Response Surface Optimization of Refractance Window Drying of Bitter Gourd Slices

Abstract

This study was conducted to investigate the drying behavior of bitter gourd (Momordica charantia L.) slices in a refractance window dryer. Various drying parameters such as water temperature (70, 80 and 90 °C), sample thickness (1, 2 and 3 mm) and blanching time (2, 3 and 4 min) were investigated for their effects on drying time, dehydration ratio and color change. Out of the 18 experimental runs determined by the Box Behnken design, six central experiments, often referred to as center points, were specifically chosen to assess the reliability of results. Four different empirical models viz. Exponential, Henderson and Pabis, Page's, and Power law model were selected based on their established applicability in similar studies, and fitted to the kinetics data of refractance window drying of bitter gourd. Adequacy of fit was assessed using the coefficient of determination (R² ) and standard error of estimate (SEE). Page’s model demonstrated an excellent fit to the experimental drying data with a higher R² value of 0.996 and correspondingly lower SEE of 0.0217 compared to the other three models. Furthermore, the drying process parameters were optimized for the responses using the Response Surface Methodology (RSM). The best values (within the chosen range) of water temperature, sample thickness and blanching time were found to be 90 °C, 1 mm and 4 min, respectively at desirability value of 0.889. At above condition of water temperature (90 °C), sample thickness (1 mm) and blanching time (4 min), the predicted values for the drying time, dehydration ratio and color change were found to be 52.2 min, 9.7 and 55.25, respectively. The findings of this study will be useful for refractance window drying of bitter gourd in particular and for high moisture foods in general.