原料乳体细胞数对UHT乳贮藏期间品质的影响
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摘要
为了探究体细胞数与蛋白质、脂肪水解的关系及其对凝胶和脂肪上浮等劣变的影响。试验采集30,80万个/mL两组不同体细胞数的原料乳,制成UHT乳,20℃下做180 d的贮藏期试验,每隔30 d测定酶活、蛋白含量、游离脂肪酸、脂肪球粒径等指标。结果显示,经UHT处理,两组产品中纤维溶酶和脂肪酶基本丧失活性,贮藏期间无显著性变化(P>0.05)。各酪蛋白组分发生显著水解(P<0.05),κ-酪蛋白和αS2-酪蛋白降幅高达90%以上,均未发生蛋白间的相互交联,体系的黏度并无显著变化(P>0.05)。脂肪球粒径在第60天迅速增加,之后无明显变化;高体细胞数组脂肪球表面的蛋白膜崩解,脂肪球聚集,从贮藏期第120天开始出现脂肪上浮;而低体细胞数组脂肪球膜蛋白也发生水解,未出现脂肪上浮。本研究表明在现有工艺条件下UHT乳出现的主要问题是脂肪上浮而非蛋白凝胶,将原料乳体细胞数控制在30万个/mL的水平,可以有效防止产品贮藏期内发生脂肪上浮,为UHT乳的品质控制提供了理论依据。
In order to explore the relationship between somatic cell count and protein and fat hydrolysis, and its influence on the gelation and fat separation. Raw milk with different somatic cell count(300 000 m L and 800 000 mL)were collected and processed into UHT milk. Samples were stored under 20 ℃ for 180 days and tested every 30 days for enzyme activity, protein content, free fatty acids, viscosity, fat globule size and other indicators. The study showed that after UHT sterilization, milk plasmin and lipase has been nearly completely deactivated and were constant during storage(P >0.05). The casein components were significantly hydrolyzed(P <0.05), κ-casein and α_(S2)-casein decreased by more than 90%, But no protein cross-linking occurred, no significant change in viscosity during storage period. Particle size of UHT milk fat globules increased rapidly in the first 60 day, no significant change later. The fat globule membrane in high somatic cell count was hydrolyzed under CLSM, the fat globules have aggregated since the reduction of protein,which causing fat separation from the 120 day after storage. No fat separation occurred in low somatic cell count though fat globule membrane hydrolyzed obviously. The results showed the main problem with UHT milk under existing process conditions is fat separation rather than the gelation, then the occurrence of fat separation could be prevented effectively by controlling the raw milk somatic cell count under 300 000/mL in the storage period, which provided the theoretical basis for the quality control of UHT milk.
In order to explore the relationship between somatic cell count and protein and fat hydrolysis, and its influence on the gelation and fat separation. Raw milk with different somatic cell count(300 000 m L and 800 000 mL)were collected and processed into UHT milk. Samples were stored under 20 ℃ for 180 days and tested every 30 days for enzyme activity, protein content, free fatty acids, viscosity, fat globule size and other indicators. The study showed that after UHT sterilization, milk plasmin and lipase has been nearly completely deactivated and were constant during storage(P >0.05). The casein components were significantly hydrolyzed(P <0.05), κ-casein and α_(S2)-casein decreased by more than 90%, But no protein cross-linking occurred, no significant change in viscosity during storage period. Particle size of UHT milk fat globules increased rapidly in the first 60 day, no significant change later. The fat globule membrane in high somatic cell count was hydrolyzed under CLSM, the fat globules have aggregated since the reduction of protein,which causing fat separation from the 120 day after storage. No fat separation occurred in low somatic cell count though fat globule membrane hydrolyzed obviously. The results showed the main problem with UHT milk under existing process conditions is fat separation rather than the gelation, then the occurrence of fat separation could be prevented effectively by controlling the raw milk somatic cell count under 300 000/mL in the storage period, which provided the theoretical basis for the quality control of UHT milk.
引文
[1]雷晓薇,王根林,韩兆玉.应用体细胞计数监测奶牛隐性乳房炎[J].畜牧与兽医,2003,35(12):35-37.
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[12]MA Y,RYAN C,BARBANO D M,et al.Effects of somatic cell count on quality and shelf-life of pasteurized fluid milk[J].Journal of Dairy Science,2000,83(2):264-274.
[13]张树利.嗜冷菌脂肪酶对UHT乳脂肪上浮的影响及控制措施的研究[D].呼和浩特:内蒙古农业大学,2005.
[14]NEWSTEAD D F,PATERSON G,ANEMA S G,et al.Plasmin activity in direct-steam-injection UHT-processed reconstituted milk:Effects of preheat treatment[J].International Dairy Journal,2006,16(6):573-579.
[15]HUPPERTZ T,FOX P F.High pressure-induced denaturation of alpha-lactalbumin and beta-lactoglobulin in bovine milk and whey:A possible mechanism[J].Journal of Dairy Research,2004,71(4):489-495.
[16]ISMAIL B,NIELSEN S S.Invited review:Plasmin protease in milk:Current knowledge and relevance to dairy industry[J].Journal of Dairy Science,2010,93(11):4999-5009.
[17]CHOI I W,JEON I J.Patterns of fatty acids released from milk fat by residual lipase during storage of ultra-high temperature processed milk[J].Journal of Dairy Science,1993,76(1):78-85.
[18]KOCAK K R,ZADOW J G.Controlling age gelation of UHT milk with additives[J].Australian Journal Dairy Technology,1985,40(2):58-64.
[19]KOHLMANN K L,NIELSEN S S,LADISCH M REffects of a low concentration of added plasmin on to ultra-high temparature processed milk[J].Journal of Dairy Science,1991,74(4):1151-1156.
[20]DATTA N,DEETH H C.Age gelation of UHTmilk-a review[J].Food and Bioproducts Processing,2001,79(4):197-210.
[21]FERNANDES A M,MORETTI T S,BOVO F,et al.Effect of somatic cell counts on lipolysis,proteolysis and apparent viscosity of UHT milk during storage[J].International Journal of Dairy Technology,2008,61(4):327-32.
[22]张爱霞.耐热酶与乳成分对UHT乳稳定性影响的研究[D].保定:河北农业大学,2003
[23]张书文.原料乳中耐热蛋白酶对UHT乳品质的影响研究[D].北京:中国农业科学院,2012.
[2]VERDI R J,BARBANO D M.Properties of proteases from milk somatic cells and blood leukocytes[J].Journal of Dairy Science,1991,74(7):2077-2081.
[3]RAUH V M,SUNDGREN A,BAKMAN M,et al Plasmin activity as a possible cause for age gelation in UHT milk produced by direct steam infusion[J].International Dairy Journal,2014,38(2):199-207.
[4]陆淳,黄龙,张列兵.乳制品中脂肪上浮的机理及影响因素[J].中国乳品工业,2009,37(4):42-45.
[5]SANTOS M V,MA Y,BARBANC D M.Effect of somatic cell count on proteolysis and lipolysis in pasteurized fluid milk during shelf-life storage[J].Journal of Dairy Science,2003,86(6):2491-2503
[6]KELLY A L,FOLEY J.Proteolysis and storage stability of UHT milk as influenced by milk plasmin activity,plasmin/β-lactoglobulin complexation,plasminogen activation and somatic cell count[J].International Dairy Journal,1997,7(6/7):411-420.
[7]AULDIST M J,COATS S J,SUTHERLAND B J,et al.Effect of somatic cell count and stage of lactation on the quality and storage life of ultra-high temperature milk[J].Journal of Dairy Research,1996,63(3):377-386
[8]付文菊.不同体细胞数原料乳对UHT乳贮存期间品质的影响[D].呼和浩特:内蒙古农业大学,2007.
[9]STRZALKOWSKA N,JOZWIK A,POLAWSKA EA relationship between somatic cell count,polymorphic form of beta 4-defensin and susceptibility of cow milk fat to lipolysis[J].Animal Science Papers and Reports,2014,32(4):307-316.
[10]HARRIS J L,BACKES B J,LEONETTI F,et al Rapid and general profiling of protease specificity by using combinatorial fluorogenic substrate libraries[J].Proceedings of the National Academy of Sciences of the America,2000,97(14):7754-7759.
[11]GAUCHER I,MOLLE D,GAGNAIRE V,et al.Effects of storage temperature on physico-chemical characteristics of semi-skimmed UHT milk[J].Food Hydrocolloids,2008,22(1):130-143.
[12]MA Y,RYAN C,BARBANO D M,et al.Effects of somatic cell count on quality and shelf-life of pasteurized fluid milk[J].Journal of Dairy Science,2000,83(2):264-274.
[13]张树利.嗜冷菌脂肪酶对UHT乳脂肪上浮的影响及控制措施的研究[D].呼和浩特:内蒙古农业大学,2005.
[14]NEWSTEAD D F,PATERSON G,ANEMA S G,et al.Plasmin activity in direct-steam-injection UHT-processed reconstituted milk:Effects of preheat treatment[J].International Dairy Journal,2006,16(6):573-579.
[15]HUPPERTZ T,FOX P F.High pressure-induced denaturation of alpha-lactalbumin and beta-lactoglobulin in bovine milk and whey:A possible mechanism[J].Journal of Dairy Research,2004,71(4):489-495.
[16]ISMAIL B,NIELSEN S S.Invited review:Plasmin protease in milk:Current knowledge and relevance to dairy industry[J].Journal of Dairy Science,2010,93(11):4999-5009.
[17]CHOI I W,JEON I J.Patterns of fatty acids released from milk fat by residual lipase during storage of ultra-high temperature processed milk[J].Journal of Dairy Science,1993,76(1):78-85.
[18]KOCAK K R,ZADOW J G.Controlling age gelation of UHT milk with additives[J].Australian Journal Dairy Technology,1985,40(2):58-64.
[19]KOHLMANN K L,NIELSEN S S,LADISCH M REffects of a low concentration of added plasmin on to ultra-high temparature processed milk[J].Journal of Dairy Science,1991,74(4):1151-1156.
[20]DATTA N,DEETH H C.Age gelation of UHTmilk-a review[J].Food and Bioproducts Processing,2001,79(4):197-210.
[21]FERNANDES A M,MORETTI T S,BOVO F,et al.Effect of somatic cell counts on lipolysis,proteolysis and apparent viscosity of UHT milk during storage[J].International Journal of Dairy Technology,2008,61(4):327-32.
[22]张爱霞.耐热酶与乳成分对UHT乳稳定性影响的研究[D].保定:河北农业大学,2003
[23]张书文.原料乳中耐热蛋白酶对UHT乳品质的影响研究[D].北京:中国农业科学院,2012.
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