A kinetic study of oxidation development in sunflower oil under microwave heating: Effect of natural antioxidants

The antioxidative effects of carnosic acid and sesamol on sunflower oil under temperature-controlled microwave heating were investigated as a function of time and temperature. The concentration of conjugated diene hydroperoxide and p-anisidine value were determined spectrophotometrically, as measures of oxidation, during microwave heating of sunflower oil with or without added antioxidants at 40 °C, 60 °C and 80 °C. The kinetics of hydroperoxide formation was examined on the basis of previously proposed mechanisms and found to be of the half-order with respect to the concentration of conjugated diene hydroperoxide. The amounts of added antioxidants remaining in sunflower oil after different microwave heating periods at different temperatures were determined by HPLC-DAD. The results were interpreted in terms of antioxidative effects of carnosic acid and sesamol. Carnosic acid was found to be a more effective antioxidant than sesamol for sunflower oil.     

Inhibition of lipid oxidation in refrigerated and frozen salted raw minced chicken breasts with electron beam irradiated almond skin powder

Antioxidant effects of electron beam irradiated almond skin powder (ASP) in raw minced chicken breasts (MCB) during refrigerated and frozen storage were studied. MCB samples were treated with BHT, non-irradiated ASP (0 kGy), irradiated ASP (10 kGy, 20 kGy and 30 kGy) and compared to MCB without antioxidants. Colour was determined on initial and final day of analysis while conjugated dienes (CD), peroxide values (POV), TBARS and hexanal content were evaluated periodically for 12 days of refrigerated storage and seven months of frozen storage. ASP addition lowered L* values compared to MCB without ASP or BHT. During refrigerated storage, MCB containing ASP had decreased formation of lipid oxidation products ranging from 0 to 66%, 7 to 24%, 0 to 37% and 4 to 71% reduction in POV, CD, TBARS and hexanal content, respectively, as compared to MCB without antioxidants over duration of study. A 15–65%, 3–25%, 14–50% and 28–82% reduction in POV, CD, TBARS and hexanal content, respectively, for frozen MCB was detected.     

Effect of Methanol and Water Extract of African Lettuce (Lactuca taraxacifolia) on Stability of Refined Palm Kernel Oil

African Lettuce extract was evaluated for parameters related to its antioxidant activity during twelve months storage of Refined Palm Kernel Oil (RPKO) in white transparent plastic bottles at room temperature (27 °C – 33 °C). Extracts of Wild Lettuce were prepared by separately soaking dried, ground and sieved African Lettuce into methanol and water in ratio 1:10 for 72 h. The Methanol African Lettuce Extract (MALE) and Water African Lettuce Extract (WALE) were separately added at varying concentrations (200 ppm to 1000 ppm) to RPKO. Another set of RPKO which contained no additive (0 ppm [control]) and 200 ppm BHT was set up. The colour units and refractive indices of oil samples were immediately determined while Free Fatty Acid (FFA), Acid Value (AV) and Peroxide Value (PV) of RPKO samples were monitored monthly using standard methods for a period of twelve months. The colour of RPKO containing MALE (12.0 – 15.0 units) was higher than RPKO containing WALE (10.5 – 12.0 units) while the colour of RPKO sample containing no additive (0 ppm) was 10.0 units and 11.5 units for RPKO containing 200 ppm BHT. The refractive index of RPKO containing MALE and WALE ranged between 1.454 and 1.455 while that of RPKO containing no additive (0 ppm) and 200 ppm BHT was 1.455. The FFA, AV and PV of RPKO containing MALE and WALE were lower than RPKO containing 200 ppm BHT. The results showed that WALE (Water African Lettuce Extract) is more effective in stabilizing RPKO (hydrolytically and oxidatively) than MALE.     

Caffeic acid derivatives in dried Lamiaceae and Echinacea purpurea products

The concentrations of caffeic acid derivatives within Lamiaceae and Echinacea (herb, spice, tea, and dietary supplement forms) readily available in the US marketplace (n = 72) were determined. After the first identification of chicoric acid in Ocimum basilicum (basil), the extent to which chicoric acid could be found within the family Lamiaceae was investigated. The dominant phenolic acid in all Lamiaceae samples was rosmarinic acid, which ranged from 2.04 mg/100 g (one of 12 oregano samples) to 622.28 mg/100 g (lemon balm). Of the herbs tested in this study (marjoram, oregano, peppermint, rosemary, sage, spearmint, and thyme from the family Lamiaceae), only basil and lemon balm (Melissa officinalis) contained chicoric acid. Basil samples (starting material and resulting end product) obtained from an industry cooperator, showed substantial phenolic deficiency as a result of processing (approximately 78% loss).     

Role of Melissa officinalis in cholesterol oxidation: Antioxidant effect in model systems and application in beef patties

Cholesterol oxidation products (COPs) constitute a known health risk factor. The antioxidant effect of a lyophilized aqueous Melissa officinalis extract against cholesterol degradation and COPs formation during a heating treatment was evaluated in a model system (180 °C, 0–180 min) at a ratio of 2 mg extract/100 mg cholesterol. Furthermore, the plant extract was subsequently added to beef patties alone or incorporated within an oil-in-water olive oil emulsion to assess its effectiveness during cooking. Melisa extract protected cholesterol from thermal degradation in the model system, yielding higher remaining cholesterol and lower COPs values throughout the whole heating process. Maximum total COPs were achieved after 30 and 120 min of heating for control and melisa-containing samples, respectively. In cooked beef patties, even though the olive oil emulsion was used as flavor-masking approach, melisa extract off-flavor limited the maximum dose which could be added. At these doses (65 μg/g and 150 μg/g without and with the emulsion, respectively), no additional protective effect of melisa over the use of the emulsion was found. Addition of natural extracts into functional foods should definitively take into account sensory aspects.     

Chemiluminescent assay of lipid hydroperoxides quantification in emulsions of fatty acids and oils

Lipid hydroperoxides (LOOH) are relatively stable intermediates which arise during oxidation of fats and lipids. The luminol-enhanced chemiluminescent (LCL) method has been applied to detect the LOOH formed during thermal oxidation. The method was optimized for best signal to noise ratio what gave reliable and sensitive data up to 50 pM of detected hydroperoxides (approximately 1 μmol hydroperoxides/kg lipid). The observed LCL signal was calibrated with 13-HPODE (13-(S)-hydroperoxy-9Z,11E-octadecadienoic acid) as an external hydroperoxide standard. This allowed quantitative determination of LOOH formed during thermal oxidation of linoleic acid and phosphatidylcholine (PC) in emulsion and during storage of linseed oil. The obtained LCL results were validated using HPLC, spectrophotometric assay for conjugated dienes at 234 nm and iodometric titration peroxide value (PV) methods.The described LCL method is direct, sensitive, fast and simple, however, it is not specific to the lipids and may be used to determine the presence of the other types of hydroperoxides or the other oxidizing agents what finally gives overall total antioxidant estimation of the sample.     

The antioxidative activity of summer savory (Satureja hortemis L.) and rosemary (Rosmarinus officinalis L.) in dressing stored exposed to light or in darkness

For an oil-in-water emulsion dressing, addition of 0.15% of dried leaves of summer savory (Satureja hortensis L.) or more significantly of rosemary (Rosmarinus officinalis L.), resulted in a significantly better antioxidative protection than addition of 80 ppm propyl gallate (standard concentration for this type of product) during dark storage at 19 °C for up to 24 weeks, as determined by development of conjugated dienes, peroxide value, head space hexanal and thiobarbituric acid-reactive substances. Addition of freeze-dried methanol extract of the two spices, in an equivalent concentration, had less antioxidative effect, but was comparable to the effect of propyl gallate. Exposure to fluorescent light (850 lux) during storage had a clear pro-oxidative effect for dressing with or without spice or spice extract added, when compared to dark storage. For dressing with extract of savory added, the antioxidative effect found for dark storage was during light exposure, changed to a pro-oxidative effect, and a hexanal level as high as 600 mg kg⁻¹ oil was detected after 8 weeks of storage, while the net antioxidative effect of rosemary was maintained for storage exposed to light.     

Food matrices affect the bioavailability of (n − 3) polyunsaturated fatty acids in a single meal study in humans

The aim of this study was to investigate the role of the food matrix on bioavailability of (n − 3) PUFA and oxidative stress in plasma. The study was a randomized, cross-over study and included 12 healthy male participants. The participants ingested a test meal, which consisted of a fitness bar, a yoghurt drink, eight oil capsules, bread and butter; 4 g of fish oil was incorporated into one of the matrices. Blood samples were collected and fatty acid composition of chylomicrons was determined together with plasma levels of conjugated dienes and α-tocopherol. Fish oil incorporated into food products were absorbed differently from those simply administered as supplements alongside of food products, and yoghurt was the best matrix for providing fast absorption of lipids in general, including (n − 3) fatty acids. No significant difference was observed in the level of plasma α-tocopherol after ingestion of test meals.     

Lipase-catalyzed synthesis of acetylated EGCG and antioxidant properties of the acetylated derivatives

(−)-Epigallocatechin-3-O-gallate (EGCG) acetylated derivatives were prepared by lipase catalyzed acylation of EGCG with vinyl acetate to improve its lipophilicity and expand its application in lipophilic media. The immobilized lipase, Lipozyme RM IM, was found to be the optimum catalyst. The optimized conditions were as follows, 1:1 of the molar ratio of EGCG to vinyl acetate, 2.0% (w/w of both substrates) of enzyme amount, and 84.5% conversion was obtained after 8 h reaction at 40 °C in acetonitrile. The presence of mono-, di- and tri-acetylated derivatives in acetylated EGCG were confirmed by LC–MS–MS and the tri-acetylated EGCG was identified as 5′,3″,5″-3-O-acetyl-EGCG by NMR. Their enhanced lipophilicity was confirmed by octanol–water partition coefficient. The antioxidant activity of the acetylated EGCG derivatives were superior to butylated hydroxytoluene (BHT), tert-butyl hydroquinone (TBHQ) and EGCG as determined by peroxide values (POVs) in sunflower oil as well as by the p-anisidine method. Acetylated EGCG exhibited the highest 1,1-Diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity (IC₅₀ of 0.09 mg/mL) compared to EGCG, BHT and TBHQ. Acetylated EGCG might be used as a potent antioxidant for controlling oxidation of sunflower oil.     

Aroma profiles of vegetable oils varying in fatty acid composition vs. concentrations of primary and secondary lipid oxidation products

The aroma compositions of oxidised sunflower oil, linseed oil and a blend thereof (85/15) were compared with frequently used indicators for primary and secondary lipid oxidation. Primary lipid oxidation was followed by the formation of conjugated dienes, secondary lipid oxidation by proponal and hexanal formation. Highest concentrations of conjugated dienes and propanal were measured in the linseed oil, followed by the blend and sunflower oil, respectively. Highest concentrations of hexanal were determined in the blend. At similar primary oxidation levels, volatile compounds of the oils were isolated in a model mouth system and subsequently analysed by gas chromatography/sniffing port analysis. Propanal, pentanal, 1-penten-3-one, hexanal, 1-pentanol, octanal, 1-octen-3-one, 1-octen-3-ol and (E,Z)-2,4-heptadienal possessed detectable odours. Comparing the three oils, most aroma compounds and greatest intensities were determined in the blend. Conjugated diene concentrations did not predict the formation of aroma compounds adequately. Although propanal and hexanal concentrations were reasonable indicators for aroma development in linseed and sunflower oil, respectively, neither of the indicators predicted aroma development in all three oils sufficiently.     

Effect of composition and antioxidants on the oxidative stability of fluid milk supplemented with an algae oil emulsion

The oxidative stability of an algal oil emulsion dispersed in water, or fluid milk of varying fat contents, was assessed from measurements of lipid hydroperoxide and propanal concentration. All of the milk samples, independent of their milk fat content, were stable compared to the aqueous samples. The extent of oxidation was unaffected when sodium azide (200 ppm) was added to inhibit microbial growth. Added iron (100 ppm) accelerated the oxidation rate in the aqueous samples, but had no effect on the milk samples. The antioxidant properties of milk were ascribed to the iron binding of casein. Added protein antioxidants (0.8 wt%) [i.e. sodium caseinate, whey protein isolate (WPI) and thermally denatured WPI] had minimal effects whereas EDTA and ascorbic acid (160 ppm) were effective antioxidants.     

Stability of flocculated particles in concentrated and high hydrophilic solid layer-by-layer (LBL) emulsions formed using whey proteins and gum Arabic

The objective of the present study was to investigate flocculation in layer-by-layer (LBL) emulsion systems with high total solids content and deflocculation at various pH conditions, and the effects of whey protein isolate (WPI) concentration and total solids content on the stability of LBL emulsions. WPI (1.96% (1WPI) or 10.71% (10WPI), w/w in water) was prepared in water and high-pressure homogenized with sunflower oil (10%, w/w, of total emulsion). Gum Arabic (0.15%, w/w, in total emulsion) was added to assemble electrostatically on WPI at oil particle interfaces at pH 3.5 using aqueous citric acid (10% w/w) forming LBL emulsion. The ζ-potential measurements showed charge reversal upon addition of gum Arabic solution into single layer (SL) emulsion confirming the formation of LBL interface. Trehalose:maltodextrin mixture (1:1, w/w, total emulsion, 28.57% (28) or 57.14% (57), w/w, in water) was used in the continuous phase. The high total solids content of the system results in depletion flocculation of the particles leading to bridging flocculation without coalescence as deflocculation into individual particles occurred with increasing pH from pH 3.5 to pH 6.5 in 10WPI systems. Deflocculation was evident in 10WPI-28 and 10WPI-57 as found from a decreased ζ-average diameter and visually under microscope. Coalescence was observed in 1WPI systems. Viscosity of the systems was significantly (P < 0.05) increased with higher total solids content. Accelerated destabilization test showed that systems at higher WPI and total solids contents exhibited the highest stability against creaming. Deflocculation in LBL systems can be controlled by pH while high solids in the aqueous phase provide stability against creaming.     

Antioxidant activity of 1,4-dihydropyridine derivatives in β-carotene-methyl linoleate,sunflower oil and emulsions

The antioxidant activity of six synthetic 1,4-dihydropyridine (DHP) derivatives was tested in an azobis-amidinopropane dihydrochloride initiated β-carotene-methyl linoleate peroxidation model system. Radical scavenging activity of the derivatives was estimated by measuring their reactivity with stable N,N-diphenyl-N′-picrylhydrazyl radicals. The antioxidant activity of these different derivatives was also evaluated in traditional sunflower oil and its 20% oil-in-water emulsion in the dark at 60°C, as well as during storage of sunflower oil in the dark and with light exposure at ambient temperatures. The primary (conjugated diene hydroperoxides) and secondary (hexanal, pentanal) oxidation products were monitored during different periods of storage. Butylated hydroxytoluene was used as a standard antioxidant and different plant extracts were used for comparison of antioxidant activities throughout this study. All synthetic compounds showed antioxidant activity, while plant extracts acted as pro-oxidants upon light exposure. Three derivatives of DHP, without substitution at position 4, showed highest antioxidative activity in model system and sunflower oil and its emulsion in the dark at 60°C as well as during storage of sunflower oil in the dark and with light exposure at ambient temperature. The hydrophilic derivative of DHP with a phenyl group at position 4 showed high radical scavenging activity, and high antioxidant activity in sunflower oil-in-water emulsion, but was less active in model system and sunflower oil. The hydrophobic derivatives of DHP with a phenyl group at position 4 showed high antioxidant activity in model system but were the lowest active derivatives in sunflower oil and its emulsion. ©     

Use of natural food/plant extracts: cloudberry (Rubus Chamaemorus), beetroot (Beta Vulgaris “Vulgaris”) or willow herb (Epilobium angustifolium) to reduce lipid oxidation of cooked pork patties

The antioxidant activity of plant extracts (100 and 500 mg/kg) from cloudberry, willow herb and beetroot on thiobarbituric acid (TBA) reactive substances (TBARS) development and hexanal content of cooked pork patties was investigated. Pure quercetin, rutin and caffeic acid were tested in parallel for comparison. The most potent antioxidants on stabilizing oxidation were cloudberry extract and quercetin. The lowest antioxidant activity was found with the addition of pure rutin to the meat. Caffeic acid showed an intermediate activity. At a concentration of 100 mg/kg, beetroot and willow herb extracts showed an antioxidant activity on TBARS and hexanal contents similar to that observed for caffeic acid during 3 days of refrigerated display, while cloudberry extract was as potent as quercetin. At a concentration of 500 mg/kg, beetroot and willow herb extract stabilized hexanal production of cooked pork patties after 6 days of refrigerated storage in a way comparable to that observed for pure quercetin and cloudberry extract. TBARS numbers were well correlated with hexanal content in cooked pork patties on day 3 of refrigerated storage. However, hexanal production and TBARS numbers were not highly correlated in samples with the highest level of beetroot (500 mg/kg). Hexanal production was inhibited by the high level of beetroot, but TBARS production was not, perhaps because the red color of beetroot extract interfered with the determination of the pink TBA chromogen.     

Antioxidant properties and components of some commercially available varieties of rice bran in Pakistan

The antioxidant activity of five indigenous rice bran varieties, i.e. Rice bran-Super kernel (RB-kr), Rice bran-Super 2000 (RB-s2), Rice bran-Super Basmati (RB-bm), Rice bran-Super-386 (RB-86) and Rice bran-Super fine (RB-sf), collected from the same agricultural plots, was evaluated. The order of antioxidant activity was evaluated by measurement of total phenolic content, antioxidant activity in linoleic acid system, reducing power, metal chelating ability, scavenging capacity by DPPH radical and ABTS cation radical and conjugated dienes. Determination of major antioxidant components reported in rice bran, i.e. tocopherols, tocotrienols and γ-oryzanol, was made using reverse phase HPLC. However, for comparison of tocopherol content, quantification was also done by voltammetry. The overall order of antioxidant activity was RB-kr > RB-s2 > RB-bm > RB-86 > RB-sf. However, according to the chelating activity and conjugated dienes assays the antioxidant efficacy of RB-sf was higher than RB-bm and RB-86. Antioxidant power was correlated with growth period and irrigation water demand by a particular variety. A strong correlation of these two parameters with antioxidant activity was observed. RB-kr has the longest growth period and takes the least amount of water out of the series and exhibits highest antioxidant activity. Strongly reverse behavior was observed in case of RB-sf.     

Characterization of emulsion stabilization properties of quince seed extract as a new source of hydrocolloid

The capability of seed extracts in stabilizing emulsions has particularly received interest in recent years. Upon soaking quince seeds into water, biopolymers inside the seeds are extracted to water, forming mucilage. This study investigates the physical stability, rheology and microstructure of oil (sunflower oil) in water emulsions, stabilized by 2% (w/v) whey protein isolate with varying concentrations of xanthan and quince seed gum. Quince seed gum resulted in emulsions with smaller low-shear viscosities and shear thinning capabilities compared to the same concentrations of xanthan. Quince seed gum emulsions with concentrations ≤ 0.1 (w/v), displayed rapid creaming due to bridging flocculation. Despite the difference in apparent viscosities, for gum concentrations < 0.2 (w/v), both gums demonstrated comparable stability with xanthan gum in general yielding marginally more stable emulsions. Gum concentrations > 0.3 (w/v) resulted in physically stable emulsions even after 5 months. Overall, quince seed gum displayed significant emulsification and stabilization properties.     

Ability of dietary antioxidants to affect lipid oxidation of cooked turkey meat in a simulated stomach and blood lipids after a meal

Oxidized lipids that form during digestion of a meal have the potential to promote reactions that incur vascular disease. A grape seed extract (1% of the meat weight) and butylated hydroxytoluene (0.2% of the lipid weight) were each effective at preventing formation of lipid oxidation products for 3 h during co-incubation with cooked turkey meat in simulated gastric fluid (SGF). Grape seed extract (GSE) at 0.1% of the meat weight accelerated lipid peroxide formation in SGF. Increasing concentrations of GSE decreased the ability of iron to partition into isolated microsomes. Swine trials were conducted in which cooked meat or cooked meat with added antioxidants were fed (seven meals during seven days). Lipid oxidation products were measured in chylomicrons from blood samples that were withdrawn 3 and 4 h after the last meal. Each of the antioxidant treatments that prevented lipid oxidation in SGF also inhibited formation of conjugated dienes in blood chylomicrons (P < 0.05). Mechanisms of polyphenol effects are discussed.     

Ready-to-eat chickpea flour purée or cream processed by hydrostatic high pressure with final microwave heating

It was shown that high hydrostatic pressure (HHP) induces either starch gelatinization or protein aggregation in chickpea flour (CF) slurries. The aim of this work was to develop a new “ready-to-eat” semi-solid CF product by using HHP at 600 MPa and 50 °C for 15 or 25 min combined with final microwave heating prior to consumption. Eight combinations with a formulation that includes raw or toasted CF, with or without lemon juice, were evaluated using physicochemical (color and protein content, mechanical and rheological behavior), microbiological and sensory analyses. All the CF products were microbiologically safe and stable during two months at refrigerated storage. Mainly, the HHP-treated CF products differed in their texture depending on the CF used, the holding time and the presence of lemon juice, whereby each individual product could be classified as a CF purée or a cream. Moreover, all the formulations showed similar very high sensory quality.Industrial relevanceHHP at 600 MPa and 50 °C, applied for 15 or 25 min to chickpea flour (CF) slurries formulated with raw or toasted CF, water in which chickpeas had been cooked, extra virgin olive oil, soy milk, salt, and, optionally, lemon juice induced starch gelatinization (HHP-induced gelatinization) and microbiological preservation that was sustained for two months in refrigerated storage at 4 °C. After microwave heating prior to consumption, CF products with the rheology and texture characteristic of purée or cream were obtained. The development of these refrigerated gluten-free HHP-induced semi-solid CF products which can be given a quick final heating in a microwave oven would be commercially interesting and foreseeably successful, providing the catering industry and consumers with various new CF products with high protein content, thus also helping to increase consumption of pulses and their contribution to food and nutritional safety.     

Extraction of boldo (Peumus boldus M.) leaves with supercritical CO2 and hot pressurized water

High-activity fractions in boldo leaves were extracted with supercritical CO₂ (SC-CO₂) and hot pressurized water (HPW). Total yield after 3 h of extraction (0.6–3.5%) in low-pressure SC-CO₂ experiments increased with process pressure (60–150 bar) and decreased with temperature (30–60 °C), as expected. The extract obtained with SC-CO₂ at 50 °C and 90 bar contained approximately 50% of essential oil components. In higher pressure experiments with solvent mixtures, the yield increased with pressure (300–450 bar) and modifier concentration (2–10% ethanol), ranging 0.14–1.95 ppm for the alkaloid boldine and 1.8–4.8% for total solids following 1.5 h treatment at 50 °C. Boldine recovery was solubility-controlled, reaching 7.4 ppm after 7-h extraction at 450 bar and 50 °C using an ethanol–SC-CO₂ mixture (5% co-solvent). Boldine solubility and yield decreased when using pure CO₂ at higher pressure (600 bar, 50 °C). The extract yield after 3 h batch-wise HPW extraction increased from 36.9% at 100 °C to 53.2% at 125 °C, and then decreased as temperature was increased to 175 °C. Boldine yield decreased from 26.8 ppm at 100 °C to 0.7 ppm at 125 °C, and was negligible at ⩾150 °C. The essential oil yield increased to a maximum at 110 °C and was negligible at ⩾150 °C also. The ranking of antioxidant potency of various extracts was as follows: HPW at 110 °C > methanol (soxhlet extraction) ≫ high-pressure SC-CO₂ with or without polar co-solvent > low-pressure SC-CO₂.     

Effect of β-sitosterol in the antioxidative activity of oxidized lipid–amine reaction products

Phosphatidylethanolamine (PE), phosphatidylcholine (PC), lysine (Lys), and mixtures of them were tested for activity in a polar compound-stripped olive oil (SOO) and in the same oil after addition of 1500 ppm of β-sitosterol (phytosterol-added olive oil, PAO) to evaluate the role of phytosterols in the antioxidant activity of oxidized lipid–amine products. None of the added compounds protected either SOO or PAO, when tested alone at 0–400 ppm. However, mixtures of PE/Lys and PC/Lys (100/300, 200/200, and 300/100 ppm) significantly increased the induction periods of both oils. Furthermore, there was a synergism between the phospholipids and Lys, which was a consequence of the reaction between the carbonyl compounds produced in the oxidation of the phospholipid fatty acid chains and the amino group of Lys. Some of these carbonyl–amine reaction products were determined by gas chromatography–mass spectrometry after converting them into volatile derivatives. In addition, stepwise multiple regression analysis demonstrated the relationship between the induction periods and the formed products. However, the contribution of carbonyl–amine reaction products to oil stability also depended on the type of oil, therefore suggesting a role of β-sitosterol in the antioxidative activity of the compounds produced by carbonyl–amine reactions. This contribution was also confirmed by the higher synergism observed for PE/Lys and PC/Lys mixtures in PAO than in SOO.