番石榴果肉的酶促褐变及其抑制措施

Study on the mechanism and control of the enzymatic browning in Psidium guajava jujube

采用分光光度法,对番石榴多酚氧化酶(PPO)的催化特性、最适波长、最适反应时间、最适温度、最适pH等性质进行了研究,同时实验了肉桂酸、抗坏血酸、苯甲酸、L-半胱氨酸四种添加剂对番石榴多酚氧化酶活性的影响,以寻求在果品的保鲜以及果肉初加工过程中抑制PPO活性的各控制手段与果品加工的有机结合方法,为防止褐变提供有效、合理的措施。实验结果表明:以邻苯二酚为反应底物时,番石榴多酚氧化酶催化氧化产物的最适波长为422nm,最佳反应时间为约20min左右,最适反应温度为25℃,最适pH为6.8,90℃水浴处理5min该酶基本已失活。四种添加剂对该酶均表现出不同的抑制效果,单一添加剂对番石榴多酚氧化酶酶促褐变抑制效果的强弱次序为:抗坏血酸>L-半胱氨酸>肉桂酸>苯甲酸,其中抗坏血酸的有效抑制浓度为0.1%,而两种浓度为0.05%的添加剂协同作用又以L-半胱氨酸+抗坏血酸的效果最好。

Polyphenol oxidase（PPO） properties of Psidium guajava jujube were studied by spectrophotometer, including its catalytic characteristics,the maximum absorption wavelength of Psidium guajava jujube,the optimum temperature,the optimum pH, the thermo stability of enzyme and so on. It was also studied the effects of the inhibitors ascorbic acid,citric acid and L-cysteine affecting the activity of PPO of Psidium guajava jujube. When catechot was used as substrate,the results showed that the optimum conditions were as follows： λ =422nm, pH = 6.8,t =25℃,the time of reactivity≈20min for PPO. However,the PPO was inactivated in 90℃ water for 5min. Four kinds of inhibitors had different inhibition effects on PPO activity. The anti-browning effect sequence of single inhibitors was ascorbic acid 〉 L- cysteine 〉 4- Hydroxycinnamic acid 〉 benziond acid. The effective concentration of inhibitor ascorbic acid was 0.1%.