Change of Spectral Photoluminescent Properties of Milk during Souring

Abstract

Introduction. The use of digital technologies will increase the efficiency of animal husbandry. These technologies include optical monitoring of product quality. The aim of the research is to study the dependence of the spectral characteristics and parameters of excitation and luminescence of milk during souring. Materials and Methods. The milk with a fat content of 3.2% was used for measurements. The acidity was controlled by the titrimetric method. The excitation and luminescence registration spectra were measured on a Fluorat-02-Panorama spectrofluorimeter in the range of 200–500 nm. Spectra parameters were calculated in the PanoramaPro and Microcal Origin programs. Results. When milk sours, excitation spectra shift downwards, while a qualitative change in characteristics is observed with the range of 350–500 nm, although the photoelectric signal absolute level is almost an order of magnitude less than with a range of 220?340 nm. The photoluminescence flux when excited by the radiation with wavelength of 262 nm decreases during the souring process. The flux excited by the radiation with wavelength of 385 nm increases especially in the first three days. The flux at wavelength of 442 nm decreases slightly. Statistical parameters and energy of photoluminescence spectra are not informative for the milk souring control. The dependence of the ratio of photoluminescence fluxes excited by the radiation of 385 and 442 nm on acidity is linearly approximated with a determination coefficient of 0.99. Discussion and Conclusion. The change in the milk luminescent properties can be used as a marker of its souring with acidity control. To create a method for monitoring milk quality indicators during souring, the most informative is the use of excitation wavelengths of 385 and 442 nm with subsequent registration of photoluminescence in the ranges 440–490 and 490–600 nm respectively.