Sun/solar drying of differently treated grapes and storage stability of dried grapes

The effects of pretreatment solutions and drier types (salar vs sun) were investigated for grapes (var. sultanas). Pretreatment solutions containing 5% K2CO3 plus 1.5% olive oil and 4% K2CO3 plus 2% ethyl oleate accelerated drying rates nearly to the same extent, as compared to untreated grapes. Drying rates were classified for the tested drying methods: solar drying > sun drying on concrete ground > sun drying on wooden racks, or on polypropylene canvas sheets. Increasing K2CO3 concentration from 4 to 7% in ethyl oleate (2%) solution increased drying rates on concrete ground. Treatment with SO2 gas (645 mg/kg) in addition to ethyl oleate, further increased the drying rates but the color of the product was rated to be too light and unacceptable to the market. The moisture content and color intensities of the sun-dried grapes were found to be non-uniform. Storage stability of treated, dried grapes was investigated in (1) modified atmosphere (1% O-2 plus 13% CO2), (2) vacuum packed and (3) ordinary plastic pouch packed storage at 6 degrees C. Untreated grapes had the lowest Hunter L (lightness), a (redness) and b (yellowness) values compared to treated grapes. Storage caused color parameters to decline, but this reduction was less pronounced for SO2 gas treated products. Copyright (C) 1996 Elsevier Science Limited