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 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.     

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.     

牛乳酪蛋白性质的研究

研究和比较了牛乳中α＿ｓ－酪蛋白和β－酪蛋白的酸凝性质和酶水解性质，指出牛乳中α＿ｓ－酪蛋白的大量存在是造成不易消化的根本原因。     

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.     

牛血清白蛋白的乳化和起泡特性

研究蛋白质量浓度、pH 值、CaCl2 质量浓度和温度对牛血清白蛋白(BSA)的乳化性、乳化稳定性、起泡性和起泡稳定性的影响。结果表明：蛋白质量浓度为0.1g/100mL 时乳化性和乳化稳定性最大,pH 值为5 时乳化性和乳化稳定性最小,乳化性随着CaCl2 质量浓度的增加而缓慢增大,乳化稳定性随着CaCl2 质量浓度的增加而减小,60℃时乳化性较好,乳化稳定性在60℃后显著下降;随着蛋白质质量浓度的增加,起泡性呈上升趋势,起泡稳定性先上升后下降,在质量浓度为1.5g/100mL 时起泡稳定性最好;pH 值为5 时起泡性最小,而此时起泡稳定性最好;CaCl2 质量浓度对起泡性和起泡稳定性没有影响。     

Factors Affecting the Emulsifying Capacity of Bovine Muscle and Muscle Proteins

Semitendinosus muscle samples were excised prerigor from 64 crossbred beef animals. Eight animals of each sex condition (bullocks and steers) were slaughtered when they reached age end–points of 8-, 12-12-, 16- and 20-months. The results indicated a significant effect of sex on all hydrometric muscle properties. The values for these traits were generally higher in muscle from bullocks. These differences were especially pronounced in animals 16 months and older. Sex had little effect on muscle pH or the percentages of salt soluble, extractable, and total muscle protein. However, most traits were highly correlated with age. No significant effects of sex regardless of age on emulsifying capacity were noted and many of these traits were unaffected by animal age between 16 and 20 months. Although older animals have less salt soluble protein, its emulsifying capacity is greater and more efficient.     

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。     

Relative Emulsifying Activity of Bovine Serum Albumin and Casein as Assessed by Three Different Methods

The relative emulsifying activities of bovine serum albumin (BSA) and casein as determined by computerized optical microscopy, electron microscopy and spectroturbidimetry at a protein concentration of 0.135 mM (pH 7) and an oil:water (o:w) ratio of 4:6, was compared. Repeated homogenization led to a more homogeneous distribution of dispersed phase globules. BSA stabilized globules became smaller, e.g. the mean globule diameter determined by the different methods decreased from 3.1 μ at an energy input of 7.6 × 10⁷ J m^?3 to 2.2μ, at 182 × 10⁷ J m^?3. Casein stabilized globules became larger with energy input, e.g. mean d_vs increased from 5.0μ at 7.6 × 10⁷ J m^?3 to 5.8μ. at 182 × 10⁷ J m^?3 indicating structure dependent differences in the emulsifying activity of protein.     

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.     

Use of a Flow Cell Apparatus to Determine the Emulsifying Properties of Casein

A newly designed flow cell apparatus was used to investigate the effect of protein concentration and oil fraction on casein stabilized emulsions. Emulsifying capacity showed an exponential decrease with increasing casein concentration. The microstructure of the emulsion suggested that insufficient surface coverage and mechanical stress on oil droplets' membranes were factors responsible for its collapse. Protein load and membrane thickness calculations, showed that the minimal surface coverage, or the minimal membrane thickness required to prevent emulsion collapse, increased with the oil fraction. This last relationship is suggested as a membrane resistance indicator for film forming proteins.     

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.     

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.     

Determination of Emulsifying Properties of Some Proteins by Conductivity Measurements

A method was developed to measure the emulsifying activity and emulsion stability of proteins using a simple apparatus consisting of a glass column with a conductivity cell. A significant correlation was observed between the emulsifying activity and emulsion stability of 10 proteins determined by the conductivity method examined in this paper and the turbidity method of Pearce and Kinsella (1978). These results suggest that the emulsifying properties can be estimated by measuring changes in the conductivity of emulsion. The advantages of the conductivity method are to measure accurately and simply the emulsifying properties of proteins, because this method directly and automatically measures changes in the physical constant (that is, conductivity) of emulsion.     

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.     

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)%。     

Emulsifying Peptides from the Tryptic Hydrolysis of Casein

ABSTRACT: Casein was hydrolyzed by trypsin to 5% degree of hydrolysis, and the hydrolysate was fractionated by ultrafiltration. While screening for the best emulsifying properties, the retentate fraction was systematically fractionated by ammonium sulfate precipitation, ion exchange, and reverse-phase high-performance liquid chromatography (HPLC). Residue from 30% ammonium sulfate saturation yielded 3 fractions on anion exchange chromatography. Preparative reverse-phase HPLC was used to isolate 4 peptides with good emulsifying properties for characterization. Computational methods were used to complement amino acid sequencing, and the peptides were identified as originating from αs-1 casein (f167-208), β-casein (f48-63), and (f129-184). A 4th peptide could not be conclusively identified. Properties of the emulsifying peptides are discussed.     

牛血浆蛋白凝胶特性研究

研究不同加工条件如蛋白浓度、加热温度、离子强度和pH对牛血浆蛋白凝胶特性的影响。结果表明:蛋白浓度的提高有利于凝胶的形成,且形成凝胶的最低血浆蛋白浓度是4.0%;4.8%的血浆蛋白,线性升温到85℃保温20 min,能够很好形成凝胶,呈果冻状,光滑有弹性;NaCl浓度在1.0 mol/L以下时,血浆蛋白凝胶强度随离子强度的变化是先增加后减小,0.3 mol/L时取得最佳效果;在pH6.0~9.0范围内,pH为9.0时牛血浆蛋白凝胶的凝胶强度较好,保水性高,蒸煮损失低。NaCl和pH对于牛血浆蛋白的凝胶特性有极显著的互作效应。     

牛乳酪蛋白的人乳化改性研究

由于牛乳酪蛋白不易为婴儿消化吸收，通过对牛乳酪蛋白人乳化改性的研究，即运用犊牛皱胃酶的作用，减少牛乳α＿ｓ＿１－酪蛋白的量，使β－酪蛋白与α＿ｓ＿１－酪蛋白的比例由原来的０．７提高到３．ｏ以上，从而接近了人乳的消化吸收性。经人乳化改性后的牛乳可适用于新生婴儿配方乳的制造。     

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.