Modulation of sodium distribution and digestion properties in low salt myofibrillar protein gel incorporating γ-polyglutamic acid and transglutaminase: Conformation and microstructure

The weak gelling and poor digestion properties of myofibrillar protein (MP) under low-salt conditions constrain the development of functional sodium-reduced meat products. This study investigated how modification with gamma-polyglutamic acid (gamma-PGA) and transglutaminase (TG) cross-linking influences the conformation, gelation, and in vitro digestion of low-salt MPs pretreated with konjac glucomannan (KGM) and ultrasound. The results revealed that gamma-PGA addition effectively facilitated the exposure of tryptophan and tyrosine residues in low salt MPs. The better dispersibility and slightly lower rheological properties of protein sols suggested the circumscribed effect of gamma-PGA in augmenting protein gelation. TG crosslinking promoted moderate aggregation of MPs through different sites in myosin fragments, augmented the uniform distribution of sodium, and remarkably enhanced the gelling behavior of MPs. Importantly, the simultaneous incorporation of gamma-PGA contributed to the refinement and uniformization of the TG cross-linked protein gel network, especially in the protein gel modified by pre-ultrasound treatment in combination with KGM. This result could also be corroborated by the augmented intermolecular interactions and enhanced digestibility observed in gamma-PGA-modified TG crosslinked protein gel. Coupled with the identification of potentially bioactive peptides, it was confirmed that myosin light chain, actin, and myomesin account for the major contribution to the gamma-PGA-induced changes in MP gels. Therefore, TG crosslinking combined with gamma-PGA could be used to regulate the conformation and gelling properties of low-salt MPs, thus influencing the sodium distribution and digestion properties of low-salt meat products.