Screening And Application Of Lactic Acid Bacteria From Seafood

Nowadays, chemical preservatives have been rejected by consumers, due to a great concernon food safety issues arising from the residual toxicity. People are tending to prefer biologicalpreservatives, lactic acid bacteria and its fermentation product are usually considered as a moreadvantageous biological preservative, beeause of its broad spectrum, high efficiency, stability,safety, nontoxicity and strong inhibition against many pathogens and spoilage microorganismsfrom food.Lactic acid bacteria are generally considered as food-grade microorganisms, itsfermentation products such as organic acids, peroxide hydrogen and bacteriocin can slow downthe process of food spoilage by inhibiting the growth of spoilage bacteria and pathogens, andextend shelf life of food preservation. Therefore, screening of lactic acid bacteria withantimicrobial activity and using them in fish preservation are the content and purpose of thisstudy.In this study, we screened67strians from the seafood, and use five kinds of the mainspoilage bacterias, Escherichia coli, Pseudomonas fluorescens bacteria, Staphylococcus aureus,Salmonella, Bacillus subtilis as indicator bacteria.15of these strains showed strong inhibitoryeffects on the group of the indicator bacteria by using the double agar diffuse method. theinhibitory effects of WBL3and WBL4strians were the most significant, they could inhibit fivekinds of indicator bacteria. The strain was preliminary indentified as Lactococcus based on theanalysis of its physiological and biochemical characters.The WBL4strain and WBL4supernatant were co-cultured with the main spoilage bacteriaPseudomonas sp. from fish, respectively. By co-culturing, the number of Pseudomonas sp. canbe reduced by WBL4from1.12×10~8CFU/mL to1.44×10~6CFU/mL. In addition, WBL4supernatant can make Pseudomonas sp. count from1.32×10~8CFU/mL reduce to2.2×10~4CFU/mL, this two kinds of methods could both inhibit the growth of pseudomonas. The resultsshowed that WBL4strains has good antibacterial activity. When the supernatant of WBL4wastreated with proteinase K, the inhibition zone and the antibacterial activity disappeared indicatingthat WBL4maybe a bacteriocin-producting strain.Different concentrations of WBL4bacterial suspension were Sprayed on the fresh meat ofAmerica red fish (Sciaenops ocellafus), and the treated meat was storaged at4℃. At the sametime, we used different concentrations of lactate and Nisin preservative to treate the fish meat inthe same way as the control groups. We took sample every24h, and the freshness of sample was determined,using the following items as freshness indicators:volatile basic nitrogen (TVBN),trimethyla-mine nitrogen (TMA-N), histamine, pH, and sensory analysis. It was concluded thatgroup WBL4, which fish meat was treated with4%WBL4bacteria suspension, and group lacticacid, which fish meat was treated with0.002%lactic acid, showed the best preservation effects.And WBL4bacterial suspension can control the increase of histamine content better than lacticacid and Nisin. Histamine content in group WBL4raised from3.76mg/100g at to15.04mg/100g in to end of storage period, however, histamine content in control groups rised quicklyand reached to24.96mg/100g and25.43mg/100g, respectively.