Shun Wada

Dietary and seasonal effects on the dorsal meat lipid composition of Japanese (Silurus asotus) and Thai catfish (Clarias macrocephalus and hybrid Clarias macrocephalus and Clarias galipinus)

The effects of dietary lipids and seasonal variation on the lipids of wild and cultured catfish (Japanese catfish, Silurus asotus; Thai catfish, Clarias macrocephalus and hybrid Clarias macrocephalus x Clarias galipinus) were determined by analysis of the lipid content and fatty acid composition of their dorsal meat. The predominant fatty acids of dorsal meat were 16:0, 18:1n-9, 18:2n-6, 20:4n-6 (arachidonic acid, AA), and 22:6n-3 (docosahexaenoic acid, DHA). The DHA content in the diet of Japanese catfish was higher than that in the diet of Thai catfish, and this was reflected in the dorsal meat of the Japanese catfish, which had a remarkably high percentage of DHA compared with the meat of the Thai catfish. Cultured Japanese catfish had a higher percentage of 18:2n-6 than Thai fish and a lower percentage of AA in winter than in summer season. There were also seasonal variations in the percentage of n-6 fatty acids in Japanese catfish. In summer, the fatty acid composition of the cultured Japanese catfish was similar to that of the wild catfish. These fatty acid changes in the lipid classes, triacylglycerol, phosphatidylcholine and phosphatidylethanolamine were similar to those observed for total lipids. These results indicate that the percentage of DHA in the dorsal meat of catfish is influenced by dietary fatty acid, and it may be that it can be increased in cultivated fish by administering a diet containing a large amount of DHA.

Influence of the position of unsaturated fatty acid esterified glycerol on the oxidation rate of triglyceride

The influence of the position of unsaturated fatty acid esterified glycerol on the oxidation rate of triglyceride was investigated at 50 C. Randomized triglycerides used were prepared by random interesterification between saturated and unsaturated monoacid triglycerides using sodium methoxide as catalyst. The monoacid triglycerides used were tripalmitin, tristearin, triolein and trilinolein. The molecular species of the randomized triglycerides were analyzed by high performance liquid chromatography (HPLC) in combination with gas liquid chromatography (GLC) and enzymatic hydrolysis. From the results of oxygen absorption measurement by GLC, the randomized triglycerides were more stable towards oxidation than the triglyceride mixtures which were prepared by mixing the equivalent quantities of the same monoacid triglycerides as used in the random interesterification. This may be due to the decrease in the contents of most unstable unsaturated monoacid triglycerides by random interesterification with saturated monoacid triglycerides. Furthermore, from the results obtained with the detailed analysis of the randomized triglycerides at different stages of oxidation, it became clear that the triglycerides having unsaturated fatty acids linked at the 2-position of glycerol are more stable towards oxidation than those linked at the 1(or 3)-position. The carbon chain length of saturated fatty acids has essentially no influence on the oxidation rates of unsaturated fatty acids esterified in the same glycerol.

Enhancing the antioxidant effect of α-tocopherol with rosemary in inhibiting catalyzed oxidation caused by Fe2+ and hemoprotein

Abstract A mixture of α-tocopherol and rosemary extract (0·035% + 0·035%) was used to inhibit fish lipid oxidation catalyzed by Fe2+ or hemoprotein. In a sardine oil model system, a mixture of α-tocopherol and rosemary extract showed a significantly stronger antioxidant effect, as it prolonged the induction period for 10 and 16 days longer than α-tocopherol alone and rosemary extract alone, respectively. In addition, the effective lifetime of α-tocopherol in samples treated with the α-tocopherol and rosemary extract mixture was 10 days longer than in samples with only α-tocopherol added even though the amount of added α-tocopherol in the latter case was twice that for the mixture. In fish dark muscle, the mixture of α-tocopherol and rosemary extract also showed a stronger anti-oxidant effect than either tocopherol or rosemary extract alone. Treatment of samples with this mixture also led to a lower rate of decomposition of highly unsaturated fatty acids, myoglobin and hemoglobin, and triglyceride compared to samples treated with tocopherol or rosemary extract alone.

Effects of three different highly purified n-3 series highly unsaturated fatty acids on lipid metabolism in C57BL/KsJ-db/db mice.

Triglycerides (TG) consisting of highly purified (>97%) n-3 series highly unsaturated fatty acids, eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA), and docosahexaenoic acid (DHA), were administered to C57BL/KsJ-db/db mice for 4 weeks by pair-feeding to compare their effects on lipid metabolism and to evaluate the effects of DPA on lipid metabolism. The hepatic TG level and total amount was decreased by treatment with DHA and DPA compared to the control. The efficacy of DPA was greater than that of EPA, but less than that of DHA. In contrast, EPA had the greatest serum TG reducing effect. The hepatic cytosol fraction of the DHA-treated group contained the lowest fatty acid synthase (FAS) and malic enzyme (ME) activity levels. Furthermore, the DHA-treated group contained the highest serum adiponectin concentrations. These findings indicate that the strong hepatic TG-lowering effect of DHA is due to the suppression of TG synthesis. The same tendencies were observed in DPA-treated mice, and the effect was stronger than that observed in EPA-treated mice, but equivalent to that observed in DHA-treated mice. Based on these results, DPA possesses lipid metabolism-improving effects. The beneficial effects of DPA for lipid metabolism were not superior to those of EPA and DHA, and the effect was always intermediate between those of EPA and DHA.

Spawning and season affect lipid content and fatty acid composition of ovary and liver in Japanese catfish (Silurus asotus)

The influences of spawning and season on lipid content, lipid classes, and fatty acid composition were assessed in ovary and liver of wild and cultured Japanese catfish (Silurus asotus). The lipid content (7.3+/-1.6 g/100 g wet wt.) of ovary from wild catfish at spawning was higher than that at post-spawn. However, no influence of spawning on the lipid content of liver was observed. Docosahexaenoic acid [DHA, C22:6(n-3)] in ovary lipids was 12.3+/-0.5% of total fatty acids. The percentage of n-7 monounsaturated fatty acids in triacylglycerol from the ovary and liver in the spawning season was high. Percentages of C22:6(n-3) in phosphatidylcholine and phosphatidylethanolamine from ovary were higher during spawning than after spawning. No significant differences were observed in the lipid content of ovary and liver from cultured catfish between seasons (summer vs. winter). Content of arachidonic acid (C20:4n-6) in ovary and liver from cultured catfish was higher in summer than in winter. There were differences in lipid classes of ovary and liver by spawning and season. These results suggest that the lipid metabolism in Japanese catfish is greatly influenced by spawning and season.

Enantiomeric separation of asymmetric triacylglycerol by recycle high-performance liquid chromatography with chiral column

In our previous studies, we employed recycle HPLC for the separation of triacylglycerol (TAG)-positional isomers (PIs). In this study, a recycle HPLC system equipped with a polysaccharide-based chiral column was applied to the enantiomeric separation of some asymmetric TAGs having straight-chain C16-C18 acyl residues. As a result, 1,2-dipalmitoyl-3-oleoyl-rac-glycerol (rac-PPO), 1,2-dioleoyl-3-palmitoyl-rac-glycerol (rac-OOP), and 1,2-dipalmitoyl-3-linoleoyl-rac-glycerol (rac-PPL) were resolved into their respective enantiomers. However, neither 1,2-dioleoyl-3-linoleoyl-rac-glycerol (rac-OOL), consisting of only unsaturated fatty acids, nor 1,2-dipalmitoyl-3-stearoyl-rac-glycerol (rac-PPS), consisting of only saturated fatty acids, was resolved. These results suggest that the asymmetric TAGs, used in this study, having both a palmitic acid moiety and an oleic acid (or a linoleic acid) moiety at the sn-1 or sn-3 positions are resolved by the chiral column. This new chiral separation method can be used in combination with atmospheric pressure chemical ionization mass spectrometry to determine the sn-OOP/sn-POO ratio in palm oil. This method is applicable for the chiral separation of asymmetric TAGs in palm oil.

1-O-alk-1′-enyl-2-acyl and 1-O-alkyl-2-acyl glycerophospholipids in white muscle of bonitoEuthynnus pelamis (Linnaeus)

The existence of ether-linked phospholipids, including 1-O-alk-1′-enyl-2-acyl and 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholines and ethanolamines in bonitoEuthynnus pelamis (Linnaeus) white muscle, was investigated by gas chromatography and gas chromatography-mass spectrometry. Chemical ionization (iso-butane) mass spectrometry of trimethylsilyl ethers derived from the corresponding ether-linked glycerophospholipids proved effective not only for determining molecular weights but also for structural identification based on the ions [M−R]+, [M−RO]+ and [M+1]+. 1-O-Alk-1′-enyl-2-acyl-sn-glycero-3-phosphocholine and ethanolamine accounted for 3.0–6.0% and 3.6–7.6% of the total glycerophospholipids, respectively. 1-O-Alkyl-2-acyl-sn-glycero-3-phosphocholine and ethanolamine were also determined for one fish and accounted for 1.4% and 0.6% of the total glycerophospholipids, respectively. The predominant long chains in thesn-1 position of the glycerol moieties were 16∶0, 18∶0 and 18∶1 in the case of the alkenylacyl and alkylacyl components. Fatty acid distribution of individual glycerophospholipids was also determined.

Pro-oxidant/antioxidant behaviours of ascorbic acid, tocopherol, and plant extracts in n-3 highly unsaturated fatty acid rich oil-in-water emulsions.

This study investigated the oxidative stability of n-3 highly unsaturated fatty acid (n-3 HUFA) rich (35% n-3 HUFA) oil-in-water emulsions (10 wt% oil) with commercial antioxidants and natural plant extracts. Ascorbic acid, α-tocopherol, and the extracts of Indian gooseberry fruit (Emblica officinalis) (IGFE) and sweet basil leaves (Ocimum basilicum L.) (SBLE) were used for the study as antioxidants. The progress of oxidation in the systems was evaluated at 35 °C over 120 h against a control (without antioxidant) by monitoring the formation of primary (conjugated dienes) and secondary (volatile carbonyl compounds) oxidation products. Volatile carbonyl compounds were trapped as derivatives of pentafluorophenyl hydrazine and quantified by headspace solid-phase microextraction analysis. About 40 volatile carbonyls were successfully identified by this method. trans,trans-2,4-Heptadienal, trans,cis-2,4-heptadienal, 3,5-octadien-2-one, and 1-penten-3-ol were predominant. The volatile carbonyl compounds and conjugated dienes were formed at low rates in emulsion systems in which α-tocopherol and natural plant extracts had been introduced, compared to the control. Emulsion systems containing ascorbic acid showed low stability, as indicated by the oxidation products that were formed at high rates compared to the control. These results indicated that ascorbic acid activated the oxidation reactions in n-3 HUFA rich water emulsions, while natural plant extracts that were rich in polyphenols and α-tocopherol were active as antioxidants. The present study further demonstrated the applicability of the polar paradox theory in the determination of stability for n-3 HUFA rich water emulsions with commercial antioxidants and natural plant extracts.

Optimization of heterotrophic culture conditions for n-alkane utilization and phylogenetic position based on the 18S rDNA sequence of a thermotolerant Prototheca zopfii strain

This study reports on the optimization of the culture conditions for a thermotolerant eukaryotic algal strain, Prototheca zopfii RND16, which can effectively degrade and assimilate n-alkanes at elevated temperatures. RND16 was able to grow on 1% (v/v) n-alkanes (C14-C17) at temperatures up to 38 degrees C. This ability differs from a previous finding that P. zopfii did not grow on hydrocarbons under temperature conditions above 25 degrees C. Increasing the temperature from 25 degrees C to 30-35 degrees C resulted in an increase in the rate of n-alkanes consumption during growth of RND16 in quiescent culture. In shaking culture at 35 degrees C, RND16 removed a 1% n-alkanes mixture almost completely at the basal medium salinity within 8 d. However, an appreciable decrease in the extent of hydrocarbon utilization was observed with increasing salinity and substrate concentration in the medium. The slow consumption of the n-alkanes in the early stage of degradation at 25 degrees C was improved by supplementing 0.1% glucose. A comparative study on the nuclear small subunit rDNA (18S rDNA) sequences of three strains within the genus Prototheca revealed that both P. zopfii ATCC 30253, which utilize n-alkanes at room temperature and P. moriformis ATCC 50081, which does not assimilate n-alkanes, are closely related to RND16.

Actual ratios of triacylglycerol positional isomers consisting of saturated and highly unsaturated fatty acids in fishes and marine mammals.

The distribution of fatty acid species at the (sn-1, 3) position or the (sn-2) position of triacylglycerol (TAG) in natural fats and oils has already been analysed by many researchers and several interesting results have been reported. However, most of these reports only focused on the distribution of fatty acids at the or positions in TAG, and did not take account of the combination of fatty acids in the TAG, i.e., the TAG positional isomers. In this study, the actual ratios of TAG positional isomer pairs, consisting of palmitic acid and highly unsaturated fatty acid (HUFA) such as DHA or EPA, in fish and marine mammals were investigated using a high-performance liquid chromatography/atmospheric pressure chemical ionisation-mass spectrometry (HPLC/APCI-MS) system equipped with tandem jointed non-endcapped polymeric ODS columns. The results show that for combinations of DHA or EPA with two palmitic acids in the TAG of marine mammals, binding was almost all at the α position. In contrast, binding of DHA or EPA was mainly at the β position in fish. The preferred DHA and EPA positions in TAG were the same in the same marine mammal or fish. The binding position tendency of HUFA in TAG positional isomers consisting of two HUFAs and one palmitic acid was the same as that for combinations of one HUFA and two palmitic acids. These results were interpreted as showing that the preferred fatty acid species of sn-glycerol-3-phosphate acyltransferase and 1-acyl-sn-glycerol-3-phosphate acyltransferase in marine mammals are different to those in fish and other animals, or that diacylglycerol acyltransferase in marine mammals favours 1,2-dipalmitoyl-sn-glycerol formed from 1,2-dipalmitoyl-sn-glycerol-3-phosphatidate if HUFA is the reaction substrate.