Shrinkage and quality characteristics of whole fruit of Chinese jujube (Zizyphus jujuba Miller) in microwave drying
2010
Fang, Shuzheng | Wang, Zhengfu | Hu, Xiaosong | Li, Hui | Long, Wanrong | Wang, Ran
Drying characteristics of whole fruit Chinese jujube was studied as distinct from fruit slices. Shrinkage, density, vitamin C, colour and rehydration of Chinese jujube were measured in microwave drying at power level of 1.2, 1.67 and 2.5 W/g (dry base, db). Unlike fruit slices or lumps where, no matter at the beginning or at the end of drying, shrinkage volume typically equals the volume of removed water, ratio of the shrinkage volume to the volume of removed water of Chinese jujube could range from 2 to 2.6 at the beginning of drying, and at the end of drying, it could be 1.15 for higher microwave level (2.5 W/g, db), whereas, for lower power level (1.2 W/g, db), it was about 1. Unlike shrinkage curves in hot air drying that could be described with a three‐segment linear model, shrinkage curves in microwave drying could be well described with a cubic polynomial (R² > 0.99). When compared with the low power level (1.2 W/g, db), higher microwave power level(2.5 W/g, db) increased by 87.9% of the retention of vitamin C, 14.6% of the density and 8.7% of the extent of browning, decreased by 12.9% of the soluble solids content.
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