Effect of Pre-treatments and Open Sun Drying of Grapes on its Quality

Pre-treatment is a necessary step in raisin production in order to ensure the increased rate of water removal during the drying process. Drying grapes can help preserve it for a longer duration. In present paper, the grapes of Manikchaman variety was treated with Treatment T1 = 2.5% NaOH for 3 sec followed by 2% KMS for 2 minutes and Treatment T2 = 2.5% potassium carbonate + 2% ethyl oleate solution for 5 minutes and dried by open sun drying. The drying time for treatment T1 was 85 hrs and the drying rate was 0.1243 g to 7.30 × 10-3 g. The drying data was fitted with various models the Page model, the Lewis model, the Henderson and Pabis model, and the Two-term exponential model. Exponential two terms Logarithmic drying model was well fitted to the experimental data with r2 = 0.9991 and 0.9947; MSE = 8.481 × 10-5 and 4.996 × 10-5; χ2 = 0.0150 and 0.0649 for treatment-1and treatment-2 solution, respectively. Nutritional analysis of fresh ripened grapes and grape raisins has also been determined i.e., Moisture content, TSS, Titrable acidity, pH, Reducing sugar, Total sugar, Non-reducing sugar, Ascorbic acid, color (yellowness index) and Hardness. The moisture content in grape raisins 14.54%, TSS 72.67 oB, Titrable acidity 2.75%, pH 4.77, Reducing sugar 63.10%, Total sugar 65.67 %, Non-reducing sugar 2.67, Ascorbic acid 20.98 mg, yellowness 71.72 and hardness 3.76 for Treatment-1. The sensory score for best Treatment T1 was color 6.75, flavor 7.30, texture 7.37, and taste 7.25.