Preparation and physicochemical characterisation of resveratrol–ovalbumin microparticles

Resveratrol (RES) is a phenolic compound which has many biological activities, but its poor stability and water solubility limit its function and application. This study developed microparticles (MPs) using ovalbumin (OVA) as a matrix to encapsulate RES. Encapsulation efficiency, solubility and structural characteristics have been evaluated. The antioxidant activity of encapsulated RES has also been examined using the methods of the 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) and 2,2′‐azinobis(3‐ethylbenzothiazoline‐6‐sulphonic acid) (ABTS) radical scavenging assays. Moreover, the stability of the MPs in simulated gastric and intestinal fluid has been studied. In conclusion, RES can be effectively encapsulated by OVA to form spherical MPs resulting in its high water solubility. RES–OVA MPs may not only keep the antioxidant activity of RES but also promote its stability. This kind of MPs can have a potential application in the formulation of functional soft drink based on RES.     

酶法改善卵白蛋白乳化性研究

采用碱性蛋白酶通过酶法改性以改善卵白蛋白乳化性。在单因素实验的基础上,以乳化活性为响应值,选取酶解时间、pH、酶解温度为考察因素,根据Box-Behnken中心组合设计原理建立数学模型,进行响应面分析。获得卵白蛋白乳化性的酶法改性最佳工艺为:底物浓度1.0%、酶用量30000 U/g、酶解时间195 min、p H9.0、酶解温度38℃。在此条件下改性卵白蛋白乳化活性为0.967±0.031,乳化活性相比未改性提高89.61%,说明碱性蛋白酶改性改善卵白蛋白乳化性效果理想。      

Ferulic acid and EGCG alter the structural characteristics of ovalbumin and its application in mineral loading

This study aims to fabricate mineral-loading nanocarriers using natural materials. The interaction patterns between ovalbumin (OVA) and four water-soluble polyphenols, namely ferulic acid (FA), (-)-Epigallo-catechin 3-gallate (EGCG), gallic acid (GA) and epicatechin (EC), were investigated. Results showed that the optimised conditions for preparing stable OVA–polyphenol complexes are at the OVA–polyphenol ratio of 4:1 at pH 6, under which OVA–FA and OVA–EGCG showed the highest stability and mineral-loading capacity among four OVA–polyphenol complexes. The fluorescence results indicated that the addition of EGCG and FA induced a significant fluorescence quenching to OVA. The interaction between OVA and polyphenols involved hydrogen bonding, hydrophobic interaction and electrostatic interaction. Fourier transform infrared spectroscopy (FTIR) analysis suggested that both FA and EGCG enhanced the stability and orderliness of the structure of OVA. The transmission electron microscopy images also exhibited the spherical structure of OVA after the addition of FA and EGCG. Furthermore, scanning electron microscope–energy dispersive X-ray spectrum results suggested that OVA–FA and OVA–EGCG complexes were better mineral carriers than OVA–GA and OVA–EC. This study may serve as the theoretical support for the promising application of OVA in the fabrication of mineral-loading nanocarriers in functional food and pharmaceutic.     

卵清蛋白肽对小鼠机体的免疫增强作用

对蛋白酶水解鸡卵清蛋白获得的肽类物质的理化特性及对免疫功能的调节作用进行研究。方法为凯氏定氮法测定蛋白质含量。多肽含量测定,首先经三氯醋酸沉淀样品中大分子蛋白质,按凯氏定氮法测定上清液的多肽含量。HPLC色谱法测定肽的分子量范围。免疫功能检查包括细胞免疫和体液免疫两项功能测定。与实验对照组比较,迟发型变态反应实验、小鼠半数溶血值测定实验、小鼠巨噬细胞吞噬鸡红细胞实验及NK细胞活性测定实验均有显著增强作用。提示卵清蛋白肽对实验小鼠的机体具有免疫增强作用。     

Differential scanning calorimetry study of pressure/temperature processed β-lactoglobulin: The effect of dextran sulphate

β-Lactoglobulin at pH 7 in the presence or absence of dextran sulphate (1:1 weight ratio) was subjected to a combined pressure and temperature treatment (pressures up to 280 MPa, temperature up to 60 °C and time up to 30 min). The effect of the treatment was assessed post-processing using differential scanning calorimetry. The thermograms in absence of dextran sulphate were very broad with possibly a shoulder on the low temperature side and showed a decrease in calorimetric enthalpy as the intensity of treatment increased. In the presence of dextran sulphate the thermograms had a much sharper shape. The calorimetric enthalpy was reduced further than in the absence of dextran sulphate. This demonstrated that the polysaccharide sensitised the protein to the combined treatment. Treatment with pressure and temperature alone demonstrated that dextran sulphate sensitised the protein structure to pressure. The species created by the combined process could be in the molten globule state and possess improved functional properties. Also the operating parameters applied could potentially be conditions for improved functionality.     

卵白蛋白多肽的酶解制备及抗氧化活性研究

以DPPH自由基清除率和水解度为指标,采用碱性蛋白酶酶解卵白蛋白制备抗氧化活性肽,考察底物质量分数、酶解时间、加酶量、温度等因素对制备的影响。正交实验结果表明,碱性蛋白酶的最佳水解条件为:底物质量分数4%、酶解时间6h、加酶量5500U/g,温度65℃,此条件下DPPH自由基清除率达到96.92%、水解度为57.14%。酶解时间对DPPH自由基清除率的影响最大,而底物质量分数对水解度的影响最大。      

卵白蛋白对变应性鼻炎小鼠模型的影响

目的研究卵白蛋白(ovalbumin, OVA)对变应性鼻炎(过敏性鼻炎)小鼠模型的影响。方法小鼠随机分为7组:对照组、高浓度OVA模型+PBS组、中浓度OVA模型+PBS组、低浓度OVA模型+PBS组、高浓度OVA+阳性药组、中浓度OVA+阳性药组、低浓度OVA+阳性药组。采用OVA全身致敏及局部攻击相结合的方法构建变应性鼻炎小鼠模型,以PBS、丙酸氟替卡松(0.008 mg/kg)滴鼻,观察小鼠鼻部抓挠、喷嚏数症状和脏器指数; ELISA法定量检测血清免疫球蛋白E(IgE)、白细胞介素-4(IL-4)、白细胞介素-10(IL-10)和干扰素-γ(IFN-γ)的含量;制备脾细胞悬液对比脾细胞悬液CD4+CD25+T细胞变化。结果建模成功后,高浓度OVA+阳性药组与高浓度OVA模型+PBS组相比,血清IgE、IL-10、IL-4、IFN-γ水平和CD4+CD25+T细胞水平变化不明显,差异无统计学意义(P0.05);中、低浓度OVA+阳性药组与中、低浓度OVA模型+PBS组相比,血清IgE、IL-10和IL-4水平显著降低, CD4+CD25+T细胞水平和IFN-γ水平显著升高, IFN-γ/IL-4比值升高,差异有统计学意义(P0.001或P0.05)。结论卵白蛋白的浓度选择对变应性鼻炎模型影响较大,致敏用卵白蛋白为中浓度时对阳性药的检测效率较高。     

卵白蛋白提取及其可食性膜制备

提取鸡蛋清中的卵白蛋白,制备卵白蛋白粉。采用考马斯亮蓝标准曲线法和凯氏定氮法分析蛋白含量,SDS-PAGE电泳测定纯度。用甘油塑化卵白蛋白,制备可食性蛋白膜。     

Rheological behavior and organoleptic effects of ovalbumin addition in yogurt mousse production

Yogurt mousse is a novel, high added-value dairy product that has been well received by the market. This paper presents a study of the effect of the addition of ovalbumin to the product on its rheological and organoleptic qualities. The ovalbumin was previously separated from egg white with a high grade of purity using an ion exchange resin synthesized by the authors. Diverse rheological tests at different temperatures and corresponding sensorial assessments were conducted to compare samples without and with added ovalbumin.The obtained results confirm that the product is viscoelastic and combines the properties of foams and emulsions; the elastic component is greater than the viscous component. Moreover, at temperatures ranging from 5 to 15°C, a usual interval of consumption, the product behaves rheologically in a similar way. Conversely, the addition of ovalbumin under the assayed conditions also makes the elastic character of the product increase at a given temperature. Finally, the sensorial assessment tests and determinations of stability and volume yield enabled us to verify that the addition of ovalbumin at an amount of 1.3% hardly alters the stability, resistance to shear stress, or the texture and improves the degree of foaming. Therefore, the product with additive is of good commercial quality.     

60Co辐照对卵清蛋白结构和抗氧化性的影响

采用6种钴60辐照剂量(0、2、4、6、8、10 k Gy)处理鸡蛋卵清蛋白(OVA),并探明辐照技术对卵清蛋白结构和抗氧化性的影响。以新鲜鸡蛋为原料,经0、2、4、6、8、10 k Gy 6种钴60辐照剂量处理;硫酸铵沉淀法提取卵清蛋白;并测定不同辐照条件下卵清蛋白溶解度、自由巯基含量、内源性荧光、还原力、DPPH自由基清除率的变化。实验结果表明:辐照对于卵清蛋白的结构和理化性质影响较大,随着辐照剂量的增加,OVA的可溶性蛋白含量、自由巯基含量、DPPH清除能力和还原力,均有不同程度的提高;内源荧光呈现先上升后下降趋势,当辐照剂量为10 k Gy时,内源荧光值显著低于对照组(p<0.05)。此研究为辐照卵清蛋白产品的工业应用提供了理论依据。      

卵白蛋白源抗菌肽的分离纯化与结构鉴定

以卵白蛋白为原料,采用胃蛋白酶水解制备具有抑菌活性的蛋白肽。通过超滤和Superdex peptide 10/300凝胶色谱分离技术获得高抑菌性组分,以抗菌肽对大肠杆菌和沙门氏菌的抑菌性为试验指标,筛选最佳抑菌性组分,再进行反相高效液相色谱分离,测定分离得到的9个组分抑菌活性,发现C3组分的抑菌活性和得率最高,其中大肠杆菌及沙门氏菌抑菌圈直径分别为(19.32±1.45),(18.74±1.27)mm。最后采用高效液相色谱—电喷雾—质谱鉴定抗菌肽的结构,显示氨基酸序列为GlyLeu-Glu-Pro-Ile-Asn-Phe-Gln(GLESINFQ)。该肽经固相合成纯度为95.84%,其抑菌活性与C3组分无显著性差异(P0.05),从而证明卵白蛋白源抗菌肽发挥抑菌活性的成分主要是肽段GLESINFQ。     

Emulsifying properties of ovalbumin in mixtures with sulphated polysaccharides: effects of pH,ionic strength,heat and high‐pressure treatment

The influence of sulphated polysaccharides (dextran sulphate (DS), ι‐carrageenan (ι‐CAR) and κ‐carrageenan (κ‐CAR)) on the emulsifying properties of ovalbumin (OVA) has been investigated over a range of pressures and temperatures. Oil‐in‐water emulsions (10 g l⁻¹ protein, 200 ml l⁻¹ n‐tetradecane, pH 6.2) prepared with heat‐treated (80 °C for 10 min) mixtures of OVA + DS (1:0.25 by weight) had increased creaming stability but unchanged average droplet size compared to those made with untreated OVA and OVA + DS. Emulsions made with pressure‐processed (600 MPa for 20 min) OVA + DS (1:0.25 or 1:0.5 by weight) mixtures had the best emulsifying efficiency and stability. Under similar experimental conditions, replacement of DS with either ι‐ or κ‐CAR gave emulsions with larger droplets and more rapid serum separation, probably owing to depletion flocculation. High‐pressure treatment (600 MPa) of the OVA and mixed biopolymer solutions at pH 6.2 in the presence of salt (>0.04 M ) led to unstable emulsions, and so the protective effect of DS was lost. High‐pressure treatment (600 MPa) of emulsions prepared with native OVA or OVA + DS mixtures induced significant levels of flocculation, as indicated by changes in the average droplet size and creaming behaviour. © 2000 Society of Chemical Industry     

Immunochemical detection of ovalbumin in dairy-based foods

Commercially available antibodies were used for the detection and quantitation of ovalbumin in ice cream and cheese. Electrophoretic separation of protein components, followed by blotting and immunochemical recognition of ovalbumin allowed the detection of the addition of 50 g kg^-1 egg white to processed cheese and allowed detection of egg in ice cream. For quantitative purposes a competitive ELISA method was set up. Calibration curves for ovalbumin in various products were obtained. A marked matrix effect was evident in ice cream, cheese and yoghurt. Different types of cheese gave nearly identical matrix effects. Analytical application of the method should therefore be possible, at least within a given class of products. A study on the influence of thermal treatments on the ELISA response showed that melting of cheese at various temperatures modifies only slightly the ELISA response for ovalbumin.     

High Hydrostatic Pressure Effects on Color and Milk-Fat Globule of Ewe's Milk

ABSTRACT: The influence of high hydrostatic pressure treatments on lipolysis, color, and size distribution of milk fat globule (MFG) on ewe's milk was studied. Treatments consisted of combinations of pressure (100 to 500 MPa) and temperature (4, 25, and 50 °C) for 10 min. Pressurized samples showed FFA levels lower than control. Pressurizations at 25 and 50 °C showed a tendency to increase MFG in the range 1-2 μm and to decrease MFG between the range 2 to 10 μm, whereas at 4 °C the effect was the reverse. A decrease of lightness (L*)value, and an increase of (−a*) and (+b*) values occurred in color with pressure increase.     

Changes in the surface protein of the fat globules during ultra-high pressure homogenisation and conventional treatments of milk

Disruption of fat globules upon homogenisation provokes a reduction of their size and a concomitant increase in their specific surface area. In order to overcome this phenomenon, the milk fat globule membrane (MFGM) adsorbs non-native MFGM proteins. The aim of the present study was to examine the effects of UHPH conditions (temperature and pressure) on the milk fat globule and the surface proteins by comparison with conventional treatments applied in the dairy industry. Transmission electron microscopy and SDS-PAGE revealed major differences. In UHPH-treated milk, casein micelles were found to be adsorbed on the MFGM in a lesser extent than in conventional homogenisation–pasteurisation. However, greater adsorption of directly bonded casein molecules, released by UHPH through the partial disruption of casein micelles, was observed especially at high UHPH pressures. Adsorption of whey proteins on the MFGM of conventionally homogenised–pasteurised milk was mainly through intermolecular disulfide bonds with MFGM material, whereas in UHPH-treated milk, disulfide bonding with both indirectly and directly adsorbed caseins was also involved.     

Influence of sodium chloride and glucose on acid-induced gelation of heat-denatured ovalbumin

ABSTRACT:  We examined the effects of NaCl and glucose on cold-set ovalbumin gelation. Cold-set gels were prepared by adding glucono-δ-lactone (GDL) to a 2% heated ovalbumin solution. For the gel prepared from ovalbumin heat-denatured with NaCl and glucose, the gel with 10 mM NaCl was most transparent and had high gel strength. Its maximum complex shear modulus ( G *) and turbidity were 2.5 times greater and 3 times lower, respectively, than those of the gel without NaCl. The turbidity of the gel with the higher NaCl content increased steeply after the addition of GDL and did not change during the experimental period. The maximum G * of the gel exhibited positive correlations with the molar mass, radius, and surface hydrophobicity of soluble aggregates and the NaCl content, but the turbidity exhibited negative correlations with these factors. The presence of glucose did not significantly affect the turbidity or rheological properties of the gel. For the gel prepared by adding NaCl and glucose with GDL, the presence of glucose did not affect the turbidity, but the maximum G * decreased in inverse proportion to the glucose content. The turbidity of the gel with higher NaCl content (≥ 50 mM) was the greatest among all samples, and the increased turbidity was maintained throughout the measurements. The gels with 50 and 100 mM NaCl exhibited thixotropy during shearing at a constant shear rate. Therefore, the presence of NaCl and glucose during cold gelation could facilitate the preparation of cold-set gels having various properties for food applications.     

食品添加物对卵清蛋白/卡拉胶共混凝胶特性的影响

研究了pH、电解质、非电解质和表面活性剂时卵清蛋白/卡拉胶凝胶强度和弹性的影响.结果表明,pH在卵清蛋白等电点附近时,卵清蛋白/卡拉胶凝胶强度和弹性最好;低浓度的电解质和非电解质时卵清蛋白/卡拉胶凝胶强度和弹性有一定改善;表面活性剂对卵清蛋白/卡拉胶凝胶强度和弹性无改善.     

High hydrostatic pressure modification of whey protein concentrate for improved functional properties

Whey protein concentrate (WPC) has many applications in the food industry. Previous research demonstrated that treatment of whey proteins with high hydrostatic pressure (HHP) can enhance solubility and foaming properties of whey proteins. The objective of this study was to use HHP to improve functional properties of fresh WPC, compared with functional properties of reconstituted commercial whey protein concentrate 35 (WPC 35) powder. Fluid whey was ultrafiltered to concentrate proteins and reconstituted to equivalent total solids (8.23%) as reconstituted commercial WPC 35 powder. Solutions of WPC were treated with 300 and 400 MPa (0- and 15-min holding time) and 600 MPa (0-min holding time) pressure. After HHP, the solubility of the WPC was determined at both pH 4.6 and 7.0 using UDY and BioRad protein assay methods. Overrun and foam stability were determined after protein dispersions were whipped for 15 min. The protein solubility was greater at pH 7.0 than at pH 4.6, but there were no significant differences at different HHP treatment conditions. The maintenance of protein solubility after HHP indicates that HHP-treated WPC might be appropriate for applications to food systems. Untreated WPC exhibited the smallest overrun percentage, whereas the largest percentage for overrun and foam stability was obtained for WPC treated at 300 MPa for 15 min. Additionally, HHP-WPC treated at 300 MPa for 15 min acquired larger overrun than commercial WPC 35. The HHP treatment of 300 MPa for 0 min did not improve foam stability of WPC. However, WPC treated at 300 or 400 MPa for 15 min and 600 MPa for 0 min exhibited significantly greater foam stability than commercial WPC 35. The HHP treatment was beneficial to enhance overrun and foam stability of WPC, showing promise for ice cream and whipping cream applications.     

Molecular studies of pressure/temperature‐induced structural changes in bovine β‐lactoglobulin

β‐Lactoglobulin in 50 mM Tris/HCl buffer at pH 7 was subjected to combined pressure and temperature treatments using a central composite experimental design. Pressures up to 294 MPa, temperatures up to 62 °C and processing times up to 30 min were studied. The molecular structure at the secondary and tertiary levels was analysed post‐processing using far‐ and near‐UV circular dichroism. It was found that, although the pressures applied were moderate, the far‐UV circular dichroism spectra showed important changes corresponding to an increase in α‐helix content. The tertiary structure was almost completely lost for the highest processing intensities. This suggests a transition to the molten globule state. The percentage change in molar ellipticity at 293 nm (tertiary structure) was found to be linearly connected to the three independent variables, hence possibly allowing process optimisation for that response. Pressure was found to be the most important parameter to bring about the molecular changes at the two molecular levels investigated. Copyright © 2004 Society of Chemical Industry     

Conformation affects the potential allergenicity of ovalbumin after heating and glycation

Ovalbumin (OVA), one of the major allergens in hen egg white, and has widespread use in experimental models of allergy. The aim of this research was to assess the effect of glycation and heat treatment on the potential allergenicity of OVA prepared from hen egg white. Secondary and tertiary structures of OVA were also characterised to show the relationship between potential allergenicity and the conformation of OVA after heating and glycation. Glycation significantly reduced the potential allergenicity of OVA tested with egg allergy patients’ sera, which was caused by conformation changes. An increased IgG reactivity was measured using rabbit anti-OVA and was supposed to be caused by protein unfolding which exposed hidden epitopes. Heating reduced the potential allergenicity of OVA at the expense of increased IgG reactivity. It is suggested that conformational changes of OVA induced by glycation and controlled heating significantly reduced its potential allergenicity.