Abstract:
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.
