Effect of hot air temperature on drying kinetics of palmyra (Borassus aethiopum Mart.) seed-sprout fleshy scale slices and quality attributes of its flour

Abstract

This study investigated the influence of different drying air temperatures (40, 50, 60 and 70 °C) on moisture removal ratio and drying rate of pre-cooked and uncooked palmyra ( Borassus aethiopum ) seed-sprout fleshy scale (SFS) slices and quality of the resultant flours. Through drying kinetic analysis, it was found that the drying process of pre-cooked and uncooked palmyra SFS slices took place in the falling rate period and the drying time decreased with increasing air temperature in all samples. The colour parameters (L*, a* and b*) were affected by the drying air temperature and treatment type (pre-cooked and uncooked), with significantly higher ΔE values in uncooked samples compared to the pre-cooked samples. Drying of uncooked SFS slices maintains relatively high total antioxidant activity and low content of vitamin C compared to the pre-cooked samples. Beta-carotene, total phenol and total flavonoid contents however showed no specific trend in pre-cooked and uncooked SFS samples. Generally, pre-cooking palmyra SFS before drying significantly (P ˂ 0.05) improved their water absorption capacity, swelling index and swelling capacity while decreasing bulk density. However, treatment type and drying air temperature was observed to greatly (P ˂ 0.05) influenced all pasting properties without any observable trend. Based on the results, the quality of palmyra SFS flour showed opposite behaviours, thus indicating a compromise decision on processing conditions involved to meet the quality properties of interest. • Pre-cooked and uncooked palmyra seed-sprout fleshy scale (SFS) were dried at 40–70 °C. • Drying rate of pre-cooked and uncooked palmyra SFS took place in the falling rate period. • Colour values of both pre-cooked and uncooked palmyra SFS were affected during drying process. • Uncooked palmyra SFS retained higher antioxidant activity and lower vitamin C compared to pre-cooked samples. • Pre-cooking of palmyra SFS before drying improved WAC, SI and SC while decreasing bulk density.