Effect of vacuum impregnation on quality characteristics and drying kinetics of pear

The first aim of our thesis is the optimization of vacuum impregnation which is one of the pre-treatments that can be applied before drying the pear with Response Surface Method, The second aim is to examine the effect of drying temperature and vacuum impregnation on drying kinetics of pear. The pears were blanched before vacuum impregnation process in order to inactivation of the polyphenoloxidase enzyme. Independent variables were determined as vacuum pressure (200-350-500 mbar), vacuum time ( 15-30-45 min.) and impregnation solution concentration (30-40-50 °Brix) for optimization vacuum impregnation process by Respnse Surface Metodology. The changes in the responses which were selected as solid gain, water loss, total phenolic compound, and lightness (L*) value were optimized by 'Centrak Composite design'. The deionized apple juice concentrate was used an impregnation solution. The parameters which were kept constant in the vacuum impregnation process were temperature (35°C), restoration time (60 min) and a ratio of food over solution (1/5)(w/w) . Optimized conditions were determined as 225 mbar, 45 min. and 50 ⁰Brix. Drying experiments were performed at different temperatures (55, 65 and 75 °C). The air velocity was 1 m/s and was kept constant at the process. The drying was going on the moisture content of the product became 15%. The Page model was best fitted model for non -vacuum impregnated pearss dried at 55 and 65 °C and diffusion model were determined for dried at 75 °C.The appropriate model for vacuum impregnated pears dried at 55 and 65 °C were Diffusion and the Page model was suitable model for dried at 75 °C. The effective diffusion coefficient (Deff) and the activation energy were calculated for vacuum impregnationed and non-vacuum impregnated samles. The effective diffusivity coefficients for the non-vacuum impregnated pears was between 3.65x10-11 and 7.31x10-11 m2/s and range effective diffusivity coefficients for vacuum impregnated was from 2.74x10-11 to 4.57x10-11 m2/s. The activation energy for the non-vacuum impregnated pears was 32.93 kJ / mol and the activation energy for the pears with vacuum impregnation was calculated as 24.25 kJ /mol. When the effect of temperature is examined in drying of pear samples without vacuum impregnation, pH, titration acidity, a * and b * before increasing and after decreasing as the temperature increases. L *, adhesiveness, antioxidant activity values decreased and hardness increased with increasing temperature. When the effect of temperature on drying of pear samples with vacuum impregnation was examined, it was seen that pH, b * L *, antioxidant activity values increased with increasing temperature and then decreased. It was observed that titration acidity, a *, hardness values increased with increasing temperature and adhesivenes decreased. As a result of the scoring test, the sample with the highest score was vacuum-impregnated and dried at 65 °C.