Polyphenol content and in vitro evaluation of antioxidant, antimicrobial and prebiotic properties of red fruit extracts

A diet rich in fruit provides nutrients that are vital for human health. In particular, the anthocyanins contained in fruit have received attention due to their health-promoting properties and antioxidant, anti-inflammatory and antimicrobial activities. In this study, total phenolic, anthocyanin, flavonoid content and antioxidant activity were determined in extracts from plum skins, Italian red grape skins, and different parts of elderberry. Furthermore, it was analysed the activity of the fruit extracts in inhibiting several pathogens and in stimulating the growth of three probiotic strains and one blend SYNBIO®. All extracts show a good content of anthocyanins, exhibited high antioxidant activity and significantly inhibited the pathogens tested. The extracts had no inhibitory activity on the probiotic strains, but rather, they stimulated the growth of all the probiotics. In order to test the potential prebiotic properties of these anthocyanin-rich red fruit extracts, the kinetic growth of all probiotics was monitored, and it was found that probiotics in presence of elderberry and plum extracts had a significant increase in mean doubling time. The combined formulation of elderberry extracts and each of the four probiotics showed higher antioxidant activity compared to that of the extract alone, indicating the ability of probiotics to increase the antioxidant activity of the elderberry extracts. The fruit extracts used in this study can be considered beneficial for human health, due to their high content of polyphenols, particularly anthocyanins. Based on their antioxidant and antimicrobial activities, these fruit extracts can be considered good candidates for designing new functional foods and beverages, as well as nutraceuticals. Moreover, the ability of the fruit extracts to stimulate the growth of the probiotics merits further study to ascertain whether they can be defined as prebiotics.