Apples contain disease-fighting vitamin A, C, E and K, minerals such as potassium and magnesium1 and antioxidants,2 making them one of the top-ranked fruits for your health.

Compared to other commonly consumed fruits in the U.S., apples rank second only to cranberry for total phenolic compound concentration and total antioxidant activity,3 and highest for the proportion of free phenolic compounds,4 which means the phenolic compounds are not bound to other compounds in the fruit and therefore may be more easily absorbed into your bloodstream.5

Notably, much of apples’ antioxidant power is contained in the peel,6 where you’ll find antioxidants like quercetin, catechin, phloridzin, chlorogenic acid and more.7 However, recent research shows the core of the apple should not be overlooked, as that’s where a majority of beneficial bacteria (probiotics) are found.

Apple core — A surprising source of beneficial bacteria

As reported by Study Finds,8 recent research9,10 published in Frontiers in Microbiology reveals “a typical 240-gram apple contains around 100 million bacteria, mostly in the seeds and skin,” and organic apples have far greater diversity compared to conventional apples, “potentially making them healthier, tastier and better for the environment.”

In a press release,11 senior author, professor Gabriele Berg with Graz University of Technology in Austria, noted, “The bacteria, fungi and viruses in our food transiently colonize our gut. Cooking kills most of these, so raw fruit and veg are particularly important sources of gut microbes.”

Interestingly, the core of the apple contains the highest amounts of beneficial microbes, and eating the whole apple, including core and seeds, can provide you with 10 times more probiotics than discarding this central portion.12 As reported in the study:13

“Each apple fruit harbors different tissues (stem, peel, fruit pulp, seeds, and calyx), which were colonized by distinct bacterial communities … Interestingly, fruit pulp and seeds were bacterial hot spots, while the peel was less colonized …

Our results suggest that we consume about 100 million bacterial cells with one apple. Although this amount was the same, the bacterial composition was significantly different in conventionally and organically produced apples …

A significant management effect on the microbiota was … apparent for all tissues, even for seeds. Organic and conventional apples are occupied by a similar quantity of microbiota; consuming the whole apple includes an approximate uptake of 100 million bacterial gene copy numbers.

However, freshly harvested, organically managed apples harbor a significantly more diverse, more even and distinct microbiota, compared to conventional ones; the abundance of almost 40% of bacterial genera and orders differed significantly between organically and conventionally managed apples.

Moreover, organic apples conceivably feature favorable health effects for the consumer, the host plant and the environment in contrast to conventional apples, which were found to harbor potential food-borne pathogens.”

Bacterial differences may affect health effects and flavor

Organic apples were the only ones found to contain Lactobacilli, bacteria that break down sugars, associated with healthy digestion, robust immune function and even mental health.14,15 By creating an acidic environment, Lactobacilli also help protect against disease-promoting pathogens.16

Organic apples also contained higher amounts of Methylobacterium, a flavor-enhancing bacterium found in fruit and berries.17 This helps explain why organic apples (and many other organic foods) tend to have a more robust and pleasant taste.

Conventional apples, on the other hand, were found to contain Escherichia coli and Shigella — two Enterobacteriaceae species18 associated with foodborne illness, as both produce potent shigatoxin.19Neither of these species was found in organic apples. In the press release, lead author Birgit Wasserman suggested:20

“The microbiome and antioxidant profiles of fresh produce may one day become standard nutritional information, displayed alongside macronutrients, vitamins and minerals to guide consumers.

Here, a key step will be to confirm to what extent diversity in the food microbiome translates to gut microbial diversity and improved health outcomes.”

Apples and cardiovascular health

Apples also modulate your microbial composition by way of its fiber content. As explained in a 2015 paper21 on apples and cardiovascular health in the journal Nutrients:

“Apples are among the most frequently consumed fruits and a rich source of polyphenols and fiber. A major proportion of the bioactive components in apples, including the high molecular weight polyphenols, escape absorption in the upper gastrointestinal tract and reach the large intestine relatively intact.

There, they can be converted by the colonic microbiota to bioavailable and biologically active compounds with systemic effects, in addition to modulating microbial composition.

Epidemiological studies have identified associations between frequent apple consumption and reduced risk of chronic diseases such as cardiovascular disease … Quercetin glycosides may also reach the colon and could serve as a substrate for human gut bacteria.”

The Nutrients paper also cites research22 showing eating two apples per day for two weeks significantly increased beneficial Bifidobacteria and Lactobacillus while reducing Enterobacteriaceae and other pathogens.

In conclusion, the paper notes there’s supporting evidence to suggest apples can modulate risk factors for cardiovascular disease, improving lipid metabolism and vascular function, and lowering inflammation — in part by microbiota-derived metabolites and the apples’ prebiotic impact.

The microflora of fruits and vegetables

While beneficial bacteria have gained plenty of attention in recent years, the idea of fruits and vegetables as a significant source of live bacteria has received less consideration. We typically relate their impact on the gut microbiome based on their beneficial fiber content.

However, as noted in a paper23 dating all the way back to 1963, “The Microflora Within the Tissue of Fruits and Vegetables,” bacteria are a natural occurrence in “normal, sound fresh fruit tissues.” Higher amounts are typically found in low-growing vegetables, with tree borne fruits having lower amounts. This makes sense, since soil is rich microbes, provided its healthy.

However, different fruits and vegetables harbor higher amounts of bacteria in different parts. In cucumbers, for example, the bacteria are located closer to the periphery, with few at the core.

In tomatoes, the highest amounts of bacteria are found closest to the stem-scar and central core, decreasing as you go outward toward the peel. As you ferment fruits and vegetables, the naturally-occurring bacteria multiply exponentially through the plant tissue.

According to this 1963 paper, there are several routes or pathways of entry for bacteria into plant tissue. According to a 2016 study,24 one route of bacterial colonization begins at pollination, and the ultimate composition of a fruit’s microbiota is actually influenced by the microbial community found in the pollen to begin with.

Pollination impacts bacterial microbiota of apples

The study25 in question, published in the Environmental Microbiology, found “pollen provides a unique microhabitat,” with different plant pollens providing a wide variety of different bacterial species.

“Both plant species and pollination type significant influenced structure and diversity of the pollen microbiota,” the authors note, adding that “insect-pollinated species possessed a more similar microbiota in comparison to the wind-pollinated ones, suggesting a levelling effect by insect vectors …

Many plants are emitting large quantity of pollen during spring to autumn and several types of plant pollen may cause serious pollen-related diseases.

Therefore, pollen-associated bacteria may have a potential ecological and medicinal impact. In addition, they may also enter the plant reproduction processes and be directly transmitted to the next generation as seed endophytes …

The extreme low overlap of bacterial species between the investigated pollens demonstrated that the culturable fraction of the pollen microbiota had a surprisingly high level of species-specificity.

Only Rosenbergiella nectarea was isolated from three of the four pollen species, thus confirming that flower organs are the preferred habitat of this genus.”

While the different pollen species varied in their bacterial composition, the most dominant type of bacteria was Proteobacteria, followed by Actinobacteria, Acidobacteria and Firmicutes. The tectum surface, the outermost layer of the pollen, is the preferred location for bacterial colonization.

Interestingly, the bacteria found in pollen are in turn brought there by honeybees and other insects, weather, various plant materials and even human activities, showing just how circular ecology is. For optimal health, there needs to be a healthy transfer of bacteria from one species to another, from one location to another.

Bacteria modulate composition of nectar as well

Bacteria and yeast have also been shown to alter the characteristics of a flower’s nectar. As noted in a 2014 review in the Duluth Journal of Undergraduate Biology:26

“Plants present pollinators with nectar as an energetic reward, while pollinators transfer genetic material to help plants achieve full reproductive success. The constituents of nectar play a crucial role in facilitating this mutual relationship. A new area of research is emerging that may change the way biologists view this binary system; it may no longer be a two-way interaction.

Microorganisms — yeasts and bacteria — have been found to inhabit nectars across a wide geographic range and across a large range of plant species. These microorganisms change the characteristics of nectar in such a way to alter pollinator behavior.”

One nectar characteristic modified by bacteria is the actual concentration of the nectar. Another is its sugar composition, which is what the pollinators are primarily after.

So, in summary, both the plants’ propagation and the success of the pollinators depend in large part on the microbial communities in the nectar, and as noted earlier, these pollinators in turn distribute bacteria to pollen, ultimately affecting the microbial composition of pollinated fruits and vegetables. It seems no matter where you look, microbes are essential for life, playing crucial roles in the health of soil, plants and their fruits, and humans.

An organic apple a day keeps the doctor away

To learn more about the health benefits of apples, see “What Are the Health Benefits of Apples?” For example, studies have demonstrated apples can help protect against oxidative stress-induced neurotoxicity, reducing your risk for neurodegenerative disorders.

Aside from heart disease, apple consumption has also been shown to lower your risk for stroke, diabetes and cancer. For optimal health benefits, consider eating the whole apple, including the core, and make sure they’re organic.

Not only will organic apples provide you with a healthier composition of probiotics, you’ll also be able to eat the peel without exposing yourself to toxic pesticides.

According to the U.S. Department of Agriculture’s Pesticide Data Program, 47 different pesticide residues have been found on conventional apples, many of which are known or probable carcinogens, suspected hormone disruptors, neurotoxins and developmental or reproductive toxins.27

Now, you may have heard that eating apple seeds can be hazardous. The seeds contain amygdalin, a chemical that produces cyanide when the seeds are crushed.

But as noted by Dr. Jennifer Ashton, chief medical correspondent for ABC News, a 150-pound individual would have to crush and chew “literally hundreds of apple seeds,” in order to experience toxic effects.28

Sources and References 1-28

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