| Abstrakt: |
Introduction. The aim of the research is to investigate the influence of different drying methods, including freeze drying, vacuum drying, microwave drying and microwave vacuum drying, on the bioactive compounds and antioxidant activity of beetroots. Materials and methods. Bioactive compounds and antioxidant activity of dried beetroots prepared by freeze drying (FD), vacuum drying (VD), microwave drying (MD), and microwave vacuum drying (MVD) were investigated. Moisture analyzer was used to determine moisture content of beetroots. Beetroot powder was extracted three times with 50% ethanol (v/v). Colorimetric methods were used to determinate contents of betalain, ascorbic acid and total phenolic, and 1,1-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, ferric reducing antioxidant power (FRAP) and 2,2′-azino-bis-(3- ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging activity of dried beetroots. Results and discussion. Drying methods significantly affected the drying time, bioactive compounds and antioxidant activity of beetroots. The shortest drying time (0.56±0.01 h) was occurred at MVD, while FD required the longest drying time of 29.67±0.58 h. There was no significant difference in the final moisture content of dried beetroots prepared by different drying methods. It was found that the dried beetroots prepared by VD showed the highest ascorbic acid content of 8.73±0.23 mg/g, and the beetroots dried by FD displayed the highest betaxanthin content of 2.57±0.01 mg/g, while the beetroots obtained by MD showed the lowest betacyanin content of 2.98±0.02 mg/g, and FD led to significantly lower total phenolic content of beetroots in comparison with other drying methods. In terms of antioxidant activity, the beetroots prepared by MD and MVD showed significantly higher DPPH radical scavenging activity than the beetroots prepared by VD and FD. Meanwhile, the beetroots obtained by VD exhibited the largest ABTS radical scavenging activity of 17.22±0.35 mg trolox equivalent (TE)/g. Besides, the beetroots prepared by MVD displayed the highest FRAP value of 13.36±0.17 mg TE/g. Compared to beetroots prepared by other drying methods, the beetroots prepared by FD showed the lowest FRAP, DPPH and ABTS values, indicating the weakest antioxidant activity. Conclusions. Considering the drying time, bioactive compounds and antioxidant activity, MVD is recommended to prepare dehydrated beetroots, which can reduce drying time and better preserve bioactive compounds and antioxidant activity of beetroots. [ABSTRACT FROM AUTHOR] |
