A PHYSIOLOGICAL APPROACH TO EVALUATE THE ANTIOXIDANT CAPACITY OF THE DIFFERENT MATRIXES OF GRAPEFRUIT

Grapefruit is rich in polyphenols, which exhibit antioxidant and antiflammatory properties. The study aimed at evaluating the influence of an enzymatic in vitro gastrointestinal digestion (GAR method1), followed by fermentation, on the antioxidant capacity of the different matrixes of grapefruit. This physiological-resembling approach allows to extract antioxidants from the following grapefruit parts: zest, rind, pulp, and juice (obtained from red and white grapefruit), including two commercial juices. The analyses were conducted on the fresh soluble fractions obtained after in vitro digestion and fermentation (potentially absorbable fraction), and on the lyophilized solid fractions obtained after fermentation (non-absorbable fraction). The antioxidant capacity was evaluated with ABTS, FRAP and Indigo Carmin Hydroxyls, AAPH, and Reduction methods. The results showed that rind possesses the highest antioxidant capacity, probably due to the elevate concentration of naringin. Of note, the soluble fractions derived from digestion possess higher scavenging activity rather than the soluble fractions from fermentation, which on the contrary have a considerable reducing ability. The insoluble fractions from fermentation showed no antioxidant activity in any of the assays. These data were corroborated through the analysis of polyphenols and their metabolites by means of  mass spectrometry, in both digested and fermented soluble fractions.