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.