Determination of crude protein content in oilcakes by photoluminescence fluxes

Determination of crude protein in animal feed using photoluminescence spectroscopy can significantly accelerate the feed preparation process. This study aimed to analyze the dependencies of photoluminescence parameters in sunflower and soybean oilcakes on their crude protein content to identify informative parameters and optimal spectral ranges. The experiment was conducted using a SM 2203 diffraction spectrofluorometer. The research involved determining the excitation and photoluminescence spectral characteristics of sunflower and soybean oilcake particles ground to 1.8 mm with varying crude protein levels. Integrated spectral parameters, specifically absorptivity and photoluminescence flux, were calculated. The excitation characteristics of the studied feeds are located in the 300-500 nm range and represent a superposition of peaks at 290, 362, and 414/424 nm, with a weaker peak at 485 nm. It was found that spectral absorptivity increases with higher protein content. The dependencies of integrated photoluminescence fluxes on protein content are statistically significant (coefficients of determination = 0.84-0.99) and can be approximated by linear regression equations. For the photoluminescencebased determination of crude protein, the most suitable excitation wavelengths are 362 and 414 nm for sunflower oilcake, and 362 and 424 nm for soybean oilcake. For a unified methodology, it is advisable to use an excitation wavelength of 362 nm while recording the photoluminescence flux in the 410-600 nm range. The resulting spectral parameters and regression equations can be utilized to develop rapid-testing instruments and optimize technological processes in the preparation of feed mixtures.

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