Correlation Analysis of Hot Water Treatment on Quality Improvement and Membrane Lipid Metabolism of Fresh Jujube Stored at Near Freezing Point Temperature

The effects of hot water treatment on cold tolerance and fatty acid compositions of membrane lipids of fresh jujube fruit were investigated at a near freezing point temperature storage by Zizyphus jujube Mill. cv. Linzexiaozao experimental material. The harvested fresh jujube fruits were immersed in hot-water at 60 ℃ for 1 min, and dried naturally, then packed into polyethylene plastic boxes with several small holes about 2 mm of diameter and stored at (−1.5~−2)℃. Chilling injury index, cellular membrane permeability, malondialdehyde (MDA), lipoxygenas (LOX) activity and fatty acid constituents of membrane lipids in fresh jujube fruits during cold storage were measured at fixed periods. As compared to the control fruit, the fruit chilling injury index, cellular membrane permeability, MDA content and LOX activity decreased by 7.56, 17.93%, 17.93 μmol/g·FW and 15.84 U/g·FW, respectively, after storage for 50 days. The relative contents of unsaturated fatty acids oleic acid (C_18:1), linoleic acid (C_18:2) and linolenic acid (C_18:3), index of unsaturated fatty acids (IUFA) and unsaturation degree of fatty acids (UFA/FA) increased in jujube pulp by 11.10%, 9.13%, 8.60% and 55.17, 0.65, respectively, while the relative contents of saturated fatty acids myristic acid (C_14:0), palmitic acid (C_16:0), stearic acid (C_18:0) and arachidic acid (C_20:0) decreased in jujube pulp by 54.10%, 18.66%, 17.93% and 3.37%, respectively, and the difference were significant (P<0.05). Especially, there was a very significant negative correlation (P<0.01) between LOX activity and the relative percentage content of linolenic acid (C_18:3) (r=−0.931) in the control. The results showed that there was a correlation between the degree of chilling injury of fresh jujube and the relative content of linolenic acid (C_18:3) in the membrane lipid. Hot water treatment inhibited the decrease of the index of unsaturated fatty acids and the unsaturated degree of fatty acids of fresh jujube, and induced the slowdown of the degradation rate of unsaturated fatty acids of membrane lipid, so as to maintain the high stability of membrane fat and enhance the cold tolerance of postharvest fresh jujube during near freezing point temperature storage.