Fermentation of orange pomace: Impact on essential oil composition and antimicrobial activity

Since fermentation has been shown to be a valid approach to improve the antimicrobial activity of plant materials and food by-products, the present work aims to investigate the effect of this bioprocess on the composition of orange essential oils and their antimicrobial activity against food-related microorganisms. Fermentation with Lactiplantibacillus plantarum resulted in an increase in α-terpineol in the extracted essential oil, which is strongly correlated with the increase in the antimicrobial activity against Candida albicans, Staphylococcus aureus, Escherichia coli and Salmonella enterica. The increase in α-terpineol (about 27% in the oil recovered from fermented orange pomace and 0.13% in the unfermented control) was accompanied by a decrease in limonene (about 66% and 95% in the oils obtained from fermented and unfermented orange pomace, respectively), suggesting its metabolism during fermentation. To the best of our knowledge, no study has previously investigated the effect of orange pomace fermentation on the essential oil composition and antimicrobial activity, however, from these preliminary results, the application of fermentation prior to essential oil extraction seems to be a valid strategy for obtaining essential oils with enhanced antimicrobial activity.