无核白葡萄在脱水过程中易褐变，绿品级率降低。该试验通过无核白葡萄细胞膜脂相变、激光共聚焦扫描电镜的观察、荧光值的对比、丙二醛、相对电导率及褐变指数等指标，探究30 ℃（1.5 m/s）、30 ℃（0 m/s）、25 ℃（1.5 m/s）和25 ℃（0 m/s）的脱水条件下褐变与未褐变的无核白葡萄细胞的膜脂相变和完整性的差异。结果表明：无核白葡萄失水量达60%时，细胞膜因氧化降解发生断裂，细胞质及液泡中的内容物溶出，FM4-64与受损的细胞膜结合产生大量的红色荧光物质，红色荧光强度值升高；FDA与酯酶结合的绿色荧光物质随细胞质溶出无法聚集，绿色荧光强度降低，细胞膜完整性破坏，无核白葡萄出现不同程度褐变；此时的荧光比值、丙二醛含量及相对电导率增幅较大。其中未褐变的葡萄细胞膜脂相变温度均低于脱水温度，细胞膜处于液晶相，液晶相可以保持细胞膜的结构，具有优异的稳定性；褐变的葡萄样品则相反，细胞膜处于凝胶相，不利于细胞膜结构的稳定。而且褐变的葡萄荧光比值、丙二醛含量和相对电导率均高于未褐变的葡萄，细胞膜破坏程度高于未褐变的葡萄。脱水过程中使细胞膜始终处于液晶相，可以更好的维持细胞膜的结构，并且提高脱水速率也可以降低褐变的产生，此结果可为无核白葡萄在脱水过程减少褐变现象提供一定理论基础。

Thompson seedless grapes are prone to browning during dehydration, with their green grade rate decreasing as a result. In this study, laser confocal scanning electron microscopy, fluorescence value comparison, malondialdehyde, relative conductivity, and a browning index were used to determine the differences in the membrane lipid phase transition and integrity between browning and non-browning Thompson seedless grape cells under conditions of dehydration at 30 ℃ (1.5 m/s), 30 ℃ (0 m/s), 25 ℃ (1.5 m/s), and 25 ℃ (0 m/s). The results showed that when the water loss of Thompson seedless grapes reached 60%, the cell membrane was broken due to oxidative degradation, the contents of the cytoplasm and vacuoles were dissolved, and FM4-64 combined with the damaged cell membrane to produce a large number of red fluorescence substances. As a result, the red fluorescence intensity value was increased. The green fluorescent substances bound by FDA and esterase did not aggregate with cytoplasmic dissolution, the green fluorescence intensity decreased, the integrity of the cell membrane was destroyed, and the Thompson seedless grape showed varying degrees of browning. Simultaneously, the fluorescence ratio, malondialdehyde content, and relative conductivity increased greatly. Among these, the lipid phase transition temperature of the non-browning grape cell membrane was lower than the dehydration temperature, and the cell membrane was in the liquid crystal phase, maintaining the structure of the cell membrane and showing excellent stability. Browning grape samples, on the contrary, were characterized by cell membranes in the gel phase, which is not conducive to a stable cell membrane structure. Moreover, the fluorescence ratio, malondialdehyde content, and relative conductivity of browning grapes were higher than those of non-browning grapes, as well as the degree of cell membrane destruction. During the dehydration process, the cell membrane is always in the liquid crystal phase, which allows for a better maintenance of the cell membrane structure. An increase in the dehydration rate can also reduce the generation of browning. These findings provide a certain theoretical basis for reducing browning in the dehydration process of Thompson seedless grapes.

国家自然科学基金项目（32060546）