Diacylglycerol-mediated casein aggregation in yogurt: Insights into coagulation kinetics and protein network assembly

As a functional structural lipid, diacylglycerol (DAG) is reported to strengthen the gel structure of the fermented dairy. However, whether DAG accelerates the coagulation process, how it affects gel network structure, and the mechanisms underlying above effects remain unknown. In this study, soybean diacylglycerol (SDAG)-fortified yogurt was prepared and the mechanisms of DAG-mediated casein aggregation were investigated through the coagulation kinetics and protein network assembly. The results showed that SDAG group completed coagulation 1 h earlier than control groups and exhibited an 18.6% increase in gel strength. Mechanistically, it was proposed that DAG may promote the proliferation of lactic acid bacteria, enhance lactose utilization and lactic acid production, and accelerate the destabilization and coagulation of casein micelles to shorten the coagulation process. DAG increased the proteolytic activity by 1.86 times and was associated with reduced α-casein and β-casein band intensities (by 2.4% and 3.95%, respectively), which may expose hydrophobic regions and thiol sites, thereby forming a compact network. The proportion of intermolecular β-sheet increased from 16% (CK) to 28% (SDAG group), while β-turn decreased from 20% to 17%, indicating a conformational transition from disordered to ordered structures. Molecular docking suggested that free hydroxyl groups of DAG may serve as molecular bridges to crosslink caseins via hydrogen bonds, potentially promoting coagulation. DAG accelerated acid production, facilitated structural ordering, and may enhance protein cross-linking, thereby shortening coagulation time and facilitating a compact gel network, although the esterase-glycerol pathway remained to be confirmed. This study provides mechanistic support for developing functional dairy products.