Effect of two-step drying of black currant grape on the quality of raisin

Achieving optimum drying conditions can affect the processing time and improvement of raisin quality. In this research, drying quality of Black currant grape in two-step temperature and different pretreatments was studied. Drying Was accomplished in two steps: The first step involved temperature at four levels of 50,60,70, and 80 ºC and Then followed the second step in which step which samples were placed at two temperatures. In this step, samples were placed at 80 ºC and while moisture content was reduced to 50, temperature was reduced to 70, 60 and 50 ºC. Four pretreatments including hot water, %5 potassium carbonate, %0.4 olive oil, %0.5 sodium hydroxide(caustic soda) and without pretreatment were performed. The results showed that some factors such as temperature and pretreatment have significant effects on browning index, dehydration ratio and shrinkage and only temperature factor was significant on acidity. Raisins dried at two-step temperature by changing the second step’s temperature to 60ºC in pretreated of %5 potassium carbonate, %0.4 olive oil and %0.5 sodium hydracids have better quality. Also raisins dried at 70ºC and pretreated in %0.5 sodium hydracids have better quality.