[目的]乳清蛋白粉水解产物中α-氨基小分子物质含量较高,寻找一种检测方法对此部分物质进行含量的检测,并以占蛋白质的含量报出,做为水解程度的参考值。[方法]凯氏定氮法检测总蛋白质含量,同时利用茚三酮与α-氨基的显色反应,读取反应液的吸光度值,代入工作曲线得出含α-氨基小分子物质含量,与总蛋白质的比值即为含量（占蛋白质）。[结果]α-氨基小分子物质含量（占蛋白质）结果标准偏差为1.91,相对标注偏差为3.5 %,方法重复性较好,且回收率也符合加标回收的要求。[结论]茚三酮显色法检测含α-氨基的小分子物质有明显的优势,可与凯氏定氮法结合使用,监测蛋白水解效果。

[Objective] The hydrolysate of whey protein powder contains α- amino small molecule substances of the content in product is relatively high. Find a detection method to detect the content of this part of the substance,and report the proportion of protein as a reference value for the degree of hydrolysis.[Method] Kjeldahl nitrogen determination method was used to detect total protein content,while using ninhydrin and α- amino groups take color reaction,read the absorbance value of the reaction solution,and substitute it into the working curve to obtain the content of α- amino small molecule substances of the ratio amino to total protein is the content （in protein）.[Result] α- amino of small molecule content （in protein） standard deviation results is 1.91,with a relative labeling deviation of 3.5%. The method has good repeatability and the recovery rate also meets the requirements for spiked recovery. [Conclusion] Ninhydrin colorimetric method for detecting the presence of α- amino small molecule substances have obvious advantages and can be used in combination with Kjeldahl method to monitor the protein hydrolysis effect.