Impact of vacuum drying on drying characteristics and functional properties of beetroot (Beta vulgaris)

Beetroot has been considered as an attractive raw material to dehydrate owing to possessing valuable essential nutrients. In the present work, it was appraised whether vacuum drying (VD) could be a proper alternative to freeze-drying (FD). Hence, the impact of both drying techniques on the physicochemical properties, betalainic pigments, antioxidant potential and individual phenolic compounds of beetroot was studied. Vacuum drying kinetics for obtaining the predominant drying rate period of beetroot was also evaluated. Results showed that the increase of temperature conducive to an increase of drying rate and effectively shorten drying time. In general, VD samples retained the proximate composition content of beetroot better than FD. FD and VD samples led to a better conservation of betacyanin content and antioxidant capacity (DPPH) at 50 and 80°C, respectively. Nevertheless, VD (50°C) stands out above FD in the Total Polyphenol Content (TPC) and the Oxygen Radical Absorbance Capacity (ORAC) values. In addition, the syringic acid appears identified and quantified in VD samples at 50°C but not in FD samples. In consequence, this work shows that for vacuum dried beetroot, 50°C can be a suitable drying temperature in replacement of freeze-drying.