| Browning and haze have been crucial technical problems in apple juice concentrate (AJC) processing. Polyphenols were always thought to be connected with browning and haze in apple juice concentrate. Polyphenols of plants were secondary metabolic production, which could lead apple juice to browning and haze through taking part in the reactions of enzymatic browning, non-enzymatic browning and haze.In this paper, several main contents were particularly studied. Firstly, the mensuration of Chlorogenic acid and caffeic acid in apple juice concentrate by HPLC were studied. Secondly, the effects of main unit operations in apple juice processing were detailed investigated. And the dynamic changes of polyphenols in wholly processing chain and in entirely processing season were further studied. Thirdly, the characteristics of PPO in apple fruit could be attained. The aspects we have studied were temperature, pH value and heating stability, based on which the optimal extraction conditions could be confirmed. Fourthly, the main apple varieties of northwest region were Fuji, Qinguan and Granny Smith. Comparison study on the abilities of enzymatic browning and their Michaelis-Menten Equation parameters of PPO in above three apple varieties could be obtained. The order of the abilities of enzymatic browning within those three apple varieties and the Km and the Vmax values of enzymatic browning in those three apple varieties were acquired. We also studied on the effects of apple varieties to the quality of apple juice concentrate and the effects of adding different rate of Granny Smith to Fuji and Qinguan to the quality of apple juice concentrate. Finally, we investigated the effect of ion exchange fiber to removing polyphenols and pigments in detailed. And the qualities of apple juice which were before and after adsorption by fiber were also studies. We could obtain the adsorption dynamics curve of polyphenols and pigments of ion exchange fiber. The optimal concentration of desorption solution were selected. The relationship between the desorption times of ion exchange fiber and absorption efficiency of polyphenols and pigments by ion exchange fiber in apple juice were mainly studied.Through a great deal of experiments, we could draw conclusions as follows:1) The experimental results showed that enzymatic treatment, ultrafiltration andadsorption operations were effective unit operations for removing of the polyphenols and the average removal rate of those were 4.26%, 7.18% and 63.77% apart. In practical processing we must pay more attention to clean and regenerate resin in order to ensure the adsorption effect. Meanwhile, the dynamic variation regularity of polyphenols in chain of processing of apple juice concentrate indicated that the contribution of above three unit operations to removal of total amount of polyphenols from apple juice were 1.79%, 9.47% and 21.86% respectively.2) Different processing season have a great effect on the contents of polyphenols in apple juice concentrate. Dynamic analysis based on the polyphenols content in production season from August 2004 to January 2005 revealed that the polyphenols content tended to be greatly decreased from the last ten-day of August to the last ten-day of September, and it tended to be stable after October. Hence, in juice processing, optimal ripe degree of apple should be chosen in order to reduce the content of polyphenols, which could control browning and haze of apple juice at a certain extent.3) The results showed that with the catechol being substrate, the optimal pH value and temperature were 6.5 and 35 "C respectively. About 88% PPO were inactivated in 90 *C bath temperature for 3min and the PPO activities were almost inhibited.4) The results indicated that Fuji apple has the highest browning degree, followed by Qinguan, and the lowest one was Granny Smith. The main reasons were as follows: content polyphenols in Granny Smith was significantly lower than that of Fuji and Qinguan; Titration acid of Granny Smith was greatly higher than that of Fuji or Qinguan; the PPO activity in Granny Smith was lower than that in Fuji and Qinguan. With the catechol being substrate, the Km values of Fuji, Qinguan and Granny Smith were 0.04, 0.07 and O.llmolL"1, respectively, and the Vmax Values of those were 0.35, 0.38 and 0.39 U-min'1, apart. Comparing on Michaelis-Menten parameters of the three apple varieties, we can draw the conclusion that the highest browning degree of three kinds of apple is Fuji apple, and the lowest degree is Granny Smith.5) The results showed that adding 30% Granny Smith to Fuji and Qinguan could enhance quality of apple juice concentrate and control juice browning. Titration acid of apple juice concentrate made by above rate of different apple varieties could be notability improve, which can reach the demand of high acid juice. This is the mainly approach in the future to increase acid and price of juice.6) The qualities of apple juice which were before and after adsorption by ion...
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