Purification of Antimicrobial Peptide from Antarctic Krill (Euphausia superba) and its Function Mechanism

The preliminary purification and antimicrobial mechanism of antimicrobial peptide from Antarctic Krill were studied in this paper.The results showed that the molecular weight range of antimicrobial polypeptide(CMCC-1) obtained by cation exchange chromatography was between 245-709D as detected by molecular sieve chromatography,and the minimum inhibition concentration(MIC) of CMCC-1 against Staphylococcus aureus was 5.0 mg mL-1.The antimicrobial mechanism of CMCC-1 was studied with S.aureus as indicator bacterium.Compared with control group,the results of the experimental group in which S.aureus was treated with CMCC-1 were as follows: 1) CMCC-1 could inhibit cell division at logarithmic phase.2) The protein and reducing sugar content,and the conductivity of culture medium increased,and the activity of alkaline phosphatase and β-galactosidase could be detected in the culture medium.3) Observation under scanning electron microscope revealed that somatic morphology became irregular,and then somatic surface became coarse.The cell became much smaller,and most somatic cells gathered.The boundary between cells became dim and finally fused as a whole.4) Observation under transmission electron microscope showed that the surface of S.aureus became rough and the reproducing ability was restrained.The cell wall became thin and the cytoplasm shrunk.Substances inside cell leaked out,which caused cells death.5) SDS-PAGE analysis showed that some bands disappeared,and the residual bands became vague.6) The genomic DNA electrophoresis results showed that the genomic DNA bands of S.aureus were not degraded but the brightness significantly reduced.Thus,it is supposed that CMCC-1 could destroy the cell wall and membrane of S.aureu,increase the cell membrane permeability and the leaking-out of intracellular substances,and thus cause the death of S.aureu.

High Pressure Treatment Changes Spoilage Characteristics and Shelf Life of Pacific Oysters(Crassostrea gigas)During Refrigerated Storage

The effects of high pressure(HP) treatment on spoilage characteristic and shelf life extension of Pacific oysters(Crassostrea gigas) during refrigerated storage were studied.Results showed that HP treatment of 275 MPa for 3 min or 300 MPa for 2 min could achieve 100% full release of oyster adductor muscle,pressures higher than 350 MPa caused excessive release as the shells of oysters were broken,thus use of higher pressures should be cautious in oyster processing industry because of its adverse impact on the appearance of shells.HP treatment(300 MPa,2 min) was proper for the shucking of Pacific oyster(Crassostrea gigas) in China.This treatment caused no organoleptic disadvantage.Moreover,HP treatment resulted in obvious differences in biochemical spoilage indicators(p H,TVB-N and TBARS) changes and volatile compounds profile determined by electronic nose during storage.HP treatment(300 MPa,2 min) also led to a reduction of aerobic bacterial count(APC) by 1.27 log cycles.Furthermore,the APC values of oysters treated by HP were always lower than those of the control samples during storage.Based on the organoleptic,biochemical and microbiological indicators,shelf life of 6-8 d for control and 12 d for HP-treated oysters could be expected.HP treatment showed great potential in oyster processing and preservation.

Immobilization of Chitosanase on Magnetic Nanoparticles: Preparation, Characterization and Properties

Chitosanase could cleaveβ-1,4-linkage of chitosan to produce chitooligosaccharides(COS)with diverse biological activities.However,there are many limitations on the use of free chitosanase in industrial production.Enzyme immobilization is generally considered a valuable strategy in industrial-scale applications.In this study,the chitosanase Csn-BAC from Bacillus sp.MD-5 was immobilized on Fe_(3)O_(4)-SiO_(2) magnetic nanoparticles(MNPs)to enhance its properties,which could be recovered easily from reaction media using magnetic separation.The activities of Csn-BAC immobilized with MNPs(MNPs@Csn-BAC)were de-termined with temperature and pH,and the thermal-and pH-stabilities,respectively.The reusability of the MNPs@Csn-BAC was determined in repeated reaction cycles.Immobilization enhanced the thermal and pH stability of Csn-BAC compared with the free enzyme.After eight reaction cycles using MNPs@Csn-BAC,the residual enzyme activity was 72.15%.Finally,the amount of COS released by MNPs@Csn-BAC was 1.86 times higher than that of the free Csn-BAC in the catalytic performance experiment.The immobilized Csn-BAC exhibits broad application prospects in the production of COS.

Chitosan Extends the Shelf-life of Filleted Tilapia (Oreochromis niloticus) During Refrigerated Storage

Shelf-life extension of aquatic products is of significant economical importance. To determine the potential effect of chitosan on the shelf-life of filleted tilapia, this study analyzed the bacterial community diversity in fresh and spoiled tilapia fillets stored at (4 ± 1)℃ and examined the antimicrobial activity of chitosan against relevant bacteria isolates. Results showed that Pseudomonas (20%) and Aeromonas (16%) were abundant in fresh tilapia fillets, whereas Pseudomonas (52%), Aeromonas (32%) and Staphylococcus (12%) were dominant in the spoiled samples. Chitosan showed wide-spectrum antibacterial activity against bacteria isolated from tilapia and 5.0 g L-1 chitosan was selected for application in preservation. We further determined the shelf-life of chitosan-treated, filleted tilapia stored at (4 ± 1)℃ based on microbiological, biochemical and sensory analyses. Results showed that the shelf-life of chitosan-treated, filleted tilapia was extended to 12 d, whereas that of untreated, control samples was 6 d. These indicate that chitosan, as a natural preservative, has great application potential in the shelf-life extension of tilapia fillets.

Application of Lactic Acid Bacteria(LAB) in Freshness Keeping of Tilapia Fillets as Sashimi

Aquatic products are extremely perishable food commodities. Developing methods to keep the freshness of fish represents a major task of the fishery processing industry. Application of Lactic Acid Bacteria(LAB) as food preservative is a novel approach. In the present study, the possibility of using lactic acid bacteria in freshness keeping of tilapia fillets as sashimi was examined. Fish fillets were dipped in Lactobacillus plantarum 1.19(obtained from China General Microbiological Culture Collection Center) suspension as LAB-treated group. Changes in K-value, APC, sensory properties and microbial flora were analyzed. Results showed that LAB treatment slowed the increase of K-value and APC in the earlier storage, and caused a smooth decrease in sensory score. Gram-negative bacteria dominated during refrigerated storage, with Pseudomonas and Aeromonas being relatively abundant. Lactobacillus plantarum 1.19 had no obvious inhibitory effect against these Gram-negatives. However, Lactobacillus plantarum 1.19 changed the composition of Gram-positive bacteria. No Micrococcus were detected and the proportion of Staphylococcus decreased in the spoiled LAB-treated samples. The period that tilapia fillets could be used as sashimi material extended from 24 h to 48 h after LAB treatment. The potential of using LAB in sashimi processing was confirmed.

Comparative Study on Antineoplastic Activity of Polysaccharide from Four Kinds of Sea Cucumber

The antineoplastic activity of polysaccharide was investigated in Stichopus chlorontus, Isostichopus badionotus, Stichopus horrens and Holothuria lessoni massin. Crude polysaccharide was prepared with enzyme hydrolyzation method and purified by anion exchange chromatography using DEAE-sepharose fast flow column. The effect of polysaccharide on cells apoptosis of SiHa and U87 was examined with cell counting kit-8 colorimetry method. Western blotting was used to analyze related proteins of cellular apoptosis including p53 and Bcl-2. Results showed that there were two main components in each sea cucumber polysaccharide, which could be eluted down by 1.0 mol/LNaCl solution. The four types of polysaccharide in the second component were named as SC-2, IB-2, HLM-2 and SH-2, respectively. They were used for comparing the antineoplastic activity. Results showed that SC-2, IB-2, HLM-2 and SH-2 could promote apoptosis of U87 and SiHa cells. SH-2 and HLM-2 were selected for the subsequent experiment to explore the additional effect of U87 and SiHa cells, The protein expressions of Bcl-2 and p53 decreased considerably with the increase of polysaccharide concentration in U87 cells. In SiHa cells, protein expressions of Bcl-2 and high dosage group of p53 decreased significantly, whereas no obvious decrease was observed in other groups. The polysaccharides are more effective in promoting apoptosis of U87 and SiHa cells from S. horrens and H. lessoni massin than from the rest species.

Action Mechanism of Antibacterial Hydrolysate from Ruditapes philippinarum

[Objectives] The antibacterial mechanism of protein hydrolysate from Ruditapes philippinarum（ named RPPH） was studied in this article. [Methods]The integrity of bacteria＇s wall and membrane was determined by some traditional ways. [Results]The growth of Staphylococcus aureus and Bacillus subtilis were inhibited by RPPH in the logarithmic phase. The activity of alkaline phosphatase could be detected in the culture solution. The results showed that the protein content and the conductivity of two kinds of bacteria increased with the extension of incubation time. The results of scanning electron microscope revealed that it emerged the phenomenon of agglomeration with the extension of response time in the culture solution of S. aureus,and the cell shape became irregular,a large number of cells stuck together,afterwards intracellular material was released from bacteria,and the boundaries among cells completely disappeared. The cell surface of B. subtilis became rough,the cells began to adhere,intercellular boundaries became blurred,subsequently cells broke,and then intracellular material leaked out after treating for 9 h. The form of B. subtilis could be roughly identified from the remnants of the bacterial debris,and most of the bacteria had been completely cracked and died. Transmission electron microscope results showed that the surface of S. aureus became rough,with uneven distribution of cytoplasm,and darker substances appeared in the middle,followed by leakage of large numbers of intracellular material. Massive cells became dead when treating for 9 h. B. subtilis cells began to shrink,and cytoplasm was distributed unevenly. The significant phenomenon of plasmolysis and rupture of cell wall could be observed. Afterwards,intracellular material spilled out,only the residual and ambiguity nucleoplasm area could be seen,and cells were killed. [Conclusions] Therefore,it was speculated that the RPPH could destroy cell wall and membrane of the two kinds of bacteria,change the permeability of cells membrane,result in the leakage of intracellular substances and enter within the bacterial cells to affect their normal physiological metabolism which led to death.

Coconut Press Cake Alkaline Extract—Protein Solubility and Emulsification Properties

The solubility and the emulsification properties of a crude freeze dried alkaline protein extract (APE), 30% protein, obtained from coconut milk press cake by one step extraction at pH 11, were characterized at pH 2 to 11, and the cream and subnatant fractions of the emulsion studied by SDS-PAGE electrophoresis. The protein solubility followed U profile, showing a minimum at pH 3 to 4, close to but not identical to reported iso-electric points of 4 - 5 for many coconut protein fractions. The extract showed good capacity to form oil-in-water emulsion outside the low solubility pH range. The bands that appeared to play a role in the emulsification were found at 32 and 42 kDa in SDS-PAGE electrophoresis, but the most predominant absorbed band was at 23 kDa.

Heat Induced Gels from Coconut Press Cake Proteins

Freeze-dried coconut press cake powder (CPP), 43% w/w protein, was used to investigate the heat-induced gelation by heating in rheometer to 75℃ in a wide range of pH values, from 4 to 9. Low strain oscillatory method applied the measure visco-elastic propertieson 15% w/w CPP. The gel strength was also assessed by a texture analyzer. SDS-PAGE electrophoresis was conducted to identify the proteins evolved in the gel network structure and the gel micro-structure was also evaluated. At low pH, the CPP proteins formed soft (elastic modulus <100 Pa) particulate gels prone to syneresis, with aggregate size of the order of 4.2 micrometers. In the alkaline region, homogenous gels were induced by heating. Gel strength started to increase dramatically from 64℃ to 67℃, for pH 9 and pH 8 respectively, reaching the maximum gel elastic modulus over 1000 Pa at pH 9. The SDS-PAGE showed that the polypeptide sub-unities at 24, 32 - 34 and 53 kDa were the most prominent in gelation.