Desalting Process And Spoilage Microflora Analysis In Pickles And Its Preservative Study Based On ?-polylysine

Pickled vegetable is a kind of vegetable product which is made from fresh vegetable by different salting technology.Because of its unique flavor and taste,it is favored by the majority of the consumers.In recent years,with the development of low-salt healthy diet structure,It is an inevitable trend of development to reduce salt content of pickled vegetables.However,the desalting of the pickled vegetables leads to product spoilage,thus reducing the commodity value of products and bringing economic losses to enterprises.Therefore,the aim of this paper was to solve the problem of short shelf life caused by the desalination of pickled vegetables and to investigate the antimicrobial mechanism of ?-polylysine against yeast.The main results were shown as follows:1.According to the determination of mass,NaCl and water content changes at different temperatures,mass balance was proved in the desa lting process.The effective diffusion coefficient of the samples by using the dynamic transfer process model at 15?,25? and 35? were 5.28×10-10m2/s,5.43×10-10m2/s and 5.48×10-10m2/s respectively,which demonst rated that the desalination rate was affected by temperature,and NaCl di ffusion rate of the samples at 15? was the slowest but no significant d ifferences were observed between two samples at 25 ? and 35 ?.With d ynamic equation for the weight changes-time at 25 ?,the pickled vegeta bles containing 1.89%,6.12%and 10.23%salt could be obtained by des alination time of 3.24h,2.27h and 1.19h.2.The microflora of pickled vegetables with different salt concentra tions were assessed.The results indicated that the pickled vegetables wit h2%salt contained diverse kinds of microorganisms including bacteria a nd yeasts.The microbial structure was mainly consisted by spoilage yea sts in the pickled vegetables with 10%salt.By using traditional ecology and molecular biology methods in combination,five kinds of spoilage m icroorganisms were isolated and identified as the follows:Bacillus subtili s,Baillus sp,Rhodotorula mucilaginosa,Cryptococcus albidus and Meye rozyma guilliermondii in the pickled vegetables.The resistance of the fiv e strains to NaCl and acid was studied.The results showed that the yea sts had the better salt and acid tolerance than bacteria.3.Aiming at the isolated spoilage strain,three preservatives of ?-po lylysine(?-PL),Nisin and EDTA-2Na were selected by determining the minimal inhibitory concentration(MIC).Based on the the synergism testi ng,it was confirmed that ?-PL and Nisin had synergistic effects against bacteica and ?-PL and EDTA-2Na exhibited good synergism against yeas ts.The formula of compound preservatives in pickled vegetables was ob tained by response surface methodology:?-PL 51.86mg/kg,Nisin 62.18m g/kg and EDTA-2Na 111.88mg/kg respectively.Compared with the com mercial chemical preservatives,the compound preservatives effectively co ntrol the decrease of colony numbers and pH,and slowed down the con sumption of reducing sugars,showing a good antibacterial effect.4.The antibacterial mechanism of ?-PL against Rhodotorula mucilag inosa was studied by determining the inhibition kinetics curve of ?-PL o n yeast and investigating its effect on cell permeability,hydrophobicity a nd cell morphology.With the action time of the ?-PL extending,the con ductivity,absorbance and the hydrophobicity of the bacterial liquid incre ased.The results showed that ?-PL could increase the permeability and hydrophobicity of the membane surface by treating the cell.Scanning el ectron microscope images displayed that when the concentration of ?-PL increased to a certain level,the cell membrane was severely damaged with the curvature of double layer increasing and obvious pores and mic elles appearing.Based on above results,it was concluded that the antiba cterial mechanism of ?-PL against yeast was that ?-PL adsorbed on the surface of cell membrane,which destroyed the integrity of plasma mem brane and increased the permeability of membrane.The destruction of m embrane function may lead to the central carbon metabolism of the yeas t cell inhibited,thus resulted in cell death.