Apples are popular and an excellent source of nutrients, vitamins C and B-complex, antioxidants, minerals, and dietary fibers. They are also a model for the study of fruit biome. A recent study on apples was published by Frontiers of microbiology to analyze their bacterial quality and quantity of resident microbes. It showed that a single apple contains up to 100 million bacteria. They reside in the apple tissues – the stem, peel, fruit pulp, seeds, and calyx. Among these, fruit pulp and seeds are bacterial hotspots.
A study was conducted by Graz University of Technology in Austria which focused on bacteria present on the organically and conventionally harvested fruits. The result showed that each apple provided unique niches for bacterial communities and diverse bacteria were noticed.
Management of fruits, soil quality, surrounding environment, abiotic and biotic conditions, storage factors, etc. contributed to this diverse community of bacteria.
Although the number of bacteria was the same in both chemically grown apples and organic apples, the amount of health-contributing bacteria varied. The community included 44 different phyla, 325 taxonomic orders, and 1,755 genera. Among these, an abundance of cytophagales were indicators for organically grown apples while conventional apples showed a prevalence of Burkholderiales, Pseudomonadales, Enterobacteriales, and Flavobacteriales.
The order Enterobacteriales contained taxa responsible for foodborne outbreaks and was thus used to test the potential outbreaks through convention and organic apples. It revealed that conventionally grown apples carried a greater number of Enterobacteriales than organically grown ones. Ralstonia, a soil-borne pathogen which hampers the growth of many crops was found abundantly in apples grown through conventional growing methods. The number of Lactobacillus was relatively high in organic apples than chemically grown ones. They are also frequently used in probiotics for their health-supporting factors.
Shannon diversity index revealed that organic and unprocessed apples harbor more diverse bacteria than conventionally-managed ones. This diversity helped out-compete pathogenic bacteria, and also proved advantageous for the prevention of allergic diseases and reduced the possibility of developing resistant strains of pathogen.
The study concluded that both growing methods played significant roles in contributing to the microbial diversity. Organic methods led to health-benefiting effects for both consumers and nature while conventionally-grown products had the potential of raising food-borne pathogens along with adversely affecting the soil quality. 100 million bacteria are not necessarily all a threat, some in fact help strengthen our gut immunity.