乳清蛋白变性率测定方法研究进展

乳制品的生产加工过程中,必然要进行热处理,一方面可以杀菌灭酶,另一方面会使乳清蛋白发生变性。乳清蛋白的变性会引起免疫球蛋白、如过氧化物酶等活性物质失活,对乳制品的感官、质构、营养等存在极为重要的影响,是酸奶、奶酪加工成功的重要影响因素,也是其品质优劣的重要评价指标。本文综述了乳清蛋白的热变性机理和各种测定乳清蛋白变性率的方法,并对这些方法的优缺点、研究现状进行了详细介绍,为研究者在适宜的情况下选择最便捷、快速、低成本的乳清蛋白变性率测定方法提供依据。     

鱼肉蛋白的热变性研究进展

在鱼肉蛋白的加工过程中,加热处理是最常见的工序之一。热处理造成的蛋白热变性会对蛋白质的理化性质和功能特性产生很大的影响,且这种影响多难以复原。本文总结了近几年来国内外关于鱼肉蛋白在加热过程中蛋白组成成分、总巯基和羰基、溶解度、浊度、黏度、Ca2+-ATPase活性、凝胶、质构等特性指标的变化趋势的研究进展,结合蛋白质热变性的机理深入分析其变化原因,提出今后在鱼类加工方面对于鱼肉蛋白热变性的研发方向,旨在为鱼制品选择合理的热加工工艺的提供理论依据。     

日本蛋白肽系列配料市场动向

从乳蛋白得来的配料中，有将脱脂奶粉以酸、酵素处理后，把蛋白分离精制，从酪蛋白和乳清中提取得到的乳清蛋白、乳清分离蛋白等。还有将脱脂奶粉维持在未变性状态下共沉淀所得的总乳蛋白质和以膜分离方式得到的乳蛋白浓缩物等，这些产品可作为营养价值高的配料在食品工业中进行利用。但这些乳蛋白配料几乎都依赖进口，所以常因生产国的情况和海外需求的动向，产生价格和进口量的变动。     

蛋白溶解性分析法研究大米焙炒过程中蛋白质热变性行为

考察了焙炒过程中大米蛋白质的热变性行为,通过大米蛋白在不同功能溶剂中的溶解度变化了解大米蛋白质在焙炒过程中次级结构的变化及热变性信息。发现热变性主要发生在焙炒的前期,热变性包括蛋白质次级结构的变化和更高能级的化学变化。与传统蒸煮方法相比,焙炒大米的蛋白质热变性程度较低。粳米和糯米中的蛋白质热变性行为基本相似,选用不同的加热介质对大米蛋白的热变性没有影响。     

加工工艺对荞麦蛋白热性质和体外模拟消化过程的影响

本实验研究了加工工艺对荞麦蛋白(BWP)的热性质和体外模拟消化过程的影响。荞麦蛋白有两个变性温度,在80℃和102℃附近,分别对应8S和13S球蛋白的变性。脂肪的存在对荞麦蛋白的变性温度影响不大,但会降低其热焓。在模拟的胃蛋白酶消化过程中,BWP的氮释放量较大豆分离蛋白(SPI)先高后低;而在胰蛋白酶消化过程中,BWP的氮释放量较SPI高。这与其蛋白组成以及SPI中存在活性较高的胰蛋白酶抑制剂有关。荞麦蛋白的球蛋白(13S和8S)易被降解(胃蛋白酶消化阶段),而2S清蛋白的降解主要集中在胰蛋白酶消化阶段。经脱脂处理、超声协助提取的荞麦蛋白(DFU-BWP)和搅拌提取的荞麦蛋白(FM-BWP)的氮释放量在整个胃蛋白酶消化过程中类似,均明显高于超声提取的荞麦蛋白(FU-BWP)(p<0.05),说明胃蛋白酶对BWP的降解过程与其脂肪含量以及加工工艺有关。     

乳清蛋白的热变性及其在酸乳生产中的应用

介绍了乳清蛋白与酪蛋白热缔合过程的模型，乳清蛋白热变性的动力学以及热变性作用对酸奶质构的影响，乳清蛋白的变性度与酸奶最终质量存在密度的关系。应用β－乳球蛋白的等变性度曲线可以选择酸奶生产中的最适热处理条件。     

影响低温棉籽蛋白KOH蛋白质溶解度因素的研究

使用有机溶剂将棉仁中的棉籽油和棉酚萃取后,余下的棉籽蛋白是一种优良的动物饲料原料。棉籽蛋白KOH蛋白质溶解度的高低直接影响动物对饲料中蛋白质的吸收率。结合生产实际研究了醇、热等变性因素在加工过程中对低温棉籽蛋白KOH蛋白质溶解度的影响,确定了最佳工艺参数,优化了低温棉籽蛋白加工工艺。     

乳清蛋白的热变性及其在酸奶生产中的应用

介绍了乳清蛋白与酪蛋白热缔合过程的模型、乳清蛋白热变性的动力学以及热变性作用对酸奶质构的影响。乳清蛋白的变性度与酸奶最终质量存在密切的关系。应用β-乳球蛋白（β-LG）的等变性度曲线可以选择酸奶生产中的最适热处理条件（温度／时间）。     

大豆蛋白对鲢鱼肌原纤维蛋白凝胶特性的影响

将大豆分离蛋白经不同的变性温度及变性时间处理后,与鲢鱼肌原纤维蛋白以不同的比例混合制备热诱导凝胶。通过测定混合蛋白体系的凝胶强度及保水性,分析热变性大豆分离蛋白对混合凝胶特性的影响。结果表明,热变性后的大豆分离蛋白可以改善混合蛋白凝胶体系的凝胶强度及保水性,其中,大豆分离蛋白经过100℃变性180 min后,二者以1∶4的比例混合,得到的混合凝胶强度及保水性最佳。     

中式芝士酱的研制

本实验主要是针对芝士酱制作工艺进行研究,对芝士粉、脱脂奶粉、乳清粉、复合磷酸盐、变性淀粉和食盐等的添加量分别进行了单因素实验。主要从感官和质构上进行评价,最终确定出最佳工艺配方：芝士粉的添加量为14％,复合磷酸盐的添加量为2．5％,脱脂奶粉和乳清粉的添加量为20％,变性淀粉的添加量为1．75％,食盐的添加量在1．8％。     

不同热处理脱脂乳粉对褐色乳酸菌饮料稳定性的影响

比较了不同热处理脱脂乳粉的理化性质,并将其应用于褐色乳酸菌饮料生产,以鲜制脱脂乳为对照,探讨了不同脱脂乳原料以及褐色乳酸菌饮料生产工艺对饮料稳定性的影响.结果表明:不同热处理脱脂乳粉的蛋白质、脂肪、水分含量以及乳酸度均无显著差异(P>0.05);但其乳化性、起泡性及乳清蛋白氮指数存在显著差异(P<0.05),随着乳粉受...     

Comparison of Rat Hepatic Cholesterol Biosynthesis During Skim Milk Versus Whey Permeate Ingestion

Whey permeate is an ultrafiltrate of whey that is devoid of protein but contains lactose, salts, and other soluble low molecular weight compounds. These experiments compared cholesterol concentrations of blood plasma, hepatic lipids, and hepatic cholesterol biosynthesis of rats ingesting skim milk powder versus whey permeate powder. Groups of young male rats weighing 90 to 92 g were fed a casein-based diet into which skim milk powder or whey permeate powder was incorporated isocalorically. No effects of skim milk or whey permeate on plasma cholesterol concentrations were observed at any time during 5-wk of feeding. However, 3-hydroxy-3-methylglutaryl coenzyme A reductase activity was increased by either skim milk or whey permeate feeding. Hepatic cholesterol, triglyceride, and phospholipid concentrations at wk 5 were unchanged. Plasma and hepatic cholesterol responses of rats to whey permeate ingestion are similar to those that occur with skim milk consumption, and plasma and hepatic cholesterol concentrations do not reflect necessarily an increase in hepatic cholesterol biosynthesis.     

Lactosylation of milk proteins during the manufacture and storage of skim milk powders

Extensive lactosylation of milk proteins in standard skim milk powder dried against air between 185 and 90°C (inlet and outlet temperatures of the air) was detected by capillary electrophoresis. Optimisation of the drying conditions included keeping the outlet temperature low (preferably <80°C), since this was the parameter which most affected the extent of lactosylation of milk proteins. The inlet temperature was set in order to obtain the best compromise between a low extent of lactosylation and a high drying rate (170–175°C). These conditions allowed the manufacture of low-lactosylated skim milk powder. Storage of freeze-dried and control low-lactosylated skim milk powder at different temperatures showed that both temperature and moisture content affected the progress of lactosylation during storage. Further drying to less than 2.5% moisture content (w/w) and storage at low temperatures were required to prevent the development of lactosylation in the low-lactosylated skim milk powder.     

Effect of elevated temperature storage on the digestible reactive lysine content of unhydrolyzed- and hydrolyzed-lactose milk-based products

The study aimed to evaluate the effects of storage at elevated temperatures on reactive Lys content and true ileal reactive Lys digestibility in a skim milk powder and a hydrolyzed-lactose skim milk powder. A validated bioassay based on guanidination of food and digesta samples was applied. Semisynthetic diets containing the milk powders as the sole sources of protein were formulated and fed to growing rats. Chromic oxide was included in each diet as an indigestible marker. Digesta were collected posteuthanasia and analyzed along with the diets for reactive Lys (homoarginine), and true ileal reactive Lys digestibility was calculated after correction for endogenous Lys loss. For the skim milk powder, there was no decrease in reactive Lys digestibility (Lys availability) when the powder was stored at 30 and 35°C for 18 mo. In contrast, when stored at 40°C for 12 mo, a small but statistically significant (6%) decrease was observed. For the hydrolyzed-lactose product, a 22% decrease in Lys availability was observed after storage at 35°C for 18 mo, and a 17% decrease was observed when stored at 40°C for only 6 mo. Digestible reactive (available) Lys content decreased by more than 20% for the skim milk powder stored at 30 and 35°C for 18 mo and 40% when stored at 40°C for 12 mo. Furthermore, available Lys decreased in the hydrolyzed-lactose skim milk powder by 41% when stored at 30°C for only 18 mo and 34 and 65% when stored at 35 and 40°C, respectively, for 6 mo. Elevated temperatures and prolonged storage periods negatively influenced the available Lys contents of both milk powders. The decrease in available Lys content and Lys availability was greater for the hydrolyzed-lactose skim milk powder compared with the normal skim milk powder, after storage at elevated temperatures.     

差示扫描量热法测定奶粉的热稳定性

以差示扫描量热法对全脂奶粉、脱脂奶粉、全脂甜奶粉及中老年奶粉的热稳定性进行了研究,运用Ozawa和Kissinger方程求得各种奶粉的活化能,比较了这几种不同成分的奶粉的热稳定性,分析了奶粉成分对奶粉热稳定性的影响。结果表明,热稳定从高到低的顺序依次为脱脂奶粉、全脂奶粉、中老年奶粉、全脂甜奶粉,并且牛乳脂肪、植物油、蔗糖会降低奶粉的热稳定性。     

PREPARATION OF SOYBEAN CHEESE USING LACTIC STARTER ORGANISMS. Effects of Mold Ripening and Increasing Concentrations of Skim Milk Solids

SUMMARY– Soybean cheeses were prepared from blends of skim milk powder and soybean milk in which the skim milk powder contributed 0, 25, 50 and 75% of total dry weight. The amount of skim milk had little effect on the flavor of the finished cheese, due to the dominating effect of the beany flavor of the soybeans. Similarly, the skim milk had little effect on the texture of the finished cheese, indicating that only a small amount of fibrous matter from the soybeans is necessary to impart a mealy texture to the product. Mold ripening resulted in desirable changes in texture, but these were offset by the development of bitter flavors.     

Partitioning of nitroxynil,oxyclozanide and levamisole residues from milk to cream,skim milk and skim milk powder

Veterinary drugs are necessary to control fluke in animals, and if not properly used, residues of these drugs may be found in milk. The aim of this study was to determine whether residues of nitroxynil, levamisole and oxyclozanide in milk partition into skim milk powder during processing. Milk targeted to contain high, medium or low levels of residue was obtained following treatment of trial animals. On separation of cream and skim milk, > 90% of the residue partitioned with the skim milk in all cases. During powder processing, the residues were not degraded with almost 90% of the residue detected in the powder.     

Small and large deformation rheology and microstructure of κ-carrageenan gels containing commercial milk protein products

The rheological behaviour of commercial milk protein/κ-carrageenan mixtures in aqueous solutions was studied at neutral pH. Four milk protein ingredients; skim milk powder, milk protein concentrate, sodium caseinate, and whey protein isolate were considered. As seen by confocal laser microscopy, mixtures of κ-carrageenan with skim milk powder, milk protein concentrate, and sodium caseinate showed phase separation, but no phase separation was observed in mixtures containing whey protein isolate. For κ-carrageenan concentrations up to 0.5 wt%, the viscosity of the mixtures at low shear rates increased markedly in the case of skim milk powder and milk protein concentrate addition, but did not change by the addition of sodium caseinate or whey protein isolate. For κ-carrageenan concentrations from 1 to 2.5 wt%, small and large deformation rheological measurements, performed on the milk protein/κ-carrageenan gels, showed that skim milk powder, milk protein concentrate or sodium caseinate markedly improved the strength of the resulting gels, but whey protein isolate had no effect on the gel stength.     

Investigation of the migration of triclabendazole residues to milk products manufactured from bovine milk,and stability therein,following lactating cow treatment

Triclabendazole (TCB) is a flukicide used in the treatment of liver fluke in cattle; however, its use is currently prohibited in lactating dairy cows. In this study, following administration of 10% Fasinex (triclabendazole, Novartis Animal Health UK Ltd., Camberley, UK) the milk of 6 animals was used to manufacture dairy products, to ascertain if TCB residues in milk migrate into dairy products. The detection limit of the ultra-high-performance liquid chromatography-tandem mass spectrometry method used was 0.67 μg/kg. The highest concentrations of TCB residue measured, within the individual cow milk yield, was 1,529 ± 244 µg/kg (n = 6), on d 2 posttreatment. Days 2 and 23 posttreatment represented high and low residue concentrations, respectively. At each of these 2 time points, the milk was pooled into 2 independent aliquots and refrigerated. Milk products, including cheese, butter, and skim milk powder were manufactured using pasteurized and unpasteurized milk from each aliquot. The results for high residue milks demonstrated that TCB residues concentrated in the cheese by a factor of 5 (5,372 vs. 918 µg/kg for cheese vs. milk) compared with the starting milk. Residue concentrations are the sum of TCB and its metabolites, expressed as keto-TCB. Residues were concentrated in the butter by a factor of 9 (9,177 vs. 1,082 μg/kg for butter vs. milk) compared with the starting milk. For milk, which was separated to skim milk and cream fractions, the residues were concentrated in the cream. Once skim milk powder was manufactured from the skim milk fraction, the residue in powder was concentrated 15-fold compared with the starting skim milk (7,252 vs. 423 µg/kg for powder vs. skim milk), despite the high temperature (185°C) required during powder manufacture. For products manufactured from milk with low residue concentrations at d 23 posttreatment, TCB residues were detected in butter, cheese, and skim milk powder, even though there was no detectable residue in the milk used to manufacture these products. Triclabendazole residues were concentrated in some milk products (despite manufacturing treatments), exceeding residue levels in the starting milk and, depending on the storage conditions, may be relatively stable over time.     

Rheological and sensory properties of stirred yoghurt with inulin‐type fructans

This study concerns physicochemical and sensory analysis of stirred yoghurts, in which skim milk powder was partly replaced by different inulins. The composition of basic solutions contained 12% skim milk powder and 4% inulin, while reference yoghurts contained 16% SMP or whole milk powder. Rheological and sensory analysis showed that one‐quarter of milk powder could be substituted by long‐chain inulin in low‐fat stirred yoghurt. Short‐chain inulin and oligofructose can potentially be applied in the production of drinking yoghurt. Sensory evaluation showed that milk fat cannot be successfully substituted by inulin.