甲基蓝褪色光度法测定酱油中半胱氨酸含量

Determination of Cysteine Content in Soy Sauce by Methyl Blue Fading Spectrophotometry

在碱性硼砂-氢氧化钠缓冲溶液中,半胱氨酸能与酸性三苯甲烷染料甲基蓝发生加成反应,形成无色的硫醚衍生物,体系的吸光度降低,溶液褪色,最大吸收波长和最大褪色波长均为592 nm。于波长592 nm处测定体系的吸光度,确定最佳反应条件后建立标准曲线,用对照品标准曲线法测定样品中半胱氨酸的含量。半胱氨酸在质量浓度在0.20~2.40 mg/L内,与吸光度差值ΔA呈现良好的线性关系,相关系数r=0.9995,表观摩尔吸光系数为6.752×10^(4) L/(mol·cm)。该方法用于市售酱油和半胱氨酸护肝胶囊样品中半胱氨酸含量的测定,测定值的相对标准偏差(n=6)均小于3%,加标回收试验平均回收率为100.4%(一级酱油)、98.08%(三级酱油),护肝胶囊中测定值与标示量基本一致。建立的方法快速简便、专属性强,结果准确可靠。

In the alkaline borax-sodium hydroxide buffer solution,cysteine can react with the acidic triphenylmethane dye methyl blue to form a colorless thioether derivative,which decreases the absorbance of the system and discolors the solution with both the maximum absorption wavelength and maximum discoloration wavelength of 592 nm.Determine the absorbance of the system at the wavelength of 592 nm,and establish a standard curve after determining the optimal reaction conditions.The content of cysteine in the samples is determined by the control standard curve method.When the mass concentration of cysteine is 0.20~2.40 mg/L,it shows a good linear relationship with the absorbance differenceΔA,the correlation coefficient r=0.9995,and the apparent molar absorption coefficient is 6.752×10^(4) L/(mol·cm).This method is used for the determination of cysteine content in commercially available soy sauce and cysteine liver care capsule samples.The relative standard deviations(n=6)of the measured values are all less than 3%,the average recovery rates of the spiked recovery tests are 100.4%(primary soy sauce)and 98.08%(tertiary soy sauce),and the measured values in the liver care capsules are basically consistent with the labeled amount.The established method is rapid,simple,specific,and the results are accurate and reliable.