Screening Of Lactic Acid Bacteria With Decomposition Ability To Milk Fat And Its Application In Sour Cream

Fermented sour cream is the fermented dairy product with smooth appearing,relatively heavy,rich nutrition and unique acidic flavor.As the improvement of food nutrition cognitive level and the concern on healthy food,fermented sour cream has a great potential for future development.At present,the lack of local lactic acid bacteria starter,immature technology and the single kind of products are the main problems in the development of sour cream industry in China.Therefore,the aim of this paper is to filter to get lactic acid bacteria starter can be applied in sour cream and to study the effect of processing conditions on the quality of sour cream that providing reference for our country sour cream production.The results were as follows:(1)Screening,identification and characteristic analysis of lactic acid bacteria with milk fat degradation ability.Lactobacillus delbrueckii grx601 and Lactococcus lactis grx602 were isolated from fresh cow milk by domestication,primary screening,re-screening,16S rDNA gene identification and growth characteristics.The characteristics of lipase production and enzymology of two strains were determined,the intracellular and extracellular lipases activity of L.delbrueckii grx601 reached a maximum of 14.14 U/mL and 11.45 U/mL in 48 h;the intracellular lipase activity of L.lactis grx602 reached a maximum of 9.33 U/mL in 24 h and the extracellular lipase activity reached a maximum of 12.43 U/mL in 48 h.The intracellular and extracellular lipases produced by two strains had the same enzymological characteristics that the optimum reaction substrate,pH and temperature were respectively p-Nitrophenyl palmit,7.0 and 40?,and the lipases activity remained above 50%when the NaCl concentration was 5%.The fermentation characteristics of two strains were determined,as the fermentation proceeded,the number of viable bacteria and acidity of samples increased.The maximum viable count of L.delbrueckii grx601 was 8.12 lg cfu/mL,and the acidity was 68°T;the maximum viable count of L.lactis grx602 was 11.841g cfu/mL,and the acidity was 74°T.After fermentation,the acid value and the content of free fatty acid of strains fermentation broth increased,and the content of long chain fatty acid increased significantly.The probiotic characteristics of two strains were determined,the survival rate of L.delbrueckii grx601 was 83.87%in artificial gastric juice after 3 h,the survival rate in the bile salt medium with a bile salt concentration of 0.1%and 0.3%after 3 h were 69.39%and 47.70%,and the cholesterol degradation rate was 7.95%;the survival rate of L.lactis grx602 was 87.05%in artificial gastric juice after 3 h,the survival rate in the bile salt medium with a bile salt concentration of 0.1%was 68.74%,while in the bile salt concentration of 0.3%couldn't survive,and the cholesterol degradation rate was 10.93%.(2)The effect of processing conditions of butter-based cream on the quality of sour cream.L.delbrueckii grx601 and L.lactis grx602 were respectively inoculated into butter-based cream under different processing technology to make sour cream,and measured textural and rheological properties of sour cream.When homogenization pressure was 15.0 MPa,homogenization temperature was 70?,strain inoculation amount was 1%and fermentation temperature was 37?,the textural and rheological properties of L.delbrueckii grx601 sour cream and L.lactis grx602 sour cream were the best.The correlation between the processing conditions of butter-based cream and the textural and rheological properties of sour cream was analyzed,for L.delbrueckii grx601 sour cream:the changes of homogenization pressure,homogenization temperature and fermentation temperature were positively correlated with hardness,cohesiveness,adhesion,elasticity and apparent viscosity of sour cream,and the change of strain inoculation amount was negatively correlated with the indexes of textural and rheological properties;for L.lactis grx602 sour cream:the change of homogenization pressure was positively correlated with hardness,cohesiveness,adhesiveness,elasticity and apparent viscosity of sour cream,while the change of homogenization temperature was positively correlated with adhesiveness and apparent viscosity,but negatively correlated with hardness,cohesiveness and elasticity,the changes strain inoculation amount and fermentation temperature had negative correlation with the indexes of textural and rheological properties.(3)The research on fermentation characteristic and quality during storage of sour cream.The physical and chemical indexes,microbial indexes,free fatty acids and microstructure of sour cream after fermentation were determined,L.delbrueckii grx601 sour cream and L.lactis grx602 sour cream had good quality,the pH,acidity,acid value and viable count of L.delbrueckii grx601 sour cream were respectively 4.55,60°T,1.6 mg/mL and 9.08 1g cfu/mL;the pH,acidity,acid value and viable count of L.lactis grx602 sour cream were respectively 4.50,70°T,1.6 mg/mL and 11.51 1g cfu/mL.After fermentation,18 kinds of fatty acids were detected in L.delbrueckii grx601 sour cream,while 16 kinds of fatty acids were detected in L.lactis grx602 sour cream;palmitic acid,stearic acid,oleic acid,conjugated linoleic acid and other fatty acids increased.And two sour creams both had a compact and regular micro-structure.During storage,the pH,viscosity,water holding capacity,acidity and acid value of two sour creams decreased,and the number of viable bacteria increased and then decreased.The hardness,adhesiveness,cohesiveness,elasticity and apparent viscosity of two sour creams decreased with the increase of time,these indexes of L.delbrueckii grx601 sour cream decreased more rapidly than L.lactis grx602 sour cream.The content of fatty acids of two sour creams both increased at first and then decreased;the kinds of fatty acids of two sour creams increased continuously,there were 21 and 22 kinds of fatty acids detected from L.delbrueckii grx601 sour cream and L.lactis grx602 sour cream.