Optimization of Process Variables for Osmo- freeze drying of Strawberry Slices Using Response Surface Methodology

Abstract

The production of high-quality Osmo freeze-dried strawberry slices was studied by response surface methodology. The osmotic treatment and experiment were conducted according to Box-Bohnken Design. The low and high levels of the process variables were 40% (w/w) and 60% (w/w) for sucrose concentration of osmotic solution; 2 and 4 mm for slice thickness and - 10 and -30 ⁰C for operating temperatures in freeze dryer. Responses studied comprised final moisture content (M), colour Index (L), water activity (a_w), rehydration ratio (R_R) and overall acceptability (O_a). It was found that effects of all the process variables were significant on all responses. Optimum conditions (desirability = 0.692) obtained by numerical optimization were 51% sucrose concentration; 2 mm slice thickness and - 22 ⁰C   operating temperatures to achieve maximum rehydration ratio &organoleptic score and lower final moisture content, colour variation and water activity. Corresponding to the optimum conditions, the predicted value were 5.55% for final moisture content, colour  68.9, water activity  0.40, rehydration ratio  3.27 and overall acceptability  6.31.