Effect of Pre-treatments and Solar Drying of Grapes on its Quality Evaluation

Pre-treatment is a necessary step in raisin production in order to ensure the increased rate of water removal during the drying process Drying of grape can help in preserving it for 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 solar drying. The quality of dried raisins were evaluated. The drying data was fitted with various models the Henderson and Pabis model, the Lewis model, the Page model, and Two-term exponential model models fitted to the experimental data. Henderson and pabis and Exponential two term drying model was well fitted to the experimental data with r² = 0.9825 and 0.9902; MSE = 1.712 × 10^-3 and 1.045 × 10^-3; χ² = 0.1949 and 0.1045 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, colour yellowness index, Hardness. The moisture content in grape raisins 14.54%, TSS 73.88°B, Titrable acidity 2.52 %, pH 4.13, Reducing sugar 64.65 %, Total sugar 66.13 %, Non-reducing sugar 1.48, Ascorbic acid 21.33 mg, yellowness 86.15 and hardness 8.57 for Treatment-2. The sensory score for best Treatment T₂ was colour 8.2, flavour 7.90, texture 8.22 and taste 8.08.