Effect of pretreatments and temperature on rehydration kinetics of naga chili (Capsicum chinense)

Naga chili (Capsicum chinense) is rich in capsaicin content that provides a distinctive aroma and strong pungency. Drying with pretreatment is regarded as a cost-effective approach to retain better nutrient quality, whereas rehydration properties consider a quality index to optimize the drying conditions. This study aimed to determine rehydration kinetics and rehydration characteristics of pretreated hot-air dried Naga chili. The pretreatment was consisting of water blanching (90°C for 5 mins), steam blanching (100° C for 1 min), microwave treatment (650 W for 100 s), and dipping into sugar 70°Bx, 0.5% citric acid, 2% ethyl oleate + 3% potassium carbonate, and 2% potassium meta bi-sulfite solution. After drying at 60°C, the rehydration was done at 25°C, 50°C, and 75°C, respectively. The rehydration kinetics were evaluated by fitting the experimental data into empirical kinetic models: Peleg's model, 2^nd order, 1^st order, and Zero-order kinetics. Among these models, the rehydration behavior was best described by Peleg's model, where the highest R² (0.9964), lowest χ² (0.0001) and RMSE (0.0064) values were obtained. Different rehydration characteristics such as moisture content, equilibrium moisture content, rehydration ratios were also determined. The highest moisture content (8.10 g moisture/g dry sample) was found at higher rehydration temperature (75°C), whereas the lowest moisture content ranges were recorded at 25°C. After moisture contents got equilibrium, the rehydrated samples gain weight to 100.15% at 75°C in comparison to the untreated samples. The rehydration ratios were also getting higher with increasing rehydration temperatures.