Tyrosinase-aided protein cross-linking: effects on gel formation of chicken breast myofibrils and texture and water-holding of chicken breast meat homogenate gels

The effects of Trichoderma reesei tyrosinase-catalyzed cross-linking of isolated chicken breast myofibril proteins as a simplified model system were studied with special emphasis on the thermal stability and gel formation of myofibrillar proteins. In addition, tyrosinase-catalyzed cross-linking was utilized to modify the firmness, water-holding capacity (WHC), and microstructure of cooked chicken breast meat homogenate gels. According to SDS-PAGE, the myosin heavy chain (MHC) and troponin T were the most sensitive proteins to the action of tyrosinase, whereas actin was not affected to the same extent. Calorimetric enthalpy (DeltaH) of the major thermal transition associated with myosin denaturation was reduced and with actin denaturation increased in the presence of tyrosinase. Low-amplitude viscoelastic measurements at constant temperatures of 25 degrees C and 40 degrees C showed that tyrosinase substantially increased the storage modulus (G') of the 4% myofibrillar protein suspension in the 0.35 M NaCl concentration. The effect was the most pronounced with high-enzyme dosages and at 40 degrees C. Without tyrosinase, the G' increase was low. Tyrosinase increased the firmness of the cooked phosphate-free and low-meat chicken breast meat homogenate gels compared to the corresponding controls. Tyrosinase maintained gel firmness at the control level of the low-salt homogenate gel and weakened it when both salt and phosphate levels were low. Tyrosinase improved the WHC of the low-meat and low-salt homogenate gels and maintained it at the level of the corresponding controls of phosphate-free and low-salt/low-phosphate homogenate gels. Microstructural characterization showed that a collagen network was formed in the presence of tyrosinase. Keywords: Chicken myofibrillar proteins; protein modification; cross-linking; tyrosinase; gelation; thermal stability; texture; water-holding capacity; microstructure.     

Gelation of chicken pectoralis major myosin and heat-denatured beta-lactoglobulin

Thermal, rheological, and microstructural properties of myosin (1 and 2% protein) were compared to mixtures of 1% myosin and 1% heat-denatured beta-lactoglobulin aggregates (myosin/HDLG) and 1% myosin and 1% native beta-lactoglobulin (myosin/beta-LG) in 0.6 M NaCl and 0.05 M sodium phosphate buffer, pH 6.0, 6.5, and 7.0 during heating to 71 degrees C. Thermal denaturation patterns of myosin and myosin/HDLG were similar except for the appearance of an endothermic peak at 54-56 degrees C in the mixed system. At pH 7.0, 2% myosin began to gel at 48 degrees C and had a storage modulus (G') of 500 Pa upon cooling. Myosin/HDLG (2% total protein) had a gel point of 48 degrees C and a G' of 650 Pa, whereas myosin/beta-LG had a gel point of 49 degrees C but the G' was lower (180 Pa). As the pH was decreased, the gel points of myosin and myosin/HDLG decreased and the G' after cooling increased. The HDLG was incorporated within the myosin gel network, whereas beta-LG remained soluble.     

Heat-induced gelation of chicken Pectoralis major myosin and beta-lactoglobulin

The denaturation, aggregation, and rheological properties of chicken breast muscle myosin, beta-lactoglobulin (beta-LG), and mixed myosin/beta-LG solutions were studied in 0.6 M NaCl, 0.05 mM sodium phosphate buffer, pH 7.0, during heating. The endotherm of a mixture of myosin and beta-LG was identical to that expected if the endotherm of each protein was overlaid on the same axis. The maximum aggregation rate (AR(max)) increased, and the temperature at the AR(max) (T(max)) and initial aggregation temperature (T(o)) decreased as the concentration of both proteins was increased. The aggregation profile of <0.5% myosin was altered by the presence of 0.25% beta-LG. Addition of 0.5-3.0% beta-LG decreased storage moduli of 1% myosin between 55 and 75 degrees C, but increased storage moduli (G') when heated to 90 degrees C and after cooling. beta-LG had no effect on the gel point of > or =1.0% myosin, but enhanced gel strength when heated to 90 degrees C and after cooling. After cooling, the G' of 1% myosin/2%beta-LG gels was about 1.7 times greater than that of gels prepared from 2% myosin/1% beta-LG.     

高密度CO2处理虾肌球蛋白形成凝胶的临界浓度与凝胶强度

为了探讨高密度CO_2(dense phase carbon dioxide,DPCD)诱导蛋白质形成凝胶的机制,以凡纳滨对虾肌球蛋白为研究对象,研究了DPCD处理压强、温度和时间对虾肌球蛋白形成凝胶的临界浓度和对虾肉糜凝胶强度的影响。研究结果表明:DPCD处理压强和温度对虾肌球蛋白溶液形成凝胶的临界浓度有显著影响,处理时间对肌球蛋白溶液形成凝胶的临界浓度无显著影响,但增加处理时间,可以形成更加紧实的凝胶。在40℃和5~30 MPa时虾肌球蛋白溶液形成凝胶的临界质量浓度为14 mg/mL,在50℃和5、10 MPa时虾肌球蛋白溶液形成凝胶的临界质量浓度为12 mg/mL,在50℃和15~30 MPa时虾肌球蛋白溶液形成凝胶的临界质量浓度为11 mg/mL,在60℃和5~30 MPa时虾肌球蛋白溶液形成凝胶的临界质量浓度为10 mg/mL。DPCD处理压强和温度对虾肉糜的凝胶强度也具有显著影响(P0.05),且随着压强增加和温度升高,虾肉糜凝胶强度呈增加趋势(P0.05);在50℃和25 MPa下处理虾肉糜20 min,形成的凝胶强度较好,达到了(14.28±0.57)N·mm。DPCD处理温度越高,虾肌球蛋白形成凝胶的临界浓度就越低,而虾肉糜形成凝胶的强度越高;DPCD处理压强越高,虽然对虾肌球蛋白形成凝胶的临界浓度影响较小,但能使虾肌球蛋白和虾肉糜形成凝胶的强度增加。从分析中还可以推断,DPCD低压(5~10 MPa)诱导虾肉糜形成凝胶主要是热效应的作用,DPCD较高压强(10 MPa)诱导虾肉糜形成凝胶是热和CO_2分子效应的共同作用。研究结果为进一步阐明DPCD诱导蛋白质形成凝胶的机制提供了基础数据。     

Characteristics of the salt-soluble fraction of hake (Merluccius merluccius) fillets stored at -20 and -30 degrees C

Natural actomyosin (NAM) extracted in 0.6 M NaCl from hake fillets stored at -20 and -30 degrees C for up to 49 weeks was studied. The extracted protein decreased as storage progressed and became poorer in myosin while the proportion of actin remained constant. Two major peaks composed of myosin plus actin and actin plus tropomyosin plus troponins were obtained by size exclusion chromatography. SDS-PAGE analysis of the protein retained in the precolumn filter showed that there was protein aggregated by covalent bonding. Surface hydrophobicity increased while Ca(2+)-ATPase activity, apparent viscosity, and SH groups decreased as storage progressed. The loss of Ca(2+)-ATPase activity was due mainly to denaturation of the extracted myosin, whereas the minimum viscosity values occurred earlier and were not directly due to the lower proportion of myosin in the extracts. Thus, the extracted NAM exhibited changes during frozen storage. The temperature-dependent difference was mainly quantitative due to a smaller amount of protein extracted at -20 degrees C.     

Conformational and rheological changes in catfish myosin as affected by different acids during acid-induced unfolding and refolding

Changes in the conformation of catfish (Ictalurus punctatus) myosin due to (i) anions, (ii) acid pH, and (iii) salt addition were determined using tryptophan fluorescence, hydrophobicity measurements, differential scanning calorimetry, and circular dichroism. The relationship between conformation and storage modulus (G') of acid-treated myosin was studied. Three acids, HCl, H2SO4, and H3PO4, were used for unfolding myosin at three acidic pH conditions, 1.5, 2.0, and 2.5. Unfolded myosin was refolded to pH 7.3. Denaturation and unfolding of myosin was significantly (p < 0.05) lower when salt (0.6 M NaCl) was present during acid unfolding than in the absence of salt. When salt was added before unfolding, the alpha-helix content of myosin treated at pH 1.5 was significantly lower than that treated at pH 2.5. When salt was added after refolding, the alpha-helix content of myosin was unaffected by different pH treatments. The G' of myosin increased with an increase in myosin denaturation. The G' of myosin was significantly (p < 0.05) higher when salt was added to myosin after refolding than before acid unfolding. Among the different anion treatments, the G' of acid-treated myosin decreased in the order Cl- approximately SO42- > PO43-. Among the different pH treatments, the G' of myosin treated at pH 1.5 was significantly (p < 0.05) higher than myosin treated at pH 2.5. The conditions that would result in maximum myosin denaturation and maximum G' were unfolding of myosin at pH 1.5 using Cl- (from HCl) followed by refolding at pH 7.3 and subsequent addition of 0.6 M NaCl.     

Physicochemical changes and mechanism of heat-induced gelation of arrowtooth flounder myosin

Physicochemical changes of myosin during heating were investigated to elucidate the mechanism of heat-induced gelation of arrowtooth flounder (ATF) myosin at high ionic strength. Changes in dynamic properties indicated ATF myosin formed a gel in three different stages as shown by the first increase in G' (storage modulus) at 28 degrees C, followed by the decrease at 35 degrees C and the second increase at 42 degrees C. DSC thermogram showed the onset of myosin denaturation at 25 degrees C with two maximum transition temperatures at 30 and 36 degrees C. The decrease in alpha-helical content indicated ATF myosin began to unfold at 15 degrees C and the unfolding continued until it reached 65 degrees C. Turbidity measurement showed myosin began to aggregate at 23 degrees C and the aggregation was complete at 40 degrees C. Surface hydrophobicity increased consistently in the temperature range studied, 20-65 degrees C. Sulfhydryl contents decreased significantly at 20-30 degrees C due to the formation of disulfide linkages but remained constant at temperatures >30 degrees C. ATF myosin was shown to be extremely sensitive to heat, resulting in denaturation at lower temperature than other fish myosin. Denaturation was initiated by unfolding of the alpha-helical region in myosin followed by exposure of hydrophobic and sulfhydryl residues, which are subsequently involved in aggregation and gelation processes.     

Effects of proteolysis and mechanism of gel weakening in heat-induced gelation of fish myosin

Addition of papain decreased the onset temperature and the rate at which G' developed during heat-induced gelation of arrowtooth flounder myosin. Frequency sweep results revealed that G' markedly decreased in proportion to the amount of papain added. However, use of E-64, a cysteine proteinase inhibitor, reversed the effects of papain and protected myosin heavy chain from degradation. DSC thermograms indicated papain significantly decreased the enthalpy required to induce myosin denaturation without significant changes in onset and maximum transition temperatures. Thermal denaturation kinetics indicated decreases in both the activation energy and the rate of myosin denaturation. CD studies revealed a rapid decrease in alpha-helical content, indicating the initial degradation of myosin molecules mostly occurred in the tail region. These results suggested that proteolysis affected thermal properties and reactivity of myosin during heating. Although myosin gel could be formed, structural disruption resulted in lower gelling ability and rigidity of the formed gel.     

Effect of pentosanase and oxidases on the characteristics of doughs and the glutenin macropolymer (GMP)

Rheological characteristics of dough and glutenin macropolymer (GMP) extracted thereof were investigated. Three single enzymes, pentosanase (PP), glucoseoxidase (GLZ), and laccase (LAC), and their combinations were used. GLZ gave the least extensible and most resistant dough, and pentosanase/glucoseoxidase (PPGLZ) resulted in dough with improved extensibility. The enzymes improved gluten quality. The glutenin macropolymer (GMP) was characterized in terms of wet weight, protein content, pentosan association, and dynamic rheological properties. Enzymatic addition decreased the wet weight of GMP but increased the protein content. PP decreased the content of pentosans on the GMP, but single oxidases increased the content of pentosans associated with GMP. PP did not modify the elastic modulus (G') of the GMP, whereas GLZ increased G' by increasing the polymerization of proteins and LAC diminished G'. The combination PPGLZ produced a synergic increase of G'.     

肉蛋白-畜产源非肉蛋白互作的物理化学研究

为了研究典型畜产源非肉蛋白与肌原纤维蛋白(MP)的相互作用,建立了模拟肉制品加工条件下二者等比例用量的溶液及热致凝胶模型,将血浆蛋白(PPP)、鸡蛋白分离蛋白(EPI)和酪蛋白酸钠 (SC)分别与MP 按照1∶1比例混合,以各单一蛋白为对照,利用流变仪、质构仪和低场核磁等仪器测定各蛋白粘度、加热过程的动态粘弹性、凝胶强度和水分子状态等指标。结果表明,PPP和EPI在加热过程中自身可形成凝胶,但与MP相比,储能模量(G')较弱,SC在加热过程中未能形成凝胶。将PPP和EPI分别与MP混合时,流变结果显示,PPP+MP、EPI+MP相互作用指数均大于零,与单独的MP相比,其G'无显著差异;加入PPP未能显著改变MP的凝胶强度,但加入EPI显著提高了MP的凝胶强度(P<0.05);PPP、EPI的加入均能使凝胶保水性显著提高,不易流动水比例增大(P<0.05)。SC会对MP产生一定不利影响,二者相互作用指数小于零,其G'、凝胶强度及凝胶保水性显著降低(P<0.05)。总体而言,PPP、EPI与MP之间在加热后均产生正向相互作用,而SC对MP产生不利影响。本研究结果为凝胶乳化类肉制品中非肉蛋白的应用提供了一定的理论借鉴。     

Phospholipid/fatty acid-induced secondary structural change in beta-lactoglobulin during heat-induced gelation

Effects of phosphatidylcholine (PC) and the predominant fatty acids (FAs) in milk, butyrate, oleate, and palmitate, on secondary structural changes in beta-lactoglobulin (beta-LG) during heat-induced gelation were analyzed on the basis of circular dichroism (CD) spectra. Small-strain oscillatory measurements were carried out to characterize viscoelastic properties of the heat-induced gels. In the absence of added salt, PC and FAs induced helix formation of beta-LG on heating to 80 degrees C and increased the storage moduli (G') of heat-induced gels. In the presence of 500 mM NaCl, PC did not change the CD spectrum of beta-LG but decreased G'. In contrast, butyrate substantially unfolded beta-LG in 500 mM NaCl on heating, forming very elastic gels with increased G' values. Palmitate and oleate induced beta-LG gel formation at 25 degrees C without heating; heating to 80 degrees C almost completely unfolded beta-LG in 500 mM NaCl.     

Combined influence of NaCl and sucrose on heat-induced gelation of bovine serum albumin

The combined influence of a strongly interacting cosolvent (NaCl) and a weakly interacting cosolvent (sucrose) on the heat-induced gelation of bovine serum albumin (BSA) was studied. The dynamic shear rheology of 4 wt % BSA solutions containing 0 or 20 wt % sucrose and 0-200 mM NaCl was monitored as they were heated from 30 to 90 degrees C at 1.5 degrees C min(-)(1), held at 90 degrees C for 120 min, and then cooled back to 30 degrees C at -1.5 degrees C min(-)(1). The turbidity of the same solutions was monitored as they were heated from 30 to 95 degrees C at 1.5 degrees C min(-)(1) or held isothermally at 90 degrees C for 10 min. NaCl had a similar effect on BSA solutions that contained 0 or 20 wt % sucrose, with the gelation temperature decreasing and the final gel strength increasing with increasing salt concentration and the greatest changes occurring between 25 and 100 mM NaCl. Nevertheless, the presence of sucrose did lead to an increase in the gelation temperature and final gel strength and a decrease in the final gel turbidity. The impact of NaCl on gel characteristics was attributed primarily to its ability to screen electrostatic interactions between charged protein surfaces, whereas the impact of sucrose was attributed mainly to its ability to increase protein thermal stability and strengthen the attractive forces between proteins through a preferential interaction mechanism.     

Solubility improvement of shellfish muscle proteins by reaction with glucose and its soluble state in low-ionic-strength medium

When myofibrillar proteins of scallop striated adductor muscle were reacted with glucose through the Maillard reaction, the change in the solubility of myofibrillar proteins in 0.05-0.5 M NaCl solutions during glycosylation and their soluble states were investigated. The solubility in low-ionic-strength media increased greatly with the progress of the Maillard reaction. The solubility in 0.1 M NaCl reached 83% when more than 60% of lysine residues in myofibrillar proteins were modified by glucose. However, the excess progress of the Maillard reaction impaired the improved solubility of myofibrillar proteins in a low-ionic-strength medium. Myosin, actin, and paramyosin in glycosylated myofibrillar proteins were solubilized independently regardless of NaCl concentration. In addition, the glycosylated myosin lost its filament-forming ability and existed as a monomer in 0.1 M NaCl.     

Acid-induced gelation of enzymatically modified, preheated whey proteins

Low-pH whey protein gels are formulated using a sequential protocol of heat treatment, enzyme incubation, and cold-set acidification. The heat-induced disulfide and enzyme-catalyzed epsilon-(gamma-glutamyl)lysine linkages, both at neutral pH, produce a polymerized protein solution. The molecular weights of these samples show an exponential increase with protein concentration. The additional enzyme-catalyzed cross-links cause little change in molecular weight from that of heat-treated samples at low protein concentrations, indicating predominant intramolecular cross-linking. Enzyme treatment at higher protein concentration however causes increase in molecular weight, possibly due to formation of intermolecular cross-links. Acidification of the polymerized protein solutions through glucono-delta-lactone acid leads to gel formation at pH 4. The elastic (G') and viscous (G' ') moduli of gels with and without enzyme treatment show similar frequency dependence, indicating comparable microstructures, consistent with all samples exhibiting similar fractal dimensions of approximately 2 obtained independently using rheology and confocal microscopy. A substantial increase in fracture strain and stress of the gel is achieved by enzyme treatment. However, the elastic modulus (G') is only slightly larger after enzyme treatment compared with heat-treated samples. These results indicate that factors responsible for fracture properties may not be apparent in the gel microstructure and linear viscoelastic properties.     

Capillary electrophoresis analysis of orange juice pectinesterases

Pectinesterase (PE) was extracted from orange juice and pulp with 1 M NaCl, desalted, and separated using capillary electrophoresis (CE) gel procedures (CE-SDS-CGE) and isoelectric focusing (CE-IEF). PE resolved as a single peak using noncoated fused silica columns with CE-SDS-CGE. CE-IEF separation of PE required acryloylaminoethoxyethanol-coated columns, which had limited stability. Thermal stability of PE extracts before and after heating at 75 degrees C for 30 min and at 95 degrees C for 5 min established heat labile and heat stabile fractions with identical PE migration times by CE-SDS-CGE or CE-IEF. Peak magnitude decreased to a constant value as heating time increased at 75 degrees C. Regression analysis of CE-SDS-CGE peak migration times of molecular weight (MW) standards estimated both heat labile and heat stable PE at MW approximately 36 900. Traditional SDS-PAGE gel separation of MW standards and active PE isolated by IEF allowed estimation of MW approximately 36 000. CE-SDS-CGE allowed presumptive, but not quantitative, detection of active PE in fresh juice.     

Heat-induced gel formation by soy proteins at neutral pH

Heat-induced gel formation by soy protein isolate at pH 7 is discussed. Different heating and cooling rates, heating times, and heating temperatures were used to elucidate the various processes that occur and to study the relative role of covalent and noncovalent protein interactions therein. Gel formation was followed by dynamic rheological measurements. Heat denaturation was a prerequisite for gel formation. The gelation temperature (84 degrees C) was just above the onset denaturation temperature of glycinin. The stiffness of the gels, measured as the elastic modulus, G', increased with the proportion of denatured protein. An increase in G' was also observed during prolonged heating at 90 degrees C. This increase is explained by the occurrence of rearrangements in the network structure and probably also by further incorporation of protein in the network. The increase in G' upon cooling was thermoreversible indicating that disulfide bond formation and rearrangements do not occur upon cooling.     

Interactions of whey proteins during heat treatment of oil-in-water emulsions formed with whey protein isolate and hydroxylated lecithin

The interactions of proteins during the heat treatment of whey-protein-isolate (WPI)-based oil-in-water emulsions with and without added hydroxylated lecithin were studied by examining the changes in droplet size distribution and the quantity and type of adsorbed and unadsorbed proteins. Heat treatment at 90 degrees C of WPI emulsions resulted in an increase in total adsorbed protein; unadsorbed beta-lactoglobulin (beta-lg) was the main protein interacting with the adsorbed proteins during the first 10 min of heating, but after this time, unadsorbed alpha-lactalbumin (alpha-la) also associated with the adsorbed protein. In emulsions containing hydroxylated lecithin, the increase in total adsorbed protein during heat treatment was much lower and the unadsorbed beta-lg did not appear to interact with the adsorbed proteins during heating. However, the behavior of alpha-la during heat treatment of these emulsions was similar to that observed in the emulsions containing no hydroxylated lecithin. In the presence of NaCl, the particle size of the emulsion droplets and the quantities of adsorbed protein increased markedly during heating. Emulsions containing hydroxylated lecithin were less sensitive to the addition of NaCl. These results suggest that the binding of hydroxylated lecithin to unfolded monomers or intermediate products of beta-lg reduces the extent of heat-induced aggregation of beta-lg and consequently decreases the interactions between unadsorbed beta-lg and adsorbed protein. This was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of heated whey protein and hydroxylated lecithin solutions.     

Gelling properties of heat-denatured beta-lactoglobulin aggregates in a high-salt buffer

Thermal denaturation, rheological, and microstructural properties of gels prepared from native beta-lactoglobulin (beta-LG) and preheated or heat-denatured beta-LG (HDLG) aggregates were compared. The HDLG was prepared by heating solutions of 4% beta-LG in deionized water, pH 7.0, at 80 degrees C for 30 min and then diluted to the desired concentration in 0.6 M NaCl and 0.05 M phosphate buffer at pH 6.0, 6.5, and 7.0. When reheated to 71 degrees C, HDLG formed a gel at a concentration of 2% protein. At pH 7.0, 3% HDLG gelled at 52.5 degrees C and had a storage modulus (G') of 2200 Pa after cooling. beta-LG (3%) in 0.6 M NaCl and 0.05 M phosphate buffer, pH 7.0, did not gel when heated to 71 degrees C. The gel point of 3% HDLG decreased by 10.5 degrees C and the G' did not change when the pH was decreased to 6.0. The HDLG gel microstructure was composed of strands and clumps of small globular aggregates in contrast to beta-LG gels, which contained a particulate network of compacted globules. The HDLG formed a gel at a lower concentration and lower temperature than beta-LG in the high-salt buffer, suggesting an application in meat systems or other food products prepared with salt and processed at temperatures of < or =71 degrees C.     

Effect of salts on the gelatinization and rheological properties of sago starch.

The effects of various salts on the gelatinization and rheological properties of sago starch have been studied using differential scanning calorimetry, small deformation oscillation, and large deformation techniques. The presence of salts affected the gelatinization peak temperature, T(p), gelatinization enthalpy, DeltaH, swelling properties, storage modulus, G', gel strength, GS, and gelation rate constants, k, depending on the type of salt and the concentration. Their influence followed the Hofmeister series, and the effect of anions was more pronounced than that of cations. Sulfate ions increased T(p), G', GS, and k and reduced the swelling properties, whereas iodide and thiocyanate ions reduced T(p), G', GS, and k but increased the swelling properties. For all of the salts studied except for Na(2)SO(4), T(p) increased to a maximum and then decreased again at higher salt concentrations while DeltaH reduced with concentration. In the presence of MgCl(2), CaCl(2), and LiCl complex behavior was observed such that at approximately 3.5 M MgCl(2) and CaCl(2) and 8 M LiCl the starch samples were gelatinized at room temperature, whereas at much higher concentration T(p) increased again and the transition became exothermic.     

Effect of pH on the rheological and structural properties of gels of water-washed chicken-breast muscle at physiological ionic strength

Adjustment of pH from 6.4 to neutrality improved gelling ability and water-holding capacity of twice water-washed, minced chicken-breast muscle significantly at physiological ionic strength, at which the majority of the myofibrillar proteins, including myosin, are not soluble. A strain value of 2.2 was obtained at neutral pH. Myofibrils were the main components of the gel network at both pH 6.4 and 7.0; however, the myofibrillar distribution varied with the pH value. At pH 6.4, myofibrils formed a network of localized aggregates leaving large voids between, whereas at neutral pH, an evenly distributed network of myofibrils was formed. In addition, at neutral pH, a network of fine strands was found within the network of myofibrils. The network was much less developed at pH 6.4. The thin and thick filaments within each myofibrillar structure were disorganized at both pH values. The intramyofibrillar spaces were larger at neutral pH than at pH 6.4. It was proposed that adjustment of pH to neutrality increased electrostatic repulsion leading to a more even distribution of the myofibrillar proteins, a key factor responsible for the improved gel strength and water-holding capacity.