Abstract: The aim of this work was to obtain the appropriate pretreatment to improve the drying rate and raisin quality of seedless white grapes in air-drying shelters in Turpan. The experiments were carried out in Turku village in Turpan. The grape samples were divided into control group and three pretreatment groups. Daily data of temperature, humidity, air flow rate, grape moisture content and image were collected during the whole drying process. The eternal quality of grapes such as chromaticity was obtained by image processing using Matlab software. The changes in chromaticity and moisture were plotted against drying time. The results showed that compared with the control group, the drying time of grapes pretreated with 3.0% of drying agent was reduced by 6 days and the surface chromaticity changed more steadily during the drying process. Moreover, the browning rate of raisin was decreased by 67% and the percentage of green raisin was increased by 20.5%. Overall, this pretreatment was found to be optimal for the production of raisin in air-drying shelters. The experiments also validated the use of olive oil to improve the percentage of green raisin during the drying process.

Key words: seedless white grape, drying, air-drying shelters, pretreatment