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



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 (aw), rehydration ratio (RR) and overall acceptability (Oa). 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.


Osmotic, freeze, rehydration, hardness, colour, water activity

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