邹佳健外文翻译最终版.doc

分子量和羧甲基纤维素的取代对酸性乳饮料的稳定性的影响（食质102：邹佳健 指导老师：李红心）（陕西科技大学生命科学与工程学院 西安 710021）摘要：对酸性乳饮料的分子量（Mw，250,000，700,000）和取代的羧甲基纤维素（DS，0.7，0.9 ，1.2）（CMC）中的酪蛋白胶束的酸化在稀释的分散体中的直径和-电势对稳定度的影响进行了研究。实验结果表明，CMC与分子量高或低的DS会导致厚的吸附层到酪蛋白胶束。涂层酪蛋白胶粒的电位的增加而增加CMC的分子量具有相同的DS，而在一个固定CMC的电位高的DS（1.2）与为CMC具有低RDS（相比增加了0.7和0.9）。Mw和CMC的DS的影响酸性乳饮料稳定性。CMC具有增加的高Mw酸性奶饮料的粘度显著，因此在稳定做出了贡献。CMC具有较高的DS导致CMC涂层的酪蛋白胶束高电位，增加酪蛋白颗粒，防止其在酸性乳饮料的相分离之间的静电斥力。有人还发现，CMC的用量决定酪蛋白胶束的有效覆盖增加与CMC的增加的Mw。上面的有效覆盖范围的浓度，具有较高分子量的CMC酸性乳饮料的长期稳定性比用低分子量的CMC更好。关键字：酸性乳饮料，羧甲基纤维素，分子参数，酪蛋白胶束，稳定性1 引言酸性乳饮料可以被描述为一种酸化的蛋白质液系统的稳定性和粘度类似于天然牛奶。这种饮料通常包含大范围的产品，有别于一般从发酵乳稳定剂和果汁与糖准备那些通过直接酸化。这些产品的pH值范围为3.6至4.6（中村，吉田，前田，及Corredig，2006）。在中性pH下，在胶束的形式，这是由空间排斥由于-酪蛋白的存在主要是胶束（德Kruif，1998和Tuinier和德Kruif，2002）的表面上的伸展构象稳定存在的酪蛋白。在酸化过程中，在pH值接近等电点（pH 4.6）的酪蛋白胶束聚集，因为-酪蛋白（霍尔特，1982）的伸展构象的崩溃为主。关于酪蛋白在上述pH值范围内的不稳定性，稳定剂必须加入以避免乳蛋白和随后的宏观乳清分离的絮凝。高甲氧基果胶（Boulenguer和洛朗，2003年，Liu等人，2006年和帕克等人，1997）和大豆可溶性多糖（SSPS）（浅井等人，1994年，中村等人，2003年和Nakamura等人。，2006）经常被用来达到这个目的，并且许多受到人们的重视。另外，藻酸丙二醇酯（PGA）和羧甲基纤维素（CMC）中也提到了能够将其用作稳定剂（庆一，2006年，司等人，2004，曼恩，2004，正木等人用，2004，美利，2000，西山，1978年，小笠原等人，2003年，Syrbe等人，1998年和年轻Bluestein，2002）。作为纤维素的最重要的一种衍生物，CMC是一种典型的阴离子多糖和已被广泛地用作食品的稳定剂。CMC链是线性的（14） -连接的吡喃葡萄糖残基。替代CMC的（DS）的平均度被定义为每重复单元的羧甲基基团的平均数目，并且其范围通常为0.4-1.5。CMC是根据钠盐形式，水溶性产物的DS0.5通常发现 1，5替代的最大程度是允许的，但更典型的DS是在食品应用（科菲等人，2006年和穆雷，2000）的范围是0.6-0.95。CMC通常选择作为其在酸性乳饮料代替果胶在亚洲作为低成本稳定剂，特别是在中国（陈，郑，陈，和饶，1996）。近年来（Liu等人，2006和Nakamura等人，2006），果胶中的SSPS在酸性乳饮料的稳定机制已被广泛研究。然而，酪蛋白胶束在低pH下的稳定性可以通过CMC得到改善。在以前的工作（Du等人，2007），我们发现，电吸附会在酪蛋白胶束发生pH值低于5.2和吸附CMC层酪蛋白的表面上可以防止酪蛋白胶束的絮凝空间位阻斥力。此外，非吸附的CMC增加的血清的粘度和减缓酪蛋白颗粒的沉降。将吸附CMC层作为-酪蛋白做在中性pH值以同样的方式引起了酪蛋白胶束在低pH值之间的排斥作用。酸性乳饮料的稳定性在很大程度上取决于（TROMP等人，2004和Tuinier等人，2002），pH值（Nakamura等人的酪蛋白和多糖之间的相互作用，这可以通过蛋白和多糖的浓度的影响，2003），多糖（洛朗和Boulenguer，2003年分子特性，Maroziene和德Kruif，2000年和佩雷拉等人，1997），离子环境（Ambjerg佩德森和约根森，1991），牛奶中的蛋白质组成和处理（Boulenguer和洛朗，2003年，格拉恩，1982年和Sedlmeyer等，2004;)，样品的温度（霍恩，1998年，卢西等人，1999年和Zaleska等人，2000）等。尽管酪蛋白胶束和CMC和的酸性乳饮料的稳定性之间的相互作用可能是主要依赖于pH值CMC的浓度和如先前报道（Du等人，2007），羧甲基基团对CMC的分子量和取代模式应要强调的是因为在酸性乳饮料的实际加工的性能，包括的饮料的稳定性可以通过调整对CMC的分子参数获得。在目前的工作中，我们的目标是调查的Mw和CMC的DS对CMC和酪蛋白胶束之间的稳定性，因而对酸性乳饮料稳定性的相互作用的影响。2 材料与方法2.1 物料一系列的CMC具有不同分子量（250,000 Da和700,000道尔顿）和不同的DS（0.7，0.9和1.2）从ACROS有机物（莫里斯平原，新泽西州）进行购买。脱脂奶粉是从恒天然合作集团（惠灵顿，新西兰）获得。一水柠檬酸从上海化学试剂有限公司（上海，中国）获得的。2.2 用于动态光散射样品（DLS）和-电势实验的准备该样本是由在模拟牛奶超滤液（SMUF）（杰尼斯Koops的，1962年）（1:100）分散为80g /公斤复原脱脂乳。 SMUF含有钠，钾，钙，镁，磷酸盐和柠檬酸盐和用于稀释的混合物中，将模拟的盐系统中牛奶的环境。然后用5克/千克的CMC溶液中加入到稀释的复原脱脂乳在约中性pH（6.6-6.7），得到含有400毫克/公斤的CMC800毫克/公斤脱脂奶粉。在此测量所有溶液用超纯水18.2兆欧/厘米（Millipore公司，贝德福德，马萨诸塞，美国），并通过0.22微米的膜过滤器在使用前过滤。酪蛋白胶束的表观直径和-电位酸化稀释复原脱脂乳用柠檬酸中进行了监测。2.2 动态光散射测量法（DLS）动态光散射测量进行了马尔文激光粒度仪3000HSA（马尔文仪器，伍斯特郡，英国）配备了10瓦最大输出He-Ne激光和633nm的。测量发生在从入射光束90，得到粒子的估计平均直径分布的强度。样品的温度通过一个焦耳 - 帕尔贴恒温器在20下被控制每次测量的表示结果为10次测量的平均值。并且所有测量均进行三次。测量的最大变异为10以下。2.3 电位测量酪蛋白胶束的电位作为pH的函数被使用粒子电泳仪器（纳米激光粒度仪ZS，马尔文仪器，伍斯特郡，英国），其测量方向和施加电场的液滴运动的速度在20下测定。-电势提供的净电荷在“剪切面”，它依赖于实际的粒子（在这种情况下，酪蛋白胶束和多糖）的电荷测定的粒子的的估计值加上与该移动沿任何离子相关联的电荷在电场的粒子。该样品是类似于那些用于DLS测量。一个单独的-电势是从对同一样品取3个读数的平均值来确定。所有测量均进行三次。2.4 酸化乳饮料的制备80克/千克复原脱脂乳的制备是将脱脂奶粉和蒸馏水在45下30分钟。同时，CMC和蔗糖干混在一起，然后将混合物溶解在蒸馏水中在75下搅拌20分钟。稳定剂和复原脱脂乳混合，按1:1的比例，得到含有4克/千克的CMC和80克/千克蔗糖为40g /公斤脱脂奶粉。这个混合物的pH值在20下，直接酸化至4.0以500克/千克柠檬酸酸性乳饮料被预热到65，然后均匀在200度与两阶段的均质机Rannie的型号8.30 H（APV Rannie的A / S，丹麦）。所有样品储存在密封的玻璃瓶中。每个样品（500毫升）的瓶在90下进行30分钟的加热的水浴中。叠氮化钠（0.02）溶液中加入，以防止细菌的生长。测量进行贮存后的样品在室温搅拌过夜。所有测量均进行三次。2.5 对酸性乳饮料表观粘度的测定 酸性乳饮料的表观粘度是通过Brookfield粘度计LVDV-I，型号NDJ-79，用1号转子，在100rpm/分钟，25下测定。2.6 酸性乳饮料的粒径的测定 酸化的乳饮料中稀释至可测量的浓度（100-200倍）与蒸馏水。然后将粒径的测定使用激光衍射粒度分析仪，马尔文的Mastersizer 2000（马尔文仪器有限公司，伍斯特郡，英国）。2.7 对酸性乳饮料的贮存稳定性的测量 存储过程中发生沉降和血清相观察与光学分析仪TURBISCAN均线2000（Ramonville-ST-昂内，法国）。保存于25下含有5ml样品的圆柱形玻璃管沉淀和血清相分数作为时间的函数绘制制备后的样品30天的图像。2.8 相分离 40克/公斤脱脂牛奶和CMC以不同浓度（0-5克/千克），将混合物酸化至pH值4.70.1和3.80.1，分别，而无需酸化该混合物的pH为约6.70.1。 10毫升样品置于有刻度的玻璃管盖在25室温从视觉观察制剂后3天，得到的混合物的稳定性。该样品被认为是稳定的，如果该系统是单一的，而该样品是不稳定的，如果明显的相分离发生。3 结论Mw的DS影响CMC和酪蛋白胶束之间的相互作用，从而影响酸化性饮料的稳定性。在pH值为6.7，由于电荷斥力和酪蛋白的混合物中酪蛋白和CMC之间没有相互作用和CMC稳定性在较低的CMC浓度更稳定。超过一定的CMC浓度，发生絮凝导致相分离。 pH值低于5.2的CMC吸附到酪蛋白胶束。在低CMC浓度的情况下，CMC /酪蛋白胶束的混合物相通过架桥絮凝分离。随着CMC浓度的酪蛋白胶束得到有效包覆，因此空间稳定。所需的有效覆盖到酪蛋白胶束的CMC的用量增加而增加CMC的分子量。人们发现，高的分子量的CMC或低DS 的CMC导致了厚吸附层上的酪蛋白胶束。但是，此厚层不直接影响酸化奶制饮料的长期稳定性，因为影响酸性乳饮料的稳定性有-电势的酪蛋白胶束，酪蛋白胶束的粒径，表现为影响了乳饮料的粘度。具有较高的Mw的 CMC对酸性饮料中表现出良好的稳定性，由于双方的厚吸附层和该系统的高粘度。CMC涂覆的酪蛋白胶束电位的绝对值增加时，CMC的取代度足够高，以1.2与CMC为0.7和0.9的DS进行比较。高-电势通过静电斥力有助于系统的稳定性。它是假定该吸收层和静电斥力的两个空间排斥的影响对酸性乳饮料的稳定性的影响。参考文献1Ambjerg Pedersen ，Jorgensen.食品亲水胶体.1991.第323-328页2S.G.ANEMA，H.Klostermeyer. 国际乳品杂志.1996.第627-687页3西成，土井（合编）.食品胶体：结构，性质和功能.Plenum出版社.纽约.1994.第51-1564Gosta Bylund.1986.乳品加工手册.利乐处理系统.第221页.瑞典.Influence of molecular weight and degree of substitution of carboxymethylcellulose on the stability of acidified milk drinksAbstract:The influence of molecular weight (Mw, 250,000, 700,000) and degree of substitution (DS, 0.7, 0.9 and 1.2) of carboxymethylcellulose (CMC) on the diameter and -potential of casein micelles during acidification in diluted dispersions and on the stability of acidified milk drinks was investigated. The experimental results suggested that CMC with highMwor low DS would result in thick adsorbed layer onto casein micelles. The -potential of CMC-coated casein micelle increased with increasing theMwof CMC with the same DS while at a fixedMwthe -potential for CMC with high DS (1.2) increased in comparison with those for CMC with low DS (0.7 and 0.9). BothMwand DS of CMC influenced the stability of acidified milk drinks. CMC with highMwincreased the viscosity of acidified milk drinks significantly and therefore contributed to the stability. CMC with high DS resulted in high -potential of CMC-coated casein micelles, increasing the electrostatic repulsion between casein particles, which prevented the phase separation in acidified milk drinks. It was also found that the amount of CMC needed for efficient coverage of casein micelles increased with increasing theMwof CMC. Above the efficient coverage concentration, the long-term stability of acidified milk drinks with highMwCMC was better than that with lowMwCMC.Key Words: acidified milk drinks,carboxymethylcellulose,molecular parameter,casein micelle,stability1. IntroductionAcidified milk drinks can be described as an acidified protein liquid system with stability and viscosity similar to natural milk. Such drinks usually comprise a large range of products, from those usually prepared from fermented milk with stabilizers and sugar to those prepared by direct acidification with fruit juices and/or acids. The pH of these products ranges from 3.6 to 4.6 (Nakamura, Yoshida, Maeda, & Corredig, 2006). At neutral pH, caseins exist in the form of micelles, which are stabilized by steric repulsion due to the extended conformation of -casein present mainly on the surface of micelles (de Kruif, 1998andTuinier and de Kruif, 2002). During acidification, at a pH close to the isoelectric point (pH 4.6) the casein micelles aggregate mainly because of the collapse of the extended conformation of -caseins (Holt, 1982). On account of the instability of casein in the abovementioned pH range, stabilizer needs to be added to avoid the flocculation of milk proteins and subsequent macroscopic whey separation. High methoxyl pectin (Boulenguer and Laurent, 2003,Liu etal., 2006andParker etal., 1997) and soybean soluble polysaccharides (SSPS) (Asai etal., 1994,Nakamura etal., 2003andNakamura etal., 2006) are often used to achieve this, and much attention has been paid to pectin. In addition, propylene glycol alginate (PGA) and carboxymethylcellulose (CMC) are also mentioned to be able to use as stabilizers (Keiichi, 2006,Koji etal., 2004,Mann, 2004,Masaki etal., 2004,Murray, 2000,Nishiyama, 1978,Ogasawara etal., 2003,Syrbe etal., 1998andYoung and Bluestein, 2002).As one of the most important derivatives of cellulose, CMC is a typical anionic polysaccharide and has been widely used as a stabilizer in food. CMC chains are linear (14)-linked glucopyranose residues. The average degree of substitution (DS) of CMC is defined as the average number of carboxymethyl groups per repeating unit and is usually in the range 0.41.5. CMC is generally found under sodium salt form, a water-soluble product for DS0.5. A maximum degree of substitution of 1.5 is permitted, but more typically DS is in the range 0.60.95 for food applications (Coffey etal., 2006andMurray, 2000).CMC is commonly chosen as a stabilizing agent for its low cost in acidified milk drinks instead of pectin in Asia, especially in China (Chen, Zheng, Chen, & Rao, 1996). The application and the stabilization mechanism of pectin and SSPS in acidified milk drinks have been extensively studied in recent years (Liu etal., 2006andNakamura etal., 2006). However, the stabilizing effects of CMC on this kind of drinks are less reported. The stability of casein micelles at low pH could be improved by CMC. In a previous work (Du etal., 2007), we found that electrosorption of CMC onto casein micelles took place below pH 5.2 and the adsorbed CMC layer on the surface of casein could prevent flocculation of casein micelles by steric repulsion. In addition, the non-adsorbed CMC increased the viscosity of serum and slowed down the sedimentation of casein particles. The adsorbed CMC layer caused a repulsive interaction between the casein micelles at low pH in the same way as -caseins do at neutral pH. This phenomenon is related to the interaction between protein (mainly casein micelles) and CMC.The stability of acidified milk drinks depends largely on the interactions between casein and polysaccharides, which can be influenced by the concentrations of protein and polysaccharides (Tromp etal., 2004andTuinier etal., 2002), pH (Nakamura etal., 2003), molecular properties of polysaccharides (Laurent and Boulenguer, 2003,Maroziene and de Kruif, 2000andPereyra etal., 1997), ionic environment (Ambjerg Pedersen & Jorgensen, 1991), milk protein composition and processing (Boulenguer and Laurent, 2003,Glahn, 1982andSedlmeyer etal., 2004;), and thermal history of the sample (Horne, 1998,Lucey etal., 1999andZaleska etal., 2000) etc.Although the interactions between casein micelles and CMC and the stability of the acidified milk drinks might be primarily dependent on pH and concentration of CMC as previously reported (Du etal., 2007), the molecular weight and substitution pattern of carboxymethyl groups on CMC should be emphasized because in the practical processing of acidified milk drinks the properties including stability of the drinks can be obtained by the adjustment on the molecular parameters of CMC. In the present work, we aim to investigate the influence ofMwand DS of CMC on the interaction between CMC and casein micelles and thus on the stability of acidified milk drinks.2. Materials and methods2.1 MaterialsA series of CMC with differentMw(250,000Da and 700,000Da) and different DS (0.7, 0.9 and 1.2) were purchased from the Acros organics (Morris Plains, New Jersey). Skim milk powders were obtained from Fonterra Co-operative Group (Wellington, New Zealand). Citric acid monohydrate was obtained from Shanghai Chemical Reagent Co., Ltd. (Shanghai, China).2.2 Preparation of samples for dynamic light scattering (DLS) and -potential experimentsThe sample was made by dispersing 80g/kg reconstituted skim milk in simulated milk ultra filtrate (SMUF) (Jenness & Koops, 1962) (1:100). SMUF contains Na, K, Ca, Mg, phosphate and citrate and was used to dilute mixtures in an environment which would simulate the salt system in milk. Then 5g/kg CMC was added to the diluted reconstituted skim milk at about neutral pH (6.66.7) to obtain 800mg/kg skim milk powders containing 400mg/kg CMC. All solutions in this measurement were prepared with ultra-pure water with 18.2M/cm (Millipore, Bedford, MA. USA), and filtered through 0.22m membrane filters prior to use. The apparent diameter and -potential of casein micelles were monitored during acidifying the diluted reconstituted skim milk with citric acid.2.3 Dynamic light scattering measurement (DLS)Dynamic light scattering measurements were carried out with a Malvern Zetasizer 3000HSA (Malvern Instruments, Worcestershire, UK) equipped with a 10W max output HeNe laser and at aof 633nm. Measurement occurred at 90 from the incident beam and gave an estimation of the particle mean diameter distribution in intensity. The temperature of the samples was controlled by a JoulePeltier thermostat at 20C. The stated results of each measurement were the average of 10 measurements. And all measurements were performed three times. The biggest variance of the measurement was below 10%.2.4 -Potential measurementThe -potential of casein micelles as a function of pH was determined using a particle electrophoresis instrument (Zetasizer Nano ZS, Malvern Instruments, Worcestershire, UK) which measures the direction and velocity of droplet movement in applied electric field at 20C. The -potential provides an estimate of the net charge of a particle measured at the shear plane, which depends on the charge on the actual particle (in this case casein micelles and polysaccharides) plus the charge associated with any ions that move along with the particle in the electric field. The sample was similar to those for DLS measurements. An individual -potential was determined from the average of three readings taken on the same sample. All measurements were performed three times.2.5 Preparation of acidified milk drinksThe 80g/kg reconstituted skim milk was prepared by mixing skim milk powders and distilled water at 45C for 30min. Meanwhile, CMC and sucrose were dry mixed together and then the mixture was dissolved in distilled water at 75C by stirring for 20min. Stabilizer and reconstituted skim milk were mixed at a 1:1 ratio to obtain 40g/kg skim milk powders containing 4g/kg CMC and 80g/kg sucrose. The pH of this mixture was directly acidified to 4.0 with 500g/kg citric acid at 20C. The acidified milk drinks were preheated to 65C and then homogenized at 200 bar with a two-stage value homogeniser Rannie TYPE 8.30 H (APV Rannie A/S, Denmark). All samples were stored in sealed glass bottles. The bottle of each sample (500ml) was heated in a water bath at 90C for 30min. Sodium azide (0.02%) was added to prevent bacterial growth. Measurements were performed after the samples were stored at room temperature overnight. All measurements were performed three times.2.6 Measurement of apparent viscosity for the acidified milk drinksThe apparent viscosity of acidified milk drinks was measured by a Brookfield Viscometer LVDV-I, Model NDJ-79 with No. 1 rotor, at 100rpm/min, and 25C.2.7 Measurement of particle size for the acidified milk drinksThe acidified milk drinks were diluted to a measurable concentration (100200 times) with distilled water. Then the particle size was measured with a Laser Diffraction Particle Size Analyser, Malvern MasterSizer 2000 (Malvern Instruments Ltd., Worcestershire, UK).2.8 Measurement of storage stability for the acidified milk drinksSedimentation and serum phase occurred during storage were observed with the optical analyser TURBISCAN MA 2000 (Ramonville-St-Agne, France). The cylindrical glass tubes containing 5ml of sample were stored at 25C. Sedimentation and serum phase fraction as a function of time were followed after the sample was prepared for 30 days.2.9 Phase separationThe mixtures of 40g/kg skim milk and CMC with different concentrations (05g/kg) were acidified to pH values 4.70.1 and 3.80.1, respectively, while without acidification the pH of the mixture was ca. 6.70.1. 10ml sample was placed in a graduated glass tube with lid at room temperature of 25C. The stability of the mixture was obtained from visual observation 3 days after preparation. The sample was regarded as stable if the system was homogeneous whereas the sample was unstable if obvious phase separation took place.3. ConclusionsBothMwand DS of CMC influenced the interaction between CMC and casein micelles and thus the stability of acidified milk drinks. At pH 6.7, there was no interaction between caseins and CMC due to charge repulsion and mixtures of casein and CMC were stable at low C