Non-Destructive Analysis of Food Protein Content by Near Infrared Spectroscopy

研究了食品成分、温度和pH对近红外光谱透射式测定水溶液中蛋白质的影响。以牛血清白蛋白为模型蛋白。在1692、1738、1856、2056、2170和2286 nm处观察到明显的二阶导数吸收，其来源为蛋白质。在这些吸收中，即使在盐、糖、氨基酸、油和洗涤剂存在的情况下，即使在pH和温度改变的情况下，2170 nm处的吸收在波长和吸收强度方面也没有明显的影响。这些结果表明，需要选择2170 nm的波长才能高精度地测定蛋白质含量。其次，为了建立油/水乳状液中蛋白质含量的校正方法，考察了油含量对蛋白质含量测定的影响。用2170 nm(蛋白质)和2306 nm(油脂)的光强建立了修正方程，在较宽的含油量范围内(1-15%)获得了高精度的蛋白质(0-10%)的测定结果。这些结果表明，近红外透射法测定牛奶中的蛋白质含量是有效的。

Effects of food constituents, temperature and pH on near infrared spectroscopy for protein in aqueous solution in a transmittance mode were investigated. Bovine serum albumin was used as the model protein. Clear absorptions of the second derivative spectrum, which were due to protein, were observed at 1692, 1738, 1856, 2056, 2170 and 2286 nm. of these absorptions, the absorption at 2170 nm was not significantly influenced in terms of wavelength and absorption intensity even when salt, sugar, amino acid, oil and detergent were present, and even when pH and temperature were changed. These results suggest that a choice of the wavelength 2170 nm is required to determine protein content with a highly accuracy. Next, in order to establish a calibration for protein content in oil/water emulsions, effect of oil content on the determination of protein content was investigated. An amended equation was derived using optical intensities both at 2170 nm(protein)and 2306 nm(oil), and a highly accurate determination of protein(0-10%)was obtained over a wide range of oil content(1-15%). These results suggest that NIR measurements by transmittance mode are effective for the determination of protein content in milk.