| The aim of this paper was to propose a research on the processingtechnology of quick-frozen Chinese-yam, to study the application of microwavetechnology in the blanching process and freeze law of Chinese-yam under differenttemperature and quality changes after thaw. The quality characteristic of Chinese-yamafter quick-frozen process would be measured by sensory properties, texturecharacteristics and nutrients.Firstly, the research into the influences of different color fixatives, such as citricacid, ascorbic acid, calcium chloride and sodium chloride on the polyphenol oxidaseactivity and browning degree of Chinese-yam. The optimal combination of colorprotection solutions and the treatment method had been obtained through orthogonaltest. The sequent factors of synthetic refresh of browning restraining on Chinese yamwas vitamin C> citric acid> salt> calcium chloride, and the best compositepreservation formula as follows:0.2%vitamin C，0.2%citric acid，0.6%salt，0.3%calcium chloride.Secondly, the good processing of Chinese-yam blanching was found by studyinghot water blanching and microwave bleaching. The influences of hot water blanchingand microwave blanching on the quality of quick frozen Chinese-yam had beenexplored by testing the contents of peroxidase activity, polyphenol oxidase activity,soluble solids content, vitamin C content, total free amino acid content, viscositycoefficient and protein content at different bleaching levels. The result indicates thathot water blanching and microwave bleaching could undermine efforts of enzymeChinese-yam soonly, which the losses of nutrients could be reduced and sensoryproperties though microwave thawing could be maintained. The optimal blanchingcondition was90℃for140seconds with hot water blanching and407.6W for60seconds with microwave bleaching.Thirdly, the freeze law of Chinese-yam had been discussed through measuringfreezing curve, the freezing rate, the TPA characteristics and observing the thawed cellstructure. The result showed that freezing point of Chinese-yam was-0.5℃and-2.5℃, the largest ice crystals generated band was-0.5℃and-7.8℃,which is in line with the fruits and vegetables freeze law. The irreversible in the freezing process hadbeen inhibited greatly and product quality had been improved, Chinese-yam frozenat-40℃can pass maximum ice crystal formation with the least time under the lowerlimit temperature of-12℃.Fourthly, the research had explored the activity changes in polyphenol oxidaseand peroxidase of Chinese-yam that frozen under different temperature,the loss of thenutrition as well as the prediction of shelf life and the thaw quality changes thoughcolor protection process and microwave blanching process. According to the trendschanging with time and temperature of Vc content under different frozen storagetemperature, the Vc degradation kinetics model can be established in order to predictthe shelf life of the pregnant yam. During frozen storage, polyphenol oxidase andperoxidase enzymes had increased firstly and then decreased, and the trend wassimilar. Low temperature had contributed to the suppression of residual enzymesactivity and reduced the forming of undesirable flavors; frozen solids and Vc contenthad decreased with time, besides, the Vc degradation rate had declined with thereduction of the frozen storage temperature. Under the frozen Temperature, the Vcdegradationc had followed a chemical reaction model (Arrhenius equation) and had ahigh similarity with the actual measure value. besides,the effect of the TPA and sensoryproperties of Chinese-yam room on room temperature thawing and microwave thawing.The results showed that the effect of microwave thaw was better. |
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