The Effect Of Adding Modified Lactobacillus Plantarum On Cheddar Cheese Ripening

Lactobacillus Plantarum was often added into cheddar cheese as adjunct culture, because itcontained aminoPePtidase which was able to Promote hydrolysis of Proteins and reduce thebitterness. AminoPePtidase was intracellular enzyme, and it was released when the strainsautolyzed. So it had a very imPortant significance for cheese riPening to select the LactobacillusPlantarum with high aminoPePtidase activity and autolytic.The imProvement of aminoPePtidaseactivity and autolytic was limited in the natural conditions of the strain screened by Plate, and itwas difficult to select the strain with the two characters achieved excellent. If the quantity of thestrain that selected for adding into the cheese was imProPer, it would lead to defects, so the strainshould be used after modifying theoretically. This PaPer combined different modification methodstogether to treate Lactobacillus Plantarum based on the methods of advantages and disadvantagesof modification in order to research the effects on cheese riPening,and discussed a suitablemodification methods for Lactobacillus Plantarum, It Provided a Proof for modified strains inPractical aPPlication of the Production of cheese.This Project used Lactobacillus Plantarum S-1selected in the laboratory as the original strain,and treated it with ultrasonic and diethyl sulfate for comPound mutagenesis in order to modify itbecame a strain with high aminoPePtidase activity and autolytic. After researching the biologicalcharacteristics, the mutant was attenuated by heat shock or low-Power ultrasonic to reduce acidProduction of the strains, and then used into cheddar cheese to research the effect caused byLactobacillus Plantarum that was modified from comPosition, microorganism, PH, Proteolysis,texture, sensory. There were some results and conclusions of the study:1.To researched the effect on mortality rate caused by different times and Power of theultrasonic and different times of diethyl sulfate, The results showed that the oPtimum conditionsfor ultrasonic was500W,15min, and for diethyl sulfate was40min. After comPound mutagenesisunder the oPtimum conditions for4times, there were14Positive mutants that aminoPePtidaseactivity were imProved among31mutant. Autolytic of the14Positive mutants was measured, thenthe strain D-11was determined, its aminoPePtidase activity was23.833,which was higher by61%than the original strain, and the autolytic was43.55%, which was higher than the original strain by38%.2.The results of biological characteristics of the mutant D-11showed that, the aminoPePtidase activity and autolytic of each generation of the mutant D-11had not significantdifference subcultured until the eighth generation. The results indicated that genetic characteristicsof the mutant D-11was stable;The results of hyPothermia salt and acid tolerance showed that thestrains modified by comPound mutagenesis still adjust to the system of the cheese. the Parameterof heat shock was determined to be50℃,15s by discussing the effect on acidifying and survivalcaused by factor of heat shock, under the conditions of this Parameter, the changes inacid-Producing ability of the strain was0.57, and the survival rate of the strain was26.733%.3.The effect on the riPening of cheddar cheese caused by modified strains were studied.Therewere no significant differences in each grouP on the main comPonent of the cheese,which is in thestandard of cheddar cheese.The microorganisms in the exPerimental cheese that manufactured withthe Lactobacillus Plantarum modified by comPound mutagenesis and attenuated by low Powerultrasonic grew faster;and the first control cheese, that manufactured with the LactobacillusPlantarum modified by comPound mutagenesis and attenuated by heat shock was slowest,and thesecond control cheese, only manufactured with the Lactobacillus Plantarum modified bycomPound mutagenesis was between them. At the riPening of60days, the value of PH in theexPerimental cheese was4.92, the first control cheese was4.83,and the second control cheese was4.79, there were significant difference on the value of PH which showed that attenuation canreduce acid Production of the strain, and the effect of low-Power ultrasonic is better. There wereno significant difference on the value of PH4.6WSN in the three grouP. The concentration of12%TCASN of the exPerimental cheese was12.95%, the first control cheese was10.64, and thesecond control cheese was9.4%. Total free amino acids concentrations of the exPerimental cheesewas higher than the others, and the second control cheese was the lowest. The exPerimental cheesehad better texture, higher sensory, good milk flavor, and the first control cheese had a littlebitterness,and the second control cheese was harder, more acid, and Poor accePtance showed bythe results of texture and sensory.The Project showed that it was better that combining the twomethods together to modify the strain than using a single method,and the method that modified bycomPound mutagenesis and attenuated by low Power ultrasonic was better than the others,it wasable to accelerate the hydrolysis of Proteins in the Cheddar cheese, shorten the time of cheeseriPening.