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损害，并过度软化。以胡萝卜和大白菜为材料，研究了冷冻过程中不同工艺参数对细胞结构、质构和果胶含量变化的影响。因此，认为以下治疗有效。(1)液氮速冻（PF ;冷冻速率：-5 ℃/min），静电解冻（ET）（-3 ℃）。冻后样品硬度大小顺序为：PF-5 ℃/min>PF-2 ℃/min>-80 ℃冰箱（F）>-30 ℃ CF>-20 ℃ CF; ()-3 100 ℃>5 ℃>20 ℃>100 ℃。组织结构的光镜、透射电镜和冷冻扫描电镜观察的组织学变化最小到最大：PF-5 ℃/min<PF-2 ℃/min<-80 ℃ CF <-30 ℃ CF <-20 ℃ CF。冷冻速度越快，组织中残留的果胶量越多。当原料冷冻样品在20 ℃解冻时，果胶的酯化度降低。(2)低温热烫（60 ℃，30 min或70 ℃，5 min）后再进行98 ℃的常规热烫。低温处理激活了胡萝卜中果胶甲酯酶的活性，从而使胡萝卜中的果胶脱甲氧基而增加硬度。(3)在2%的醋或0.05M的CaCl_2溶液中烫漂。果胶在酸性或CaCl_2溶液中很难分解，因此在这些溶液中烫漂可以防止过度软化。(4)在20%蔗糖、葡萄糖或山梨醇溶液中烫漂。这些糖能产生显著的紧肤效果。

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.