Investigating the role of lemon peel fiber in the casein gelation mechanism of low-fat yogurt

Incorporation of insoluble dietary fibers (IDFs) into yogurt can serve as both a nutritional supplement and texture modifier. However, the understanding of the interaction between IDFs and casein particles in yogurt, as well as their effect on the gelation mechanism of casein particles, remains limited. This study investigated the impact of varying contents of insoluble lemon peel fiber (LPF) on the casein gelation in low-fat yogurt. The gelation process of casein was monitored via oscillatory rheology, and the critical gel point was determined from time sweep curves. The post-gelation process was analyzed through the percolation model, and the topological structure after gelation was quantified using skeleton analysis. The incorporation of moderate content of LPF was found to reduce fermentation time (with the highest decrease being up to 1.2 h). This effect could be attributed to the enhanced main intermolecular forces (hydrophobic interactions and disulfide bonds), as well as the formation of casein-LPF-casein linked clusters with an elevated gelation rate exponent (α) value. These factors facilitated gel formation. Moreover, a moderate content of LPF facilitated cross-linking between caseins through a bridging effect, resulting in the development of a densely interconnected network with enhanced link density (88.25%) and reduced pore fraction (7.71%). Consequently, this led to a significant 17.6% inhibition in wheying off rate compared to low-fat yogurt without LPF during a 21-day storage time. However, the formation of weak or coarse gels was observed when the LPF content was low or high, the gelation rate was excessively rapid (exponent α = 3.05), or the presence of steric hindrance effect was present. The findings offered valuable insights for the application of insoluble particulate components in the food industry.