Changes in Nutritional Properties of Jujube Fruits during Different Stages of Vacuum Freeze-drying
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Abstract:
Variations in nutritional properties and antioxidant activity of jujube fruits during different stages of vacuum freeze-drying were investigated to provide a scientific basis for selecting the appropriate drying time during production and processing. The results showed that during freeze-drying of the jujube fruits reducing sugar content increased significantly by the end of drying (p<0.05). The titratable acid content of freeze-dried jujube fruits was 0.92 times as much as fresh jujube fruits, which is one of the reasons for the drop in the sugar:acid ratio observed in freeze-dried products. Additionally, freeze-drying produced a higher retention rate of vitamin C (99.58%) over time, as compared to its fresh counterpart. The organic acid content of fruits is an important factor in determining flavor, and this study found that the freeze-dried jujube fruit oxalic acid, tartaric acid, and citric acid content were 1.64 times, 1.32 times, and 3.83 times as much as the fresh fruit, respectively. During freeze-drying, jujube fruits appeared to increase their ABTS+? scavenging power and antioxidant capacity (p<0.05), with the former increasing by 6.91% and antioxidant capacity increasing by 92.01%. Therefore, freeze-drying time has a significant effect on the nutrient content and antioxidant activity of the fruits being processed. The freeze-drying time ranging from 6 to 9 is beneficial in reserving moisture, and maintaining nutritional and functional property.
