Control of milk acidity by photoluminescence

For a quality assessment of milk and dairy products, the optical methods are used. In this paper, the use possibility is investigated of the optical method of photoluminescence for the milk acidity value finding out. The spectral measurements were carried out on a diffraction spectrofluorimeter in the range of 200–500 nm. The milk acidity measurement accuracy was controlled by the titrimetric method. It is established that as far as milk sours, the excitation spectra in the range of 200–500 nm decrease; but there are qualitative changes in the range of 350–500 nm. With acidity growth, the photoluminescence flux decreases if it is excited by the radiation value λ_e = 262 nm, grows at λ_e = 385 nm and decreases at λ_e = 442 nm. It is advisable to control the milk acidity in terms of the photoluminescence fluxes ratio Φ₃₈₅/Φ₄₄₂. The linear approximation of the function Φ₃₈₅/Φ₄₄₂(K) is statistically reliable (the determination factor R² = 0.99).