In vitro assessment of prebiotic effect of coffee and its by-products on human intestinal Microbiota.

The human intestinal microbiota has long been known to influence human health and disease, but recently, its improvement by modulation of gut microbiota is an upcoming evolving strategy [1]. The microbiota present in the human body provides numerous benefits, including enhancement of overall well being and also protection against pathogenic microorganisms. Gut microbiota exerts its protective role through the production of different signaling molecules which can modify the functionality of other organs. When the gut bacterial composition is altered (dysbiosis), there is a strong association with the pathogenesis of many inflammatory diseases and infections. Prebiotics supplementation could be a good strategy to improve intestinal microbiota of the target host, conferring health benefits. Currently, other substances beside carbohydrates, i.e. polyphenols, might fit the updated definition of prebiotics presenting evidence of beneficial effects in the host [2]. Coffee and its by-products are very interesting substrates in this sense, because they contain plenty of polyphenols and other essential compounds like melanoidins and chlorogenic acid, which make them potential prebiotic food components. The aim of the present study was to characterize and assess the potential prebiotic properties of seven coffee by-products, studying in vitro the modifications on human gut microbiota and its metabolic products. The coffee by-products, all from Coffea arabica, were selected and studied to evaluate compounds and bioactive substances, responsible for their prebiotic activities on the intestinal microbiota. The selection of coffee by-products was made of: Green Coffee Bean (coarsely ground), Silver Skin (generated from the roasting process of the bean), Spent Coffee Ground (generated from the coffee preparation), two extracts from Silver Skin and from Spent Coffee, finally the Roasted Coffee and an Espresso freshly made. A fermentation system (batch culture) in anaerobic conditionswas used to mimic the human intestine. During all fermentation cycles, the biodiversity of gut microbiota was analysed and selected bacterial groups were enumerated using Real-Time PCR analysis. At the same time points the detection and quantification of short chain fatty acids (SCFA) was also performed. Inulin was chosen as well-defined prebiotic substrate, to compare the results obtained from all the considered coffee substrates. The general trend is an increase in the bacterial counts of beneficial bacterial groups (Lactobacillus spp. and Bifidobacterium spp.), and a decrease for Clostridium coccoides-Eubacterium rectale group. These data are supported also by the SCFA that resulted to accumulate during fermentation especially acetic and propionic acids. The valorisation as prebiotics of these by-products highlights that their recovery from the coffee industry is of great importance, not only because of their significant properties, but also because it could exploit a part of industry wastes.