Comparative study of the molecular species of chloropropanediol diesters and triacylglycerols in milk fat

In an effort to establish the origin of the fatty acid esters of 3-chloropropanediol, which recently have been isolated in small amounts from goat milk, we compared the molecular species composition of the chlorohydrin diesters and of goat milk triacylglycerols. The chloropropanediol diesters were found to be composed of molecular species containing C₁₀−C₁₈ fatty acids and corresponded closely in carbon number to those calculated for the long chain sn-1,2-diacyl-glycerol moieties of goat milk triacylglycerols. The molecular species of goat milk total triacylglycerols contained C₄−C₁₈ fatty acids. It is suggested that triacylglycerols and chloropropanediol diesters are derived from the same pool of long chain fatty acids. A molecular distillate of bovine milk fat did not contain chloropropanediol diesters, while the available samples of human milk fat were shown to contain alkyldiacylglycerols as the major components of a neutral lipid fraction corresponding in polarity to the chloropropanediol diesters.     

Milk fat structure of a patient with type 1 hyperlipidemia

Structural analyses were performed on milk fat samples obtained 3–10 days postpartum from a lactating patient with primary Type 1 hyperlipidemia. The milk triacylglycerols contained 3–7% C₁₀, 14–21% C₁₂, 20–30% C₁₄, 22–26% C₁₆ and 20–30% C₁₈ (largely oleic) acids. Gas liquid chromatographic (GLC) analyses of the X-1,3- and X-1,2-diacylglycerols on polar siloxane columns showed a markedly non-random association of acyl chains. Stereospecific analyses indicated that the short chain length fatty acids were confined essentially to the sn-3-position of the triacylglycerol molecule. Furthermore, these acids were largely absent from the phosphatidylcholines and the endogenous sn-1,2-diacylglycerols of the milk fat. It is concluded that the short chain fatty acids are incorporated into the milk triacylglycerols during the final stage of biosynthesis via the phosphatidic acid pathway, and that the overall fatty acid distribution is consistent with the 1-random 2-random 3-random hypothesis.     

Molecular species and fatty acid distributions of triacylglycerols from germinating soybean cotyledons

Molecular species and fatty acid distributions of triacylglycerols obtained from cotyledons of soybean seedlings were investigated. Changes observed in triacylglycerol content were closely related to levels of total lipids present in the cotyledons. At day 12 of seedling growth, ca. 85% of triacylglycerols had been consumed. Immediately after the beginning of imbibition the oil consisted of triacylglycerols with even carbon numbers (from C-50 to C-60) based on the combined length of the fatty acyl chains present in a triacylglycerol. The dominant components throughout germination were C-52 and C-54 triacylglycerols. Fourteen molecular species of triacylglycerols were identified in the cotyledons. As soybean seedlings grew, the percentages of triacylglycerols decreased to 0.9–36.2% during the 12 days. Triacylglycerols containing one or more saturated fatty acids were hydrolyzed slightly faster than other species. Unsaturated fatty acids were dominant in the 2-position throughout germination. These results suggest the mechanism of initial triacylglycerol hydrolysis may be different in various molecular species.     

The high content of monoene fatty acids in the lipids of some midwater fishes: Family myctophidae

The total lipids of eleven species of Myctophids caught at depths between 20 and 700 m in the northern Pacific Ocean were analyzed using silicic acid column chromatography (lipid classes) and capillary gas chromatography (fatty acid and fatty alcohol composition). The major components in the lipid classes were triacylglycerols or wax esters; triacylglycerols were the dominant acyl neutral lipids (68.1–96.1%) in eight species, and wax esters were found as the dominant lipid (85.5–87.9%) in three species. The major fatty acids and alcohols contained in the was esters of the three fishes were 18:1n–9, 20:1n–9, 20:1n–11, and 22:1n–11 for fatty acids, and 16:0, 18:1, 20:1, and 22:1 for fatty alcohols. Fatty acids in the triacylglycerols ranging from C₁₄ to C₂₂ were predominantly of even chain length. The major components were 16:0, 16:1n–7, 18:1n–9, 20:1n–11, 22:1n–11, 20:5n–3 (icosapentaenoic acid), and 22:6n–3 (docosahexaenoic acid). In both the triacylglycerols and the wax esters, the major fatty components were monoenoic acids and alcohols. It is suggested from the lipid chemistry of the Myctophids that they may prey on the same organisms as the certain pelagic fishes such as saury and herring, because the large quantities of monoenoic fatty acids are similar to those of saury, herring, and sprats whose lipids originate from their prey organisms such as zooplanktons which are rich in monoenoic wax esters.     

Postparturition changes in the triacylglycerols of cow colostrum

The changes in the triacylglycerol (TAG) composition of colostrum fat of three cows were studied. In addition to the determination of fatty acid composition by gas chromatography, the distribution of TAG according to the acyl carbon number (ACN) and molecular weight was analyzed utilizing both supercritical fluid chromatography (SFC) and ammonia negative-ion chemical ionization mass spectrometry (MS). Colostrum TAG contained substantially less stearic and oleic acids and more myristic and palmitic acids than the normal Finnish milk fat. The major trends in the changes of fatty acids and TAG were similar for each cow, although clear differences between individuals were found. During the first week of parturition, the proportions of short-chain fatty acids (C₄–C₁₀) typically increased as well as those of stearic and oleic acids, whereas the relative amounts of C₁₂–C₁₆ acids decreased, especially those of myristic and palmitic acids. Distinct changes occurred also in TAG distributions: the proportions of molecules with ACN 38–40 increased and those with ACN 44–48 decreased. Although there were distinct differences between individuals shortly after delivery, both the fatty acid compositions and TAG distributions of the milk samples of the cows started to resemble each other after one week. The theoretical profiles of colostrum TAG calculated based on the fatty acid compositions differed clearly from the ACN distributions analyzed by SFC and MS. Thus, the analysis of TAG is essential, because the changes in molecular species composition of colostrum TAG cannot be estimated according to the fatty acid analysis alone.     

Changes in the structure of soybean triacylglycerols due to heat

Commercially refined soybean oil was heated at 180 C for 50, 70 or 100 hr with aeration. The triacylglycerol fractions separated from the oils by column chromatography on silica gel were fractionated further by silicic acid thin layer chromatography (TLC), and species compositions were determined by argentation TLC and lipase hydrolysis. There was a decrease in the absolute amounts of the triacylglycerols with longer heating periods, such as 21% for 50 hr and 42% for 100 hr. Relatively large changes occurred in the proportion of the molecular species of the triacylglycerols during heating; there was an increase in the more saturated species, 1–4 double bonds, and a decrease in species containing 5–7 double bonds. Although these changes occurred in the percentage of each triacylglycerol species, the positional distribution of the fatty acids in the 2-position remained virtually unchanged throughout heating. Oleic and linoleic acids were commonly found in the 2-position of the acylglycerol moiety, whereas most of the palmitic and stearic acids favored esterification in the 1- and 3-positions. The results indicate that unsaturated fatty acids located in the 2-position are protected significantly from thermal oxidative decomposition.     

Cholestane as a digestibility marker in the absorption of polyunsaturated fatty acid ethyl esters in Atlantic salmon

Salmonid fish require long-chain n−3 fatty acids in their diet. The digestibility of different chemical forms of fish oil fatty acids, fed as triacylglycerols, free fatty acids or ethyl esters, was examined in 300 g farmed Atlantic salmon (Salmo salar) using cholestane as an indicator of fat absorptionin lieu of the chromium oxide (Cr₂O₃) which is commonly used as a marker in digestibility studies. It was established that the two digestibility markers gave similar results. Conveniently, cholestane does not require a separate analysis if fatty acids are to be determined by appropriate gas-liquid chromatography. The long-chain polyunsaturated fatty acids were particularly well absorbed, the apparent digestibility being 90–98% when feeding triacylglycerols or free fatty acids. However, the digestibility of monounsaturated fatty acids (75–94%) was lower, and lower still for saturated fatty acids (50–80%). Ethyl esters of fatty acids were significantly less well absorbed (P<0.05) than were the corresponding fatty acids in free acid or triacylglycerol form. Irrespective of dietary fat type, only free fatty acids were identified in feces, indicating total hydrolysis of triacylglycerols and ethyl esters. Presented in part at the World Aquaculture Society meeting, June 10–14, 1990, Halifax, Canada.     

Evidence that palmitic acid is absorbed assn-2 monoacylglycerol from human milk by breast-fed infants

Milk fatty acids consist of about 20–25% palmitic acid (16∶0), with about 70% of 16∶0 esterified to thesn-2 position of the milk triacylglycerols. Hydrolysis of dietary triacylglycerols by endogenous lipases producessn-2 monoacylglycerols and free fatty acids, which are absorbed, reesterified, and then secreted into plasma. Unesterified 16∶0 is not well absorbed and readily forms soaps with calcium in the intestine. The positioning of 16∶0 at thesn-2 position of milk triacylglycerols could explain the high coefficient of absorption of milk fat. However, the milk lipase, bile salt-stimulated lipase, has been suggested to complete the hydrolysis of milk fat to free fatty acids and glycerol. These studies determined whether 16∶0 is absorbed from human milk assn-2 monopalmitin by comparison of the plasma triacylglycerol total andsn-2 position fatty acid composition between breast-fed and formula-fed term gestation infants. The human milk and formula had 21.0 and 22.3% of 16∶0, respectively, with 54.2 and 4.8% 16∶0 in the fatty acids esterified to the 2 position. The plasma triacylglycerol total fatty acids had 26.0±0.6 and 26.2±0.6% of 16∶0, and thesn-2 position fatty acids had 23.3±3.3 and 7.4±0.7% of 16∶0 in the three-month-old exclusively breast-fed (n=17) and formula-fed (n=18) infants, respectively. Marked differences were found in the plasma total and the 2 position phospholipid percentage of 20∶4ω6, i.e., 11.6±0.3 and 6.9±0.6 (total), 17.7±1.4 and 9.7±0.6 (sn-2 position) and percentage of 22∶6ω3, 4.6±0.3 and 2.1±0.3 (total), 5.6±0.6 and 2.0±0.2 (sn-2 position) for the breast-fed and formula-fed infants, respectively. These studies provide convincing evidence that 16∶0 is absorbed from human milk assn-2 monoacyl-glycerol. The metabolic significance of the differences in positional distribution of fatty acids in the plasma lipids of breast-fed and formula-fed infants is not known.     

Lipid composition of high-melting seed crystals formed during cocoa butter solidification

High-melting seed crystals which form during the early stages of cocoa butter solidification possess a lipid composition different than the cocoa butter from which the seed crystals were grown. Significantly large quantities of glycolipids, 11.1%, and phospholipids, 6.6–8.1%, were found in the high-melting seed crystals along with a dramatic decrease in the simple lipid class. The fatty acids comprising the simple lipid fraction of the seed crystals were considerably more saturated than the fatty acids present in the same fraction of the original cocoa butter. The increase in the degree of saturation was reflected in the triacylglycerol composition. Cocoa butter samples were predominantly monounsaturated triacylglycerols while the seed crystal samples were mainly trisaturated triacylglycerols. The elevated melting point (60–70°C) of the seed crystals was due to the presence of higher melting complex lipids as well as to the increase in saturated triacylglycerol species. As a result of the evidence provided, the high-melting seed crystal is indeed a distinct crystalline entity and not an additional polymorphic form of cocoa butter.     

Quantitation of acyl migration during lipase-catalyzed acidolysis, and of the regioisomers of structured triacylglycerols formed

Various MLM-type (M, medium-chain fatty acids; L, long-chain fatty acids) structured triacylglycerols were produced in pilot- or small-scale packed-bed reactors by lipasecatalyzed acidolysis. The incorporation and acyl migration of octanoic acid were measured by gas chromatography and Grignard degradation, and ranged from 39.0 to 48.7% and 0.6 to 9.3%, respectively. Quantitation of triacylglycerol molecular species was performed by ammonia negative ion chemical ionization (NICI) mass spectrometry (MS). The proportion of ACN (acyl carbon number) 34 species that contained one C₁₈ fatty acid and two C_8∶0′ in samples analyzed, varied from 12.5 to 23.2%. The selected regioisomers MLM and MML within the ACN 34 species group were quantified by NICI tandem MS (MS/MS) and were in the range of 97.1 to 98.4% and 1.6 to 2.9%, respectively. There was no correlation between the level of acyl migration during lipase-catalyzed esterification and the level of regioisomers of the selected MLM-type triacylglycerols in the structured lipid samples.     

cis-5-olefinic unusual fatty acids in seed lipids of gymnospermae and their distribution in triacylglycerols

Open-tubular gas chromatographic analysis of fatty acids in the lipids from the seeds of 20 species of Gymnospermae showed that they all contained nonmethylene-interrupted polyenoic (NMIP) acids as minor components and palmitic, oleic, linoleic and α-linolenic acids as major components. The NMIP acids have an additional 5,6-ethylenic bond in ordinary plant unsaturated fatty acids and the following C₂ elongation acids:cis-5,cis-9-octadecadienoic acid (5,9–18∶2) (I); 5,9,12–18∶3 (II); 5,9,12,15–18∶4, 5,11–20∶2, 5,11,14–20∶3 (III); and 5,11,14,17–20∶4 (IV). The main NMIP acids found in neutral lipids are I in two species ofTaxus, II in seven species of Pinaceae, III in two species of Podocarpaceae,Torreya nucifera, Cycas revoluta, andGinkgo biloba, and III and IV in each of three species of Taxodiaceae, and Cupressaceae. The polar lipids constitute the minor fraction of seed lipids in general. The content and composition of NMIP acids in these lipids differe considerably from those in neutral lipids. Analysis of the partial cleavage products of triacylglycerols showed that the NMIP acids distribute mainly in the 1,3-position.     

Fatty acid composition of rat hearts as influenced by age and dietary fatty acids

Fatty acid composition of neutral and polar lipid fractions from rat hearts was determined in rats of different ages as their diet source changed. Piebald rats were weaned at 21 days and were fed standard lab chow. Lipids from rat hearts, mothers milk and lab chow were purified on a Sephadex G-25 fine column and separated into neutral and polar lipid fractions by silicic acid column chromatography. These lipid fractions were then hydrolyzed and methylated with BF₃ in methanol, prior to gas liquid chromatographic separation on a 1/8 in. × 10 ft aluminum column of 15% EGS on 80–100 mesh acid-washed Chromosorb W. Three major fatty acids in the neutral lipid fraction comprised 72% of total neutral lipid fatty acids from young hearts. At sexual maturity (at least 74 days old) C_18∶1 was the major fatty acid, followed by C_16∶0 and C_18∶0. The same three fatty acids comprised 83% of total polar lipid fatty acids, but C_18∶0 was the major fatty acid, followed by C_16∶0 and C_18∶1. The fatty acid composition of dietary lipids influenced the total neutral lipid fatty acid composition of the rat heart, but had little influence on the fatty acid composition of the polar lipid fraction. Presented in part at the AOCS Meeting, New Orleans, April 1970.     

Accumulation of neutral lipids by human skin fibroblasts: Differential effects of saturated and unsaturated fatty acids

The accumulation of neutral lipids by human skin fibroblasts grown in medium supplemented with fatty acids has been investigated. GM-10 cells incorporated exogenous fatty acids into both phospholipids and neutral lipids. More [¹⁴C] oleate, linoleate, or linolenate was incorporated into triacylglycerol than was [¹⁴C] palmitate or stearate. Supplementation of medium containing delipidized serum with unsaturated fatty acids resulted in far more stimulation of [¹⁴C] glycerol incorporation into triacylglycerol than did supplementation with saturated fatty acids. Palmitate- and stearate-fed cells incorporated sizable amounts of [¹⁴C] fatty acids and [¹⁴C] glycerol into diacylglycerol as well as triacylglycerol, especially at higher fatty acid concentrations. Increased oleate supplementation from 10–300 μM resulted in increased triacylglycerol synthesis and accumulation of discrete cytoplasmic lipid droplets; palmitate concentrations above 70 μm were toxic. Micrographs of the palmitate-fed cells showed electron translucent slits, suggesting solid depositions of saturated fat, rather than the discrete osmiophilic droplets found in oleate-fed cells. Although GM-10 cells can synthesize fully saturated triacylglycerols, these data suggest that in cells fed saturated fatty acids, solid depositions of neutral lipids may sequester diacylglycerols and thus limit triacylglycerol synthesis.     

The lipid composition of microsomal preparations from lactating bovine mammary tissue

The microsomes isolated from lactating bovine mammary tissue contained 4.3 mg lipid per milligram nitrogen. Phospholipids comprised 83% of the lipids. The neutral lipids were composed of triglycerides (20–30%), diglycerides (5–10%), free fatty acids (15–30%, cholesterol (35–40% and cholesterol esters (10–12%, respectively. Phosphatidylcholine was the predominant phospholipid component (>50%), and the remainder consisted of phosphatidylethanolamine (21–13%), phosphatidylserine (4–6%), phosphatidylinositol (8%), sphingomyelin (9%) and lysophosphatidylcholine (2%) respectively. The composition of the microsomal phospholipids was similar to that of isolated mammary cells and tissue homogenates but quite different from milk and fat globule membrane phospholipids. The triglycerides contained short chain fatty acids but their relative concentrations were lower than in milk triglycerides. The various lipid fractions had a variable proportion of saturated fatty acids, i.e., triglycerides (47.7%), diglycerides (86.7%), free fatty acids (70.6%), phosphatidylcholine (50.6%), phosphatidylethanolamine (50.8%), phosphatidylserine (35.3%), phosphatidylinositol (40.5%) and sphingomyelin (82.3%), respectively. The molecular distribution of fatty acids in the microsomal triglycerides and phosphatidylcholine was similar to that occurring in milk, i.e., the short chain and unsaturated fatty acids were concentrated in the primary positions (sn1 andsn3) of the triglycerides, and the unsaturated acids were preferentially located in positionsn2 of the phosphatidylcholine. The compositional data indicate that mammary microsomes are not the direct source of the phospholipids of the milk fat globule.     

Linoleoyl-enriched triacylglycerol species increase in maternal liver during late pregnancy in the rat

In view of the previously reported changes in the fatty acid composition of maternal liver triacylglycerols in late pregnancy, changes in the composition of maternal liver triacylglycerol species were assessed in rats fed a semipurified diet during pregnancy. Between day 18 and day 21 of pregnancy, total maternal liver triacylglycerols increased by 50%. Triacylglycerol species with a total acyl carbon number (C) of 50 or 60 (C50, C60) remained unchanged while C48 and C52–C58 were relatively increased. The individual triacylglycerol species containing one, two or three linoleoyl moieties were incompletely recovered using a polar high temperature gas-liquid chromatography (GLC) column. Nevertheless, at day 21 compared to day 18, the linoleoyl-containing species were relatively increased by 62–463%, while tripalmitin was decreased by 38%. Our data suggest that despite an adequate intake of linoleic acid (25 g/kg in the diet), maternal hepatic triacylglycerol content of linoleic acid decreased during mid-pregnancy but increased significantly toward term possibly in preparation for the transfer of linoleic acid to the neonate during lactation.     

Composition of the lipids in human milk: A review

Recent publications on the composition of human milk are reviewed. The importance of proper sampling is discussed. Fat contents of 2.6–4.5% and cholesterol amounts of 200–650 mg/100 g fat were reported. The phytosterols in milk were increased by the consumption of these sterols. Phytosterols could contribute to the “total cholesterol” in milk if analyses are done colorimetrically. The fatty acid composition is remarkably uniform unless bizarre diets are consumed; the amounts of linoleic acid vary the most. Phospholipids contained more long chain polyunsaturated fatty acids than triacylglycerols. Scientific Contribution No. 786, Storrs Agricultural Experiment Station, University of Connecticut, Storrs, CT 06268.     

Site-specific differences in the fatty acid composition of human adipose tissue

The fatty acid composition of triacylglycerols from fifteen distinct adipose depots taken from each of seven adult male human subjects was compared. Oleic, palmitic, linoleic, stearic, myristic, palmitoleic and vaccenic acids accounted for more than 90% of the triacylglycerol fatty acids in all sites from all subjects; a number of other fatty acids were also identified and quantified. There were large differences in theaverage fatty acid composition between individual subjects. There were no site-specific differences in the proportions of myristic (3.8–4.7% of triacylglycerol fatty acids), palmitic (23–29%), linoleic (6.7–9.8%) or vaccenic (4.1–4.7%) acids or in the proportions of any of the less abundant fatty acids. There were some significant site-specific differences in the proportions of palmitoleic, oleic and stearic acids. The calf depot contained more palmitoleic acid (6.41±1.09%) than the trapezius (3.12±0.55%), perirenal (3.59±0.50%) and mesenteric (3.70±0.43%) depots, more oleic acid (42.13±1.27%) than the trapezius (36.03±2.18%), perirenal (36.50±1.56%) and breast (37.13±1.55%) depots and less stearic acid (5.18±0.89%) than the trapezius (8.57±0.97%), perirenal (8.49±0.75%), mesenteric (7.87±0.42%), breast (8.02±0.75%) and clavicular (8.34±0.78%) depots. The buttock depot contained less stearic acid (6.06±0.65%) than the perirenal, mesenteric and clavicular depots, while the anterior thigh depot contained less stearic acid (6.07±0.70%) than the perirenal depot. These findings indicate that, while most human adipose depots differ little in fatty acid composition, some sites, in particular the calf, perirenal, trapezius and mesenteric depots, have site-specific properties.     

Polyunsaturated fatty acids and neutral lipids in developing larvae of the oyster,Crassostrea virginica

The fatty acid composition of oyster larvae at various stages, as well as of the algal diet, were determined by gas liquid chromatography (GC). Saturated fatty acids are the major fatty acid components in all larval stages and account for 34–62%, 30–35% and 35–81% of the neutral, polar and total lipids of algal-fed larvae respectively. Weight percentage of saturated fatty acid in “starved” larvae was consistently higher (63–81%) during the whole period. The total polyunsaturated fatty acids were higher in the polar lipids than in the neutral lipids. The concentration of the ω3 fatty acids also was comparatively higher in the polar lipids than in the neutral lipids. In the total and neutral lipid fractions, the weight percentage of polyunsaturated and ω3 fatty acids was higher in the eyed than in the pre-eyed (pediveliger) larvae. Eicosapentaenoic acid (20∶5ω3) and 22∶6ω3 were not detected in lipids of “starved” and young larvae. There was an accumulation of 20∶5ω3, 22∶6ω3, and total ω3 fatty acids in the older larvae. Lipid classes were separated by thin layer chromatography (TLC). There was no qualitative change in lipid composition during larval development, but a marked increased of triacylglycerol in larvae up to the stage of maturation in algae-fed larvae. Contribution number 1195 of the Virginia Institute of Marine Science, Gloucester Point, VA 23062     

Influence of triacylglycerol structure and fatty acid profile of dietary fats on milk triacylglycerols in the rat. A two-generation study

We investigated the influence of dietary fatty acid profile and triacylglycerol structure on the fatty acid profile and triacylglycerol structure of milk lipids in two generations of rats. Three groups of rats received diets containing 20% fat of which approximately 20% was n-3 fatty acids located in different positions of the triacylglycerol: a fish oil-based diet [docosahexaenoic acid (22:6n-3) predominantly in thesn-2 position], a seal oil-based diet (22:6n-3) predominantly in thesn-1/sn-3 position or a plant oil-based diet [α-linolenic acid (18:3n-3) distributed evenly between the three positions]. This design allowed us to investigate (i) the effect of the triacylglycerol structure of the dietary fat; (ii) the effect of receiving the n-3 fatty acids as long-chain derivatives or as the precursor, 18:3n-3; and (iii) the long-term effects over two generations. The fatty acid profiles of the milk lipids largely reflected the diets, but in the second generation, the level of medium-chain fatty acids was higher (P<0.05) in the milk from rats fed the fish oil diet (24%) compared with the other dietary groups (15 and 18%). This suggests an increased endogenous synthesis of fatty acids in the mammary glands of the fish oil-fed rats. The levels of long-chain n-3 fatty acids in milk were higher (P<0.05) in rats fed maire n-3 fatty acids in milk were higher (P<0.05) in rats fed marie oils (8–12%) compared with rats fed vegetable oil (1%) in both generations. The level of long-chain n-3 fatty acids was significantly higher in the milk from the fish oil-fed rats (12.3%) compared to the seal-oil fed rats (8.0%) in the first generation, but not in the second generation (8.9 vs. 9.1%). The general structure of milk triacylglycerols was maintained in the three experimental groups with 16:0 acylated in thesn-2 position and 18:1 in thesn-1/sn-3 positions. The triacylglycerol structure of mammalian milk appears to be conserved even during extreme dietary manipulation over two generations and an extensive enrichment with long-chain n-3 polyunsaturated fatty acids requires their presence in the diet.     

Lipid components and enzymatic hydrolysis of lipids in muscle of Chinese freshwater fish

The lipid and fatty acid composition of muscle of 10 species of freshwater fish obtained from a market of Shanghai City was examined. Total lipids (TL) ranged over 0.9–4.7% of muscle for all samples. The content of triacylglycerol (TG) in muscle ranged over 0.2–3.4% and that of polar lipids (PL) was 0.5–1.3%. Differences of TL content were dependent on TG contents. The predominant important fatty acids (>10% of the total fatty acids in TL) were 16∶0 and 18∶1n−9 with some 16∶1n−7, 18∶2n−6, and 22∶6n−3. The polyunsaturated fatty acids (PUFA) content was 10.2–43.4%, and especially Chinese sea bass contained above 20% of 22∶6n−3 in the total fatty acids. There were higher levels of PUFA such as 20∶5n−3 and 22∶6n−3 in PL than in neutral lipids. Muscle of the silver carp was stored at 20°C, and changes of lipid classes during storage were examined. Free fatty acids increased, and PL decreased during storage. This phenomenon was inhibited by heating the muscle, suggesting that lipid hydrolysis by phospholipase occurred in silver carp muscle.