Identification and quantification of aminophospholipid-linked Maillard compounds in model systems and egg yolk products

While the Maillard reaction of free amino acids and proteins is a well-established process, no defined structures from the nonenzymatic browning of aminophospholipids in foodstuffs have been described so far. Phosphatidylethanolamine (PE)-linked glucosylamines (Schiff-PE), Amadori products (Amadori-PE), 5-hydroxymethylpyrrole-2-carbaldehydes (Pyrrole-PE), and carboxymethyl (CM-PE) as well as carboxyethyl (CE-PE) derivatives were detected and quantified by liquid chromatography- electrospray mass spectrometry (LC-(ESI)MS). Model incubations of soy-PE and D-glucose were employed to firmly establish the LC-(ESI)MS procedure. Analyses of spray-dried egg yolk powders and lecithin products derived therefrom show one-fourth of the native D-glucose content of egg yolk to be transformed to Amadori-PE, corresponding to a PE derivatization quota of 11-15.5 mol %. Schiff-PE and Pyrrole-PE were present only in low amounts, no CM-PE and CE-PE could be identified in any of the investigated samples. The high glycation rate of egg yolk PE will influence the emulsifying properties and perhaps even the oxidation resistance of the respective products.     

解冻方式对调理猪肉饼品质的影响

为探索不同解冻方式对猪肉饼品质和蛋白质氧化程度的影响,本试验将-18℃冻藏的调理猪肉饼分别采用室温解冻、冷藏解冻、流水解冻以及盐水解冻4种方式进行解冻,通过测定解冻后肉饼的保水性(解冻损失率、离心损失率)、pH值、TBARS值、TVB-N值,并测定猪肉饼肌原纤维蛋白羰基含量、巯基含量、蛋白溶解等,分析不同解冻方式对其蛋白氧化程度的影响。结果表明,解冻对调理猪肉饼保水性有较大影响,其中空气解冻与冷藏解冻组的保水性最好,解冻损失维持在5.03%~5.75%之间,离心损失率在31.02%~32.19%之间;同时与新鲜肉饼组相比,空气解冻、盐水解冻和流水解冻组猪肉饼TVB-N值显著上升(P<0.05),盐水解冻组TVB-N值上升至3.17 mg·100g^-1;但解冻对调理肉饼pH值、TBARS值、色泽的影响均不显著(P>0.05);通过对肌原纤维蛋白氧化程度的测定发现,解冻会引起肌原纤维蛋白羰基含量上升、巯基含量和溶解度下降,SDS-PAGE试验也证明解冻会引起蛋白质发生不同程度的降解。本研究为实际生产中冻结肉制品解冻工艺的选择与优化提供了一定的理论依据。     

Efficient analysis of egg yolk proteins and their thermal sensitivity using sodium dodecyl sulfate polyacrylamide gel electrophoresis under reducing and nonreducing conditions

The multiple functional properties of egg yolk are mostly influenced by its complex protein composition. The high lipid content of egg yolk as well as the low solubility of delipidated egg yolk lipoproteins make analysis by conventional chromatographic or electrophoretic techniques a difficult task. This work describes a method to profile egg yolk proteins after delipidation with acetone using sodium dodecyl sulfate polyacrylamide gel electrophoresis on precast 8-18% T polyacrylamide gradient gels. Twenty bands were obtained for the whole egg yolk profile with molecular weights ranging between 5 and 221 kDa. The bands were identified based on their molecular weight and by comparison with isolated egg yolk subfractions. The dissociation behavior under reducing and nonreducing conditions provided additionally helpful information for identification and characterization of the yolk proteins. The method presented is very well suited for assaying the thermal sensitivity of whole yolk and its components and thus for the characterization of heat treatment processes.     

Residues of veterinary drugs in eggs and their distribution between yolk and white

Veterinary drugs and feed additives (especially some coccidiostats) can be absorbed by the digestive tract of laying hens and transferred to the egg. Physicochemical characteristics of these compounds determine their pharmacokinetic behavior and distribution to and within the egg. Traditionally the quite lipid soluble drugs and additives are expected to yield residues only in the fat-rich yolk. However, the quite lipid soluble drug doxycycline--as well as many other drugs--showed during long-term administration higher residues in white than in yolk. In a model study with 11 sulfonamides differing in pK(a) value and lipid solubility, their distribution in vivo between yolk and white was determined. Neither differences in pK(a) values nor those in lipid solubility could explain the distributions found. Binding to egg white macromolecules in vivo as an explanatory factor was tested with five sulfonamides, and no correlation between binding and the distribution of sulfonamides between white and yolk was found. Literature data on the distribution of drugs between egg white and yolk showed a reasonable consistency within drugs and a large variability among drugs (as could be expected). This larger database also did not provide a clue as to what factor determines the distribution of a drug between egg white and yolk when given to laying hens.     

Ascorbic acid and ascorbic acid 6-palmitate induced oxidation in egg yolk dispersions

The oxidation in aqueous dispersions of egg yolk powder and the influence of addition of the proposed antioxidants ascorbic acid and ascorbic acid 6-palmitate indicate that both ascorbic acid and ascorbic acid 6-palmitate propagated the oxidation of egg yolk powder dispersions. Ascorbic acid 6-palmitate was found to be more prooxidative than ascorbic acid. Moreover, it was found that addition of ascorbic acid or ascorbic acid 6-palmitate gave rise to an increase in the amount of free iron Fe(II) in the egg yolk dispersions. It is proposed that ascorbic acid and ascorbic acid 6-palmitate react with the phosvitin-Fe(III) complex found in egg yolk and release Fe(II), which subsequently propagates lipid oxidation. It appears that less oxidation occurs in egg yolk dispersions exposed to high concentrations of peroxy radicals with added ascorbic acid than egg yolk dispersions with added ascorbic acid without exposure to peroxy radicals.     

Impact of a treatment with phospholipase A2 on the physicochemical properties of hen egg yolk

Changes in physicochemical properties of egg yolk were investigated after a treatment with phospholipase A 2 (PLA 2), where phospholipids are converted in lyso-phospholipids. Protein solubility and protein denaturation before and after modification by PLA 2 was monitored as well as the functionality of egg yolk by means of interfacial tension. Enzymatic treatment showed a significant impact on the properties of egg yolk with regard to protein solubility and denaturation behavior. To gain a closer insight, egg yolk was separated in its water-soluble fraction called plasma and the insoluble granules. Both fractions were separately modified by PLA 2. The granule fraction shows a higher protein solubility, and the plasma proteins show very high heat stability after modification by PLA 2. Hypotheses regarding related changes in the low-density lipoprotein (LDL) particles are discussed. Results suggest that significant differences in the functional properties of untreated and PLA 2-modified egg yolk do not primarily result from the existence of lyso-phospholipids but from structural changes in egg yolk granules and LDL particles.     

Oxidation of myofibrillar proteins and impaired functionality: underlying mechanisms of the carbonylation pathway

The potential impact of protein oxidation on the functional properties of myofibrillar proteins (MP) was investigated in the present study. To accomplish this purpose, myofibrillar proteins were oxidized in vitro for 12 days at 37 °C in the presence of Cu(2+), Fe(3+), and Mb in combination with H(2)O(2) and analyzed at sampling times for chemical changes induced by oxidative reactions and functional properties. The oxidation measurements included specific protein carbonyls (α-aminoadipic semialdehyde, AAS), advanced lysine oxidation products (α-aminoadipic acid, AAA, and Schiff bases), and thiobarbituric acid-reactive substances (TBARS). The factors and mechanisms involved in the oxidative degradation of lysine residues through the carbonylation pathway are precisely described. According to the present results, intense lipid and protein carbonylation, principally induced by Cu(2+)/systems, leads to a fast and severe loss of MP functionality, including impaired water-holding, foaming, and gelling capacities. The implication of Mb in the oxidation events enhances the production of AAA and Schiff bases, compromising to a larger extent the solubility of MP and worsening the aggregation and the gelling capacity. The connection between the oxidation-induced chemical changes and the loss of protein functionality is thoroughly discussed.     

15N‐Labeling of Egg Proteins for Studying Protein Network Formation During Pound Cake Making

Proteins from wheat and egg are important for pound cake texture, but their exact role is insufficiently understood. A clear, analytical distinction between proteins from wheat flour, egg white, or egg yolk has been a main challenge. However, this can be addressed by using egg proteins carrying ¹⁵N. Therefore, egg white and yolk protein were enriched in ¹⁵N by mixing ¹⁵N‐labeled leucine into hen feed. Incorporation of egg and flour proteins in the protein network was monitored based on changes in their extractability during cake making. The relative contribution of different noncovalent and covalent bonds could be determined by using different extraction media. We for the first time distinguished between the contribution of egg white, egg yolk, and wheat protein in network formation during pound cake making. Our results show that during batter mixing hardly any intermolecular disulfide bonds are formed and that baking induces tremendous changes in protein extractability. A protein network based on both disulfide bonds and hydrophobic interactions is formed during baking. This covalent network includes almost all egg white protein and most of the yolk and wheat flour protein. The remaining protein fraction most probably lacks sulfhydryl groups and/or intramolecular disulfide bonds.     

咸蛋黄快速腌制过程中理化性质变化规律

该研究以新鲜蛋黄为原料,利用快速腌制模具,探究在咸蛋黄的上表面添加食盐单侧腌制过程中,食盐添加量和腌制时间对咸鸡蛋黄快速腌制过程中形貌特征和理化性质变化规律的影响。借助多种仪器分析手段对蛋黄腌制过程中形貌与物性的变化、水分及盐分的迁移规律进行了表征。低场核磁及成像结果表明：在腌制过程中,蛋黄中的水分不断向外迁移,含水率显著降低,当增加食盐的添加量和延长腌制时间,会加快水分的迁移速率;原子吸收结果表明：增加食盐添加盐量越多和腌制时间越长盐分迁移速率越快,质构、色差结果共同表明咸蛋黄腌制过程中,由于水分的向外迁移和盐分的向内渗入,使得蛋黄的蛋白质发生聚集使颜色加深;同时与市售整个腌制后分离的鸡蛋黄产品相比,当腌制时间为7d,添加盐量为3%;腌制时间为3d,添加盐量为5%时,所得的样品与市面的成品咸鸡蛋黄的感官品质及量化指标差异不显著（P<0.05）,为咸蛋黄单侧腌制技术提供理论的可行性。     

Effect of ascorbic acid on iron release from the emulsifier interface and on the oxidative flavor deterioration in fish oil enriched mayonnaise

This research examines the effect of ascorbic acid (0-800 ppm) on the sensory perception of mayonnaises containing 16% fish oil and on the levels of iron and copper in the aqueous phase. Ascorbic acid increased the formation of fishy off-flavors in fresh mayonnaise. Simultaneously, the iron concentration increased from below the detection limit (1.8 microM) to 34 microM in the aqueous phase of mayonnaises. Model mayonnaises with various concentrations of egg yolk (1-7% w/w) and ascorbic acid (0-8000 ppm) were prepared. Iron concentrations in the aqueous phase increased with increasing ascorbic acid levels, whereas iron concentrations in the assumed interfacial layer decreased. It is proposed that ascorbic acid is able to complex and reduce Fe(3+) to Fe(2+) from phosvitin in the egg yolk, whereby iron is released from the interface. The ascorbic acid-iron complex subsequently reacts with lipid hydroperoxides, resulting in increased lipid oxidation and in the immediate formation of rancid and fishy off-flavors.     

Effect of aldehyde lipid oxidation products on myoglobin

The effects of aldehyde lipid oxidation products on myoglobin (Mb) were investigated at 37 degrees C and pH 7.2. Oxymyoglobin (OxyMb) oxidation increased in the presence of 4-hydroxynonenal (4-HNE) compared to controls (P < 0.05). Preincubation of metmyoglobin (MetMb) with aldehydes rendered the heme protein a poorer substrate for enzymatic MetMb reduction compared to controls, and the effect was inversely proportional to preincubation time; unsaturated aldehydes were more effective than saturated aldehydes (P < 0.05). The order of MetMb reduction as affected by preincubation was control > hexanal > heptanal > octanal > nonanal = decanal = hexenal > heptenal = octenal > nonenal = decenal = 4-HNE (P < 0.05). Preincubation of MetMb with 4-HNE enhanced the subsequent ability of the heme protein to act as a prooxidant in both liposomes and microsomes when compared to controls (P < 0.05); the effect was reduced in microsomes containing elevated concentrations of alpha-tocopherol (P < 0.05). MetMb preincubation with mono-unsaturated aldehydes enhanced the catalytic activity of MetMb to a greater degree than saturated aldehydes (P < 0.05). These results suggest that aldehyde lipid oxidation products can alter Mb stability by increasing OxyMb oxidation, decreasing the ability of MetMb to be enzymatically reduced and enhancing the prooxidant activity of MetMb.     

Effect of moisture content during dry-heating on selected physicochemical and functional properties of dried egg white

This article addresses the effect of moisture content (0.8-9.9%) during dry-heating (80 degrees C) on selected physicochemical (solubility, turbidity, residual denaturation enthalpy, aggregation, surface hydrophobicity, and sulfhydryl content) and functional (foaming ability, foam density, and stability) properties of freeze-dried egg white (FDEW). Moisture content during dry-heating proved to be a parameter determining the functionality of the resulting egg white powder. The degree of conformational changes induced in the egg white proteins by dry-heating was strongly dependent on the amount of water present. Preferentially, dry-heating at 80 degrees C should be performed on egg white powder with a moisture content below 6.8%, as the loss of protein solubility above this value is extensive. In addition to insoluble aggregates, soluble, strongly stabilized aggregates were also formed, especially at higher moisture contents. The decrease in denaturation enthalpy, increase in surface hydrophobicity, and exposure of SH groups previously hidden in the protein core and their subsequent oxidation were more pronounced at prolonged dry-heating times and at higher moisture contents. These conformational changes resulted in improved foaming ability and foams with lower density. No effect of dry-heating on the foam stability was observed.     

基于海藻酸钠与鸡蛋黄静电聚集作用的低脂蛋黄酱制备

为了拓展海藻酸钠和鸡蛋黄蛋白质在低脂蛋黄酱质构设计方面的应用,该研究首先探究了海藻酸钠和鸡蛋黄分散液在不同酸性pH值条件下的聚集行为,并基于两者的静电聚集作用设计出油相比为30%(体积分数)且具有明显黏弹性和触变性的低脂蛋黄酱产品,同时以油相比为75%的蛋黄酱作对照。结果表明,当pH值低于5.0时,海藻酸钠携带负电荷,鸡蛋黄分散液携带正电荷,两者可发生明显的静电聚集作用,海藻酸钠和鸡蛋黄复合体系的结构强度增加。当白醋添加量高于2%(体积分数)时,海藻酸钠和鸡蛋黄复合体系的pH值降低至5.0以下,可诱导复合体系发生静电聚集作用,白醋添加量越高,聚集作用越明显,低脂蛋黄酱的结构化程度也越高。然而,过量的白醋添加降低了低脂蛋黄酱的热稳定性,同时也影响了产品的风味和感官接受度。综合而言,当白醋添加量为4%时(pH值4.6),制备的低脂蛋黄酱流变学特性和对照组最为接近,且感官接受度较好。该研究结果可为构建低脂食品提供理论参考。     

Increasing the oxidative stability of liquid and dried tuna oil-in-water emulsions with electrostatic layer-by-layer deposition technology

Omega-3 Fatty acids have numerous health benefits, but their addition to foods is limited by oxidative rancidity. Engineering the interfacial membrane of oil-in-water emulsion droplets to produce a cationic and/or thick interface is an effective method to control lipid oxidation. Cationic and thick emulsion droplet interfacial membranes can be produced by an electrostatic layer-by-layer deposition technique resulting in droplets that are coated by multiple layers of emulsifiers. Tuna oil-in-water emulsion droplets coated by lecithin and chitosan produce cationic emulsion droplets that are more oxidatively stable than emulsions coated by lecithin alone. Ethylenediaminetetraacetic acid (EDTA) was able to increase the oxidative stability of emulsions stabilized with lecithin and chitosan more effectively than mixed tocopherols. The combination of EDTA and mixed tocopherols was not more effective than EDTA alone suggesting that control of prooxidant metals was the most important antioxidant technology. The production of emulsion droplets coated with lecithin and chitosan could be an excellent technology for stabilization of oxidatively unstable lipids for use in a variety of food products.     

鸭蛋蛋心颜色等级模型研究

应用机器视觉技术，研究出鸭蛋蛋心颜色自动分级系统中的蛋心颜色分级模型。鸭蛋蛋壳颜色与蛋心区域颜色信息有关，可用光密度值进行模糊识别。无论是青壳蛋还是白壳蛋，其蛋心颜色等级G与H，S(色饱和度)，I三个变量间存在着显著的线性相关关系。     

Solubility improvement of shellfish muscle proteins by reaction with glucose and its soluble state in low-ionic-strength medium

When myofibrillar proteins of scallop striated adductor muscle were reacted with glucose through the Maillard reaction, the change in the solubility of myofibrillar proteins in 0.05-0.5 M NaCl solutions during glycosylation and their soluble states were investigated. The solubility in low-ionic-strength media increased greatly with the progress of the Maillard reaction. The solubility in 0.1 M NaCl reached 83% when more than 60% of lysine residues in myofibrillar proteins were modified by glucose. However, the excess progress of the Maillard reaction impaired the improved solubility of myofibrillar proteins in a low-ionic-strength medium. Myosin, actin, and paramyosin in glycosylated myofibrillar proteins were solubilized independently regardless of NaCl concentration. In addition, the glycosylated myosin lost its filament-forming ability and existed as a monomer in 0.1 M NaCl.     

Effects of wheat antioxidants on oxygen diffusion-concentration products in liposomes and mRNA levels of HMG-CoA reductase and cholesterol 7alpha-hydroxylase in primary rat hepatocytes

Three wheat antioxidant fractions were investigated for their potential effects on oxygen diffusion-concentration products in liposomes prepared with egg yolk phosphatidycholine (yolk PC) and rat liver PC (liver PC), using the electron spin resonance (ESR) oximetry method with 2,2'-azobis(2-aminopropane) dihydrochloride (AAPH) and 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN) as radical generators. Both water-soluble wheat antioxidant (WWA) and the second lipophilic antioxidant (LWA2) fractions were able to inhibit oxygen diffusion-concentration product induced by either AAPH or AMVN. The first lipophilic wheat antioxidant (LWA1) fraction only showed antioxidant activity in yolk PC liposomes with AAPH as the radical initiator but had pro-oxidant activity under other testing conditions. Both liposome composition and radical initiator altered the antioxidative properties of WWA, LWA1, and LWA2. WWA also showed the strongest DPPH(*) scavenging capacity on a per grain weight basis. HPLC analysis showed that WWA had a much higher level of total phenolic acids, which may partially explain their antioxidant properties. In addition, wheat antioxidants significantly down-regulated the mRNA of HMG-CoA reductase, the key enzyme for cholesterol biosynthesis, and up-regulated the mRNA of cholesterol 7alpha-hydroxylase (CYP7A1), the key enzyme for cholesterol metabolism, in primary rat hepatocytes. These data indicated the potential of wheat antioxidants in reducing the risk of atherosclerosis through multimechanisms.     

Oxidation in fish oil enriched mayonnaise: ascorbic acid and low pH increase oxidative deterioration

The effect of ascorbic acid (0-4000 ppm) and pH (3.8-6.2) on oxidation and levels of iron and copper in various fractions of mayonnaise enriched with 16% fish oil was investigated. Ascorbic acid induced release of iron from the assumed oil-water interface into the aqueous phase at all pH levels, but this effect of ascorbic acid was strongest at low pH (pH 3.8-4.2). Ascorbic acid generally promoted formation of volatile oxidation compounds and reduced the peroxide value in mayonnaises. Peroxide values and total volatiles generally increased with decreasing pH values, suggesting that low pH promoted oxidation. It is proposed that iron bridges between the egg yolk proteins low-density lipoproteins, lipovitellin, and phosvitin at the oil-water interface are broken at low pH values, whereby iron ions become accessible as oxidation initiators. In the presence of ascorbic acid, oxidation is further enhanced due to the reduction of Fe(3+) to Fe(2+) that rapidly catalyzes lipid oxidation via lipid hydroperoxide decomposition at the oil-water interface in mayonnaise.     

Strecker degradation of phenylalanine initiated by 2,4-decadienal or methyl 13-oxooctadeca-9,11-dienoate in model systems

The reaction of 2,4-decadienal and methyl 13-oxooctadeca-9,11-dienoate with phenylalanine was studied to determine if alkadienals and ketodienes are able to produce the Strecker-type degradation of amino acids to the corresponding Strecker aldehydes. When reactions were carried out at 180 degrees C, both carbonyl compounds degraded phenylalanine to phenylacetaldehyde, among other compounds. The yield of the phenylacetaldehyde produced depended on the reaction pH and increased linearly with both the amount of the lipid and the reaction time. The yield of this conversion was approximately 8% when starting from decadienal and approximately 6% when starting from methyl 13-oxooctadeca-9,11-dienoate, and the reaction rate was lower for the ketone than for the aldehyde. Simultaneous to these reactions, the lipid was converted into pyrrole, pyridine, or aldehyde derivatives as a result of several competitive reactions. In particular, 9-14% of the decadienal was converted into hexanal under the assayed conditions. All these reactions are suggested to be produced as a consequence of the oxidation of the alkadienal or the ketodiene to the corresponding epoxyalkenal or unsaturated epoxyketone, which were identified in the reaction mixtures by GC-MS. All these results suggest that alkadienals and ketodienes, which are quantitatively important secondary lipid oxidation products, can degrade amino acids to their corresponding Strecker aldehydes. Therefore, under appropriate conditions, these products are not final products of the lipid oxidation and can participate in carbonyl-amine reactions analogously to other lipid oxidation products with two oxygenated functions.     

超高压前处理对虾仁冻藏期品质的影响

为研究超高压辅助脱壳所得到的中华管鞭虾虾仁在冻藏期的品质变化,以虾仁色泽、质构、肌原纤维蛋白相对含量、表面疏水性、总巯基相对含量和Ca²⁺-ATPase活性为指标,探讨超高压前处理对虾仁品质的影响。结果表明,冻藏6个月后虾仁L^*值、a^*值和b^*值均有所变化,与对照组相比,超高压前处理对虾仁L^*值的影响不显著,但能延缓冻藏后期a^*值的增加,对保持虾肉色泽的稳定有一定作用;超高压前处理对虾仁的咀嚼性和弹性影响不显著,但能增加虾仁的硬度。超高压前处理使冻藏初期虾仁肌原纤维蛋白的表面疏水性增加,而对其溶解性、巯基含量及Ca²⁺-ATPase活性的影响不显著;冻藏后期由于虾仁蛋白冷冻变性,致使肌原纤维蛋白溶解性、巯基含量及Ca²⁺-ATPase活性下降。综上所述,超高压辅助脱壳在一定程度上有利于保持冻虾仁的色泽和硬度。本研究结果为利用超高压技术辅助脱除中华管鞭虾虾壳,生产冷冻虾仁提供了新思路。