ANTIOXIDANT POTENTIAL AND INHIBITORY EFFECT OF IN VITRO DIGESTED YAM (DIOSCOREA ROTUNDATA AND DIOSCOREA CAYENENSIS) ON CHOLINESTERASES AND LIPID PEROXIDATION

Abstract

Foods have been used for many years as a source of traditional medicine to treat various diseases and conditions. Many of these functional foods are also excellent sources for phytochemicals, with potential health benefits. This study was aimed at investigating the antioxidant activities, phenolic composition and the anticholinesterase activities of fresh and old white and yellow yam (commonly called ‘isu titun’ and ‘isu egbe’ in Yoruba language in Nigeria). In addition, the lipid peroxidation inhibitory ability of these yam species was determined. Phytochemical examination revealed the presence of alkaloid, saponin, terpenoid and flavonoid. HPLC-DAD qualitative estimation of phenolic compounds revealed the presence of some flavonoids and phenolic acids in the raw and cooked samples. The quantitative estimation of the phenolic compounds revealed that there was a reduction in the level of most of the phenolic compounds after boiling. Similar results were obtained for total phenolic content, total flavonoid content, Ferric reducing antioxidant power (FRAP), ABTS radical scavenging activity, lipid peroxidation and hydroxyl radical (OH) scavenging activity with the exception of DPPH scavenging activity. The in vitro enzyme digested samples of the yams showed higher total phenolic content than that of the methanolic extracts. Similar results were obtained for total flavonoid, FRAP, ABTS, DPPH radical scavenging activity and inhibitory action against lipid oxidation with the exception of hydroxyl radical (OH) scavenging activity. The ability of the methanolic extract and enzyme digested samples of the yams to inhibit lipid oxidation using brain and liver homogenate decreases as the concentration of the extract increases. The result further revealed that white yam has higher total phenolic content, FRAP, ABTS, DPPH, hydroxyl radical scavenging activity and lipid oxidation inhibitory potential with the exception of total flavonoid content than yellow yam. . Moreover, the result further revealed that fresh yam has higher total phenolic content, total flavonoid, FRAP, ABTS , DPPH radical scavenging activity, inhibitory action against lipid oxidation and hydroxyl radical scavenging activity than old yam for both studied species. The anticholinesterase and antibutyrylcholinesterase activity of the studied yam revealed that the in vitro digested samples has no inhibitory activity while the methanolic extract of old yam showed some level of inhibitory activity. The result of this study implies that the selected yam varieties possess moderate antioxidant capacity, with raw white yam ranking high, therefore can be considered as health supplements and nutraceutical foods.