Spent coffee (Coffea arabica L.) grounds positively modulate indicators of colonic microbial activity

Spent coffee grounds (SCG; MR-medium and DR-dark-roasted) were submitted to an in vitro gastrointestinal digestion followed by a colonic fermentation using two microbiota communities (lean and overweight). The in vitro protective colonic effect of SCG was evaluated on colonic enzyme activities (beta-glucosidase, beta-glucuronidase, tryptophanase, and urease). The bioaccessibility of oligosaccharides and melanoidins, as well as colonic short-chain fatty acids (SCFAs) and ester production were determined and correlated with evaluated colonic enzymes. Melanoidins (8-17 mg/100 g) were highly correlated with antioxidant capacity (16-80 mu mol Trolox/g sample; r=-0.78, p=0.0001, ABTS), while raffinose was only detected during the colonic phase (1.22-4.23 mg/g) suggesting SCG use as human microbiota substrate. The extract obtained from MR-SCG colonic fermentation inhibited enzyme activity (up to 80%) at a rate similar to or even higher than inulin (used as a positive control during colonic fermentation). Using the same substrate (MR-SCG), microbial communities produced different amounts and SCFAs ester patterns, linked to the enzymatic inhibition effects. OW-microbiota produced the highest cumulative SCFAs (36 nmol/L; 55% more than L-microbiota). Molecular studies, and in vivo assays are needed to further elucidate the mechanisms exerted by SCG. Microbial communities need to be identified to determine the colonic effects of SCG and support their use as a functional food ingredient. Industrial relevance: Our results support the added value of this industrial by-product to be used as a nutraceutical or functional ingredient for food products. Reducing food losses and waste 'is essential' to improve the sustainability of food systems, and contribute to broader systemic changes, including nutrition and health. SCG are digested under in vitro human gastrointestinal condition, where nutraceutical compounds are released from the matrix exerting health benefits, including antioxidant capacity, and positively modulating indicators of colonic microbial activity.