Isolated And Control Of Psychrophile In Raw Milk

Psychrophile,especially Pseudomonas fluorescens was the particular factor among these many which impacted the quality of UHT milk.The psychrophile protein and fat enzyme were very heat-resistant and capble of partially surviving pasteurization and UHT treatment.quality and sensory quality would also decline by enzyme residued.Through this study,Psychrophile were isolated from a local cattle-farm of Baoding by GB,Thus the growth,fermentation condition and enzyme production of Pseudomonas fluorescens were studied in this paper to provide a foundation for its industrial production.The main results were shown as follows:1.12 strains of psychrophile were isolated,Among these,8 strains were identified as pseudomonas fluorescens,1 strain as Sphingobacterium spiritiuvorum,and 3 strains as Flavobacterium based on the properties of cell morphological,physic-biochemical characteristics and homology in 16S rDNA sequence.It was found that Pseudomonas fluorescens took up more than 40%of whole microflora in raw milk sampled from the cattle-farm over one year.2.The optimum growth temperature of Pseudomonas fluorescens was 30℃,and an initial pH of 7 favored the growth of Pseudomoans strains.pH in media rose slowly from 7.0 to 8.3 in the presence of Pseudomonas fluorescens grown at 30℃for 24h,and tended to stabilize and began to produe proteinase as its growth continued.Mg²⁺ had a significant activation on the growth of Pseudomonas fluorescens.The orthogonal test of the four factors showed that the optimized media was:skimmed milk 0.1%,yeast extract 0.25%,tryptone 0.05%,glucose 0.2%,MgSO40.03%.3.The fermentation conditions of Pseudomonas fluorescens PF-5 was determined on the basis of the optimum medium,a small number of internally enzyme was produced at the late growth of PF-5,and reached a stable value near total activity 500U when PF-5 grew 31 hours later,then intracellular proteinase and extracellular proteinase were started to be produced.Intracellular enzymes was produced higher early and reached its peak 202U after 47 hours,then significantly reduced although the subsequent fluctuations,then a large number of extracellular enzyme was produced and reached 144U the highest value at about 94h after a smaller peak at about 78 hours. with the study of variety enzymes Pseudomonas fluorescens produced,its total activity was about 500U, extracellular enzyme was about 30%,intracellular enzyme was about 40%,and the remaining 30% might be cell wall enzyme.UHT dairy was more damaged with a large number of intracellular enzyme which was mostly leaked under a high homogeneous pressure.4.Intracellular and extracellular enzyme were collected respectively after Pseudomonas fluorescens PF-5 was fermentated for 47 hours and 94 hours at optimal culture conditions,and the molecular weight of intracellular and extracellular enzyme were the molecular weight of extracellular enzyme were tested by adopting filtration,ammonium sulfate fractionation, SDS-PAGE,wich indicated that the molecular weight of extracellular enzyme was 37KD. intracellular protease was about 35KD.5.After Pseudomonas fluorescens were polluted with 10⁸cfu/ml in the UHT milk,the effect of cleaning the bacteria and the protease was got,80℃water was the worst,followed by 2.0%hot alkali, and 0.8%hot nitric acid was the best.But with any kind of them alone can not be complete,further more combined with other enzyme in UHT milk,it is necessary to first using 80℃water,2%hot alkali, 80℃water,0.8%hot nitric acid,80℃water followed by cleansing,thus the milk is basic safety...