Effects of Penetrating Microwave Hot-Air Rolling Blanching Pretreatment for the Drying of Hawthorn Slices: Evaluation of Enzyme Activity, Drying Characteristics, Moisture Migration, Microstructure, and Quality Attributes

Drying can overcome the drawback of the high moisture content of hawthorn, which is difficult to store, but studies involving drying through microwave pretreatment are lacking. We here investigated the effects of penetrating microwave hot-air rolling blanching (PMHRB) pretreatment on the enzymatic activity, drying characteristics, physicochemical properties, and microstructure of hawthorn slices under different powers (0, 2, 3, 4, 5, and 6 W/g) and for a fixed time (15 min). PMHRB significantly inactivated polyphenol oxidase and peroxidase which improved the appearance of dried hawthorn products. Additionally, PMHRB allowed moisture redistribution and altered the microstructure, which shortened the drying time by 28.75-68.75%. Shrinkage, hardness, and microstructure analyses showed that the pretreated hawthorn expanded in volume and changed the texture of the dried hawthorn. The optimum pretreatment power (5 W/g) significantly improved the quality of hawthorn, as compared to the unpretreated samples, total flavonoids, total phenols, 1,1-diphenyl-2-picrylhydrazyl (DPPH), and 2,2 '-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) were increased by 27.06%, 36.44%, 63.54%, and 39.21%, respectively. Thus, PMHRB pretreatment dramatically enhanced the drying features and quality and is a potentially effective drying technique for hawthorn.