Oxidation in EPA‐ and DHA‐rich oils: an overview

Oxidation of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) rich omega‐3 oils (hereafter referred to as either EPA and DHA or omega‐3) is a complicated topic, but an important one to understand. A significant number of consumers cite fishy burp and/or taste, thought to be the result of oxidation, as one of the main reasons they do not consume EPA and DHA rich oils. In addition, consumers note that some articles have raised concerns about the potential for adverse effects associated with consumption of oxidized oils. Measuring oxidation in omega‐3 oils is complicated due to the differences in chemical and physical characteristics of many commercially available products, which means not all methods to determine quality are appropriate for all types of oils. A number of consumer advocacy groups, product quality seal programs and academic groups have published data on levels of oxidation in omega‐3 oils. Overall, this data shows that commercially available omega‐3 supplements are low in oxidation. If consumers have a poor sensory experience with their omega‐3 product, they should try another product as an alternative.     

The Effects of Omega‐3 Polyunsaturated Fatty Acid Consumption on Mammary Carcinogenesis

The consumption of omega‐3 polyunsaturated fatty acids (n‐3 PUFA) is associated with a reduced risk of breast cancer. Studies in animals and in vitro have demonstrated mechanisms that could explain this apparent effect, but clinical and epidemiological studies have returned conflicting results on the practical benefits of dietary n‐3 PUFA for prevention of breast cancer. Effects are often only significant within a population when comparing the highest n‐3 PUFA consumption group to the lowest n‐3 group or highest n‐6 group. The beneficial effects of n‐3 PUFA eicosapentaenoic and docosahexaenoic on the risk of breast cancer are dose dependent and are negatively affected by total n‐6 consumption. The majority of the world population, including the most highly developed regions, consumes insufficient n‐3 PUFA to significantly reduce breast cancer risk. This review discusses the physiological and dietary context in which reduction of breast cancer risk may occur, some proposed mechanisms of action and meaningful recommendations for consumption of n‐3 PUFA in the diet of developed regions.     

Presence of Fatty‐Acid Ethyl Esters in Krill Oil Dietary Supplements

Krill oil dietary supplements are increasingly used for their high concentrations of phospholipids (PL), which offer reportedly greater bioavailability of n‐3 polyunsaturated fatty acids (PUFA) than those of triacylglycerols or fatty‐acid ethyl esters (FAEE) commonly found in fish oils and fish‐oil concentrates. This work evaluated the lipid composition of 22 commercial krill oil (CKO) supplements available in the US market, and found ten products (i.e. 45%) contained significant amounts of FAEE, varying from 41% to 75%, by weight. These concentrations of FAEE differed from the minor abundances of FAEE (<3%, by weight) found in manufacturer‐supplied krill oil. The potential clinical and regulatory implications for these findings warrant further investigation.     

Lipase‐catalysed enrichment of DHA and EPA in acylglycerols resulting from squid oil ethanolysis

The fatty acid specificity of four lipases towards eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) was evaluated when performing ethanolysis of squid oil. During the first part of ethanolysis, no DHA ethyl esters were detected when using the lipases from Thermomyces lanuginosus, Pseudomonas cepacia or Pseudomonas fluorescens (in the case of the second and third lipases, no EPA ethyl esters were detected either). This indicates that these three lipases could not catalyse the conversion of DHA located in a triacylglycerol to ethyl ester, and that the Pseudomonas lipases could not catalyse the conversion of EPA either. This pattern was not found for the lipase from Rhizomucor miehei. The lipase from Thermomyces lanuginosus showed the lowest specificity towards DHA and the highest DHA recovery during DHA enrichment in the acylglycerol fraction. It was thus used to catalyse the ethanolysis of squid oil on a larger scale. The ethyl esters formed were removed using short‐path distillation, resulting in a product containing mainly mono‐ and diacylglycerols. The product contained 34 mol‐% DHA and 17 mol‐% EPA, compared with 19 mol‐% DHA and 12 mol‐% EPA in the original squid oil.     

Plasma Omega-3 Fatty Acid Response to a Fish Oil Supplement in the Healthy Elderly

Little information is available concerning whether incorporation of dietary omega-3 fatty acids into plasma lipids changes during healthy aging. Elderly (74 ± 4 years old) and young (24 ± 2 years old) adults were given a fish oil supplement for 3 weeks that provided 680 mg/day of docosahexaenoic acid and 320 mg/day of eicosapentaenoic acid, followed by a 2 week wash-out period. Compliance was monitored by spiking the capsules with carbon-13 glucose, the excretion of which was measured in breath CO₂. In response to the supplement, plasma docosahexaenoic acid rose 42% more in the elderly but eicosapentaenoic responded similarly in both groups. Despite raising docosahexaenoic acid intake by five to tenfold, the supplement did not raise plasma free docosahexaenoic acid (% or mg/dL) in either group. We conclude that healthy aging is accompanied by subtle but significant changes in DHA incorporation into plasma lipids.     

Fatty acid composition of selected roes from some marine species

Fifteen roes from different marine fish species available in Spain were analyzed in order to determine their fatty acid (FA) composition, especially the eicosapentaenoic acid (20:5n‐3, EPA) and docosahexaenoic acid (22:6n‐3, DHA) contents. Roes from Atlantic bonito (Sarda sarda), European squid (Loligo vulgaris), cuttlefish (Sepia spp.), lumpfish (Cyclopterus lumpus), European hake (Merluccius merluccius), Atlantic salmon (Salmo salar) and gonads of male Atlantic mackerel (Scomber scombrus) reached EPA + DHA amounts higher than 30% of the total FA, and among them, roes from lumpfish, European hake and salmon provide different FA type ratios that could make them adequate as dietary sources of EPA and DHA.     

Combination of Urea Complexation and Molecular Distillation to Purify DHA and EPA from Sardine Oil Ethyl Esters

Urea complexation (UC) and the molecular distillation (MD) technique were applied jointly to purify eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from sardine oil ethyl esters (SOEE). Response surface methodology (RSM) was used to measure the influences of the variables to the responses and the optimal conditions. Regression analysis and variance analysis of the models demonstrated that each multinomial correctly represented the relationships between the responses and the variables. The urea‐to‐SOEE ratio was much more significant than crystallization temperature in UC, and the quadratic term of rotation speed of swept‐surface scrapers was the most significant variable in MD. Optimal UC conditions were 1.9:1 urea‐to‐SOEE ratio and ?1 °C crystallization temperature at which the purity and total recovery of EPA and DHA were 65.6 % and 46.8 %, respectively. The best conditions predicted for MD were 75 °C distillation temperature, 54.8 °C preheat temperature, 4.5 °C condensation temperature, and 307 rpm rotation speed at which the purity of EPA and DHA was 83.5 %. The predicted values were verified to be reasonably close to the experimentally observed values.     

The Percentage of n-3 Highly Unsaturated Fatty Acids in Total HUFA as a Biomarker for Omega-3 Fatty Acid Status in Tissues

A blood biomarker of omega-3 fatty acid intake and tissue status could serve as a modifiable risk factor for cardiovascular disease. The percentage of omega-3 highly unsaturated fatty acid (HUFA ≥ 20 carbons and ≥3 double bonds) in the total HUFA pool (the n-3 HUFA score) was examined as a potential blood biomarker of omega-3 fatty acids in tissues. The fatty acid composition of total lipid extracts (TLE) and phospholipid (PL) fractions were determined for plasma and erythrocytes samples of human subjects (n = 20) and the n-3 HUFA score and the sum of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were compared. Omega-3 fatty acids in blood and tissues of rats (n = 31) and pigs (n = 48) were also determined and the associations were compared. The n-3 HUFA score is more consistent across plasma and erythrocytes, with strong correlations between TLE and PL in plasma (r = 0.93) and erythrocytes (r = 0.94). The n-3 HUFA score was less variable and blood levels correlated strongly with various animal tissues. The n-3 HUFA score is a useful blood biomarker that does not require the isolation of the PL class thereby supporting high throughput analyses. The strength of association between the n-3 HUFA score and disease risk needs to be examined.     

Fatty Acid Composition and Contents of Seven Commercial Fish Species of Genus <Emphasis Type="Italic">Coregonus</Emphasis> from Russian Subarctic Water Bodies

In several Russian northern lakes and rivers, Arctic cisco Coregonus autumnalis, least cisco C. sardinella, peled C. peled, tugun C. tugun, broad whitefish C. nasus, whitefish C. lavaretus and vendace C. albula were sampled in periods of officially permitted commercial fishery. Special attention was paid to contents (mg g^?1 of wet weight) of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in muscle tissues (filets), which are essential for human nutrition. The highest values of EPA + DHA content in semi‐anadromous fish and freshwater fish were recorded for C. autumnalis from the Yenisei River, 17.60 mg g^?1 wet weight, and for C. lavaretus from the Sobachye Lake, 16.61 mg g^?1 wet weight, respectively. Intra‐genus variations of EPA + DHA contents of Coregonus species were from 1.87 to 17.60 mg g^?1 wet weight. Since the congeneric species were genetically close to each other, the variations in EPA and DHA contents were thought to be caused primarily by ecological factors: migrational capability, type of feeding and trophic status of aquatic ecosystems. In general, the majority of studied species appeared to be of a high nutritive value for humans, although unfavorable environmental conditions could considerably diminish this value.     

Single-Cell Oils as a Source of Omega-3 Fatty Acids: An Overview of Recent Advances

Omega-3 fatty acids, namely docosahexaenoic acid and eicosapentaenoic acid, have been linked to several beneficial health effects (i.e. mitigation effects of hypertension, stroke, diabetes, osteoporosis, depression, schizophrenia, asthma, macular degeneration, rheumatoid arthritis, etc.). The main source of omega-3 fatty acids is fish oil; lately however, fish oil market prices have increased significantly. This has prompted a significant amount of research on the use of single-cell oils as a source of omega-3 fatty acids. Some of the microbes reported to produce edible oil that contains omega-3 fatty acids are from the genus Schizochytrium, Thraustochytrium and Ulkenia. An advantage of a single cell oil is that it usually contains a significant amount of natural antioxidants (i.e. carotenoids and tocopherols), which can protect omega-3 fatty acids from oxidation, hence making this oil less prone to oxidation than oils derived from plants and marine animals. Production yields of single cell oils and of omega-3 fatty acids vary with the microbe used, with the fermentative growing conditions, and extractive procedures employed to recover the oil. This paper presents an overview of recent advances, reported within the last 10 years, in the production of single cell oils rich in omega-3 fatty acids.     

Preferential Partitioning of Rumen-Protected n-3 and n-6 Fatty Acids into Functionally Different Adipose Tissues

Lipids are stored at various sites inside the body as adipose tissue (AT). These include subcutaneous, abdominal, and intermuscular locations. The AT substantially differ in their metabolic function. It is, however, unclear whether AT have specific requirements for individual essential n-3 and n-6 fatty acids (FA). If so, control mechanisms would partition FA from the blood. To investigate the hypothesis of a selective FA incorporation, 18 beef heifers were fed diets supplemented with 60 g/kg diet with lipids from either fish oil (FO) or sunflower oil (SO). The lipids had partially been rumen-protected to ruminal biohydrogenation of n-3 and n-6 FA. The AT analyzed for n-3 and n-6 FA by gas chromatography were obtained from pericardial, longissimus thoracis (LT) intermuscular, perirenal, and subcutaneous sites. The greatest proportions of n-3 and n-6 FA were found in the pericardial AT. Despite generally low abundance, n-3 FA proportions increased with FO compared to SO supplementation in all AT, but to a different extent. No such partitioning was found for the n-6 FA when supplementing SO. Concomitantly, the n-6/n-3 FA ratio was reduced with FO in all AT, except in the pericardial AT. The latter has specific metabolic functions and thus appears to be quite resistant to diet-induced changes in FA profile in order to maintain its function. The present findings showed the special role of specific n-3 and n-6 FA in bovine AT.     

Application of Silver Ion High-Performance Liquid Chromatography for Quantitative Analysis of Selected n-3 and n-6 PUFA in Oil Supplements

The aim of this study was to develop a simple method for simultaneous determination of selected cis/cis PUFA–LNA (18:2), ALA (18:3), GLA (18:3), EPA (20:5), and DHA (22:6) by silver ion high‐performance liquid chromatography coupled to a diode array detector (Ag‐HPLC‐DAD). The separation was performed on three Luna SCX Silver Loaded columns connected in series maintained at 10 °C with isocratic elution by 1 % acetonitrile in n‐hexane. The applied chromatographic system allowed a baseline separation of standard mixture of n‐3 and n‐6 fatty acid methyl esters containing LNA, DHA, and EPA and partial separation of ALA and GLA positional isomers. The method was validated by means of linearity, precision, stability, and recovery. Limits of detection (LOD) for considered PUFA standard solutions ranged from 0.27 to 0.43 mg L^?1. The developed method was used to evaluate of n‐3 and n‐6 fatty acids contents in plant and fish softgel oil capsules, results were compared with reference GC‐FID based method.     

Combined Urea Complexation and Argentated Silica Gel Column Chromatography for Concentration and Separation of PUFAs from Tuna Oil: Based on Improved DPA Level

Eicosapentaenoic acid (EPA, 20:5n‐3), docosapentaenoic acid (DPA) isomers (22:5n‐6 and 22:5n‐3) and docosahexaenoic acid (DHA, 22:6n‐3) derived from tuna oil were concentrated by three stages of urea fractionation at various crystallization temperatures and different fatty acid/urea ratios. Thereafter, polyunsaturated fatty acids concentrate containing comparatively enriched DPA levels was purified by argentated silica gel column chromatography. A product containing 22.2 ± 0.6 % EPA, 4.6 ± 0.0 % DPAn‐6, 5.9 ± 0.1 % DPAn‐3 and 42.3 ± 1.2 % DHA was obtained at 1:1.6 fatty acid/urea ratio (w/w) by crystallization at ?8 °C for 16 h, ?20 °C for 8 h, and ?8 °C for 16 h. A DPA isomer concentrate containing 26.1 ± 0.5 % DPAn‐6 and 22.3 ± 0.4 % DPAn‐3 was achieved by argentated silica gel chromatography in the 6 % acetone/n‐hexane solvent fraction (v/v), and the recovery of both fatty acids was 66.1 ± 3.2 and 70.7 ± 2.2 %, respectively. Furthermore, 91.9 ± 2.5 % EPA and 99.5 ± 2.1 % DHA with recoveries of 47.8 ± 2.0 and 56.7 ± 3.3 %, respectively, were obtained in various fractions.     

Characterization of Trimethylolpropane‐Based Biolubricant

The oxidative stability index (OSI) of fatty acid methyl esters (FAME) and trimethylolpropane (TMP) esters or TMPE produced from five vegetable oils (Brassica rapa L., Linum usitatissimum L., Zea mays L., Brassica napus L., Camelina sativa L.) are compared. The highest stability is observed in vegetable oils while the processed products are less stable. The major causes in loss of OSI are attributed to excess FAME in the crude product and the loss of natural antioxidants due to refinement with silica and celite. The low‐temperature flow properties of TMPE produced from four different vegetable oils (B. juncea L., L. usitatissimum L., B. rapa L., and C. sativa L.) are investigated by proton nuclear magnetic resonance (¹H‐NMR). The T2 relaxations of different TMPE are measured to observe how the mobility of oil changed as temperature decreased. Increased oil mobility (represented by T2) is correlated with rising temperature. The Gaussian widths of the singlet in ¹H‐NMR spectra of each oil demonstrated increased molecular mobility as temperature increased. Extrapolation of the relation of T2 signals of these four oils indicates that T2 approached zero between 232 K and 239 K, suggesting the molecular motion leading to a T2 relaxation has largely ceased. Practical Applications: The OSI is determined for four vegetable oils as well as the product FAME and TMPE. The vegetable oils are more stable than their products. The loss of natural antioxidants during purification of FAME and TMPE contributes to the lower OSI compared to vegetable oil. The low‐temperature flow behavior of TMP‐based biolubricants is determined between 238 K and 298 K using T2 relaxation. As temperature decreases, a singlet resonance in ¹H‐NMR spectra attributed to TMP protons broadens until it disappears. The results suggest that the log of the spin‐spin relaxation time is linearly correlated with rising temperature and oil mobility.