Quantitative image analysis of influence of polysaccharides on protein network formation in GDL-acidified milk gels

Abstract

Exopolysaccharides (EPS) are commonly used to improve the texture of yogurt. These polysaccharides interact with casein micelles, the major protein in milk, via electrostatic and depletion mechanisms during fermentation by lactic acid bacteria (LAB). However, the relationship between the physicochemical properties and monosaccharide composition of EPS and their impact on yogurt texture is not yet fully understood. To address this knowledge gap, we studied the effects of polysaccharides commonly used as food additives on acid-induced milk protein networks. Confocal laser scanning microscopy (CLSM) was used to image the network microstructures. Image analysis, including Fourier transform, autocorrelation, and binarization-based techniques, was applied to quantify key structural features of the mixed milk protein/polysaccharide gels. These parameters were then related to the macroscopic properties of the model food matrices, such as elastic and viscous moduli and yield point. We found that the addition of neutral polysaccharides resulted in a concentration-dependent increase in structure factor, protein domain size, and pore fraction. In contrast, the presence of charged polysaccharides led to an increase in protein domain size, a decrease in pore fraction, and a decrease in elastic and viscous moduli. These results demonstrate the use of a quantitative image analysis method for selecting LAB with favorable EPS properties to improve yogurt texture.