Effects of Different Cooking Methods on the Quality of Quick-Frozen Cooked Purple Sweet Potato

The effects of different cooking methods namely, steaming, microwave and roasting on the quality of quick-frozen cooked purple sweet potatoes (cv. Ziluolan) were investigated by measuring its volatile components, color, microstructure, anthocyanin content and antioxidant activity. The results showed that different cooking methods affected the volatile flavor composition of frozen cooked purple potatoes, providing more aroma compounds and a unique flavor. After cooking, the internal structure of frozen cooked purple sweet potatoes changed, making it easier to digest, and there were significant differences in the anthocyanin contents of purple potatoes processed by different cooking methods; the anthocyanin content of steamed purple sweet potatoes was 4.12 mg/g, which significantly higher than that of fresh purple sweet potatoes (3.36 mg/g) (P < 0.05). Six categories of purple sweet potato anthocyanins were identified by liquid chromatography tandem mass spectrometry (LC-MS/MS), the major ones being paeoniflorin and cornflowerin, and the proportion of paeoniflorin in steamed purple sweet potatoes was largest (84.12%), suggesting better preservation of nutrients and color. In addition, cooking increased the release of anthocyanins from quick-frozen cooked purple sweet potatoes during gastrointestinal digestion, which in turn significantly improved the antioxidant activities (1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) radical scavenging capacity, 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radical scavenging capacity and superoxide anion radical scavenging capacity) and inhibited the activity of digestive enzymes (α-amylase and α-glucosidase), while changing the acylation rate and improving the stability of purple sweet potato anthocyanins. It was concluded that steaming could better stabilize anthocyanins in quick-frozen cooked purple sweet potatoes, imparting it with good storage stability. This study can provide a theoretical reference for the development of convenience purple sweet potato foods.