Factors Affecting the Structure of Pectins in Dairy Systems: Protein Interaction Mechanisms during Acid Coagulation

<jats:p>The protein-fat matrix of fermented milk products is instable, manifesting as syneresis, stratification, and deterioration of texture. It requires effective natural stabilizers. However, the mechanisms of interaction between pectins and casein micelles under acid coagulation remain understudied, which limits the development of targeted technological approaches. This article describes the factors that determine the structure formation of pectins in dairy systems, as well as the mechanisms of their interaction with casein during acid coagulation. The research featured citrus and apple pectins, casein micelles, whey proteins, and starter microorganisms of the genera Lactococcus, Streptococcus, and Lactobacillus. It involved scientific publications indexed in Russian Science Citation Index, Scopus, and WoS. The nature of pectin structure formation depends on the pH, the ionic strength of the medium, the charge density of macromolecules, and the ratio of product components. The acid coagulation of casein proceeds through four stages, with the key trigger being the rate of lactic acid accumulation by the starter microflora. Low-esterified pectins at pH below 5.0 are adsorbed on the surface of casein micelles by charged fragments of the polygalacturonate chain. Uncharged regions form sterically stabilizing loops that prevent excessive protein aggregation and syneresis (whey separation). Adding 0.1 % pectin to yogurt increases the firmness to the level of its full-fat equivalent and reduces syneresis by 25 %, without affecting the fermentation process or final acidity. The species composition of the starter determines the pH kinetics, the exopolysaccharide synthesis, the proteolytic activity, and the protein matrix density. The effectiveness of pectins depends on the degree of esterification, pH, and ionic strength. The stabilization is achieved through electrostatic adsorption and steric effect while pectin acts as a prebiotic and plasticizer. Research prospects include finding optimal combinations of pectin type and starter composition to produce foods with desired rheological characteristics.</jats:p>