Reactions of polyphenols in masticated apple fruit with nitrite under stomach simulating conditions: Formation of nitroso compounds and thiocyanate conjugates

- Apple polyphenols can react with salivary nitrite in the stomach.
- Apple catechins and procyanidins can be nitrosated in the stomach.
- Apple chlorogenic acid can be transformed into a thiocyanate conjugate in the stomach.
- The thiocyanate conjugate is hydrolyzed to an oxathiolone derivative.

By the ingestion of fresh apple fruit, it is masticated squeezing apple juice into the oral cavity and the juice is mixed with saliva. The mixture of saliva and apple juice is swallowed into the stomach where the pH is around 2. This paper deals with the reactions of polyphenols in the juice obtained by mastication of apple fruit with salivary nitrite under acidic conditions. The concentrations of catechins, procyanidins, and chlorogenic acid in the apple juice were approximately 55, 55, and 170 μM, respectively, and the polyphenols were oxidized by salivary nitrite under conditions of the stomach. Rates of the oxidation increased in order chlorogenic acid < catechins < procyanidins. The oxidation of catechins and procyanidins resulted in the formation of the nitroso compounds, and the oxidation of chlorogenic acid resulted in the formation of the thiocyanate conjugate. The production of dinitroso compounds is proposed to be due to the addition of nitric oxide (NO) to radicals of catechins and procyanidins. As the mechanism of thiocyanate conjugate formation, reaction of o-quinone of chlorogenic acid with a salivary component thiocyanate is proposed, and the formation of the thiocyanate conjugate is discussed from the point of detoxification of chlorogenic acid quinone.