Gelation of methylcellulose-protein mixtures: effect of methylcellulose molecular weight and protein characteristics

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Methylcellulose (MC) is a widely used functional ingredient due to its thermo-reversible gelation properties, which is particularly important in applications such as meat analogues. Since these products have a high protein content, understanding the gelation behaviour of MC-protein mixtures is essential. This study investigated the gelation of MC-protein systems using methylcelluloses with molecular weights ranging from 100 to 300 kg/mol and two distinct protein isolates; pea protein isolate (PPI), a denatured and aggregated protein, and potato protein isolate (PoPI), a native and highly soluble protein. Confocal microscopy revealed that addition of PPI to MC resulted in MC gels in which PPI was present as microphase-separated domains that became more interconnected with increasing PPI concentration. PPI addition did not influence the mechanical properties of the gels, but strongly impacted the syneresis of the gels, which increased significantly—up to 10 wt%. Syneresis was more pronounced for MCs with higher molecular weight due to the formation of denser network structures upon contraction, leading to more expelled liquid. This syneresis was amplified by the presence of interconnected PPI domains resulting from the microphase separation. In systems with low PoPI concentrations, the protein acted as a dispersed phase within an MC matrix, without altering the gel moduli. However, at sufficiently high PoPI concentration (7.5 wt%), the protein formed its own space-spanning network next to that of MC, leading to a synergistic increase in gel strength—up to a threefold enhancement. This enhanced gel strength likely stemmed from increased effective concentrations of MC and PoPI, as well as hydrophobic interactions between MC and PoPI within the networks. MCs with lower molecular weight formed less interconnected networks, which resulted in a more pronounced contribution of PoPI to the gel moduli. MC gels containing PoPI did not exhibit syneresis due to the water-retaining capacity of the protein network. We conclude that protein characteristics have a broad impact on the structural, mechanical and syneresis properties of MC-protein gels, whereas the molecular weight of MC primarily affects syneresis.