The degradation and antioxidant capacity of anthocyanins from eggplant peels in the context of complex food system under thermal processing

A model of complex food system composed of dietary fiber, protein, starch (3/2/2), added with anthocyanins extracted from purple eggplant peels was constructed to investigate impacts of thermal treatments (including steaming, boiling, microwave and frying) on the degradation and antioxidant capacity of anthocyanins. The content of anthocyanins was reduced by 84.48% under frying treatment (185 ± 5 °C), and the degradation of anthocyanins was in line with second-order kinetics as with microwave treatment (700 W). Under boiling and steaming conditions, the degradation of anthocyanins followed first-order kinetics. Additionally, the antioxidant capacity was positively correlated with the contents of total anthocyanins and polyphenols. During thermal treatments, anthocyanins were mainly decomposed into gallic acid, phloroglucinaldehyde, and 2,4-dihydroxybenzoic acid (frying), in which phloroglucinaldehyde could be further isomerized into phloroglucinic acid. The results of scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) also supported that frying showed the most robust effect on influencing the structure of anthocyanins during these four thermal treatments.