Emulsifying and foaming properties of Phaseolus vulgaris and coccineus proteins

Protein isolates from two Phaseolus cultivars, common bean (Phaseolus vulgaris L.) and scarlet runner bean (Phaseolus coccineus L.), were prepared by wet extraction methods (isoelectric precipitation – 4000 rpm, ultrafiltration, extraction with NaCl 2%, and isoelectric precipitation – 9900 rpm). The protein isolates were characterized by sodium dodecyl sulfate–polyacrylamide gel electrophoresis and then evaluated for their solubility. The emulsion stability of emulsions produced at pH 7.0 and 5.5 with 1% or 2% or 3% w/v protein isolate was evaluated by average droplet size diameter, viscosity and creaming measurements. Emulsions with 1% protein content were unstable through storage. Emulsions with 3% w/v protein isolate concentration, extracted by ultrafiltration at pH 5.5 from both cultivars, were flocculated; this was more pronounced for coccineus isolates. The foaming properties, for the respective foams, were investigated. Foams with 1% w/v protein showed little foaming ability Ultrafiltration isolates produced more foam, which was especially stable at pH 5.5.     

The effect of pH on gel structures produced using protein–polysaccharide phase separation and network inversion

Forming heat-induced gels through combined effects of micro-phase separation of whey protein isolate (WPI; 5%, w/v, 100 mm NaCl) by pH change (5.5, 6.0, and 6.5), and addition of κ-carrageenan (0–0.3%, w/w), were evaluated. The microstructure of WPI gels was homogeneous at pH 6.0 and 6.5 and micro-phase separated at pH 5.5. Addition of 0.075% κ-carrageenan to WPI solutions caused the microstructure of the gel to switch from homogeneous (pH 6.0 and 6.5) to micro-phase separated; and higher concentrations led to inversion of the continuous network from protein to κ-carrageenan. Protein solutions containing 0.075% (w/w) κ-carrageenan produced gels with increased storage modulus (G′) at pH 6.5 and decreased G′ at pH 5.5. All gels containing 0.3% (w/w) κ-carrageenan had κ-carrageenan-continuous networks. It was shown that microstructural and rheological changes were different in WPI and κ-carrageenan mixed gels when micro-phase separation was caused by pH rather than ionic strength.     

Stabilization of multilayered emulsions by sodium caseinate and κ-carrageenan

The influence of the κ-carrageenan concentration and pH on the properties of oil-in-water multilayered emulsions was studied. Multilayered emulsions were prepared by the mixture of a primary emulsion stabilized by 0.5% (w/v) sodium caseinate (Na-CN) with κ-carrageenan solutions with different concentrations (0.05–1% w/v). The emulsions were evaluated at pH 7 and 3.5. At pH 7, there was little adsorption of κ-carrageenan onto the droplet surface and a depletion flocculation was observed when the polysaccharide concentration exceeded 0.5% (w/v). At pH 3.5, a mixed κ-carrageenan–Na-CN second layer was formed around the protein-covered droplets and the emulsions showed bridging flocculation at lower polysaccharide concentrations (0.05–0.25% w/v). Stable emulsions could be formed with the highest κ-carrageenan concentration (1% w/v) at both pH values (7.0 and 3.5). Thus, stable emulsions were successfully produced using protein–polysaccharide interfacial complexes, and the oil droplet diameter, zeta potential and rheological properties of these emulsions were not affected by changes in the pH.     

Optimization of extraction and isolation for 11S and 7S globulins of soybean seed storage protein

A new method was developed for extraction and isolation of 7S and 11S fractions from soybean seed, based on methods of Nagano et al., Thanh and Shibasaki [Nagano, T., Hirotsuka, M., & Mori, H. (1992). Dynamic viscoelastic study on the gelation of 7S globulin from soybeans. Journal of Agricultural and food chemistry 40, 941–944 and Thanh, V. H., & Shibasaki, K. (1976). Major proteins of soybean seeds. A straightforward fraction and their characterization. Journal of Agricultural and Food Chemistry 24, 1117–1121]. Optimization of the extraction and isolation of 11S and 7S globulins from soybean seed was investigated under various conditions by the Kjeldahl method and SDS-PAGE. The optimal conditions were as follows: 0.03–0.06 M Tris–HCl buffer (pH 8.5) containing 0.01 M sodium bisulfite as extract solution, extraction twice at 45 °C for 1 h, and with a 1:15 ratio (w/v) of flour:Tris–HCl. The 11S fraction was precipitated at pH 6.4, and the supernatant, after centrifugation, was adjusted to pH 5.5 to remove the insoluble intermediate fraction by further centrifugation. The supernatant obtained was then adjusted to pH 4.8 to afford the 7S fraction as a precipitate by centrifugation. With the improvements, the protein contents and purities of the isolated 11S and 7S fractions were significantly increased. The contents of all subunits of the isolated 11S and 7S fraction were markedly higher than those by Thanh and Shibasaki method, while the contents of α, β and B₃ were also significantly higher than those by Nagano et al. method.     

Thermal stability of soy protein isolate and hydrolysate ingredients

The objective of this study was to characterize the effects of pH, protein concentration and calcium supplementation on thermal stability, at 140 °C, of soy protein isolate (SPI) and soy protein hydrolysate (SPH) ingredients. Increasing pH between 6.4 and 7.5 led to significantly (p < 0.05) higher mean heat coagulation times (HCTs) at 140 °C, for all soy protein ingredients at 1.8, and 3.6% (w/v) protein. Increasing protein concentration from 1.8 to 7.2% (w/v) led to shorter HCTs for protein dispersions. Calcium supplementation up to 850 mg/L, except in the case of supplementation of SPI 1 with calcium citrate (CaCit), decreased HCT for soy protein ingredient dispersions, at pH 6.4 – 7.5. No significant differences (p < 0.05) were found in mean HCT for dispersions supplemented with calcium chloride (CaCl₂) and those supplemented with CaCit at 450, 650 and 850 mg/L Ca²⁺, in the pH range 6.4–7.5.     

The impact of concentration,temperature and pH on dynamic rheology of psyllium gels

Structural aspects of the psyllium gum prepared from the seed husk of the plant of Plantago ovata Forsk was characterized by dynamic rheology and microscopy. Dynamic rheological properties of psyllium gel in the linear viscoelastic region, as a function of concentration (2, 2.5 and 3% w/w), temperature (5–95 °C) and pH (2.5–10) were investigated. Mechanical spectra of the psyllium gels were obtained by frequency sweep measurement classified into that of weak gels because G′ was larger than G″ throughout the tested frequency range and the separation of the two moduli (tan δ) was greater than 0.1. The phase angle increased with temperature and a peak associated with gel melting appeared at about 40 °C. All gels at different pH presented a typical weak gel spectrum. Scanning electron microscopy showed porous structures with different pore-size distribution for psyllium gels under different conditions in terms of concentration, pH and temperature.     

Influence of oxidative browning inhibitors and isolation techniques on sweet potato protein recovery and composition

Effects of oxidative browning inhibitors on sweet potato protein (SPP) recovery and quality were studied. Oxidative browning inhibitors successfully decreased sweet potato oxidative browning, but reduced both SPP extractability and recovery. Ultrafiltration/diafiltration processed sweet potato (UDSP) protein (at pH 4, 6 and 7) showed significantly (p < 0.05) higher yield, purity, solubility, thermal stability and amino acid constituents than that of isoelectrically precipitated sweet potato (IPSP) protein (at pH 4). The yield of UDSP proteins was more than twice that of IPSP protein. Denaturation temperature (T_d), enthalpy change (ΔH) and solubility (at pH 3 and 8) of UDSP proteins were in the ranges 82.89–90.29 °C, 6.34–11.35 (J/g) and 71.4–94.2%, respectively, while that of IPSP protein were 85.27 °C, 2.35 (J/g) 31.2% and 55.5%, respectively. Ratio of SPP essential amino acid to the total amino acid ratio ranged from 0.49 to 0.51. SPP in vitro digestibility and digestibility-corrected amino acid score (PDCAAS) ranged 70–80.7% and 44.79–51.08%, respectively.     

Emulsifying properties of sweet potato protein: Effect of protein concentration and oil volume fraction

The effect of protein concentrations (0.1, 0.25, 0.5, 1.0, 1.5 and 2.0% w/v) and oil volume fractions (5, 15, 25, 35 and 45% v/v) on properties of stabilized emulsions of sweet potato proteins (SPPs) were investigated by use of the emulsifying activity index (EAI), emulsifying stability index (ESI), droplet size, rheological properties, interfacial properties and optical microscopy measurements at neutral pH. The protein concentration or oil volume fraction significantly affected droplet size, interfacial protein concentration, emulsion apparent viscosity, EAI and ESI. Increasing of protein concentration greatly decreased droplet size, EAI and apparent viscosity of SPP emulsions; however, there was a pronounced increase in ESI and interfacial protein concentration (P < 0.05). In contrast, increasing of oil volume fraction greatly increased droplet size, EAI and emulsion apparent viscosity of SPP emulsions, but decreased ESI and interfacial protein concentration significantly (P < 0.05). The rheological curve suggested that SPP emulsions were shear-thinning non-Newtonian fluids. Optical microscopy clearly demonstrated that droplet aggregates were formed at a lower protein concentration of <0.5% (w/v) due to low interfacial protein concentration, while at higher oil volume fractions of >25% (v/v) there was obvious coalescence. In addition, the main components of adsorbed SPP at the oil–water interface were Sporamin A, Sporamin B and some high-molecular-weight aggregates formed by disulfide linkage.     

Surface tension of Phaseolus vulgaris and coccineus proteins and effect of polysaccharides on their foaming properties

The surface tension of protein isolates from common bean (Phaseolus vulgaris L.) and scarlet runner bean (Phaseolus coccineus L.), prepared by isoelectric precipitation and ultrafiltration was evaluated, with respect to protein concentration (0.001–0.1% w/v) and pH (pH 4.5, 5.5, 7.0 and 8.0). Surface tension was most reduced, and with a higher rate of reduction at higher protein concentration and at pH 8.0. Foams (1, 2% w/v protein), at the same pH values, with and without the addition of polysaccharides, were studied. The proteins’ foaming behaviour was related to their adsorption behaviour. Arabic gum, locust bean gum (0.1% and 0.25% w/v), xanthan gum and a xanthan/locust bean gum mixture (0.1% w/v) had a positive effect on foam creation. All polysaccharides increased foam stability, probably due to the viscosity increase and to the creation of a network, which prevents the air droplets from coalescence. Isolates from P. coccineus and isolates obtained by ultrafiltration seemed to exhibit better foaming properties.     

Highly acetylated pectin from cacao pod husks (Theobroma cacao L.) forms gel

A pectin (OP) obtained from cacao pod husk with a high acetyl content, which is a structural feature that could disturb the pectins' gel formation, was able to form gels at low pH and a high sucrose content. Pectin gels (1.32% GalA equivalent, w/w) were prepared at pH 2.5–3.3 in the presence of 60% sucrose (w/w). Rheological analyses were performed to determine the optimal pH for further studies. Next, the OP samples were prepared at pH 2.7 in concentrations ranging from 0.33 to 1.98% GalA (w/w) with 60% sucrose (w/w) and subjected to rheological analysis. Dynamic oscillatory experiments at 25 °C indicated the presence of gels for all of the analysed concentrations. Measurements of the elastic (G′) and viscous (G″) moduli at 25 °C also indicated that increasing the pectin concentration resulted in stronger gels. Rotational experiments revealed a shear-thinning behaviour in which the apparent viscosities of the samples increased as the concentration increased. Although the OP had a high degree of acetylation, this pectin was able to form gels, which suggests its potential for use as a gelling and thickening additive.     

Effects of konjac glucomannan on physicochemical properties of myofibrillar protein and surimi gels from grass carp (Ctenopharyngodon idella)

The cryoprotective effect of konjac glucomannan (KGM) on myofibrillar protein from grass carp (Ctenopharyngodon idella) during frozen storage at −18 °C and the influence of five levels of KGM (0%, 0.5%, 1%, 1.5%, and 2%) on texture properties, water-holding capacity, and whiteness of grass carp surimi gels were investigated. KGM as a novel cryoprotectant could significantly mitigate the decrease in salt extractable protein (SEP), Ca²⁺-ATPase activity, and total sulphydryl and active sulphydryl contents of myofibrillar protein during frozen storage. KGM at the level of 1% showed the same good cryoprotective effect as a conventional cryoprotectant (10% sucrose–sorbitol, 1:1, w/w). As the levels of KGM increased, breaking force and deformation of grass carp surimi gels increased significantly. Water-holding properties of the surimi gels are improved with the increasing addition of KGM, but the whiteness decreased and the colour became darker. The optimum addition level of KGM was suggested to be 1%.     

Brewster angle microscopy of adsorbed protein films at air–water and oil–water interfaces after compression,expansion and heat processing

Recent Brewster angle microscopy (BAM) observations of adsorbed films of proteins at the air-water (A–W) and oil–water (O–W) interfaces are reviewed and compared. At the A–W interface β-lactoglobulin (β-L) and ovalbumin (OA) were studied at pH 7 and 5. At the O–W interface β-L, α_s1-, β- and κ-caseins were studied at pH 7. The adsorbed films were periodically subjected to compression and expansion cycles such that the film area was typically varied between 125% and 50% of the original film area. At the A–W interface, little structure was observable on compression or expansion or aging, especially at pH 7. For ovalbumin at pH 5, some cracks and ridges in the films appeared. But, for both β-L and OA, such features became much more obvious on addition to the interface of a low area fraction (<0.01%) of 20 μm polystyrene latex (PS) particles. With particles present the structuring was also more obvious at pH 5 (closer to the protein isoelectric point) than at pH 7, and for greater adsorption times and/or higher bulk protein concentration (C_b). Particle addition was not necessary to highlight folding and ridges that occurred at the O–W interface for β-L. After heating to 80 and 90 °C, β-L films adsorbed from low C_b (0.005 wt%) even greater film structuring was evident. However, β-L films adsorbed from higher C_b (≥0.05 wt%) showed fewer, but more pronounced ridges and cracks. The caseins at the O–W interface showed comparatively little evidence of structuring, either before or after heating. A measure of the dilatational elastic modulus of the films correlated with the observed variations in the structural integrity of the films. Clearly, protein films subjected to these types of thermal and mechanical perturbations can become highly inhomogeneous, depending on the type of protein and the bulk solution conditions, with implications for the stability of the corresponding foams and emulsions. This is in agreement with earlier computer simulations. Protein films at the O–W interface (particularly after heating) appear to be more resilient and less aggregated than films at the A–W interface.     

Ultrasonic generation of aerated gelatin gels stabilized by whey protein β-lactoglobulin

Dispersed air provides an additional phase within gel-type foods may accommodate new textural and functional demands. This paper addresses the effect of using whey protein β-lactoglobulin (β-lg), with different degrees of denaturation, as stabilizing agent in the formation of aerated gelatin gels using ultrasound as a novel method to incorporate bubbles in model foods. The heat denaturation, aggregate formation and surface properties of β-lg dispersions were studied at three pHs (6.0, 6.4 and 6.8) and at a heating temperature of 80 °C. β-Lg dispersions with four degrees of denaturation (0%, 20%, 40% and 60%) were used to stabilize bubbles generated by high intensity ultrasound in aerated gelatin gels. Experimental methods to determine gas hold-up, bubble size distributions and fracture properties of aerated gelatin gels stabilized by β-lg (AG), as well as control gels (CG), aerated gelatin gels without β-lg, are presented. Gas hold-up of AG peaked at a degree of denaturation of 40% when AG were fabricated using β-lg heated at pH 6.4 and 6.8, whereas using β-lg heated at pH 6.0 gas hold-up decreased constantly with increasing degree of denaturation. The use of β-lg as surfactant at pH 6.8 and 6.4 reduced the bubble sizes of AG compared with CG, but no effect was observed at pH 6.0. AG showed values of stress and strain at fracture lower than CG (5.86 kPa and 0.62), probably because of the lower gas hold-up of CG. However, both type of aerated gels were weaker and less ductile than non-aerated gels, with a decrease in stress and strain at fracture for AG between 56–71% and 33–43%, respectively. This study shows that the presence of bubbles in gel-based food products results in unique rheological properties conferred by the additional gaseous phase.     

Physico-mechanical properties of chitosan films with carvacrol and grape seed extract

The physico-mechanical properties of 3 films composed by carvacrol, grape seed extract (GSE) and chitosan in different proportions were studied. The films, prepared by solvent casting technique with the following compositions of the casting solutions in carvacrol, GSE and chitosan: film-1: 9.6 ppm–684 ppm–1.25% w/v, film-2: 60 ppm–400 ppm–1.2% w/v and film-3: 90 ppm–160 ppm–1.24% w/v and were compared to a control (1.25% w/v chitosan) film. Mechanical, structural, barrier and colour properties of the films were evaluated. Film-3 presented the lowest water vapour and carbon dioxide permeabilities (WVP and CO₂P) and tensile strength (TS) values and the highest oxygen permeability (O₂P), whereas film-1 presented the highest water content and the lowest crystallinity, CO₂P, TS and luminosity. These results suggest that in the range studied, carvacrol and GSE affect the film structure and its mechanical properties due to hydrophilic (GSE) and hydrophobic (carvacrol) compounds. This work will help the development of edible films, based on physico-mechanical properties, contributing to food preservation and shelf-life extension.     

Effect of Lepidium perfoliatum seed gum addition on whey protein concentrate stabilized emulsions stored at cold and ambient temperature

In this study the effect of Lepidium perfoliatum seed gum on the properties of whey protein concentrate (WPC) stabilized corn oil-in-water emulsions at pH 7 was investigated. Various concentrations (0–0.6% w/v) of L. perfoliatum seed gum were used together with 2% (w/v) WPC to emulsify corn oil in water at a ratio of 1:5. Quality attributed such as particle size distribution, creaming profile and coalescence rate during storage at 4 and 25 °C; surface and interfacial tension; zeta potential and viscosity of the emulsions were determined. The results indicated that the addition of L. perfoliatum seed gum had no significant effect on zeta potential but the surface and interfacial tension increased with the rise of gum concentration. It was also found that the addition of L. perfoliatum seed gum to WPC emulsions at a critical concentration of 0.2% (w/v) caused flocculation of oil droplets, which resulted in marked increase in particle size and the creaming rate. However at higher gum concentrations beyond this value, the particle size remained constant, apparently because of the high viscosity of the aqueous phase. At all concentrations tested, emulsions stored at 4 °C were more stable except for those containing 0.2% L. perfoliatum seed gum.     

Whey protein concentrate: Autolysis inhibition and effects on the gel properties of surimi prepared from tropical fish

Effects of whey protein concentrate (WPC) on autolysis inhibition and gel properties of surimi produced from bigeye snapper (Priacanthus tayenus), goatfish (Mulloidichthys vanicolensis), threadfin bream (Nemipterus bleekeri) and lizardfish (Saurida tumbil) were investigated. WPC (0–3%) showed inhibitory activity against autolysis in all surimi at both 60 and 65 °C in a concentration-dependent manner. Myosin heavy chain (MHC) of surimi was more retained in the presence of WPC. Breaking force and deformation of kamaboko gels of all surimi increased as added levels of WPC increased (P < 0.05). This was associated with lower levels of protein degradation, as evidenced by the decrease in trichloroacetic acid-soluble peptide content (P < 0.05). WPC at 3% (w/w) significantly decreased the whiteness of gels. However, water-holding capacity of kamaboko gels was improved with increasing concentration of WPC. The microstructure of surimi gels generally became denser with the addition of WPC.     

Improvement of gelling properties of porcine blood plasma using microbial transglutaminase

The effect of microbial transglutaminase (MTGase) on the texture and water-holding capacity (WHC) of heat-induced gels prepared from porcine blood plasma at pH 5.5 was investigated. Different concentrations of commercial MTGase were added to plasma and incubated for several times under specific conditions of temperature and pH. From the results obtained, it can be postulated that enzymatic treatment enhances textural properties and WHC of plasma gels at pH 5.5, especially when incubated with 3% of the commercial product for 3 h at 30 °C and pH 7. This treatment increased by 0.4 N the hardness of gels and reduced by 3% the water released after gel centrifugation with respect to the control samples. SDS–PAGE confirmed that cross-linking took place when MTGase was added to plasma solutions. However, the results suggest that the sole addition of MTGase was not effective enough to improve the gelling properties of plasma proteins under acidic conditions.     

Gelation properties of salt-extracted pea protein isolate catalyzed by microbial transglutaminase cross-linking

Gelation is a fundamental functional characteristic of plant proteins. In this paper, a salt-extracted pea protein isolate (PPI) was mixed with microbial transglutaminase (MTG) to produce gels and the gelation properties were studied. When the MTG level increased, the magnitude of both the G′ and G″ moduli also increased, which means the gel strength increased. A second order polynomial equation was used to describe the relationships between the G′, G″ modulus and TG level. It was found that with increased heating and cooling rate at the same MTG level, G′ and G″ tended to decrease, resulting in a weaker gel. This was attributed to the rearrangement time of pea protein molecules; slower heating and cooling rates enabled protein molecules to have more time to rearrange and therefore form a stronger gel. At the same MTG level, higher pea protein concentration resulted in higher G′ and G″ values and a power law relationship was found between G′ and pea protein concentration or G″ and pea protein concentration. Frequency sweep data of PPI show that the MTG treatment resulted in higher G′ values and lower tan delta values, indicative of a stronger more elastic gel. The minimum gelation concentration was found to be 3% (w/v) with 10 U MTG treatment, lower than 5.5% required when no MTG was present. When compared to PPI and soy protein isolate (SPI) with and without 10 U MTG treatment, the gel strength of PPI with MTG was stronger than that of SPI with MTG treatment, whereas the opposite was true without the MTG treatment. SDS-PAGE showed that at the same pea protein concentration, higher MTG level induced more cross-linking as fainter bands were seen on the gel and there was a shift in the relative intensities of the bands in the molecular weight range of 35–100 kDa.     

Hydrolysis of β-lactoglobulin by trypsin under acidic pH and analysis of the hydrolysates with MALDI–TOF–MS/MS

Trypsin (EC 3.4.21.4) hydrolysis of food proteins are done at the optimum pH (7.8) and temperature (37 °C). Little information is available on the effect of sub-optimal conditions on hydrolysis. Bovine β-lactoglobulin (β-Lg) was hydrolysed by trypsin under acidic pH (pH 4–7) between 20 and 60 °C and the substrate concentration from 2.5% to 15% (w/v) and compared with hydrolysis at pH 7.8 and 37 °C. Aliquots were taken at different times (t = 0 up to 10 min). Samples were analysed using matrix-assisted laser desorption/ionisation time-of-flight tandem mass spectrometry (MALDI–TOF–MS/MS) with α-cyano-4-hydroxycinnamic acid (HCCA) and 2,5-dihydroxyacetophenone (DHAP) matrices. Hydrolysis patterns of β-Lg were generally similar at pH 7.8, 7, 6 and 5 while at pH 4 fewer peptides were detected except a unique fragment f(136–141). The different cleavage sites of β-Lg showed low resistance to trypsin at optimum conditions and pH 7 while being random and simultaneous. At lower pH, some cleavage sites showed increased resistance, while hydrolysis was relatively slow and ordered. Initial attack by trypsin occurred at Arg⁴⁰–Val⁴¹, Lys¹⁴¹–Ala¹⁴² and Arg¹⁴⁸–Leu¹⁴⁹ resistance was at Lys⁶⁰–Trp⁶¹, Arg¹²⁴–Thr¹²⁵ and Lys¹³⁵–Phe¹³⁶. Five domains were identified based on β-Lg resistance to trypsin in the order f(1–40) < f(41–75) < f(76–91) > f(92–138) > f(139–162). Results suggest that hydrolysis away from trypsin optimum offer better hydrolysis process control and different peptides. This strategy may be used to protect target bioactive or precursor peptides, or avoid the production of unwanted peptides.     

Effect of zinc sulphate on gelling properties of phosphorylated protein isolate from yellow stripe trevally

Impacts of zinc sulphate (ZnSO₄) (0–140 μmol/kg) on gel properties of yellow stripe trevally surimi added with sodium tripolyphosphate (STPP) (0.25% and 0.5%, w/w) and protein isolate phosphorylated with STPP at 0.25% and 0.5% (w/w) were studied. Gels from surimi added with 60 μmol ZnSO₄/kg in the absence and presence of 0.5% STPP had the increases in breaking force and deformation by 20.9% and 33.3%, and 11.6% and 18.6%, respectively, compared with the control surimi gel (without additives). Gel of protein isolate phosphorylated with 0.5% STPP containing 100 μmol ZnSO₄/kg had the increases in breaking force and deformation by 14.87% and 5.6%, respectively, compared with the gel from non-phosphorylated protein isolate at the same ZnSO₄ level, suggesting that the phosphorylated protein isolate was more crosslinked by Zn²⁺. The addition of ZnSO₄ at the suitable level lowered the expressible moisture content, but increased whiteness of surimi or protein isolate gels (P < 0.05). Non-covalent bonds, more likely salt bridge and ionic interactions, played a major role in cross-linking of proteins in both surimi and protein isolate added with ZnSO₄, regardless of phosphates incorporated. Microstructure study revealed that a gel having highly interconnected and denser network with smaller voids was formed when protein isolate phosphorylated with 0.5% STPP was added with ZnSO₄ at a level of 100 μmol/kg. Thus, gel with improved properties could be obtained from protein isolate from yellow stripe trevally phosphorylated with STPP in conjunction with addition of ZnSO₄ at an appropriate level.