Enzymatically Modified Shea Butter and Palm Kernel Oil as Potential Lipid Drug Delivery Matrices

Drug formulations based on lipids can enable a significantly better delivery of a pharmaceutically active substance and thus enhance their bioavailability. However, natural fats and oils usually have properties, which do not allow their direct use for drug delivery. Therefore, we have modified palm kernel oil (PKO) and shea butter (SB) via lipase‐catalyzed transesterification using either glycerol – to create a diglyceride‐enriched lipid – or using hexanoic acid via acidolysis – to alter their fatty acid composition – and hence to improve drug solubility of Celecoxib serving as model compound. The most suitable enzyme was immobilized Thermomyces lanuginosus lipase (Novozyme TL IM). The solubility of Celecoxib as determined in SB, pharmaceutical grade SB, glycerol‐modified SB, hexanoic acid‐modified SB, PKO, glycerol‐modified PKO, and hexanoic acid‐modified PKO. Incorporation of one or two equivalents of hexanoic acid enabled higher Celecoxib solubilization than the diglyceride rich oil. Although structured SB and PKO (15.8 ± 0.4 mg mL^?1) do not differ significantly (p < 0.05) as per the amount of Celecoxib dissolved, the use of the modified oils enhanced Celecoxib solubility in SB (15.5 ± 1.3 mg mL^?1) in comparison to shea butter (7.9 ± 0.5 mg mL^?1). The lipase‐catalyzed modification also improved the miscibility of the oils with surfactants such as Tween 20 and resulted in reduced droplet sizes (<70 nm at oil/surfactant ratios of 1:2 and 1:1) and reduced polydispersity index values of the resulting emulsions. Practical Application: The structured triglycerides synthesized in this work on the basis of natural shea butter oils could function as suppository bases and oil phase in oral and parenteral lipid‐based formulations for improving the solubility and absorption of poorly soluble drugs. As various lipases with distinct selectivity are available for the enzymatic synthesis of structured triglycerides and useful for this purpose, further tailor‐designed formations should be accessible. With the aim of developing novel lipid drug delivery matrices palm kernel oil (PKO) and shea butter (SB) were modified via lipase‐catalyzed transesterification to alter their fatty acid composition and hence to improve drug solubility of the model compound Celecoxib. Incorporation of one or two equivalents of hexanoic acid enabled better Celecoxib solubilization than the diglyceride‐rich oil. Overall, the successful modification process yielded structured lipids with promising miscibility with selected surfactants and potential enhancement of Celecoxib solubility and thus represents a promising approach for the development of novel safe and effective lipid‐based delivery systems.

     

Why Tyrosol Derivatives Have to Be Quantified in the Calculation of “Olive Oil Polyphenols” Content to Support the Health Claim Provisioned in the EC Reg. 432/2012

The viewpoint is the outcome of the scientific expertise of the scientists that sign it and work collaboratively in the frame of the OLEUM project. The project aims to better guarantee olive oil quality and authenticity by empowering detection and fostering prevention of olive oil fraud and by an effort of harmonization, correct interpretation, and use of official and supporting analytical methods. Practical Applications: The consensus among scientists, the European food authorities, IOC, and the olive industry on which compounds should be determined to support the health claim on olive oil polyphenols (EC Reg. 432/2012) is of utmost importance and can be supported by the evidence provided in this viewpoint article. The exact interpretation of this health claim involves the clarification of the compounds that should be summed up to give the amount of at least 5 mg phenols per 20 g of oil.     

An automated shotgun lipidomics platform for high throughput,comprehensive, and quantitative analysis of blood plasma intact lipids

Blood plasma has gained protagonism in lipidomics studies due to its availability, uncomplicated collection and preparation, and informative readout of physiological status. At the same time, it is also technically challenging to analyze due to its complex lipid composition affected by many factors, which can hamper the throughput and/or lipidomics coverage. To tackle these issues, we developed a comprehensive, high throughput, and quantitative mass spectrometry‐based shotgun lipidomics platform for blood plasma lipid analyses. The main hallmarks of this technology are (i) it is comprehensive, covering 22 quantifiable different lipid classes encompassing more than 200 lipid species; (ii) it is amenable to high‐throughput, with less than 5 min acquisition time allowing the complete analysis of 200 plasma samples per day; (iii) it achieves absolute quantification, by inclusion of internal standards for every lipid class measured; (iv) it is highly reproducible, achieving an average coefficient of variation of <10% (intra‐day), approx. 10% (inter‐day), and approx. 15% (inter‐site) for most lipid species; (v) it is easily transferable allowing the direct comparison of data acquired in different sites. Moreover, we thoroughly assessed the influence of blood stabilization with different anticoagulants and freeze‐thaw cycles to exclude artifacts generated by sample preparation. Practical applications: This shotgun lipidomics platform can be implemented in different laboratories without compromising reproducibility, allowing multi‐site studies and inter‐laboratory comparisons. This possibility combined with the high‐throughput, broad lipidomic coverage and absolute quantification are important aspects for clinical applications and biomarker research. This MS‐based automated shotgun lipidomics platform for comprehensive analysis of the blood plasma lipidome (covering 22 lipid classes) achieves high inter‐day and inter‐site reproducibility and accuracy and enables unprecedented large scale lipidomics studies.     

Can chemometrics protect pumpkin seed oil buyers from false Styrian PGI labels?

A group of scientists from Loeben Universtity is proposing the use of chemometrics in the detection of authenticity of Styrian PGI pumpkin seed oil. They have shown that pumpkin seeds from Austria and foreign countries differ in the composition of various element traces. Based on that they are able to differentiate between false and authentic PGI pumpkin seed using mathematical modeling.     

Quantification of Phorbol Esters in Jatropha curcas by HPLC‐UV and HPLC‐ToF‐MS with Standard Addition Method

Established analytic methods for the quantification of phorbol esters (PE), which are some toxic components in Jatropha curcas L., include HPLC with UV‐detection with the commercially available phorbol myristate acetate (PMA) as internal standard or HPLC coupled with MS detection with an external calibration, mostly also with PMA. The differences in the fatty acid side chains and connection to the base structure of PMA compared to PE leads to different UV absorption and MS ionization effects and cause problems for exact quantitative measurements. In this paper, a method is presented which combines both detection types and shows differences between both results. For this purpose, an extraction routine is performed on a PE‐containing seed oil to get a PE standard in high purity, which was used for a standard addition method on two real J. curcas oil samples, derived from Ghana and Mexico. Furthermore, a detection window of ±10 ppm for the high accurate ToF‐MS detection is set to eliminate isobaric interferences from co‐eluting material. Method evaluation of inter‐ and intra‐day variance as well as the recovery rate are performed and determined. With this method a limit of detection of 62 ng mL^?1 (UV) and 11 ng mL^?1 (MS) can be achieved. Practical Applications: Due to the good biological and technical properties of Jatropha curcas L., its seed oil seems perfect for the application as biodiesel feedstock. The toxicity on the other hand could cause problems when converting side products from the oil production to products of higher value. With the here described method an accurate and precise analysis procedure for the quantification of the toxic compounds namely, phorbol esters, could be applied for toxicity studies or routine checks in industry which is converting plant material from J. curcas, so that no toxic material is used for example as animal feed. In this paper, an exact and robust analysis method is described for the quantification of phorbol esters (PE) in Jatropha curcas L. seed oil. This method procedure includes the extraction of PE in methanol, chromatographic separation on a reverse phase C18 HPLC column and the quantification by standard addition method. For the standard addition method a highly pure PE standard is used, which is extracted and purified by semi preparative HPLC right before the measurements. The used detector for identification and quantification is UV set at 280 nm and ESI‐ToF‐MS with a ±10 ppm mass difference of the deprotonated and formate adduct pseudo molecular ion of PE.

     

抗氧化活性综合评价方法研究

根据油脂氧化机理和抗氧化剂主要作用机制,以羟基自由基清除率、超氧阴离子清除率和硫代巴比妥酸法（TBARS）为指标,对复合抗氧化剂JN-H1和K Liquid的抗氧化活性进行评价,并结合油脂过氧化值的测定。结果表明,JN-H1和K Liquid在油脂氧化过程的诱导期和氧化后期所起的抗氧化效果不同。综合评价结果不仅有助于说明抗氧化剂的主要作用机制,而且对抗氧化剂组分的选择和高效抗氧化剂的研制也有一定的指导意义。     

Tocopherol and tocotrienol homologs in parenteral lipid emulsions

Parenteral lipid emulsions, which are made of oils from plant and fish sources, contain different types of tocopherols and tocotrienols (vitamin E homologs). The amount and types of vitamin E homologs in various lipid emulsions vary considerably and are not completely known. The objective of this analysis was to develop a quantitative method to determine levels of all vitamin E homologs in various lipid emulsions. An HPLC system was used to measure vitamin E homologs using a Pinnacle DB Silica normal phase column and an isocratic, n‐hexane:1,4 dioxane (98:2) mobile phase. An optimized protocol was used to report vitamin E homolog concentrations in soybean oil‐based (Intralipid®, Ivelip®, Lipofundin^® N, Liposyn^® III, and Liposyn^® II), medium‐ and long‐chain fatty acid‐based (Lipofundin^® , MCT and Structolipid®), olive oil‐based (ClinOleic® ), and fish oil‐based (Omegaven®) and mixture of these oils‐based (SMOFlipid®, Lipidem®) commercial parenteral lipid emulsions. Total content of all vitamin E homologs varied greatly between different emulsions, ranging from 57.9 to 383.9 µg/mL. Tocopherols (α, β, γ, δ) were the predominant vitamin E homologs for all emulsions, with tocotrienol content < 0.3%. In all of the soybean emulsions, except for Lipofundin® N, the predominant vitamin E homolog was γ‐tocopherol, which ranged from 57–156 µg/mL. ClinOleic® predominantly contained α‐tocopherol (32 µg/mL), whereas α‐tocopherol content in Omegaven® was higher than most of the other lipid emulsions (230 µg/mL). Practical applications: The information on the types and quantity of vitamin E homologs in various lipid emulsions will be extremely useful to physicians and healthcare personnel in selecting appropriate lipid emulsions that are exclusively used in patients with inadequate gastrointestinal function, including hospitalized and critically ill patients. Some emulsions may require vitamin E supplementation in order to meet minimal human requirements. Vitamin E homologs (tocopherols and tocotrienols) contain a chromanol ring and a hydrophobic side chain.     

Comprehensive and quantitative profiling of lipid species in human milk,cow milk and a phospholipid‐enriched milk formula by GC and MS/MSALL

Here we present a workflow for in‐depth analysis of milk lipids that combines gas chromatography (GC) for fatty acid (FA) profiling and a shotgun lipidomics routine termed MS/MS^ALL for structural characterization of molecular lipid species. To evaluate the performance of the workflow we performed a comparative lipid analysis of human milk, cow milk, and Lacprodan^® PL‐20, a phospholipid‐enriched milk protein concentrate for infant formula. The GC analysis showed that human milk and Lacprodan have a similar FA profile with higher levels of unsaturated FAs as compared to cow milk. In‐depth lipidomic analysis by MS/MS^ALL revealed that each type of milk sample comprised distinct composition of molecular lipid species. Lipid class composition showed that the human and cow milk contain a higher proportion of triacylglycerols (TAGs) as compared to Lacprodan. Notably, the MS/MS^ALL analysis demonstrated that the similar FA profile of human milk and Lacprodan determined by GC analysis is attributed to the composition of individual TAG species in human milk and glycerophospholipid species in Lacprodan. Moreover, the analysis of TAG molecules in Lacprodan and cow milk showed a high proportion of short‐chain FAs that could not be monitored by GC analysis. The results presented here show that complementary GC and MS/MS^ALL analysis is a powerful approach for characterization of molecular lipid species in milk and milk products. Practical applications : Milk lipid analysis is routinely performed using gas chromatography. This method reports the total fatty acid composition of all milk lipids, but provides no structural or quantitative information about individual lipid molecules in milk or milk products. Here we present a workflow that integrates gas chromatography for fatty acid profiling and a shotgun lipidomics routine termed MS/MS^ALL for structural analysis and quantification of molecular lipid species. We demonstrate the efficacy of this complementary workflow by a comparative analysis of molecular lipid species in human milk, cow milk, and a milk‐based supplement used for infant formula. A workflow for milk lipid analysis based on combined gas chromatography and high‐resolution shotgun lipidomics. In‐depth structural characterization and quantification of molecular lipid species in milk and milk products.     

Novel Method for the Synthesis of Cholesteryl Glucosides starting from Disaccharides

Steryl glucosides (SG) and acylated steryl glucosides (ASG) are natural components of plant cell membranes and present in different concentrations in various plant foods. Currently, their positive effects on human health are under investigation. The present work presents a new and efficient synthesis method for cholesteryl glucosides starting from disaccharides. A five‐step synthesis protocol is done to obtain the desired product in 35% overall yield. In the first step, the hydroxy groups of the starting material sucrose are protected using benzyl ethers. After the subsequent acidic hydrolysis the obtained pyranosyl moiety of the disaccharide is transformed to its trichloroacetimidate derivative. Next, the formation of the glycosidic bond to cholesterol is performed and catalytic transfer hydrogenation in order to remove the protecting groups leads to the desired product. In this context, APCI‐MS‐TOF has turned out to be an excellent analytical tool for the high sensitive analysis of SG as well as intermediates. Practical Applications: Due to the comparatively high amounts of SG and ASG in seeds and oils, not only the food industry but also in biodiesel production, these natural compounds are of increasing interest. However, analysis of the compounds is difficult, commercially available pure standard materials are costly and their synthesis often requires time‐consuming work‐up procedures. The described preparation method allows the synthesis of cholesteryl glucosides which can be used as reference or standard material for the quantitative analysis of phytosteryl glucosides in plant derived samples. The general synthesis method could be also applied to other SG and ASG derivatives. Cholesteryl glucosides are synthesized using a new and efficient five‐step synthesis protocol starting from disaccharides. The preparation method provides products with good overall yield and high purity and, therefore, the synthesized glucosides can be used as reference or standard material for the quantitative analysis of phytosteryl glucosides in plant derived samples. APCI‐MS‐TOF is extensively used as analytical tool for the sensitive analysis of cholesteryl glucosides as well as intermediates.     

Phytosterol oxidation products (POP) in foods with added phytosterols and estimation of their daily intake: A literature review

To evaluate the content of phytosterol oxidation products (POP) of foods with added phytosterols, in total 14 studies measuring POP contents of foods with added phytosterols were systematically reviewed. In non‐heated or stored foods, POP contents were low, ranging from (medians) 0.03–3.6 mg/100 g with corresponding oxidation rates of phytosterols (ORP) of 0.03–0.06%. In fat‐based foods with 8% of added free plant sterols (FPS), plant sterol esters (PSE) or plant stanol esters (PAE) pan‐fried at 160–200°C for 5–10 min, median POP contents were 72.0, 38.1, and 4.9 mg/100 g, respectively, with a median ORP of 0.90, 0.48, and 0.06%. Hence resistance to thermal oxidation was in the order of PAE > PSE > FPS. POP formation was highest in enriched butter followed by margarine and rapeseed oil. In margarines with 7.5–10.5% added PSE oven‐heated at 140–200°C for 5–30 min, median POP content was 0.3 mg/100 g. Further heating under same temperature conditions but for 60–120 min markedly increased POP formation to 384.3 mg/100 g. Estimated daily upper POP intake was 47.7 mg/d (equivalent to 0.69 mg/kg BW/d) for foods with added PSE and 78.3 mg/d (equivalent to 1.12 mg/kg BW/d) for foods with added FPS as calculated by multiplying the advised upper daily phytosterol intake of 3 g/d with the 90% quantile values of ORP. In conclusion, heating temperature and time, chemical form of phytosterols added and the food matrix are determinants of POP formation in foods with added phytosterols, leading to an increase in POP contents. Practical applications: Phytosterol oxidation products (POP) are formed in foods containing phytosterols especially when exposed to heat treatment. This review summarising POP contents in foods with added phytosterols in their free and esterified forms reveals that heating temperature and time, the chemical form of phytosterols added and the food matrix itself are determinants of POP formation with heating temperature and time having the biggest impact. The estimated upper daily intakes of POP is 78.3 mg/d for fat‐based products with added free plant sterols and 47.7 mg/d for fat‐based products with added plant sterol esters. Phytosterols in foods are susceptible to oxidation to form phytosterol oxidation products (POP). This review summarizes literature data regarding POP contents of foods with added phytosterols that were exposed to storage and heat treatments.     

Lipophilization of dihydrocaffeic acid affects its antioxidative properties in fish‐oil‐enriched emulsions

The aim of the present study was to evaluate the antioxidative effect of lipophilized dihydrocaffeic acid, i.e., octyl dihydrocaffeate and oleyl dihydrocaffeate. Furthermore, the relationship between the measured efficacy of the antioxidants in emulsions, their partitioning into different phases of an emulsion system and their in vitro antioxidant properties was also evaluated. Lipid oxidation in the emulsions was affected by the antioxidants applied. Thus, despite a reduced antioxidant activity of lipophilized dihydrocaffeic acid in the antioxidant assays, lipophilized dihydrocaffeic acid was more efficient than caffeic and dihydrocaffeic acids. Octyl dihydrocaffeate had a significantly higher antioxidative effect than oleyl dihydrocaffeate in emulsions. The results partly supported the polar paradox hypothesis, since lipophilized compounds resulted in increased oxidative stability. However, the decreased antioxidative efficacy with increasing alkyl chain length esterified to dihydrocaffeic acid supported a newly suggested cut‐off effect hypothesis. This hypothesis suggests that when a certain level of hydrophobicity is obtained for lipophilized phenolic acids, the ester forms micelles in the aqueous phase rather than being located at the interface or oil phase. This phenomenon is suggested to explain the reduced antioxidant activity of oleyl dihydrocaffeate compared with octyl dihydrocaffeate. Practical application: The finding that lipophilization of phenolic compounds increase their efficacy opens up new possibilities for producing new and more efficient antioxidants for food systems. However, the results also show that optimization of the chain length for each type of phenolic compound may be necessary. Since these compounds may have a much higher efficacy against lipid oxidation a lower amount of antioxidant will be necessary to obtain the same effect. This would decrease the costs. In addition, the use of synthetic antioxidants, that might have toxic effect in vivo, can be avoided. The raw materials used for the lipophilized compounds are natural compounds, however the fate of the lipophilized compounds in vivo should eventually be evaluated.     

Cover Image,Volume 93, Issue 3

The cover image, by Qi Chen et al., is based on the Research Article A novel photocatalytic membrane decorated with RGO‐Ag‐TiO2 for dye degradation and oil‐water emulsion separation, DOI: 10.1002/jctb.5426 .

     

Oxidative stability and non‐enzymatic browning reactions in Antarctic krill oil (Euphausia superba)

Antarctic krill oil has gained much consideration recently due to its rich content of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in the form of phospholipids and its powerful antioxidant known as astaxanthin. To secure these valuable bioactive nutrients in krill oil, a gentle and immediate on‐board processing of freshly captured krill is recommended. Compared to fish oil, krill oil has a more complex matrix, which leads to the formation of additional compounds from non‐enzymatic browning reactions. Lipid oxidation occurs through different pathways in krill oil and cannot be detected through classical analytical techniques such as determination of peroxide and anisidine value. Therefore selection of appropriate methods to evaluate the oxidative stability of krill oil is of high importance.

Figure 1 Open in figure viewer PowerPoint Development of lipid derived volatiles: (a & b) 1‐penten‐3‐ol and (c & d) 2‐pentylfuran in krill oil upon storage at two different incubation temperatures (20 and 40°C). The same pattern as (a & b) was obtained for (Z)‐2‐penten‐1‐ol and benzaldehyde, whereas the same pattern as (c & d) was obtained for 2‐heptanone and 2‐octanone. Values are mean ± SD (n = 3). Means sharing the same letter are not significantly different at 5% significant level. Reproduced from Lu et al. 2 with permission from Elsevier.     

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

Effects 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.     

Cover Image,Volume 93, Issue 9

The cover image, by Yi Yang et al., is based on the Research Article Catalytic wet peroxide oxidation of m‐cresol over novel Fe2O3 loaded microfibrous entrapped CNT composite catalyst in a fixed‐bed reactor, DOI: 10.1002/jctb.5609 .

     

Antioxidative effect of the main sinapic acid derivatives from rapeseed and mustard oil by‐products

Amongst oilseeds, rapeseed and mustard are rich sources of phenolic compounds, which also prominent in the by‐products of their respective oil processing or in commercial rapeseed and mustard press cakes. These cakes are rich sources of sinapic acid derivatives, which could be extracted as free sinapic acid or sinapine, the choline ester of sinapic acid. Sinapic acid is a widely investigated antioxidative compound. However, the main compound in the press cakes is present as sinapine. Investigations on the free‐radical‐scavenging activity of sinapic acid and sinapine indicate that sinapine had a significant but lower activity as compared to sinapic acid. Apart from this, sinapic acid, sinapine and different tocopherols were compared as antioxidants for inhibition of the formation of lipid oxidation products in purified rapeseed oils. The oxidation at 40 °C was monitored by the formation of hydroperoxides and propanal. The experiments indicate that in contrast to tocopherol mixtures addition of sinapic acid causes increasing inhibition of hydroperoxide formation when enhancing the concentration from 50 to 500 μmol/kg oil. Sinapine was not able to inhibit the formation of hydroperoxides, compared to sinapic acid. This indicates that sinapic acid‐rich extracts, as compared to sinapine‐rich fractions, could better inhibit the lipid oxidation in bulk lipid systems.     

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

Lipid 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.     

Temperature-Dependent Mechanism of Antioxidant Activity of o-Hydroxyl,o-Methoxy,and Alkyl Ester Derivatives of p-Hydroxybenzoic Acid in Fish Oil

The autoxidation of purified fish oil in the presence of different concentrations of o‐hydroxyl, o‐methoxy, and alkyl ester derivatives of p‐hydroxybenzoic at 35–55 °C was evaluated by different kinetic parameters including the stabilizing factor as a measure of effectiveness, the oxidation rate ratio as a measure of strength, and the antioxidant activity which combines the two parameters. Methyl gallate as the most reactive antioxidant participated only in the main reaction of chain termination (ROO· + InH ROOH + In·). Gallic acid, ethyl protocatechuate, protocatechuic acid, vanillic acid, and syringic acid, were able to protect fish oil against oxidation in terms of the extent of their participation in the pro‐oxidative side reactions of chain initiation (InH + ROOH In· + RO· + H₂O and InH + O₂ In· + HOO·) and the antioxidative side reactions of chain propagation (In· + ROO· In‐OOR and In· + In· products).     

Impact of Phosphoethanolamine Reverse Micelles on Lipid Oxidation in Bulk Oils

Phospholipids are important minor components in edible oil that play a role in lipid oxidation. Surface active phospholipids have an intermediate hydrophilic–lipophilic balance value, which allows them to form association colloids such as reverse micelles in bulk oil. These association colloids can influence lipid oxidation since they create lipid–water interfaces where prooxidants and antioxidants can interact with triacylglycerols. In this study, we examined the formation of reverse micelles in a stripped oil system by dioleoyl phosphoethanolamine (DOPE) and the effect of these physical structures on lipid oxidation kinetics. The critical micelle concentration (CMC) of DOPE was approximately 200 µmol/kg oil at 45 °C. Oxidation kinetics studies showed that DOPE was prooxidative when it was above its CMC (400 and 1,000 µM), reducing the lag phase from 14 days (control) to 8 days. The addition of combinations of DOPE and dioleoyl phosphocholine (DOPC) resulted in formation of mixed micelles with a CMC of 80 µmol/kg oil at 45 °C. These mixed micelles were also prooxidative when concentrations (100 and 500 µM) were above the CMC, decreasing the lag phase from 14 to 8 days. These findings provide a better understanding of the role of phospholipids in lipid oxidation of edible oil and could contribute to better antioxidant solutions.     

Phenol antioxidant efficiency in various lipid substrates containing hydroxy compounds

The oxidation stability of triacylglycerols of sunflower oil (TGSO) at 80 �C in the presence of 0.1 mM 2, 6‐di‐tert‐butyl‐4‐methylphenol (BHT) was found to decrease in the presence of 40 mM lipid hydroxy compounds (R'OH), 1‐tetradecanol (1‐TD), 1‐octadecanol (1‐OD), and 1‐monopalmitoylglycerol (1‐MP). Taking into account the significant effect of these compounds on the chain initiation via an acceleration of the hydroperoxide decomposition, the relative protection activity of BHT was found to increase in the presence of R'OH in the sequence: (TGSO) < (TGSO+1‐TD) < (TGSO+1‐OD) < (TGSO+1‐MP). This result was explained with the so‐called “micellar effect”: the relatively higher concentration of polar species such as hydroperoxide, peroxyl radicals and BHT within and nearby the micro aggregates formed in the presence of R'OH, leads to an increase of the rate of chain termination compared to that in the bulk lipid. When free radicals are generated in the bulk oil via the decomposition of a special nonpolar initiator, azo‐bis‐isobutyronitrile, 1‐OD and 1‐MP do not affect the BHT antioxidant efficiency. The effect of the lipid medium (linoleate or oleate type) on the antioxi‐dant activity of α‐tocopherol (TOH), 1.3 mM, in the presence of 1‐OD has been assessed on an example of oxidation of sunflower oil (SO) and lard (L) at 100 �C. Inspite of their different oxidizability 1‐OD caused the same relative decrease in the TOH efficiency during SO and L oxidation.