Determination of Foaming Properties of Proteins by Conductivity Measurements

A new method was established to estimate the foaming properties of proteins from the conductivity of foams using a simple apparatus that consisted of a glass column with the conductivity cell. A close correlation was observed between the initial conductivity of foams and the foam volumes of heat-denatured ovalbumins or 11 native proteins, suggesting that the initial conductivity of foams can be used as a measure of foaming power. In addition, a close correlation was obtained between the foam stability determined from changes in the conductivity and foam volume with time of heat-denatured ovalbumins or 11 native proteins, suggesting that foam stability also can be estimated from changes in the conductivity of foams. The advantages of the conductivity measurements are to determine the foaming properties more simply and accurately than the currently used methods.     

Relationship of Absorptive and Interfacial Behavior of Some Food Proteins to Their Emulsifying Properties

The relationship between surface and interfacial tension of 14 food proteins and their hydrophilic/lipophilic characteristics was studied. Maximum lowering of surface and interfacial tension was achieved when the water-oil absorption index (WOAI), calculated by measuring the spontaneous water and oil uptake was nearly two; the protein absorbed twice as much water as oil. The ability of a protein to decrease interfacial tension between oil and water was related to its ability to emulsify oil, being determined by the WOAI. However, stability of emulsions was not ensured by a large decrease in interfacial tension.     

棕榈酰化大豆蛋白的制备及其乳化性能的研究

棕榈酰基通过碱催化的酯交换反应与大豆蛋白的ε-NH2共价结合，以棕榈酸N-羟琥珀酰亚胺酯为酰化试剂。在pH9．0，温度25℃条件下，棕榈酰基与大豆蛋白结合得到不同改性程度的棕榈酰化蛋白。测定了改性对大豆蛋白表面疏水性和乳化性的影响。随着酰化程度的增加，大豆蛋白表面疏水性增加，溶解性下降。改性程度迭30．21％的棕榈酰化蛋白具有较原料蛋白明显改善的乳化性能，其表面疏水性较高，而溶解性又没有明显降低。     

Emulsifying Properties of Bovine Blood Globin: A Comparison with Some Proteins and Their Improvement

The emulsifying properties of bovine blood globin were compared with those of bovine serum albumin, hemoglobin and ovalbumin. Although the emulsifying activity of globin was greater than that of hemoglobin and ovalbumin, it decreased in the isoelectric zone owing to the low solubility of globin. Acetylation increased the emulsifying activity of globin in the isoelectric zone, but decreased in the acidic pH region. Pepsin digestion did not increase the emulsifying activity of globin, but addition of CMC to pepsin-digested globin improved both its emulsifying activity and the emulsion stability.     

Emulsifying Properties of Food Proteins: Bovine Serum Albumin

Emulsifying activity (EA) of bovine serum albumin (BSA), at concentrations of 0.07 to 0.45 mM, was maximum at oil:water ratios (o:w) <2:8, in the pH range 4 to 8. At pH 8, the EA was greater than that at pH values below, i.e., < pH 7, but the energy required to form emulsions was higher., EA and emulsion stability (ES) were directly related and improved in NaCl; ES was maximum at pH 4. Surface load was directly related to the o:w and the increase in viscosity with protein load apparently reflected protein unfolding that was marked at an energy input of 680 10⁶ J m^-3. Data indicate that some native structure and flexibility of the BSA molecule are required for optimum emulsifying properties.     

Emulsifying Properties of Proteins Isolated from Various Rice Cultivars

The emulsifying properties of rice proteins isolated from various non-waxy and waxy rice cultivars were studied to evaluate their potential application as oil-in-water (O/W) emulsifier and to compare the emulsifying properties of the rice proteins isolated from various rice cultivars. The solubility of the rice proteins was measured at different pHs (2–10), and O/W emulsions were prepared with the proteins at pH 2, 7, and 10. The rice protein-stabilized O/W emulsions were analyzed by measurement of particle size and zeta-potential, and observation under an optical microscope. The results indicated the potential of the rice proteins as emulsifiers at low and high pH values, and that, in particular, rice proteins isolated from waxy-rice cultivars could form stable emulsions even at neutral pH. The information obtained in this study may be useful for development of emulsion-based food products using rice protein isolate.     

Relationships of Hydrophobicity to Emulsifying Properties of Heat Denatured Proteins

Effects of heating on the emulsifying properties of selected food proteins and the protein surface hydrophobicity (S_o) as a predictor of these properties were investigated. The emulsifying properties of the proteins studied were differently affected by heating. Heat-denaturation was not always accompanied by loss of emulsifying properties, but, on the contrary, in some cases resulted in great improvement. The emulsifying properties could well be predicted solely on the basis of S_o level but not on the basis of solubility level, which indicated that S_o is a very important property determining protein functionality. However, the emulsifying activity, emulsion stability and fat binding capacity of the proteins studied could be explained and more accurately predicted using S_o and solubility together.     

Effect of Oxidation on the Emulsifying Properties of Myofibrillar Proteins

The aim of this work was to investigate the effect of chemical oxidation on the emulsifying properties of myofibrillar proteins. Myofibrillar proteins were oxidized by a hydroxyl radical generating system (Fenton reaction). Structural changes of oxidized or non-oxidized myofibrillar proteins were determined using surface hydrophobicity (H₀) and Fourier transform infrared (FTIR) spectroscopy. The results suggested that H₀ increased (p?<?0.05) after treatment with oxidizing agent. Result from FTIR suggested that protein aggregation occurred and there was an increase in β-sheet structure accompanied by a decrease in turns, alpha helix, and random structures with the increase of oxidizing agent. Changes in zeta potential of the test emulsions suggested that protein oxidation could alter the electric charge of myofibrillar proteins. The analysis of the emulsions showed that protein oxidation had a negative effect on the emulsifying properties of myofibrillar proteins due to changes in electric charge, surface active properties, and protein molecular flexibility.     

Emulsifying Properties of Food Proteins: Bovine Mi cellar Casein

The capacity of micellar casein isolated from bovine milk to stabilize oil in water (0:w) emulsions was studied. Emulsion surface area per unit mass of protein, i.e., emulsifying activity (EA), was highest at a protein concentration of 1% and o:w ratio of 1:9. The surface concentration of micellar casein was related to the o:w ratio being highest at an o:w of 4:6. Interfacial surface area decreased at pH 6.7 reflecting micellar stability and improved with increasing pH apparently because of destabilization of the casein micelle. Emulsion stability was high when the EA was high. The apparent viscosity of the emulsions was inversely related to EA.     

淘汰蛋鸭盐溶蛋白的乳化和起泡性质

研究淘汰蛋鸭的胸肉和腿肉组织的总蛋白质和盐溶蛋白含量及盐溶蛋白的功能性质,并与肉鸭进行比较。采用微量凯氏定氮法测定肉鸭和淘汰蛋鸭的胸、腿部肌肉组织的总蛋白质和盐溶蛋白含量,并测定盐溶蛋白的乳化活性和起泡性。结果发现,肉鸭和淘汰蛋鸭的胸部肌肉和腿部肌肉中的总蛋白质含量在22%左右,胸部肌肉的总蛋白质含量稍大于腿部的肌肉总蛋白质含量;肉鸭的胸、腿肌肉中的盐溶蛋白含量分别为(24.61±1.19)%和(28.90±1.57)%,而淘汰蛋鸭的分别为(29.09±1.23)%和(27.27±1.63)%;肉鸭的胸、腿肌肉盐溶蛋白的乳化活性分别为(51.13±2.27)%和(46.53±2.16)%,而淘汰蛋鸭的分别为(50.00±0.73)%和(43.69±2.08)%;肉鸭的胸、腿肌肉盐溶蛋白的起泡性分别为(52.25±2.50)%和(47.67±0.93)%,而淘汰蛋鸭的分别为(54.38±4.27)%和(42.98±1.89)%。     

Comparison of the Emulsifying Properties of Fish Gelatin and Commercial Milk Proteins

ABSTRACT: We have compared the flocculation, coalescence, and creaming properties of oil-in-water emulsions prepared with fish gelatin as sole emulsifying agent with those of emulsions prepared with sodium caseinate and whey protein. Two milk protein samples were selected from 9 commercial protein samples screened in a preliminary study. Emulsions of 20 vol% n -tetradecane or triglyceride oil were made at pH 6.8 and at different protein/oil ratios. Changes in droplet-size distribution were determined after storage and centrifugation and after treatment with excess surfactant. We have demonstrated the superior emulsifying properties of sodium caseinate, the susceptibility of whey protein emulsions to increasing flocculation on storage, and the coalescence of gelatin emulsions following centrifugation.     

淀粉对鸡胸肉盐溶性蛋白乳化特性的影响

添加不同质量分数淀粉处理鸡胸肉盐溶性蛋白,研究淀粉含量对鸡胸肉蛋白质乳化特性的影响。结果表明：随着淀粉质量分数的增加,处理组淀粉蛋白乳化液的乳化活性和乳化稳定性均先上升后下降,乳化液中D10、D50和D90的粒径值逐渐降低,剪应力和黏度均为先下降后上升。此外,随着剪切速率的升高,不同处理组剪应力逐渐增加,而黏度均先下降随后趋于稳定。相关性分析结果表明：乳化液中淀粉质量分数与微粒D10的粒径（相关系数r＝－0.598）成极显著负相关（P＜0.01）,乳化活性与微粒D50的粒径（相关系数r＝0.549）、微粒D90的粒径（相关系数r＝0.558）均成显著正相关（P＜0.05）。这些结果说明适宜含量的淀粉添加至鸡胸肉盐溶性蛋白中,使得乳化液体系更稳定,形成的淀粉-蛋白质复合物会影响鸡胸肉蛋白质的加工特性。     

Emulsifying Properties of Food Proteins: Development of a Standardized Emulsification Method

A recirculating valve-homogenizer was used to compare the emulsifying properties of bovine serum albumin and milk proteins. The energy input per unit volume was directly obtained from the mean maximum valve head pressure per stroke. The mean maximum velocity of the emulsion in the valve head was 83m sec^?1 during a valve opening time of 150 × 10 ^?3 sec reflecting a large velocity gradient per stroke of 4.2 × 10^?6 m³ The method detected changes in the emulsifying activity of proteins resulting from chemical modification, and from process or environmental factors, e.g., ionic strength. The valve-head pressure profile was used to compare the fluidity of the emulsions at different levels of energy input per unit volume (E) and an apparent viscosity index (AVI) has been proposed.     

Hydrophobicity and Solubility of Meat Proteins and Their Relationship to Emulsifying Properties

Surface hydrophobicity (S_o) of crude salt extracts of meat was determined fluorometrically using cis-parinaric acid as a probe. Upon heating the extracts to 70°C, S_o increased two- to threefold, whereas protein solubility (s) decreased to 20%. Further heating (to 85°C) resulted in slight decreases in both S_o and s. Backwards stepwise multiple regression equations for prediction of emulsifying activity index (EAI) and emulsifying capacity (EC) were: EAI = 2.658 + 0.0001308 sS_o, and EC =−35.30 + 6.459 s + 0.001317 sS_o− 0.05463 s². S_o was most important for predicting emulsifying properties of samples with high (>50%) solubility, whereas solubility parameters were more influential for samples with low (<50%) solubility.     

Emulsifying Properties of Food Proteins Conjugated with Glucose or Lactose by Two Methods (Spray-Drying Or Freeze-Drying)

Emulsifying properties of two commercial food proteins (plasma protein or egg albumen) conjugated with two sugars (glucose or lactose) by spray-drying or lyophylization were studied. Changes in protein structure were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, sulfhydryl group, Fourier transform infrared spectroscopy and differential scanning calorimetry, emulsion properties (emulsion capacity and stability, emulsion work, and emulsifying activity index). Protein conjugation increased proteins molecular weight and decreased sulfhydryl groups, coinciding with lower denaturation enthalpies, corroborating structural changes by conjugation with glucose or lactose by either spray-drying or freeze-drying. Glucose conjugation of the proteins employed at the experimental conditions resulted in structural changes that emulsify more oil with no detrimental effect on emulsion superficial area formation. Although freeze-drying conjugation improved emulsifying properties, spray-drying also enhanced these properties, as compared to non-conjugated proteins. Spray-drying was a faster way to conjugate food proteins via Maillard reaction with improved emulsifying properties.     

6种云南核桃蛋白质乳化性及其乳化稳定性

以6种云南主栽品种核桃为原料,利用碱溶酸沉法提取核桃蛋白质,研究氯化钠浓度、蔗糖浓度、pH值、植物油种类、油相体积、均质转速、水浴温度对不同品种核桃蛋白质乳化性及其乳化稳定性的影响。结果表明：NaCl浓度和蔗糖浓度越低,6种云南核桃蛋白质乳化性和乳化稳定性越好;pH值在等电点附近时,6种云南核桃蛋白质的乳化性最差,乳化稳定性随pH值的升高而增大;同种植物油对不同品种核桃蛋白质的乳化效果影响不同,且同一品种的核桃蛋白质加入不同植物油乳化效果也有差异;油相体积越大,6种云南核桃蛋白质的乳化性及其乳化稳定性越好,均质转速在10 000 r/min时,6种云南核桃蛋白质乳化性及其乳化稳定性差别较小,水浴温度为80℃时,核桃蛋白质的乳化稳定性最好。     

Chaotropic离子对肌球蛋白乳化特性影响的研究进展

食盐的过量摄入与高血压、心脑血管疾病等慢性疾病之间的矛盾日益加深,而降低乳化型肉制品的盐含量会影响产品品质特性,如何避免减盐引起的质量缺陷是低盐肉制品研究领域的重点。不同离子诱导肌球蛋白分子空间构象产生不同变化,影响肌球蛋白在脂肪球表面的吸附特性,并最终影响产品品质。本文主要论述乳化过程中Chaotropic离子属性对肌球蛋白分子构象、构象变化驱动力的影响,为开发优质低盐肉制品提供新途径。     

Evaluation of Emulsion Stability by Centrifugation with Conductivity Measurements

An industry problem when evaluating stability of emulsions is lack of a method reproducing, in a short time, aging of the emulsion. A method that combines centrifugation and conductivity measurements could be used for this purpose. Centrifugation accelerates destabilization of the product and thus simulates aging. Conductivity measurement of the aqueous phase, a function of the oil concentration, evaluates destabilization. Our method was compared with a creaming-measurement method based on fat content. The increase in conductivity was representative of the creaming rate, with correlation higher than 0.93. The combined method, applied to different oil-in-water (O/W) emulsions, enables following stability during aging and assures the need of industry for a fast, easy method to evaluate emulsion stability.     

大米蛋白乳化性质研究

本文研究了大米分离蛋白(RPI)、酶法大米分离蛋白(E-RPI)、谷蛋白等在不同pH和Na2SO3存在条件下的乳化性能及其表现特点，并与大豆分离蛋白(SPI)的乳化性能进行了比较，结果表明，增加大米蛋白溶解性的措施均有利于改善大米蛋白的乳化性能。谷蛋白一旦溶解其乳化能力与大豆蛋白相当。RPI、E-RPI经Na2SO3处理后，乳化性能明显提高，说明通过解除大米蛋白分子中亚基的聚合，可以改善大米蛋白的物化功能性。