Detection and quantification of soymilk in cow–buffalo milk using Attenuated Total Reflectance Fourier Transform Infrared spectroscopy (ATR–FTIR)

Milk consumption is steadily increasing, especially in India and China, due to rising income. To bridge the gap between supply and demand, unscrupulous milk vendors add milk-like products from vegetable sources (soymilk) to milk without declaration. A rapid detection technique is required to enforce the safety norms of food regulatory authorities. Fourier Transform Infrared (FTIR) spectroscopy has demonstrated potential as a rapid quality monitoring method and was therefore explored for detection of soymilk in milk. In the present work, spectra of milk, soymilk (SM), and milk adulterated with known quantity of SM were acquired in the wave number range of 4000–500 cm−1 using Attenuated Total Reflectance (ATR)–FTIR. The acquired spectra revealed differences amongst milk, SM and adulterated milk (AM) samples in the wave number range of 1680–1058 cm−1. This region encompasses the absorption frequency of amide-I, amide-II, amide-III, beta-sheet protein, α-tocopherol and Soybean Kunitz Trypsin Inhibitor. Principal component analysis (PCA) showed clustering of samples based on SM concentration at 5% level of significance and thus SM could be detected in milk using ATR–FTIR. The SM was best predicted in the range of 1472–1241 cm−1 using multiple linear regression with coefficient of determination (R2) of 0.99 and 0.92 for calibration and validation, respectively.