Stability of model emulsions prepared using whey and muscle proteins

The amount of water (SW) and oil (SO) separated from model emulsions and emulsion stability (ES) of these emulsions prepared from corn oil and of fluid whey, total muscle protein (TMP), whey + TMP and sarcoplasmic protein (SP) were examined. The SW value of whey + TMP emulsions was lower (26,33%) than that of TMP (31,33%), SP (39,0%) practically the same as that of whey only. However, the SO value of whey emulsions was higher (9,40%) than that of muscle protein emulsions (0,0%). It was found that there was no oil separation in whey + TMP emulsions. Whey proteins had the lowest ES (64,6 ± 0,96) among the proteins studied. Nevertheless, whey + TMP emulsions had the highest ES (73,67 ± 0,58).     

Effect of thermal treatment on the proteins of amaranth isolates

The effect of thermal treatment of proteins from Amaranthus hypochondriacus was studied. Two protein isolates were obtained from the defatted flour by water extraction at a pH of 9 (A9 isolate) and 11 (A11 isolate), followed by isoelectric precipitation at a pH of 5. Effect of thermal treatment (70 and 90 °C, during 3, 5, 10, 15 and 30 min) on A9 and A11 dispersions were analyzed by differential scanning calorimetry (DSC), polyacrylamide gel electrophoresis, UV spectrophotometry, superficial hydrophobicity and solubility in water. Thermal treatment induced the aggregate formation of high molecular mass stabilized by disulfide and non‐covalent bond. Thermal treatment at 70 °C produced a 30% denaturation in both, while at 90 °C A9 was more denatured than A11 (75% and 55% of denaturation, respectively). An increase in thermal stability was also detected by DSC in A9 treated at 90 °C. The denaturation process was accompanied at short heating times by an increase in UV absorbance and changes in superficial hydrophobicity. A decrease in water solubility (35–50%, depending on time–temperature conditions) was also observed for the A9 isolates. The results suggest that the A9 isolates, enriched in a globulin protein fraction, are more sensitive to thermal treatment than isolates A11 enriched in glutelin protein fraction. The changes shown by both isolates, indeed, could affect their functional properties and could definitely limit their use in food products. Copyright © 2007 Society of Chemical Industry     

The proteins of grain amaranth

Proteomics, as a significant and potent postgenomic tool in the field of meat science, allows researchers to decipher underlying molecular mechanisms behind different meat quality traits. In recent years, growing attention has been paid to biomarkers accounting for meat quality attributes by means of potent proteomic technologies with the objective to gain deeper insight. This review will focus on the biomarkers of protein changes associated with the most important meat quality traits, including tenderness, color, and water-holding capacity. Molecular understanding of meat quality through application of proteomics will be conducive to generating a large amount of scientific knowledge that helps improve our understanding of meat quality, improve control, and tailor better meat quality.     

Stability and opacity of orange oil cloudy emulsions based on gum elemi and gum arabic

Orange oil cloudy emulsions based on naturally occurring oil-soluble gum elemi and naturally occurring water-soluble gum arabic have been prepared and evaluated. Cloud and emulsion stability, as well as the opacity of each emulsion, were recorded and compared. It was demonstrated that the emulsion stability is determined by the gum elemi/orange oil ratio, the orange oil content, and the gum arabic/orange oil ratio. The opacity is a function of the orange oil content and to a lesser extent also depends on the gum elemi/orange oil ratio. Since the gum elemi/orange oil ratio is a critical parameter affecting both opacity and stability it should be carefully chosen and controlled.
Gum arabic is not the sole emulsifier, as gum elemi also adsorbs on the oil droplets and plays a role in emulsion stability.     

Characterization of amaranth proteins modified by trypsin proteolysis. Structural and functional changes

Amaranth protein isolates were prepared from Amaranthus hypochondriacus and hydrolyzed using trypsin. Degrees of hydrolysis varied between 2% and 7% with the time of hydrolysis reaction. The structure, solubility and foaming properties of protein isolates were studied. SDS-PAGE analysis demonstrated that polypeptides from 11S-globulin and P globulin were the main targets for the protease, while a polypeptide of 45 kDa from the 7S globulin was more resistant to trypsin action. The FPLC analysis of hydrolyzed proteins showed that the structure is partially conserved, while an increase of the fraction of lower molecular weight is observed. Such structure exhibits a single endotherm of lower denaturation heat than the protein isolate.The solubility and foaming properties of protein isolates and hydrolysates were analyzed, in the later case at two protein concentrations (1 mg and 2.5 mg of solid matter per ml). Protein solubility increased markedly with hydrolysis, while changes in foaming properties were less dramatic. Nevertheless, foams obtained with amaranth protein hydrolysates were more dense and stable than those prepared with non-digested proteins, specially for foams produced with the protein hydrolysate of higher concentration.     

Effect of edible oils and oil emulsions on the perception of basic tastes

The intensity of sweet, bitter or astringent tastes is reduced by con-sumption of edible oil or oil emulsions immediately before the inges-tion of test solutions. The basic taste substances were dissolved in 30% aqueous ethanol, flavoured with plant extracts. The time-intensity dependence was influenced similarly. The sensitivity of taste receptors returned to the original value within 15—20 min. Intensities of acidic or salty tastes were not affected.     

乳化剂类型、浓度及水相pH对水包核桃油乳状液物理稳定性的影响

为了了解在水包核桃油乳状液中乳化剂类型、浓度及水相p H对其物理稳定性的影响,考察四种乳化剂即乳清分离蛋白(WPI)、十二烷基磺酸钠(SDS)、十二烷基三甲基溴化铵(DTAB)以及失水山梨醇聚氧乙烯酯(Tween20)在p H3.0和p H7.0条件下形成稳定的水包核桃油乳状液所需要的最低浓度。结果表明,p H对阳离子表面活性剂DTAB、非离子表面活性剂Tween20乳化效果影响较大,在p H3.0和7.0条件下形成稳定乳状液所需DTAB最低浓度分别为0.8%、2.0%,而Tween20最低浓度分别为0.6%、0.3%;p H(等电点除外)对两性大分子表面活性剂WPI和阴离子表面活性剂SDS的乳化效果影响较小。研究结果表明不同类型乳化剂在不同p H条件下对水包核桃油乳状液的物理稳定性影响差异较大。      

Fabrication and stability of Pickering emulsions using moringa seed residue protein: Effect of pH and ionic strength

Food-grade Pickering emulsions stabilised by plant protein have low toxicity. In this study, to explore the potential of Moringa seed residue protein (MSRP) as Pickering particles, MSRP was obtained from Moringa seed residue and used to fabricate emulsions at different pH and ionic strength. The molecular weight of MSRP ranged between 5 and 25 kDa. The particle diameter of MSRP with positive charge was > 233 nm. The highest MSRP solubility was achieved at pH 5 (206.89 mg g⁻¹) and 0.2 M NaCl (202.55 mg g⁻¹). MSRP generated an excellent interfacial layer as verified by confocal laser scanning microscope imaging, and had lower droplet size, and formed well-developed elastic networks at pH 5 and 0.2 M NaCl. MSRP-stabilised emulsion through steric hindrance, possessing excellent tolerance in salt (< 0.2M) and weakly acid (pH 5–7) environment. Our study finds MSRP can be used as potential Pickering particles applying in food and beverages industries.     

Secondary structure of proteins on oil release in aqueous enzymatic extraction of rapeseed oil as affected hydrolysis state

In this study, the relationship between protein hydrolysis and oil release was studied by fluorescence microscopy and Fourier Transform Infrared (FTIR) spectroscopy, respectively. Five commercial proteases (Flavourzyme 1000L, Neutrase 1.5MG, Protamex, Alcalase 2.4L, and Thermolysin) were evaluated for oil extraction from rapeseed, and Alcalase 2.4L was found to be the best enzyme for highest free oil yield (81.81%). When use this enzyme, the results showed that parts of proteins restricted the release of oil, and the oil released almost completely was achieved after hydrolysis for 3.0 h. To further reveal the relationship between oil release and protein hydrolysis, the effects of hydrolysis time on the degree of hydrolysis of protein, and free oil yield were studied. The results showed that the release of oil was only related to the hydrolysis of parts of proteins, and when the degree of hydrolysis of protein was more than 17.05%, the effect of protein hydrolysis on oil release was greatly reduced. The intrinsic relationship between the structural changes of proteins and the release of oil in the hydrolysis process was analyzed by comparing protein secondary structure of different hydrolysis time, and the results showed that the transition of protein structure from order to disorder was an important factor for oil release.     

Solubility and density of egg white proteins: Effect of pH and saline concentration

Influence of different pH values (3.0, 4.6, 6.0, 8.0 and 9.0) and salt concentrations (0.05, 0.1, 0.2, 0.35 and 0.5 mol/l) for three types of salt (NaCl, Na₂SO₄ and (NH₄)₂SO₄) on the solubility of egg white protein and density of egg white, at room temperature (25 °C) was studied. The results showed that the solubility of egg white protein was influenced by pH as well as concentration and type of salt present in the medium. Protein solubility increased with increase in pH, with higher solubility showed at pH 9.0 and lower solubility at pH 4.6. This behavior was verified for all the salts analysed. At acid pH (pH 3.0), it was observed the tendency of solubility elevation on the increase of the saline concentration, due to the salting-in effect. The density increased with increase in the salt concentration.     

酶解对乳清蛋白抗原性影响的研究

研究了酶解对乳清蛋白抗原性的影响。选择了7种常见蛋白酶在同一水解模式下水解乳清蛋白，用竞争ELISA法测定水解物的残留抗原性，从而间接测定其过敏性变化。结果表明，酶解能有效降低乳蛋白抗原性，但水解物仍能与特异抗体反应，保留一部分抗原性。不同酶对乳清蛋白过敏原的影响不同，酶的特异性对乳清蛋白水解物的抗原性有较大的影响，碱性蛋白酶降低乳蛋白抗原性的效果最佳，对抗β-乳球蛋白（β-LG）和抗α-乳白蛋白（α-LA）抗体的抗原性分别降低了50．02％和99．72％。     

Textural perception of liquid emulsions: Role of oil content,oil viscosity and emulsion viscosity

This work describes a study on the in-mouth textural perception of thickened liquid oil-in-water emulsions. The variables studied are oil content, oil viscosity, and the concentration of polysaccharide thickener. Gum arabic was chosen as the thickener because of the nearly Newtonian behavior of its solutions and special care was taken to suppress aroma clues. Based on the experimental results and findings from previous studies, this work shows that the emulsion droplets influence textural sensory perception of liquid emulsions by three main mechanisms, each of which relate to changes in specific sensory attributes, and none of which were found to be significantly dependent on the viscosity of the oil: 1) by increasing the viscosity, 2) by becoming incorporated in the mucous oral coating, and 3) by spreading oil at the oral surfaces. Based on these results, the possibility for replacement of emulsified fat by a polysaccharide thickener is evaluated.     

Effect of carrier oils on the physicochemical properties of orange oil beverage emulsions

In this study, the effect of carrier oils on the physicochemical properties of orange oil beverage emulsions was investigated. The beverage emulsions were prepared by soybean soluble polysaccharides (SSPS) using a two-stage processing of homogenization. Results showed that the presence of carrier oils could improve the physical properties of beverage emulsions, including droplet size, size distribution and turbidity, compared with only orange oil in oil phase of the beverage emulsion. And the effect of long chain triglycerides on the physical stabilities of beverage emulsions was significant (p < 0.05) than that with medium chain triglycerides (MCT). The oxidation rate of orange oil in the emulsion was faster compared to that of the orange oil/carrier oils in emulsions. However, the rheological properties of beverage emulsions were hardly dependent on the carrier oils. In addition, all the emulsions exhibited near-Newtonian fluid behavior. These findings revealed that the physicochemical properties of the beverage emulsions could be effectively improved by the presence of carrier oils.     

Stability and rheology of concentrated O/W emulsions based on soybean oil/palm kernel olein blends

Droplet size distribution and rheological properties of egg yolk-stabilized emulsions were studied before and after storage (25 °C, 30 days). The dispersed phase (70%) of the emulsions was based on soybean oil (SBO) and 10–40% palm kernel olein (PKO) replacements of SBO. Replacement of PKO resulted in a significant increase in droplet mean diameters and a decrease in rheological properties of the emulsions. All emulsion exhibited a gel-like characteristic with storage modulus higher than loss modulus and tan δ greater than 0.3. Significant increase (p < 0.05) was found for droplet mean diameters and rheological properties of the emulsions after storage. Emulsion with fully SBO and the highest PKO replacement (40%) were found to be the most unstable, which was ascribed to a strong flocculation. With 10–30% PKO replacements, the emulsions displayed a better stability after storage, most probably promoted by significant content of short-medium chain fatty acids in PKO.     

High pressure gelation of soy proteins: Effect of concentration, pH and additives

The global demand for soybean protein has increased dramatically over the last few years due to its versatility. High pressure (HP) processing is emerging as an effective alternative to thermal processing of foods. The HP treatment of protein solutions at different process conditions can cause partial unfolding of proteins that can lead to the irreversible gelation of the product. In this study, the influence of protein concentration (5–20% w/v), pH (3–7), sugar (5% w/v), CaCl₂ (5% w/v), pressure level (up to 650 MPa) and holding time (0.1 and 10 min), and process temperature (20 and 40 °C) on the dynamic rheology of soybean protein concentrate (SPC) solutions was evaluated. Furthermore, the protein structural changes caused by HP were studied, through the use of the extrinsic fluorescence of the probe 8-anilino-1-naphthalene sulfonic acid (ANS) and Fourier transform infrared (FTIR) spectroscopy. Results indicated a strong influence of protein concentration on both elastic (G′) and viscous (G″) moduli, increasing with concentration. Increase in pressure and holding time produced an increase on both G′ and G″ for SPC concentrations higher than 10%; at 15% SPC concentration, a relatively low pressure treatment of 250 MPa achieved the cross-over of G′ over G″. The structure of the soybean proteins suffered limited changes after HP treatment; hydrophobicity increased, as well as the relative proportion of random coil, while the β-sheet content decreased. HP treatment can be used to enhance the viscoelastic behavior of SPC after which SPC can be used to enrich both protein content and textural properties of foods.     

5种植物油乳液的理化性质

以菜籽油、棕榈液油、橄榄油、稻米油和椰子油5种植物油为油相,以乳清分离蛋白为乳化剂,制备水包油（O/W）型乳液。分析了5种植物油中的生育酚和谷维素含量,测定了5种植物油乳液Zeta-电位和贮藏稳定性,并采用铁离子还原法对5种植物油乳液的抗氧化能力进行了评价。结果表明：5种植物油均不含β-生育酚和δ-生育酚,总生育酚含量菜籽油最高,椰子油最低,且仅稻米油中含谷维素,含量为1 542.78 mg/kg;椰子油乳液的Zeta-电位绝对值最高,达到57 mV,28 d后乳液未出现分层现象,乳液粒径变化最小且分布范围窄,贮藏稳定性最好;棕榈液油乳液抗氧化能力最强,其次是菜籽油乳液、橄榄油乳液和稻米油乳液,三者的抗氧化能力无显著性差异,椰子油乳液抗氧化能力最弱。     

Phytosterol oxidation in oil-in-water emulsions and bulk oil

Dietary plants sterols (phytosterols) have been shown to lower plasma cholesterol level in humans. Since phytosterols may protect against coronary heart diseases, they are being incorporated into functional foods. However, phytosterols are susceptible to oxidative degradation. The purpose of this study was to evaluate the formation of phytosterols oxidation products (POPs) in oil-in-water emulsions and bulk corn oil. The extent of lipid oxidation was monitored by measuring the lipid hydroperoxides and hexanal, whereas 7-keto derivatives of phytosterols were determined by gas chromatography to follow sterol oxidation. A higher POPs level and formation rate was found in the oil-in-water (o/w) emulsion than in the bulk oil. Interfacial tension measurements showed that phytosterols had a high degree of surface activity, which would allow them to migrate to the oil–water interface of the emulsion droplets where oxidative stress is high.     

Effect of pH on the antimicrobial activity and oxidative stability of oil-in-water emulsions containing caffeic acid

ABSTRACT:  Antioxidant properties in food are dependent on various parameters. These include the pH value and interactions with food components, including proteins or metal ions. Food components affect antioxidant stability and also influence the properties of microorganisms and their viability. This paper describes an investigation of the effect of pH on the antioxidant and antibacterial properties of caffeic acid in different media. The pH values studied, using an oil-in-water emulsion as model system, were 3, 5 (with and without phosphate buffer), and 9. Effects of mixtures of caffeic acid, bovine serum albumin (BSA), and Fe (III) on oxidative deterioration in the emulsion samples were studied. The results show that the antioxidant activity of caffeic acid was increased by the presence of BSA. This effect was pH dependent and was affected by the presence of iron ions. Antibacterial properties were also pH dependent. The minimum concentration of caffeic acid required to inhibit some microorganisms in the pH range of 5 to 7 was determined. A concentration of 0.4% (w/w) caffeic acid was enough to inhibit the growth of some of the studied microorganisms in the pH range of 5 to 7. However, near-neutral pH concentrations higher than 0.4% were needed to inhibit some microorganisms, including Listeria monocytogenes , E. coli, and Staphylococcus aureus , in the medium.