Study Of Starter Cell Modified By Lysosyme And Ultrasound And Its Accelerated Cheese Ripening

Cheese ripening is a time-consuming process of the breakdown and subsequent transformation of degradation catalyzed by microbial enzymes and rennet remaining in cheese curt to develops typical flavor. This reactions usually require lower temperature leading higher cost .So cheese ripening has been the subject of consideration investigation in the filed of milk research. One of the most efficient ways to increase the bacterial enzyme pool in cheese curd, without altering the primary starter and cheese make, is to add whole lactic acid bacteria, unable to grow and to produce significant levels of lactic acid, but still delivering active ripening enzymes during cheese ageing. This starter is normally weakened by various treatments. I studied lysosyme and lysosyme combined ultrasound modified starter cell in this paper. The modified starter marks are activity of lactate dehydrogenase(LDH) and proteinase and the number of cells. Modified starters were added to cheese to study its influence of cheese ripening. The results show that:1 The starter culture adding 2.0mg/ml lysosyme to were treated for 1hr under 37 ℃ can release LDH with 467.8U/g and proteinase with 777.1U/g, which in turn higher 381.74U/g, 289.25U/g than not treated starter, and only survival rate with 0.0022%, This indicated that starter treated by lysosyme can effectively reduce numberof cell, and benefit to releasing cell enzymes. Conditions of lysosyme and ultrasound treating starter were defined. The result showed that: the starter culture were treated by ultrasound under 120W for 6min after adding 0.8mg/ml lysosyme to were treated for 4hr under 37 °C can release 522.50U/g of LDH , 1085.5U/g of proteinase, which in turn higher 436.44U/g, 597.65U/g than not treated starter, and only 0.0005% of survival rate. This indicated that starter treated by lysosyme combined ultrasound can effectively reduce number of cell, and benefit to releasing cell enzymes.2 Moisture, fat, protein and salt content of experiment and control cheeses were not obviously difference (P>0.05) after cheese composition were determined during cheese ageing. It were determined that pH value between control 1 (adding 2.0% starter) and control 2 (adding 2.0+0.5/0.7% starter) during cheese ripening. But content of WSN, TCA-SN, PTA-SN and free fatty acid in experimental were higher than control groupcheese during cheese ageing. And difference between the two groups is increasing along cheese age extending. This indicate that to add modified starter by lysosyme and lysosyme combined ultrasound can obviously restrain lactic acid bacteria producing significant levels of lactic acid, but still accelerating catabolic reaction of protein and fat ,which benefit to shorten time of cheese ripening .The results of sensory analysis show that: the added the modified starter cheese has more flavor intensity and texture than control group, which indicates that adding modified starter by lysozyme or lysozyme combined ultrasound can shorten potently ripening time.