蛋白质含量测定方法的比较

蛋白质与生命的起源、存在和进化都密切相关,蛋白质含量测定涉及到生产和科研的众多领域.目前常用的方法有凯氏定氮法、双缩脲法(Biuret)、紫外吸收法、考马斯亮蓝法(Bradford).本文总结各种方法的特点及适用条件,针对不同的待测样品以及对测定结果准确性的要求不同,我们可以采用不同的方法来测定样品中蛋白质的含量.     

食品中蛋白质含量的测定

我国现行标准GB/T5009.5-2003《食品中蛋白质的测定》中的两种方法＂凯氏定氮法＂和杜马斯（Dumas）燃烧法是先将样品硝化后测出含氮量,然后根据氮元素与蛋白质换算系数计算蛋白质的含量,如果添加含氮量高的物质,如三聚氰胺,就可以测出较高的＂蛋白质含量＂。介绍4种直接测定蛋白质的方法：考马斯亮兰法、双缩脲法、Folin-酚试剂法和紫外吸收光谱法,可以避免上述由于添加违规化学物质造成测定蛋白质含量虚高的结果。     

蛋白质测定方法比较与研究进展

蛋白质是生物体中含量最高,功能最重要的生物大分子,与生命的起源和进化都密切相关,因此蛋白质也是生命科学中极为重要的研究对象.关于蛋白质的分析研究,一直是化学家及生物学家极为关注的问题,其含量的测定在生化分析和临床分析中具有重要意义,研究和开发新的、高灵敏度的蛋白质测定方法是生物化学研究的一个活跃领域本文综述了近年来蛋白质测定的方法的研究进展,包括分光光度法、双缩脲法、凯氏定氮法、电泳分析法、质谱分析法在蛋白质测定中的应用.总结各种方法的特点及适用条件.质谱分析是测定结果最准确的测定方法;凯氏定氮法适用范围最广泛,分光光度法是最为简便快速的测定方法.     

凯氏定氮法测定蛋白质的氮含量

蛋白质是人体肌肉、血液、内脏、神经、骨骼、韧带、毛发、指甲和皮肤等组织的主要成分,人体许多与生命活动有关的活性物质,如酶、抗体、激素等,都是由蛋白质或蛋白质的衍生物构成。凯氏定氮法用于测定有机物的含氮量,若蛋白质的含氮量已知时,则可用此法测定样品中蛋白质的含量。     

考马斯法测定棉籽蛋白发酵液中蛋白质含量

介绍了利用生物法来发酵棉籽蛋白,并使用考马斯亮蓝法测定酵液中蛋白质含量的方法。利用蛋白质与考马斯亮蓝显色原理,用紫外分光光度法测定蛋白质含量,检测波长为595 nm,蛋白质含量在0～16.67 mg/L时与吸光度有良好的线性关系,测定所得标准曲线方程为y=0.044 x+0.09,其中R=0.999。结果表明:这种方法快速、简便,RSD=3.86%(n=6),相对标准偏差小于4%,回收率>90%,该法用于实际样品测定取得了令人满意的结果。     

阿莫西林中蛋白质含量的测定

采用考马斯亮蓝G-250法测定阿莫西林中微量蛋白质含量。该法具有良好的准确度、灵敏度、稳定性和重现性,蛋白质浓度与吸光度具有很好的线性关系,符合阿莫西林中蛋白质的测定要求。     

考马斯法测定棉籽蛋白发酵液中蛋白质含量

介绍了利用生物法来发酵棉籽蛋白,并使用考马斯亮蓝法测定酵液中蛋白质含量的方法。利用蛋白质与考马斯亮蓝显色原理,用紫外分光光度法测定蛋白质含量,检测波长为595nm,蛋白质含量在0—16．67mg／L时与吸光度有良好的线性关系,测定所得标准曲线方程为Y=0．044x＋0．09,其中R=0．999。结果表明：这种方法快速、简便,RSD=3．86％（n=6）,相对标准偏差小于4％,回收率〉90％,该法用于实际样品测定取得了令人满意的结果。     

Determination on the Content of Protein in Amoxicillin

采用考马斯亮蓝G-250法测定阿莫西林中微量蛋白质含量。该法具有良好的准确度、灵敏度、稳定性和重现性,蛋白质浓度与吸光度具有很好的线性关系,符合阿莫西林中蛋白质的测定要求。     

考马斯法测定棉籽蛋白发酵液中蛋白质含量

介绍了利用生物法来发酵棉籽蛋白,并使用考马斯亮蓝法测定酵液中蛋白质含量的方法.利用蛋白质与考马斯亮蓝显色原理,用紫外分光光度法测定蛋白质含量,检测波长为595 nm,蛋白质含量在0～ 16.67 mg/L时与吸光度有良好的线性关系,测定所得标准曲线方程为y=0.044x+0.09,其中R=0.999.结果表明:这种方法...     

无患子种仁中几种营养素的测定

以提取无患子籽油后的无患子种仁为材料,采用直接干燥法、索氏提取法、考马斯亮蓝法和重铬酸钾-碘量法分别测定其水分、残留脂肪、蛋白质、纤维素的含量。结果测得提取油后的无患子种仁中水分含量为20.06%、脂肪的残留量为0.16%、蛋白质的含量为8.69%和纤维素的含量为2.21%。从而表明无患子种仁提取油后还具有丰富的营养价值和利用价值。     

旋管膜强化牛奶蛋白分离速率实验研究

介绍分离牛奶蛋白中酪蛋白和乳清蛋白的必要性以及普通分离方法存在的缺点和强化分离速率的方法,自主建立了过滤实验流程,设计出相应的旋管膜强化膜滤器,以脱脂奶溶液为实验物料,过滤实验测定在不同的操作压力和不同旋管膜旋转转数下的相关实验数据,绘制出不同状态下的旋管膜过滤分离速率随过滤时间变化的曲线,分析了原因。得到了本实验范围内可获得理想旋管膜过滤分离速率的最佳操作压力和旋管膜的最佳旋转转数的操作条件。     

A Comprehensive Review on the Interaction of Milk Protein Concentrates with Plant-Based Polyphenolics

Functional properties and biological activities of plant-derived polyphenolic compounds have gained great interest due to their epidemiologically proven health benefits and diverse industrial applications in the food and pharmaceutical industry. Moreover, the food processing conditions and certain chemical reactions such as pigmentation, acylation, hydroxylation, and glycosylation can also cause alteration in the stability, antioxidant activity, and structural characteristics of the polyphenolic compounds. Since the (poly)phenols are highly reactive, to overcome these problems, the formulation of a complex of polyphenolic compounds with natural biopolymers is an effective approach. Besides, to increase the bioavailability and bioaccessibility of polyphenolic compounds, milk proteins such as whey protein concentrate, sodium caseinate, and milk protein concentrate act as natural vehicles, due to their specific structural and functional properties with high nutritional value. Therefore, milk proteins are suitable for the delivery of polyphenols to parts of the gastrointestinal tract. Therefore, this review reports on types of (poly)phenols, methods for the analysis of binding interactions between (poly)phenols–milk proteins, and structural changes that occur during the interaction.     

Soybean protein food in China

This paper introduces the history of soybeans and soybean protein foods in China. For 4,000 years, soybeans have been one of the main crops cultivated in this country. The history of extracting protein to prepare a protein food (bean curd, tu-fu) is about 1,000 years old. Our ancestors had long been aware of the edible value of the soybean and had developed a technique for preparing many kinds of soybean foods. The traditional methods of preparing soybean protein foods such as bean curd (tu-fu), fermented bean curd (fu-ru) and dried bean milk cream (fu-tsu) are discussed.     

The nutritive value of Brazilian soy products tested in malnourished children

The nutritive value of a soya milk and soya protein isolate available in Brazil was tested in formulas fed to 30 malnourished children during a period of 25 days. The chemical composition of all formulas was similar, including their energy and protein content. The protein (1.5 g/100 ml) was supplied by either cow's milk, unfortified soy milk, unfortified soy protein isolate, and methionine-enriched soy milk or methionine-enriched soy isolate. Methionine was added at the level of 1.5 g/100 g of protein. The trials included clinical, biochemical and nitrogen balance studies, and results indicated that these soy products formulas did not have the same nutritive value of cow's milk. However, the nutritional quality of soy milk was improved by methionine supplementation, but the soy protein isolate was not affected by the addition of the same amino acid. Average nitrogen retention as percent of intake ranged from 31.8 to 34.7 in the children fed cow's milk. Those that received soy milk retained 10.5 to 15.3%, and when methionine was added the average retention increased from 17.2 to 24.8%. When the isolated soy protein was fed, the average retention values were 14.7 to 16.5% without methionine, and 11.0% when the methionine-supplemented formula was used. Factors that could influence the results and the importance of the subject are discussed.     

Soybean meal in calf milk replacers

Major research efforts by university and industry workers throughout the world have been directed toward improving the utilization of soybean protein by the calf. This paper reviews the literature and summarizes the questionable characteristics and methods of improving utilization of soya protein sources for young calves. Current application of soya protein in calf milk replacers is discussed.     

A method for isolation of milk fat globules

The traditional procedure for isolating milk fat globules involves repeated cycles of centrifuging to obtain globules and redispersion of them in fresh buffer to eliminate other milk components. We have evaluated a simpler, less manipulative method whereby globules are centrifuged out of the milk and through an overlying buffer layer. Human milk samples ranging from 0.1 to 35 ml were centrifuged at 1500×g for 20 min after deposition under a suitable quantity of buffer. This yielded purified globules, in less time, which could be dispersed more satisfactorily than those by the traditional procedure. Protein, phospholipid and cholesterol contents of globules by the two methods were quite similar. A lower protein content (10.4 vs 13.2 mg/g of lipid) was characteristic of globules prepared by the multiple wash method. However, large differences could not be seen in gel electrophoresis patterns of the proteins. By using plastic centrifuge tubes, tube freezing and cleavage just below the globule layer enables clean separation of globule and nonglobule phases for analysis of milk component distributions. Macro (5 to 35 ml of sample) and micro (200 μl or less) versions of the method are described. Limited trials showed that the method can be applied satisfactorily to cow's and goat's milks, but for highly pure globules a deeper buffer column than that used with human milk is required because of their much higher casein content.     

Vegetable protein application in whey soy drink mix and ice cream

Full fat and defatted soy flours have been used successfully as major ingredients in a low cost replacement for milk solids in beverages for human consumption in several countries of the world. Milk solids replacement products using vegetable protein may have limited potential as long as surplus milk solids exist on a world basis. Some of the milk trends that are occurring in the U.S. are discussed as they pertain to future use of vegetable protein. It appears likely that there will be a decline in milk production with a higher per capita disposable income available for the purchase of processed dairy products utilizing vegetable protein. Ice cream is one of the more sensitive test systems in which to evaluate the flavor and functional properties of vegetable protein for use in dairy products. Sensory panel data have shown that properly processed soybean isolate protein can be used as a 50% replacement for milk solids protein with no discernible differences from a control product. These sensory tests in ice cream show significant differences among commercial soy isolates.     

Development of Insolubility in Dehydration of Dairy Milk Powders

The insolubility of milk powder is affected by the degree of heating in the drying process. This phenomenon was studied with milk products of different moisture content that were subjected to treatments of defined temperature (5−55°C) and time. Skim milk powder (SMP, protein content 36%) was most sensitive over a range of moistures from 15% to 40%. Milk protein concentrate (MPC) powder (73% protein) was most sensitive at higher moisture contents than SMP. At the fastest reaction rates, and for both SMP and MPC, the ratio of moisture to protein (calculated on a dry basis) was approximately one part moisture to one part protein. The rates of development of insolubility in the moist products were fitted to the Arrhenius relationship; this allows extrapolation of the rate of reaction to conditions in a spray dryer. The factors that affect the insolubility reaction are discussed, in particular the effects of the concentrations of lactose and minerals. The results explain certain features of the current design of milk powder driers and will facilitate overcoming problems with the insolubility in high protein powders.     

Milk skin formation during drying

Mass transfer during the drying of skim milk and whole milk films is examined using a combination of experiments and mathematical modeling. Microwave power is used rather than the traditional convective heating characteristic of spray drying to provide greater heating uniformity. In all experiments a period of constant rate drying is observed, followed by a period of diffusion control that is characterised by a rapid increase in sample temperature. The onset of diffusion control is shown to be directly related to the amount of both fat and protein in whole milk samples and to the amount of protein in skim milk samples. These changes occur as a result of the lower diffusivity of protein and fat relative to other milk solids. Over time this difference in diffusivities causes these higher molecular weight solids to segregate from the remaining solids, forming a thickening milk skin. The skim milk data has been successfully fitted to a moisture transport model that incorporates such a milk skin region. The diffusion coefficient within the skin is proportionately lower than in the bulk. The simulated rate of skin thickening is observed to be a simple function of the sample protein content and the sample temperature.