Study On The Characteristics Of Strains Of Cheese Starter Cultures And Its Application In Cheddar Cheese

Cheddar is a hard mature cheese and is one of the main varieties of the world cheeseproduction which is also the maximum cheese in the world’s purchase and consumption. Comparedwith other cheese, Cheddar’s flavor is mild which is more easily accepted by Chinese consumers.With the development of China’s dairy industry and the dietary structure optimization, cheeseconsumption demand is growing. In China, cheese industrial production is in the developmentstage and nearly all the nature cheese on the market is imported product, therefore, thedevelopment of cheese induetry is imminent. First problem we faced to get industrial production isto obtain stable, good performance cheese starter cultures. At present, foreign companies hadcompleted the high activity of direct-vat-strain, and monopolized the domestic and foreign markets.Our country is still relatively backward.This experiment has studied two identified lactococcus lactis strains’ fermentationcharacteristics which included acid-producing ability, extracellular polysaccharide property andproteolytic activity. And high-density medium has been improved. Texture, protelysis, flavorcomponents and sensory evaluation of cheddar cheese produced with single strain and combinationwith lactococcus lactis sub.lactis KLDS4.0424and lactococcus lactis sub.cremoris KLDS4.0326strains were evaluated during ripening.The experimental results show that: KLDS4.0424is the main acid producing strain;Compared with the commercial starter cultures, the extracellular polysaccharide property andproteolytic activity of laboratory strains are relatively weak.Whey was used as the basic medium for lactococcus lactis, added yeast extract, caseinenzymatic hydrolyste and calcium carbonate to increase viable count. The single factor testsresults show that: viable count of KLDS4.0424respectively reached the highest level at calciumcarbonate5g/L, yeast extract12g/L and casein enzymatic hydrolyste12g/L; viable count ofKLDS4.0326respectively reached the highest level at calcium carbonate6g/L, yeast extract12g/Land casein enzymatic hydrolyste12g/L. Based on the results of single factor tests, determine theresponse center point tese levels and each level step.The experiment indicated that the viable cells of strain KLDS4.0424after being cultivated for12h in the optimized medium. Using the path of steepest aseent experiments and RSM methodBox-Behnken design, the quadratic regression fitting was carried out by Design Expert software, the quadratic polynomial regression equation of the casein enzymatic hydrolyste, yeast extract, andcalcium carbonate was:Y1=334.20+9.75*X₃+23.75*X₁+16.75*X₂+4.50*X₃*X₁+4.00*X₂*X₃-24.50*X₁*X₂-65.85*X₃²-85.35*X₂¹-54.35*X₂²The optimal fermentation medium was calcium carbonate5.57g/L, yeast extract9.80g/L andcasein enzymatic hydrolyste8.74g/L, the maximum response value that the model predicted was3.12*109cfu/mL.The Similar experiment indicated that the viable cells of strain KLDS4.0326after beingcultivated for12h in the medium consisting of casein enzymatic hydrolyste, yeast extract, andcalcium carbonate. The quadratic polynomial regression equation was:Y2=166.20+2.38*X₃+7.50*X₁+10.63*X₂+2.50*X₃*X₁+12.25*X₂*X₃+7.00*X₁*X₂-14.98*X₂3-29.23*X₁²-20.97*X₂²The optimal fermentation medium was calcium carbonate5.28g/L, yeast extract9.60g/L andcasein enzymatic hydrolyste9.04g/L, the maximum response value that the model predicted was1.61*109cfu/mL.Improved medium was further optimized in a wider range. Fermentation in the fermenter withconstant pH, adding50%（V/V） ammonia to adjust pH, under the temperature30℃, stirringspeed100r/min, constant pH=6.5, inoculation of1%, after being cultivated for12h in the2.5litergrowing medium according to the optimization medium, strain KLDS4.0424viable count reached2.6*1010cfu/mL, strain KLDS4.0326viable count reached8.8*109cfu/mL.Cheddar cheese trial was carried out by using prepared starter cultures, at the same time,Danisco company starter culture was also used to produce Cheddar cheese as a control group.Texture, protelysis, flavor components and sensory evaluation of cheddar cheese produced withsingle strain and combination with lactococcus lactis sub.lactis KLDS4.0424and lactococcuslactis sub.cremoris KLDS4.0326strains were evaluated during ripening. The results showed thatproteolytic capacity of combined starters was moderate, which fermented cheese taste light.Cheddar cheese had a good maturity, texture and flavor composition which was produced with aratio of1:1between strain KLDS4.0424and KLDS4.0326.