Characterization and anti-oxidant properties of powder from differently dried beetroot (Beta vulgaris L.) slices

Objective This research work was aimed at investigating the changes in phytochemical constituents during the dehydration of beetroot slices using microwave vacuum drying and freeze drying. The results are reported in terms of the overall quality attributes of the resulting powder from the beetroot slices. Methods Powder characteristics and antioxidant properties of beetroot ( Beta vulgaris ) slices of varying (1 and 2 mm) thickness dried under microwave (power, 160 and 320 W) vacuum (710, 660 and 610 mm Hg, absolute pressure) drying (MVD) and freeze drying (FD) (0.062 mbar chamber pressure and -42 °C condenser temperature) were investigated in this study. Quality of the beetroot powder was evaluated based on moisture content, water activity, colour attributes, powder properties, functional characteristics, antioxidant activity and betalain content. Results Significant ( p ≤ 0.05) difference was observed across all the parameters under the different drying conditions. MVD significantly reduced drying time while producing powder with high antioxidant activity, porosity an improved solubility. However, FD samples for lower thickness (1 mm) exhibited superior retention of colour, and betalain pigments due to low temperature processing but antioxidant activity was found 24.51% RSA. Among MVD conditions, higher microwave power (320 W) combined with moderate vacuum ≤660 mm Hg resulted in an improved retention of bioactive compounds, colour quality and %RSA (60-72%) for the powder. Conclusions The findings of the study highlight that MVD can be effectively utilized as an alternative for FD, as a low cost drying for the production of pigment enriched beetroot powder for versatile commercial food colouring applications.