Assessment of pretreatments on drying kinetics and quality characteristics of thin-layer dried red pepper

Abstract

In this study, the effect of pretreatments (hot water blanching, microwave blanching, and ohmic heating) on the drying kinetics and quality characteristics of red pepper, dried at 60 and 70 degrees C, was investigated. The drying times varied between 205-290 min, depending on the pretreatment and temperature applied. The drying rate also changed based on the pretreatment and the falling rate period was observed. Four mathematical models were fitted to experimental data and the logarithmic model was found to be the best for all of the samples. Effective moisture diffusivity values obtained from Fick's second law of diffusion ranged from 6.11 x 10(-10) to 9.31 x 10(-10) m(2) s(-1). The total phenolic contents, antioxidant capacities, and red pigment amounts of the dried peppers varied between 6.95 and 9.45 mg GAE g(-1)dry matter (DM), 2610.43 and 4463.96 mmol AEAC 100 g(-1)DM, and 184 and 443mg 100 g(-1)DM, respectively. Rehydration ability of pretreated samples was similar to or slightly lower than that of the untreated samples. As a result, it can be suggested that ohmic heating before drying at a temperature of 70 0 C. could be a promising alternative pretreatment to decrease drying time and produce high-quality dried red pepper.