Analysis of phenolic compounds in pickled chayote and their effects on antioxidant activities and cell protection.

Although pickled chayote is a favorite Chinese fermented vegetable with high nutritional values, little is known about its bioactive compounds and antioxidant activities. In the work, changes of phenolic components and antioxidant activities in pickled chayote during 90 days' natural fermentation period were investigated. The results revealed a total of 15 phenolics were positively or tentatively recognized and quantified in pickled chayote. Among these phenolics, flavonoid aglycones (i.e., luteolin, apigenin, diosmetin, and isorhamnetin) significantly increased during fermentation (p < 0.05). In addition, total phenolic content, total flavonoid content, and antioxidant activities (ABTS and DPPH assays) were detected with the highest values in pickled chayote at the late stage of fermentation (56 - 90 days). Furthermore, pickled chayote could protect HepG-2 cells against HO-caused oxidative damage by the reduction of reactive oxygen species generation and the promotion of innate antioxidant defense system (p < 0.05). Correlation analysis showed that 8 phenolic compounds were highly associated with the increase of extracellular and intracellular antioxidant activities. Besides, Lactobacillus alimentarius and Lactobacillus futsaii could increase the content of apigenin derivatives and Pichia membranifaciens could promote the production of flavonoid aglycones. In general, fermentation is an effective approach to enhance antioxidant potentials of pickled chayote and thereby increasing its functional values.