Degradation Kinetics of Anthocyanins from Purple Eggplant in a Fortified Food Model System during Microwave and Frying Treatments

A model food system was designed with dietary fiber and crude anthocyanins from purple eggplant peel to explore the degradation mechanism of anthocyanins during microwave and frying treatments. Our results found that delphinidin-3-O-rutinoside was either hydrolyzed into delphinidin or condensed with p-coumaric acid to form p-coumaroyl-delphinidin-3-O-glucoside. Delphinidin was cleaved into gallic acid and phloroglucinaldehyde, which might be further oxidized into pyrogallol and phloroglucinol, respectively. The total anthocyanin degradation followed the first-order kinetics in fried and microwaved solid matrix samples as well as microwaved liquid matrix samples. However, the total anthocyanin degradation followed the second-order kinetics in the heated liquid matrix samples at the frying temperature. The brown/polymeric color index, which negatively correlated with the anthocyanin content, increased faster in the liquid matrix samples than in the solid matrix samples. Compared with frying treatment, a higher rate of anthocyanin degradation in solution was observed under microwave treatment. However, anthocyanins were subject to much more damage under frying treatment than microwave treatment in a solid food system.