Bio-accessibility of phenols, flavonoid and antioxidant capacity of tropical leafy vegetables through in-vitro gastro-intestinal digestion

To provide a new insight to the nutritionist and processing industries, in-vitro digestion studies of 20 tropical green leafy vegetables were conducted. The results indicated significant (P < 0.05) changes in phenolics, flavonoids and antioxidants level based on food matrix properties where the leaf extracts exhibited higher antioxidant activity than corresponding stem extracts. The most flavonoids bio-accessibility were observed in Ipomoea aquatic leaves (463.4%), Colocasia esculenta stem (335.5%), Alternanthera philoxeroides (260.7%). The transformation of phenolic compounds during in-vitro digestion may lead to different structural forms possessing different chemical properties and functions. Compared to fresh state, except for Trigonella foenum graecum, Ipomoea aquatica stem, all vegetables exhibited decrease in antioxidant activity (DPPH) value (4.7%-76.9%), nine vegetables exhibited a decrease in antioxidant activity (ABTS) value (3.01%-22.8%) and except for Amarantus cruentas, all vegetables exhibited decrease in FRAP value (15.29%-85.24%). Only four vegetables (Colocasia esculenta stem and leaf, Amaranthus cruentas and Murraya koenigii) had shown decrease (1.7%-13.2%) and rest 16 vegetables followed 9.6%-314.13% increase in fi-carotene bleaching. Interestingly, all vegetables displayed sharp increase in Super Oxide Dismutage (SOD) value (94.99%-174.78%) after duodenal phase even significant changes in phenolic content and flavonoid contents were observed. Correlation analysis showed weak correlation between phenolic content with antioxidant activity in successive gastric and duodenal phase.