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

研究了食品成分、温度和pH值对蛋白质水溶液近红外透射光谱的影响。牛血清白蛋白被用作模型蛋白。在1692、1738、1856、2056、2170和2286 nm处观察到由蛋白质引起的二阶导数光谱的清晰吸收。其中，即使存在盐、糖、氨基酸、油和洗涤剂，以及即使改变pH和温度，2170 nm处的吸收在波长和吸收强度方面也没有显著影响。这些结果表明，需要选择波长2170 nm以高精度测定蛋白质含量。接下来，为了建立油/水乳液中蛋白质含量的校准，研究了油含量对蛋白质含量测定的影响。利用2170 nm（蛋白质）和2306 nm（油）处的光强度推导出修正的方程，并在宽的油含量范围（1-15%）内获得了蛋白质（0-10%）的高准确度测定。这些结果表明，透射模式的近红外测量是有效的牛奶中蛋白质含量的测定。

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.