超声波、紫外线、超声波联合紫外线对鲜切香菇多酚氧化酶与过氧化物酶的钝化及其机理研究

Effects of Ultrasound,Ultraviolet,Ultrasound Synchronized Ultraviolet on the Inactivation of Polyphenol Oxidase and Peroxidase of Fresh-cut Lentinus edodes and Its Mechanisms

酶促褐变是影响鲜切蔬菜质量的重要因素之一。本文对比研究了单一紫外线、单一超声波、超声波联合紫外线处理对鲜切香菇中多酚氧化酶(PPO)与过氧化物酶(POD)的抑制效果,通过酶的紫外光谱、二级结构含量以及X衍射光谱分析,初步探讨了作用机理。结果表明:超声波处理和超声波联合紫外线处理能够有效钝化PPO与POD活性;在超声功率密度70 W/L、双频超声20 kHz与40 kHz顺序工作15 min,PPO和POD相对酶活分别为30.6%和44.3%;紫外剂量为1.8 kJ/m^2处理后,PPO和POD相对酶活分别为66.5%和60.8%;在上述超声参数和紫外剂量联合处理后,PPO和POD相对酶活分别为31.0%和46.2%。紫外光谱表明,超声波、紫外线或超声联合紫外线处理后,酶分子C端的疏水性基团发生暴露。二级结构含量分析和X-衍射图谱表明,POD与PPO失活的原因在于α-螺旋、无规则卷曲含量的上升,β-折叠含量的减少,以及酶分子三维构象和衍射峰强弱的改变。本文能够为鲜切果蔬的钝酶提供理论依据和参考借鉴。

Enzyme-promoted browning is one of the important factors affecting the quality of fresh-cut vegetables.In the present study,ultrasound treatment,ultraviolet treatment,ultrasound synchronized ultraviolet treatment was applied to inhibit the activity of polyphenol oxidase(PPO)and peroxidase(POD),which were the major enzymes leading to browning of fresh-cut Lentinus edodes.Moreover,the mechanism of inactivation of enzyme was discussed from the aspects of ultraviolet-vis spectra,change in the content of secondary structures and X-ray diffraction spectra.The results showed that ultrasonic treatment or ultrasound synchronized ultraviolet treatment was effective to inhibit the activity of PPO and POD.Having undergone treatment under the parameters of power density of 70 W/L,dual-frequency 20 kHz and 40 kHz at sequential operation for 15 min,the relative activity of PPO and POD were 30.6%and 44.3%,respectively.Ultraviolet treatment at a dosage of 1.8 kJ/m^2 resulted in reduction of relative activity of PPO and POD,which were 66.5%and 60.8%respectively,and ultrasound synchronized ultraviolet treatment led to a relative activity of PPO and POD with a value of 31.0%and 46.2%,respectively.Ultravioletvisible spectra showed that hydrophobic groups located at the C end of enzyme molecules were exposed after treatment,irrespective to the kind of treatments.The analysis of secondary structural content and showed that the inhibition of PPO and POD might result from increase in the content of α-helix and random coil,and decrease in the β-sheet content.The results of X-ray diffraction indicated the change in the 3-dimensional conformation as well as intensity of diffraction peaks of PPO and POD might lead to the inactivation of enzymes.In conclusion,the present study can provide theoretical basis for inhibition enzyme in fresh-cut fruits and vegetables.