EFFECTS OF HEAT TREATMENT ON NUTRITIONAL SAFETY AND BIOLOGICAL VALUE OF DAIRY PRODUCTS: A MECHANISTIC STUDY USING QURT AS A MODEL FERMENTED MATRIX

Heat treatment is a cornerstone of dairy processing, yet its effects on nutritional safety and biological value remain a subject of active investigation, particularly for traditional fermented products of Central Asian origin. This study systematically characterizes the inactivation kinetics of Listeria monocytogenes and Salmonella spp. across a range of High-Temperature Short-Time (HTST) pasteurization regimes (63–85 °C, 15–30 s), and quantifies the concurrent impact on whey protein denaturation, Maillard reaction progress, and essential amino acid bioavailability. Using qurt — a dried fermented dairy product endemic to Uzbekistan and Central Asia — as a model fermented matrix, the work further investigates the physicochemical composition of qurt whey and develops an optimized whey-based functional beverage (qurtoba) via Response Surface Methodology with Central Composite Design (RSM-CCD). At the standard HTST condition of 72 °C / 15 s, reductions of 5.8 and 6.1 log₁₀ CFU/mL were achieved for L. monocytogenes and Salmonella spp., respectively, satisfying Codex Alimentarius requirements. β-Lactoglobulin denaturation reached 62.4 ± 3.1%, while reactive lysine loss remained below 3%. Qurt whey exhibited high protein density (8.2 ± 0.3 g/100 mL) with all essential amino acid scores exceeding FAO/WHO reference values. Among six beverage formulations, variant V6 (65% whey, 8 g/L pumpkin seed extract, 80 °C pasteurization) achieved the highest composite desirability (D = 0.947) with 5.42 g protein/100 mL and 54.3% DPPH radical scavenging activity. These findings provide an evidence-based framework for optimizing HTST pasteurization in qurt production and valorizing whey as a functional ingredient.