Co-gels of milk proteins and oat starch: A rheological, textural and microstructural perspective

This study explored the influence of milk proteins on rheological, textural, and microstructural properties of oat starch-milk protein co-gels. Steady-state rheological analysis revealed that the viscosity of protein-oat starch gels was both dependent on the type of protein and its concentration, with the gels exhibiting shear-thinning behaviour at higher shear rate. Dynamic rheological tests showed that the addition of protein to oat starch gels formed viscoelastic gels, in which elastic property dominated the gels (G' > G″). Moreover, the G' for both WPI-oat starch gels (WOS) and CaCN-oat starch gels (COS) decreased in contrast to the control samples, except for those containing 100% protein, which displayed an opposite trend. COS showed greater tan δ than WOS and the control gels suggesting COS are weaker gels with lower elasticity. Gels with 100% protein exhibited higher thixotropic behaviour, while WOS gels containing 25%, 50%, and 75% protein showed lower thixotropic values. Increased protein concentrations increased hardness and brittleness while reducing elasticity. Confocal laser scanning microscopy (CLSM) showed an effect of milk proteins on starch molecules and displayed larger protein aggregates at 60 °C, while at 90 °C, WPI penetrated starch granules, and CaCN adsorbed onto the granule surfaces. These findings provide valuable insights into starch-protein interactions, offering a foundation for tailoring biopolymer networks to achieve specific structural and functional properties. The results are particularly relevant for the food industry, where such understanding can support the formulation of high-protein, texture-modified dairy-based products with improved stability and consumer acceptability.