Thermal stability of fish natural actomyosin affects reactivity to cross-linking by microbial and fish transglutaminases

Purification and Characterization of Transglutaminase Isolated from Sardine (Sardina pilchardus) Flesh Waste

Transglutaminase (TGase) is an enzyme that catalyzes acyl transfer reactions by creating covalent cross-links between protein molecules and has been used to improve the physical and functional properties of protein-based foods. The objectives of this study were the extraction, purification, and biochemical characterization of TGase from sardine (Sardina pilchardus) flesh in order to provide a suitable TGase enzyme for food industry applications. The results showed a specific activity, yield, and purification fold of 357.14 U/mg protein, 36.74%, and 183.15, respectively. The enzyme exhibited maximal activity at 40 °C and pH 8.0, with a molecular weight of around 57 kDa. The effect of time on TGase thermal stability at 40 °C showed a gradual decrease in its catalytic activity during the incubation time until the enzyme was completely inactivated at 60 min. Additionally, the sardine TGase was found to be calcium-dependent. However, Mg2+ and Ba2+ ions were found to be effective in its activation to some extent and a total inhibition was shown by Zn2+ and Sr2+ ions. The TGase activity was affected markedly by NaCl and EDTA, and lost, respectively, about 80.7% and 36.49% from its activity by increasing the concentration (1.5 M NaCl and 20 mM EDTA). Based on the surface hydrophobicity and solubility results, the cross-linking of natural actomyosin mediated by TGase increased to a greater extent. The results revealed that sardine TGase possessed attractive qualities, making it a potential alternative to other TGase sources for food industry applications.

Reduced fat content of fried batter-breaded fish nuggets by adding dietary fibers: Insight into wheat starch and gluten conformations, fiber properties and anti-fat absorption capacities

Dietary fibers with excellent processing characteristics and water-holding capacity garnered significant attention in low-fat fried products manufacturing, but further research is lacking to elucidate fat reduction mechanisms. Three dietary fibers were added to the batter of fried batter-breaded fish nuggets, the increased maximum wavelength, fluorescence intensity, surface hydrophobicity value, and S-S/free-SH ratio revealed the enhanced exposure and interaction of hydrophobic groups within gluten. Conversion from both -SH into S-S bonds, and α-helix into β-turn confirmed the establishment of the gluten gel network and a substantially increased gel strength. X-ray diffraction demonstrated the inhibition of amylose-lipid complex formation due to the competitive amylose binding to dietary fiber. Finally, reduced oil effects were evident in surface and penetrated oil contents and oil distribution fluorescence diagram. The work clarified the interactions among dietary fiber, wheat starch and gluten, indicating the composite gel network formation and the crust characteristics alterations, ultimately inhibiting oil penetration.

In Vitro Pepsin Digestion Characteristics of Silver Carp (Hypophthalmichthys molitrix) Surimi Gels with Different Degrees of Cross-Linking Induced by Setting Time and Microbial Transglutaminase

Surimi gels are favored for their abundant proteins and unique taste. In this study, the pepsin digestion behaviors of surimi gels with different degrees of cross-linking induced by microbial transglutaminase (MTGase) and different setting times were investigated. For gels without (CK group) and with (TG group) MTGase, the slowest digestion rate (t_M/2 = 20.13 and 79.19 min for CK and TG group, respectively), the least amino acid concentration (5.32 and 3.73 μmol/mL for CK and TG group, respectively), and the peptide amounts (1355 and 1788 for CK and TG group, respectively) were obtained at a moderate setting time (1-4 h) with the finest microstructure. However, the excessive setting time (8-12 h) formed an inhomogenous network, which accelerated the hydrolysis of gel proteins (t_M/2 = 9.40 and 52.33 min for CK and TG group, respectively) and produced more amino acids (6.63 and 5.15 μmol/mL for CK and TG group, respectively) and peptide amounts (1644 and 2143 for CK and TG group, respectively). The above results also demonstrated that the presence of MTGase strengthened the compactness of gels as well as slowed down the digestion process with the release of less amino acids but more peptides. A large proportion of unique peptides were from the tail domain of myosin heavy chain. The discrepancy in bioactive peptides between different gels might be reduced in the subsequent intestinal digestion according to the in silico methods, demonstrating the diminished difference in the gastrointestinal digestion process in the aspect of releasing functional peptides. This study provides the theoretical basis and guideline in the field of gelation food digestion and surimi food industry to produce healthier surimi-based food.

Aggregation and conformational changes of silver carp myosin as affected by the ultrasound-calcium combination system

BACKGROUND

Ultrasound and Ca²⁺ have been used separately to increase myosin properties in fish processing. However, little is know about how myosin changes are affected by Ca²⁺ and ultrasound in combination. The present study aimed to investigate the effects of the ultrasound-calcium combination system on aggregation and conformational changes of silver carp myosin.

RESULTS

Ultrasound facilitated a Ca²⁺ -induced increase in turbidity. As the Ca²⁺ concentration increased from 0 to 100 mmol L^-1 , there was an obvious increase in the turbidity, solubility and mean hydrated particle size of myosin after ultrasound treatment compared to without treatment. Moreover, changes of total and reactive SH contents depended on the ultrasound-calcium combination conditions. Under this combination system, myosin surface hydrophobicity significantly increased for the synergistic effect of ultrasound and Ca²⁺ . Furthermore, the ultrasound-calcium combination conditions could affect myosin gelation, with better gelation properties being observed for myosin treated with a combination of 60 mmol L^-1 Ca²⁺ and 9 min of ultrasound.

CONCLUSION

The combination system reported in the present study was beneficial for myosin unfolding, facilitating intermolecular interactions between Ca²⁺ and myosin. Ultrasound treatment promoted myosin aggregation via the induction of Ca²⁺ and reduced the critical concentration of Ca²⁺ required to aggregate myosin. In the fish processing industry, this combination system can enhance the gelation properties of surimi-based products. © 2018 Society of Chemical Industry.

Angiotensin-I-Converting Enzyme Inhibitory Activity and Antioxidant Properties of Cryptides Derived from Natural Actomyosin of Catla catla Using Papain

Natural actomyosin (NAM) from the freshwater fish Catla catla was extracted and hydrolyzed using papain enzyme at different enzyme-to-substrate ratios (0.5%, 1.0%, 2.0%, 5.0%, and 10%) to obtain the cryptides with different degrees of hydrolysis (DH). Derived cryptides were evaluated for bioactive properties such as angiotensin-I-converting enzyme (ACE) inhibitory activity and antioxidant properties. The pattern of hydrolysis of NAM as a function of time revealed that major protein components such as myosin and actin were hydrolyzed within 10 min of hydrolysis. The cryptides obtained with the DH of 29.4% had significantly higher ACE inhibitory activity and linoleic acid peroxidation inhibitory activity (P<0.05). A higher DPPH free radical-scavenging activity and ferric-reducing power were exhibited by the NAM cryptide mixture obtained with the DH of 17.38 and 26.2%, respectively. The natural actomyosin could be a potential precursor to produce the cryptides with therapeutical and antioxidant properties.

Protein structural development of threadfin bream ( Nemipterus spp.) surimi gels induced by glucose oxidase

This study investigated the effect of glucose oxidase on the gel properties of threadfin bream surimi. The gel strength of surimi increased with the addition of 0.5‰ glucose oxidase after two-step heating. Based on the results of the chemical interactions, the hydrophobic interaction and disulfide bond of glucose oxidase-treated surimi samples increased compared with the control samples at the gelation temperature and gel modori temperature. The surface hydrophobicity of samples with glucose oxidase and glucose increased significantly ( p < 0.05) and total sulfhydryl groups decreased significantly ( p < 0.05). The analysis of Raman spectroscopy shows that the addition of glucose oxidase induced more α-helixes to turn into a more elongated random and flocculent structure. Glucose oxidase changes the secondary structure of the surimi protein, making more proteins depolarize and stretch and causing actomyosin to accumulate to each other, resulting in the formation of surimi gel.

New Alternatives in Seafood Restructured Products

A general overview, focusing on new trends in the different techniques used in restructured seafood product processing has been described in this work. Heat-induced gelation has been more widely studied in scientific literature than cold gelation technology. This latter technology includes the use of hydrocolloids (alginates and glucomannan) or enzymes (microbial transglutaminase) for making both raw and cooked restructured products. In restructuration processes, fortification processing with some functional ingredients is studied, giving as a result extra value to the products as well as increasing the variety of new seafood products. The process of alleviating heavy metals and organic pollutants from the raw material used has also been reviewed in the present paper.

Effect of ultrasonication on secondary structure and heat induced gelation of chicken myofibrils

Ultrasonication has been suggested as a new promising technique to improve the quality of meat and other meat products. In this study ultrasonication at low frequency (20 kHz) was carried out to investigate the effect on structural and biochemical properties of myofibril proteins. The possible implications between ultrasonication-induced structural changes and gelation properties were also investigated. Structural changes were investigated by ATPase activity, SDS-PAGE, circular dichroism and fluorescence spectroscopy. Microstructural changes in heat induced gels were observed by SEM and water holding capacity was determined by centrifugation. Ultrasonic treatment for 30 min significantly reduced the Ca²⁺-ATPase activity. Moreover significant change in structure of proteins at secondary level, as indicated by marked decrease in α-helicity, was observed. Marginal change in fluorescence at 10 min was followed by significant increase at 20 and 30 min reflecting exposure of hydrophobic residues on surface during unfolding. Microstructural analyses of gels showed marked improvement in regular three dimensional network at 20 and 30 min of sonication. WHC at 20 min and 30 min were significantly higher than control. Our results suggest that ultrasonication at low frequency (20 kHz) can prove beneficial for improving functional properties of meat and meat products.

Emulsifying and gelling properties of weakfish myofibrillar proteins as affected by squid mantle myofibrillar proteins in a model system

The aim of the present work was to investigate the physicochemical, biochemical and functional characteristics of both the myofibrils (MF) and actomyosin (AM) of squid mantle (Illex argentinus) and weakfish (Cynoscion guatucupa) muscles, and evaluate the influence of the addition of myofibrilar proteins from the squid mantle on the physicochemical and functional properties of those of the weakfish. After extraction, purification and characterization of the MF and AM of both species, emulsions of each protein fraction from each muscle were formulated. Mixtures of the MF or AM of both species were also analyzed. The emulsifying properties were monitoring using the Emulsifying Activity Index (EAI) and Emulsion Stability (ES). In addition, gel pastes were formulated from the squid mantle, weakfish muscle and the mixture of both species, and the following functional properties of the gels assessed: water holding capacity, colour, textural profile analysis (TPA) (hardness, elasticity, cohesiveness, gumminess) and gel strength. The EAI values of emulsions formulated with the MF of the mantle were significantly (p<0.05) higher than those formulated from those of weakfish. The incorporation of squid MF in the mixture increased the EAI values. Conversely, the highest ES values were obtained with weakfish MF, and the incorporation of MF weakfish in the mixture increased the ES values. Similar EAI and ES behaviours were observed for the AM of the corresponding species. Irrespective of the thermal treatment, the gel strength of the gelled paste of squid muscle was significantly (p<0.05) lower than that of weakfish muscle and of those obtained with the different mixtures. The behaviours of the expressible moisture (EM) from the gelled pastes were similar to those of gel strength. Irrespective of the thermal treatment, the pastes formulated with a high weakfish: mantle ratio showed less water loss. The gelled pastes of squid mantle showed the highest values for whiteness (WI) and the incorporation of squid muscle protein improved the WI of the mixtures.

Structural changes and dynamic rheological properties of sarcoplasmic proteins subjected to pH-shift method

Structural changes and dynamic rheological properties of sarcoplasmic proteins from striped catfish ( Pangasius hypophthalmus ) treated by various pH-shift processes were investigated. Isoelectric precipitation of acid-extracted sarcoplasmic proteins led to the lowest solubility in water. Sarcoplasmic proteins were unfolded after extremely acidic and alkaline extraction, exposing tryptophan and aliphatic residues. The alpha-helical structure was converted to beta-sheet following acidic extraction, whereas alkaline treatment did not disturb the alpha-helical structure of sarcoplasmic proteins. Disulfide formation, hydrogen bonding via tyrosine residues, and hydrophobic interactions occurred under extreme pH extraction. Acidic extraction induced denaturation and aggregation of sarcoplasmic proteins to a greater extent than did alkaline treatment. Hydrophobic interactions via aliphatic and aromatic residues were formed during isoelectric precipitation. Sarcoplasmic proteins were partially refolded after isoelectric precipitation followed by neutralization. Sarcoplasmic proteins prepared from an alkaline pH-shift process readily aggregated to form a gel at 45.10 degrees C, whereas higher thermal denaturation temperatures (>80 degrees C) and gel points ( approximately 78 degrees C) were observed in acid-treated sarcoplasmic proteins. The pH condition used for extraction, precipitation, and neutralization greatly affected structural changes of sarcoplasmic proteins, leading to different thermal and dynamic rheological properties.