上海青在真空预冷过程中的冻伤研究

以研究导致绿叶蔬菜——上海青在真空预冷过程中冻伤的内外因素及其作用机理为目的,将3组上海青分别在600、700和800Pa的终压下做真空预冷处理,并用热电偶测量同一片叶子的大叶脉附近、小叶脉附近和叶边3处的温度随时间变化值;再分别将3种终压下叶子冻伤部位剥皮、制作载玻片,在显微镜下观察其细胞间隙大小。结果表明:在以600、700和800 Pa为终压的真空预冷过程中,上海青叶子表面温度均呈现出从中心到边缘逐渐降低的趋势,且叶边温度都达到了-2~5℃,导致叶边细胞冻伤,冻伤后的叶边叶肉细胞间隙平均当量半径分别为23.5、19.2和17.3μm。在真空预冷中,上海青的冻伤现象主要发生在叶边,冻伤的主要原因是细胞间隙中生成的胞外冰对细胞造成了机械损伤;冻伤程度大小随终压的降低而加强;对上海青做真空预冷处理时,将终压设置在800 Pa以上较好。

The Damage Mechanism of Shanghaiqing in the Vacuum Pre-cooling Process

The damage mechanism of Shanghaiqing and its internal and external factors in the vacuum pre-cooling process were studied in this paper.Firstly,three groups of Shanghaiqing were used in the vacuum pre-cooling experiments under 600Pa,700 Pa and 800 Pa;In each pre-cooling process,three thermocouples marked No.0,No.1,No.2 were individually stick to its different parts(main vein,fine vein and margin) to measure their temperature changes with the time;then,the frostbitten parts of leaves in these three vacuum pre-cooling processes were peeled and sampled in the study of comparing the sizes of their mesophyll intercellular spaces.Results show that: in this vacuum pre-cooling cooling-damage experiment,under the different final pressures,the leaves surfaces temperature distributions were all uneven and reduced from the main vein to fine vein and to the leaf margin where temperature was to-2℃ to-5℃,which caused the damage of frostbite of leaf margins;the average equivalent radius of the frostbitten mesophyll intercellular spaces at different conditions were 23.5 μm,19.2 μm and 17.3 μm.The conclusion is: in the vacuum pre-cooling processes for Shanghaiqing,leaf margin is most likely to be frostbitten by the mechanical force in the extra-cellular ice;and degrees of frostbite enhanced with the decrease of final pressures;for Shanhaiqing,the final pressure should set up more than 800Pa.