Improvement in Texture of Frozen Vegetables

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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.