Differences in the yoghurt gel microstructure and physicochemical properties of bovine milk containing A1A1 and A2A2 β-casein phenotypes

Abstract

β-casein (β-CN) comprises a major portion of milk caseins and are present as several genetic variants. In this study, we investigated the effects of the β-CN A² variant versus the A¹ variant on the calcium distribution, acid gelation and foaming properties of milk, and the microstructure of acid milk gels. The results showed that milk containing the β-CN phenotype A²A² had a higher proportion of free ionic calcium, enhanced foam formation capability and required a longer time for gelation to occur. The storage modulus at the end of fermentation was significantly lower for β-CN A²A² milk gel compared with that from β-CN A¹A¹ milk. The microstructures of the gels characterised by both confocal microscopy and Cryo-SEM demonstrated the differences in the gel porosity and protein strand thickness. The more porous microstructure and thinner protein strands in the β-CN A²A² milk gel resulted in a lower gel strength compared to β-CN A¹A¹ milk gel. These findings provide new insights to the subtle differences in the physical properties of milk containing β-CN A²A² and A¹A¹ phenotypes, which could support dairy producers in the development of new dairy products with different functional properties.

Keywords: Foaming; Gelation kinetics; Rheology; Texture; Yoghurt microstructure; β-casein phenotypes.