Evacuated tube solar and sun drying of beetroot slices: Comparative assessment of thermal performance, drying kinetics, and quality analysis

In this research work, the thermal performance of an evacuated tube solar dryer (ETSD) was investigated at no-load and with load of beetroot slices for drying. The experiments were performed in both ETSD and sun drying to compare drying kinetics, mass transfer phenomena, colour changes, and retention of bioactive compounds of beetroot slices. At no-load condition, maximum ambient and drying chamber temperature achieved were 41.50 degrees C and 75 degrees C respectively. The initial moisture content was found to be 84.05% which reduced to 9.25% and 13.56% in ETSD and sun-drying, respectively. Average drying rate was found to be 8.5 g water/g dry solid. hr and 7.94 g water/g dry solid. hr . in ETSD and sun-drying respectively. Weibull and Midilli kucuk models precisely described the drying kinetics of beetroot slices in ETSD and sun-drying, respectively. The effective moisture diffusivity range, activation energy, and maximum mass transfer coefficient of beetroot slices dried in ETSD were 1.01 x 10(-7) to 2.45 x 10(-7) m(2)/s, 27.60 kJ/mole, and 3.23 x 10(-4) m/s respectively while for sun drying these parameters are 1.19 x 10(-7) to 2.24 x 10(-7) m(2)/s, 57.15 kJ/mole, and 3.18 x 10(-4) m/s. Betalain pigment retention was higher by 63.98% in ETSD drying than sun drying. The colour changes were found to be higher in sun drying. The average phenolic content and antioxidant capacity were higher by 31.07% and 21.87% in ETSD as compared to sun drying. Therefore, the ETSD can effectively dry other food commodities with reduced drying time and significant retention of quality attributes.

Automated summary

The research found that the ETSD performed better than sun drying in terms of drying effectiveness for beetroot slices, with a shorter drying time and better retention of quality attributes.