从蛋黄中提取及纯化卵磷脂

本文以鸡蛋的卵黄为原料,采用含水乙醇与乙醚提取,通过丙酮脱水去油,得到粗品卵磷脂;进一步以氯仿/甲醇为洗脱液,硅胶柱层析法分离纯化自制的粗品卵磷脂,得到高纯度的纯白色固体卵磷脂,由薄层色谱定性检测,仅含一个斑点;用薄层扫描仪定量检测纯度大于97.4%。     

Separation of Immunoglobulin G from Cheddar Cheese Whey by Avidin-Biotinylated IgY Chromatography

High-purity immunoglobulins (Ig), which may be useful for immunologic supplementation of food products, were isolated from Cheddar cheese whey in a one-step process using avidin-biotinylated yolk immunoglobulin (IgY) column chromatography. Yolk antibodies specific to bovine IgG (IgY_IgG) were biotinylated with biotinyl amido-hexanoic acid-N-hydroxy-sulfo-succinimide ester without any notable effect on antigen-binding activity, and coupled to immobilized avidin columns. The resulting avidin-biotinylated IgY_IgG columns, with binding capacity of 50–55% (w/w percent ratio of IgG to immobilized IgY_IgG), were used for specific binding of IgG from cheese whey. Elution with a commercially available eluent (Actisep) or 0.1 M glycine-HCl buffer at pH 2.8 yielded IgG with purity of 99% by radial immunodiffusion.     

Effectiveness of chitosan‐based coating in improving shelf‐life of eggs

Despite eggs having a natural packaging—shell—they are perishable and can lose their quality during storage. Chitosan‐based coatings were applied to shell eggs to examine potential effects on egg quality properties (weight loss, Haugh unit, yolk index) during 4 weeks of storage. Mineral amounts in yolks were also evaluated after 4 weeks of storage. Three chitosan‐based coatings produced with organic acids (acetic‐(C‐AA), lactic‐(C‐LA), and propionic (C‐PA)) were evaluated on shelf‐life enhancements of fresh egg quality. All chitosan‐coated eggs showed greater interior quality than the non‐coated eggs. The coatings significantly maintained weight loss compared to the control specimen (4.96%). Lower weight loss (3.45% for C‐PA, 3.53% for C‐LA) was observed in the coated eggs. Eggshell chitosan coat containing lactic and propionic acids maintained higher Haugh unit and yolk index than eggs coated with acetic acid. Uncoated (UC) eggs changed from grade ‘A’ to ‘B’ after 1 week of storage. Chitosan‐based coating containing lactic and propionic acids maintained eggs in grade ‘A’ for 4 weeks. Haugh unit showed that C‐LA and C‐PA effectively maintained eggs at grade ‘A’ quality for at least 3 weeks more than control and 1 week more than C‐AA. Results also indicated that the chitosan coating maintained mineral amounts at nutritional values (especially calcium, iron and magnesium concentration) in yolks after 4 weeks storage. Copyright © 2006 Society of Chemical Industry     

Stability and rheology of egg-yolk-stabilized concentrated emulsions containing cereal β-glucans of varying molecular size

The effects of barley and oat β-glucans on rheological and creaming behaviour of concentrated egg-yolk-stabilized model emulsions were investigated. Four polysaccharide preparations were used, two from each cereal; one sample with high and one with low molecular weight, i.e. the molecular weights were alike in pairs (110×10³ and 40×10³, respectively). In order to elucidate the mechanism of action of β-glucans in emulsions, Tween 20-stabilized emulsions were also examined. Tween 20 enhances neither the continuous phase viscosity nor the interactions between the droplets, so the changes could be easily attributed to β-glucans. It appeared that the low Mw β-glucan samples stabilize emulsions against creaming by means of network formation in the continuous phase while their high molecular weight counterparts enhance the viscosity of the continuous phase. Comparison of dynamic rheological tests between a reference emulsion without β-glucans and emulsions containing β-glucans showed that the polysaccharides largely affects the viscoelastic behaviour of the emulsion. Ageing of β-glucan-containing emulsions did not affect significantly the viscoelastic properties except for the emulsions containing low Mw β-glucans extracted from oat. Interestingly, all emulsions containing β-glucans creamed approximately the same after 30 days of storage regardless which preparation was used. The egg yolk constituents seemed to play a dominant role on the viscoelastic and the creaming behaviour of the emulsions, i.e. the viscoelastic behaviour was further enhanced and this could not only be attributed to the presence of the β-glucans but also to the stronger interactions between the oil droplets. Ageing did not affect the viscoelastic properties of β-glucan-containing emulsions while the reference emulsion, prepared only with egg yolk, showed a decrease in the value of storage modulus. The former could be interpreted as a steady consistency of the product during storage independent of the creaming behaviour. The creaming behaviour varied among the samples with the high molecular weight β-glucans from oat showing the highest stability.     

牛初乳中免疫球蛋白G双抗夹心ELISA检测方法的建立

将牛免疫球蛋白G（immunoglobulin G,IgG）作为免疫原免疫BALB/c小鼠,通过细胞融合、筛选获得分泌抗牛IgG单克隆抗体的细胞株。制备小鼠腹水抗体,进一步纯化获得抗牛IgG单克隆抗体。建立双抗夹心酶联免疫吸附法检测牛初乳中IgG质量浓度,该方法在7.8～1 000 ng/mL范围内有良好的线性关系,最低检出限为7.06 ng/mL,批内变异系数为4.52%,批间变异系数为4.94%,回收率为91.85%～102.45%。此法操作简便、准确度高、稳定性好,可用于实际牛初乳样品的快速检测。     

热处理对酶改性蛋黄液乳化性的影响及拉曼光谱分析

蛋黄液对热敏感,64 ℃左右开始变性形成凝胶,加工过程中的热处理会导致其乳化性质下降,限制了其在食品工业中的应用。因此,本实验研究不同热处理条件（60、65、70 ℃均处理4 min）对酶改性蛋黄液乳化性质及蛋白质结构的影响。结果表明：随着热处理温度的升高,蛋黄液的乳化活性呈现下降的趋势,所形成的乳化体系平均粒径表现出增大的趋势。同一热处理条件下,酶改性蛋黄液的乳化活性及乳化稳定性均显著高于未改性蛋黄液（P＜0.05）,酶改性蛋黄液所形成的乳化体系粒径明显减小,粒径分布更加接近正态分布。拉曼光谱分析结果显示,在不同热处理条件下酶改性蛋黄液中蛋白质二级结构发生变化,在65 ℃以下随温度升高α-螺旋结构相对含量显著升高,无规卷曲结构相对含量显著下降（P＜0.05）;其色氨酸残基、酪氨酸残基及脂肪族疏水基团较未改性蛋黄液更倾向于暴露。采用偏最小二乘法建立了基于拉曼光谱的蛋黄液乳化性质模型,结果表明蛋黄液中蛋白质二级结构及构象变化（特别是低密度脂蛋白的构象变化）对蛋黄液乳化性质影响最大。     

挤压对蛋黄粉性质的影响

采用双螺杆挤压膨化机对蛋黄粉进行加工,研究挤压工艺对蛋黄粉挤压产品色泽、可溶性蛋白质和氨基酸的影响。结果显示,提高进料水分,降低机筒温度,有利于降低挤压蛋黄粉的色差值,并能减少可溶性蛋白质和氨基酸的损失;螺杆转速提高,挤压蛋黄粉的色差值呈总体降低趋势,而可溶性蛋白和氨基酸的含量呈先提高后降低的趋势。     

牛初乳加工预处理方式对免疫球蛋白活性的影响

以新鲜牛初乳为原料,考察不同的贮藏方法(直接冷冻保存,脱脂牛初乳冷冻保存,乳清冷冻保存)及解冻方法(60℃热水水浴解冻,室温解冻,微波解冻),对牛初乳中免疫球蛋白的提取率和活性的影响。实验结果表明:工业化提取牛初乳中免疫球蛋白时,将生鲜牛初乳从牧场取回后直接放入-20℃冷冻贮藏一个月,解冻时采用60℃水浴加热解冻。