Grass pea (Lathyrus sativus L.) protein gels and microgels: effect of pH on structure, rheology and lubrication

Microgels derived from plant proteins are increasingly being explored as structuring elements to modulate texture and lubrication in food systems; however, information on the use of underutilized legume proteins for microgels formation remains scarce. Thus, this study aimed to investigate thermally induced gels from grass pea (Lathyrus sativus L.) protein isolate prepared at different pH levels (2, 3, 7, and 9) and to evaluate their impact on the formation and properties of microgels derived from these parent gels. Prior to gelation, the surface hydrophobicity, ζ-potential, and particle size of the protein isolates at four different pH values were evaluated. Thermally induced gels were subsequently prepared and the rheological properties of the resulting gels were characterized through strain and frequency sweep tests. Microgels were then produced via a top-down approach by fragmenting the parent gels through high shear homogenization. The resulting microgels were assessed for surface hydrophobicity, droplet size, ζ-potential, flow behavior, and tribological performance. Particle size and ζ-potential analyses showed that acidic conditions promoted microgel aggregation, yielding larger particles within the size range of 156–345 nm. Consistently, acidic pH conditions (2 and 3) led to the formation of stiff parent gels and highly aggregated microgels with shear-thinning behavior and poor lubrication properties. In contrast, neutral (pH 7) and alkaline (pH 9) conditions resulted in more weakly structured parent gels and in more dispersed microgels, exhibiting near-Newtonian (pH 7) or weakly shear-thinning (pH 9) flow behaviour and reduced friction. Overall, the results demonstrate that pH-driven modulation of parent gel structure governs the flow and lubrication behaviour of grass pea protein microgels. These structure–function relationships provide a mechanistic basis for the rational use of microgels derived from underutilized legume proteins in soft and semi-solid food matrices.