg/hr of water
- Percent solids balance:
(1000 kg/hr)(1 – 0.8) = W (0) + (1 – 0.02 – 0.3) P
(1000 kg/hr)(0.2) = (0.68) P
200 kg/hr = 0.68 P
P = 294.12 kg/hr of potato chips
- Water in final product:
294.12 kg/hr × 0.02 = 5.88 kg/hr of water in potato chips
- Percent water balance:
(1000 kg/hr)(0.8) = W (1) + 5.88 kg/hr
W = 800 kg/hr – 5.88 kg/hr
W = 794.12 kg of water removed from raw potatoes in one hour
-
(b) Determine the amount of oil per hour added to the potato chips in the fryer.
Chips have 30% oil. Thus,
-
\( 0.30 = \frac{\text{oil in chips (kg/hr)}}{\text{total weight of chips (kg/hr)}} \)
-
\( 0.30 = \frac{\text{oil in chips (kg/hr)}}{294.12\text{ (kg/hr)}} \)
oil in chips = (0.30) × 294.12 kg/hr
oil in chips = 88.24 kg/hr
- (c) Determine number of bags per 8-hr day:
amount of chips per day = (294.12 kg/hr) × 8 hr/day
= 2,352.96 kg chips/day × (1000 g/kg) = 2,352,960 g/day
number of bags per day = (2,352,960 g/day) × (1 bag/50 g)
= 47,059 bags per day
This example illustrates how the engineer uses knowledge of material balances and food composition to determine production throughput of a continuous fryer.
Example \(\PageIndex{5}\)
Example 5: Energy requirement for an industrial fryer
Problem:
For an industrial fryer with a production capacity of 5,000 kg of corn chips per hour, how much energy is required to reduce the water content of the pre-baked masa (the product that will be fried to make the chips) from 50% w.b. to 4% w.b.? If the frying time takes 60 seconds at a frying temperature of 180°C, calculate:
- (a) initial feed rate of the chips,
- (b) total amount of water removed,
- (c) amount of heat required to evaporate the water,
- (d) total energy required for the frying process, and
- (e) power required for the frying system.
Assume that the oil has already been pre-heated, the temperature of the oil does not drop during frying, but heat is needed to increase the corn chips feed temperature from 25°C to the frying temperature. The specific heat capacity ( C p ) of the cooking oil is 2.0 kJ kg −1 °C −1 , the specific heats of the corn chips before and after frying are 2.9 kJ kg °C −1 and 1.2 kJ kg°C −1 , respectively, and the latent heat of evaporation of water at 100°C is 2,256 kJ/kg. (Hint: 1 kW = 1 kJ/s and water evaporates at 100°C.)
Solution
Calculate the initial mass of the pre-baked masa using Equation 6.3.5:
\( \%\ w.b. = (\frac{\text{water content (kg)}}{\text{total weight of product (kg)}}) \cdot 100 \) (Equation \(\PageIndex{5}\))
4% = (kg of water/5,000 kg)
weight of water = 200 kg
weight of solid = 5,000 kg – 200 kg = 4,800 kg
MC = 50% w.b.
Find the mass of water using Equation 6.3.5:
50% = (kg of water/(kg of water + kg of solid))
50% = W /( W + 4,800 kg)
0.5× ( W + 4,800 kg) = W
W = (0.5 × 4,800 kg)/(1 – 0.5)
weight of water = 4,800 kg
Initial feed rate of corn chips = weight of water + weight of solid = 9,600 kg/hr
Calculate the amount of water removed as initial – final:
Initial weight of water = 4,800 kg
Final weight of water = 200 kg
Water removed = 4,800 – 200 = 4,600 kg
Calculate Q required to remove the water (to evaporate the water)
Q = water removed × latent heat of evaporation
Q = (4,600 kg × 2,256 kJ/kg)
Q = 10,377,600 kJ
Calculate sensible heat (25° – 100°C and 100° – 180°C) using Equation 6.3.3:
\( Q=\Delta H = \dot{m}C_{p}\Delta T=\dot{m}C_{p}(T_{1}-T_{2}) \) (Equation \(\PageIndex{3}\))
Q = (9,600 kg) × (2.9 kJ/kg °C) × (100°C – 25°C)
Q = 2,088,000 kJ
Likewise for 100° – 180°C,
Q = (5,000 kg) × (1.2 kJ/kg °C) × (180°C – 100°C)
Q = 4,800,000 kJ
Calculate total Q as the sum of both sensible and latent heat:
Q total = Q sensible + Q latent
Q total = 2,088,000 kJ + 4,800,000 kJ + 10,277,600 kJ = 17,265,600 kJ
Calculate power as total heat per unit time:
Power = Q/t
t = 60 seconds
Q = 17,265,600 kJ
Power = 287,760 kW
Example \(\PageIndex{6}\)
Example 6: Water removal rate during frying
Problem:
12 kilograms of fresh bananas were purchased at 0.50 US$/kg. After 4 kg of peel were removed, the bananas were sliced 2 mm thick and vacuum fried at 110°C for 45 minutes. This process reduced the moisture content from 75% w.b. to 2.5% w.b. Determine the rate of water removed from the fresh peeled bananas (kg/min) during the frying process. Assume bananas are composed of water and solids, and that the amount of oil absorbed is negligible (oil content = 0%).
Solution
Draw a schematic of the problem, enter the given data, and identify the unknowns. Then, write down the material balance equations and solve for the unknowns.
Total material balance: in = out
Remember that oil is zero in this example. Therefore, B = W + P
- Solids balance: (0.25) B = (0) W + (0.975) P
- Water balance: (0.75) B = (1.00) W + (0.025) P
From B = 8 kg, find P from the solids balance:
P = (0.25)(8 kg)/(0.975)
P = 2.05 kg of fried bananas
From the total material balance, find the amount of water removed during the process:
W = B – P = 8 kg – 2.05 kg
W = 5.95 kg of water removed from the fresh peeled bananas
The rate of water removal is the amount of water removed per unit time. Since the frying time was 45 minutes the rate of water removal in is:
rate of water removal = (5.95 kg)/(45 min)
rate of water removal = 0.132 kg water/min
Why is this important? In a vacuum frying process, water is removed from the product during frying, trapped, and separated before it reaches the vacuum pump in order to maintain low pressure inside the frying system. The volume of the water trap and the capacity of the vacuum pump are needed in order to select the most efficient vacuum pump and heat exchanger for cooling the water vapor from the fryer. For example, if 20 kg of potato chips with an initial moisture content of 60% w.b. is fried, it can be assumed that almost 12 kg of water (approximately 12 L) must be removed and collected in a water trap. If the water is not condensed and collected, it will enter the pump and cause a decrease in vacuum pressure.
Image Credits
Figure 1. Yamsaengsung, R. (CC By 4.0). (2014). General schematic of the heat and mass transfer processes occurring during frying of a food product.
Figure 2. Yamsaengsung, R. (CC By 4.0). (2002). Schematic of non-hygroscopic and hygroscopic material.
Figure 3. Yamsaengsung, R. (CC By 4.0). (2020). Typical drying curve (frying curve) showing the constant rate period and the falling rate period.
Figure 4. Yamsaengsung, R. (CC By 4.0). (2020). Process for a simple mass balance consisting of air and water entering and leaving a system.
Figure 5. Yamsaengsung, R. (CC By 4.0). (2020). A schematic of the problem with the given data and the unknowns.
Figure 6. Yamsaengsung, R. (CC By 4.0). (2014). Schematic of a vacuum frying operation.
Example 1. Yamsaengsung, R. (CC By 4.0). (2020). Example 1: Material Balances.
Example 2. Yamsaengsung, R. (CC By 4.0). (2020). Example 2: Moisture content of fried chips.
Example 3. Yamsaengsung, R. (CC By 4.0). (2020). Example 3: Drying curve.
Example 4. Yamsaengsung, R. (CC By 4.0). (2020). Example 4: Production throughput of a continuous fryer.
Example 6. Yamsaengsung, R. (CC By 4.0). (2020). Example 6: Water removal rate during frying.
References
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11.8A: Cytotoxic T Lymphocytes and Mucosal Surfaces
- Describe the features of the lymphatic system as they relate to the immune response
Lymphatic system
Lymph, the watery fluid that bathes tissues and organs, contains protective white blood cells, but does not contain erythrocytes (red blood cells). Lymph moves about the body through the lymphatic system, which is made up of vessels, lymph ducts, lymph glands, and organs such as tonsils, adenoids, thymus, and spleen. Although the immune system is characterized by circulating cells throughout the body, the regulation, maturation, and intercommunication of immune factors occur at specific sites that are known as lymph nodes.
The blood circulates immune cells, proteins, and other factors through the body. Approximately 0.1 percent of all cells in the blood are leukocytes, which include monocytes (the precursor of macrophages) and lymphocytes. Most cells in the blood are red blood cells. Cells of the immune system can travel between the distinct lymphatic and blood circulatory systems, which are separated by interstitial space, by a process called extravasation (passing through to surrounding tissue).
Recall that cells of the immune system originate from stem cells in the bone marrow. B cell maturation occurs in the bone marrow, whereas progenitor cells migrate from the bone marrow and develop and mature into naïve T cells in the organ called the thymus. On maturation, T and B lymphocytes circulate to various destinations. Lymph nodes scattered throughout the body house large populations of T and B cells, dendritic cells, and macrophages. Lymph gathers antigens as it drains from tissues. These antigens are filtered through lymph nodes before the lymph is returned to circulation. Antigen-presenting cells (APCs) in the lymph nodes capture and process antigens, informing nearby lymphocytes about potential pathogens.
The spleen houses B and T cells, macrophages, dendritic cells, and NK cells. The spleen is also the site where APCs that have trapped foreign particles in the blood can communicate with lymphocytes. Antibodies are synthesized and secreted by activated plasma cells in the spleen, which filters foreign substances and antibody-complexed pathogens from the blood. Functionally, the spleen is to the blood as lymph nodes are to the lymph.
Key Points
- The lymphatic system contains lymph: a fluid that bathes tissues and organs and contains white blood cells (not red blood cells).
- Once B and T cells mature, the majority of them enter the lymphatic system, where they are stored in lymph nodes until needed.
- Lymph nodes also store dendritic cells and macrophages; as antigens are filtered through the lymphatic system, these cells collect them so as to present them to B and T cells.
- The spleen, which is to blood what lymph nodes are to lymph, filters foreign substances and antibody -complexed pathogens from the blood.
Key Terms
- lymph : a colorless, watery, bodily fluid carried by the lymphatic system, consisting mainly of white blood cells


15.8A: Bacterial Gastroenteritis
- Describe the cause and effect of bacterial gastroenteritis
Gastroenteritis is a medical condition characterized by inflammation (“-itis”) of the gastrointestinal tract that involves both the stomach (“gastro”-) and the small intestine (“entero”-), resulting in some combination of diarrhea, vomiting, and abdominal pain and cramping. Although unrelated to influenza, it has also been called ‘stomach flu’ and ‘gastric flu’.
Globally, most cases in children are caused by rotavirus. Less common causes include other bacteria (or their toxins) and parasites. Transmission may occur due to consumption of improperly prepared foods, contaminated water, or via close contact with individuals who are infectious. The foundation of management for this illness is adequate hydration. For mild or moderate cases, this can typically be achieved via oral rehydration solution. For more severe cases, intravenous fluids may be needed. Gastroenteritis primarily affects children and those in the developing world. Gastroenteritis typically involves both diarrhea and vomiting, or less commonly, presents with only one or the other. Abdominal cramping may also be present.
Signs and symptoms usually begin 12–72 hours after contracting the infectious agent. Some bacterial infections may be associated with severe abdominal pain and may persist for several weeks. In the developed world, Campylobacter jejuni is the primary cause of bacterial gastroenteritis, with half of these cases associated with exposure to poultry. In children, bacteria are the cause in about 15% of cases, with the most common types being Escherichia coli , Salmonella , Shigella , and Campylobacter species. If food becomes contaminated with bacteria and remains at room temperature for a period of several hours, the bacteria multiply and increase the risk of infection in those who consume the food. Toxigenic Clostridium difficile is an important cause of diarrhea that occurs more often in the elderly. Infants can carry these bacteria without developing symptoms. It is a common cause of diarrhea in those who are hospitalized and is frequently associated with antibiotic use. Staphylococcus aureus infectious diarrhea may also occur in those who have used antibiotics. “Traveler’s diarrhea” is usually a type of bacterial gastroenteritis. Acid-suppressing medication appears to increase the risk of significant infection after exposure to a number of organisms, including Clostridium difficile , Salmonella , and Campylobacter species.
Transmission rates are also related to poor hygiene, especially among children, in crowded households, and in those with pre-existing poor nutritional status. After developing tolerance, adults may carry certain organisms without exhibiting signs or symptoms, and thus act as natural reservoirs of contagion. While some agents (such as Shigella ) only occur in primates, others may occur in a wide variety of animals (such as Giardia ).
Gastroenteritis is typically diagnosed clinically, based on a person’s signs and symptoms. Determining the exact cause is usually not needed as it does not alter management of the condition. However, stool cultures should be performed in those with blood in the stool, those who might have been exposed to food poisoning, and those who have recently traveled to the developing world. Electrolytes and kidney function should also be checked when there is a concern about severe dehydration.
A supply of easily accessible uncontaminated water and good sanitation practices are important for reducing rates of infection and clinically significant gastroenteritis. Personal measures (such as hand washing) have been found to decrease incidence and prevalence rates of gastroenteritis in both the developing and developed world by as much as 30%.
Key Points
- Gastroenteritis typically involves both diarrhea and vomiting, or less commonly, presents with only one or the other.
- Transmission rates are also related to poor hygiene, especially among children, in crowded households, and in those with pre-existing poor nutritional status.
- A supply of easily accessible uncontaminated water and good sanitation practices are important for reducing rates of infection and clinically significant gastroenteritis.
Key Terms
- inflammation : A condition of any part of the body, consisting in congestion of the blood vessels, with obstruction of the blood current, and growth of morbid tissue. It is manifested outwardly by redness and swelling, attended with heat and pain.
- gastroenteritis : Inflammation of the mucous membranes of the stomach and intestine; often caused by an infection.


1.2: What Is Geography?
The Greek word geographos from which geography is derived, is literally translated as writing ( graphos ) about the Earth ( geo ). Geography differs from the discipline of geology because geology focuses mainly on the physical Earth and the processes that formed and continue to shape it. On the other hand, geography involves a much broader approach to examining the Earth, as it involves the study of humans as well. As such, geography has two major subdivisions, human (social science) and physical (natural science) . This text focuses primarily on human geography, but because the physical aspects affect humans and vice versa, physical geography will not be completely excluded, but will receive less emphasis.
Geography is the study of the physical and environmental aspects of the world, from a spatial perspective. As geographers study the Earth, the one element that binds the discipline of geography and makes it unique is studying the Earth from a spatial perspective. The spatial perspective means that the phenomenon you are studying can be displayed on a map, so geography focuses on places around the world. Geography , then, is a physical (or natural) and social science that asks the fundamental questions, “What is where , and why?” Human geography is a social science that focuses on people, where they live, their ways of life, and their interactions in different places around the world. A simple example of a geographic study in human geography would be where is the Hispanic population concentrated in the U.S., and why? A physical geography research endeavor might ask where do most hurricanes strike the U.S. coastline, and why? In addition, because the Earth is dynamic, geographers also look at how places change through time, and why, so there is a natural connection with history.
1.2.1 Geography and its relationship to other disciplines
Not only is there a connection between geography and history, but geography is also related to a broad range of other academic disciplines ( Figure 1.1 ). If you examine Figure 1.1, you may find your own major on the outside margin of the circle, with the corresponding subdiscipline in geography on the interior of the circle. Again, if a phenomenon can be depicted on a map and studied from a spatial perspective, it is geographical. A basic example would relate to the health sciences or medical geography, the subfield of geography that focuses on the spatial patterns of various aspects of health. For example, when the spread of a disease from its source area is mapped, medical professionals can get a better idea of the causes of a disease and the mechanisms of its transmission. Often, the understanding of cultural practices or the environmental conditions (such as the habitat for a mosquito-borne disease) can shed light on the process of how the disease operates. Another example of how geography relates to other disciplines is in economicgeography, the subfield that examines the different economic activities in various places, and how places interact economically. A fundamental concept in economic studies is that the location of a business is often important to the success of that business. If the business is located in close proximity to its clientele, for example, the customers might be more likely to visit that restaurant, store, etc. on a regular basis. A business owner would be wise to consult maps of both transportation networks as well as the population of the customers to which they intend to cater.


6.1.5: The Symbolic-Interactionist Perspective on Aging
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The Symbolic Interactionist Perspective
The symbolic interactionist perspective posits that age is socially constructed and determined by symbols resembling social interactions.
Learning Objectives
Argue that the perception of aging is better either in the United States or in Japan, using Goffman’s theory of social presentation
Key Points
- The notion of age is socially constructed, meaning that it has no universal value. Rather, various cultures ascribe aging with different meanings and values.
- In The Presentation of Self in Everyday Life, Erving Goffman argued that people try to control or guide the impression they create on other people by comporting themselves in specific ways.
- The desire to look younger than one’s biological years is frequently the impetus for cosmetic surgeries that can hide the physical effects of aging. These surgical practices suggest a Goffmanian understanding of social presentation.
- Social value is highly dependent on context and culture. Many Eastern societies associate old age with wisdom and value old age much more than their Western counterparts.
Key Terms
- Erving Goffman : Erving Goffman (June 11, 1922 – November 19, 1982) was a Canadian-born sociologist and writer. The 73rd president of American Sociological Association, Goffman’s greatest contribution to social theory was his study of symbolic interaction in the form of dramaturgical analysis. This began with his 1959 book, The Presentation of Self in Everyday Life.
- socially constructed : The social construction of age means that there is no inherent cultural meaning to the biological process of aging.
The Symbolic Interactionist Perspective and Aging
According to the Symbolic Interactionist Perspective, old age, and aging, are socially constructed and determined by symbols that resemble aging in social interactions. While aging itself is a biological process, the Symbolic Interactionist Perspective posits that the meaning behind being “young” or “old” is socially constructed. This means that there is no inherent cultural meaning attached to the biological process of aging. Rather, cultures imbue youth and age with particular meanings. Given the socially constructed nature of age, there are certain behaviors that people typically associate with certain age groups as being “appropriate” or “acceptable”.
Aging is perceived differently around the world, demonstrating its social construction. Frequently, the average life expectancy in a given region impacts what age counts as “old.” For example, in the United States, where the average life expectancy is over 78 years, one isn’t considered “old” until he or she is in their sixties or seventies. However, in Chad, the average life expectancy is less than 49 years, and people in their thirties or forties are therefore already considered middle-aged or “old.” These variations in people’s perceptions indicate that notions of youth and age are culturally constructed, and that there is no such thing as a universal age at which point one becomes old.
Japanese Perceptions of Aging
In addition to defining terms differently, cultures treat their elderly differently and place different values on age. Many Eastern societies associate old age with wisdom and value old age much more than their Western counterparts. In Japan, adult children are expected to care for their aging parents in different ways than in the United States. 65% of Japanese elders live with their children, and very few live in nursing homes. In Japan, if a youth was to put an aging parent in an assisted living home, the behavior would be considered tantamount to neglect. Cultural norms suggest that parents should move in with their children when they are unable to care for themselves. The Japanese celebration of old age is further illustrated by the existence of Respect for the Aged Day, a national holiday to celebrate elderly citizens.
Western Perceptions of Aging
Japanese perceptions of elders diverge markedly from public perceptions of old age in the United States. Western societies tend to place such an increased value on youth that many people take extreme measures to appear young. A desire to look younger is frequently the impetus for cosmetic surgeries that can hide the physical effects of aging. These surgical practices, combined with huge expenditures on makeup and clothing, suggest a Goffmanianunderstanding of social presentation. Erving Goffman was a sociologist writing in the mid-twentieth century. His most famous work, The Presentation of Self in Everyday Life (1959), argued that whenever individuals come into contact with other people, they will attempt to control or guide the impression that others might have of them by intentionally comporting themselves in different ways. Thus, individuals take sometimes drastic action to control the appearance of their age so that others will perceive them as younger. Significantly, these social interactions occur in a social milieu that values youth. In this light, people try to appear younger to increase their sense of social value.
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14.5: Ethical Issues in Digital Marketing and Social Media
By the end of this section, you will be able to:
- Describe ethical issues with respect to digital marketing and social media.
- Explain why ethical issues exist.
Privacy, Transparency, and Awareness
Although digital marketing tools and social media provide online marketers with effective ways to engage with customers, build relationships, and drive consumers toward a purchase, there are ethical issues that marketers must consider when utilizing these tools.
First, because of the highly targeted capabilities of digital and social media, companies have access to large amounts of personal data, including name, email address, and phone number, as well as personal interests, social and political views, and shopping behavior. Consumers are increasingly concerned about data privacy. In a recent survey by KPMG , 86% of the respondents have a growing concern about data privacy, and 78% fear the amount of data being collected (Whitney, 2021).
Given this growth in distrust of how personal data is handled, some companies have responded with updated policies designed to be more transparent about how data will be used. Seventy-five percent of consumers polled reported that they want increased transparency (Whitney, 2021).
In 2021, Apple released features for iPhone and iPad users that allow consumers to have stronger control of how their data is used (Price, 2022). Using pop-ups, Apple device users can allow or disallow companies to track their activity across apps and the websites they link to. This move by Apple resulted in some back-and-forth commentary by Meta ’s Mark Zuckerberg and Apple CEO Tim Cook. Tech companies such as Facebook and Google depend on being able to target the advertising on their applications to users using personal data. Giving greater privacy control to iPhone users presents a threat to the core of their business models.
Social media platforms, in particular, mine personal data and then use it to sell advertising space on news feeds of consumers who match the demographics and psychographics of a company’s target market. With nearly 71% of social media users taking the time to check their privacy settings on social media, it’s clear that this issue is front and center for most users (Suciu, 2020). Companies can respect their users' privacy by being transparent about what data they collect and how they use it.
Tracking Consumer Data
The reality is that it’s not just social media companies and search engines that track consumer data. Most companies use tracking codes to follow consumers and data about them as they navigate the web. Zoho, a productivity and collaboration app, reported that in the B2B space, about 72% of businesses do not inform customers that they are being tracked by third parties (Business Wire, 2020).
The Use of Client Reviews
Client reviews involve feedback that a customer or client posts directly to a platform that can accessed by consumers during the buying process. Companies that use client or customer reviews include Amazon.com, Wayfair, and Lands’ End. Customers typically rate their experience with the product by assigning stars and commenting on their satisfaction.
Reviews can be helpful to consumers during the search phase of the buying process because reviews provide a real-world glimpse into the favorability of a product. For example, Wayfair invites customers to post pictures of items such as sofas and end tables once a customer has styled the room. This provides shoppers with a real-life view of the product, its color, and its size, among other things.
Beyond the reviews on e-commerce sites, Google is a major player in the customer review space. Consumers often rely on Google reviews when deciding whether to hire a local business. In addition to Google, consumers can find reviews for travel on Tripadvisor, restaurant reviews on Zomato, and reviews of software programs on G2.
Marketers recognize the power of customer reviews as a digital promotional tool, as consumers report that they perceive reviews as more credible than messages created by the company itself.
In January 2022, Apple took one of its most impactful steps toward protecting the privacy of iCloud users, the iCloud Private Relay (see Figure 14.11) (Apple, 2023a). When enabled on Apple devices, this feature hides a user’s IP address from the websites they visit, essentially masking a user’s entire online footprint.
The privacy feature is a game changer in the digital marketing space, as companies such as Meta and Google depend on seeing a consumer’s online journey to learn more about who they are and their interests. Tracking online activity allows companies to serve users with relevant marketing messages and offerings.
In addition to the privacy relay, Apple also released “Hide My Email,” which allows Apple device users to enter a unique email address on websites without sharing their actual email address (Apple, 2023b). Emails sent to a randomly generated address are then forwarded to a user’s inbox, thereby hiding a user’s actual email address.
Finally, Apple has updated its Mail app to prevent marketers from tracking whether or not someone has opened an email (Kaczanowski, 2022). Email marketers measure the percentage of people who open marketing emails to determine their engagement level and the email's effectiveness.
Apple appears to be taking consumer privacy to another level. Offering a collection of privacy-centric features equips consumers with tools to protect their personal information and navigate the web unseen.
Check out Apple’s website to learn more about iCloud Private Relay . Also, read about it in this Wired article .


2.2.2: Anton Chekhov (1860-1904)
A Doctor's Visit The Lady with the Dog Russian Realism Anton Chekhov was the grandson of a serf who purchased his freedom, whereas Chekhov would end up making enough money to purchase his own estate. Chekhov worked as a physician for most of his adult life, while making a name for himself as a playwright and as a short story writer. Several of his stories, in fact, draw on his experiences as a practicing physician, including "A Doctor's Visit" (1898). Four of Chekhov's plays are classics of the theater: The Seagull (1895), Uncle Vanya (1897), The Three Sisters (1900), and The Cherry Orchard (1903). Chekhov was influenced by Henrik Ibsen's use of Realism on stage, as well as his own experiences with all levels of Russian society. While Ibsen's plays focused on the middle class, Chekhov also looked at the decline of Russian aristocracy alongside the rise of the middle class, usually with neither group shown to advantage. His influence on modern theater is considerable. He proposed the dramatic convention that there should be no extraneous elements in a plot, which is called "Chekhov's gun"—if a gun is hanging on the wall onstage in the first act, it must be fired later in the play, with the same requirement if it is mentioned in a short story. This convention is often found in film, television, and modern short stories. Among Chekhov's short stories, many critics regard "The Lady with the Dog" (1899) as perhaps his best work, as well as a classic in the genre. In the story, Chekhov offers insight into the complexities of romantic relationships, balancing sympathy with realism. What could have been a cliché in another writer's hands becomes a sensitive portrayal of two people who find themselves in an impossible situation of their own making.
Written by Laura Getty


1: Introduction
What is Drawing?
Drawing is a form of visual communication. It is also a cornerstone of both studio and applied visual art fields and is often the first step in visualizing and exploring an art concept. A drawing can be a work unto itself, or a preliminary step in the execution of a work in a different medium. For example, a drawing may be transferred or directly drawn on a stretched canvas for a painting, or sketched out to help visualize a sculptural work, a cartoon, an illustrated book, a mural, and so on. It is a quick and efficient way for artists, engineers, animators, and creative individuals to ideate. Drawing is universal and a quite natural human means of expression. Even toddlers have a tendency to begin drawing at around the same 12-month age that they begin forming words.
Although drawing tools have evolved and expanded during the past 40 years to include digital pens, tablets and software, the fundamentals of drawing are still the same. The art elements are the visual tools used to create drawings and are generally recognized as Line, Value, Color, Form, Shape, Space and Texture. The Principles of Design are more numerous and are used to strategically organize the art elements to create works of art. These design principles include, but are not limited to, Composition, Perspective, Balance, Proportion, Size and Scale, Pattern and Repetition, Unity, Variety, Hierarchy of Forms, Design Systems, The Color Wheel, Positive and Negative Space, Emphasis, and Subordination. The best drawings are formed with skill utilizing the physical tools and their accompanying drawing techniques which when brought together are referred to as the drawing medium . An example would be: charcoal, charcoal paper, and a kneaded eraser which when combined equals a drawing medium (charcoal medium).
Drawing may create the illusion of our three-dimensional world on a two-dimensional plane of paper or other support. A true drawing master, through knowledge of drawing techniques, use of art elements and principles of design, can become an illusionist creating convincingly rendered three-dimensional spaces with depth and realism. But not all drawing is meant to just please the eye through beautifully rendered forms. Drawing is more than that. It can represent emotions, thoughts, ideas, points of view, didactic purposes, symbols, icons and abstract forms.
Drawing is both a Process and a Product
Drawing is an act of creating an image usually on a two-dimensional surface and thus is a process. So the word drawing is a word of action; a verb. However, a drawing is also the result of that action, something you can view. Drawing therefore is also a thing; a noun.
Drawing as a Cognitive Learning Tool
Alan Walker (23 August 1938 – 20 November 2017), in an anatomy lecture to the medical school students at John’s Hopkins University, stated when you can draw your subject with accuracy from memory, then you demonstrate that you fully comprehend your subject matter. It was enlightening and encouraging to hear those words from this world-renowned anthropologist and chair of the Hopkins anatomy department. His observation was clearly linking drawing with learning about, and comprehension of, subject matter. In his world, it was a merging of scientific inquiry, the art of close observation, and the visual recording both mentally and physically of anatomic subjects. Thus, we see a link between the cerebral imprint made when we are seeing with intent and the physical two-dimensional visual recording of the subject. Drawing, when applied in this manner, falls into the category of academia and is a true merging of art and science.
Drawing, Math and Science
Looking back over 500 years from Dr. Walker’s lecture, another brilliant mind was combining mathematical formulas with keen visual insight and documenting these new concepts through a revolutionary form of drawing. The results were documented by Filippo Brunelleschi and are now recognized as mathematical linear perspective. Applying the principles of perspective to drawing and painting revolutionized how artists represented the three-dimensional world on a two-dimensional plane. Convincing representations of drawings and paintings were now possible. Moreover, the connections between mathematical theory and drawing brought visual art into the realm of European academic centers established just prior to and during the Italian Renaissance.
Both Italian and German Renaissance artists used drawing to document and study the function and structure of forms found in nature such as the flora and fauna and, more specifically, human anatomy. Leonardo da Vinci and Michelangelo Buonarroti studied human anatomy through the dissection and subsequent written and visual documentation of these dissections using drawing. Leonardo’s greatest achievement is arguably his over 10,000 pages of writing and drawings concerning nature, anatomy, and his ingenious inventions including prototypes for flying machines, automatic transmissions, and military machinery. Albrecht Dürer, having traveled from Germany to Italy and experiencing the Italian Renaissance first hand, took drawing, engraving, and wood block printing to new heights through his mastery of drawing techniques as well as his focused observations of natural subjects. Nature was given a level of respect and dignity through careful study and visual representations by these and other 15 th and 16 th Century art masters.
Drawing and the Written Language
Drawing in the form of cave paintings and rock carvings provide insight into prehistoric people, but without written documents to augment these prehistoric drawings we are left to speculate the meaning of this incredible body of art. At the end of the Ice Age, about 10,000 years ago, mass human migration occurred leading to the formation of villages, towns and eventually cities along the great rivers of the Middle and Near East. The Tigris, Euphrates, and the Nile Rivers became essential sources of water and fertile lands for the growing human population of the region. This development of civilization also coincided with the advent and evolution of writing from rudimentary pictures, symbols, and marks representing words. These pictographs formed the basis for our modern-day alphabets and, with the ensuing written language, came documented history. Clear links in the evolution of written language demonstrate the importance of drawing pictures in the development and evolution of human communication, documented history, and civilization.
Summary
Drawing is a versatile means of visual communication. It seems fundamental to our existence as humans. We see that drawing had a special place in the tribal ceremonies taking place in prehistoric caves, and on cliffs and mountains beginning around 30,000 years ago and continuing with the few surviving Neolithic societies found in remote global locations. Additionally, drawing contributes to communicating ideas of power, conflict, the afterlife, and societal customs in the ancient world through Egyptian hieroglyphics, Sumerian images on registers, and the earliest writings in cuneiform. The evolution of writing in the west began with pictographs which evolved into letters, words, sentences, paragraphs, and longer documents such as the Epic of Gilgamesh, The Code of Hammurabi and other ancient written stories, accounting legers and other historical documents. Drawing has a link to academics through science and mathematics.


10.2: Words of Wisdom- Something Was Different
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Jacqueline Tiermini
I have earned both a bachelor’s and a master’s degree and I have nearly twenty years of teaching experience. Would you ever guess that I contemplated not going to college at all? I originally thought about going to Beauty School and becoming a Cosmetologist. It was to me, honestly the easy way out since I was sick of all the drama after high school. The thought of college seemed overwhelming. Why did I really need to have a college degree when all I ever wanted was to get married and be a stay-at-home mom? My friends weren’t going to college either, so I often wondered if going would complicate our friendship.
I decided to go anyway, and it did separate us a bit. While I was writing a ten-page paper for my summer class in Genetics and Heredity, my friends were swimming in my pool. They also had the chance to buy new cars and new clothes and to go on vacations. I just went to school, driving my used Nissan Sentra, without much more than gas money and a few extra bucks. Again, why was I doing this? It would have been easier to just do what my friends were doing.
Little by little, semesters went by and I graduated with my bachelor’s degree in Education. I started substitute teaching immediately and within six months I was offered a full-time job. Just like that, I had more money and all kinds of new opportunities and I could now consider a new car or going on vacation just like my friends. At that point, I decided to continue my education and get my master’s degree. Yes, it was a lot of hard work again, and yes, my friends wondered why I wanted to go back again, but I knew then that this was the best choice for me. The challenge wasn’t knowing where I wanted my career to go, but rather overcoming the pull to settle into a lifestyle or career because it was easy, not because it was what I wanted.
By the time I graduated with my master’s degree I realized that something was different. For all the years that I felt behind or unable to keep up with what my friends had, I was suddenly leaps and bounds ahead of them career-wise. I now had two degrees, a full-time teaching job, and a plan to keep my career moving forward. I was able to do all of the things that they had done all those years and more. None of them had careers, just jobs. None of them had long-term plans. None of them were as satisfied with their choices any longer and a few of them even mentioned that they were jealous of my opportunity to attend college.
Don’t be fooled. Being a college student is a lot of work and, like me, most students have questioned what they are doing and why they are doing it. However, the rewards certainly outweigh all of the obstacles. I used to hear, “Attending college will make you a well-rounded person” or “It sets you apart from those that do not attend,” yet it never felt true at the time. Eventually though, you will come to a point where you realize those quotes are true and you will be on your way to earning that degree!
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Foundations of Academic Success: Words of Wisdom. Edited by Thomas Priester. Essay authored by Jacqueline Tiermini. Located at: https://milnepublishing.geneseo.edu/foundations-of-academic-success/chapter/something-was-different/ License: CC BY: Attribution.