In order to investigate the effect of konjac glucomannan (KGM) on the gelling properties of shrimp myofibrillar protein (SMP), composite gel systems were prepared with different ratios to KGM and SMP (1:50, 1:20 and 1:10, m/m), named as SK50, SK20 and SK10, respectively. The surface hydrophobicity, endogenous fluorescence, turbidity, particle size, rheological properties, Fourier transform infrared (FTIR) spectra, protein composition and microstructure of the composite systems were investigated. The results showed that the surface hydrophobicity, turbidity and particle size of SMP and SMP-KGM composite systems increases with increasing KGM addition. Rheological analysis showed that shear thinning occurred in both SMP and SMP-KGM composite systems, and the storage modulus (G’) value of SK20 was the highest, indicating that the gel network in SK20 had the highest structural stability. FT-IR analysis showed the characteristic spectral bands of SMP and SMP-KGM composite systems were similar. SDS-PAGE analysis showed that addition of KGM did not significantly change the bands of SMP. After heating, the band densities of myosin heavy chain, paramyosin and actin were significantly decreased compared with the unheated group, indicating that the three proteins underwent aggregation during heating. Scanning electron microscope and fractal dimension analysis showed the formation of a dense and ordered gel with increasing KGM content. In general, adding an appropriate amount of KGM can improve the gel strength, and the product quality of shrimp surimi.

In this study, a novel esterase was purified from the liver of blue round scads via ammonium sulfate fractionation followed by a series of column chromatographies on Q-Sepharose, Q-HP, Phenyl Fast Flow and Superdex G75 with a recovery of 0.69% and 1150-fold purification factor. The esterase was a monomer with a molecular mass of 61.18 kDa as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Superdex G75 column chromatography. Peptide mass fingerprint analysis showed that the peptides showed a similarity of 100% to the predicted fatty acyl-CoA hydrolase precursor from Takifugu rubripes with 14 amino acid residues. The esterase showed an optimal activity at pH 8.0 and 50 ℃, and was comparably stable at pH 6.0-10.0 and 4-40 ℃. The metal ions K⁺, Zn²⁺, Cu²⁺, Al³⁺ and Fe²⁺ strongly suppressed the esterase activity while Ba²⁺, Ca²⁺, Mn²⁺, Co²⁺ and Mg²⁺ showed obvious activation effect on the enzyme’s activity. Moreover, the esterase exhibited strong tolerance against methanol, ethanol, acetone and isopropanol, as well as salt. Interestingly, the esterase preferably hydrolyzed esters with short carbon chain in aqueous solution, and exhibited hydrolytic activity toward long-chain esters in an emulsion system but not in aqueous solution. The results indicated that the esterase has both esterase and lipase activity.

This study investigated the effects of different concentrations (0.1%, 0.3%, 0.5%, 0.8% and 1.0% by mass relative to shrimp meat) of hyaluronic acid (HA) on the gel and physicochemical properties of surimi made from Litopenaeus vannamei. The results showed that adding a certain amount of HA improved the textural characteristics, gel strength, brightness and whiteness of shrimp surimi gel, promoted the transformation of free and immobilized water into bound water, and increased the water-binding characteristics and water-holding capacity. Rheological analysis showed that addition of a certain amount of HA improved the storage moduli of shrimp surimi, but low concentrations of HA could have adverse effects on the apparent viscosity. Chemical force analysis showed that ionic bonds first decreased and then increased, while hydrogen bonds exhibited the opposite trend with the addition of HA. An appropriate amount of HA could improve hydrophobic interactions but the formation of disulfide bonds from sulfhydryl oxidation was also inhibited by HA. Moreover, HA could interact with shrimp surimi proteins, inhibit the formation of protein polymers, change the conformation of proteins, and promote the transformation of the secondary structure of proteins from α-helix to β-structure and random coil. The microstructure of shrimp surimi gel was improved by adding an appropriate amount of HA, becoming more uniform and denser. Among all samples with different levels of HA, shrimp surimi gel with the addition of 0.8% HA had the highest hardness, gumminess, chewiness, gel strength, storage modulus and the densest microstructure, and its waterholding capacity significantly improved when compared with that of the control group (P < 0.05). However, the textural characteristics, gel strength, water-holding capacity and storage modulus of shrimp surimi gel with 0.1% HA were lower than those of the control group, and the microstructure was looser.