Effect of drying air temperature and chemical pretreatments on quality of dried chilli

The quality of dried chilli (Capsicum annuum c.v. Huarou Yon) in terms of color attributes and nutrients was studied using a lab-scale tray dryer in order to reduce the quality loss caused by sun drying. Different drying temperatures from 50-70°C, and a two-stage temperature regime (70°C and 50°C) were used to compare with the sun drying method. A one-temperature regime provided low values of lightness, chroma and hue angle compared to sun drying. The two-stage temperature provided bright–red colored dried chilli. Browning color of dried chilli was observed due to non-enzymatic browning reaction as reducing sugar was decreased. Not only did the Maillard reaction provide a dark-brown color, but thermal degradation and oxidation of total phenolic compounds and ascorbic acid also provided an unacceptable color of dried chilli. A drying temperature of 70°C and a two-stage temperature regime (70°C for 4 hours followed by 50°C) in conjunction with soaking the chilli in different chemical pretreatments were used to promote the color and nutrient preserving capacity. It was found that sodium metabisulfite preserved color stability but not the nutritional compounds chilli was dried at an air temperature of 70°C. Using sodium metabisulfite combined with calcium chloride provided the best color attributes when two-stage temperatures of 70°C and 50°C were used.