Study on the effects of temperature, air velocity and grape pretreatment methods on drying time and quality indices of raisin.
2010
Mohammadi Mazra`eh, Hossein | Amir Shaqaqi, Farid | Zomorrodi, Shahin | Farmani; Qebleh A`li
Drying of agricultural products especially horticultural crops with low shelf life is very important. Grapevine is an important crop in West Azerbaijan province. About 150000 tons of grape are produced annually. About 50000 tons enter drying process to produce about 12000-15000 tons raisin in this province. The objectives of this research were study on the effects of temperature, air velocity and pretreatment on drying time and quality of raisin. Grape was selected from a same orchard and same cultivar (i.e. Sulanti cultivar grape), with a primary moisture content, acidity, pH, TSS of 75%(wb), 0.99, 3.5 and 24 respectively. Treatments were dried at four of levels of drying temperature of 40, 50, 60 and 70°C three level of air velocity of 0.5, 1 and 1.5 and two pretreatment levels of carbonate potassium 5% plus Australian oil 2% and NaOH 0.5% plus Australian oil 2% using lab scale dryer. According to the results the optimum moisture content (17%) of raisin was achieved at 45, 32, 24 and 18 hr with drying temperature of 40, 50, 60 and 70°C , respectively. However, air velocity and pretreatment have not any significant effects on the drying time. The color of raisin was affected by drying temperature and pretreatment. The best color (light brown) of raisin was observed at 50°C, therefore by increasing drying temperature to 70°C the color was darkened. The color of raisin with NaOH and K2Co3 was same but with a white dust cover in the K2Co3.
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