Lipid Oxidation In Bulk Oil Research Articles

Chelating peptides from rapeseed meal protein hydrolysates: identification and evaluation of their capacity to inhibit lipid oxidation.

An optimized proteolysis process was applied to rapeseed meal proteins (RP) and the hydrolysate was separated by membrane filtration allowing the production of highly metal-chelating peptides in the permeate. In order to identify the chemical structure of the most active obtained metal-chelating peptides, immobilized metal affinity chromatography (IMAC) was applied. The RP-IMAC peptide fraction was mainly composed of small peptides from 2 to 20 amino acids. Using the Ferrozine assay, RP-IMAC peptides showed a significant chelating efficiency higher than sodium citrate and close to that of EDTA. The peptide sequences were identified by UHPLC-MS and several possible iron binding sites were found. β-carotene oxidation assay and lipid oxidation in bulk oils or emulsion were carried out to evaluate the potential of such peptides as efficient antioxidants to protect lipids from oxidation. While chelating peptides showed a limited efficiency in bulk oil, they performed more efficiently in emulsion.

Effects of Sweet Potato Powder Selected Based on the Polar Paradox Hypothesis on Oil Oxidation in the Preparation of Deep-Fried Croquettes.

This study investigated whether sweet potato powder (SPP) and purple SPP (PSPP) could prevent oil oxidation during deep-frying. A volume of soybean oil was repetitively used for deep-frying croquettes coated with either SPP or PSPP. An aliquot of the fried oil was collected (SPP and PSPP oils) before and after each frying to analyze moisture and lipid oxidation products (LOPs). With increasing numbers of frying, the moisture content in oils significantly increased without an appreciable difference between SPP and PSPP oils. The total oxidation values reflecting primary and secondary LOPs also significantly increased. However, the values were higher for PSPP oils despite the much higher antioxidant activity of the polar extracts from PSPP compared to SPP. This was attributed to the presence of transition metals. PSPP oils seemed to have association colloids whose interfaces were occupied more with polar antioxidants, thereby transition metals were easily reduced and their pro-oxidative activity increased. The polar paradox hypothesis stating that polar antioxidants are more effective in preventing lipid oxidation in bulk oil is not always applicable to real foods due to various food matrices.

Effect of Interfacial Activity of Eugenol and Eugenol Esters with Different Alkyl Chain Lengths on Inhibiting Sunflower Oil Oxidation

AbstractEffects of eugenol esters with different alkyl chain lengths and combinations of eugenol + eugenol esters on sunflower oil oxidation at 338, 358, and 378 K are evaluated by determining different kinetic parameters. Also, water content and reverse micelles size of sunflower oil samples are monitored during oxidation. Eugenyl acetate shows higher antioxidant activity than eugenol in sunflower oil, while eugenyl butyrate, eugenyl hexanoate, and eugenyl decanoate shows lower antioxidant activity than eugenol. Antioxidant activity of eugenol esters decreases by increasing their alkyl chain length. Eugenol shows a synergistic effect with eugenyl acetate and eugenyl butyrate on increasing the induction period and antioxidant activity values, while it shows an antagonistic effect with eugenyl hexanoate and eugenyl decanoate. Also, combinations of eugenol + eugenyl acetate, as well as, eugenol + eugenyl butyrate stabilize the reverse micelles at longer period of time (3263 min for eugenol + eugenyl acetate and 2900 min for eugenol + eugenyl butyrate) than eugenol (2750 min). In addition, eugenol + eugenyl acetate and eugenol + eugenyl butyrate decrease the magnitude of temperature‐related effects on sunflower oil oxidation to the higher extent than eugenol did.Practical applications: Recent studies have suggested that the antioxidants with ability to locate at the active sites of lipid oxidation can efficiently reduce lipid oxidation in bulk oil. Despite a remarkable focus on antioxidant activity of eugenol, there is no information regarding improving its interfacial performance through esterification method. Also, there are few published data regarding the effects of esterified antioxidants on physicochemical changes during the oxidation of bulk oil. In this study, eugenol is esterified with anhydrides with different alkyl chain lengths to increase its accessibility to the active site of lipid oxidation, that is, water–oil interface of reverse micelles in sunflower oil. Effects of eugenol esters on stability of reverse micelles and critical reverse micelles concentration of lipid hydroperoxides have been investigated for the first time.

Optimization of subcritical water extraction of phenolic compounds from Ziziphus jujuba using response surface methodology: evaluation of thermal stability and antioxidant activity

BackgroundThe jujube is mainly grown in the subtropical and tropical regions of Asia. Due to owning bioactive compounds such as polyphenols, it was considered as medicinal and nutritional plant in traditional medicine. This study aimed to extract phenolic compounds from Ziziphus jujuba using subcritical water (SCW) process. The possible combinations of temperature, time, and fruit-to-solvent ratio were investigated using response surface methodology.ResultsThe total phenolic compounds (TPC) and radical scavenging capacity (RSC) of 975.94 mg/g and 53.98%, respectively, were recovered at optimum extraction conditions (170 °C, 74.49 min, and fruit-to-solvent ratio of 1:5.29). The extract obtained in SCW optimum conditions was put under thermal treatments including low temperature long time, high temperature short time, cooking, baking, and sterilization. The results showed after baking, the amount of TPC, RSC, and absorbance at 420 nm increased. The quantity of gallic acid, chlorogenic acid, p-coumaric acid, ferulic acid, and rutin increased significantly. The efficiency of SCW extract in retarding lipid oxidation in bulk oil and O/W emulsion model was investigated at 50 °C for 10 days. After 10 days, the peroxide value of bulk oil (1.1 meq O2/kg) containing SCW extract was lower than O/W emulsion model (2.2 meq O2/kg).ConclusionThe subcritical extracted phenolic compounds seem to have good antioxidant activity as well as thermal stability for using in food or drug industries.

Lecithin Near Its Critical Micelle Concentration Increases Oxidative Stability of Non‐Stripped Corn Oil But Not Stripped Corn Oil

Effects of lecithin (HLB 4.5) on oxidative stability of non‐stripped or stripped corn oil are determined during storage at 50 °C. Headspace oxygen content of non‐stripped corn oil containing lecithin decreased less with the increasing concentration of lecithin (300–3000 ppm). Lecithin‐supplemented non‐stripped corn oil near and above critical micelle concentration (CMC, 1288 ppm) had higher oxidative stability as compared to other samples according to conjugated dienoic acid and p‐anisidine value assays. Antioxidant and tocopherol concentrations in non‐stripped corn oil samples containing lecithin near CMC are found to be the highest. Stripped corn oil has CMC of 1790 ppm lecithin and 600 ppm lecithin shows higher antioxidant properties than other concentration of lecithin from 1200 to 3000 ppm. Presence of phospholipids affected oxidative stability of bulk oils. Non‐stripped corn oil supplemented with lecithin near CMC shows the highest oxidative stability, which could be due to the incorporation of tocopherols into the association colloids formed by the added lecithin.Practical Application: Controlling rate of lipid oxidation in bulk oils is one of the important topics in lipid science. Addition of commercially available lecithin (HLB 4.5) could enhance the oxidative stability in non‐stripped corn oil especially, at the concentration of lecithin near CMC. Presence of phospholipids affected oxidative stability of bulk oils. By using knowledge shown in this study, food industries could save costs by optimizing the lecithin concentration in bulk oils, which could be used as ingredients of many processed foods.Addition of commercially available lecithin enhances oxidative stability in non‐stripped corn oil. Lecithin near or over its critical micelle concentration shows higher antioxidant activity in non‐stripped oil compared to other concentrations of lecithin. Added lecithin increases tocopherol stability, especially α‐tocopherol in non‐stripped bulk oil during storage. For stripped corn oil, 600 ppm lecithin only shows some antioxidant power and other concentrations do not enhance oxidative stability.

Impact of Phospholipids and Tocopherols on the Oxidative Stability of Soybean Oil-in-Water Emulsions

Phospholipids have been shown to act synergistically with tocopherols and delay lipid oxidation in bulk oil. The synergistic activity between phospholipids and tocopherols is due to the ability of amino-group-containing phospholipids (e.g., phosphatidylethanolamine (PE) and phosphatidylserine (PS)) to convert oxidized tocopherol back into tocopherols. This study shows the effect of PE and PS on the antioxidant activity of different tocopherol homologues in oil-in-water emulsions. Effect of emulsifier type on the interaction between tocopherols and phospholipids was also studied. δ-Tocopherol and PE exhibited greater antioxidant activity as compared to α-tocopherol and PE. PS displayed 1.5-3 times greater synergism than PE with Tween 20 as emulsifier whereas both PE and PS had a similar antioxidant activity in the presence of α-tocopherol when bovine serum albumin was used as the emulsifier. This study is the first to show that PE and PS can act synergistically with tocopherols to inhibit lipid oxidation in oil-in-water emulsions and can present a new clean label antioxidant strategy for food emulsions.

Antioxidative effect of Arthrospira platensis biomass on the lipid oxidation

Introduction : Cyanobacteria are promising natural sources of antioxidants. Environmental conditions that influence synthesis of substances in cultures of cyanobacteria have been studied. Objective : This investigation aimed to evaluate the antioxidative effect of Arthrospira platensis biomass on the process of lipid oxidation in bulk oil and oil/water emulsion. Method : Arthrospira platensis growth potential for antioxidant production under different cultivation conditions using an experimental design. The antioxidative effect of the methanolic extracts and the biomass on preventing lipid oxidation was measured by peroxide value (PV). Results : The results showed that the growing conditions to obtain the biomass promoted change in the protective ability of different biomass extracts. Extracts obtained from the cultivated biomass grown under 150 μmol photons/m2s-1, 1.875 g.L-1 NaNO3; 13.5 g.L-1 NaHCO3 (assay14) and 50 μmol photons/m2s-1, 2.5 g.L-1 NaNO3; 18.0 g.L-1 NaHCO3 (standard) showed the most antioxidative effect on preventing lipid oxidation, therefore used in the formulation of mayonnaise. The mayonnaise made with soybean oil and 0.5% biomass was preserved against lipid photodegradation during seven days of storage, but the peroxide value related to control varied from 2.9 to 3.1 mEqO2.Kg-1, with no significant difference in the preservation afforded by tert-butilhydroquinone, in the same period of storage. In mayonnaise made with sunflower oil, biomass, independent of concentration, was unable to protect the product against photooxidation. Conclusions : The results demonstrate the protective ability on preventing lipid oxidation of Arthrospira platensis biomass and its potential for use in food lipid-based of soybean oil.

Role of Water and Selected Minor Components on Association Colloid Formation and Lipid Oxidation in Bulk Oil

AbstractThis study investigated the influence of water content in combination with selected minor components including oleic acid, stigmasterol, α‐tocopherol, and Trolox on their association colloid formation as well as their impact on lipid oxidation in bulk corn oil. First, surface activity of each minor component was evaluated by determining the ability of these components to lower the interfacial tension between bulk oil and water. All components but α‐tocopherol were able to decrease interfacial tension of stripped oil. Second, the critical micelle concentration (CMC) of each minor component was determined in bulk oil with no water added and in the presence of 1000 ppm of water. In the bulk oil without extraneous water, we could not determine the CMC of minor components in the range of concentrations studied. However, in the presence of 1000 ppm of water, only stigmasterol could form association colloids at the CMC of 20 mmol/kg oil. Last, the effect of water content (400 and 1000 ppm) and minor components on lipid oxidation in bulk oil was studied by following the lipid hydroperoxides and hexanal formation during storage at 55 °C. Different water content did not significantly impact the lag time of lipid oxidation compared with the control. Interestingly, water caused prooxidant by decreasing the lag time of lipid hydroperoxides and hexanal formation in bulk oil containing oleic acid, stigmasterol, and Trolox compared with the control of each system. On the other hand, there was not significant impact of water on the antioxidant activity of α‐tocopherol, a lipid soluble antioxidant in bulk oil. This study highlights the impact of water content on the surface activity of minor components as well as on the oxidative stability in bulk oil.

Association Colloids Formed by Multiple Surface Active Minor Components and Their Effect on Lipid Oxidation in Bulk Oil

AbstractAssociation colloids formed by surface active minor components play an important role in the oxidative stability of bulk oils. To imitate the formation of nanostructures in refined oils, multiple surface active minor components including phospholipids, free fatty acids, diacylglycerols and sterols were added to stripped corn oil. The critical micelle concentration (CMC) of the mixed components was determined. The impact of mixed minor components at below and above their CMC on oxidative stability of bulk oil and on antioxidant activity of α‐tocopherol and Trolox was investigated. The CMC of the mixed surface active components in bulk oil was 20 µmol/kg oil in the presence of 383 ± 2 ppm of water. 1,2‐Dioleoyl‐sn‐glycero‐3‐phosphocholine (DOPC) played an important role on the formation of association colloids since it was the most important component in forming the association colloids as confirmed by CMC and fluorescence probe studies. The association colloids formed by the mixed components showed prooxidative activity in bulk oil as determined by monitoring the formation of lipid hydroperoxide and hexanal. The activity of α‐tocopherol or Trolox was not changed by mixed components association colloids. These results suggest that association colloids both physically and chemically impacted the oxidative stability and activity of antioxidants in bulk oil.

Impact of Free Fatty Acids and Phospholipids on Reverse Micelles Formation and Lipid Oxidation in Bulk Oil

AbstractAssociation colloids such as phospholipid reverse micelles could increase the rate of lipid oxidation in bulk oils. In addition to phospholipids, other surface active minor components in commercial oils such as free fatty acids may impact lipid oxidation rates and the physical properties of reverse micelles. In this study, the effects of free fatty acids on changes in the critical micelle concentration (CMC) of 1,2‐Dioleoyl‐sn‐glycero‐3‐phosphocholine (DOPC) in stripped corn oil (SCO) were determined by using the 7,7,8,8‐tetracyanoquinodimethane solubilization technique. Different free fatty acids including myristoleic, oleic, elaidic, linoleic and eicosenoic were added at 0.5 % by wt along with the DOPC into the bulk oils. There was no significant effect of free fatty acids with different chain length, configuration and number of double bonds on the CMC value for DOPC in bulk oil. However, increasing concentrations of oleic acid (0.5 to 5 % by wt) caused the CMC value for DOPC in bulk oils to increase from 400 to 1,000 μmol/kg oil. Physical properties of DOPC reverse micelles in the presence of free fatty acids in bulk oils were also investigated by the small angle X‐ray scattering technique. Results showed that free fatty acids could impact on the reverse micelle structure of DOPC in bulk oils. Moreover, free fatty acid decreased pH inside reverse micelle as confirmed by the NMR studies. The oxidation studies done by monitoring the lipid hydroperoxide and hexanal formation revealed that free fatty acids exhibited pro‐oxidative activity in the presence and absence of DOPC. Different types of free fatty acids had similar pro‐oxidative activity in bulk oil.

Influence of free fatty acids on oxidative stability in water‐in‐walnut oil emulsions

The effect of free fatty acids (FFA) on lipid oxidation in water‐in‐stripped walnut oil emulsions was investigated. The formation of the primary oxidation products (hydroperoxides) and the secondary oxidation product (headspace hexanal) increased with increasing addition of oleic acid to the emulsions. However, oleic acid at high concentrations was primarily involved in accelerating hydroperoxide formation at early stage and then hydroperoxide decomposition rapidly after hydroperoxides reached the maximum point. The prooxidant effect of saturated FFA was dependent on their chain length with lipid oxidation rates being in the order of lauric acid>palmitic acid>stearic acid. The highest prooxidant activity of lauric acid among these FFA was probably due to its largest polarity and making the water droplet interface more negatively charged than the others when the aqueous phase pH was 7.0, which was above its pKa, thereby attracting prooxidant metals to the water droplet surface. The highest ability to promote lipid oxidation in water‐in‐oil emulsions was shown by linolenic acid, followed by linoleic and oleic acids, indicating that the oxidative capacity increased with increasing degree of unsaturation. The prooxidant effect of FFA with the cis double bonds was lower than those with the trans ones when oleic acid (18:1, cis) was compared to elaidic acid (18:1, trans) and linoleic acid (18:2, cis–cis) was compared to linoelaidic acid (18:2, trans–trans), which suggested that geometric isomeration of FFA influenced lipid oxidation rates of water‐in‐oil emulsions.Practical applications: FFA promote lipid oxidation in bulk oil and oil‐in‐water (O/W) emulsions. From the present study, it became clear that FFA were also strong prooxidants in water‐in‐oil (W/O) emulsions. This research pointed out the importance of using oils and fats containing minimal FFA in W/O emulsion formulation to obtain the highest quality.

Prooxidant Activity of Polar Lipid Oxidation Products in Bulk Oil and Oil‐in‐Water Emulsion

AbstractLipid oxidation products can arise when oils are subjected to high temperature and exposed to oxygen. Many of these oxidation products have higher polarity than the original triacylglycerols due to the incorporation of oxygen. These polar oxidation products could have a negative impact on oxidative stability by acting as prooxidants. In this study, the influence of polar lipid oxidation products on the oxidative stability of bulk oils and oil‐in‐water emulsions was investigated. Polar compounds were isolated from used frying oil by silica gel column chromatography. They were added to bulk stripped corn oil (with/without reverse micelles formed by dioleoylphosphatidylcholine, DOPC) and oil‐in‐water (O/W) emulsion to evaluate their prooxidative activity. Polar compounds increased lipid oxidation in bulk oil with and without DOPC. The presence of DOPC reverse micelles decreased the prooxidant activity of the polar oxidation products. On the other hand, there was no significant effect of the polar compounds on oxidation of O/W emulsions. To gain a better understanding of the polar compounds responsible for the prooxidant effect, linoleic acid and linoleic hydroperoxide were added into bulk oil at the same concentration as those in the polar fraction of the frying oil. However, they did not show the same prooxidative activity compared to oil with the polar fraction.

New Insights into the Role of Iron in the Promotion of Lipid Oxidation in Bulk Oils Containing Reverse Micelles

Formation of physical structures, known as association colloids, in bulk oils can promote lipid oxidation. However, the cause of this accelerated lipid oxidation is unknown. Therefore, the aim of this study was to investigate whether transition metals were important prooxidants in bulk oils containing reverse micelles produced from 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and water. The Fe(III) chelator deferoxamine (DFO) increased the oxidative stability of stripped soybean oil (SSO) containing reverse micelles from 2 to 7 days. Because phosphatidylcholine (1,2-dibutyl-sn-glycero-3-phosphocholine) that does not form reverse micelles is not prooxidative, these results suggest that the prooxidant activity of DOPC reverse micelles could be due to their ability to concentrate both endogenous iron and lipid hydroperoxides at the water-lipid interface, thereby increasing the ability of iron to decompose lipid hydroperoxides. DFO was also able to improve the activity of α-tocopherol and Trolox in SSO containing DOPC reverse micelles increasing the lag phase from 2 to 11 and 13 days, respectively. DOPC reverse micelles decreased iron-promoted α-tocopherol and Trolox decomposition and decreased the ability of α-tocopherol and Trolox to decrease Fe(III) concentrations. Overall, these results suggest that iron is an important prooxidant in bulk oils containing reverse micelles; therefore, finding ways to control iron reactivity in association colloids could provide new technologies to increase the oxidative stability of oils.

Minor Components in Food Oils: A Critical Review of their Roles on Lipid Oxidation Chemistry in Bulk Oils and Emulsions

Food oils are primarily composed of triacylglycerols (TAG), but they may also contain a variety of other minor constituents that influence their physical and chemical properties, including diacylglycerols (DAG), monoacylglycerols (MAG), free fatty acids (FFA), phospholipids (PLs), water, and minerals. This article reviews recent research on the impact of these minor components on lipid oxidation in bulk oils and oil-in-water emulsions. In particular, it highlights the origin of these minor components, the influence of oil refining on the type and concentration of minor components present, and potential physicochemical mechanisms by which these minor components impact lipid oxidation in bulk oils and emulsions. This knowledge is crucial for designing food, pharmaceutical, personal care, and other products with improved stability to lipid oxidation.

Antioxidant and Prooxidant Activity Behavior of Phospholipids in Stripped Soybean Oil‐in‐Water Emulsions

AbstractPhospholipids have been reported to inhibit lipid oxidation in bulk oils, but very little is known about their influence on oxidation in oil‐in‐water emulsions. In the present study, the impact of 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine (DOPC) on lipid oxidation was studied in 1% stripped soybean oil‐in‐water (O/W) emulsions as a function of DOPC concentration and pH (3 and 7). At pH 7.0, DOPC inhibited lipid oxidation in O/W emulsions, while DOPC was prooxidative at pH 3.0. DOPC did not affect emulsion droplet charge or size at either pH 3.0 or 7.0. The antioxidant activity at pH 7.0 was observed in a series of phospholipids (PL) that varied in fatty acid unsaturation level and chain length as well as type of phosphate head group. Overall, phosphatidylcholine with either oleic or palmitic acid were the most effective at inhibiting lipid hydroperoxide and hexanal formation of all of the PL tested. Antioxidant mechanism of PL could not be ascribed to their ability to decompose lipid hydroperoxides. It might be possible that, at pH 7.0, the PL antioxidant activity is related to their ability to form structures within the lipid phase of the emulsions droplets or to chelate metals.

Role of reverse micelles on lipid oxidation in bulk oils: impact of phospholipids on antioxidant activity of α-tocopherol and Trolox

Phospholipids self-assemble in bulk oils to form structures such as reverse micelles that can alter the microenvironment where chemical degradation reactions occur, such as lipid oxidation. In this study, we examined the influence of phospholipid reverse micelles on the activity of non-polar (α-tocopherol) and polar (Trolox) antioxidants in stripped soybean oil (SSO). Reverse micelles were formed by adding 1000 μM 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) to SSO. The addition of DOPC reverse micelles had a prooxidant effect, shortening the lag phase of SSO at 55 °C. DOPC improved the activity of low α-tocopherol or Trolox concentrations (10 μM) but decreased the activity of high concentrations (100 μM). Hydrophilic Trolox had better antioxidant activity than hydrophobic α-tocopherol. Fluorescence steady state and lifetime decay studies suggests that differences in the antioxidant activity of Trolox and α-tocopherol could be due to differences in their physical location in DOPC reverse micelles. These results will improve our understanding and control of lipid oxidation in bulk oils.

Physical Structures in Soybean Oil and Their Impact on Lipid Oxidation

The oxidation of edible oil yields both primary and secondary oxidation products (e.g., hydroperoxides, carbonyls, hydrocarbons, and epoxides), which produce undesirable sensory and biological effects. Consequently, the suppression of lipid oxidation in food matrices is of great importance. The rate and extent of lipid oxidation in many heterogeneous foods are strongly affected by the physicochemical characteristics of water-oil interfaces. This study examined the ability of dioleoylphosphatidylcholine (DOPC) and water to form association colloids within bulk oil, as well as their impact on lipid oxidation kinetics. Attenuation was used to show the DOPC and water concentrations at which association colloids existed without altering the optical properties of the oil. Interfacial tension and fluorescence spectrometry showed the critical micelle concentration (CMC) of DOPC in stripped soybean oil was around 650 μM at room temperature. Small-angle X-ray scattering (SAXS) and fluorescence probes showed that water had a very strong impact on the properties of the association colloids formed by DOPC. Measurement of primary and secondary lipid oxidation products revealed that the association colloids formed by DOPC had a pro-oxidant effect. The characterization of association colloids could provide a better understanding of the mechanisms of lipid oxidation in bulk oils and provide insights into new antioxidant technologies.

Antioxidant Properties of Teaw (Cratoxylum formosum Dyer) Extract in Soybean Oil and Emulsions

The antioxidant activity of an extract from Teaw (Cratoxylum formosum Dyer) leaves was studied in soybean oil and soybean oil-in-water emulsions. Samples containing the extract or reference antioxidants including chlorogenic acid, which comprises 60% of the Teaw extract, were stored at 60 degrees C and analyzed periodically for peroxide value (PV) and thiobarbituric acid reactive substances (TBARS) to allow both hydroperoxides and hydroperoxide degradation products to be monitored. Chlorogenic acid and the Teaw extract were more effective than alpha-tocopherol in inhibiting lipid oxidation in bulk oil but were less effective in an oil-in-water emulsion in accordance with the polar paradox. The PV/TBARS ratio for oil samples containing chlorogenic acid was higher than for alpha-tocopherol and BHT because chlorogenic acid inhibits both hydroperoxide formation by radical scavenging and hydroperoxide decomposition by metal chelation. The importance of the metal-chelating activity in retarding hydroperoxide decomposition was confirmed by studying the decomposition of oil samples containing added ferric ions. The PV/TBARS ratio was higher for citric acid than for alpha-tocopherol in the presence of added ferric chloride, but the order was reversed in samples lacking ferric chloride. Samples containing added chlorogenic acid gave the highest PV/TBARS ratios both in the presence and absence of ferric ions. The PV/TBARS ratios for the samples containing antioxidants fell rapidly to lower values in a soybean oil-in-water emulsion than in the soybean oil. This was due to increased hydroperoxide decomposition in the emulsion at the same PV. The Teaw extract contained 12% oil-soluble components, which contributed to a slightly higher oil-water partition coefficient than that of chlorogenic acid. The antioxidant activity of the aqueous phase of the Teaw extract was reduced more than that of chlorogenic acid by partitioning of the oil-soluble components into oil, which showed that the less-polar components contributed to the antioxidant activity of the Teaw extract in aqueous media.

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.