Abstract
Abstract Watermelon rind, comprising 35% of the fruit’s total mass, usually discarded due to its unappealing flavor and lack of sweetness. In this study, candied watermelon rind was prepared through osmotic dehydration at vacuum (VOD) and atmospheric pressure (OD). The effects of independent variables (sucrose concentration, immersion time and temperature) on the dependent variables, including solid gain (SG) and water loss (WL) of watermelon rind, were evaluated using multiple response surface methodology. The SG and WL increased with the increasing sucrose concentration, immersion time and temperature for both VOD and OD, but VOD greatly increased the mass transfer rate. The kinetic constants were obtained by fitting the data of SG and WL to the Fick’s diffusion model. The VOD had higher kinetic constants and dehydration efficiency indices than that of OD. Besides, the mass transfer model and RSM model were statistically compared by the coefficient of determination, root mean square error and absolute average deviation, based on the validation data set. The RSM and mass transfer models provide information about the osmotic dehydration for predicting the sugar content of candied product, and helping the designers and researchers find the best design parameters and the most effective process conditions.
Highlights
IntroductionWatermelon consists of about 50% red or yellow flesh which is edible; the other parts, consisting of about 35% rind and 15% peel, are usually discarded (Rimando & Perkins-Veazie, 2005)
Watermelon (Citrullus lanatus var. lanatus) is an important vegetable crop with a worldwide annual production of 104 million tons (United States Department of Agriculture, 2011)
The results revealed that the sucrose concentration (x1), immersion time (x2) and temperature (x3) were all important factors for OD and vacuum osmotic dehydration (VOD), and that they exerted a statistically significant overall effect (p < 0.05) on the responses
Summary
Watermelon consists of about 50% red or yellow flesh which is edible; the other parts, consisting of about 35% rind and 15% peel, are usually discarded (Rimando & Perkins-Veazie, 2005). Watermelon rind contains vitamins, minerals, fiber and citrulline, but most people avoid eating it due to its unappealing flavor and lack of sweetness (Al-Sayed & Ahmed, 2013; Johnson et al, 2012). Watermelon rind is about 95% water, which makes it susceptible to deterioration. It is important to reduce the moisture content of the watermelon rind in order to produce products with a stable shelf life. Osmotic dehydration can be applied to remove the water, improve the flavor and increase the sugar content of watermelon rind for the purpose of obtaining a candied product
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