The effects of drying temperature on the kinetics, color, structure, and pectin composition of Zizyphus jujuba Mill. cv. Junzao

Drying kinetics, color, and texture changes in different drying temperatures of jujubes were investigated in this study. With the increase of temperature, the drying time reached a minimum (140 min) at 80℃. At the temperature of 40℃, the retention of the original color was the greatest (ΔE = 1.66); similar results were also reflected by the measured pulp browning (4.186 ± 0.350 Abs/g) and 5-HMF (0.517 ± 0.044 mg/g). After drying, the fruit hardness decreased to 55.91%–86.59% of the initial (2,543.2 ± 181.4 g). SEM showed that the HAD temperature exceeded 60℃ and the pulp tissue sharp dramatically, causing the fruit to harden. Affected by drying temperature and polygalacturonase, WSP increased in drying, whereas CSP and NSP showed the opposite trend, and they were significantly correlated with the texture of fruits. The results expanded our understanding of the jujube drying process and provided guidance for controlling the quality of jujube during HAD processing. Practical applications The drying method of jujube fruit in China is special, which is a combination of air drying and hot air drying. However, discoloration, shrinkage, and other quality deterioration occurred during the drying process, significantly affecting the quality of jujube fruit. In this study, semi-air-dried jujubes were used to investigate the color and texture during hot air drying. These results will provide valuable information to the pilot or industrial scale processors and also served as an operational guide for the jujube fruit drying process.