Mechanochemical unfolding facilitates protein-glutaminase deamidation and charge remodeling of myofibrillar protein to reduce low-salt-induced aggregation tendency

Salt is the quiet workhorse of the meat industry. Beyond delivering flavor, the sodium chloride added at 2 to 3 percent in conventional meat processing raises the ionic strength of the system, coaxing myofibrillar protein—the dominant functional protein in muscle foods—to dissolve, hydrate, and assemble into the gels and emulsions that give sausages and restructured hams their texture. But sodium has a public health problem. Long-term overconsumption is firmly linked to hypertension and cardiovascular disease, and global health agencies keep pushing for reduction. Meat products alone contribute nearly one-fifth of the average daily sodium intake, which makes low-salt meat processing an urgent target for the food industry. The catch is physical: cut the salt, and myofibrillar protein collapses into insoluble aggregates, losing the very solubility and functionality that salt had been providing.

The aggregation problem is fundamentally electrostatic. In a low-salt environment, the repulsive forces between myofibrillar protein molecules are too weak, and hydrophobic interactions take over, driving the proteins into coarse, insoluble clumps. Researchers have tried physical, chemical, and biological fixes—mechanical treatment to improve solubility, high-pressure homogenization to limit aggregate formation, ultrasound-assisted enzymatic modification to expose enzyme action sites. Each helps at the margins, but none has resolved the core difficulty: existing approaches either act only on the protein surface or partially unfold the structure without simultaneously rebuilding the missing intermolecular repulsion. The knowledge gap is a lack of synergy between mechanically induced structural unfolding and the reconstruction of electrostatic repulsion.

A new study from Chinese food scientists proposes exactly that synergy, pairing high-pressure microfluidization with protein-glutaminase deamidation in sequence. High-pressure microfluidization is a micro-shear technology that, in under five seconds and at pressures up to 200 megapascals, subjects protein suspensions to intense shear, cavitation, and transient pressure drops. These forces disrupt existing aggregates, loosen the tightly ordered myofibrillar architecture, and expose buried hydrophobic groups, sulfhydryl groups, and charged residues. Crucially, the treatment is rapid, efficient, and leaves no chemical residues. But mechanical force alone has an inherent ceiling: it can remodel conformation, yet it cannot change the intrinsic charge of the protein. Unfolded molecules with exposed hydrophobic regions still re-aggregate when electrostatic repulsion is insufficient, and overly harsh conditions risk over-denaturation that inactivates functional groups or degrades gelling performance.

Protein-glutaminase attacks the problem from the opposite direction. The enzyme catalyzes the deamidation of glutamine side-chain residues, substituting electrically neutral amide groups with anionic carboxylates and thereby imparting a net negative charge to the polypeptide. This raises the absolute value of the zeta potential and strengthens intermolecular electrostatic repulsion—a persistent effect that does not depend on added salt ions. The approach has been applied to casein, coconut protein, and soy protein isolate. Its weakness is substrate accessibility: the tightly folded native structure of myofibrillar protein buries most of its glutamine residues, restricting contact between enzyme and substrate, so deamidation proceeds slowly and incompletely, often demanding high enzyme dosages or prolonged incubation.

The hypothesis behind the combined treatment was elegant: high-pressure microfluidization would disrupt the highly ordered myosin filament structure and generate a partially unfolded state, while subsequent protein-glutaminase deamidation would convert glutamine residues into glutamate residues, increase electrostatic repulsion, and hold the protein fragments in a charge-stabilized dispersed state. To test it, the team extracted myofibrillar protein from fresh chicken breast under refrigerated conditions, treated it with high-pressure microfluidization at 52, 69, 86, and 103 megapascals, then deamidated the samples with protein-glutaminase at 16 units per gram of protein for 16 hours at 37 degrees Celsius. Control groups received either treatment alone, and every experiment was repeated across at least three independent biological batches.

The solubility results were striking. Untreated myofibrillar protein dissolves at roughly 34 percent in low-salt solution. High-pressure microfluidization alone improved solubility, consistent with earlier reports, but the sequential treatment pushed it dramatically higher—peaking above 70 percent. The mechanism, the authors argue, is that microfluidization disintegrates and unfolds the highly ordered muscle fibers, creating priority sites for the enzyme to contact its substrate. The efficiency of the Gln-to-Glu conversion improves, ammonia is released, and the newly incorporated carboxyl functionalities raise the negative charge density on protein side chains. The deamidation also disrupts hydrogen bonding within and between protein molecules, enhancing the affinity between protein and water.

Conformational analysis traced the structural remodeling in detail. Far-UV circular dichroism showed the alpha-helix proportion rising sharply—from 5.6 percent to 23.8 percent after microfluidization alone, and to 31.6 percent in the sequential group—while beta-sheet content fell from 29.6 percent to 16.8 percent. The beta-sheets, built from repeated glutamine-rich sequences held together by intermolecular hydrogen bonds, are progressively destabilized as the growing surface charge density strengthens electrostatic repulsion between adjacent sheet regions. Intrinsic fluorescence revealed that tryptophan residues were progressively exposed as the tertiary structure loosened, and the reactive sulfhydryl content rose significantly in the sequential group, corroborating the conformational relaxation that surface hydrophobicity measurements had already suggested.

The charge remodeling delivered the decisive blow against aggregation. The degree of deamidation in the sequential group ranged from 7.98 to 12.01 percent, exceeding the 5.94 percent achieved by the enzyme alone—direct evidence that microfluidization pretreatment exposed additional deamidation-accessible regions. Particle size told the complementary story: microfluidization alone actually enlarged particles, from about 2,675 nanometers in the untreated control to as much as 6,842 nanometers, apparently by unfolding proteins and strengthening cross-linking among exposed hydrophobic patches. Subsequent deamidation reversed this tendency dramatically, cutting particle size to between roughly 1,255 and 2,589 nanometers. The zeta potential shifted from –11.63 millivolts in the control to as far as –25.96 millivolts in the sequential group, the added carboxyl groups strengthening electrostatic repulsion enough to counteract hydrophobicity-driven clumping.

Imaging and separation techniques confirmed the microscopic picture. Transmission electron microscopy showed intact fibrillar structures in untreated protein, marked fragmentation after microfluidization, and a transition toward beaded or myosin-like monomer and oligomer morphologies after deamidation, with the aggregate fraction measurably reduced. Asymmetrical flow field-flow fractionation, a gentle separation method that elutes smaller hydrodynamic components first, showed the radius of gyration falling from 120.4 nanometers in untreated protein to 92.9 nanometers in the highest-pressure sequential sample. The Turbiscan stability index fell furthest for the sequential groups, particularly at 103 megapascals, and shear viscosity dropped sharply: untreated protein behaved as a shear-thinning pseudoplastic fluid, its intact high-molecular-weight fibers entangling and generating strong internal friction, while the treated systems approached Newtonian behavior as the fragmented, electrostatically repelled molecules flowed freely.

The authors caution that their design lacked a fully incubation-matched non-enzyme control, so the observed effects should be read as the combined influence of protein-glutaminase treatment under 37-degree incubation rather than an exclusively enzymatic effect. Within that limitation, the mechanism they propose is a two-stage strategy. First, mechanical energy disaggregates the protein and exposes buried glutamine residues and charged groups, overcoming the physical barrier the native conformation imposes on enzyme access. Second, deamidation locks in the dispersion by converting neutral amides into anionic carboxylates, generating repulsion strong enough to prevent the re-association of hydrophobic sites exposed by unfolding. The best-performing sample, treated at 103 megapascals before deamidation, reached 71.94 percent low-salt solubility. The work suggests that high-pressure microfluidization-assisted protein-glutaminase deamidation is not merely a combined processing method but a mechanochemical–enzymatic strategy for producing charge-stabilized meat protein dispersions—an ideal protein base state, the authors argue, for the reduced-salt meat products that public health increasingly demands.

Subject of Research: Mechanochemical unfolding facilitates protein-glutaminase deamidation and charge remodeling of myofibrillar protein to reduce low-salt-induced aggregation tendency

Article Title: Mechanochemical unfolding facilitates protein-glutaminase deamidation and charge remodeling of myofibrillar protein to reduce low-salt-induced aggregation tendency

Article References: Yang, N., Liu, Y., Chen, X., Yang, Z., Li, Z., Xiong, Y., Xu, X., & Wang, P. (2026). Mechanochemical unfolding facilitates protein-glutaminase deamidation and charge remodeling of myofibrillar protein to reduce low-salt-induced aggregation tendency. Current Research in Food Science, Article 101606. https://doi.org/10.1016/j.crfs.2026.101606

Image Credits: AI Generated

DOI: 10.1016/j.crfs.2026.101606

Keywords: Mechanochemical, unfolding, facilitates, protein-glutaminase, deamidation, charge, remodeling, myofibrillar, protein, reduce, low-salt-induced, aggregation