Apples are among the most consumed fruits around the world. They represent a wellspring of direct human exposure to bacterial networks, which is less contemplated.
In a new study, scientists analyzed the apple microbiome to detect differences between tissues and the impact of organic and conventional management by a combined approach of 16S rRNA gene amplicon analysis and qPCR, and visualization using fluorescence in situ hybridization and confocal laser scanning microscopy (FISH-CLSM).
Scientists found that organic apples harbor a more diverse and balanced bacterial community—which could make them healthier and tastier than conventional apples, as well as better for the environment.
Study senior author Professor Gabriele Berg, of the Graz University of Technology, Austria said, “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.”
“83 million apples were grown in 2018, and production continues to rise. But while recent studies have mapped their fungal content, less is known about the bacteria in apples.”
Scientists compared the bacteria in conventional store-bought apples with those in visually matched fresh, natural ones. Stem, peel, flesh, seeds, and calyx—the straggly bit at the bottom where the flower used to be—were analyzed separately.
Berg said, “Overall, the organic and conventional apples were occupied by similar numbers of bacteria. Putting together the averages for each apple component, we estimate a typical 240g apple contains roughly 100 million bacteria. The majority of the bacteria are in the seeds, with the flesh accounting for most of the remainder.”
Are these bacteria good for you?
The good news is that they are healthy for our gut and apple eaters who devour the core are also eating ten times as much bacteria than those who discard it.
Berg explained, “Freshly harvested, organically managed apples harbor a significantly more diverse, more even and distinct bacterial community, compared to conventional ones. 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.”
“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.”
The authors suggest microbiome and antioxidant profiles of fresh produce may one day become standard nutritional information, displayed alongside macronutrients, vitamins, and minerals to guide consumers. Their study is published in Frontiers in Microbiology.