Nitrite Scavenging and Inhibition of N-Nitrosamines Formation by Phenolic Extracts From Diospyros lotus L. Leaves and Active Ingredients

Diospyros lotus L. leaves are used as a functional tea and folk medicine in several Asian countries. This study aimed to evaluate the effects of phenolic extracts of the leaves on scavenging nitrite and inhibiting N-nitrosamines (NAs) formation and to determine the active ingredients responsible for these effects. Of the 7 fractions (Fr1-Fr7) prepared from the extract of D. lotus leaves, Fr5 contained the highest phenolic content and exhibited the strongest activity. Five active ingredients of Fr5 were discovered, and 4 of them were identified as myricitrin (Mytr), myricetin (Myt), myricetin-3-O-β-d-glucoside (Myt-Glc), and myricetin-3-O-β-d-galactoside (Myt-Gal). The content of Mytr was much higher than those of the other 3 ingredients, both in Fr5 and extracts of D. lotus leaves. Finally, Mytr and Myt were proved to have stronger activities by the 1,1-diphenyl-2-trinitrophenyl hydrazine scavenging, nitrite scavenging, and inhibition of NAs formation assays. These results indicated that Mytr was the main active ingredient of D. lotus leaves. Myt, Mytr, and Fr5 from the leaves could be used as natural agents for antioxidant, nitrite scavenging, and inhibition of NAs formation in food and the human body.