Positional specificity of gastric hydrolysis of long-chain n-3 polyunsaturated fatty acids of seal milk triglycerides

Influence of Dietary Triacylglycerol Structure on the Accumulation of Docosahexaenoic Acid [22:6(n-3)] in Organs in a Short-Term Feeding Trial with Mildly Omega-3 Deficient Rats

SCOPE

To study the effect of positional distribution of docosahexaenoic acid (DHA) in dietary triacylglycerols (TAG) on the tissue fatty acid content and composition of mildly (n-3) deficient rats.

METHODS AND RESULTS

In a 5-day feeding trial, mildly (n-3) deficient rats received 360 mg daily structured TAGs: sn-22:6(n-3)-18:0-18:0, sn-18:0-18:0-22:6(n-3), sn-18:0-22:6(n-3)-18:0, or tristearin. A fifth group receives standard (n-3) adequate feed AIN-93G from birth till the end of the trial. The DHA-fed groups show significantly higher DHA levels in the liver and visceral fat compared to the tristearin or normal feed groups showing that the dose and the short feeding period of DHA were sufficient to restore the DHA content in the organs of (n-3) deficient rats. Feeding sn-1 DHA resulted in higher levels of DHA in the liver TAG compared to sn-3 DHA feeding, although the difference did not reach statistical significance.

CONCLUSION

These findings indicated a possible difference in the tissue accumulation and/or metabolic fate of DHA from the sn-1 and sn-3 positions of TAG.

Characterization of blubber fatty acid signatures in northern elephant seals (Mirounga angustirostris) over the postweaning fast

Phocids routinely fast for extended periods. During these fasts, energetic requirements are met primarily through the catabolism of blubber lipid. To assess whether fatty acid (FA) composition changes during the postweaning fast in northern elephant seals, blubber biopsies were acquired longitudinally from 43 pups at 2.3 ± 1.5 and 55.2 ± 3.7 days postweaning in 1999 and 2000. At weaning, short-chain monounsaturated FA (SC-MUFA, ≤18 carbons) dominated the blubber while saturated FA (SFA) were found in the next highest proportion. The major FA (all ≥1 % by mass) comprised approximately 91 % of total blubber FA. In both years, 18:1n-9 and 16:0 were the most prevalent FA. Major FA mobilized during the fast consisted of polyunsaturated FA (PUFA), SFA, and SC-MUFA. Long-chain MUFA (>18 carbons) tended to be conserved. The fractional mobilization value of 20:5n-3 was the highest, resulting in significant reductions of this PUFA. Although concentrations of some blubber FA changed significantly during the postweaning fast, the general FA signature of blubber was similar at weaning and near the end of the fast. Changes in some FA differed across years. For example, the concentration of 20:4n-6, a minor PUFA, was significantly reduced in 1999 but not in 2000. FA mobilization patterns in northern elephant seal pups are somewhat similar to those reported previously for other fasting phocids and terrestrial mammals, though there are some notable differences. Differences in FA mobilization patterns across mammalian species may be related to differences in diets, geographical distribution, environmental factors, physiological adaptations, and life history stage.

The intramolecular position of docosahexaenoic acid in the triacylglycerol sources used for pediatric nutrition has a minimal effect on its metabolic use

Docosahexaenoic acid (DHA) plays an important role in normal development of the brain and retina in the human. In utero, DHA is incorporated in the fetus, and its accretion continues throughout early postnatal life. Although human breast milk contains this fatty acid, several organizations recommend supplementing infant formulas with DHA for infants and premature infants. Traditionally, certain types of fish oil have been used for fortifying some infant formulas, but with the decline in world fisheries, the search for alternative sources of DHA continues. Among the viable ingredient sources of DHA is oil derived from single-cell organisms (marine microorganisms); however, these oil sources display different positional specificity of DHA in the glycerol lipids compared with that found in human breast milk lipids. In the latter, the DHA is mainly esterified in the central position of the glycerol backbone. Because of these differences in human milk and oils derived from single-cell organisms, recent research in biotechnology has focused on developing new structured triacylglycerols with an intramolecular structure resembling that found in human milk lipids. This research is justified by the potential differences in metabolism of DHA based on the hypothetical bioavailability and benefits in DHA found in human milk lipids. Presented herein is a review of the published research on the metabolism of DHA from different triacylglycerol sources including in vitro studies and animal studies. Despite small differences observed in digestion, the current data reveal a minimal effect on the parameters of development studied for the intramolecular position in which DHA is esterified.

Stratification and intra- and inter-specific differences in fatty acid composition of common dolphin (Delphinus sp.) blubber: Implications for dietary analysis

Sixty-five fatty acids were quantified in the blubber of common dolphins (Delphinus delphis, D. capensis) incidentally caught off the coast of southern California. Dolphins were grouped by sex, reproductive status and species, and a blubber sample was collected at a mid-lateral site located caudal to the trailing edge of the dorsal fin. Samples were divided horizontally into inner, middle and outer layers and gradients in fatty acid content (mass percent) were observed across the depth of the blubber. Levels of monounsaturated fatty acids were greatest in the outer layer, whereas levels of saturated and polyunsaturated fatty acids were greatest in the inner layer. Degree of stratification was greatest in sexually mature dolphins. Blubber of sexually immature, but physically mature, male dolphins was also highly stratified, suggesting that this difference may be attributed to differences in diet. Classification and regression tree analysis resulted in the fewest misclassifications when dolphins were grouped by species, possibly indicating that these closely related animals forage on different prey species. Dietary-derived fatty acids were typically selected as splitting criteria in classification and regression tree analyses, suggesting that the observed differences in fatty acid composition between the various groups of dolphins may be attributed to differences in diet.

Dynamics of blood chylomicron fatty acids in a marine carnivore: implications for lipid metabolism and quantitative estimation of predator diets

Blubber fatty acid(s) (FA) signatures can provide accurate estimates of predator diets using quantitative FA signature analysis, provided that aspects of predator FA metabolism are taken into account. Because the intestinal absorption of dietary FA and their incorporation into chylomicrons (the primary transport lipoproteins for dietary FA in the blood) may influence the relationship between FA composition in the diet and adipose tissue, we investigated the metabolism of individual FA at these early stages of assimilation. We also investigated the capacity of chylomicron signatures to provide quantitative estimates of prey composition of an experimental meal. Six captive juvenile grey seals (Halichoerus grypus) were fed either 2.3 kg (n = 3) or 4.6 kg (n = 3) of Atlantic herring (Clupea harengus). Although chylomicron FA signatures resembled diet signatures at all samplings, absolute differences were smallest at 3-h post-feeding, when chylomicrons were likely largest and had the greatest ratio of triacylglycerol to phospholipid FA. Specific FA that differed significantly between diet and chylomicron signatures reflected either input from endogenous sources or loss through peroxisomal beta-oxidation. When these aspects of metabolism were accounted for, the quantitative predictions of diet composition generated using chylomicron signatures were extremely accurate, even when tested against 28 other prey items.

Vitamin E status and the dynamics of its transfer between mother and pup during lactation in grey seals (Halichoerus grypus)

Concentrations of vitamin E, a powerful antioxidant, were measured in milk and serum of 18 grey seal (Halichoerus grypus) mothers and in the serum of their pups sampled up to 6 times between parturition and weaning on the Isle of May, Scotland, in 1998 and 2000. The vitamin E concentration in colostrum (89.4 ± 22.5 mg/kg milk; mean ± SD) was 4.5 times greater than that in later milk (20.9 ± 5.0 mg/kg milk). It then remained constant until the end of lactation. The decline in concentration of vitamin E in grey seal milk corresponded to a drop in the vitamin E concentration in mothers' serum between parturition (14.0 ± 4.8 mg/L serum) and the second half of the lactation period during which the serum vitamin E concentration remained stable (9.6 ± 3.2 mg/L serum). Circulating vitamin E concentrations varied significantly among mothers but there was no relationship with mother's age. Despite these differences between mothers, individuals produced milk with very similar vitamin E concentrations. The vitamin E concentration in grey seal pups' serum was low at birth (lowest concentration 3.1 mg/L serum) but increased sharply to a peak around days 1–3 (31.2 ± 5.2 mg/L serum). It then fell, before stabilizing until the end of lactation (21.1 ± 4.5 mg/L serum), reflecting the changes reported in the milk.

JE, Smith LK. Changes in the diet of free-ranging black bears in years of contrasting food availability revealed through milk fatty acids

We studied patterns of fatty acid signatures in milks and major foods of free-ranging lactating black bears (Ursus americanus) in western Massachusetts to examine the degree to which changes in milk fatty acids could be related to measured changes in food availability and scat analysis, and to assess whether fatty acids could be used to infer aspects of the diets of individuals. Milk samples (n = 45) were obtained from 17 individual bears during years of contrasting hard-mast abundance. Paired winter-den and spring-foraging samples were obtained from females in 1994 (n = 10), 1995 (n = 2), and 1996 (n = 8). In seven of these females, paired den and foraging samples were collected in both 1994 and 1996, representing two consecutive lactation periods. Milk fatty acid patterns indicated that the diet of individuals responded strongly to food availability both prior to denning and during spring foraging. During spring foraging, although females likely continued to mobilize stored fat, the greatest contribution to milk fatty acids appeared to be from dietary fat intake. Hence, qualitative changes in spring diets of individual bears could be reasonably inferred from milk fatty acid signatures. During the year of lowest hard-mast abundance, milk fatty acid patterns suggested that females relied predominantly on a diet of skunk cabbage, although this varied among individuals. This study demonstrates that milk fatty acid signatures can be used to provide insight into the nutritional ecology of bears at the level of the individual.

Comparison of the Bligh and Dyer and Folch methods for total lipid determination in a broad range of marine tissue

For many studies, it is important to measure the total lipid content of biological samples accurately. The Bligh and Dyer method of extraction was developed as a rapid but effective method for determining total lipid content in fish muscle. However, it is also widely used in studies measuring total lipid content of whole fish and other tissues. Although some investigators may have used modified Bligh and Dyer procedures, rarely have modifications been specified nor has their effectiveness been quantitatively evaluated. Thus, we compared this method with that of the classic Folch extraction in determining total lipid content of fish samples ranging from 0.5 to 26.6% lipid. We performed both methods as originally specified, i.e., using the chloroform/methanol/water ratios of 1:2:0.8 and 2:2:1.8 (before and after dilution, respectively) for Bligh and Dyer and of 8:4:3 for Folch, and with the initial solvent/sample ratios of (3+1):1 (Bligh and Dyer) and 20:1 (Folch). We also compared these with several other solvent/sample ratios. In samples containing <2% lipid, the results of the two methods did not differ. However, for samples containing >2% lipid, the Bligh and Dyer method produced significantly lower estimates of lipid content, and this underestimation increased significantly with increasing lipid content of the sample. In the highest lipid samples, lipid content was underestimated by up to 50% using the Bligh and Dyer method. However, we found a highly significant linear relationship between the two methods, which will permit the correction of reported lipid levels in samples previously analyzed using an unmodified Bligh and Dyer extraction. In the future, modifications to procedures and solvent/sample ratios should be described.

Effect of a low-Fat diet on body composition and blubber fatty acids of captive juvenile harp seals (Phoca groenlandica)

We investigated the effects of a change from a high-fat diet to a low-fat diet of differing fatty acid (FA) composition on the body composition and blubber FA of five captive juvenile harp seals. Seals that had been maintained for 1 yr on a diet of Atlantic herring (>/=9% fat) were switched to a diet of Atlantic pollock (1. 7% fat) for 30 d. On days 0, 14, and 30, mass and body composition (using isotope dilution) were measured, and blubber biopsies (5 cmx6 mm) were taken for FA analysis. Fat accounted for 38%-49% of body mass at the start of the experiment. When switched to the pollock diet, and despite food intakes averaging 6.5 kg/d (32.3 MJ/d), body fat declined by an average of 6.4 kg or by 32% over the 30-d experiment. In contrast, body protein increased in direct relation to protein intake (r2=0.836, P=0.030). Despite substantial loss of body fat, blubber FA signature changed significantly to reflect the changes in dietary intake of FA, and the deposition of FA was quantifiably predictable. Our results suggest that young growing phocids are unable to maintain body fat stores on low-fat diets even when protein intakes are high. This may have significant implications for juvenile pinniped survival in the wild. In addition, turnover and deposition of dietary FA in blubber takes place in nonfattening seals.

Vitamin E and vitamin A contents, fatty acid profiles, and gross composition of harp and hooded seal milk through lactation

This study reports fatty acid profiles and vitamin A and vitamin E contents of the milk of the harp seal (Phoca groenlandica) and hooded seal (Cystophora cristata) throughout the lactation period, as well as standard compositional analyses. The milk for this study was collected from harp and hooded seals breeding on the pack ice in the Gulf of St. Lawrence. Mother-pup pairs were serially captured, or point-sampled, in order to obtain milk samples during different lactation stages. Milk lipids showed the respective species' typical patterns during lactation, with a significant increase for harp seal milk and a relatively constant value for hooded seal milk. The profiles of most of the milk fatty acids remained relatively stable over the course of lactation in both species. Vitamin A content was also quite stable through lactation. By contrast, vitamin E content underwent a dramatic drop between the day of birth and early lactation for harp seals and from birth to midlactation for hooded seals. It then continued to decrease at a slower rate until the end of lactation in both species. The highest vitamin E content of colostrum reached 125 mg/kg of milk for harp seals and 200 mg/kg of milk for hooded seals. These concentrations subsequently dropped to 20-50 mg/kg of milk by early or mid lactation. These changes in this lipophilic, antioxidizing vitamin were not correlated with milk lipid content or its polyunsaturated fatty acid profiles.

Enhancement of both reaction yield and rate of synthesis of structured triacylglycerol containing eicosapentaenoic acid under vacuum with water activity control

Production of structured triacylglycerols (sTAG) containing eicosapentaenoic acid (EPA) at the sn-1 (or 3) position using Lipozyme in a solvent-free system was studied. Optimal water activity (a(w)) for the synthesis of the sTAG was investigated. Vacuum was applied to shift reaction equilibrium toward the synthesis reaction by removing by-products. During vacuum application, the water level of the reaction system was controlled at the optimal level by addition of a suitable amount of water at a predetermined interval. Intermittent periodic addition of a suitable amount of water into the reaction mixture made the reaction rate faster than that without adding water. A molar yield of 89.7% of the targeted sTAG was obtained after 16 h reaction with a(w) control during the vacuum application as compared with the yield of 87.0% after 24 h of reaction without a(w) control during the vacuum application.

Milk fatty acid signatures indicate both major and minor shifts in the diet of lactating Antarctic fur seals

Fatty acid signature analysis is based on the principle that unique arrays of fatty acids within groups of organisms can be transferred, largely unaltered, up the marine food chain and thus may be an indicator of diet composition. We applied fatty acid signature analysis to milks collected from Antarctic fur seals (Arctocephalus gazella) at South Georgia in 1990–1991, during the perinatal period (N = 19) and subsequently during early (N = 11), mid (N = 11), and late (N = 8) foraging trips. In lactating otariid females, milk fatty acids secreted during the perinatal fast are derived largely from blubber mobilization and thus are influenced by dietary history prior to parturition. Conversely, milk fatty acids secreted during foraging trips are derived primarily from immediate dietary intake. The fatty acid signature of perinatal milks was significantly different from that of all other milks, suggesting differences in the prepartum diet when females are away from the breeding grounds. At the onset of foraging periods, the fatty acid composition of milks' changed dramatically to reflect a diet composed mainly of krill. However, during late foraging periods, milk fatty acids again changed from those of early and mid foraging, and suggested a predominance of teleost fish in the diet. These findings were consistent with independent assessments of diet by faecal analysis and indicate the potential value of fatty acid signature analysis in studying foraging ecology in free-ranging pinnipeds.

Chylomicron triacylglycerol fatty acids in suckling northern elephant seals (Mirounga angustirostris) resemble the composition and the distribution of fatty acids in milk fat

Following birth, the northern elephant seal (Mirounga angustirostris) pups rapidly gain weight by ingesting milk with a high fat content, as much as 50%. To better understand the metabolism of the pups during the suckling period, the positional distributions of triacylglycerol fatty acids in both the milk and chylomicra were determined. Extracts of enzymatically digested lipids were separated by thin layer chromatography and the constituent fatty acids were separated and quantified by gas liquid chromatography. Over 84% of the fatty acids were either monoenoic or saturated, with the ratio of monoenoic to saturated fatty acids ranging between 2.9-4.0. Positional distributional analyses revealed that the very long chain monoenoics (20:1 and 22:1) were located primarily at the sn-1,3 positions of milk triacylglycerols. In the interval between the onset of lactation to the time of weaning, the content of these very long chain monoenoic fatty acids at the sn-1,3 positions increased from 13-37%. At the sn-2 position, the percentage of 18:1 was 3-5-fold higher than 16:1. Analyses indicated that the triacylglycerols in both milk and suckling pup chylomicra were similar. This particularly was true for the distributions at the sn-2 position, indicating that milk fats are being absorbed primarily via the 2-monoacylglycerol pathway.

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 the sn-2 position], a seal oil-based diet (22:6n-3) predominantly in the sn-1/sn-3 position, or a plant oil-based diet [alpha-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 (ii) 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 marine 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 the sn-2 position and 18:1 in the sn-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.

Lipoprotein lipase activity and its relationship to high milk fat transfer during lactation in grey seals

Lipoprotein lipase regulates the hydrolysis of circulating triglyceride and the uptake of fatty acids by most tissues, including the mammary gland and adipose tissue. Thus, lipoprotein lipase is critical for the uptake and secretion of the long-chain fatty acids in milk and for the assimilation of a high-fat milk diet by suckling young. In the lactating female, lipoprotein lipase appears to be regulated such that levels in adipose tissue are almost completely depressed while those in the mammary gland are high. Thus, circulating fatty acids are directed to the mammary gland for milk fat production. Phocid seals serve as excellent models in the study of lipoprotein lipase and fat transfer during lactation because mothers may fast completely while secreting large quantities of high fat milks and pups deposit large amounts of fat as blubber. We measured pup body composition and milk fat intake by isotope (deuterium oxide) dilution and plasma post-heparin lipoprotein lipase activity in six grey seal (Halichoerus grypus) mother-pup pairs at birth and again late in the 16-day lactation period. Maternal post-heparin lipoprotein lipase activity increased by an average of four-fold by late lactation (P = 0.027), which paralleled an increase in milk fat concentration (from 38 to 56%; P = 0.043). Increasing lipoprotein lipase activity was correlated with increasing milk fat output (1.3-2.1 kg fat per day) over lactation (P = 0.019). Maternal plasma triglyceride (during fasting) was inversely correlated to lipoprotein lipase activity (P = 0.027) and may be associated with the direct incorporation of long-chain fatty acids from blubber into milk. In pups, post-heparin lipoprotein lipase activity was already high at birth and increased as total body fat content (P = 0.028) and the ratio of body fat: protein increased (P = 0.036) during lactation. Although pup plasma triglyceride increased with increasing daily milk fat intake (P = 0.023), pups effectively cleared lipid from the circulation and deposited 70% of milk fat consumed throughout lactation. Lipoprotein lipase may play an important role in the mechanisms involved with the extraordinary rates of fat transfer in phocid seals.

Lipid metabolism in pediatric nutrition

The abrupt transition from carbohydrate to fat as the main energy source that occurs at birth is not matched by commensurate endogenous fat-digesting capacity in the newborn. Newborn infants are, however, able to digest fat efficiently through the activities of gastric lipase and the exogenous digestive lipase of human milk, which compensate for the low activity of pancreatic lipase. Fat absorption is well-developed at birth and is commensurate with the high fat intake of the infant. Tissue uptake of dietary fat is also adequate, based on sufficient lipoprotein lipase (above 26 to 27 weeks' gestation) and rapid postnatal increase of lecithin:cholesterol acyl transferase, the enzymes that regulate tissue uptake of circulatory lipoprotein triglyceride and cholesterol.

Prenatal and postnatal transfer of fatty acids from mother to pup in the hooded seal

Unlike most mammals, hooded seal (Cystophora cristata) pups are born with a substantial layer of adipose tissue. Subsequently, during the brief lactation period of only 4 days, fasting mothers mobilize enormous amounts of lipid from blubber and secrete milk (60% fat) at rates of 10 kg.day-1. Pups gain 7 kg.day-1 due primarily to the deposition of fat in blubber. We measured blubber content and fatty acid composition of blubber and milk in hooded seal mother-pup pairs at birth and over the 4-day lactation period to examine the nature and source of fetal lipids, the incorporation of maternal blubber fatty acids into milk lipid, and patterns of fatty acid deposition in suckling young. The fatty acid composition of the blubber of the newborn was notably different from that of its mother. Fetal deposition was likely due to a combination of both fetal synthesis and direct placental transfer of maternal circulating fatty acids. The blubber of the newborn was characterized by high levels (> 90% of total fatty acids) of saturated and monounsaturated fatty acids of primarily endogenous origin. In particular, the fetus appeared to have high delta-9 desaturase activity as evidenced by the large amounts of 14:1n-5 (4.2%) and 16:1n-7 (37.0%) in newborn blubber compared to maternal blubber (0.2% and 14.1%, respectively). Nevertheless, essential and long-chain polyunsaturated fatty acids of the n-3 and n-6 families, which could only have originated by direct transfer from the mother, comprised > 7% of pup blubber fatty acids and indicated greater rates of placental transfer than found in humans. In hooded seal mothers, rapid lipid transfer during the brief lactation period appeared to be facilitated by direct incorporation of mobilized fatty acids into milk. Although some differences in proportions of specific fatty acids were found between milk and maternal blubber, most of these differences declined over the course of lactation. However, selective mobilization of 20:5n-3 from maternal blubber into milk was apparent throughout lactation and resulted in elevated levels in pup blubber at weaning compared to maternal blubber. Ingested fatty acids were deposited directly and without modification into the blubber of pups, and by 4 days the fatty acid composition of pup blubber was virtually identical to that of the milk consumed.

Lymphatic absorption of n - 3 polyunsaturated fatty acids from marine oils with different intramolecular fatty acid distributions

Male Wistar rats were given 0.5 ml of either fish oil or seal oil intragastrically. The intramolecular fatty acid distributions of the triacylglycerols administered were determined by non-specific Grignard degradation followed by isolation and analysis of the 2-monoacylglycerols. The n - 3 polyunsaturated fatty acids (PUFAs), especially eicosapentaenoic acid (20:5(n - 3)) and docosahexaenoic acid (22:6(n - 3)), were located in outer positions (sn-1/3) in the seal oil triacylglycerols whereas the sn-2 position of fish oil triacylglycerols was enriched in 20:5(n - 3) and 22:6(n - 3). The mesenteric lymph was collected over the following 24 h and the absorption patterns of n-3 PUFAs were determined. In the lymph, the n - 3 fatty acids characteristic of the marine oils rapidly increased both with regard to mole percentage and transport (micrograms/min). There were, however, no overall significant differences in the absorption patterns over a 24 h period. The ratio between mole percentage in the oil and mole percentage in the lymph calculated at the steady-state period was significantly greater for both 20:5(n - 3) and 22:6(n - 3) following fish oil administration compared with seal oil. Initially, the recovery of n - 3 PUFAs as a percentage of the total amount transported over the experimental period was higher following injection of fish oil than seal oil but seal oil resulted in greater recovery in the last two fractions at 8 and 24 h post injection, respectively. This indicated that n - 3 PUFAs from fish oil may have been better absorbed in the initial period of digestion but overall the structure of dietary triacylglycerols had negligible effects on the assimilation of n - 3 PUFAs when these were administered as native marine oils.

Fatty acid and positional selectivities of gastric lipase from premature human infants: in vitro studies

Gastric lipase activity in aspirates from premature human infants was tested for fatty acid and positional selectivity using racemic diacid triacylglycerols (TG) as substrates. The resulting free fatty acids and monoacylglycerols (MG) were recovered and analyzed. Octanoic acid (8:0) and decanoic acid (10:0) were hydrolyzed with a preference of 61.5:1 and 2.4:1 compared to palmitic acid (16:0) from rac-16:0-8:0-8:0 and rac-16:0-10:0-10:0, respectively. The ratio of lauric acid (12:0) to oleic acid (18:1) hydrolyzed from rac-18:1-12:0-12:0 was 13:1. Myristic acid (14:0), 18:1 and linoleic acid (18:2) were released at similar rates. These data and the composition of the MG suggest that, in vitro, the lipase is selective for shorter chain fatty acids and for fatty acids on the primary positions of the TG backbone.

Triacylglycerol structure of human colostrum and mature milk

Because triacylglycerol (TAG) structure influences the metabolic fate of its component fatty acids, we have examined human colostrum and mature milk TAG with particular attention to the location of the very long chain polyunsaturated fatty acid on the glycerol backbone. The analysis was based on the formation of various diacylglycerol species from human milk TAG upon chemical (Grignard degradation) or enzymatic degradation. The structure of the TAG was subsequently deduced from data obtained by gas chromatographic analysis of the fatty acid methyl esters in the diacylglycerol subfractions. The highly specific TAG structure observed was identical in mature milk and colostrum. The three major fatty acids (oleic, palmitic and linoleic acids) each showed a specific preference for a particular position within milk TAG: oleic acid for the sn-1 position, palmitic acid for the sn-2 position and linoleic acid for the sn-3 position. Linoleic and alpha-linolenic acids exhibited the same pattern of distribution and they were both found primarily in the sn-3 (50%) and sn-1 (30%) positions. Their longer chain analogs, arachidonic and docosahexaenoic acids, were located in the sn-2 and sn-3 positions. These results show that polyunsaturated fatty acids are distributed within the TAG molecule of human milk in a highly specific fashion, and that in the first month of lactation the maturation of the mammary gland does not affect the milk TAG structure.

Fatty acid composition of black bear (Ursus americanus) milk during and after the period of winter dormancy

Black bears give birth and lactate during the 2-3-mon fast of winter dormancy. Thereafter the female emerges from the den with her cubs and begins to feed. We investigated fatty acid patterns of milk from native Pennsylvania black bears during the period of winter dormancy, as well as after den emergence. Throughout winter dormancy, milk fatty acid composition remained relatively constant. The principal fatty acids at all times were 14:0, 16:0, 16:1, 18:0, 18:1, 18:2n-6, 18:3n-3 and 20:4n-6. After den emergence, large changes occurred in almost all the fatty acids, particularly in 18:2n-6 and 18:3n-3. Large variability among the active free-ranging animals likely reflected differences in diet. In a carnivore, with apparently limited de novo synthesis of fatty acids, milk fatty acid composition may be affected by factors such as transition from reliance on stored lipids to feeding, and by temporal changes in dietary intake.