Colloidal insights into acid dairy gels: Role of exocellular polysaccharides from lactic acid bacteria

Texture building lactic acid bacteria (LAB) cultures are widely employed in dairy products to improve the structure of fermented milk matrices. Despite the large body of knowledge available, still very little is understood about the mechanisms underpinning the texturizing properties of LAB. During fermentation, LAB simultaneously reduce the pH by secreting lactic acid and produce exocellular polysaccharides (ExoPS). Colloidal biomolecules interact dynamically in this environment creating evolving supramolecular structures at various length and time scales, resulting in the final rheological properties of the bulk fermented milk product. The simplified model systems used so far have developed a mechanistic understanding of the impact of LAB in texturizing yogurt, but grossly overlook the colloidal interactions at play between the various components within the fermentation matrix, during LAB growth and ExoPS production, as well as their importance at the various stage of the acidification, gel formation, cooling and post processing. This review builds on the great advances made in the last two decades in understanding how to select and control texturizing LAB during fermentation, and focuses on the remaining research challenges, with focus on the recent research efforts which could aid in linking the mechanisms of structure formation at various length scales to the final, bulk quality of the fermented products. • Lactic acid bacteria produce exocellular polysaccharides during acid fermentation. • Polysaccharide-milk components colloidal interactions drive microstructure and texture changes. • AI-assisted analytics enable predictions in these complex dairy systems. • Advances in physical methods provide new insights into structure formation.