大米中蛋白质含量测定方法初探

The Effect of Adding Rice Interferences on Determination of Protein Content

大米蛋白是优质蛋白,然而,当前存在着严重的掺假现象。为降低生产成本,向大米产品中添加非蛋白含氮物质。采用大米蛋白作为研究对象,以尿素等为干扰物,利用Lowry、CBB、凯氏定氮法,研究干扰物对蛋白质含量测定方法的影响。研究发现,三聚氰胺的加入量低于300g/kg时,对测定结果无明显干扰作用,误差基本保持在3%以内;尿素的含量在低于100g/kg时,对测定结果无明显干扰作用,而随着加入量的继续增大,使CBB法和Lowry法的测定数据均有一定程度的下降,其中CBB法表现更为明显;硫酸铵对蛋白质含量的测定的影响最为微弱,添加量超过50g/kg时,蛋白质的测定结果反而呈现下降的趋势。分析表明,相比较凯氏定氮法、CBB法,Lowry法准确度更高,但由于蛋白质所含的氨基酸种类和比例不同,因而适合蛋白质的测定方法也不同,应根据情况选择最优方法,力求达到最佳效果。

Rice protein is a kind of high-quality protein. However, there is a serious adulteration phenomenon in the current dairy products and food raw materials. In order to reduce production costs, some companies and businesses add non-protein nitrogen material to rice products to simulate high protein products. This research took rice protein as testing objects, used melamine, urea and ammonium sulfate as disruptors by three protein determination methods： Lowry, CBB methods, Kjeldahl method and studied different disruptors on three kinds of protein content determination methods. These results showed that the melamine amount was less than 300 g/kg, had no obvious interference effect on the determination results,keeping within 3% error; The content of urea at less than 100 g/kg had no obvious interference effect on the determination results. With addition continuing to increase, the CBB and Lowry measuring data had a certain degree of decline, and the CBB method performance was more obvious; Ammonium sulfate＇s influence on the determination of protein content was the weakest. The protein determination results showed a trend of decline when adding amount was more than 50 g/kg. These conclusions showed that compared with Kjeldahl method and CBB method, Lowry method was more weakest. but different kinds of proteins had different types and proportions of amino acids, so the most suitable method to every protein for determination should not be treated as the same. The best method should be chosen according to the specific circumstances to achieve the best results.