Development and physicochemical evaluation of a low-phenylalanine and anti-urolithiasis yoghurt based on casein glycomacropeptide and coconut water: in vitro study

Abstract Individuals with metabolic disorders such as phenylketonuria (PKU) and kidney stone disease may be unable to consume conventional dairy products because of their high phenylalanine content. This study used different concentrations of glycomacropeptide (GMP; 2.5% and 3.0%) and starch (1.5% and 2.0%), which served as the independent formulation variables. All other ingredients, including coconut water (CW), Yoghurt culture, fermented unsalted butter, iota-carrageenan, inulin, sugar, stevia and stabilizers, were added at the same levels in all formulations. Physicochemical properties, antioxidant capacity, lactic acid bacteria viability, phenylalanine concentration and in vitro inhibition of calcium oxalate (CaOx) nucleation, growth and aggregation were assessed in the prepared Yoghurt samples during 14 days of 4°C storage. Among the tested formulations, F-4 (3% GMP and 2% starch) exhibited the most favourable physicochemical, microbiological and functional properties. The resulting reduced-sugar Yoghurt contained ultra-low phenylalanine (only 8.403 mg/100 g), well below the recommended dietary intake for individuals with PKU. Furthermore, F-4 demonstrated superior antioxidant stability, the highest microbial viability and the lowest syneresis during storage. It inhibited CaOx crystal nucleation, growth and aggregation by up to 30.87%, 33.24% and 36.85%, respectively, suggesting potential anti-urolithiasis activity. Sensory evaluation of the F-4 GMP–CW Yoghurt confirmed high consumer acceptability. Collectively, these findings indicate that the optimized F-4 GMP–CW fermented Yoghurt may provide metabolically tailored nutrition by combining phenylalanine restriction with moderate anti-urolithiatic activity. It may therefore have potential as a functional food to support nutritional management while offering antioxidant and anti-urolithiasis-related benefits.