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When you bite into the skin of an apple, you don’t tend to think about the bacteria inside but rather the sweet, almost candy-like tissue. In fact, apples are one of the most-eaten fruits in the world, with 10.2 billion pounds produced in 2018 in the US alone.
Now, a new study in Frontiers in Microbiology suggests you are also consuming roughly 100 million bacteria for every single apple you eat – core, seeds, and all. This bacteria isn’t necessarily the kind to be squeamish about but in some cases fostered, according to the team. The diverse bacteria in organic apples could make them healthier, tastier, and superior for the environment than traditional apples.
"The bacterial community of organically managed apples was significantly more diverse, more balanced and showed a distinct composition compared to conventional apples, although the number of bacteria was almost the same," said lead author Birgit Wasserman, from Graz University of Technology, Austria, to IFLScience. "Which means that you eat the same number of bacteria with organic and conventional apples, but you eat very different ones."
The seeds hosted the most bacteria by far, while the peel and pulp were least abundant. However, the diversity of bacteria was highest for the peel and pulp regions, with organic apples having more healthy bacteria groups.
Escherichia-Shigella, a group of bacteria that includes pathogens, was found often in conventional apple samples but not at all in organic ones. Lactobacilli, well known for its probiotic uses, was found in organic but not conventional apples. The diverse bacteria count of organically managed apples may "limit overgrowth of any one species, and previous studies have reported a negative correlation between human pathogen abundance and microbiome diversity of fresh produce."
The apples used in the study were Arlet (also known as Swiss Gourmet) – a cross between Golden Delicious and Idared – and grown in Austrian soil. Only four apples were selected from each of the management groups, a rather small sample size from a specific location. Separate bits of the apples were analyzed, including the stem, peel, seeds, flesh, and calyx.
Wasserman notes that humans are referred to as holobionts "which describes an assemblage of different species forming one unit. Plants are holobionts as well. We also know that specific bacteria survive our stomach and become inhabitants in our gut system, at least temporarily, featuring important properties for our health. Vegetables and fruits, especially consumed raw, represent an important source for a diverse microbial community."
"From previous studies we know that apple polyphenols (procyanidines) alleviate allergic symptoms, promote the growth of beneficial Lactobacillus and Bifidobacterium in the human gut and reduce the abundance of food-borne pathogens. Another study described specific microorganisms to potentially reduce food allergies."
The findings provide another lens through which to look at the health of the food we eat. As Wasserman added, "we've become more and more aware of the importance of the gut-associated microorganisms for human health."
"With our study we were simply able to describe differences between organic and conventional apples and showed 'who is there', but the question remains 'what are they doing there?'. This has to be investigated in future studies."
