Simultaneous Determination of Protein and Fat in Milk Powder by FTIRS

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%.