Study On The Production Of Enzyme Modified Cheddar Cheese Using Heat-shocked Lactobacillus

Enzyme modified cheese （EMC） is a highly accelerated ripened cheese product made bythe addition of enzymes and other additives to a slurry of curd or cheese and then ripened atelevated temperatures. With the nutrition and flavor accepted by Chinese people, Cheese as aningredient, is more and more widely used in food processing. Because of the special flavorand processing characteristics, and the advantage of addition level being less and improvingthe quality more observably as compared to natural cheese, EMC was used in bakery food,processed cheese more widely, while in our country it’s completely dependent on import.With the development of food industry, it’s every important to research and process a highquality EMC.This paper deals with the influence of heat-shocked Lactobacillus helveticus on theproteolysis of cheese slurry. The main contents include:（1） According to the physiological characteristics of Lactobacillus helveticus, the optimalfermentation condition were10%skim milk medium,2-3%amount of inoculation amount,40℃incubating temperature, initial pH7.1and12h incubating time. Under these conditions,the concentration of cell could reach108-109cfu/ml.（2） Discussed the correlation between the characteristics of Lactobacillus helveticus anddifferent temperatures-time combination, and optimized the conditions of heat shocktreatment. A completely random block design was used to test the influence of fourtemperatures （65oC,67oC,69oC and71oC） and four times （10s,15s,20s and25s） on thecharacteristics of Lactobacillus helveticus. The results showed that the acid-producing activity,cell viability and enzyme activity of bacteria decreased with increasing of heat-shock intensity.Multiple Second Order Regression analysis was used to develop the relationship functionsamong characteristics of cell, heat-shock temperature and time. The predictive formulas wereas follows:Y₁=-6.678X₁-10.960X₂+0.036X₁²+0.249X₂²+0.014X₁X₂+387.952Y2=-1.217X₁+22.033X₂-0.01X₁²+0.026X₂²-0.392X₁X₂+229.791 Y3=15.067X₁+13.732X₂-0.115X₁²-0.046X₂²-0.223X₁X₂-392.911Under the experimental conditions, heat-shock was acted below67oC or the treatmenttime was less than15s, there was no significant retardation of lactic acid production. Whilethe treatment temperature was above69oC or the time was more than20s, the residualintracellular enzyme activity declined sharply, with no more than20%activity left. Therefore,the heat shock temperature and time were in the range of67-69oC and15-20s, respectively.（3） The effects on the processing EMC were researched using optimized heat-shocked（67oC/20s;68oC/15s;69oC/10s） and viable cells of Lactobacillus helveticus. The cells wereadded to cheddar cheese slurry at a level of5%, control slurry sample was prepared with noaddition of cell suspension. It suggested that the overall composition and primary caseinhydrolysis were scarcely affected. But the level of amine nitrogen and volatile compounds ofcheese slurrys adding with viable and heat-shocked Lactobacillus helveticus were bothincreased. RP-HPLC analysis of pH4.6-SN showed that the hydrophilic peptides increasedand generated new peptides in the cheese slurrys added with heat-shocked （67oC/20s;68oC/15s） cells as compared with the cheese slurrys made with heat-shocked （69oC/10s） and viablecells. The sensory evaluation result showed that adding appropriate heat-shocked startersincreased flavor intensity and reduced the acid taste and hardness of cheese slurry. However,prolonged incubation （>5d） resulted in growth of other bacterium, which adversely influencedthe sensory profile.In this paper, The optimum condition of heat shocked （67℃/20s） Lactobacillushelveticus was added to cheddar cheese slurry at a level of5%, and then fermented at37℃for5days. The level of amine nitrogen was increased by59.51%, and the content of volatilecompounds was also enhanced, and the hydrophilic peptides increased and generated newpeptides as compared with the cheese slurrys made with heat-shocked （69oC/10s） and viablecells.