【作者】 谢爱英；

【导师】 张富新；

【作者基本信息】 陕西师范大学 ， 食品科学， 2006， 硕士

【摘要】 干酪成熟过程中主要的变化是残存在干酪中的酶与乳酸菌发酵剂中的蛋白酶和肽酶催化酪蛋白降解,生成典型干酪风味的过程。通常干酪成熟要求在低温下进行,需耗费的时间较长,成熟费用很高,因此,加速干酪成熟已成为国内外乳品研究领域关注的热点。在发酵剂种类及干酪制作工艺不变的条件下,加速干酪成熟的一种最有效方法是提高发酵剂的添加量。然而提高发酵剂的添加量虽然可以促进干酪成熟期间活性成熟酶的释放,同时也会产生大量的乳酸,影响干酪的质量。因此,采用不同方法对发酵剂进行处理,抑制其在干酪成熟中的产酸量,不仅可加速干酪成熟效果,也可提高干酪的品质。本研究采用溶菌酶处理发酵剂和溶菌酶与超声复合处理发酵剂,以乳酸脱氢酶活性(LDH)、蛋白水解酶活性和活细胞数为处理指标,研究了不同因素对干酪发酵剂处理效果及其对加速干酪成熟的影响。结果如下: 1、用溶菌酶处理发酵剂时,当溶菌酶添加量为4.0kU/mL的溶菌酶,处理温度为37℃,处理时间为1h,发酵剂的乳酸脱氢酶(LDH)活性为467.8U/g,蛋白水解酶活性为777.1U/g。分别较未处理发酵剂的LDH和蛋白水解酶活性高381.74U/g和289.25U/g,同时发酵剂细胞的存活率仅为0.0022%,表明通过溶菌酶处理可有效的降低活细胞数量,有利于细胞酶的释放。用超声和溶菌酶复合处理发酵剂时,在溶菌酶添剂量为1.6kU/mL,溶菌酶作用时间为4h,超声作用时间为6min,在此条件下处理的发酵剂中LDH酶活性为522.5U/g,蛋白水解酶活性1085.5U/g。分别较未处理发酵剂的LDH和蛋白水解酶活性高436.44U/g和597.65U/g,同时发酵剂细胞的存活率0.0005%,表明用超声与溶菌酶复合处理发酵剂可有效的降低活细胞数量,并有利于细胞酶的释放。用溶菌酶与超声复合处理效果优于单独用溶菌酶处理。 2、干酪成熟期间的理化指标变化表明,添加溶菌酶处理发酵剂和溶菌酶与超声复合处理发酵剂的干酪在成熟期间水分含量、蛋白质含量、脂肪含量和食盐含量与对照组(未添加处理发酵剂)干酪差异不明显(P>0.05),各试验组干酪的pH值在整个成熟期处于对照1(添加发酵剂量为2.0%)干酪和对照2(添加发酵剂量为2.0+0.5/0.7%)的pH值之间;试验组的WSN、TCA-SN和PTA-SN值在整个成熟期均高于对照组1,并且随着成熟期的延长逐渐升高;试验组干酪中成熟期游离脂肪酸的含量较对照组1干酪高,表明通过溶菌酶处理发酵剂和溶菌酶与超声复合处理发酵剂可明显抑制干酪成熟期间的产酸量,同时可加快蛋白质降解和更多还原

【Abstract】 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.更多还原