Valorization of Dairy and Plant By-Products as Functional Ingredients in Kurt (Dried Fermented Milk Product): Effects on Nutritional, Physicochemical, and Sensory Properties

This study developed enriched kurt formulations using buttermilk protein sediment, spray-dried whey, soy protein concentrate, and flaxseed cake, and assessed their effects on composition, physicochemical parameters, microbiological stability, and sensory quality. Protein content increased from 46.2% in the control to 48.7-52.4% in experimental samples. Calcium levels rose from 750 mg/100 g to 856 mg/100 g in Experiment 1 and 880.7 mg/100 g in Experiment 3 (<i>p</i> < 0.05), demonstrating strong mineral enhancement. Moisture decreased from 13.61% in the control to 11.68-12.90% in enriched variants (<i>p</i> < 0.05), indicating more efficient dehydration and a denser structure. pH remained within 4.1-4.3 and water activity stayed below 0.60, supporting long-term microbial stability. Amino acid profiling showed higher levels of essential amino acids, particularly leucine and lysine, in samples containing buttermilk protein sediment and whey. Microbiological analysis confirmed low total viable counts values (9.0 × 10²-1.2 × 10³ CFU/g), consistent with the high acidity and low moisture of traditional kurt. Sensory evaluation revealed significant variation among formulations. The control and Experiment 2 received the highest taste and aroma scores (4.67 points), while Experiment 3 showed the lowest values (3.33 points; <i>p</i> < 0.05). Appearance scores decreased notably in darker samples, with Experiment 3 showing a reduction from 4.67 to 2.67 points (<i>p</i> < 0.05). Texture also differed across variants; Experiment 2 maintained acceptable hardness and cohesiveness (4.33 points), whereas Experiment 3 displayed increased crumbliness (3.0 points; <i>p</i> < 0.05). The findings demonstrate that functional enrichment of kurt is feasible when ingredient levels remain within an optimal range. The Experiment 2 formulation achieved improved nutritional value without compromising sensory quality, providing a promising basis for further technological development and commercial application.