Properties Of Bacteriophage Of Shewanella Putrefaciens And Its Application On Fresh Keeping Effects

Aquatic resources are very rich in China, which is one of the biggest countries inaquatic products farming and trading all over the world. With the development of theliving standard of the modern people, aquatic products have become more and morepopular because of their nutrition properties such as containing various protein andsmall account of fat. Hence, freshness, acting as one of the limiting factorsin aquaticproduction, is taken as priority when food safety is taken into consideration. Thegrowth and metabolism of microorganisms is the main reason of aquatic products’spoilage. Moreover, only some of the bacteria are responsible for food spoilage,which are specific spoilage organisms of aquatic products. Inhibiting specific spoilagebacteria growth can prevent aquatic products’ spoilage effectively.Bacteriophages are viruses that can infect bacterium. They are made up ofprotein coat and nucleic acid. They are strictly parasitic in their host bacterium.Bacteriophages are common and safe, and they have no side effects on people andenvironment. It is reported that bacteriophage has been used to preserve food.A strain of bacteriophage named Spp001was separated from environment andits properties were researched. The antibacterial activities of Spp001as well as theinfluences of physical and chemical factors on antibacterial activities were studied.And then, Spp001was applied to chilled Paralichthy solivaceus samples.Shewanella putrefaciens Sp225was used as host bacteria, Shewanellaputrefaciens bacteriophage Spp001was separated and purified using double-layerplate method. The purified phage had a good lytic ability and the plaque was clear andof equal size.The phage was identified as a kind of typical phage belonging toSiphoviridae whose nucleic acid was DNA. The phage is like a tadpole whose head isabout50nm and tail is about150nm. The MOI of the phage was10, and one-stepgrowth curve showed that the latent phase was10min, while the rise phase was20 min, withan average burst size of98.The antibacterial activities of Shewanella putrefaciens bacteriophage Spp001were studied. The growth of Shewanella putrefaciens were prevented by Spp001notonly in nutrient broth but also in fish matrix. In nutrient broth, the growth ofShewanella putrefaciens were completely prevented by Spp001whose concentrationwas higher than102pfu/mL. The slowly increasing OD600nmof matrix suggested thatShewanella putrefaciens is growing when the concentration of Spp001was lower than102pfu/mL.The antibacterial activity of Spp001was greatly affected by temperature, thesurvival rate of the phage was79.2%when it was under the condition of40℃for60min; when it was under the condition of60℃for60min,the phage concentration stillreached8.0×104pfu/mL; While the temperature was higher than70℃, the phagelost his activity. The antibacterial activity of Spp001was best at pH7, the phageconcentration was1.6×108pfu/mL; Spp001had good alkali resistance but poor acidresistance; at pH3, the phage has lost his activity. Spp001has a stronganti-inactivated ability to the chlorine-containing disinfectant-chloramines andsodium hypochlorite. The phage activities were only reduced about3%inchloramines of10mg/L-20mg/L, in1g/L-2g/L chloramines, phage activities werereduce about12.5%,12.5%of Spp001were inactivated by500mg/L-600mg/Lsodium hypochlorite,22.1%of Spp001were inactivated by5g/L-6g/L sodiumhypochlorite. The titer and antibacterial activity of phage were slightly decreased by3KGray electron beam irradiation, while the antibacterial activity of Spp001weresignificantly reduced by5KGray electron beam irradiation. When the irradiation dosewas greater than7KGray, there was no antibacterial activity.It was obvious that Spp001preventing bacterium and keeping fish fresh when itwas applied to chilled Paralichthy solivaceus samples. It was evident from thesensory analysis that the phage had a good effect on keeping fish fresh. The totalbacteria count and Shewanella putrefaciens count of the experimental group wassignificantly lower than that of the control group. What’s more, the count of theexperimental group of higher Spp001concentration were less than that of potassium sorbate solution experimental group， which was less than that of the lowerconcentration Spp001phage experimental group.The tendency of pH changing of theSpp001experimental groups and potassium sorbate experimental group were moregently than that of control group. TVBN of the experimental groups weresignificantly lower than that of the control group, and high concentration of phageexperimental groups and potassium sorbate experimental group were still less than30mg/100g on the fourteenth day. It was obvious that the phage Spp001could extendthe shelf life of chilled Paralichthy solivaceus.In summary, Spp001had a stable nature and a good antibacterial activity. And thecorrosion inhibition effect is evident when it was appiled in chilled Paralichthysolivaceus samples.