Beetroot slices dried by refractance window dryer and conventional drying: drying kinetics, physicochemical properties and antioxidant capacity

Abstract

This investigation evaluated the effect of drying methods, including tray drying (TD), fixed bed drying (FBD), and refractive window drying (RWD) of beetroot slices (1 mm thickness) at 60, 75, and 85 °C. Then, drying kinetics, color, texture, total polyphenol content (TPC), total flavonoid content (TFC), and antioxidant capacity (AC) were assessed. The moisture ratio and drying rate depended on temperature and method of drying. Beetroot slices processed on RWD showed lower moisture content and the highest drying rate than TD and FBD. For this reason, RWD required less time drying (60-100 min) in comparison to TD (100-150 min) and FBD (240-285 min) at temperatures evaluated. The color and firmness of dried beetroot slices by RWD were more similar to the control (fresh beetroot) than other drying methods. Similarly, the TPC, TFC, and AC were higher at low drying temperatures (60 °C) for the three methods evaluated. However, as the temperature increased, TPC, TFC, and AC were significantly reduced (P<0.05) for samples processed on TD and FBD. This study showed that RWD could effectively be used to dry thin layers of heat-sensitive products such as beetroot in a shorter time with minimum alteration in quality compared to conventional drying methods.