Prebiotic effects of olive pomace powders in the gut: in vitro evaluation of the inhibition of adhesion of pathogens, prebiotic and antioxidant effects

Olive pomace is a biowaste rich in polyphenols and insoluble dietary fibre with high potential to develop new value chains towards a sustainable and circular bioeconomy. Regarding gut health, olive pomace phenolics and insoluble dietary fibre (after possible fermentation) could act as antioxidants, antimicrobial and prebiotic agents. These potential beneficial effects on the gut were analysed for two powders from olive pomace: liquid-enriched powder (LOPP) - mostly source of phenolics - and pulp-enriched powder (POPP) - main source of insoluble dietary fibre. LOPP and POPP were subjected to an in vitro simulated gastrointestinal digestion followed by in vitro faecal fermentation. The undigested fraction retained in the colon was analysed regarding its potential antioxidant, antimicrobial and prebiotic effects. LOPP and POPP did not impact the gut microbiota diversity negatively, showing a similar ratio of Firmicutes/Bacteroidetes compared to a positive control (FOS). LOPP exhibit a positive (similar to FOS) effect on the Prevotella spp./Bacteroides spp. ratio. Both powders promoted more the production of short-chain fatty acids (mainly acetate > butyrate > propionate) than FOS and showed also significant total phenolic content and oxygen radical absorbance capacity during faecal fermentation until 48 h. Besides that, these powders showed mucin-adhesion inhibition ability against pathogens, principally POPP against Bacillus cereus (22.03 ± 2.45%) and Listeria monocytogenes (20.01 ± 1.93%). This study demonstrates that olive pomace powders have prebiotic effects on microbiota, including the stimulation of short-chain fatty acids production, potential antioxidant and antimicrobial activity which could improve the human gut health.