Optimization of osmo-vacuum drying of pear (Pyrus communis L.) using response surface methodology

Abstract

In the two-stage optimization of the osmotic dehydration and vacuum drying of the pear slices using response surface methodology, using face-centred central composite design (FCC), it was shown that the independent variables for osmotic dehydration were temperature (25–55 °C), solution concentration (50–70 % w/w), and immersion time (60–120 min) and for vacuum drying were vacuum pressure (10–30 kPa), drying temperature (50–70 °C) and drying time (180–300 min). Statistical analysis of results showed that the linear terms of all process variables in both stages have a significant effect on the responses. The second-order polynomial models for all response variables were found to be statistically significant with high values of R2 (>0.8). The optimum osmotic dehydration conditions for maximum water loss, minimum solute gain and maximum weight reduction were: 55 °C temperature, 50 % sucrose solution concentration, and 115 min immersion time. Dehydrated pear slices at optimized osmotic dehydration conditions were then subjected to vacuum drying. Optimum drying conditions of 10 kPa vacuum pressure, 55 °C temperature and 250 min drying time were established for vacuum drying of pear. At this optimum point, moisture content (MC), rehydration ratio and shrinkage were found to be 23.26 % (w.b.), 1.46 and 67.45 %, respectively. Separate validation experiment was conducted at the derived optimum conditions to verify the predictions and adequacy of the models. Two-stage optimization led to obtaining the best condition for production of dried quince slices with lowest MC, and shrinkage.