Improvement in Texture of Frozen Vegetables

质地是冷冻水果和蔬菜最重要的品质。冷冻会对细胞膜造成严重破坏，并导致过度软化。研究了不同加工参数对冷冻胡萝卜和大白菜细胞结构、质构和果胶变化的影响。结果表明：(1)用程序冷冻机(PF；冷冻速度：-5ﾟC/ﾟ)用LN_2快速冷冻，并在-3ﾟC下进行静电解冻(ET)，解冻后的样品的硬度从大到小依次为：[冷冻方法]PF-5ﾟC/分钟&GT；PF-2ﾟC/分钟&GT；-80ﾟC冷冻机(F)&GT；-30 Min C&GT；分别为-20ﾟCF和-3\f25[融化方法]-3\f25 ET()-3\f25 SY.>Req.-3\f25()-3\f25ﾟC&>5-3\f6(-3\f25 5-3\f25ﾟC&>T；20ﾟC&>T；100ﾟC-3\f6)。光镜、透射电子显微镜和低温扫描电子显微镜对组织结构的组织学改变最小到最大：PF-5ﾟC/min&lt；PF-2ﾟC/min&lt；-80ﾟCF&lt；-30ﾟCF&lt；-20ﾟCF，。冷冻速度越快，组织中残留的果胶越多。当冷冻样品在20ﾟC下解冻时，果胶的酯化程度降低。(2)在98ﾟC下正常漂烫前先进行低温热烫(60ﾟC，30min或70ﾟC，5min)。果胶甲酯酶在低温处理下被激活，从而增加了胡萝卜中果胶的去甲氧基化。(3)在2%醋或0.05M CaCl2溶液中热烫。果胶在酸性或CaCl2溶液中很难分解，因此在这些溶液中热烫可以防止过度软化。(4)在20%的蔗糖、葡萄糖、蔗糖、或者山梨醇溶液。这些糖产生了显著的紧致效果。

Texture is the most important quality of frozen fruits and vegetables. Freezing causes severe damage to the membranes of cells, and excessive softening. The effects of processing variables on the cell structure, texture, and pectic change of frozen carrots and Chinese cabbages were determined. As a result, the following treatments were deemed effective.(1) Rapid freezing with LN_2 using a program freezer (PF ; freezing rate : -5ﾟC/min), and Electrostatic thawing (ET) at -3ﾟC.The firmness of the frozen-thawed samples was greatest to least : [freezing method] PF-5ﾟC/min>PF-2ﾟC/min>-80ﾟC freezer (F)>-30ﾟCF>-20ﾟCF, and [thawing method] ET(〕SY.gtoreq.〔)-3ﾟC>5ﾟC>20ﾟC>100ﾟC, respectively. Histological changes by LM, TEM and cryo-SEM observations of the tissue structure were least to greatest : PF-5ﾟC/min<PF-2ﾟC/min<-80ﾟCF<-30ﾟCF<-20ﾟCF, respectively. The amount of pectin remaining in tissues was greater as freezing rate was quick. When raw frozen samples were thawed at 20ﾟC, the degree of esterification of pectin decreased.(2) Low temperature blanching (60ﾟC, 30min or 70ﾟC, 5min) prior to normal blanching at 98ﾟC.Pectin methyl esterase was activated by low temperature treatment, therefore increasing in firmness caused by the demethoxylation of pectin in carrots.(3) Blanching in 2% vinegar or 0.05M CaCl_2 solutions.Pectin was difficult to break down in acidic or CaCl_2 solutions, so blanching in these solutions prevented excessive softening.(4) Blanching in 20% sucrose, glucose, or sorbitol solutions.These sugars produced a notable firming effect.