•Urea, SDS and NEM impacted surimi gel properties by disrupting hydrogen bonds, hydropholic interactions and disulfide bonds.•Secondary structure of surimi gels was changed in the presence of bond disrupting agents. More random coil was formed accompany with decreasing content of β-sheet.•Textural properties were in correlation with protein secondary structure.Urea, sodium dodecyl sulfate (SDS) and N-ethylmaleimide (NEM) were employed to monitor the contributions of hydrogen bonds, hydrophobic interactions and disulfide bonds in heat-induced surimi gel. Surimi gels were prepared with the bond disrupting agents followed by texture profile, gel strength, rheological and Raman analysis. The rheological analysis demonstrated that remarkable changes of storage moduli (G′) were presented below the critical temperature, especially for SDS treatments. Gel strength significantly decreased as the concentration of urea and NEM increased, while it was slightly improved by 1% SDS. With the involvement of bond disrupting agents, hardness and gumminess of surimi gel presented a dramatical decrease. The Raman results indicated that protein secondary structure tended to transform to random coil, with content of α-helix and β-sheet decreasing. Textural properties were in correlation with protein conformation. Less of random coil led to improvement of gel strength, and springiness was mainly contributed by β-sheet and β-turn. The results suggested that different bond disrupting agents induced various changes in surimi gel properties and protein secondary structure.Download high-res image (174KB)Download full-size image

•COS-O-Ger was synthesized via substitution and deprotection reaction.•COS-O-Ger was characterized by FT-IR, NMR, TGA, UV–vis, etc.•COS-O-Ger exhibited a good solubility and antibacterial properties.The novel derivatives of geraniol grafted chitosan oligosaccharide were synthesized via substitution and deprotection reaction, respectively. The products were identified by Fourier transform infrared (FT-IR), 1H nuclear magnetic resonance (NMR), X-ray diffraction analysis (XRD), Thermogravimetric analysis (TGA) and UV–vis absorption spectroscopy. It is revealed that the derivatives exhibited a good solubility, thermal stability and antibacterial properties.

Previous studies verified the protective effects of fish lipids against diseases caused by oxidative damage. Fish brains are rich in lipids. However, the actions and mechanisms of fish brain lipids on potent antioxidant activities remain unclear. In this study, total lipids (TLs) extracted from silver-carp brain were separated into neutral lipids (NLs) and polar lipids (PLs), and the protective roles of lipid fractions (LFs) against H2O2-induced oxidative damage were examined in a human embryonic kidney 293 (HEK-293) cell line. LFs effectively resisted H2O2-induced oxidative injury in HEK-293 cells by reducing cellular reactive oxygen species levels, protecting cellular antioxidant enzyme systems, inhibiting cell apoptosis and necrosis, and diminishing loss of mitochondrial-membrane potential. Among the TLs, PLs surpassed NLs in conferring antioxidant activities. The present study may help to explain the protective role of fish lipids against diseases caused by oxidative damage and promote fish-brain-derived lipids as potential preventive and therapeutic agents for human health.

•The roles of different proteases during fast fish fermentation were determined.•Lactobacillus plantarum from fish had low proteinase activities.•Gel strength was mainly weakened by endogenous lysosomal proteases.•Lactobacillus plantarum led to pleasant taste and volatile compounds precursors.The study was aimed to investigate different roles of endogenous and Lactobacillus plantarum proteases during fast fermentation of silver carp. The results show that endogenous proteases could degrade both sarcoplasmic and myofibrillar proteins. In contrast, L. plantarum had low proteinase activities and could only hydrolyze sarcoplasmic peptides. This indicates that gel properties could be mainly affected by endogenous proteolysis while microbial proteolysis contributed to the production of smaller peptides and free amino acids which may be related to flavor and taste. Texture and free amino acid analyses verified these hypotheses. It shows that endogenous lysosomal proteases were the major contributors for the decrease of gel strength while L. plantarum proteolytic activities could lead to the increase of aspartic acid, glutamic acid, and alanine, which may result in umami and sweet taste; and also lead to a rise in some amino acids which were volatile compounds precursors.

•Endogenous proteolytic activities in a fermented cod product were investigated.•Effect of endogenous proteases on proteins at different pHs was investigated.•Effect of proteases on gel strength in fermentation and storage was investigated.•Cathepsin B showed the highest activities during fermentation and storage.•The product showed a firm texture despite high catheptic activities.The aim of this study was to investigate endogenous proteolytic activities in a cod product and their impact on muscle proteins and textural properties during fermentation and storage. The result of specific proteolytic activities showed that cathepsins, especially cathepsin B, had the highest activities during fermentation and storage. SDS–PAGE indicated more degradation of myofibrillar proteins by cathepsin L than other proteases and that the hydrolysis by cathepsins was pronounced in the last stage of fermentation. Texture analysis showed that cathepsins had a negative impact on gel strength and this impact increased in the last stage of fermentation. However the product still had a firm texture. During storage (4 °C) for one week, no significant changes were seen in the gel strength. In conclusion, cathepsins had more impact on muscle proteins and textural properties than other proteases during fermentation but had little impact on gel strength during storage at 4 °C.

In this paper, a novel chitosan oligosaccharides derivative—chitosan oligosaccharides–kojic acid graft copolymer (COS/KA), COS, and KA were selected to investigate the binding to bovine serum albumin (BSA) using UV–Vis spectroscopy, fluorescence, synchronous fluorescence, and circular dichroism (CD) at pH 7.4. The results indicated that the tryptophan residues of BSA to the distance of COS/KA, COS, and KA were <8 nm, the quenching constants K0 were decreased, and the value of Kq were much >2.0 × 1010 L mol−1 s−1 for COS/KA–BSA, COS–BSA, and KA–BSA at 298, 302, 306, 310 K, respectively, those confirmed that the quenching process belongs to static quenching. The thermodynamic parameters ∆H°, ΔG°, ΔS° at different temperatures were calculated and indicated that hydrophobic and electrostatic forces played important roles in the binding process, and the enhanced binding affinity mainly associated with the increase of the hydrophobicity. Moreover, the CD data demonstrated that the secondary structure of BSA was slightly altered in the presence of COS/KA, COS, and KA, with different reduced α-helix contents (46.30 ± 0.20, 48.60 ± 0.40, 50.70 ± 0.20), respectively. The work provides basic data for the binding mechanism of COS/KA with BSA in vitro.

Cysteine cathepsin-associated degradation of muscle proteins have been assumed to be crucial to the softening of chilled fillet. The effect of aqueous extract of Alliums on cathepsin-induced proteolysis and texture deterioration of ice-stored carp fillets was evaluated. Among all treatments, extracts of scallion and garlic were the most effective inhibitor of cathepsin B, reducing the enzyme activity by more than 40 % after storage of 3 days, whereas extracts of scallion and leek had the greatest inhibitory effects on the cathepsin L activity, resulting in corresponding reduction in enzyme activity of 65 and 57 %, respectively. Extracts of scallion and garlic were the most effective treatments in impeding accumulation of TCA-soluble peptides and breakdown of myofibrillar proteins as validated by SDS-PAGE pattern. After storage of 21 days, the shear force of fillets treated with scallion and garlic extracts were approximately 30 % higher than those of control, whereas the treatments with other Allium extracts showed no inhibitory effect on textural deterioration. The results demonstrated that the treatment of grass carp fillets with extract of scallion and garlic has the potential to mitigate the endogenous cathepsin-induced softening of ice-stored grass carp fillets.

A novel water-soluble chitosan oligosaccharide (COS) derivative, chitosan oligosaccharide/kojic acid grafts assigned as COS/KA, was prepared by using the selective partial alkylation of N-benzylidene COS and chlorokojic acid in the presence of dimethyl sulfoxide (DMSO) and pyridine (Py). The derivative was characterized by UV–vis spectroscopy, FTIR, 1H NMR, TGA, SEM, and XRD techniques, which showed that the alkylation reaction took place at the C-6 and C-3 positions of COS. The results showed that the degree of substitution (DS) for COS/KA was from 0.38 to 1.21, and the product exhibited an excellent solubility in organic solvents and distilled water. The antibacterial results indicated that the antibacterial activity of COS/KA was strengthened relative to COS with the increase of DS for Staphylococcus aureus, Escherichia coli, Aspergillus niger and Saccharomyces cerevisiae. These findings provide important supports for developing new antibacterial agents and expand the scope of application of COS in the food industry.

The physicochemical and functional properties of seinat seed flour (SSF), defatted seinat flour (DSSF), and protein isolates were studied. Protein was extracted from DSSF using an alkali solution with isoelectric precipitation and freeze drying. Freeze dried seinat seed protein isolates (FSSPI), SSF, and DSSF were evaluated for their physicochemical and functional properties. SSF contained high levels of crude fat and fiber (31.13% and 24.75%, respectively). FSSPI contained 91.83% protein versus 28.58% for SSF. The amounts of potassium, the mineral with the highest content, were 9,548.33, 6,439.03, and 1,029 mg/100 g in SSF, DSSF, and FSSPI, respectively. The functional properties were variable among samples. The protein solubility of FSSPI was significantly higher (p<0.05) than for DSSF and SSF. FSSPI has a significantly better (p<0.05) foaming capacity, water/fat absorption capacity, and bulk density than SSF and DSSF. FSSPI also showed an emulsifying capacity comparable to commercial soy protein isolates.

•Effects of HPLC and VSP methods on ACE-inhibition assay were compared.•The HPLC method exhibits higher precision and reproducibility than VSP.•VSP provides a simplistic and rapid mean for the chemical analysis.The linearity, precision and repeatability of visible spectrophotometric (VSP) and high-performance liquid chromatography (HPLC) methods for analysis of inhibitory activity of angiotensin I-converting enzyme (ACE) were compared by using several inhibitors and Hip-His-Leu (HHL) as substrates. IC50 values (concentration at which ACE activity is inhibited by 50%) of 0.00206 ± 0.00005 μg/mL for captopril, 192 ± 4.53 μg/mL for soybean peptides, and 153 ± 4.29 μg/mL for grass carp peptides determined by the VSP method, and these values were 1.07, 1.07, 1.18 and 1.44-fold, respectively, higher than those from the HPLC method. In addition, the inhibitory constant (Ki value) of captopril was determined to be 7.09 nM and 4.94 nM using VSP and HPLC method, respectively. These results showed that the HPLC method revealed a higher level of sensitivity and precision, suitable for assaying ACE inhibition activity of antihyper-sensitive peptides. In contrast, the VSP method can simultaneously measure several samples with simple operations, suitable for analysis of ACE inhibition activity of food protein enzymatic hydrolysates.

The hypolipidemic activities of high and low molecular weights of chitosan nanopowders (HMW-chitosan-NP: 315 kDa; LMW-chitosan-NP: 51 kDa) prepared by ultrafine milling were evaluated in rats. The results showed that the hypolipidemic activity of chitosan nanopowder was better than ordinary chitosan, and LMW-chitosan-NP was superior to HMW-chitosan-NP in hypolipidimic activity. Compared with ordinary chitosan, chitosan nanopowder increased the fecal lipids and the activities of serum and liver lipoprotein lipase (LPL) and hepatic lipase (HL) of rats. Rats receiving LMW-chitosan-NP excreted less lipids in feces, but showed higher serum and liver LPL and HL activities compared with those fed HMW-chitosan-NP. These results suggested that compared with ordinary chitosan, the increased hypolipidemic activity of chitosan nanopowder might be attributed to its ability on increasing fecal lipid excretions and stimulating LPL and HL activities, and the better stimulation of LMW-chitosan-NP in activities of these lipases might help it to exceed HMW-chitosan-NP in hypolipidemic activity.Highlights► The hypolipidemic activities of two chitosan nanopowders were studied in rats. ► Chitosan nanopowder showed better hypolipidemic activity than ordinary chitosan. ► The 51.4-kDa nanopowder was superior to 315.2-kDa nanopowder in hypolipidemic activity. ► The hypolipidemic mechanism of chitosan nanopowder was studied.

Acid hydrolysis and subsequent quantification of glucosamine (GlcN) are widely used for chitosan quantification. Degradation of GlcN during chitosan hydrolysis was the main reason for the decrease of recovery, which made the method improper for the quantification of chitosan. Ten milligram of chitosan hydrolyzed with 10 mL mixed acid solution of HCl–H3PO4 (75:25 in molar ratio) showed the highest recovery, significantly higher than HCl hydrolysis. Further study revealed that the optimum conditions involved the hydrolysis with HCl–H3PO4 (4.5:1.5 M) for 24 h at 110 °C. The hydrolysate was neutralized and derived with 9-fluorenylmethoxycarbonyl chloride (FMOC-Cl) before HPLC quantification. The optimum ratio of FMOC-Cl:GlcN was 53:1, with excess FMOC-Cl induced by the high ionic strength of the solution. This quantification procedure was then validated and proved to be specific, with good linearity, accuracy, and precision, making it well-suited for the determination of chitosan.Graphical abstractHighlights► HCl–H3PO4 (75:25 in molar ratio) showed higher recovery of chitosan than HCl hydrolysis. ► Hydrolysis with HCl–H3PO4 (4.5:1.5 M) for 24 h at 110 °C showed highest recovery for chitosan hydrolysis. ► In high ionic strength solution, optimum FMOC-Cl:GlcN ratio increased to 53:1 for GlcN derivation. ► The modified method improved the recovery from about 90% to 97.7% for the determination of chitosan.

Large amounts of utilizable by-products are produced concomitant with silver carp processing. The lipids from fish brain contain considerable essential fatty acids which however have seldom been studied. In this study, the lipids extracted from the brain of silver carp exhibited good physicochemical properties. Forty volatile compounds were identified, of which hydrocarbons and aromatics predominated. The ratios of polar lipids and phospholipids to total lipids were 22.73 and 10.95 % respectively. Phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylserine (PS) accounted for 83.9 % of the phospholipids. Major fatty acids of neutral lipids, polar lipids, PC, PE and PS differed significantly. PE had the most polyunsaturated fatty acids (PUFA), while PC, PE and PS were rich in docosahexaenoic and eicosapentaenoic acids. Moreover, the ratios of fatty acids were considered to be reasonable due to high levels of n3 PUFA. The lipids from silver carp brain have been demonstrated to be healthy and nutritious. The results herein confirm that silver carp brain lipids are a commercially and industrially feasible prospect.

The structural changes and aggregation properties of silver carp actomyosin acidified with d-gluconic acid-δ-lactone (GDL) were investigated. Results showed that silver carp actomyosin underwent aggregation and formation of precipitate as indicated by turbidity and centrifugation coupled electrophoresis analysis. Circular dichroism indicated that myosin rod unfolded during acidification, resulting in a gradual decrease in α-helical content. The changes in tertiary structure of actomyosin under acidic conditions were demonstrated by second-derivative UV spectra and intrinsic fluorescence. Tyrosine residues were exposed to the surface of proteins when pH was decreased to 5.5, and were buried inside the protein aggregates with further reduction in pH. In contrast, more tryptophan residues were exposed to the polar environment with decreasing pH. 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide crosslinking experiments showed that the intensity of myosin heavy chain (MHC) bands decreased sharply with decreasing pH and the actin bands decreased more slowly, suggesting that MHC is the major protein component involved in the non-covalent cross-linking and formation of aggregates during acidification of silver carp actomyosin.Highlights► Acid-induced aggregation and structural changes of actomyosin were investigated. ► Secondary and tertiary structure of actomyosin changed rapidly under acidic conditions. ► Aggregation occurred prior to completion of denaturation process during acidification. ► Myosin heavy chain was the major protein involved in non-covalent cross-linking and acid-induced aggregation.

The residual proteins in commercially available chitosan products potentially induce immunological responses, thus compromising their clinical usage. Conventional deproteinization processes use diluted base and heat. However this heterogeneous hydrolysis is inefficient. In the present study, pepsin was selected and immobilized with tetramethoxysilane (TMOS) and 3-aminopropyltriethoxysilane (APTES). The immobilized pepsin was utilized in an alternative approach for the purification of chitosan. Optimum deproteinization was carried out at pH 4.5 and 45 °C. Amino acid analysis proved a removal of 53.8–80.4% protein in chitosan after 160 min incubation, which was more efficient than conventional sodium hydroxide deproteinization. When chitosan was deproteinizated by immobilized pepsin, its molecular weight decreased, but in a much milder manner than the free pepsin. The study revealed that immobilized pepsin was an efficient method for deproteinizing chitosan.Highlights► Pepsin was immobilized and was used for deproteinization of chitosan. ► Optimum deproteinization was carried out at pH 4.5 and 45 °C. ► Protein removal more effective than NaOH deproteinization. ► The decrease of molecular weight was much milder than free pepsin.

Two different molecular weights of chitosan were pulverized to nanopowders by ultrafine milling. The nanopowders were characterized by viscometry small angle X-ray scattering (SAXS), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), FT-IR spectroscopy and UV–vis spectroscopy. Our results showed that ultrafine milling effectively reduced the particle size of chitosan to a nanoscale. The viscosity average molecular weight (Mv) of chitosan was decreased by the milling treatment. The crystalline structure of chitosan was destroyed by the milling since the nanopowder exhibited an amorphous XRD pattern. In addition, thermal stability of the low molecular weight chitosan was decreased after the milling treatment. FT-IR and UV–vis spectra showed that the milling process did not cause significant changes in the chemical structure of chitosan.Highlights► The chitosan nanopowder was prepared by ultrafine milling. ► Some physicochemical properties of chitosan changed during the milling process. ► The milling did not cause great change in chemical structure of chitosan.

The physicofunctional and chemical properties of acid-aided protein isolate (AcPi), alkaline-aided protein isolate (AlPi) and soy protein isolate (SPI) prepared from tilapia muscle and defatted soy flour as a function of pH and/or NaCl concentration were investigated. Both acid- and alkali-aided processes lead to significant recoveries (P < 0.05) of proteins with substantial reduction of lipids in AlPi (0.81%) and AcPi (0.96%), the lowest for SPI (0.336%) facilitated by the processing method and sample used. There is greater lipid reduction at alkali pH, effective removal of impurities such as bones and scales, indicated by percentage ash (AcPi, 4.53%; AlPi, 3.75% and SPI, 3.51%). No major difference noted in sodium dodecyl sulphate polyacrylamide gel electrophoresis protein bands (14.4–97.4 kDa) possibly representing partial hydrolysis of myosin. Solubility was the highest at pH 3.0 and 11.0 and the lowest at isoelectric point with foam capacity showing similarity at varying pH. The addition of NaCl improved foam stability, possibly due to the increased solubility and surface activity of the soluble protein. On the whole, AcPi, AlPi and SPI manifested lower solubility and foamability at pH 4.0 and 5.0. AlPi exhibited appreciable levels of solubility, emulsion capacity, oil-holding capacity, viscosity and whiteness, whereas SPI had appreciable water-holding capacity. AcPi, AlPi and SPI have excellent relevance for product development based on their functionality.

A novel water-soluble chitosan derivative, O-fumaryl-chitosan (OFCS), was prepared by using the selective partial acylation of chitosan and fumaric acid in the presence of H2SO4. The chemical structure and physical properties of OFCS were characterized by FTIR, 1H NMR, 13C NMR, and TG techniques. Our results showed that the degree of substitution (DS) for the chitosan derivatives was from 0.07 to 0.48 and the prepared derivatives had good solubility over a wide pH range, for example, the solubility of OFCS increased from 10.5 to 52.6 mg/ml as the DS increased. The antibacterial activity of chitosan and OFCS was investigated against Escherichia coli and Staphylococcus aureus. The results indicated that the antibacterial activity of OFCS was much stronger than that of chitosan and it increased with increasing DS increasing. These findings suggest that the OFCS with a DS of 0.48 is preferable for use as a food preservative.

The effect of fermentation with Pediococcus pentosaceus at different temperatures ranging from 15 to 37 °C on the quality characteristics of silver carp sausages was investigated. Higher temperature stimulated the rapid growth of lactic acid bacteria, resulting in a rapid decline in pH, and consequently suppressed the growth of Pseudomonas, Micrococcaceae and Enterobacteriaceae. However, increasing fermentation temperature gave a progressive increase in total volatile basic nitrogen and biogenic amines in fermented silver carp sausages. Histamine was the main biogenic amine, exceeding 100 mg/kg after 48 h of fermentation at temperatures above 30 °C. Higher content of non-protein nitrogen and α-amino nitrogen correlated with the electrophoretic studies, which showed that proteolysis of high molecular weight myofibrillar and sarcoplasmic proteins was more prominent at higher fermentation temperatures. Products fermented at 23–30 °C showed greatest consumer preference and most favourable textural properties.

Chitosans (CHI) with different degree of deacetylation (DD) (60.5%, 65.4%, 70.8%, 77.3%, 86.1%) and different molecular weight (MW) (299, 410, 600, 706, 880 kDa) were obtained. Heat-induced composite gels were prepared from 4% salt-soluble meat proteins (SSMP) with chitosans at 0.6 mol/L NaCl, pH 7.0. Penetration forces and storage modulus of SSMP–CHI composite gels increased proportionally with increasing amount of molecular weight. Gel containing chitosan with DD 77.3% exhibited the highest penetration force and storage modulus. The SEM observations showed that SSMP–CHI incorporated gels were compact and fine compared with that of SSMP. Chemical forces involved in SSMP–CHI composite gels were investigated by determining the effects of NaCl, urea, propylene glycol, and 2-MeSH on penetration forces. Results of these studies demonstrated that interaction between CHI and SSMP contributed to the enhancement of texture of the SSMP–CHI composite gels by electrostatic interactions and hydrogen bonds.

The types of interactions and the proteins involved in the formation of gel network of fermented silver carp mince were investigated. Results showed that the amount of each type of protein interactions varied significantly depending on fermentation time. The content of sulphydryl groups decreased continually with a concomitant increase in disulphide bonds during fermentation. The higher gel strength and more compact fibrous network of fermented silver carp mince corresponded to a higher percentage of hydrophobic interactions, disulphide bonds and non-disulphide covalent bonds. SDS–PAGE showed that the major myofibrillar proteins, particularly myosin heavy chain were involved in the formation of aggregates through hydrophobic interactions and disulphide bonds during fermentation. Furthermore, low molecular weight proteins probably produced by proteolysis were also involved in the formation of gel matrix.

Changes in protein composition and physicochemical properties of silver carp sausages during fermentation were investigated. As fermentation progressed, the amount of salt-soluble and water-soluble proteins decreased gradually with a concomitant increase in insoluble proteins and non-protein constituents. The rapid reduction in pH to 4.5 within 48 h of fermentation coincided with a progressive increase in titratable acidity. The increasing content of TCA-soluble peptides during fermentation indicated intensive degradation of muscle proteins. SDS–PAGE showed that muscle proteins tended to aggregate into large polymers through disulphide bonds and non-disulphide covalent bonds during fermentation, which may be responsible for the formation of superior textural properties of silver carp sausages.

An exo-β-d-glucosaminidase gene was cloned from Aspergillus sp. CJ22-326 and expressed in Escherichia coli. The purified protein showed an exo-chitosanase activity in a viscosimetric assay and TLC analysis. This is the first report on cloning of a gene encoding an Aspergillus sp. exo-β-d-glucosaminidase.The cDNA encoding exo-β-d-glucosaminidase from Aspergillus sp. CJ22-326 was cloned, expressed and its product was purified from Escherichia coli. This is the first report on cloning of the gene encoding Aspergillus sp. exo-β-d-glucosaminidase.

A chitosanolytic enzyme without lipolytic activity was purified to apparent homogeneity from a commercial lipase preparation by using a combination of DEAE-Sepharose CL-6B exchange chromatography, Phenyl-Sepharose CL-4B hydrophobic interaction chromatography, and Sephacryl S-200 gel filtration chromatography, and the purified enzyme was characterized. The molecular mass of the homodimeric protein was about 130 kDa. The optimum action temperature and pH of the enzyme on chitosan were 60 °C and 4.6–4.8, respectively, and the enzyme was stable at temperatures lower than 60 °C and at pH 4–9. The purified enzyme exhibited the highest activity toward chitosan which was 73–82% deacetylated. TLC analysis shows that the purified enzyme released glucosamine residues successively from the substrates and final hydrolysis products of both chitosan tetramer and pentamer were glucosamine, indicating that the enzyme exhibited exo-β-d-glucosaminidase activity.

The effect of a commercial lipase on chitosan degradation was investigated. When four chitosans with various degrees of deacetylation were used as substrates, the lipase showed higher optimal pH toward chitosan with higher DD (degree of deacetylation). The optimal temperature of the lipase was 55 °C for all chitosans. The enzyme exhibited higher activity to chitosans which were 82.8% and 73.2% deacetylated. Kinetics experiments show that chitosans with DD of 82.8% and 73.2% which resulted in lower Km values had stronger affinity for the lipase. The chitosan hydrolysis carried out at 37 °C produced larger quantity of COS (chitooligosaccharides) than that at 55 °C when the reaction time was longer than 6 h, and COS yield of 24 h hydrolysis at 37 °C was 93.8%. Products analysis results demonstrate that the enzyme produced glucosamine and chitooligosaccharides with DP (degree of polymerization) of 2–6 and above, and it acted on chitosan in both exo- and endo-hydrolytic manner.

An endo-chitosanase gene was cloned from Aspergillus sp. CJ22-326 and expressed in Escherichia coli. The purified protein showed an endo-chitosanase activity during viscosimetric assay and TLC analysis. The enzyme had higher chitosanolytic activity than previously reported fungal chitosanases.The cDNA encoding endo-chitosanase from Aspergillus sp. CJ22-326 was cloned, expressed and its product was purified from E.coli. Chitosanase activity of the recombinant protein was much higher than other heterologous expression fungal proteins.

The hypolipidemic mechanism of chitosan was investigated in male Sprague-Dawley rats. Animals were divided into 5 groups (n = 8): a normal fat control group, a high-fat control group (HF), a positive control group (CR), and 2 chitosan groups (CIS1 and CIS2). Chitosan was fed at the beginning (CIS1) and after 2 weeks (CIS2). A commercial diet with 5% (wt/wt) cellulose (HF), cholestyramine (CR), or chitosan (CIS1, CIS2) was fed for 6 weeks. Chitosan did not affect food intake but decreased body weight gain and significantly increased fecal fat and cholesterol excretion, reduced the lipid level in plasma and liver, increased liver hepatic and lipoprotein lipase activities compared with HF (P < .05), and tended to relieve the degenerated fatty liver tissue. No significant differences in all measurements were found between the CIS1 and CIS2 groups although the CIS1 rats exhibited lower lipid levels compared to those in the CIS2 group. The results suggest that chitosan reduced the absorption of dietary fat and cholesterol in vivo and could effectively improve hypercholesterolemia in rats.

In this paper, the operating parameters of spray drying after a series of pre-processing were investigated and the properties and qualities of the freshwater mussel meat (FMM) powder were also analyzed. The considerable optimum conditions of spray drying were as follows: the inlet and outlet air temperature of the both deodorization were 180 °C and 80 °C, respectively; the optimum feed concentration for composite deodorization (CD) FMM powder was 30%, and for stewing deodorization (SD) FMM powder 27%; on top of all that, the feed temperature was 50 °C, 45 °C, respectively. In the later analysis, FMM powder was shown to be rich in protein and glycogen, up to 52.7%, 27.71% and 53.4%, 27.69%; meanwhile both the contents of essential amino acids (EAAs) in FMM powders were as high as 44%, which were close to the pattern of FAO/WHO. Thus the FMM powder of the both kinds, namely CD and SD FMM, were thought to be acceptably edible resources with high nutrition for human.Highlights► Mass of by-products from freshwater mussel by was taken use effectively. ► Viscosity was taken to optimize the feed temperature. ► The parameters of spray-drying on all meat of aquatic product was studied. ► The quality of FMM powder was analyzed in detail. ► The results showed that the powder was good food ingredients with high nutrition.

Peptides inhibiting angiotensin-I converting enzyme (ACE, EC. 3.4.15.1) are possible cures of hypertension. Food-derived ACE-inhibitory peptides are particularly attractive because of reduced side effects. Previously, we reported ACE-inhibitory activity of grass carp protein hydrolysates. In this work, we report steps for purifying the ACE-inhibitory peptide from the hydrolysate and its biochemical properties. Following steps of ultrafiltration, macroporous adsorption resin, and two steps of reversed phase high performance liquid chromatography (RE-HPLC), a single Val-Ala-Pro (VAP) tripeptide was identified. The tripeptide with excellent ACE-inhibitory activity (IC50 value of 0.00534 mg/mL) was a competitive ACE inhibitor and stable against both ACE and gastrointestinal enzymes of pepsin and chymotrypsin. This is the first report of food-derived VAP. The identified unique biochemical properties of VAP may enable the application of grass carp protein hydrolysates as a functional food for treatments of hypertension. The developed purification conditions also allow the production of VAP for pharmaceutical applications.Highlights► The first report of food-derived Val-Ala-Pro (VAP) tripeptide. ► Excellent ACE-inhibitory activity of VAP (IC50 value of 0.00534 mg/mL). ► VAP is a competitive ACE inhibitor. ► VAP is stable against ACE and digestive enzymes. ► Purification of VAP from hydrolysate of grass carp protein was achieved.

•Preservation effects of chitosan coating with different concentrations of glycerol monolaurate are researched.•Chitosan enriched glycerol monolaurate coating presents better preservation than chitosan coating alone.•Chitosan with 0.3% glycerol monolaurate extends the shelf life of approximately 8 days for refrigerated grass carp fillets.A novel chitosan-based coating solution was prepared by combining glycerol monolaurate (GML) for shelf life extension of refrigerated grass carp fillets. The control and coated fillets were analyzed periodically for physicochemical (pH, thiobarbituric acid (TBA) value, total volatile basic nitrogen (TVB-N) value, K value, and shear force), microbiological (total viable counts (TVC), psychrophilic bacteria counts (PTC), Pseudomonads and H2S-producing bacteria) and sensorial characteristics. The results showed that chitosan-GML coated samples presented better quality preservation effects than chitosan coating alone. In addition, 2% chitosan enriched with 0.3% GML showed the significant (P < 0.05) effectiveness in inhibiting microbial growth, nucleotide breakdown, the formation of alkaline components and texture deterioration, and maintaining sensory acceptability among the groups. These findings confirmed that chitosan coating enriched with GML was a promising method to extend the shelf life of refrigerated fillets.