Determination of the Mass Fraction of Milk Fat in Bottled Milk Using a Contactless Colorimetric Method

A contactless method is proposed for determining the mass fraction of milk fat in bottled milk by the diffuse reflectance LED at the wavelengths 365, 390, 850, and 880 nm using a smartphone and a specialized device. The analytical signal was recorded using OnePlus 10 Pro and iPhone 14 smartphones, equipped with PhotoMetrix PRO®, ColorGrab, and RGBer applications, as well as using an FTIR spectrometer for the near-IR region (4000–10 000 cm^–1). Specialized software, including TQ Analyst, The Unscrambler X, and XLSTAT, was used to process the experimental data. It was found that using all LEDs with different wavelengths simultaneously yielded results with the smallest relative deviation compared to using individual LEDs. Additionally, a slight change in the diffuse reflectance of milk through polyethylene terephthalate-based packaging was identified, which enabled contactless analysis without opening the packaging. The milk fat content of the test milk samples was evaluated using a multivariate calibration data algorithm—partial least squares regression. The relative standard deviation of the analysis results did not exceed 8%. The consistency of the analysis results was confirmed by FTIR spectroscopy in the near-IR region.