Effect of antioxidant active coatings on osmotic dehydration efficiency and quality parameters of Shahroodi dried grape

The application of coating on food prior to osmotic dehydration has been introduced as an effective solution to decrease the solid gain. In this research, two types of coatings (based on pectin and carboxymethyl cellulose) containing two antioxidant and reducing ingredients (ascorbic acid and cysteine) for pretreating of Shahroodi grapes were used before osmotic process. For osmotic dehydration, constant osmotic solution with similar composition to natural fruits ingredients (containing fructose, calcium chloride and citric acid) were used (sample of solution 1 to 10). The optimum samples were chosen according to the maximum osmotic efficiency coefficient, maximum water loss and the minimum solids gain. The control and pretreated samples were subsequently dried by air drying and the effects of coating solutions and osmotic dehydration on dried raisins quality attributes (including vitamin C, color and rehydration ratio) were studied. The coated and osmotic samples showed the highest amount of vitamin C than the control and uncoated samples and the least rehydration ratio than the control and uncoated samples. Coating and osmotic dehydration also caused the decrease in overall color change.