Oxidative stability of mayonnaise and milk drink produced with structured lipids based on fish oil and caprylic acid

The oxidative stabilities of traditional fish oil (FO), randomized lipids (RFO), or specific structured lipids (SFO) produced from fish oil were compared when incorporated into either milk drink or mayonnaise. Furthermore, the effect of adding the potential antioxidants EDTA (240 mg/kg) or lactoferrin (1000 mg/kg) to the milk drink based on SFO was investigated. The lipid type significantly affected the oxidative stability of both mayonnaises and milk drinks: The oxidative stability decreased in the order RFO>FO>SFO. The reduced oxidative stability in the SFO food emulsions could not be ascribed to a single factor, but was most likely influenced by the structure of the lipids and differences in the processes used to produce and purify the lipids. In milk drinks based on SFO, EDTA slightly reduced oxidation, while lactoferrin did not exert a distinct antioxidative effect.     

Ability of whey protein isolate and/or fish gelatin to inhibit physical separation and lipid oxidation in fish oil-in-water beverage emulsion

The effect of pH on the capability of whey protein isolate (WPI) and fish gelatin (FG), alone and in conjugation, to form and stabilize fish oil-in-water emulsions was examined. Using layer-by-layer interfacial deposition technique for WPI–FG conjugate, a total of 1% protein was used to prepare 10% fish oil emulsions. The droplets size distributions and electrical charge, surface protein concentration, flow and dynamic rheological properties and physiochemical stability of emulsions were characterize at two different pH of 3.4 and 6.8 which were selected based on the ranges of citrus and milk beverages pHs, respectively. Emulsions prepared with WPI–FG conjugate had superior physiochemical stability compare to the emulsions prepared with individual proteins. Higher rate of coalescence was associated with reduction in net charge and consequent decrease of the repulsion between coated oil droplets due to the proximity of pH to the isoelectric point of proteins. The noteworthy shear thinning viscosity, as an indication of flocculation onset, was associated with whey protein stabilized fish oil emulsion prepared at pH of 3.4 and gelatin stabilized fish oil emulsion made at pH of 6.8. At pH 3.4, it appeared that lower surface charge and higher surface area of WPI stabilized emulsions promoted lipid oxidation and production of hexanal.     

Lipid Encapsulation in Glassy Matrices of Sugar-Gelatin Systems in Freeze-Drying

Entrapment of lipid in glass forming matrices in freeze-drying was investigated. Dispersion of lipid in aqueous solutions of three different sugars was formed by addition of protein and using homogenisation process. Two different levels of proteins in the ratios of 9:1 and 8:2 (sugar:protein) were used. Three different homogenisation processes were used to vary the emulsion droplet size of dispersed lipid. A novel ultra high-pressure homogenisation treatment with pressure levels up to 255 MPa (5MPa in second stage) was used to form emulsion before freeze-drying. The non-fat solids formed a glass in freezing which led to entrapment of dispersed oil. Ultra high-pressure homogenisation at pressure levels higher than 155 MPa caused alterations in emulsifying properties of sugar/gelatin systems. Changes in emulsifying properties of encapsulation matrices affected entrapment of dispersed lipid components. Droplet size of the dispersed phase was a significant factor for encapsulation efficiency. Emulsions with smaller droplet diameter gave higher entrapped amounts of lipid than emulsions with larger droplets. The glass forming properties and physical state of freeze-dried matrices were also determined. Knowledge of glass forming properties of an encapsulation matrix is needed for entrapment and predicting the stability and release properties of entrapped components.     

Effect of blackberry and raspberry juice on whey protein emulsion stability

The effect of raspberry and blackberry juice on oil-in-water (o/w) emulsion oxidative stability was investigated with different concentrations of whey proteins and rapeseed oil. The extent of lipid oxidation was measured by determining conjugated diene hydroperoxides and thiobarbituric acid reactive substances and that of protein oxidation by loss of natural tryptophan fluorescence and formation of protein carbonyl compounds. In addition, the anthocyanin colour stability and emulsion turbidity were measured. The increasing concentration of whey proteins and berry juices led to enhanced stabilization of the interface formed during emulsification. The anthocyanin concentration and colour decreased during oxidation leading to whiter emulsions. Raspberry juice provided a better overall antioxidant protection towards lipid and protein oxidation compared to blackberry juice. The antioxidant activity of berry juices towards lipid oxidation varied with concentration. The antioxidant activity increased with increasing concentration of berry juices. In conclusion, red berry juice anthocyanins, as well as other phenolic compounds, act as antioxidants improving the oxidative stability of whey protein emulsions. However, the antioxidant protection is different towards protein and lipid oxidation, and is also affected by other components present.     

Butteroil Emulsification with Milk-Derived Membrane and Protein Fractions

Butteroil was emulsified by homogenization or ultrasound dispersal into aqueous phases containing milk lipid globule membrane, or combinations of membrane with lipid globule-derived and milk serum proteins. Stable emulsions containing about 50 mg protein/g butteroil were produced with all combinations. Protein composition of emulsions closely reflected protein composition of starting materials. Emulsions of equal stability, and with churn times equivalent to that of cream, were obtained with unprocessed butteroil and with a cholesterol-reduced butteroil produced by steam-stripping. Electron microscopic examination of fixed material showed that emulsions produced with all formulations predominantly were of the water-in-oil type, and not the oil-in-water type typical of milk lipid globules.     

Antioxidant properties of caseins and whey proteins in model oil-in-water emulsions

The oxidative stabilities of both wheyproteinisolate (WPI)- and sodiumcaseinate-stabilized linoleic acid emulsions with different droplet sizes, protein concentrations and protein concentrations in the continuous phase were examined by determining lipid hydroperoxide and hexanal in the headspace. Emulsions with small droplet size had greater oxidative stability than emulsions with large droplet size in both WPI and sodiumcaseinate-stabilized emulsions. Lipid oxidation was in general lowered by an increase in the protein concentration. At high protein concentrations, the antioxidative effect of the protein in the emulsions appeared to offset the effects of emulsion droplet size and protein type. Replacing the unadsorbed protein in the continuous phase with water markedly decreased the oxidative stability of the emulsions. In contrast, the oxidative stability of the emulsions increased with increasing protein concentration in the continuous phase. This suggests that the antioxidative mechanism of protein in the interfacial region, such as binding trace metal ions from the lipid phase and free-radical-scavenging activity, may involve a dynamic exchange process with protein molecules from the continuous phase.     

单、双脂肪酸甘油酯(亚麻酸)乳液的制备及特性研究

针对单、双脂肪酸甘油酯（亚麻酸）极易氧化的特点,该研究以乳清浓缩蛋白（WPC）、大豆分离蛋白（SPI）、酪蛋白酸钠（SC）和吐温80（T80）为乳化剂制备乳液,考察乳化剂类型对乳液的理化性质、氧化稳定性和消化特性的影响。结果表明,乳液均具有较小的粒径（131.97~224.87 nm）,且在两周贮藏期内保持稳定。乳液包载能够提高单、双脂肪酸甘油酯（亚麻酸）的氧化稳定性,相比T80（过氧化值为377.40 mmol/kg）,蛋白质对油脂的氧化保护效果更好,其中SPI稳定的乳液过氧化值最低为197.73 mmol/kg。体外模拟消化试验表明,乳化剂类型对游离脂肪酸的释放影响较小,但蛋白稳定的乳液在胃消化阶段更容易发生液滴聚集;亚麻籽油的脂质水解程度最低为23.93%,而单、双脂肪酸甘油酯（亚麻酸）的初始消化速度更快,最终脂解程度更高（46.33%）。因此,蛋白质乳液能有效提高单、双脂肪酸甘油酯（亚麻酸）的氧化稳定性,且单、双脂肪酸甘油酯（亚麻酸）相比亚麻籽油具有更好的消化效率,有望替代亚麻籽油作为人体亚麻酸的食物来源。     

Aspects of milk-protein-stabilised emulsions

Milk proteins are widely used as ingredients in prepared foods, in which they perform a wide range of key functions, including emulsification, thickening, gelling and foaming. An important functionality of milk proteins in food colloids is their ability to facilitate the formation and stabilisation of oil droplets in emulsions. The ability of milk proteins to adsorb at the oil–water interface and to stabilise emulsions has been exploited by the food industry in the manufacture of nutritional products, specialised medical foods, dietary formulations, cream liqueurs and dairy desserts. This article provides an overview of the properties and functionalities of food emulsions formed with milk proteins, focusing on the structure and composition of adsorbed protein layers, competition between proteins and the physical and chemical stability of emulsion droplets. Of particular importance is the understanding of the behaviour of milk-protein-based emulsions under the conditions relevant to digestion in the human gastrointestinal tract. Recent relevant research in this area is reviewed and discussed.     

Effect of α-lactalbumin and β-lactoglobulin on the oxidative stability of 10% fish oil-in-water emulsions depends on pH

The objective of this study was to investigate the influence of pH on lipid oxidation and protein partitioning in 10% fish oil-in-water emulsions prepared with different whey protein isolates with varying ratios of α-lactalbumin and β-lactoglobulin. Results showed that an increase in pH increased lipid oxidation irrespective of the emulsifier used. At pH 4, lipid oxidation was not affected by the type of whey protein emulsifier used or the partitioning of proteins between the interface and the water phase. However, at pH 7 the emulsifier with the highest concentration of β-lactoglobulin protected more effectively against oxidation during emulsion production, whereas the emulsions with the highest concentration of α-lactalbumin were most stable to oxidation during storage. These differences were explained by differences in the pressure and adsorption induced unfolding of the individual protein components.     

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.     

Iron‐mediated lipid oxidation in 70% fish oil‐in‐water emulsions: effect of emulsifier type and pH

The objective of this study was to investigate the protective effect of five different emulsifiers on iron‐mediated lipid oxidation in 70% fish oil‐in‐water emulsions. The emulsifiers were either based on protein (whey protein isolate and sodium caseinate) or based on phospholipid (soy lecithin and two milk phospholipids with different phospholipid contents, MPL20 and MPL75). Lipid oxidation was studied at pH 4.5 and 7.0, and results were compared to lipid oxidation in neat fish oil. Results showed that all emulsions oxidised more than neat oil. Furthermore, emulsions prepared with proteins oxidised more at low pH than at high pH, and casein emulsions oxidised the least (Peroxide value (PV) at day 7 was 0.5–0.7 meq kg^?1). Among emulsions prepared with phospholipids, emulsions with MPL75 were the most oxidised followed by emulsions prepared with lecithin and MPL20. Thus, PV in MPL75 emulsions was 5.0–5.5 meq kg^?1 at day 7 compared with 0.9–1.9 meq kg^?1 in MPL20 emulsions.     

Influence of anionic dietary fibers (xanthan gum and pectin) on oxidative stability and lipid digestibility of wheat protein-stabilized fish oil-in-water emulsion

The influence of two anionic dietary fibers (xanthan gum and pectin) on the oxidative stability and lipid digestibility of fish oil emulsions stabilized by wheat protein (gliadin) was investigated. Lipid oxidation was determined by measuring lipid hydroperoxides and TBARS of the emulsions during storage, while protein oxidation was measured using fluorescence spectroscopy. Lipid and protein oxidation was faster at pH 3.5 than at pH 7, which may have been due to increased iron solubility under acidic conditions. Xanthan gum inhibited lipid and protein oxidation, which was attributed to its ability to bind iron ions. Conversely, pectin promoted oxidation, which was attributed to the presence of endogenous transition metals in the polysaccharide ingredient. In vitro digestion was carried out to evaluate the digestibility of oil droplets in emulsions with or without polysaccharides. Both xanthan gum and pectin significantly increased the rate of lipid digestion, which was attributed to their ability to inhibit droplet aggregation under gastrointestinal conditions. These results have important implications for designing emulsion-based functional foods with improved oxidative stability and lipid digestibility.     

双蛋白纳米颗粒Pickering乳液的构建及稳定性研究

为获得稳定性较好的蛋白基Pickering乳液,实验采用pH循环法以绿豆蛋白和乳清蛋白为原料制备双蛋白纳米颗粒并进行表征,进一步以此为基质制备Pickering乳液,并对Pickering乳液微观结构、粒径及流变学等进行表征,同时探讨了乳液的加工稳定性。结果：获得了粒径为100~250 nm的蛋白纳米颗粒;其制备的Pickering乳液为水包油型,且具有良好稳定性;与单一蛋白纳米颗粒乳液比较,双蛋白纳米颗粒乳液的乳化特性及其本身的稳定性有所提高。乳液的流变学说明乳液出现了剪切稀化现象,形成了凝胶网络结构。随着双蛋白中乳清蛋白比例的增加,乳液粒径减小,稳定性增加。因此,双蛋白制备的纳米颗粒Pickering乳液理化性质得到改善。研究结果可为混合蛋白构建稳定的乳液体系及活性成分的递送提供参考。     

Mechanisms of lipid oxidation in water-in-oil emulsions and oxidomics-guided discovery of targeted protective approaches

Lipid oxidation is an inevitable event during the processing, storage, and even consumption of lipid-containing food, which may cause adverse effects on both food quality and human health. Water-in-oil (W/O) food emulsions contain a high content of lipids and small water droplets, which renders them vulnerable to lipid oxidation. The present review provides comprehensive insights into the lipid oxidation of W/O food emulsions. The key influential factors of lipid oxidation in W/O food emulsions are presented systematically. To better interpret the specific mechanisms of lipid oxidation in W/O food emulsions, a comprehensive detection method, oxidative lipidomics (oxidomics), is proposed to identify novel markers, which not only tracks the chemical molecules but also considers the changes in supramolecular properties, sensory properties, and nutritional value. The microstructure of emulsions, components from both phases, emulsifiers, pH, temperature, and light should be taken into account to identify specific oxidation markers. A correlation of these novel oxidation markers with the shelf life, the organoleptic properties, and the nutritional value of W/O food emulsions should be applied to develop targeted protective approaches for limiting lipid oxidation. Accordingly, the processing parameters, the application of antioxidants and emulsifiers, as well as packing and storage conditions can be optimized to develop W/O emulsions with improved oxidative stability. This review may help in emphasizing the future research priorities of investigating the mechanisms of lipid oxidation in W/O emulsion by oxidomics, leading to practical solutions for the food industry to prevent oxidative rancidity in W/O food emulsions.     

Iron-catalyzed lipid oxidation in emulsion as affected by surfactant,pH and NaCl

Corn oil-in-water emulsions stabilized by sodium dodecyl sulfate (SDS), Brij 35 or dodecyltrimethylammonium bromide (DTAB) were prepared to determine the influence of surface charge on iron-catalyzed lipid oxidation. Oxidation was measured using lipid peroxides, conjugated dienes, and thiobarbituric reactive substances. At pH 6.5, initial oxidation rates were in the order of SDS> Brij>DTAB. As pH was decreased from 8 to 3, oxidation of SDS-stabilized emulsions increased, while oxidation of Brij and DTAB emulsions were unaffected. NaCl (1.0%) decreased oxidation of the SDS-stabilized emulsion by 20% but had minimal influence on oxidation of Brij and DTAB emulsions. These results indicate that the surface charge of emulsion droplets plays an important role in their oxidative stability.     

Structure and oxidative stability of oil in water emulsions as affected by rutin and homogenization procedure

The structural properties of oil-in-water (O/W) emulsions, as well as their oxidative stability upon storage at 50 °C, were studied. Eight different formulations were prepared, with the aim of studying the effect of three variables: the composition of the oil phase, the presence of the flavonoid rutin and the homogenization procedure on the structure and the oxidative stability. It was found that high pressure homogenization, through droplet size reduction, stabilized the emulsions both against creaming and oil oxidation. The interfacial protein was also partially replaced by rutin, further improving the stability of the emulsions, whereas purification of the oil phase had hardly any effect. Thus, the structural and oxidative stability of emulsions was controlled by the size of the droplets and improved by the addition of rutin.     

Microstructural design to reduce lipid oxidation in oil-inwater emulsions

The influence of emulsifier type (Tween 20 and sodium caseinate (CAS)) and oil phase volume fraction (5% and 30%) on emulsion oxidative stability was investigated. The primary and secondary lipid oxidation products of emulsions stored at 40 °C were measured over 7 days. The results indicated that the oxidative stability of samples stabilised with CAS was significantly higher compared with emulsions stabilised with Tween 20. We propose that this is due to iron binding ability of CAS. Moreover, the impacts of Pickering emulsions (Silica particles) on lipid oxidation were studied and compared with Tween 20 stabilised emulsions. The results showed that silica particles could increase the oxidative stability of 20% sunflower oil-in-water emulsions by acting as a physical barrier between pro-oxidants located in continuous phase and hydroperxide at droplet interface.     

Effect of oil content and processing conditions on the thermal behaviour and physicochemical stability of oil-in-water emulsions

The destabilisation mechanism of oil-in-water (o/w) emulsions was studied as a function of oil content (20% and 40% o/w), homogenisation conditions and crystallisation temperatures (10, 5, 0, −5 and −10 °C). A mixture of anhydrous milk fat and soya bean oil was used as the lipid phase and whey protein isolate (2 wt%) as emulsifier. Crystallisation and melting behaviours were analysed using differential scanning calorimetry. Physicochemical stability was measured with a vertical scan macroscopic analyser. Emulsions with 20% oil were found to be less stable than those with 40% oil. For 20% o/w emulsions, the crystallisation was delayed and inhibited in emulsions with smaller droplets and promoted in emulsions with larger droplets when compared with 40% o/w emulsions. Depending on the droplet sizes in the emulsion, the formation of lipid crystals (in combination with the emulsifier) either stabilises (small droplets) or destabilises (big droplets) the emulsion.     

苹果提取物对花生蛋白水解物水包油乳状液氧化稳定性的影响

将苹果提取物(apple extract,AE)添加到花生蛋白水解物(peanut protein hydrolysate,PPH)制备的乳状液中,通过测定絮凝稳定性、凝结稳定性、氧化稳定性、色氨酸荧光损失及蛋白分布等指标,探讨PPH与AE对乳状液脂质氧化的联合抑制作用以及乳状液的氧化稳定性。研究结果表明,蛋白质与多酚化合物能够形成共价结合,提高乳状液的稳定性。还能增加PPH在界面上的吸附量,有效的降低PPH制备的乳状液在贮藏期间的过氧化物和丙二醛的生成量。界面膜上的AE和PPH协同作用提供改进的物理屏障,促进乳状液在储存期间的氧化稳定性。添加AE浓度为100μg/mL时,乳状液在储藏期间最为稳定,但是AE的添加量超过100μg/mL会与PPH形成竞争吸附,影响PPH在界面上的分布,导致稳定性下降。