Abstract:

The objective of this study was to investigate the effects of different microwave-assisted drying methods on the physical properties, bioactive compounds and antioxidant activity of beetroots. Beetroots were subjected to high-power microwave drying followed by low-power microwave drying (HMD+LMD), high-power microwave drying (HMD), low-power microwave drying (LMD), high-power microwave drying followed by hot air drying (HMD+HAD), hot air drying followed by low-power microwave drying (HAD+LMD), high-power microwave drying followed by vacuum drying (HMD+VD), and vacuum drying followed by low-power microwave drying (VD+LMD). The drying time, moisture content, hardness, color, microstructure, betalains, ascorbic acid, total flavonoids, 2,2′-azino-bis-(3-ethylbenzоthiazoline-6-sulfonic acid) (ABTS) radical scavenging activity and ferric reducing antioxidant power (FRAP) of beetroots were analyzed. The shortest drying time (67.0 min) was observed in HMD, while VD+LMD required the longest drying time of 308.0 min. There was no significant difference in the moisture content of dried beetroots prepared by different microwave-assisted drying methods. Beetroots dried by HMD+HAD showed the highest hardness of 1332.0 g, VD+LMD led to the most desirable color with the lowest total color change. Porous structures were found in beetroots produced by HMD+LMD, HMD and LMD. Beetroots prepared by VD+LMD displayed the highest content of betacyanin, betaxanthin and total flavonoids. While beetroots dried by HMD illustrated the highest ascorbic acid content of 272.3 mg/100 g dry weight (DW). In terms of antioxidant activity, the highest FRAP value of beetroots obtained using VD+LMD was 14.95 mg trolox equivalent (TE)/g DW. Meanwhile, beetroots dried by VD+LMD exhibited the largest ABTS radical scavenging activity (16.92 mg TE/g DW). Compared to other microwave-assisted drying methods, VD+LMD is a more promising method for drying beetroots. Supporting Agency Sincere gratitude to Guangxi Key Laboratory of Health Care Food Science and Technology, and Hezhou Key Laboratory of Microwave Application Technology for providing laboratory facilities and technical support during this research work. This study was funded by Guangxi First-class Discipline Food Science and Engineering Cultivation Project (GXYLXKP1816). Author Biographies Yan Liu, Sumy National Agrarian University; Hezhou University Postgraduate Student, Senior Lecturer Department of Engineering Technologies for Food Production School of Food and Biological Engineering

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