Organic apples contain a more diverse and balanced bacterial community, which could make them healthier – particularly for the bowel -- and tastier than conventional apples, as well as better for the environment, a new study published in Frontiers in Microbiology shows.
Researchers at Graz University of Technology, Austria, set out to analyse the microbiome of apples.
"83 million apples were grown in 2018, and production continues to rise," said Professor Gabriele Berg, who led the study. "But while recent studies have mapped their fungal content, less is known about the bacteria in apples."
Using Arlet apples (a relatively small variety) bought in Austria, the researchers compared the bacteria in conventional store-bought apples with those in visually matched fresh organic varieties. The stem (or stalk), peel, flesh, seeds and calyx (at the bottom of an apple where its flower once was) were analysed separately.
Overall, the organic and conventional apples contained similar numbers of bacteria.
“We estimate a typical 240g apple contains roughly 100 million bacteria," reported Berg.
The researchers noted that most of the bacteria are in the seeds, with the flesh accounting for most of the remainder. Discarding the core means the bacteria intake falls to falls to nearer 10 million.
But organic apples contained a greater variety. "Freshly harvested, organically managed apples harbor a significantly more diverse, more even and distinct bacterial community, compared to conventional ones," explained Berg. "This variety and balance would be expected to 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 diversity of bacteria found in organic apples suggested greater health-affecting potential, according to Berg.
"Escherichia-Shigella - a group of bacteria that includes known pathogens - was found in most of the conventional apple samples, but none from organic apples. For beneficial Lactobacilli - of probiotic fame - the reverse was true."
Organic apples taste better too, said the study
This could make them taste better than conventional varieties, she added.
"Methylobacterium, known to enhance the biosynthesis of strawberry flavor compounds, was significantly more abundant in organic apples; here especially on peel and flesh samples, which in general had a more diverse microbiota than seeds, stem or calyx."
The results mirror findings on fungal communities in apples.
"Our results agree remarkably with a recent study on the apple fruit-associated fungal community, which revealed specificity of fungal varieties to different tissues and management practices," commented Birgit Wasserman, lead author of the study.
“The bacteria, fungi and viruses in our food transiently colonise our gut,” she said. “Cooking kills most of these, so raw fruit and veg are particularly important sources of gut microbes.”
She said the next step would be “to confirm to what extent diversity in the food microbiome translates to gut microbial diversity and improved health outcomes”.
Might bacteria data start to appear on food labels?
She suggested that information about bacteria and microbes could start to appear on food labelling to inform consumers.
"The microbiome and antioxidant profiles of fresh produce may one day become standard nutritional information, displayed alongside macronutrients, vitamins and minerals to guide consumers."
'An Apple a Day: Which Bacteria Do We Eat With Organic and Conventional Apples?'
Frontiers in Microbiology
Authors: Birgit Wassermann, Henry Muller and Gabriele Berg