The effect of drying methods Asgari seedless grapes on alteration of color of raisin

Drying is one of the most important steps in grape processing. Drying causes some undesirable effects such as changing the quality of raisin by turning it to brown. Achieving optimum drying conditions can improves quality of raisin. Temperature and pretreatment are important factors in establishing the quality of raisin. In this research the effect of pretreatment (solutions of sodium Meta bisulphide 8 %، sodium Meta bisulphide 8 % and potassium carbonate 5%، ethyl oleat 2% and potassium carbonate 5%، ethyl oleat 2% and sodium Meta bisulphide 8 %، ethyl oleat 2% and sodium Meta bisulphide 8 % and potassium carbonate 5%) and different drying methods (by sun، shade and air dryers at temperature of 50، 60، 70 and 80 ◦C with the air flow rate of 1/5 m/s) was studied to understand the quality factors on colour. As some solutions contains sulphite، its remnant was studied too. The analysis of experimental data shown that the optimized drying conditions achieved by Ethyl oleat 2% and sodium Meta bisulphide 8 % and potassium carbonate 5%، sodium Meta bisulphide 8 %and drying temperature of 50،60◦C.