二次均质工艺中一次均质压力对黄油基搅打稀奶油品质的影响

以无盐黄油和脱脂乳为原料制备黄油基搅打稀奶油,采用二次均质工艺,研究了一次均质压力（二次均质压力不变）对黄油基搅打稀奶油的粒径、脂肪部分聚结率、流变学特性、搅打性能的影响,分析了各评价指标之间的相关性。结果表明,黄油基搅打稀奶油的一次均质压力在10.0~15.0 MPa时,随着均质压力的增大,脂肪球粒径D4,3由1.85 μm逐渐减小到1.57 μm,且在15.0 MPa时脂肪球粒径D4,3达到最小为1.57 μm;黄油基搅打稀奶油的脂肪部分聚结率随着一次均质压力的增大逐渐增大,由13.74%增大到17.53%;搅打时间随着均质压力的增大逐渐由314 s减小到265 s且一次均质压力在15.0 MPa时搅打时间最少为265 s;泡沫稳定性由78.09%逐渐增加到87.26%,且泡沫稳定性在15.0 MPa时泡沫稳定性达到最大87.26%。因此将黄油基搅打稀奶油的一次均质压力控制在10.0~15.0 MPa范围内较适宜。     

乳化剂用量对搅打稀奶油搅打性能和品质的影响机理研究

研究了乳化剂用量对搅打稀奶油的乳浊液粒度分布、脂肪球部分聚结、液相蛋白浓度、感官品质和泡沫稳定性的影响。研究结果表明:乳浊液冷却及解冻后脂肪球粒径随乳化剂用量增加而减小,随着乳化剂用量增加,脂肪部分聚结速度和液相蛋白质浓度增加速度加快,搅打起泡率和感官品质以乳化剂用量为0.60%时最好,搅打稀奶油稳定时间随乳化剂用量增加呈先增加后下降趋势,当乳化剂用量为0.60%时,稳定时间达到最大2.4h。综合考虑,当乳化剂HLB值为7,乳化剂用量为0.60%时,搅打稀奶油搅打性能和品质最佳。     

二段均质压力对黄油基搅打稀奶油品质的影响

该文在黄油基搅打稀奶油经高压均质、热处理后分别使用1.0~5.0 MPa压力进行二段均质处理,并以未经二段均质处理的产品为对照,比较经不同二段均质压力处理后产品稳定性及搅打品质的变化。实验发现,对照产品脂肪球粒度分布出现明显双峰现象,乳液稳定性差,搅打时间为372.00 s,起泡率仅193.70%,并且在光学显微镜下观察到大量絮凝的脂肪球簇;当二段均质压力在1.0~ 3.0 MPa范围内增大,产品脂肪球平均粒径减小,产品稳定性增强,搅打时间缩短,打发率上升,絮凝的脂肪球簇的数量明显减少;当二段均质压力达到3.0 MPa,产品粒度分布趋于稳定,搅打时间仅需306.50 s,起泡率达235.10%,光学显微镜下未观察到明显絮凝现象。相比对照组,经3.0 MPa压力处理后的产品稳定性更好,搅打成型时间由372.00 s缩短至306.50 s,起泡率由193.70%提高至235.10%,实验结果表明,在搅打稀奶油生产中使用3.0 MPa压力进行二段均质可有效阻止乳液脂肪球絮凝,提高产品的稳定性及搅打品质,可满足工业生产高品质搅打稀奶油的要求。     

酪蛋白和工艺对再制稀奶油稳定性的影响

本研究主要通过测定再制稀奶油的粒径、界面蛋白含量、黏度、微流变性质分析胶束酪蛋白浓缩粉(micelle casein concentrate,MCC)、酪蛋白酸钙(calcium caseinate,CaC)粉及工艺(灭菌、二次均质)对再制稀奶油稳定性的影响。结果表明:蛋白添加量为1.0%(质量分数,后同)和2.0%时,MCC再制稀奶油的失稳系数分别为0.396±0.011、0.032±0.001,说明稳定性随蛋白添加量的增加而提高,而CaC再制稀奶油稳定性的变化规律与之相反。灭菌后,MCC再制稀奶油脂肪球粒径D3,2、界面蛋白含量及黏度显著增加(P0.05),均方根位移(mean square displacement,MSD)明显降低,CaC再制稀奶油与MCC再制稀奶油的变化明显不同,除界面蛋白含量由3.9～5.5 mg/m~2增至5.2～7.0 mg/m~2外,粒径D3,2、黏度及MSD(2.0%CaC再制稀奶油除外)无明显变化。二次均质后,MCC再制稀奶油脂肪球粒径D3,2、界面蛋白含量及黏度显著下降(P0.05),MSD明显增加,而CaC再制稀奶油样品中除1.0%CaC再制稀奶油粒径D3,2由(2.80±0.10)μm下降至(2.06±0.11)μm外,其他理化性质变化不明显。虽然MCC乳化能力较CaC低,但其在添加量2.0%时制备的稀奶油稳定性最好。工艺会导致再制稀奶油(尤其是MCC再制稀奶油)理化性质间平衡的改变,再制稀奶油的稳定性也随之改变。     

均质压力对UHT搅打稀奶油品质的影响

以新鲜稀奶油为主要原料,考察了不同的均质压力对UHT搅打稀奶油的脂肪球粒径、流变学特性、搅打特性的影响,分析了各评价指标之间的相关性。结果表明,UHT搅打稀奶油最适均质压力范围为3～5 MPa;随着均质压力的增大(1～9 MPa),脂肪球粒径减小,但打发成型所需时间增加;在α=0.01水平上,粒径与搅打时间、起泡率显著相关;在α=0.05水平上搅打时间与起泡率显著相关。     

复配蛋白质添加量对黄油基搅打稀奶油稳定性及搅打性能的影响

该文以m(酪蛋白)∶m(乳清蛋白)=2∶1复配蛋白质,以无盐黄油和离心乳脂肪为原料制备黄油基搅打稀奶油。以搅打时间、搅打起泡率、脂肪部分聚结率、粒径分布、表观黏度和泡沫稳定性为评价指标,研究复配蛋白质的添加量对黄油基搅打稀奶油乳液稳定性及搅打性能的影响。结果表明,当复配蛋白质的添加量为0.9%～1.2%(质量分数)时,脂肪球粒径分布为0.81～7.16μm,乳液脂肪附聚率为6%～10%,乳液的搅打时间为277～296 s,搅打起泡率达到200%～203%,泡沫稳定性为95.86%～97.03%。故将黄油基搅打稀奶油中复合蛋白质添加量控制在0.9%～1.2%,搅打稀奶油的乳液稳定性及搅打性能较好,为以黄油为原料生产高品质搅打稀奶油奠定理论基础。     

油脂用量对搅打稀奶油的搅打性能和品质的影响

研究了油脂用量对搅打稀奶油的粒度分布、脂肪部分聚结、液相蛋白质浓度、搅打起泡率、质构特性、感官品质和稳定时间的影响。研究表明:随着油脂用量增加,冷却后乳浊液脂肪球粒径增大;搅打过程中脂肪部分聚结速度和脂肪球粒径d4,3均随油脂用量增加而增大,且脂肪部分聚结率与脂肪球粒径d4,3有很好的相关性;液相蛋白质浓度和搅打起泡率降低;搅打稀奶油的质构特性值增加;稳定时间呈先增后减趋势,当油脂用量为23%时,搅打稀奶油的稳定时间最长达到2.7h;搅打稀奶油的感官品质以油脂用量为20%最好,综合考虑,油脂最佳用量范围是20%-23%。     

均质的作用及影响均质效果的因素

一、前言在乳品工业中,均质主要用于防止或延缓乳或乳制品的脂肪分离,这一目的主要靠减小乳脂肪球的直径来实现。一般牛乳中脂肪球平均直径为3～4μm左右,均质后可将脂肪球平均直径降至1μm以下,且大小比较均一。均质主要有两种方式,离心均质和压力均质,后者应用得最为普遍。压力均质的作用过程是:物料在高压作用下,以100～250m/s的流速经过比脂肪球直径小许多的狭缝,由此产生强烈的剪切作用、空洞作用和湍流作用,使脂肪球被挤压伸长、变成     

冷冻解冻过程中稀奶油特性的研究

以新鲜稀奶油为原料,考察了不同冷冻时长及解冻方式对稀奶油的微观结构、脂肪球粒径、脂肪附聚率、冻融稳定率及油水分布情况的影响,并以植脂奶油为对比。结果表明:冷冻24h的稀奶油冷藏解冻后粒径值D×(50)最大,较原样增大了128%;而水浴解冻时冷冻2h的稀奶油D×(50)最大,随着冷冻时长增加,D×(50)逐渐减小。冷冻解冻后导致了新鲜稀奶油油水分离,检测到的游离脂肪信号幅度增强;脂肪球液滴被迫聚集,脂肪附聚率逐渐增加;稀奶油体系结构被破坏,冻融稳定率持续降低,冷冻24 h的样品冷藏解冻后降低了60.54%,水浴解冻后降低了53.17%,水浴解冻后稀奶油的冻融稳定率均高于冷藏解冻处理后的样品。最终稀奶油无法打发,而植脂奶油则仍保持均一稳定状态。     

微射流均质处理对碎米淀粉性质影响的研究

采用高压微射流均质处理碎米制备低蛋白含量的大米淀粉产品,并对淀粉颗粒形貌学、大小、淀粉破损率以及热学性质进行观察与测定。研究表明:高压微射流均质压力达到100MPa,均质次数为2次的情况下,可以获得最低蛋白回收率与纯度的淀粉样品,分别为15.30%和1.29%。淀粉颗粒表面积平均粒径(d32)与体积平均粒径(d43)分别从19.70μm与121.04μm降低到9.30μm与65.13μm。破损淀粉的比例从46.72%显著提高到64.66%,且对大米淀粉的热性质影响并不显著。该处理能有效解聚大米淀粉-蛋白质复合体结构,制备出结构和性质更接近天然大米淀粉的产品,有利于其在食品工业中的应用。     

RHEOLOGICAL PROPERTIES OF AGED ASEPTIC ICE CREAM MIX AND MELT1

Age thickening of UHT steam injected ice cream mix and melt was investigated by determining rheological model constants. By utilizing a cone and plate viscometer, rheological models (3 element solid) were developed for creep-relaxation. Empirical relationships were derived relating the elastic and viscous constants to storage time. Soft serve ice cream mix (4.0% fat) was processed at 149°C for 3.4, 6.9, and 20.3 s. The ice cream mix was stored at 20 and 30°C and tested at four week intervals from zero through 24 weeks. Flow properties of the mixes and melts were quite stable throughout the storage period although the lowest heat treatment (3.4 s for 149°C) suggested mild age thickening by 24 weeks. The strongest element constant for all samples was the series elastic. The viscous constant was next with the Kelvin elastic constant being quite weak. Melts had lower constants than the mixes. Model constants varied little between samples stored at 20°C and those at 30°C.     

Improvement of storage stability and foaming properties of cream by addition of carrageenan and milk constituents

The increasing automation in the dairy industry and the longer guaranteed shelf life of the packed products of cream lead to a loss in the quality of liquid and whipped cream associated with the formation of irreversible plugs, too long whipping times and high degrees of liquid separation of the whipped product. In test series 0.015% carrageenan, 0.25% protein—fat as the dry matter (whey proteins with high-melting milk fat fractions) or a combination of both were added to homogenized and unhomogenized, pasteurized or ultra-high temperature treated (UHT) cream from the winter and summer feeding period (fat content: 30%). The creaming behaviour after storage at 7 or 20°C was characterized by determining the fat content in different layers of a cream package. In cream samples without additives ünstirrable layers had been formed after 2–7 weeks, in particular during the long storage times of UHT cream without cooling. A desired (i.e. low) degree of creaming of the liquid cream as well as little separation in the whipped product could be achieved for all samples only by means of a combination of carrageenan and protein—fat powder. Of the rather varying carrageenan fractions examined, a combination of similar proportions of kappa- and iota-carrageenan has proved to be particularly effective without excessively increasing viscosity.     

Oxidative stability of ultra high temperature milk enriched in conjugated linoleic acid and trans-vaccenic acid

Milk naturally enriched in conjugated linoleic acid (CLA) and trans-vaccenic acid (TVA) was ultra high temperature (UHT)-treated at 125–145 °C for 2–20 s and stored at 4 and 25 °C for up to 120 d. The oxidative stability of treated enriched milk was evaluated in terms of changes on the contents of CLA and TVA, dissolved oxygen, hydroperoxides, thiobarbituric acid reactive substance (TBARS) and formation of volatiles. After UHT treatment, more than 78% of CLA and 87% of TVA remained. After 15 d of storage at 25 °C, the CLA and TVA were relatively stable with values in the range of 67–75 and 63–73%, respectively. During storage, CLA oxidized faster than TVA, independently of the UHT treatment and storage conditions. Heptanal was the most abundant volatile resulting from UHT processing and a potential suitable marker for heat treatment of milk rich in CLA and TVA.     

Solid phase microextraction of stale flavour volatiles from the headspace of UHT milk

Solid phase microextraction (SPME) offers a solvent‐free and less labour‐intensive alternative to traditional flavour isolation techniques. In this instance, SPME was optimised for the extraction of 17 stale flavour volatiles (C3–11,13 methyl ketones and C4–10 saturated aldehydes) from the headspace of full‐cream ultrahigh‐temperature (UHT)‐processed milk. A comparison of relative extraction efficiencies was made using three fibre coatings, three extraction times and three extraction temperatures. Linearity of calibration curves, limits of detection and repeatability (coefficients of variation) were also used in determining the optimum extraction conditions. A 2 cm fibre coating of 50/30 µm divinylbenzene/Carboxen/polydimethylsiloxane in conjunction with a 15 min extraction at 40 °C were chosen as the final optimum conditions. This method can be used as an objective tool for monitoring the flavour quality of UHT milk during storage. Copyright © 2005 Society of Chemical Industry     

Measurement of homogenisation efficiency of milk by laser diffraction and centrifugation

For ultra high temperature (UHT) milk, the development of a cream layer is a shelf life limiting factor that can be controlled by homogenising the milk correctly. This article suggests a method to measure homogenisation efficiency using laser diffraction. Milk was diluted with a protein cluster dissolving solution before measurement with a Malvern Mastersizer 3000. To avoid multiple scattering obscuration needed to be 1.5–3.5%. The D[5;3] (μm) value extracted from the particle size distribution could, with the equation developed, be directly correlated to a homogenisation efficiency (NIZO value) obtained by centrifugation of the milk sample. The equation presented is only valid for monomodal distributions and analysis should be performed on freshly produced milk.     

On the influence of non‐enzymatic crosslinking of caseins on the gel strength of yoghurt

After storage of UHT milk at 37°C resp. 50°C, yoghurt was prepared. For a storage temperature of 37°C, breaking strength of the yoghurt samples increased from 2.7 to 5.8 N with increasing storage duration of the UHT milk. A plateau is reached after 17 days of storage. This increase in breaking strength correlates with a significant increase in non‐reducible casein oligomerization from 14% for fresh UHT milk to 25% measured using size exclusion chromatography under reducing and denaturing conditions and calculated as sum of predominantly formed dimers and trimers at the total casein fraction. At a storage temperature of 50°C, a less increase in breaking strength from 2.7 to 4.6 N with a plateau after 17 days was observed while casein oligomerization increased to 63%. After acid hydrolysis, only lysinoalanine and histidinoalanine were detected in the caseinate samples via amino acid analysis. The quantified concentration of lysinoalanine and histidinoalanine could not explain the observed casein oligomerization. Thus, unknown crosslinked amino acids must have been formed during storage, inducing significant changes in the functional properties of milk proteins.     

Observations on the Whipping Characteristics of Cream

With the application of UHT technology to the processing of whipping creams, consumers 5 purchase creams with whipping characteristics different from creams processed by conventional pasteurization. This study observed differences in whipping properties among raw, pasteurized, and UHT whipping creams. Whipping time to reach maximum volume, number of days before and after retail sell-by date, and overrun were recorded. Mean whipping time and maximum overrun varied significantly by processor, product composition, and retail cream age. Mean whipping time ranged from 1.6 min for raw unpasteurized creams to 3.4 min for UHT heavy cream without whipping aids. Mean maximum overrun ranged from 141% for UHT heavy creams without whipping aids to 216% for UHT whipping creams with aids. There was considerable variation in mean whipping time and mean maximum overrun among processors for creams of the same composition. Regression analysis between whipping time and retail cream age revealed a positive relationship for some product types and a negative relationship for others. Whipping time and maximum overrun of retail whipping creams vary substantially by product type, processing treatment, and processor.     

自发气调包装对鲜切白菜货架期的影响

为延长鲜切白菜的货架期,本文采用不同透气率和不同面积的气调窗与包装袋相结合进行试验,通过对鲜切白菜包装袋内感官品质、气体成分进行统计和分析,筛选和优化出鲜切白菜最适宜的气调包装。结果表明：自发气调包装可有效改善鲜切白菜贮藏品质,鲜切白菜适宜选用O2和CO2透过速率分别为4×105和1.6×106 cm3/m2?d?atm,透气比为1:4气调窗,所需要气调窗的面积为1~2 cm2/kg,在4 ℃条件下至少可延长货架期4 d;综合计算气调窗和薄膜的透气量可知,适于鲜切白菜包装袋O2和CO2的透过量应分别为1.85×103~2.08×103 和8.59×103~9.51×103 cm3/kg?d?atm,达到鲜切白菜的适宜气体浓度,O2为3.63%~5.10%,CO2为7.77%~8.07%。研制的自发气调包装袋可使鲜切白菜处于适宜的气体状态,可很好地解决包装袋内由于无氧呼吸产生的异味问题,且保留原有的鲜切白菜气味,延长其货架期,为鲜切企业提供有力的技术支持。     

UHT Milk Processing and Effect of Plasmin Activity on Shelf Life: A Review

Abstract: The demand for ultra‐high‐temperature (UHT) processed and aseptically packaged milk is increasing worldwide. A rise of 47% from 187 billion in 2008 to 265 billon in 2013 in pack numbers is expected. Selection of UHT and aseptic packaging systems reflect customer preferences and the processes are designed to ensure commercial sterility and acceptable sensory attributes throughout shelf life. Advantages of UHT processing include extended shelf life, lower energy costs, and the elimination of required refrigeration during storage and distribution. Desirable changes taking place during UHT processing of milk such as destruction of microorganisms and inactivation of enzymes occur, while undesirable effects such as browning, loss of nutrients, sedimentation, fat separation, cooked flavor also take place. Gelation of UHT milk during storage (age gelation) is a major factor limiting its shelf life. Significant factors that influence the onset of gelation include the nature of the heat treatment, proteolysis during storage, milk composition and quality, seasonal milk production factors, and storage temperature. This review is focused on the types of age gelation and the effect of plasmin activity on enzymatic gelation in UHT milk during a prolonged storage period. Measuring enzyme activity is a major concern to commercial producers, and many techniques, such as enzyme‐linked immunosorbent assay, spectrophotometery, high‐performance liquid chromatography, and so on, are available. Extension of shelf life of UHT milk can be achieved by deactivation of enzymes, by deploying low‐temperature inactivation at 55 °C for 60 min, innovative steam injection heating, membrane processing, and high‐pressure treatments.     

Chemical properties and sensory quality of ice cream fortified with fish protein

BACKGROUND: Fish protein powder is a functional ingredient that can be used for enhancing the nutritional value of food products. In this study the effect of fortification with different levels of fish protein powder (FP) on chemical properties and sensory quality of Persian ice cream with 0, 30 and 50 g kg^?1 FP during storage at ? 18 °C for 4 months was investigated. RESULTS: Ice creams fortified with 50 and 30 g kg^?1 FP had significantly higher protein and solid‐non‐fat content than ice cream with 0% FP or 83, 69 and 51 g kg^?1 protein and 215, 204 and 181 g kg^?1 solid non‐fat, respectively. All products had the same levels of fat, lactose, acidity and pH. They had similar sensory quality after production except for colour, but sensory properties of fortified samples changed significantly after 2 months of storage. Colour faded, cohesiveness decreased, sandiness/coarseness increased, sweetness decreased and fish flavour and off‐odour increased. The control ice cream scored highest for additives odour and flavour. CONCLUSION: Development of ice cream fortified with fish protein powder could be an effective way to enhance nutritional and functional value of ice cream. But studies on storage stability, consumers' acceptance and attitudes are recommended if companies are planning to do so. Copyright © 2011 Society of Chemical Industry