Degradation Kinetics of Dairy Products and Selection of Processing Strategies Based on Critical Biomarkers

Introduction: Dairy products near or beyond the end of their recommended shelf life form a stream of food waste, yet their processing is hampered by compositional variability and different degrees of degradation. Existing valorization schemes, including fat separation, fermentation, anaerobic digestion, and drying, are mainly designed for homogeneous streams and do not sufficiently account for the specific features of mixed dairy systems, which limits the evidence-based selection of an appropriate processing route.

Purpose: To identify critical degradation parameters of mixed dairy systems near or beyond the end of their recommended shelf life and to develop algorithmic principles for an intelligent sorting system that supports the selection of a rational processing route.

Materials and Methods: The study objects were cream, sour cream, kefir, and their 50:50 binary mixtures, with fat contents ranging from 2.5 to 15% and stored for 90–120% of the manufacturer-recommended shelf life. A full-factorial accelerated storage experiment was conducted at (32 ± 1) °C, with sampling after 0, 72, and 144 h. The following parameters were determined: pH, titratable acidity, apparent viscosity, lactose content, fat-phase characteristics (peroxide value, acid value, and fatty acid composition), and organic acid profile. The Arrhenius model was used to extrapolate the results to storage at 5 °C, while regression and cluster analyses were applied to group and standardize raw material streams.

Results: The degradation rate was determined by the initial matrix and the proportion of fermented components. The most pronounced changes were observed in cream and cream-containing mixtures: the titratable acidity of cream increased from 16 to 136 °T (degrees of titratable acidity used in Russian dairy practice), pH decreased by 2.9 units, and apparent viscosity increased more than 100-fold, indicating acid coagulation and gel formation. Sour cream showed the greatest stability, whereas kefir was characterized by high initial acidity and pronounced acid accumulation. In the fat phase, the peroxide value increased to 5.1–6.6 meq O₂/kg and the acid value to 1.7–2.2 mg KOH/g. The regression models made it possible to predict changes in these parameters as a function of mixture composition and storage time. Lactic acid accumulation in the presence of residual lactose indicates the potential for lactic acid valorization, whereas a volatile fatty acid content above 1000 mg/L may serve as a criterion for redirecting the raw material, after fat separation, to anaerobic digestion. Cluster analysis based on fatty acid composition identified four stable sample groups suitable for batch standardization.

Conclusion: Degradation changes in dairy products near or beyond the end of their recommended shelf life can be interpreted as a set of critical biomarkers that relate the condition of the raw material to a rational processing route. The proposed approach can be used for intelligent sorting, preliminary assessment, and routing of dairy products withdrawn from standard circulation at the stages of storage, logistics, and processing. This creates a basis for evidence-based valorization of heterogeneous dairy streams and for reducing losses of valuable components.

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