Rapid Quantitative Analysis of the Major Components in Soymilk Using Fourier-Transform Infrared Spectroscopy (FT-IR)

Abstract

Fourier-transform infrared spectroscopy (FT-IR) on attenuated total reflectance (ATR) sampling was used for the quantitative analysis of the major components (protein, lipid, and sugar) in soymilk. Since mid-infrared spectroscopy shows specific absorption of each functional group of each molecule, it is possible to determine the amount of each component without complicated statistical computation. The determination of protein content was performed by using amide II absorbance at wavenumber 1545 cm-1 for protein, ester absorbance at 1745 cm-1 for lipid, and C-C·C-O absorbance at 1000 cm-1 for sugar. The protein and lipid contents were determined directly from these absorbencies, and the sugar content was calculated by subtracting the effect of protein. There was a linear relation (R2>0.99) between each absorbance and each concentration of purified components (soybean protein, lipid, or sugar), and the values by this method were well consistent with those by chemical method. This technique of measurement of the major components in soymilk by FT-IR with ATR is more convenient and rapid.