红富士、秦冠、澳洲青苹在果汁加工过程中褐变的比较研究

Comparison study on browning of Fuji Qinguan and Granny Smith in apple juice processing

以目前西北黄土高原苹果汁加工中主要制汁品种红富士、秦冠以及即将用于榨汁的品种澳洲青苹为试验材料,对其褐变进行比较分析.结果表明,3种苹果的褐变大小顺序为红富士>秦冠>澳洲青苹.以不同浓度的邻苯二酚为底物,得到上述3品种米氏方程参数km分别为0.04、0.07、0.11 mol/L,最大反应速度vmax分别为0.35、0.38、0.39 U/min.在红富士和秦冠中添加30%的澳洲青苹,能显著抑制果汁的褐变,提高浓缩果汁的酸度和品质.这表明澳洲青苹和其他苹果混合制汁是浓缩果汁今后加工中控制果汁褐变、提高果汁酸度的一个主要途径.

The browning of three varieties of apple, Fuji, Qinguan and Granny Smith, in juice processing was detailed investigated. Titratable acid, pH value, polyphenols content and polyphenoloxidase（PPO） activity with catechol substrate of the apple varieties were mainly studied. The results indicated that Fuji apple have the highest browning degree, followed by Qinguan, the lowest one was Granny Smith. Also, Michaelis parameters were obtained. The km value of Fuji, Qinguan and Granny Smith were 0.04, 0.07 and 0.11 moL/L respectively, and the Vmax value of there varieties were 0. 35, 0. 38 and 0. 39 U/min apart. By comparing Michaelis parameters, it is found that the highest browning apple is Fuji, and the lowest is Granny Smith. The color （T440 nm）, adsorbtion （A420 nm） and NTU of the concentrated juice were measured respectively and the results show that the juice concentrate of Granny smith is the best one. Mixing 30% quantity of Granny Smith with Fuji and Qinguan, the acid of the juice concentrate be observably improved up to 1.90%, Therefore, This approach could be used to increase the acid content of apple juice in the future.