Drying characteristics and quality analysis of pre-treated turmeric (Curcuma longa) using evacuated tube solar dryer with and without thermal energy storage

Abstract

Turmeric (Curcuma longa) was dried using evacuated tube solar dryer with and without thermal energy storage to investigate the thermal performance of the dryer, drying characteristics, and quality attributes of pre-treated (control, peeled and cured sample) turmeric slices. Two pre-treatments i.e. curing at 100 °C for 45 min and peeling of fresh turmeric was considered for the study. A comparative study of drying characteristics, mathematical modeling, and quality parameters i.e., colour, total phenolic content, antioxidant scavenging activity, curcumin content was conducted using evacuated solar dryer with phase change material (ETDP) and without PCM (ETD). Average dryer chamber, highest collector outlet and ambient temperatures were 57.8 °C, 77.2 °C, 42.9 °C, and 69.4 °C, 79.4 °C, 42.6 °C for ETDP and ETD respectively. Turmeric samples are dried from initial moisture content of 84.6% (w.b.) to a final moisture content of about 13 to 8.8% (w.b.). Highest drying rate of 17.68 g/gdm-h for cured sample using ETDP while 28.21 g/gdm-h for peeled sample using ETD was observed. Two term model was best fitted for both ETD and ETDP for control and peeled turmeric drying, however Modified Page model was best fitted for cured turmeric. Highest diffusivity of 1.97 × 10-10 m2/s was observed for cured turmeric sample dried using ETD. Cured turmeric sample dried using ETDP retained highest curcumin content: 7.49%, AA:65.92%, TPC:22.38 mg GAE/g and b*:58.63 while cured sample dried using ETD dried fastest.