Effects of antioxidants on rapeseed oil oxidation in an artificial digestion model analyzed by UHPLC-ESI-MS

A normal diet contains large quantities of oxidized fatty acids, glycerolipids, cholesterol, and their cytotoxic degradation products because many foods in the diet are fried, heated, or otherwise processed and consumed often after long periods of storage. There is also evidence that the acid medium of the stomach promotes lipid peroxidation and that the gastrointestinal tract is a major site of antioxidant action, as demonstrated by various colorimetric methods. The identity and yields of specific products of lipid transformation have seldom been determined. The present study describes the molecular species profiles of all major gastrointestinal lipids formed during digestion of autoxidized rapeseed oil in an artificial digestion model in the presence of L-ascorbic acid, 6-palmitoyl-O-L-ascorbic acid, 3,5-di-tert-butyl-4-hydroxytoluene (BHT), DL-α-tocopherol, and DL-α-tocopheryl acetate. Differences in oxidized lipid profiles were detected in the samples digested in the presence of different antioxidants, but none of them could prevent the formation of oxidized lipids or promote their degradation in a gastric digestion model. The lack of effect is attributed to the inappropriate nature of the gastrointestinal medium for the antioxidant activity of these vitamins and BHT. A fast ultrahigh performance liquid chromatographic-electrospray ionization-mass spectrometric method was developed for the analysis of lipolysis products, including epoxy, hydroperoxy, and hydroxy fatty acids, and acylglycerols, utilizing lithium as ionization enhancer.     

Homogenization conditions affect the oxidative stability of fish oil enriched milk emulsions: lipid oxidation

In this study fish oil was incorporated into commercial homogenized milk using different homogenization temperatures and pressures. The main aim was to understand the significance of homogenization temperature and pressure on the oxidative stability of the resulting milks. Increasing homogenization temperature from 50 to 72 degrees C decreased droplet size only slightly, whereas a pressure increase from 5 to 22.5 MPa decreased droplet size significantly. Surprisingly, emulsions having small droplets, and therefore large interfacial area, were less oxidized than emulsions having bigger droplets. Emulsions with similar droplet size distributions, but resulting from different homogenization conditions, had significantly different oxidative stabilities, indicating that properties of significance to oxidation other than droplet size itself were affected by the different treatments. In general, homogenization at 72 degrees C appeared to induce protective effects against oxidation as compared to homogenization at 50 degrees C. The results thus indicated that the actual composition of the oil-water interface is more important than total surface area itself.     

The relationship between the physicochemical properties of antioxidants and their ability to inhibit lipid oxidation in bulk oil and oil-in-water emulsions

Chain-breaking antioxidants differ in their effectiveness at inhibiting lipid oxidation because of their chemical properties and physical location within a food. Our objective was how the physicochemical properties of four structurally related lipid-soluble antioxidants were related to their antioxidant activity. Antioxidants differed in the number of methyl (alpha-tocopherol and delta-tocopherol) or hydroxyl (butylated hydroxytoluene (BHT) and 4-hydroxymethyl-2,6-ditertiarybutylphenol) groups. Surface activity of the antioxidants was in the order of delta-tocopherol > alpha-tocopherol approximately 4-hydroxymethyl-2,6-ditertiarybutylphenol > BHT. Free-radical scavenging activity was similar between alpha-tocopherol and delta-tocopherol as well as BHT and 4-hydroxymethyl-2,6-ditertiarybutylphenol. In bulk menhaden oil, BHT was a more effective antioxidant than 4-hydroxymethyl-2,6-ditertiarybutylphenol while alpha-tocopherol was more effective than delta-tocopherol. In menhaden oil-in-water emulsions, BHT was a more effective antioxidant than 4-hydroxymethyl-2,6-ditertiarybutylphenol while delta-tocopherol was more effective than alpha-tocopherol. These results indicate that the surface activity and polarity of lipid-soluble antioxidants were not the only determinants of their antioxidant effectiveness in food lipids.     

利用菜籽油酶法生产生物柴油的初步研究

生物柴油作为可再生能源，对环境友好，引起了世界范围内的广泛关注。该文利用固定化脂肪酶－Novo435，在无有机溶剂存在的情况下，催化菜籽油与甲醇酯交换反应制取生物柴油，对影响酯交换反应过程的因素：甲醇与油脂的摩尔比、反应温度、反应时间、脂肪酶用量、转速、水分等进行深入研究，得到了菜籽油间歇酯交换反应的适宜工艺条件：转速200 r/min、醇油摩尔比1.5∶1、反应温度50℃、酶用量10%(与油脂的质量比)、反应10 h后菜籽油的酯交换率达到47％。水分的存在不利于固定化酶在无有机溶剂系统下催化菜籽油的酯交换反应，使酯交换率降低到30％。反应所需理论甲醇量分两次加入，反应26 h后，油脂的酯交换率达到80％。     

Lipid oxidation in emulsions as affected by charge status of antioxidants and emulsion droplets

The influence of charge status of both lipid emulsion droplets and phenolic antioxidants on lipid oxidation rates was evaluated using anionic sodium dodecyl sulfate (SDS) and nonionic polyoxyethylene 10 lauryl ether (Brij)-stabilized emulsion droplets and the structurally similar phenolic antioxidants gallamide, methyl gallate, and gallic acid. In nonionic, Brij-stabilized salmon oil emulsions at pH 7.0, gallyol derivatives (5 and 500 microM) inhibited lipid oxidation with methyl gallate > gallamide > gallic acid. In the Brij-stabilized salmon oil emulsions at pH 3.0, low concentrations of the galloyl derivatives were prooxidative or ineffective while high concentrations were antioxidative. In SDS-stabilized salmon oil emulsions, oxidation rates were faster and the galloyl derivatives were less effective compared to the Brij-stabilized emulsions. Differences in antioxidant activity were related to differences in the ability of the galloyl derivatives to partition into emulsion droplets and to increase the prooxidant activity of iron at low pH.     

Lipid oxidation in milk, yoghurt, and salad dressing enriched with neat fish oil or pre-emulsified fish oil

This study compared the oxidative stabilities of fish-oil-enriched milk, yoghurt, and salad dressing and investigated the effects on oxidation of adding either neat fish oil or a fish-oil-in-water emulsion to these products. Milk emulsions had higher levels of a fishy off-flavor and oxidized faster, as determined by the peroxide value and volatile oxidation products, than fish-oil-enriched yoghurt and dressing, despite the fact that dressings had a higher fish oil content and were stored at room temperature. Additionally, fish-oil-enriched yoghurt generally had higher oxidative stability than fish-oil-enriched dressings, irrespective of the mode of fish oil addition. Yoghurt thus seemed to be a good delivery system of lipids containing n-3 polyunsaturated fatty acids. Different effects of adding fish oil either as neat fish oil or as a fish-oil-in-water emulsion were observed for milk, yoghurt, and dressing. Yoghurt and dressing enriched with neat fish oil were more stable than those enriched with a fish-oil-in-water emulsion, whereas milk enriched with neat fish oil was less stable than milk enriched with the fish-oil-in-water emulsion. Overall, it seemed that application of neat fish oil was a good option for preserving the final quality in yoghurt and dressings, but a pre-emulsion may still be considered for the fish oil enrichment of certain food products, for example, milk.     

菜籽油碱催化法制备生物柴油的工艺参数

以碱催化剂为媒介的转酯化反应制备生物柴油方法因其转化率高而倍受重视。该文以菜籽油为原料,在小型试验装置上,采用均相碱催化法,研究了菜籽油在碱性催化剂NaOH的作用下与甲醇经酯交换反应制备生物柴油的工艺条件。考察了醇油摩尔比（4︰1～8︰1）、催化剂用量（0.5%～2%）、反应温度（30～60℃）和反应时间（30～150 min）等工艺参数对酯交换反应的影响,对生物柴油的组成成分进行了气相色谱/质谱联用(GC-MS)分析。结果表明,在醇油摩尔比6︰1,催化剂用量为油质量的1%,反应温度为50～60℃,反应时间为60 min时,酯交换反应转化率最高可达到96.7%。该生物柴油主要由油酸甲酯、芥子酸甲酯、9,12-十八碳二烯酸甲酯、11-二十碳烯酸甲酯、亚麻酸甲酯等脂肪酸甲酯组成,其中油酸甲酯含量最高,相对质量分数高达50.30%。     

菜籽油酯交换制备生物柴油的工艺研究

为提高生物柴油的转化率和纯度,以菜籽油为原料,研究在KOH催化剂作用下与甲醇进行酯交换反应制备生物柴油的工艺,考察了甲醇用量、催化剂用量、反应温度和反应时间等操作条件对酯交换反应的影响。结果表明,该反应最适宜的工艺条件为：甲醇用量为菜籽油质量的20%,催化剂用量为菜籽油质量的1.2%,反应温度为65℃,反应时间为90～120 min;菜籽油制备的生物柴油品质达到美国ASTM和德国DINE生物柴油标准,其生物柴油的转化率为94.89%。若充分开发中国南方可利用的冬闲田和边际土地约1000万hm²种植油菜,按照此工艺条件加工菜籽油,则每年可加工生产生物柴油740万t,具有广阔的发展前景。     

Homogenization conditions affect the oxidative stability of fish oil enriched milk emulsions: oxidation linked to changes in protein composition at the oil-water interface

Fish oil was incorporated into milk under different homogenization temperatures (50 and 72 degrees C) and pressures (5, 15, and 22.5 MPa). Subsequently, the oxidative stability of the milk and changes in the protein composition of the milk fat globule membrane (MFGM) were examined. Results showed that high pressure and high temperature (72 degrees C and 22.5 MPa) resulted in less lipid oxidation, whereas low pressure and low temperature (50 degrees C and 5 MPa) resulted in faster lipid oxidation. Analysis of protein oxidation indicated that especially casein was prone to oxidation. The level of free thiol groups was increased by high temperature (72 degrees C) and with increasing pressure. Furthermore, SDS-PAGE and confocal laser scanning microscopy (CLSM) indicated that high temperature resulted in an increase in beta-lactoglobulin adsorbed at the oil-water interface. This was even more pronounced with higher pressure. Less casein seemed to be present at the oil-water interface with increasing pressure. Overall, the results indicated that a combination of more beta-lactoglobulin and less casein at the oil-water interface gave the most stable emulsions with respect to lipid oxidation.     

Comparison of natural polyphenol antioxidants from extra virgin olive oil with synthetic antioxidants in tuna lipids during thermal oxidation

Polyphenols extracted from extra virgin olive oil (EVOO) were tested for their ability to inhibit lipid oxidation of canned tuna. Hydroperoxide formation during oxidation was monitored by measurement of peroxide value and decomposition of hydroperoxides by static headspace gas chromatographic analysis of volatiles. In tuna oxidized at 40 and 100 degrees C, 400 ppm of the EVOO polyphenols was an effective antioxidant as compared with 100 ppm of a 1:1 mixture of the synthetic antioxidants butylated hydroxytoluene and butylated hydroxyanisole. However, at concentrations <100 ppm, the EVOO phenolic compounds promoted hydroperoxide formation and decomposition. The EVOO polyphenols were effective antioxidants when added to heated tuna muscle in the presence of either brine or refined olive oil. The oxidation rate in tuna muscle packed in brine was higher than that of tuna packed in refined olive oil. The EVOO polyphenols had higher antioxidant activity in the brine samples than in the refined olive oil. The higher antioxidant activity of EVOO polyphenols in tuna packed in brine may be explained by their greater affinity toward the more polar interface between water and the fish oil system.     

Effect of relative humidity on oxidation of flaxseed oil in spray dried whey protein emulsions

Flaxseed oil was emulsified in whey protein isolate (WPI) and spray-dried. Powder characteristics and oxidative stability of oil at relative humidities (RH) from RH approximately 0% to RH 91% at 37 degrees C were analyzed. Oil droplets retained their forms in drying and reconstitution, but the original droplet size of the emulsion was not restored when the powder was dispersed in water. The particles seemed to be covered by a protein-rich surface layer as analyzed by electron spectroscopy for chemical analysis (ESCA). Oxidation of flaxseed oil dispersed in the WPI matrix was retarded from that of bulk oil but followed the same pattern as bulk oil with respect to humidity. A high rate of oxidation was found for both low and high humidity conditions. The lowest rate of oxidation as followed by peroxide values was found at RH 75%, a condition that is likely to diverge significantly from the monolayer moisture value. A weak baseline transition observed for the WPI matrix in a differential scanning calorimetry (DSC) thermogram suggested a glassy state of the matrix at all storage conditions. This was not consistent with the observed caking of the powder at RH 91%. Scanning electron microscopy (SEM) images revealed a considerable structural change in the WPI matrix in these conditions, which was suggested to be linked with a higher rate of oxygen transport. Possible mechanisms for oxygen transport in the whey protein matrix under variable RHs are discussed.     

Use of caseinophosphopeptides as natural antioxidants in oil-in-water emulsions

Chelators are valuable ingredients used to improve the oxidative stability of food emulsions. Caseins and casein peptides have phosphoseryl residues capable of binding transition metals. Thus, the ability of enriched caseinophosphopeptides to inhibit lipid oxidation in corn oil-in-water emulsions was investigated. Enriched caseinophosphopeptides (25 microM) inhibited the formation of lipid oxidation at both pH 3.0 and 7.0 as determined by lipid hydroperoxides and hexanal. Calcium (0-100 mM) had no influence on the antioxidant activity of the enriched caseinophosphopeptides. Casein hydrolysates were more effective inhibitors of lipid oxidation than the enriched caseinophosphopeptides at equal phosphorus content. Thus, antioxidant properties might not be uniquely attributed to chelating metals by phosphoseryl residues but also by scavenging free radicals. Overall, the observed antioxidant activity of casein hydrolysates means they could be utilized to decrease oxidative rancidity in foods.     

Effect of sucrose ester addition on nucleation and growth behavior of milk fat-sunflower oil blends

The effects of addition of the sucrose esters (SE) P-1670, P-170, and S-170 to a high-melting fraction of milk fat (HMF) and its blends with sunflower oil (SFO) on nucleation and growth were studied by laser polarized light turbidimetry and polarized light microscopy (PLM). The three SE delayed nucleation of HMF at the temperatures selected. P-1670 did not modify average crystal size after 3 h at crystallization temperature (T(c)) or crystal size distribution and modified crystallization kinetics only slightly. P-170 and S-170, however, markedly diminished crystal size and narrowed crystal size distribution. Activation free energies of nucleation at equivalent supercooling, calculated using the Fisher-Turnbull equation, significantly increased with addition of SE. According to these results, among the mechanisms described in the literature for fats or emulsions, the cocrystallization hypothesis is the one that better described the effects of sucrose esters on crystallization behavior in these systems.     

水酶法提取菜籽乳化油的工艺研究

为获得温和的制油工艺，该文采用了多种细胞壁多糖酶制剂对湿磨菜籽浆进行水相酶解法提油。同时对菜籽内源硫苷酶的湿热灭活条件及硫苷的湿热稳定性进行了研究，并优化了酶解的工艺条件。结果表明：沸水处理5 min可以有效钝化菜籽内源硫苷酶，此时硫苷的降解率为11.28％；果胶酶、纤维素酶和β-葡聚糖酶经复配(4∶1∶1)后处理菜籽比单一酶制剂的作用效果好，复合酶解最适工艺条件为：固液比1∶5，加酶量3％，酶解时间5 h，在此条件下乳化油得率为92.45％。     

LC-MS investigation of oxidation products of phenolic antioxidants

Two oxidation systems were examined for the oxidation of three groups of phenolic antioxidants; five cinnamic acids, two benzoic acids, and two phenols characteristic of olive fruits. Periodate oxidation, which is reported to produce products similar to polyphenol oxidase, was contrasted with the reactivity of the Fenton system, an inorganic source of hydroxyl radicals. Reaction products were identified as various quinones, dimers, and aldehydes, but the nature of the products differed between the two oxidation systems. Structure-activity effects were also observed for the different phenols. All cinnamic acids in this study reacted with the Fenton reagent to produce benzaldehydes as the main products, with the exception of 5-caffeoylquinic acid. In contrast, periodate oxidation gave no reaction with some of the cinnamic acids. Quinone formation was observed for the two compounds, caffeic acid and 5-caffeoylquinic acid, possessing o-hydroxy groups. Caffeic acid was unusual in that dimer formation was the main initial product of reaction. Benzoic acids were readily oxidized by both systems, but no identifiable products were isolated. Oleuropein was oxidized by both oxidants used in this study, resulting in quinones in each system, whereas little or no oxidation of tyrosol was observed. This highlights the importance of conjugation between the alkene double bond and the hydroxy group. The results question the validity of many existing methods of testing antioxidant activity.     

Enrichment of anhydrous milk fat in polyunsaturated fatty acid residues from linseed and rapeseed oils through enzymatic interesterification

Lipozyme TL IM was used in a solvent-free batch and microaqueous system for enzymatic interesterification of anhydrous milkfat (AMF) with linseed oil (LO) in binary blends and with rapeseed oil (RO) in one ternary blend. The aim was to obtain and characterize physicochemically fats enriched with unsaturated C 18 fatty acids (oleic, linoleic, and, especially, linolenic acids) from natural vegetable oils. Binary blends of AMF/LO 100/0, 90/10, 80/20, 70/30, and 60/40 (w/w) were interesterified. The change in triacylglycerol (TAG) profiles showed that quasi-equilibrium conditions were reached after 4-6 h of reaction. Free fatty acid contents <1%. The decrease in solid fat content and in dropping point temperature obtained with increasing content of LO and interesterification resulted in good plastic properties for the products originating from the blends 70/30 and 60/40. This was confirmed by textural measurements. Melting profiles determined by differential scanning calorimetry showed complete disappearance of low-melting TAGs from LO and the formation of intermediary species with a lower melting temperature. Oxidative stability of the interesterified products was diminished with increasing LO content, resulting in low oxidation induction times. A ternary blend composed of AMF/RO/LO 70/20/10 gave satisfactory rheological and oxidative properties, fulfilling the requirements for a marketable spread and, moreover, offering increased potential health benefits due to the enriched content in polyunsaturated fatty acid residues.     

Partitioning of olive oil antioxidants between oil and water phases.

The partition coefficient (K(p)) of the natural phenolic antioxidant compounds in the olive fruit between aqueous and olive oil phases was determined. The antioxidants of olive oil are either present in the olive fruit or formed during the olive oil extraction process. The antioxidants impart stability to and determine properties of the oil and are valuable from the nutritional point of view. The olive oil antioxidants are amphiphilic in nature and are more soluble in the water than in the oil phase. Consequently, a large amount of the antioxidants is lost with the wastewater during processing. The determination of antioxidants was performed using HPLC, and the K(p) was estimated to be from as low as 0.0006 for oleuropein to a maximum of 1.5 for 3,4-DHPEA-EA (di-hydroxy-phenyl-ethanol-elenolic acid, oleuropein aglycon). Henry's law fitted very well to the experimental data. The partition coefficients were also estimated by applying the activity coefficients of the antioxidants in the two phases using a predictive group contribution method, the UNIFAC equation. The K(p) values estimated with UNIFAC method were of the same order of magnitude but varied from the experimental values. Nevertheless, this method may be a rough predictive tool for process optimization or design. Because the K(p) values were very low, some changes in the process are recommended in order to achieve a higher concentration of antioxidants in the oil. A temperature increase may lead to increasing the partition coefficient. Also, limiting the quantity of water during oil extraction could be a basis for designing alternative processes for increasing the antioxidant concentration in the olive oil.     

Purified phenolics from hydrothermal treatments of biomass: ability to protect sunflower bulk oil and model food emulsions from oxidation

The phenolic fractions released during hydrothermal treatment of selected feedstocks (corn cobs, eucalypt wood chips, almond shells, chestnut burs, and white grape pomace) were selectively recovered by extraction with ethyl acetate and washed with ethanol/water solutions. The crude extracts were purified by a relatively simple adsorption technique using a commercial polymeric, nonionic resin. Utilization of 96% ethanol as eluting agent resulted in 47.0-72.6% phenolic desorption, yielding refined products containing 49-60% w/w phenolics (corresponding to 30-58% enrichment with respect to the crude extracts). The refined extracts produced from grape pomace and from chestnut burs were suitable for protecting bulk oil and oil-in-water and water-in-oil emulsions. A synergistic action with bovine serum albumin in the emulsions was observed.     

Ability of surfactant micelles to alter the partitioning of phenolic antioxidants in oil-in-water emulsions

In oil-in-water emulsions, the physical location of antioxidants can be an important determinant in their activity. Surfactants can potentially influence the physical location of antioxidants in oil-in-water emulsions by causing solubilization of lipid-soluble antioxidants into the aqueous phase. Excess Brij micelles in an oil-in-water emulsion were found to increase the partitioning of phenolics into the continuous phase with polar antioxidants (propyl gallate) partitioning more than nonpolar antioxidants (butylated hydroxyltoluene). Solubilization of propyl gallate was rapid coming to equilibrium in less than 5 min. Increasing surfactant micelle concentrations from 0.3 to 2.8% increased the solubilization of propyl gallate by 2.3-fold. Solubilization of phenolic antioxidants into the aqueous phase by Brij micelles did not alter the oxidative stability of salmon oil-in-water emulsions, suggesting that surfactant micelles influenced oxidation rates by mechanisms other than antioxidant solubilization.     

大豆油体乳液稳定性和流变性分析

研究大豆油体乳液的基本物理化学性质,将为其工业应用提供参考。以水为介质提取大豆油体,方法无毒,利于食用。对其在不同pH值（pH值2～8）、NaCl浓度（0～250?mmol/L）和加热处理（30～90℃,30?min）条件下的Zeta电位、平均粒径和乳析稳定性进行测定,并对其流变性进行考察。大豆油体乳液的Zeta电位为+20?mV～-40?mV（pH值2～8）,等电点约为4.5。在pH值≤3和pH值≥6条件下,平均粒径均为0.4?μm左右;而在3＜pH＜6时,产生了乳析现象。在较高NaCl浓度下（＞25?mmol/L）,粒径较大和发生了乳析现象。大豆油体乳液在30～90℃加热处理时较稳定。大豆油体乳液呈现出弱凝胶的性质,其黏度随着油质量分数的降低而降低。研究表明,大豆油体乳液在一定的环境条件下是稳定的。