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The objective of study was to investigate the softening effect and mechanism of Garcinia gummi-gutta on grass carp bones. The pattern of change in the hardness of grass carp bones was studied during pickling using a G. gummi-gutta juice-based marinade at different temperatures (5, 10, 25, and 40 ℃). At the same time, changes in the composition and structure of grass carp bones and in the acidity and pH of the marinade were also determined. The results showed that the hardness of grass carp bones gradually decreased with pickling time, which decreased by 71.5%–79.4% after 25 days of pickling (P < 0.05). The ash content decreased by 11.90%–16.65% (P < 0.05), and the moisture content by 4.23%–13.08% (P < 0.05). The dense and ordered microstructure became loose and porous. This was because the reaction of H+ with hydroxyapatite in fish bones enabled calcium to be dissolved from fish bones and the consumption of H+ in the pickling solution decreased its acidity and increased its pH. Malic acid was played a major role in softening fish bones. Infrared spectroscopic analysis showed that the triple helix structure of fish bone collagen was not destroyed, but the absorption peak corresponding to amide A shifted to a higher wavenumber, suggesting a reduction in the number of hydrogen bonds, which might be related to the loss of hydroxyapatite in fish bones.

Objective: This study aimed to investigate the differences in enzymatic properties of endogenous transglutaminase （TGase） in silver carp and black carp. Methods: STG and BTG were purified from the muscle of silver carp and black carp, respectively, by 80% ammonium sulfate precipitation, Q-Sepharose FF, and Sephacryl S-200 HR chromatographies. Two enzymes were analyzed for relative molecular weights, peptide sequences, secondary structures, optimal reaction conditions, and thermal inactivation kinetics. Results: The purified STG and BTG showed similar relative molecular weights, of which the enzyme activities were 14.34 U/mg and 12.67 U/mg, respectively. Both enzymes showed differences in peptide sequences. The secondary structures of them were mainly the β-fold, though the content of β-fold in STG was slightly higher than that of BTG. The optimal temperatures for STG and BTG were both 50 ℃, and the optimal pH values were 8.0 and 7.5, respectively. The enzymes required Ca2+ up to 1 mmol/L for full activation. The activities of STG and BTG were enhanced by DTT, whereas PMSF, NH4Cl, NEM, EDTA, Cu2+, Ba2+, Zn2+, and Mg2+ showed inhibitory effects. When the temperature was 37~50 ℃, the passivations of STG and BTG by thermal treatment conformed to the first-order exponential decay kinetics with similar values of Ea. Conclusion: The primary and secondary structures of STG and BTG exhibited obvious differences, yet they still exhibited similar properties in terms of optimal reaction conditions and thermal inactivation kinetics.

Fish soup, a traditional Chinese broth food, is loved by consumers due to its rich nutrition, high digestion and absorption rate, umami and sweet taste, and strong aroma. However, off-flavors can be formed during the processing and storage of fish soup, restricting its industrial development. Off-flavors in fish soup are from a wide range of sources, have complex composition, and are difficult to eliminate. Therefore, it is urgent to understand the formation mechanism of the flavor quality of fish soup (especially off-flavors), identify the factors affecting the flavor quality of fish soup, and establish measures to regulate off-flavors in fish soup. In this context, this article summarizes the formation pathways of fish soup flavor, and systematically discusses the processing factors that affect the flavor quality of fish soup. It clarifies that selecting appropriate processing methods can effectively enhance the characteristic aroma of fish soup and reduce the undesirable odor, summarizes the current methods to remove the fishiness and bitterness of fish soup, and compares their advantages and disadvantages. We hope that this article will provide a theoretical basis for future research to regulate the flavor quality of fish soup and to develop portable fish soup foods.

To clarify the taste differences between surimi products from different fish species and establish a taste fingerprint of surimi products, three species of marine fish (hairtail, red sea snapper, and golden thread) and three species of freshwater fish (silver carp, grass carp, and black carp) were used to produce surimi gels. The taste profiles of the gels were analyzed by an electronic tongue, high performance liquid chromatography and gas chromatography, and a taste fingerprint of surimi was established by significance analysis of microarray (SAM), cluster analysis, and heatmap analysis. The results showed that the taste characteristics of the six surimi products were significantly different. Hairtail surimi contained high levels of glutamate (2.37 mg/100 g) and aspartic acid (1.32 mg/100 g). Golden thread surimi showed the lowest contents of glutamate and aspartic acid. In addition, grass carp surimi contained relatively high contents of proline (tasting sweet) and histidine (tasting bitter). The proportion of polyunsaturated fatty acids in marine surimi was about twice as high as that in freshwater surimi. Among the freshwater surimi products, the proportion of polyunsaturated fatty acids was relatively higher in silver carp surimi. Compared with freshwater surimi, marine fish surimi had a higher content of betaine, inosine 5’-monophosphate (IMP) and guanosine 5’-monophosphate (GMP), and a lower content of hyperxanthine (Hx). Through SAM, a total of 46 differential substances were selected between the six surimi products, and the taste fingerprint constructed based on these differential substances by heatmap analysis could directly reflect the taste differences and major differential substances between freshwater and marine fish surimi.

In this study, silver carp myofibrillar protein (MP) was oxidized with different concentrations of H2O2 (0.0‒10.0 mmol/L) in the Fenton system (H2O2-VC-FeCl3) to explore the effect of oxidation degree on protein gel formation and gel properties. The sulfhydryl content of MP was measured. The gel strength, whiteness, water-holding capacity, moisture distribution and microstructure of MP gels were determined. The results showed that as H2O2 concentration increased, the total sulfhydryl content, whiteness and water-holding capacity of MP increased first and then decreased. When the H2O2 concentration in the system was low (0.1‒0.5 mmol/L), the gel strength and whiteness were both improved. The area of pores in the three dimensional gel structure became smaller, the distribution became more uniform, and the water-holding capacity of MP gels was enhanced. However, at high H2O2 concentration (5.0‒10.0 mmol/L), the gel whiteness decreased, and the gel structure became disordered, the pore area became larger, the pore distribution became nonuniform, and the water-holding capacity decreased, indicating a deterioration in gel quality. Therefore, appropriate oxidation (0.1‒0.5 mmol/L H2O2) contributed to the improved properties of protein gels. The analysis of the peptide composition by liquid chromatography-tandem mass spectrometry (LC-MS/MS) showed that the major oxidation regions of MP by hydroxyl radicals were the heavy chain of myosin and actin. Moreover, methionine, cysteine, aspartic acid and glutamic acid were recognized as the high-frequency oxidation sites of MP.