Stability of citral in protein- and gum arabic-stabilized oil-in-water emulsions

Citral is a major flavor component of citrus oils that can undergo chemical degradation leading to loss of aroma and formation of off-flavors. Engineering the interface of emulsion droplets with emulsifiers that inhibit chemical reactions could provide a novel technique to stabilize citral. The objective of this study was to determine if citral was more stable in emulsions stabilized with whey protein isolate (WPI) than gum arabic (GA). Degradation of citral was equal to or less in GA- than WPI-stabilized emulsion at pH 3.0 and 7.0. However, formation of the citral oxidation product, p-cymene was greater in the GA- than WPI-stabilized emulsion at pH 3.0 and 7.0. Emulsions stabilized by WPI had a better creaming stability than those stabilized by GA because the protein emulsifier was able to produce smaller lipid droplets during homogenization. These data suggest that WPI was able to inhibit the oxidative deterioration of citral in oil-in-water emulsions. The ability of WPI to decrease oxidative reactions could be due to the formation of a cationic emulsion droplet interface at pH 3.0 which can repel prooxidative metals and/or the ability of amino acids in WPI to scavenge free radical and chelate prooxidative metals.     

猪血浆蛋白水解物对水包油型乳状液氧化稳定性的影响

本实验主要研究了猪血浆蛋白水解物（Porcine plasma protein hydrolysate,PPPH）对水包油型（O/W型）乳状液储藏过程氧化稳定性的影响。分别将PPPH以0、2.5、5、10和20 mg/m L的浓度添加到以Tween-20为乳化剂的菜籽油O/W型乳状液中,测定乳状液在37℃条件下储藏10 d时间内的荧光光谱分析、共轭二烯（Conjugated diene,CD）和硫代巴比妥酸值（Thiobarbituric acid reactive substances,TBARS）的变化趋势。研究结果表明,色氨酸的氧化降解发生在蛋白氧化的初级阶段,而荧光蛋白氧化产物（Fluorescent protein oxidation products,FP）的形成是蛋白氧化第二阶段的产物。另外,在乳化体系储藏期间,与对照组相比,添加2.5 mg/m L PPPH的处理组具有最高的色氨酸荧光强度和FP（p<0.05）,同时具有最低的CD和TBARS值（p<0.05）。与此同时,色氨酸荧光强度与CD含量和TBARS值之间呈现显著的负相关关系。总之,PPPH的添加能够显著提高O/W型乳状液的氧化稳定性,为其作为抗氧化剂在乳状液食品中的潜在应用奠定了理论基础。      

预热处理对乳清分离蛋白水包油乳状液特性和物理稳定性的影响

本实验主要研究了加热预处理（90℃,5 min）对乳清分离蛋白作为稳定剂所制备的菜籽油水包油型乳状液的特性和物理稳定性的影响。测定了乳状液在储藏期间的ζ-电势、粒径、絮凝指数、分层指数、流变特性和乳状液中蛋白质分配系数的变化趋势。研究结果表明,与天然乳清分离蛋白相比,经过预热处理的乳清分离蛋白能够显著降低乳状液在整个储藏期间（0¹4 d）的物理稳定性（p<0.05）,具体表现为较低的ζ-电势（p<0.05）,以及较高的粒径、絮凝指数、分层指数和粘度（p<0.05）。与此同时,加热处理导致的乳清分离蛋白变性和聚集,能够显著增加其在乳状液界面蛋白膜表面的分布（p<0.05）,从而验证了上述乳状液物理稳定性的结果。上述结果表明,加热预处理显著降低了整个乳状液在储藏期间的物理稳定性,为乳清分离蛋白在乳状液中的合理应用奠定了理论基础。      

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。      

Effects of composition and processing variables on the oxidative stability of protein-based and oil-in-water food emulsions

Because many common foods are emulsions (mayonnaise, coffee creamers, salad dressing, etc.), a better understanding of lipid oxidation mechanisms in these systems is crucial for the formulation, production, and storage of the relevant consumer products. A research body has focused on the microstructural and oxidative stability of protein-stabilized oil-in-water emulsions that are structurally similar to innovative products that have been recently developed by the food industry (e.g., non-dairy creams, vegetable fat spreads, etc.) This review presents recent findings about the factors that determine the development of lipid oxidation in emulsions where proteins constitute the stabilizing interface. Emphasis is given to “endogenous” factors, such as those of compositional (e.g., protein/lipid phases, pH, presence of transition metals) or processing (e.g., temperature, droplet size) nature. Improved knowledge of the conditions that favor the oxidative protection of protein in emulsions can lead to their optimized use as food ingredients and thereby improve the organoleptic and nutritional value of the related products.     

Improvement of stability of oil-in-water emulsions containing caseinate-coated droplets by addition of sodium alginate

ABSTRACT:  The potential of sodium alginate for improving the stability of emulsions containing caseinate-coated droplets was investigated. One wt% corn oil-in-water emulsions containing anionic caseinate-coated droplets (0.15 wt% sodium caseinate) and anionic sodium alginate (0 to 1 wt%) were prepared at pH 7. The pH of these emulsions was then adjusted to 3.5, so that the anionic alginate molecules adsorbed to the cationic caseinate-coated droplets. Extensive droplet aggregation occurred when there was insufficient alginate to completely saturate the droplet surfaces due to bridging flocculation, and when the nonadsorbed alginate concentration was high enough to induce depletion flocculation. Emulsions with relatively small particle sizes could be formed over a range of alginate concentrations (0.1 to 0.4 wt%). The influence of pHs (3 to 7) and sodium chloride (0 to 500 mM) on the properties of primary (0 wt% alginate) and secondary (0.15 wt% alginate) emulsions was studied. Alginate adsorbed to the droplet surfaces at pHs 3, 4, and 5, but not at pHs 6 and 7, due to electrostatic attraction between anionic groups on the alginate and cationic groups on the adsorbed caseinate. Secondary emulsions had better stability than primary emulsions at pH values near caseinate's isoelectric point (pHs 4 and 5). In addition, secondary emulsions were stable up to higher ionic strengths (< 300 mM) than primary emulsions (<50 mM). The controlled electrostatic deposition method utilized in this study could be used to extend the range of application of dairy protein emulsifiers in the food industry.     

不同植物油水包油型乳状液物理特性及氧化稳定性研究

以紫苏油、橄榄油、棕榈油和葵花籽油为油相,以乳清分离蛋白为乳化剂,制备水包油(O/W)型乳状液,研究其粒径、ζ-电位、絮凝指数等物理特性,比较不同乳状液在贮存期间的氧化稳定性。结果显示,4种乳状液中,紫苏油乳状液体积平均粒径D_(4,3)较小(0.824μm),ζ-电位绝对值较大(37.5mV),呈现良好的物理贮存稳定性;但由于油脂中有较高的多不饱和脂肪酸,体系易被氧化。棕榈油乳状液具有良好的氧化稳定性,体系初级和次级氧化产物浓度均最低;但乳状液粒径较大(D_(4,3)为1.845μm),物理稳定性较差。通过内源性荧光测定发现,乳状液中蛋白质氧化与脂质氧化存在一定关联性。     

Characterization of hydrophobic flavor release profile in oil-in-water emulsions

ABSTRACT:  An instrumental approach to better understand the release and persistence of flavor in oil-in-water emulsions has been developed. Emulsions were prepared with various whey protein (0.1% to 3.16%), sunflower oil (1% to 8%), and ethyl hexanoate (0% to 0.04%) concentrations. Flavor release profile in real time was measured at 37 °C using a specially designed glass cell connected directly to a gas chromatograph equipped with a flame ionization detector. The intensity of flavor released from the emulsion stirred at a shear rate of 100  s⁻¹ was monitored as a function of time and data were fitted to a 1st-order kinetic equation. Maximum intensity and decay rate constant were both determined from the model and the persistence index (inversely associated to decay rate constant) was calculated. For constant aroma concentration in the emulsion, maximum intensity significantly decreased as whey protein and oil concentrations increased. For increasing aroma concentration, maximum intensity was directly proportional to the ethyl hexanoate concentration when the oil content was kept constant but leveled off when oil content was increased. Persistence of flavor significantly increased with increasing protein and oil concentrations while aroma concentrations had no effect when oil content was constant. The results showed that oil concentration had a greater influence on flavor release characteristics than protein concentration. Aroma concentration in the oil phase, rather than in the emulsion, determines the kinetics of hydrophobic flavor release. The method provides a useful tool for the rapid and reproducible measurement of flavor release profile.     

Pea protein exhibits a novel Pickering stabilization for oil-in-water emulsions at pH 3.0

In this paper we reported that pea protein isolate (PPI) at pH 3.0 exhibits a novel Pickering stabilization for oil-in-water emulsions. At pH 3.0, most of the proteins in PPI were present in the nanoparticle form, with the hydrodynamic diameter of 134–165 nm depending on the concentration (c; 0.25–3.0 g/100 mL). For the emulsions formed at a specific oil fraction of 0.2, increasing the c from 0.25 to 3.0 g/100 mL resulted in a considerable reduction in the emulsion size, while their creaming stability progressively increased, and especially at c values higher than 2 g/100 mL, no creaming occurred even after storage of 20 days. Confocal laser scanning microscopy observations showed that increasing the c resulted in a progressive increase in extent of droplet flocculation, and at higher c values, a network consisting of flocculated droplets could be formed. The emulsions formed at c values above 1.0 g/100 mL exhibited extraordinary stability against coalescence. The flocculated droplet network formation was closely associated with the increased amount of adsorbed proteins at the interface. The results suggest that pea proteins exhibit a good potential to act as a kind of Pickering stabilizers for oil-in-water emulsions at acidic pHs.     

Antioxidant and emulsifying properties of potato protein hydrolysate in soybean oil-in-water emulsions

The efficacy of a previously developed antioxidative potato protein hydrolysate (PPH) for the stabilisation of oil droplets and inhibition of lipid oxidation in soybean oil-in-water (O/W) emulsions was investigated. Emulsions (10% lipid, pH 7.0) with PPH-coated oil droplets were less stable than those produced with Tween 20 (P < 0.05). However, the presence of PPH, whether added before or after homogenisation with Tween 20, retarded emulsion oxidation, showing reduced formation of peroxides up to 53.4% and malonaldehyde-equivalent substances up to 70.8% after 7-d storage at 37 °C (P < 0.05), when compared with PPH-free emulsions. In the emulsions stabilised by PPH + Tween 20, 8–15% of PPH was distributed at the interface. Adjustment of the pH from 3 to 7 markedly increased ζ-potential of such emulsions (P < 0.05). Inhibition of lipid oxidation by PPH in soybean O/W emulsions can be attributed to both chemical and physical (shielding) actions.     

乳清蛋白乳液界面性质及其物理稳定性和氧化稳定性的研究

以乳清蛋白与玉米油为原料,采用高压均质技术制备水包油型(O/W)乳液。探究乳清蛋白浓度(0.45%~3.60%)、离子强度(250 mmol/L Na Cl)对乳清蛋白乳液界面特性及其物理稳定性和氧化稳定性的影响。结果表明:随着乳清蛋白浓度的增加,乳液的粒径、乳析指数、过氧化值(POV)和丙二醛生成物(TBARS)都呈现降低的趋势,而乳液的界面蛋白浓度、电位随着蛋白浓度的增加而增加。乳液中加入250 mmol/L Na Cl能够增加乳液的粒径、乳析指数、界面蛋白含量、电位值、POV和TBARS值。上述结果表明乳液界面蛋白浓度增多,乳液的物理稳定性和氧化稳定性得到增强,而乳液中加入Na Cl后能够减弱乳液的物理稳定性和氧化稳定性。      

添加黄原胶的纯胶乳液稳定性及流变特性研究

通过对添加黄原胶(XG)的纯胶乳液粒径、稳定动力学参数、静态和动态流变特性的考察,探讨不同含量XG导致纯胶乳液失稳及致稳的机理,并制备出具有长期贮藏稳定性的纯胶乳液。研究发现,含0.1%、0.2%XG的纯胶乳液较易发生排斥絮凝,稳定性分析结果显示未添加XG的纯胶乳液30 d内的稳定性系数(SI)较低,90 d后底部背散射光强度(BS)降低,而含0.5%XG的纯胶乳液90 d内稳定性较好;流变特性检测结果表明随着XG含量的增加,纯胶乳液的表观黏度增加,流动性指数(n)由0.939降为0.414,触变环变大,体系的假塑性增强,含0.5%XG的纯胶乳液贮能模量(G')大于耗能模量(G″)且δ值小于45°,形成弱凝胶结构,具有长期贮藏稳定性。     

Response surface modeling for optimization of formulation variables and physical stability assessment of walnut oil-in-water beverage emulsions

The effect of Arabic gum content (5-10% w/w) and walnut-oil concentration (3-6% w/w) on properties of prepared walnut oil/water emulsion, including turbidity loss rate, density, size index, particle size and stability, was investigated using response surface methodology (RSM). For each response, a second-order polynomial model with high coefficient of determination (R²) values ranging from 0.907 to 0.989 was developed using multiple linear regression analysis. The lack of significant difference between the experimental and predicted values proved the adequacy of response surface equations for describing the physical changes of emulsions. An increase of Arabic gum content in range and initial concentration of walnut oil were associated with high emulsion stability and minimum droplet size. It can be concluded that RSM can determine the most suitable formulation (3% w/w walnut oil and 9.62% w/w Arabic gum) to achieve the highest stability in a developed beverage emulsion based on walnut oil.     

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.     

Effects of protein concentration and oil-phase volume fraction on the stability and rheology of menhaden oil-in-water emulsions stabilized by whey protein isolate with xanthan gum

The influences of protein concentration (0.2, 1, 2 wt%) and oil-phase volume fraction (5%, 20%, 40% v/v) on emulsion stability and rheological properties were investigated in whey protein isolate (WPI)-stabilized oil-in-water emulsions containing 0.2 wt% xanthan gum (XG). The data of droplet size, surface charge, creaming index, oxidative stability, and emulsion rheology were obtained. The results showed that increasing WPI concentration significantly affected droplet size, surface charge, and oxidative stability, but had little effect on creaming stability and emulsion rheology. At 0.2 wt% WPI, increasing oil-phase volume fraction greatly increased droplet size but no significant effect on surface charge. At 1 or 2 wt% WPI, increasing oil-phase volume fraction had less influence on droplet size but led to surface charge more negative. Increasing oil-phase volume fraction facilitated the inhibition of lipid oxidation. Meanwhile, oil-phase volume fraction played a dominant role in creaming stability and emulsion viscosity. The rheological data indicated the emulsions may undergo a behavior transition from an entropic polymer gel to an enthalpic particle gel when oil-phase volume fraction increased from 20% to 40% v/v.     

Influence of xanthan gum on the formation and stability of sodium caseinate oil-in-water emulsions

Studies have been made of the changes in droplet sizes, surface coverage and creaming stability of emulsions formed with 30% (w/w) soya oil, and aqueous solution containing 1 or 3% (w/w) sodium caseinate and varying concentrations of xanthan gum. Addition of xanthan prior to homogenization had no significant effect on average emulsion droplet size and surface protein concentration in all emulsions studied. However, addition of low levels of xanthan (≤0.2 wt%) caused flocculation of droplets that resulted in a large decrease in creaming stability and visual phase separation. At higher xanthan concentrations, the creaming stability improved, apparently due to the formation of network of flocculated droplets. It was found that emulsions formed with 3% sodium caseinate in the absence of xanthan showed extensive flocculation that resulted in very low creaming stability. The presence of xanthan in these emulsions increased the creaming stability, although the emulsion droplets were still flocculated. It appears that creaming stability of emulsions made with mixtures of sodium caseinate and xanthan was more closely related to the structure and rheology of the emulsion itself rather than to the rheology of the aqueous phase.