Studies On Polypheonol Oxidase Characteristic Pinklady Apple And Anti-browning Method Of Pinklady Apple Juice

Pinklady apple is a kind of high quality apple with high acidity, which is suitable to produce the popular juice on international market. In the process of apple juice production, the fresh fruit is easy to occur enzymatic browning, which not only greatly infuences the sensory quality, the favour and nutritional value of the product but also is an important reason for blocking the development of our fruit juice industry. This browning is usually due to the catalytic action of the enzyme polyphenoloxidase(PPO).o-Diphenols, present in the tissue of fruits and vegetables, are oxidized by polyphenoloxidase in the presence of oxygen. This oxidation reaction results in the production of o-quinones, which subsequently polymerize with other o-quinones, phenolic substances, proteins, amino acids, etc. to produce brown pigments. These pigments are sometimes referred to as melanins. In this experiment, PPO was extracted from Pinklady apple, and its common enzyme properties were studied. Effect of 19 inhibitor on PPO , anti-browning effect of inhibitors on fresh apple juice and apple juice during storage was investigated. The results are summarized as follows:(1)The optimum extraction conditions of polyphenol oxidase(PPO)from Pinklady apple was obtained by using the 1.5 mL·g-1 (sodium phosphate buffer/apple)sodium phosphate buffer (0.05mol/L,pH6.5) plus 2.5% PVPP and 0.25%Triton X-100.(2)PPO prperties were studied with catechol. The optimal reaction temperature of PPO was 30℃,and the optimal pH value of PPO was 4.5. Once the temperature was over 60℃,PPO became inactive quickly.The PPO was almast inactivated at 90℃for 3 min.(3)The inhibit rate of single inhibitor on PPO was:0.05%L-cysteine>0.075%Vc>0.2%benzoic acid>0.1% sodium isoascorbate>0.25% oxalic acid>0.2% phytic acid, whereby the inhibition abilities depended largely on their concentration and showed inreversible effect.(4)The anti-browning effect sequence of single inhibitors was: 0.3%benzoic acid >0.075%Vc>0.05%L-cysteine>0.1%sodium isoascorbate>0.25%oxalic acid>0.2%phytic acid. (5)The research suggested that 0.2%oxalic acid and 0.2%benzoic acid have a good effective of inhibit browning on apple juice during storage,the browning inhibitive rate were 71.04% and 78.22%.(6)In the experiment, 15 combinated inhibitor can inhibit enzymatic browning of fresh apple juice by orthogonal design. The most important was that we found a new inhibitor have a good anti-browning effective, the browning inhibitive rate was 90.34%. We called it GM-EDTA-Na2.(7)In these combinations, there were 5 combination inhibitors which could inhibit the browning of apple juice during storage and indicate good anti-browning effective. 0.3% phytic acid,0.3% oxalic acid combinated 0.5% citric acid, browning inhibit rate was 90.52%; 0.3% phytic acid,0.5% citric acid combinated sodium isoascorbate, browning inhibit rate was 89.55%; 0.3% oxalic acid,0.5% EDTA-Na2 combinated 0.5% citric acid, browning inhibit rate was 89.47%; 0.3% phytic acid,0.5% citric acid combinated 0.25%EDTA-Na2, browning inhibit rate was 84.68%.