Physical properties of egg whites and whole eggs relevant to microwave pasteurization

Microwave pasteurization is a novel thermal processing technology in which non-uniform heating may be a major challenge. In this study, the suitability of using egg whites (EWs) and whole eggs (WEs) as model foods to evaluate the heating uniformity and to determine the cold and hot spots during microwave pasteurization was investigated. The samples were prepared from mixtures of water with commercial EW or WE powders at different solid concentrations (20%, 25%, 27.5%, and 30%) and salt contents (0, 50, 100, and 200 mM). Critical physical properties for desirable model food systems include appropriate dielectric properties, gelation temperatures, gel strengths, and water holding capacities (WHCs). The gelation temperature of liquid EW and WE were 70 and 80 °C; both fell in the pasteurization temperature range. At 915 MHz, the dielectric constants of liquid EW and WE samples and their heat induced gels decreased with solid concentration while the loss factor was not affected. Loss factors of liquid EW and WE samples increased linearly with salt addition, which could be explained by the linear increase of electrical conductivities by adding salt. The strength and WHC of heat induced EW and WE gels increased linearly with solid concentration, while salt addition had no significant effect. The results demonstrated the suitability of using EW and WE as model foods to determine the heating uniformity during microwave pasteurization process.     

微小毛霉与米黑毛霉凝乳酶的制备及其凝乳质构特性研究

将经乙醇分步沉淀所制得的微小毛霉和米黑毛霉凝乳酶以小牛皱胃酶为对照在不同温度、不同时间和不同pH值下凝乳,以下压过程的平均力为衡量标准,对其物性进行了比较,得出在相同条件下,米黑毛霉凝乳酶的凝乳要好于微小毛霉凝乳酶,并在高温和酸性环境要比微小毛霉凝乳酶稳定。     

固定化米黑根毛霉脂肪酶的制备工艺优化及其酶学性质北大核心CSCD

以海藻酸钠-羧甲基纤维素钠(CMC)为复合载体,戊二醛为交联剂,探究了包埋-交联法制备固定化米黑根毛霉脂肪酶的最佳工艺条件,并对固定化米黑根毛霉脂肪酶的酶学性质进行分析。结果表明,制备固定化米黑根毛霉脂肪酶的最佳工艺条件为海藻酸钠质量分数2.5%、CMC质量分数1.5%、脂肪酶液浓度800 U/mL、CaCl_(2)质量分数5%、戊二醛质量分数0.03%、交联固定化时间30 min,在此条件下固定化米黑根毛霉脂肪酶的酶活力为245.58 U/g,与游离脂肪酶相比,固定化脂肪酶热稳定性和pH稳定性均有所提高。交联剂戊二醛的添加可以提高固定化脂肪酶的操作稳定性和储存稳定性,在重复使用7次后相对酶活力保持在57.39%,在4℃下存放7周后相对酶活力为61.89%。包埋-交联法制备的固定化米黑根毛霉脂肪酶具有更好的稳定性和适应性,为实现植物油酶法酯化脱酸工业化生产提供参考。     

产碱性脂肪酶菌株的筛选及酶学性质研究

从富油土壤中筛选出一株耐热碱性脂肪酶产生菌X-5,经菌落形态观察、生理生化实验和16S rDNA序列分析,初步鉴定为假单胞菌。采用单因素实验研究其生长条件,研究表明该菌株最适生长温度为34℃,最适生长pH为8.0,6²6h为对数生长期,26³8h为稳定期,38h开始进入衰亡期;酶学性质研究表明,该酶最适反应温度为60℃,最适反应pH为8.5,70℃保温1h仍保留60%的酶活,具有良好的耐热性。K+、Na+对酶有激活作用,Ca2+、Mg2+、Zn2+、Fe2+、Cu2+、Mn2+对酶有不同程度地抑制作用。      

Physicochemical and functional properties of shell eggs following electron beam irradiation

Low dosages of electron beam irradiation (EBI) were applied to shell eggs to examine potential effects on physicochemical and functional properties. Prior to the assessment of physicochemical and functional properties, the antimicrobial efficacy of 2, 3 and 4 kGy dosages of EBI in shell eggs was established by the reduction of inoculated Listeria monocytogenes, Escherichia coli and Salmonella typhimurium to an undetectable level. Physicochemical changes to shell eggs receiving the same dosages of EBI were quantified by Haugh unit, free sulphhydryl groups, yolk index and lipid oxidation. Functional properties were assessed by foaming capacity, emulsifying capacity and gelling properties. A loss of thick albumen and a corresponding increase in free sulphhydryl groups in the albumen were observed after EBI, resulting in a loss of foam volume and gel hardness. Negligible changes in yolk index and lipid oxidation paralleled a retention of emulsifying capacity and gelling properties. EBI proved to be an effective method for controlling microbial growth in shell eggs without adversely affecting physicochemical and functional properties. © 2002 Society of Chemical Industry     

鸡蛋清蛋白磷酸化改性及功能性质的研究

为了进一步改善蛋清蛋白的加工特性,采用三聚磷酸钠(STP)对鸡蛋清蛋白进行磷酸化改性,并针对其一些功能性质进行了探讨。主要以磷酸化程度为考察指标,通过单因素和正交实验,确定了最佳的蛋清蛋白的磷酸化工艺参数为温度30℃、pH为8.0、加热时间为3.5h,STP添加量为2.0%;此条件下磷酸化程度达到60mg/g。对比磷酸化改性前后的鸡蛋清蛋白的功能特性表明:磷酸化改性后,鸡蛋清蛋白的水溶性、保水性、乳化性和乳化稳定性都有一定程度地提高,但SEM对其微观聚集态结构观察,改性前后两者之间微观结构区别不是很明显。      

均质处理对鸡蛋全蛋液功能性质的影响

为了明确全蛋液均质处理对其功能性质影响规律,对不同压力均质处理后全蛋液蛋白溶解度、起泡性、乳化性、凝胶强度等功能性质及应用全蛋液制作的海绵蛋糕比容的变化进行了研究。结果表明:在5～40 MPa压力内,随着均质压力的升高,全蛋液起泡力、乳化活力和海绵蛋糕比容明显降低,泡沫稳定性和凝胶强度明显提高,乳化稳定性的变化比较复杂,蛋白质溶解度基本保持稳定。在实际生产中需要根据全蛋液应用时所侧重的功能性质选择适宜的均质条件。     

根霉ZZ-3脂肪酶发酵条件的优化及酶学性质研究

对根霉ZZ-3脂肪酶产酶条件的优化及脂肪酶酶学性质进行了研究。结果表明,250 mL三角瓶液体培养,培养基装液量100 mL,根霉ZZ-3产脂肪酶的最佳培养基为：黄豆粉3 g/100mL,（NH4）2S040.3 g/100mL,MgS04 0.2 g/100mL,K2HPO4 0.2 g/100mL,花生油0.3 g/100mL,pH自然。在温度28℃、转速150 r/min,摇床培养时间2 d,发酵酶活力达到124.60 U/mL。对该酶的酶学性质进行了初步研究,该酶最适pH7.5,最适反应温度37℃,在pH7～9、温度低于40℃条件下酶活稳定。     

物理改性在蛋清蛋白功能特性改善中的应用

文章对近年蛋清蛋白物理改性研究成果进行了综述,阐述了物理改性方式对蛋清蛋白功能提升的作用,分析了各种改性方式在提升蛋清蛋白不同功能特性中的特点.     

Enzymatic and extrusion pretreatments of defatted rice bran to improve functional properties of protein concentrates

This study evaluated effects of enzymatic, extrusion and combined pretreatments on functional and thermal properties of protein concentrates from defatted rice bran to improve their applicability to food formulations. After the pretreatments, protein concentrates were recovered by alkaline solubilisation and isoelectric point precipitation. Water absorption capacity, oil absorption capacity, emulsifying and foaming properties, and thermal stability were determined in protein concentrates. Yields of each pretreatment were above 62% protein. Enzymatic hydrolysis increased all functional properties studied, mainly for emulsifying activity index (an increase of 71.1%) and foaming capacity (an increase of 60.3%). The extrusion affected positively the oil absorption capacity, emulsifying activity index and foaming capacity. The combined process was able to raise the functional properties. The principal component analysis confirmed that 95.5% improvement in functional properties of concentrates had a strong positive correlation with the pretreatments. However, the pretreatments affected thermal stability and the enthalpy of denaturation negatively.     

Thermal denaturation and functional properties of egg proteins in the presence of hydrocolloid gums

The aim of this study was to investigate the thermal stability, foaming and emulsifying properties of egg white and egg yolk constituents (egg yolk plasma and egg yolk granule) in the presence of hydrocolloid gums. Differential scanning calorimetry was used to examine the thermal stability of proteins. Heat denaturation of proteins were not influenced from the presence of anionic pectin and i-carrageenan and neutral guar gum. The residual denaturation enthalpy was observed to decrease as a result of protein aggregation. Thermal treatment have been observed to be detrimental to foaming capacity of egg white, while foam stability was improved. The foam stability was enhanced in the presence of pectin which may provide a strong viscoelastic film together with protein. Emulsifying activity and stability and of egg yolk granule and plasma were reduced after heat treatment. The presence of guar gum improved the emulsifying properties, while both pectin and guar gum reduced the rate and extend of creaming of egg yolk protein – stabilized proteins after heat treatment.     

Use of polysorbate 80 to reduce cholesterol in dehydrated egg yolk

The lipid and cholesterol contents of freeze- and spray-dried egg-yolk were substantially reduced by extraction with 1% polyoxyethylene (20) sorbitan mono-oleate (polysorbate 80) in 10/90, 20/80, 50/50 and 80/20 (v/v) ethanol/water mixtures. the functionally important phospholipid content of the resulting yolk-protein concentrate was only marginally reduced when low ratio mixtures were used, but total yields were reduced. the influence of polysorbate 80 is attributed to the weakening of protein-protein bonds responsible for the stabilization of egg lipoprotein structures and subsequent release of lipids.     

蛋黄组成成分的性质研究

蛋黄用0.17mol/L氯化钠1∶1等重稀释后,进行冷冻离心可得到上清和沉淀两部分,对其进行了组成、蛋白质溶解度和乳化性质及颗粒形态的分析研究。电泳分析表明,上清部分主要为低密度脂蛋白和卵黄蛋白,沉淀部分主要为高密度脂蛋白和卵黄高磷蛋白。这三部分随着氯化钠浓度的增大,蛋白质溶解度逐渐增大,在氯化钠浓度为0.5mol/L时,蛋黄、上清、沉淀三部分的溶解度在90%以上。在蛋白质溶解度在90%以上时,测定三部分的乳化性质,得出上清部分的乳化活性最好,沉淀部分的乳化稳定性最好。     

The effect of gaseous ozone treatment on egg components

BACKGROUND: Because of the salmonella problem in poultry, disinfection technologies are necessary. Ozone is a strong oxidant used for the disinfection of surfaces, drinking water and foods. However, since ozone not only destroys bacteria but may also damage eggs, it is necessary to clarify the effects of ozone treatment on hatching egg components. In this study, doses of gaseous ozone ranging from 10 to 50 mL L^?1 were tested. The vitamin A and E contents and fatty acid composition of the egg yolk were determined. To detect possible damage to the DNA of the germ disc, single‐cell gel electrophoresis was used. Moreover, free SH groups were measured in the egg white. The soluble cuticula proteins were analysed by polyacrylamide gel electrophoresis. RESULTS: The yolk was not significantly affected by ozone treatment. However, the DNA of the germ disc was attacked and a significant decrease in free SH groups in the egg white was recorded at 50 mL L^?1 ozone. Even at low ozone doses the soluble cuticula proteins were completely destroyed. CONCLUSION: Significant alterations of egg components were caused by 50 mL L^?1 ozone. At lower ozone doses the oxidative processes occurred mainly at the egg surface and are therefore probably harmless to the developing embryo. Copyright © 2010 Society of Chemical Industry     

内生黑曲霉产脂肪酶条件研究及其粗酶酶学特性

针对新疆酿酒葡萄中获得的1株产脂肪酶的内生黑曲霉菌株C2J6,研究了该菌株的产酶条件及酶学特性。结果表明,该菌适宜的产酶条件为1%的乳糖为碳源,1%的蛋白胨为氮源,培养基初始pH值为8.0,培养温度35℃,培养时间约72h,此时所产脂肪酶的活力可达18.75U/mL。该菌所产脂肪酶粗酶液的最适反应温度为40℃,最适反应pH值为7.0,为中温中性酶;在50℃保温1h酶活力保留54.55%,具有良好的热稳定性;在pH值3.0~7.0范围内较稳定,有一定的耐酸性。金属离子Mn2+对酶活力有促进作用,Zn2+、Fe2+、Cu2+对酶活力有抑制作用,K+、Ca2+、Na+、Mg2+对酶活力影响不大。该酶在以葵花油和谷物调和油为底物时,酶活分别为228%和180%,明显高于橄榄油和油烟机废油。     

麦芽中脂肪酶活性检测及酶学性质的研究

以乙酸对硝基苯酚酯（p-NPA）为底物,采用对硝基苯酚法测定了麦芽中脂肪酶的活性,并对其酶学性质进行了研究。实验结果表明,麦芽中脂肪酶的最适反应pH为8.5,与5mmol/L的p-NPA的最适反应体积比为1∶7,金属离子Mg2+对麦芽脂肪酶活性有显著的抑制作用,Fe3+、K+则有一定激活作用;该酶热稳定性较强,40℃水浴保温120min,其酶活性几乎保持不变,70℃保温120min后接近失活。麦芽脂肪酶对p-NPA的酶动力学常数Km为0.13mmol/L,Vm值为0.016mg/min。