| Kiwifruit is affluent in variety and resource in China where is its original habitat. Kiwifruit is abundant in Vitamin C, the concentration of which is ten times more than other fruits. This gives kiwifruit the properties to prevent scurvy, hypertension, coronary heart disease etc. Kiwifruit belongs to bacca. It is sensitive to ethylene and easily decomposes after picking, which affect the plantation development of kiwifruit weightily. Therefore, studying the processing technique of kiwifruit is important to exploit it as a resource and improve its economic value. Kiwifruit is high in protein compared with many other fruits and this causes haze problems in clear juice processing and storage. The objective of this dissertation was to develop a technology for processing clear kiwifruit juice using chitosan and to investigate the mechanism involved in the clarification treatment. Chitosan was prepared from chitin with different granularity. The reactive trends were similar under the reaction condition of same temperature, same lye concentration and different reaction times. The degree of deacetylation (DD) of chitosan increased quickly in the first several hours of the reaction, and then remained stationary. DD of chitosan made from chitin with small granularity was higher than that with big granularity. Gel permeation chromatography analysis showed that the molecular weight of chitosan prepared at 10 hours reaction time was smaller than that at 8 hours reaction time and the main chain of chitosan had been ruptured at 14 hours reaction time. According to the results of single and orthogonal tests, the procedure for chitosan clarification kiwifruit pressing juice was as follows: selected kiwifruits were washed, sterilized , rinsed and pressed; the juice was filtered then added into 0.4g/L chitosan with 80% degree of deacetylation and kept for 30min at 50℃ constant temperature; and then the juice was centrifuged. Percent transmittance of clear kiwifruit juice prepared under this condition was 98%. The result of the storage experiment showed that low temperature was propitious to storage stability of clear juice.The effects of factors such as the eluate volume on the separation of chitosan by ion- exchange chromatography were also studied. The results demonstrated that increase in eluate volume were favorable to isolation with a continuous gradient. Chitosan with 80% degree of deacetylation (chitosan k) was separated. Three fractions were collected, concentrated under vacuum and lyophilized. The DD of chitosan k, a, b and c were 82%,56%,73% and 88%, respectively, as calculated from IR spectra. Their molecular weight daltons were, respectively, 1140000,1350000,740000 and 370000. Chemical change, percent transmittance and color of kiwifruit juice before and after chitosan k, a, b and c fining treatments were studied. The results showed that chitosan k, a, b and c could clarify pressed kiwifruit juice effectively. Percent transmittance of the clear juice after fining was higher than 95%. Protein concentration in juice before and after chitosan k, a, b and c treatments reduced by 67.35%,69.00%,72.70%,68.38% and polyphenoly concentration reduced by 6.49%,11.90%,16.44%,14.62%,respectively. The concentration of Vitamin C in juice and soluble solids content of juice were the same before and after chitosan k, a, b and c clarification treatments. Clear juice treated with chitosan k was lighter colored than that clarified with chitosan c. During storage kiwifruit juice fined with chitosan b was more stable than that clarified using chitosan k, a and c.Results from ultra-visual scanning study of kiwifruit juice before and after chitosan k clarification treatment showed that polyphenol in natural juice maybe flavanol and flavonoid. Several macroporous adsorption resins were studied for selecting the best one to separate polyphenol. The result showed the adsorption properties of DA201-A macroporous resin was better than that of DA201-B and DA201-C. 78.6% of the polyphenol in the juice was adsorbed, and the yield o...
|
PDF Full Text Request