Reactions of apple fruit polyphenols with nitrite under conditions of the gastric lumen: Generation of nitric oxide and formation of nitroso catechins

Abstract

Apple fruit (cultivar sunfuji) contained procyanidin B2, (-)-epicatechin, and chlorogenic acid as major polyphenols. The concentration increased in the order procyanidin B2 < (-)-epicatechin < chlorogenic acid. Nitrite reacted with the polyphenols in methanol extracts of apple fruit both in an acidic buffer solution (pH 2.0) and at the pH of acidified saliva. The rate of the reaction increased in the order chlorogenic acid < (-)-epicatechin < procyanidin B2. During the reactions, nitrous acid (pKa = 3.3) was reduced to nitric oxide (NO) by the polyphenols, and nitroso compounds of procyanidin B2 and (-)-epicatechin were produced. Our conclusion are that (i) the nitroso compounds can be produced by the reaction of NO with radicals of procyanidin B2 and (-)-epicatechin, which are formed by the nitrous acid-dependent oxidation of procyanidin B2 and (-)-epicatechin, and that (ii) polyphenols such as chlorogenic acid and (-)-epicatechin, which will react with nitrous acid slowly in the gastric lumen, can be transported to the intestine when apple is ingested. Copyright © 2014, Japanese Society for Food Science and Technology.