Microstructural analysis of network formation in milk protein-polysaccharide mixtures by timelapse confocal laser scanning microscopy

To improve the firmness and viscosity of yogurt, a widely consumed dairy product, polysaccharides are frequently utilized. Polysaccharides can modify the formation of the protein networks that make up yogurt by interacting with the milk proteins via electrostatic forces and depletion mechanisms. The interactions between milk proteins and polysaccharides during yogurt fermentation are difficult to study, because they evolve over time due to the decrease in pH. To overcome this, we examine the impact of five different types of polysaccharides (low acyl gellan, high acyl gellan, xanthan, guar gum, ι-Carrageenan) during acid-induced milk gelation using Confocal Laser-Scanning Microscopy. Additionally, we employ Fourier space analysis, time-dependent oscillatory rheology, and cross-correlation image analysis to quantitatively understand how the different polysaccharides affect yogurt microstructure and properties. Our results show that addition of xanthan, guar gum, and ι-carrageenan results in faster structure formation, at pH values above the onset of gelation. Furthermore, while having identical charge density, low acyl gellan associates faster with the protein network compared to more acetylated high acyl gellan or highly branched xanthan. In summary, this study highlights the benefits of integrating timelapse imaging with quantitative image analysis to gain insights into the influence of polysaccharides during milk gelation. • Microscopy enables localization of polysaccharides during milk gel formation. • Polysaccharides associate with the milk protein network after network formation. • The onset pH of polysaccharide association depends on its branching density. • Xanthan associates with the network at more acidic pH values than acyl gellan.