Upcycling of spent coffee grounds solid-state fermentation by<i> Aspergillus</i> strains:<i> in</i><i> vitro</i> assessment of prebiotic activity and gut health benefits

This study aimed to explore the upcycling of spent coffee ground (SCG) by solid-state fermentation (SSF) using fungal strains of Aspergillus oryzae and Aspergillus awamori. The results indicated that SCG was a suitable substrate for the growth of both fungal strains, showing a 3-log unit increase in spores. SSF significantly improved the recovery of soluble dry matter from SCG, with increases of almost 2-fold for A. oryzae and 4-fold for A. awamori. Notably, SSF resulted in a 64 % reduction in the browning index, indicating the potential of A. awamori to degrade coffee melanoidins. Both fungal strains were effective in releasing free sugars from SCG: A. awamori-fermentation yielded the highest concentrations of mannose and galactose. A. oryzae-fermentation increased the oligosaccharide content to a final level of 14.15 mg/100 g. In vitro batch fermentation showed that fermented SCG supported the short-chain fatty acid production capability especially in distal colon. The genus composition in medium supplied with fungal fermented SCG included Enterobacteriaceae, Klebsiella, Clostridium, Bacteroides, and Akkermansia. These findings suggest that solid state fermentation of SCG could produce a prebiotic ingredient having beneficial effects on gut health.