超高压激活鲜榨梨汁多酚氧化酶酶学特性的研究

摘要/Abstract

摘要： 为探究超高压(High Pressure Processing，HPP)加速梨汁褐变的机制，以鲜榨翠冠梨汁为原料，采用超高压(500 MPa 5 min)处理，以未处理的为对照，测定超高压处理对梨汁货架期色泽的影响，检测处理前后梨汁中溶解氧含量和总酚含量，并研究了多酚氧化酶(Polyphenol Oxidase，PPO)的最适pH值、最适反应温度、热稳定性、米氏常数等。结果表明，超高压组梨汁货架期6 h褐变 (ΔE =1.61)，而未处理组货架期24 h仍未见明显褐变(ΔE =0.56)。鲜榨梨汁PPO存在PPO1 (pH 5.0)和PPO2 (pH 7.0)两种形式，超高压加速褐变与PPO1和PPO2活性被激活有关，PPO1活性从6.5 U/mL上升到14.1 U/mL，上升了2.17倍，PPO2活性从2.6 U/mL上升到25.5 U/mL，上升了9.8倍。激活效应的内在原因是PPO存在潜在酶活形式，本身弱活性甚至无活性，超高压是激活潜在PPO的外在原因之一，十二烷基硫酸钠(Sodium dodecyl sulfate，SDS)、热处理等也可激活潜在PPO。超高压降低PPO的Km值，提高了与底物之间的亲和力，从而提高酶促反应速度，PPO1与底物的亲和力1/Km从2.353 L/mol上升到46.909 L/mol，上升了19.9倍，PPO2与底物的亲和力从2.852 L/mol上升到62.857 L/mol，上升了22.0倍。超高压同时会降低Vmax，Vmax对酶促反应速度的影响如超过Km的影响，将会表现出钝化效应。综合而言，超高压激活潜在PPO，提高PPO与底物的亲和力，提高酶促反应速度，加速鲜榨梨汁褐变。

关键词: 鲜榨梨汁, 超高压, 褐变, 多酚氧化酶, 潜在酶活, 激活效应

Abstract: This paper aimed to explore the mechanism of high pressure processing (HPP) accelerating browning of pear juice. Taking Cuiguan pear juice as materials, 500 MPa 5 min treatment was used to study the effect of HPP on the color of fresh pear juice in shelf life, untreated as control. The color changes of fresh pear juice in shelf life were determined. Dissolved oxygen content, total phenol, and characteristics of polyphenol oxidase (PPO) such?as?the optimal pH?value, optimal temperature, thermal stability, and?Michaelis?constant?were?measured before and after treatment. The results showed that it was obvious browning of HPP treated juice at 6 h in shelf life, while still not obvious browning of untreated juice at 24 h; there were two forms of PPO, PPO1 (pH 5.0) and PPO2 (pH 7.0), accelerated browning of HPP was associated with activated activities of PPO1 and PPO2, the activity of PPO1 was increased from 6.5 U/mL to 14.1 U/mL, by 2.17-fold, and the activity of PPO2 was increased from 2.6 U/mL to 25.5 U/mL, by 9.8-fold; the intrinsic reason of activation effect was that PPO has latent form, itself weak or inactive, HPP was one of the external reasons for activation effect, other external reasons such as sodium dodecyl sulfate (SDS), heat treatment and so on. The Km was decreased, and the affinity of PPO for substrate was increased, thereby activating latent PPO activity and enhancing the rate of enzymatic reaction, the affinity (1/Km) of PPO1 for substrate was increased from 2.353 L/mol to 46.909 L/mol, by 19.9-fold, the affinity of PPO2 for substrate was increased from 2.852 L/mol to 62.857 L/mol, by 22.0-fold; the Vmax was decreased after HPP treatment, the inactivation effect would be expressed if the effect of Vmax on the rate of enzymatic reaction exceeding that of Km. To sum up, the browning of fresh pear juice was accelerated with HPP by activating latent PPO, increasing the affinity of PPO for substrate, enhancing enzymatic reaction.

Key words: Fresh pear juice , high pressure processing, browning, polyphenol oxidase, latent enzyme activity, activating effect

中图分类号:

TS255.36

尚海涛宣晓婷崔燕林旭东俞静芬凌建刚. 超高压激活鲜榨梨汁多酚氧化酶酶学特性的研究[J]. 食品科学, 0, (): 0-0.

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