Effects of temperature on color and drying characteristics of green raisins
[Objective]The effects of hot air drying on the color and luster indexes and moisture diffusion coefficient of raisins under different temperature conditions were studied,which provided theoretical and tech-nical support for the industrial production and processing of green raisins.[Methods]Different temperatures(30,32.5,35,37.5 and 40℃)were used to dry seedless white grapes,and the effects of temperature on grape color change,moisture diffusion coefficient and raisin quality were analyzed,and the drying kinetic model was fitted.[Results]When the drying temperature was 35°C,the ratio of green raisins reached 64%,the difference between color and raw materials was the smallest,the color difference ΔE was only 6.99,and the color indexes of C,h0,L,a,b and so on were 18.23,1.4,14.57,2.99 and 17.95,respectively.Chlorophyll,chlorophyll a,chlorophyll b,carotenoids and total phenols were 0.56,0.19,0.36,0.32 and 0.18 mg/g,respectively.35℃is more suitable for green raisin processing.The most consistent mod-el for grape drying,with the largest coefficient of determination R2,the sum of squared errors and the mean of SSE and root mean square error Rmse the smallest,respectively,0.998,1,0.005,4,and 0.007,7.The most suitable effective water diffusion coefficient of green raisins is 5.334,8×10-9.[Conclusion]The effective water diffusion coefficients of 30,32.5,37.5 and 40℃were 114.13%,110.58%,95.17%and 76.58%,respectively,and the Logarithmic model could effectively illustrate the variation of grape fruit moisture under the hot air drying process.
white kernelless grapestemperaturegreen raisinshot air dryingkinetic modeleffective moisture diffusion coefficient
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