砀山酥梨酶促褐变及其影响因素的研究

采用分光光度法对砀山酥梨多酚氧化酶(PPO)酶促褐变机理进行研究。通过对其所催化的邻苯二酚氧化后所得到的产物吸光度值进行测定,分析了反应时间、pH值、温度和几种抑制剂对砀山酥梨PPO活性的影响,以及研究了破碎打浆、pH值、温度、贮存时间等不同加工过程对砀山酥梨酶促褐变变化趋势的影响。结果表明,以0.1 mol/L的邻苯二酚为底物,测得砀山酥梨PPO的最适pH值为6.5,最适温度为40℃,且随着时间的延长,砀山酥梨多酚氧化酶的活性始终保持稳定;L-半胱氨酸、柠檬酸、抗坏血酸对砀山酥梨多酚氧化酶的活性均表现出抑制作用,其中以柠檬酸的效果最好;在pH值3.5-4.6,酶促褐变对总褐变指数的贡献低于非酶促褐变,且pH值越高,酶促褐变对总褐变指数的贡献越大;在4℃,室温和37℃下,酶促褐变对总褐变指数的贡献低于非酶褐变,且温度越高,酶促褐变对总褐变指数的贡献越大,温度为37℃时,随着贮存时间的延长,酶促褐变对整个褐变反应的贡献逐渐减小。

Enzymatic Browning and its Influence Factors of Dangshansu Pear

The enzymatic browning mechanism of dangshansu pear polyphenoloxidase(PPO) is investigated by using spectrophotometer.The effects of reacting time,pH,temperature and some inhibitors on the enzyme activity of dangshansu pear polyphenoloxidase are analyzed through determining the absorbance of the product obtained from the enzymatic browning of pyrocatechol.The process conditions such as cracking and mashing,pH,temperature,storage time,etc.,are also studied.The results are as follows 0.1 mol/L pyrocatechol is as substrate,the optimal conditions of enzyme activity of dangshansu pear polyphenoloxidase are pH 6.5,temperature 40 ℃.With the extension of time,the enzyme activity of dangshan pear polyphenoloxidase can maintain at the initial level and did not decline.Some inhibitors such as L-cysteine,citric acid and ascorbic acid inhibited on the enzyme activity of dangshansu pear polyphenoloxidase.Among of them,citric acid is the most obvious one.In the range of pH 3.5~4.6,the contribution of the enzymatic browning to the total browning is less than the non-enzymatic browning.The higher pH values,the greater the contribution of the enzymatic browning to the total browning.At 4 ℃,room temperature and 37 ℃,the contribution of the enzymatic browning to the total browning is less than the non-enzymatic browning.The higher the temperature,The greater the contribution of the enzymatic browning to the total browning.With the extension of storage time,the contribution of the enzymatic browning to the total browning decrease gradually at 37 ℃.