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Effects of high‐intensity ultrasound (HIU) treatments on gelation of threadfin bream (Nemipterus spp.) surimi at various NaCl contents (0.5, 1, and 2% NaCl) were investigated. Protein extractability at 0.5% NaCl was increased with the ultrasonic intensity (p < 0.05). At all tested NaCl contents, reactive sulfhydryl group (SH) content and surface hydrophobicity of the surimi pastes were increased after HIU treatments and were accompanied by a decrease in the Ca2+‐ATPase activity and total SH content, indicating a greater extent of unfolding and conformational changes induced by HIU at higher NaCl contents. Textural properties and color of the surimi gels at 0.5% NaCl were improved concomitant to an increase in ultrasonic intensity (p < 0.05), whereas HIU treatments resulted in inferior gels at 1 and 2% NaCl. Scanning electron microscopy (SEM) revealed that HIU resulted in a more orderly gel network at 0.5% NaCl. Fourier transform infrared (FT‐IR) spectroscopy indicated that the α‐helix content of the surimi gels was decreased as the ultrasonic intensity and NaCl content increased, confirming that structural changes induced by HIU were more profound at higher NaCl contents. The results suggested that HIU technology can be applied to improve only the 0.5% NaCl surimi gel. Practical Application: High‐intensity ultrasound (HIU) improved surimi gel containing 0.5% NaCl due to an increase in protein extractability and protein conformational changes. It is likely to lay a theoretical foundation for utilization of HIU technology in production of surimi‐based products at low/reduced salt levels. [ABSTRACT FROM AUTHOR]

The combined effect of ascorbic acid (AsA) and hydrogen peroxide (H2O2) on gel‐forming ability and structural changes of lizardfish (LZ) and threadfin bream (TB) surimi were investigated. Addition of 0.15% AsA and 0.1% H2O2 greatly increased breaking force and distance of LZ surimi by 300% and 55%, respectively. Combination of 0.2% AsA and 0.15% H2O2 resulted in the maximum TB surimi gel improvement with 150% and 90% increase in breaking force and distance, respectively. Browning reaction obviously occurred when combined AsA and H2O2 was added, due to ascorbic acid oxidation. Polymerization of myosin heavy chain via disulfide bonds was promoted, and the formation of disulfide bonds was involved through oxidation of sulfhydryl groups with increasing AsA and H2O2. Fourier‐transform infrared (FT‐IR) spectroscopy revealed a decrease in α‐helix and an increase in β‐sheet content as AsA and H2O2 increased in both species. A decrease of band area of aliphatic (2,800 to 3,000 and 1,450 cm−1), aromatic (1,208, 757, and ratio 850/830 cm−1), and change of disulfide bonds (525 and 540 cm−1) suggested an increase in hydrophobic interactions and disulfide bonds with addition of these additives. Based on principal component analysis (PCA), textural characteristics were positively correlated with β‐sheet content. Our study suggested that combination of AsA and H2O2 greatly enhanced gelation of LZ and TB by increasing not only disulfide bonds but also hydrophobic interactions. Practical Application: The combined ascorbic acid and hydrogen peroxide can be used to improve gelation of two important tropical surimi species, namely threadfin bream and lizardfish surimi, without requirement of setting. The optimum concentration of each additive varied with fish species. [ABSTRACT FROM AUTHOR]

Solid wastes from threadfin bream (Nemipterus spp.) surimi production composed of head and frame were hydrolyzed by various commercial proteases (Alcalase, Flavourzyme, Neutrase, Protamex, papain, and pepsin) to produce protein hydrolysates with bioactive properties. An Alcalase-hydrolyzed sample at 24.4% degree of hydrolysis (DH) displayed the highest antioxidant activity based on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging, ferric reducing antioxidant power (FRAP) assay, and potassium ferricyanide method. In addition, it showed an inhibitory activity toward angiotensin-converting enzyme (ACE) of 25.5%. Antioxidant activity of threadfin bream by-product hydrolysates increased with hydrolysis time and reached the highest DPPH activity after 6 h, while that hydrolyzed for 3 h showed the highest reducing power based on FRAP and potassium ferricyanide assays. In addition, ACE inhibitory activity was found to be at an optimum after 3 h of hydrolysis. The hydrolysates (1 mg/mL) also retarded oxidation of a linoleic acid emulsion system to a similar extent as 0.1 mg/mL 3-tert-butyl-4-hydroxy anisole (BHA), indicating a potential use in the food system. Protein hydrolysates from threadfin bream surimi by-products could be tailor-made to possess both antioxidant and ACE inhibitory activity through controlling DH of Alcalase-catalyzed reactions. [ABSTRACT FROM PUBLISHER]

Structural changes and functional properties of threadfin bream ( Nemipterus sp.) sarcoplasmic proteins (TB-SP) subjected to various pH conditions (pH 3, 5, 6.3, 9, and 12) after subsequent pH readjustment to pH 7 were investigated. Fourier transform infrared spectroscopy revealed the loss of α-helical and β-sheet structures of TB-SP after being subjected to pH 3 or pH 12 treatments. The extent of structural and conformational changes of TB-SP subjected to pH 3 was greater than alkaline pHs (pH 9, 12) and pH 5, respectively. The water holding capacity of lyophilized TB-SP treated at pH 3 and pH 12 increased about 6.5- and 5.4-fold, respectively, as compared to the crude counterpart. Both acid and alkaline pH treatments increased fat absorption capacity of lyophilized sample about 2-fold, but drastically decreased its solubility. The water soluble fraction of extremely acidic (pH 3→7) and alkaline (pH 12→7) samples exhibited higher oil binding capacity as measured by diphenylhexatriene fluorescence and emulsifying activity. A gel-like structure was formed when water-soluble fraction of crude TB-SP and those subjected to moderate pHs (pH 5, 9) at 2 mg/mL was prepared for the emulsion containing 50% oil (v/v). Functional properties of TB-SP varied, depending on the pH-adjustment process applied. [ABSTRACT FROM AUTHOR]

Transglutaminase (TGase) from the threadfin bream ([TB]Nemipterus sp.) liver was partially purified using ion exchange, size exclusion and affinity chromatography. Three protein bands with molecular weight (Mw) of 95, 63 and 43 kDa on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) were observed. Only one distinct fluorescent band appeared on the TGase activity staining of the native-PAGE. When the protein band was eluted and analyzed on the SDS-PAGE, it showed a single band with an Mw of 95 kDa. The enzyme required Ca2+ up to 1 mM for full activation. TGase was also activated by 10 mM Sr2+ . Dithiothreitol had no effect on activity. TGase activity was unaffected by NaCl up to 0.6 M and reduced to 75% at 1.2 M NaCl. Optimum pH and temperature was 8.5–9.0 and 50C, respectively. TGase activity was markedly inhibited by the sulfhydryl reagents. The enzyme catalyzed the cross-linking of the TB myosin heavy chains. PRACTICAL APPLICATIONS Threadfin bream (TB) liver transglutaminase (TGase) exhibited Ca2+-dependent characteristic similar to muscle TGase. The enzyme catalyzed the cross-linking of myosin, and therefore, could be applied to improve the textural properties of muscle proteins. The enzyme remained its high activity up to 1.2 M NaCl (≈7% w/v), indicating its potential application in foods containing a relatively high NaCl. The biochemical characteristics of the TB liver TGase are critical information leading to more understanding in the nature of the enzyme as well as determining the optimum conditions for food applications. Moreover, the presented purification scheme could be adopted to recover TGase from the TB liver, which is currently a solid waste of the surimi industry. [ABSTRACT FROM AUTHOR]

BSTRACT The effect of Ca2+ on physicochemical and conformational changes of threadfin bream (TB) myosin and actin during setting at 25 and 40°C was investigated. Ca2+ ion at 10 to 100 mM induced the unfolding of myosin and actin as evident by an increase of surface hydrophobicity (So ANS) at 40 °C. Total SH groups also decreased with an increased Ca2+ concentration, suggesting that Ca2+ promoted the formation of disulfide bonds during setting at 40 °C. Both hydrophobic interactions and disulfide linkages were involved in formation of myosin aggregates at 40 °C and were enhanced by addition of 10 to 100 mM Ca2+. Myosin Ca-ATPase activity decreased when Ca2+ was greater than 50 mM, indicating conformational changes of myosin head. Circular dichroism spectra demonstrated that Ca2+ reduced the α-helical content of myosin and actin incubated at either 25 or 40 °C. Ca2+ induced conformational changes of TB myosin and actin incubated at 40 °C to a greater extent than at 25 °C. [ABSTRACT FROM AUTHOR]

Abstract: Threadfin bream sarcoplasmic proteins (TBSP) were identified by 2-dimensional polyacrylamide gel electrophoresis and the major proteins were likely be pyruvate kinase, creatine kinase, aldolase, and carbonic anhydrase. Emulsifying and rheological properties of emulsion stabilized by TBSP at pH 3, 7.5, and 12 were investigated. Surface hydrophobicity of TBSP increased with pH. Emulsifying activity index was highest at pH 3 followed by pH 12 and pH 7.5. The mean droplet diameter (d 3,2) was in the order of pH 7.5 > pH 3 > pH 12 at oil volume fraction ranging from 0.1 to 0.5. A decrease of oil volume fraction resulted in a reduction of oil droplet diameter. At oil volume fraction of 0.5, TBSP-stabilized emulsion at pH 7.5 and 12 exhibited gel-like characteristics, while liquid emulsion was observed at pH 3, based on visual observation and dynamic rheological analysis. Storage modulus (G′) values of emulsion at all studied pH values increased with temperature, implying the development of protein gel network upon heating. The gel-like emulsion at pH 12 absorbed more protein and water than at pH 7.5. Protein retention and water holding capacity of emulsion increased with oil volume fraction. Hydrophobic interactions between proteins and oil droplets were likely responsible for the development of a gel-like emulsion. [Copyright &y& Elsevier]

Abstract: The cross-linking of β-lactoglobulin (BLG) was efficiently catalysed by microbial transglutaminase (MTG) but not by fish (threadfin bream) liver transglutaminase (FTG). BLG cross-linking was inhibited by 2mM 5-(biotinamido) pentylamine (BPNH2) and MTG incorporated BPNH2 into BLG ∼5 times more than was FTG. The glutaminyl sites for the incorporation of BPNH2 into BLG by FTG and MTG were identified using matrix-assisted laser desorption/ionisation-time of flight mass spectrometry (MALDI-TOF MS). MALDI-TOF MS analyses showed that MTG and FTG incorporated 4 and 1 residues of BPNH2 per molecule of BLG, respectively. The BPNH2-tagged BLG was digested by trypsin and BPNH2-tagged peptides were selectively purified by avidin-affinity chromatography. Amino acid sequences of BPNH2-tagged peptides were identified by comparing their MALDI-TOF mass spectra with the theoretical mass profiles from the MASCOT database. The BPNH2-modification sites catalysed by MTG were glutamine (Q)13, Q68, Q15 or Q20, Q155 or Q159, whilst FTG only incorporated BPNH2 into BLG at Q68. The different reactivities between FTG and MTG might be due to the different accessibilities of these TGases to the Q residues as well as to differences in substrate specificities. [Copyright &y& Elsevier]

Protein hydrolysate from frame, bone and skin (FBSH) of threadfin bream was prepared using Virgibacillus sp. SK33 proteinase and fractionated using sequential ultrafiltration membranes with molecular weight cut-offs (MWCO) of 30, 5 and 1 kDa, respectively. Four fractions, namely FBSH-I (>30 kDa), FBSH-II (5–30 kDa), FBSH-III (1–5 kDa), and FBSH-IV (<1 kDa), were obtained. All fractions were rich in Lys, Glu/Gln, Gly, Pro, Ala, Asp/Asn, and Arg. FBSH-III and FBSH-IV showed the highest surface hydrophobicity measured by 8-anilino-1-naphthalenesulfonic acid (ANS) probe ( p < 0.05). FBSH-III showed the highest antioxidant activity and cytoprotective effects against tert -butyl hydroperoxide (TBHP)-induced cytotoxicity of Caco-2 cells. In addition, FBSH-III inhibited lactate dehydrogenase (LDH) leakage and intracellular reactive species (ROS) production in a dose-dependent manner. FBSH-III retained antioxidant activity and cytoprotective capacity after in vitro simulated gastrointestinal digestion. These results suggested that FBSH-III might potentially be nutraceutical peptides with antioxidative properties. [ABSTRACT FROM AUTHOR]