Influence of Luteolin on Physicochemical Characteristics, Structural Changes and Functional Properties of Casein Fermentation System

As a core nutritional component of milk, casein features excellent digestibility and biocompatibility, making it an ideal carrier for embedding natural bioactive substances in dairy product research. Luteolin, a typical flavonoid compound with superior antioxidant and anti-inflammatory bioactivities, is limited in industrial dairy applications due to poor environmental stability and low biological utilization. Moreover, the dynamic interplay mechanism between luteolin and casein throughout fermentation and cold storage remains unclear. This study hypothesized that luteolin could assemble with casein via non-covalent binding to form stable composite fermentation system, thereby optimizing the overall quality and functional attributes of fermented milk. This work aimed to explore the binding characteristics of luteolin of casein in fermented milk and its regulatory effects on products’ physicochemical properties, antioxidant capacity and nutritional digestibility. Experimental outcomes verified the hypothesis that luteolin bonded with casein through hydrogen bonding and hydrophobic interactions. With increased luteolin supplementation, the fermentation system presented lowered pH and elevated titratable acidity. Compared with control fermentation system without luteolin, the fermentatiuon system containing 0.06% luteolin achieved 31.31% higher DPPH radical scavenging rate, 27.02% higher ABTS clearance capacity, and 26.42% higher in vitro protein digestibility (p < 0.05). Dose-dependent increases in particle size and absolute zeta-potential enhanced system colloidal stability, while FTIR detection confirmed obvious variations in protein secondary structure in fermented milk. This study elucidates the distinctive structure–function correlation of the luteolin–casein fermentation system in fermented dairy matrices, providing original insights and reliable theoretical support for developing novel dairy products rich in functional nutritional factors.