Effect of Pre-treatment Methods on the Color Changes during Drying of Red Chilli (Capsicum frutescens L.)

Department of Agro-Industry Technology and Management, Faculty of Agro-Industry, King Mongkut’s University of Technology North Bangkok (KMUTNB) Prachinburi Campus, Prachinburi, Thailand

^a Corresponding author: rattapon.s@agro.kmutnb.ac.th

Abstract

Chilli was dried using conventional tray dryer with 3 different drying conditions, i.e., 60°C, 80°C and 2-stage drying (80°C and 60°C). The effects of pre-treatment methods were evaluated by soaking chilli in pre-treatment solutions prior to drying. In terms of drying characteristics, the drying time found to be shortest at 80°C. It was also found that the drying rate of pre-treated chilli increased compared with non-treated one. The modified Page’s model was suitable for describing drying characteristics at all conditions (R² = 0.97-0.99). Furthermore, the color change during drying was investigated using image analysis methods. It was found that the pre-treatment methods prevented the color change. The combined kinetic model was the best model for predicting the change of color during drying (R² = 0.98-0.99). A pre-treated chilli soaking in a mixed solution of 0.3% (w/w) Na₂S₂O₅ and 1% (w/w) CaCl₂ showed the better quality. In addition, the combined kinetics model could describe the change of L* a* and b* values in all conditions.