Conventional sun drying and infrared convective drying of spices: A comparative evaluation on kinetics and quality

Abstract

This study aims to compare the drying of turmeric slices and mace under conventional open sun drying and novel infrared convective drying methods. Moisture content of turmeric slices was decreased from 76.5 ± 0.51 % w. b. to 7.2 ± 0.84 % w.b within 9 and 6 h under open sun drying (OSD) and infrared convective (IRC) drying, respectively. Drying time for mace under open sun and infrared convective drying were 12 and 7 h, respectively to decrease the moisture content from 55.62 ± 0.71 to 8.3 ± 0.21 %. The drying rate of turmeric under OSD and IRC were 1.2 and 3.47 gwater/gdm.h, respectively. OSD and IRC dried mace exhibited drying rates of 0.97 and 2.52 water/gdm.h, respectively. Effective moisture diffusivity during OSD and IRC drying of turmeric slices were 4.6 × 10⁻⁹ m²/s and 3.16 × 10⁻⁷ m²/s, respectively. Mace showed effective moisture diffusivities of 1.95 × 10⁻⁹ m²/s and 2.47 × 10⁻⁷ m²/s during OSD and IRC, respectively. Essential oil and oleoresin contents of turmeric slices under infrared convective drying were determined to be 6.8 % and 13.98 %, respectively. Infrared convective drying of mace obtained the values of essential oil and oleoresin contents as 7.1 % and 12.8 %, respectively. Mace under open sun drying exhibited values of 6.7 % and 11.12 % for essential oil and oleoresin, respectively. The study concluded that the nutritional components were more preserved in OSD as compared to IRC drying. The research also provides a roadmap for development of a hybrid solar-infrared dryer that can reduce the drying time with improved product quality.