The Screening On Nonstarter Lactic Acid Bacteria And Study On The Influence On Accelerating Cheddar Cheese Ripening

Nonstarter lactic acid bacteria is a unique flora in cheese,belonging to cheese exogenous microorganisms.It can accelerate cheese curding and cheese ripening.Adjunct cultures is a kind of microorganisms that is screened and deliberately added to the fresh cheese to accelerate cheese ripening.Non-starter lactic acid bacteria can be used as adjunct cultures added to the cheese using to accelerate cheese ripening.In this study the strains were screened from Chinese traditional fermented food.Because these fermented food contains rich microorganism resources.It is possible that nonstarters which could accelerate cheese ripening were isolated.In screening strains methods,isolates were screened further biological characteristics by using multivariate statistical analysis,and nonstarter lactic acid bacteria which had the potential of accelerating cheese were rescreened.Multivariate statistical analysis make use of fewer index to replace and reflect the information of more index,while other screening methods index is relatively single and information insufficient.Multivariate statistical analysis avoids the scarcity of information,and is a kind of simplifying comprehensive evaluation.In addition,it was evaluated additives on cheese proteolysis using cheese slurry model.The system contained high moisture and placed in high temperature of maturity,and it was considered as a reliable evaluation tool for cheese quickly identified the additive effects of maturity.Because of no commercial adjunct cultures cheese slurry without strains screened was as control group.Specific research content and research results were as follows:Research content: The project is to select gram-positive sporeless bacterium which could grow in cheese ripening environment from Chinese northeast traditional fermented food ‘Suancai’ by applying Rogosa agar.Isolates were screened further for acidifying,autolytic,proteolytic and aminopeptidase activity by multivariate statistical analysis.The 16 S rDNA gene sequencing and blast search against the public database were used to identified the isolated strains.The isolates were evaluated for their influence on cheddar cheese slurry proteolysis,and were researched for their influence on the quality of cheddar cheese.Research results: 1.18 strains of gram positive non-spore lactobacillus were isolated by conventional plate culture method from traditional fermented foods for their good growth performance in cheese ripening conditions.The biological characteristics of the strains were analysed by multivariate statistical,then a non-starter S-1 which had good potential to accelerate cheese ripening was selected.The 16 S rDNA gene sequencing analysis identifiesd the strain S-1 to be Lactobacillus plantarum.Thus the strain S-1 was screened for the test strain.The research on biology characteristic of strain S-1 showed it can grow in MRS broth which contained pH4 to 7 and NaCl concentration of 2% to 6%,the strain S-1 could tolerate low temperature environment too.2.Cheese model which was made aseptically using fresh cheese curd was used to rapidly evaluated effect of strain S-1 on cheese ripening.PH4.6WSN,12%TCASN,protein electrophresis and free amino acids contents as the proteolysis index were regarded as ripening index.Samples were collected at 0,2,5,7,10 d in cheese ripening.The value of pH4.6WSN in cheese model indicated S-1 had no influence on casein primary proteolysis.The value of 12%TCASN in experimental cheese was higher than control cheese.It showed high peptidase in experimental cheese,accelerating small molecule polypeptide formation.The electrophoretic profile for casein degradation showed high molecular peptides degradated from protein were degraded constantly into low molecular peptides and smaller peptides.Free amino acids(FAA)concentrations also suggest experimental cheese had high concentration of FAA than control cheese,but the concentration of tyrosine was lower than experimental cheese.Slurries containing lactobacillus S-1 released more amino acids than did control slurry.The concentration of leucine,glutamate,phenylalanine and lysine were obviously higher than other amino acids.The results showed that strain S-1 accelerated the hydrolysis of proteins in the cheese system,promoting cheese mature process.3.Cheddar cheeses were manufactured in open vats to study the influence of adjunct culture of lactobacillus S-1 on proteolysis during ripening.The composition of cheese and the value of pH were on significant influence between control and experimental cheddar cheese.Lactobacilli in the experimental cheeses reached 2.1 × 107 cfu/g and then decreased.The concentration of 12%TCASN in experimental cheese was higher than control.After two months of cheddar cheese mature,texture analysis and sensory analysis of the cheeses showed significant differences between the control and experimental cheeses.Experimental cheese was soft and elastic,and strain S-1 improved the cream flavor.Thus,strain S-1 improved the quality and structure of cheese,increasing soluble nitrogen content.Strain S-1 adding in cheese can promote ripening.