Evaluation of alkaline conversion of sinapic acid to thomasidioic acid

Conditions which promote the alkaline conversion of sinapic acid (SA), the main phenolic acid in canola, to the lignan thomasidioic acid (TA) were investigated as the presence of TA could affect nutritional and functional properties of canola products. Reaction rates were studied using ultraviolet spectroscopy under oxygen, nitrogen, and air and in the presence of antioxidants. High-pressure liquid chromatography was used to quantify the conversion of SA to TA. This reaction appears to involve an oxidative coupling of SA molecules which can be controlled by purging with nitrogen. By including ascorbic acid, the reaction was slowed but not completely controlled, and the presence of sodium bisulfite accelerated the reaction. In the presence of air, there was complete conversion of SA to TA at pH 8.5 and 30% conversion at pH 7.