利用傅里叶变换红外光谱法同时测定奶粉中蛋白质和脂肪含量.以硫氰化钾为内标物,其特征峰2 061.8 cm-1为参比峰,蛋白质和脂肪的特征峰为分析峰,分别将蛋白质和脂肪的分析峰的校正面积(As)与参比峰的校正面积(AKSCN)比(R=As/AKSCN)对蛋白质和脂肪含量作工作曲线.确定酰胺Ⅰ带1 654.8 cm-1(1 600.0~1 733.3 cm-1)与参比峰(1 981.0~2 142.9 cm-1)的组合A1 654.8/AKSCN最适合进行蛋白质定量分析,其线性回归方程C=3.871 R+10.88,相关系数为0.992 3;脂肪的C=O伸缩振动1 747.4 cm-1(1 719.0~1 766.7 cm-1)与参比峰(1 985.7~2 133.3 cm-1)的组合A1 747/AKSCN最适合脂肪定量分析,其线性回归方程C=29.13 R+3.531,相关系数为0.986 6.此方法的测定结果与凯氏定氮法和碱性乙醚提取法测定结果相比相对误差均小于±2.4%.

Fourier transform-infrared spectrometry (FTIRS) was applied to the rapid determination of protein and fat in milk powder using potassium thiocyanate as internal standard and its characteristic peak of 2 061.8 cm-1 as reference peak,and the characteristic peaks of protein and fat as analytical peaks.Working curves were prepared by plotting the ratio of corrected peak area of protein or fat (As) to that of potassium thiocyanate (ASCN) versus content of protein or fat.Ratio (R1) of peak area of the amide Ⅰ band of protein at 1 654.8 cm-1 (1 600.0-1 733.3 cm-1) and the peak area of reference peak (1 981.0-2 142.9 cm-1),A1 654.8/ASCN-,was taken as parameter in determination of protein,and the linear regression equation obtained was C1=3.871 R1+10.88 (r=0.992 3).Ratio (R2) of peak area of the stretching vibration band of C=O group of fat at 1 747.4 cm-1 to that of peak area of reference peak (1 985.7-2 133.3 cm-1),A1 747.4/ASCN-,was taken as parameter in determination of fat,and the linear regression equation obtained was C2=29.13 R2+3.531 (r=0.986 6).Values of relative error between results obtained by this method and by the kjeldahl′s method for protein or the ether extraction method for fat were all within the range ±2.4%.