Impact of microbial transglutaminase on gelling properties of Indian mackerel fish protein isolates

Impacts of microbial transglutaminase (MTGase) (0–0.6 units/g sample) on gel properties of Indian mackerel unwashed mince, surimi and protein isolates with and without prewashing were studied. Generally, lower myoglobin and lipid contents were found in protein isolate with and without prewashing, compared to those of unwashed mince and surimi (P < 0.05). Protein isolate had the decreased Ca²⁺-ATPase and protein solubility, indicating protein denaturation. When MTGase was incorporated, breaking force and deformation of all gels markedly increased, especially as MTGase levels increased (P < 0.05). At the same MTGase level, gel from protein isolate with prewashing exhibited the highest breaking force and deformation (P < 0.05). The addition of MTGase could lower the expressible moisture content of most gels. No change in whiteness of gel was observed with the addition of MTGase (P > 0.05), but gel from protein isolate gels had decreased whiteness as MTGase at high level was added. The microstructure of protein isolate gels without prewashing showed a similar network to unwashed mince gels, whilst a similar network was observed between surimi gel and gel from protein isolate with prewashing. Nevertheless, a larger void was noticeable in gels from protein isolates. All gels incorporated with MTGase (0.6 units/g) showed a slightly denser network than those without MTGase. Thus, gel with improved properties could be obtained from protein isolate from Indian mackerel with added MTGase.     

Physicochemical properties and gel-forming ability of surimi from three species of mackerel caught in Southern Thailand

Physicochemical and gelation properties of surimi prepared from three species of mackerel were investigated. The highest whiteness with the lowest redness index corresponding to the lowest myoglobin content especially its oxidised form, metmyoglobin, was found in short-bodied mackerel (Rastrelliger brachysoma) surimi (p < 0.05). Frigate mackerel (Auxis thazard) surimi contained the highest lipid content (p < 0.05). The pH of all surimi was in the range of 6.58–6.80. The highest sulfhydryl group and Ca²⁺-ATPase activity was found in natural actomyosin extracted from short-bodied mackerel surimi (p < 0.05). The highest TCA-soluble peptide content was found in frigate mackerel surimi gels (p < 0.05). Kamaboko gel of short-bodied mackerel surimi exhibited the highest breaking force with the lowest expressible drip (p < 0.05). Heating regime had no effect on deformability of gels from Indian mackerel (Rastrelliger kanagurta) and short-bodied mackerel but not for frigate mackerel. The highest metmyoglobin content with the lowest whiteness was found in frigate mackerel surimi gel (p < 0.05). Therefore, short-bodied mackerel was the best suited for the production of surimi with superior functional attributes including whiteness and gel-forming ability.     

Antioxidant activity of protein hydrolysates derived from threadfin bream surimi byproducts

Antioxidant activities of protein hydrolysates from threadfin bream surimi wastes, including frame, bone and skin (FBS) and refiner discharge (RD), were investigated. FBS and RD were rich in Lys, Glu, Gly, Pro, Asp, Leu, His, Tyr and Phe. FBS was hydrolysed to a greater extent than RD regardless of proteinases tested (Virgibacillus sp. SK33 proteinase, Alcalase, pepsin and trypsin). Pepsin-hydrolysed FBS, at a 5% degree of hydrolysis (DH), showed the highest antioxidant activity based on 2,2′-azinobis (3-ethyl-benzothiazoline-6-sulphonate) (ABTS) radical (0.455 ± 0.054 mg Trolox equivalents/mg leucine equivalents), ferric reducing antioxidant power (FRAP) (0.221 ± 0.005 mM Trolox equivalents) and inhibition of β-carotene bleaching assays. FBS hydrolysates showed higher antioxidant activity based on chemical assays than their RD counterparts. However, FBS and RD hydrolysates protected HepG2 cells against tert-butyl hydroperoxide-induced oxidative damage to a similar extent. Therefore, FBS and RD hydrolysates have a potential as antioxidative neutraceutical ingredients.     

Effect of NaCl on physical characteristics and qualities of chicken breast surimi prepared by acid and alkaline processing

We investigated the effect of NaCl on the physical characteristics and qualities of chicken breast surimi prepared by acid (pH 2.5 and pH 3.0) and alkaline (pH 10.5 and pH 11.0) adjustments. Salt addition resulted in increased (p < 0.05) yellowness, but decreased (p < 0.05) lightness and whiteness of surimi, regardless of pH adjustment. Surimi prepared by alkali had the highest (p < 0.001) values of lightness and whiteness. Textural properties except cohesiveness were higher (p < 0.05) in acid-prepared surimi without salt, however, addition of salt caused higher (p < 0.05) springiness, gumminess or gel strength of chicken surimi. Salt addition also caused an increase in the sensory properties. Furthermore, alkali-treated (pH 10.5 or pH 11.0) surimi had higher (p < 0.001) values of all the sensory properties. Therefore, the alkali treatment diminished gumminess and chewiness of texture property, while better color (high lightness or whiteness), gel characteristics and sensory properties were obtained from salt-added surimi. Especially the surimi at pH 10.5 and with salt was better one which had high values of whiteness, springiness and sensory properties among the surimi.     

Morphology of starch in surimi gels

 The purpose of this work was to study the changes undergone by starch during heat-induced surimi gel preparation either with or without added egg white, and their effects on the structure of gels using light and scanning electron microscopy. Gels were made from SA-grade Alaska pollack (Theragra chalcogramma) surimi with: (1) salt (3%, w/w); (2) salt and waxy corn starch (3% and 5%, respectively w/w); or (3) salt, waxy corn starch and egg white (3%, 5% and 5%, respectively, w/w). Final moisture was adjusted to 73% or 83%. The gels were prepared by prior setting (40°C, 30 min, followed by 90°C, 30 min) or cooking (90°C, 30 min). The prepared gel was frozen and stored at –20°C (±1°C) until analysis. Samples were observed by light and scanning electron microscopy. The results show that the starch granules alter according to the processing conditions, with the predominance of crystalline or amorphous morphology depending upon the availability of heat and water. Large cavities formed in the protein gel matrix during setting can trap water; as a result, water availability is limited for starch to swell and gelatinize even in the high-moisture gel. Received: 13 March 1997     

Effects of high-temperature treatment (⩾100 °C) on Alaska Pollock (Theragra chalcogramma) surimi gels

Surimi gels from Alaska Pollock were obtained by heating and maintaining their central temperature at 100 ± 1 °C, 105 ± 1 °C, 110 ± 1 °C, 115 ± 1 °C and 120 ± 1 °C for 10 min respectively under a certain pressure (0.12 MPa). With temperature increasing, both the breaking force and gel strength decreased significantly (P < 0.05) while the deformation decreased with a much smaller gradient. The ionic bonds and the hydrophobic interactions declined with a drastic rate while the hydrogen bonds and the disulfide bonds took on an increasing trend on the whole. NMR spin–spin relaxation (T₂) measurements showed that most of the water in the gels is movable water, the peak of T₂₂ became lower and the relaxation time of T₂₂ became longer with treating temperature increasing. SDS–PAGE showed that high-temperature treatment decreased the content of myosin heavy chain (MHC) entirely and significantly decreased the content of actin. SEM showed that the gel treated with 100 ± 1 °C showed a uniform network structure with strong frames.     

Quantification of Alaska pollock surimi in prepared crabstick by competitive ELISA using a myosin light chain 1 specific peptide

A competitive enzyme-linked immunosorbent assay (ELISA) was developed for quantification of Alaska pollock (AP) surimi in crabsticks. Identification of fish species is complicated by processing, cooking, and additional ingredients. ELISA is a powerful tool for identification and quantification of fish species. Polyclonal antibodies were raised in rabbits against a 15-amino-acid peptide (Ala–Pro–Lys–Lys–Asp–Val–Lys–Ala–Pro–Ala–Ala–Ala–Ala–Lys–Lys) determined from the myosin light chain 1 (MLC 1) of AP. Immunoblotting showed the anti-pep-AP antibody had no significant cross-reactivity with protein additives. However, cross-reactivity of the MLC 1 from Pacific whiting, and threadfin bream surimi was observed. MLC 1 was purified from AP surimi and used as the coating protein in the competitive ELISA. MLC 1 was serially diluted and had a R² of 0.9845 following a logarithmic curve. All estimations of AP surimi were within 9% of the actual value. Inter-assay coefficients of variance ranged from 4.2% to 4.9%.     

Biodiversity and characterization of aerobic spore-forming bacteria in surimi seafood products

The microbial quality and safety of surimi seafood products was assessed by studying the prevalence and biodiversity of aerobic spore-forming bacteria at the beginning and end of shelf life in 100 surimi samples. Low levels of total flora and sporulated flora were numerated at the beginning of storage, however, residual spores were detected in the majority of samples during storage. Furthermore, for 34 samples, total flora counts > 10⁴ CFU/g were observed at the end of shelf life which could lead to non-compliance with good practice recommendations or product spoilage. In total, 460 strains were isolated, fingerprinted by M13-PCR and grouped into 98 different clusters. Representative strains were then identified at the species level via 16S rRNA gene sequencing. Overall, dominant species belonged to Bacillus simplex, Bacillus subtilis and Bacillus licheniformis; while B. simplex, B. subtilis as well as Sporosarcina aquimarina were clearly the dominant species found in samples with higher total flora counts. Amylolytic and proteolytic activities were very frequent amongst tested strains (80 and 92.5%, respectively). Heat resistance parameters of 4 strains in a surimi-based medium were determined. B. simplex and B. subtilis strains were the most heat resistant (δ_96 °C = 27.6 and 23.3 min and z_T = 8.6 and 7.9, respectively) which can explain their dominance in surimi samples exhibiting higher microbial counts. The heat resistance data obtained can now be used to model thermal destruction of strains using predictive microbiology tools (Sym’Previus).     

Behaviour of connective tissue in fish surimi on fractionation by sieving

The surimis prepared from the three fish species, red barracuda Sphyraena pinguis, yellow sea bream Dentex tumifrons, and spotted shark Mustelus manazo, were fractionated by sieving through a 30-mesh stainless steel sieve. Chemical analyses revealed significant differences in the collagen content among the residual fraction on the sieve (fraction A), the passed fraction (fraction C), and the original surimi before sieving (fraction B): the fractions A and B showed values 10–20 and 5–10 times higher than those of the fraction C, respectively, for all the species examined. Histological observation indicated the richness of the thick connective tissues derived from myocommata in fractions A and B, while thick connective tissue was hardly observed in fraction C. These results suggested that the present fractionation method may have an effect of reducing the collagen content to about 10–20% of the original value, and that a large part of collagen in fish surimi exists in the relatively thick connective tissue, probably derived from myocommata.     

Water retention properties and solubility of the myofibrillar proteins: Interrelationships and possible value as indicators of the gel strength in cod surimi by a multivariate data analysis

The quality of surimi made from fish aged on ice for up to 14 days was evaluated by compression test on a model product. Water holding capacity (WHC) and pH in the fish mince, and protein content, pH, salt solubility of the myofibrillar proteins and hydration index of the insoluble proteins (HUP) in the surimi, were determined. Their interrelationships and utility as indicators of surimi quality were evaluated by a multivariate data analysis. The main tendencies of variation among the chemical parameters were examined by the use of principal component analysis. Correlations between the chemical parameters (X-variables) and the gel strength of surimis (Y-variable) were studied by the use of partial least squares regression. Age of the raw material and protein content of the surimi seemed to be the main determinants of the gel strength. Among the remaining variables only HIIP showed a potential value as indicator of the gel strength. WHC and HIIP seemed to reflect two different water retention properties of the proteins.