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

•Spectral range of 1680–1058cm−1 showed clear differences between milk, AM and SM.•PCA showed clear clustering of samples based on level of adulteration.•SIMCA models could correctly (93%) classify the test samples except for 6% SM in 1639–1635cm−1.•SM could be best predicted in the spectral range of 1472–1241cm−1 (amide-III).•Amide-III has R2 values (MLR) 0.99 and 0.92 for calibration and validation. 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 4000–500cm−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 1680–1058cm−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 1472–1241cm−1 using multiple linear regression with coefficient of determination (R2) of 0.99 and 0.92 for calibration and validation, respectively.