The hydrogenation of the series of methylene-interrupted cis,cis-octadecadienoic acids by pure cultures of six rumen bacteria

Effects of unsaturation of long-chain fatty acids on rumen protozoal engulfment and microbial protein recycling in protozoa in vitro

The present study investigated the effects of long-chain fatty acids with different degrees of unsaturation on rumen protozoal engulfment and microbial protein recycling by protozoa in vitro. The seven experimental treatments included stearic acid (C18:0, Group A), oleic acid (C18:1, n-9, Group B), linoleic acid (C18:2, n-6, Group C), α-linoleic acid (C18:3, n-3, Group D), arachidonic acid (C20:4, n-6, Group E), eicosapentaenoic acid (C20:5, n-3, Group F) and calcium palmitate (C16:0, control group, G), each being included at 3% (w/w) in the total culture substrate containing starch, xylan, araban, glucan, mannan, cellulose, pectin, lignin, urea and casein. Three goats fitted with rumen cannula were used to provide rumen fluid. The incubation medium was collected for the measurement of engulfing rate of bacteria by protozoa and microbial biomass after 24 h of in vitro incubation. The results showed that the bacterial density of Group D (5.75 × 109 cells/mL) was significantly higher than that of Groups A, B, E, F and G (P < 0.05), but that of the control (Group G) as well as those of Groups A and B were lower than those of Groups D and C (P < 0.05). Similarly, the bacterial protein was the highest in Group D and the lowest in Group G. The number of bacteria engulfed by protozoa per millilitre were the highest in the Control group G (847 × 105 cells/(mL.h)) and the lowest in Group D (392 × 105 cells/(mL.h)). The recycling rate of bacterial cells was lowest in Group D (0.68%) and the recycling time of bacterial cells was the longest (147 h). The quantity of protein recycled was lowest in Group D and highest in Group G, which derived from the number of bacterial cells engulfed. Therefore, it was concluded that the effects of long-chain fatty acids on rumen microbial protein recycling and microbial protein synthesis mainly relate to their degree of unsaturation, with α-linoleic acid possessing a better ability to suppress bacterial-cell (by protozoa) and reduce protein yield.

Evidence for the Initial Steps of DHA Biohydrogenation by Mixed Ruminal Microorganisms from Sheep Involves Formation of Conjugated Fatty Acids

Incubation of DHA with sheep rumen fluid resulted in 80% disappearance in 6 h. The products were analyzed as their fatty acid (FA) methyl esters by GC-FID on SP-2560 and SLB-IL111 columns. The GC-online reduction × GC and GC-MS techniques demonstrated that all DHA metabolites retained the C22 structure (no evidence of chain-shortening). Two new transient DHA products were identified: mono-trans methylene interrupted-DHA and monoconjugated DHA (MC-DHA) isomers. Identification of MC-DHA was confirmed by their predicted elution using equivalent chain length differences from C18 FA, their molecular ions, and the 22:5 products formed which were the most abundant at 6 h. The 22:5 structures were established by fragmentation of their 4,4-dimethyloxazoline derivatives, and all 22:5 products contained an isolated double bond, suggesting formation via MC-DHA. The most abundant c4,c7,c10,t14,c19-22:5 appeared to be formed by unknown isomerases. Results suggest that the initial biohydrogenation of DHA was analogous to that of C18 FA.

Catalytic production of conjugated fatty acids and oils

The reactive double bonds in conjugated vegetable oils are of high interest in industry. Traditionally, conjugated vegetable oils are added to paints, varnishes, and inks to improve their drying properties, while recently there is an increased interest in their use in the production of bioplastics. Besides the industrial applications, also food manufactures are interested in conjugated vegetable oils due to their various positive health effects. While the isomer type is less important for their industrial purposes, the beneficial health effects are mainly associated with the c9,t11, t10,c12 and t9,t11 CLA isomers. The production of CLA-enriched oils as additives in functional foods thus requires a high CLA isomer selectivity. Currently, CLAs are produced by conjugation of oils high in linoleic acid, for example soybean and safflower oil, using homogeneous bases. Although high CLA productivities and very high isomer selectivities are obtained, this process faces many ecological drawbacks. Moreover, CLA-enriched oils can not be produced directly with the homogeneous bases. Literature reports describe many catalytic processes to conjugate linoleic acid, linoleic acid methyl ester, and vegetable oils rich in linoleic acid: biocatalysts, for example enzymes and cells; metal catalysts, for example homogeneous metal complexes and heterogeneous catalysts; and photocatalysts. This Review discusses state-of-the-art catalytic processes in comparison with some new catalytic production routes. For each category of catalytic process, the CLA productivities and the CLA isomer selectivity are compared. Heterogeneous catalysis seems the most attractive approach for CLA production due to its easy recovery process, provided that the competing hydrogenation reaction is limited and the CLA production rate competes with the current homogeneous base catalysis. The most important criteria to obtain high CLA productivity and isomer selectivity are (1) absence of a hydrogen donor, (2) absence of catalyst acidity, (3) high metal dispersion, and (4) highly accessible pore architecture.

Effects of nutrition and management on the production and composition of milk fat and protein: a review

The composition and functional properties of cow’s milk are of considerable importance to the dairy farmer, manufacturer, and consumer. Broadly, there are 3 options for altering the composition and/or functional properties of milk: cow nutrition and management, cow genetics, and dairy manufacturing technologies. This review considers the effects of nutrition and management on the composition and production of milk fat and protein, and the relevance of these effects to the feeding systems used in the Australian dairy industry. Dairy cows on herbage-based diets derive fatty acids for milk fat synthesis from the diet/rumen microorganisms (400–450 g/kg), from adipose tissues (<100 g/kg), and from de novo synthesis in the mammary gland (about 500 g/kg). However, the relative contributions of these sources of fatty acids to milk fat production are highly dependent upon feed intake, diet composition, and stage of lactation. Feed intake, the amount of starch relative to fibre, the amount and composition of long chain fatty acids in the diet, and energy balance are particularly important. Significant differences in these factors exist between pasture-based dairy production systems and those based on total mixed ration, leading to differences in milk fat composition between the two. High intakes of starch are associated with higher levels of de novo synthesis of fat in the mammary gland, resulting in milk fat with a higher concentration of saturated fatty acids. In contrast, higher intakes of polyunsaturated fatty acids from pasture and/or lipid supplements result in higher concentrations of unsaturated fatty acids, particularly oleate, trans-vaccenate, and conjugated linoleic acid (CLA) in milk fat. A decline in milk fat concentration associated with increased feeding with starch-based concentrates can be attributed to changes in the ratios of lipogenic to glucogenic volatile fatty acids produced in the rumen. Milk fat depression, however, is likely the result of increased rates of production of long chain fatty acids containing a trans-10 double bond in the rumen, in particular trans-10 18 : 1 and trans-10-cis-12 18 : 2 in response to diets that contain a high concentration of polyunsaturated fatty acids and/or starch. Low rumen fluid pH can also be a factor. The concentration and composition of protein in milk are largely unresponsive to variation in nutrition and management. Exceptions to this are the effects of very low intakes of metabolisable energy (ME) and/or metabolisable protein (MP) on the concentration of total protein in milk, and the effects of feeding with supplements that contain organic Se on the concentration of Se, as selenoprotein, in milk. In general, the first limitation for the synthesis of milk protein in Australian dairy production systems is availability of ME since pasture usually provides an excess of MP. However, low concentrations of protein in milk produced in Queensland and Western Australia, associated with seasonal variations in the nutritional value of herbage, may be a response to low intakes of both ME and MP. Stage of lactation is important in determining milk protein concentration, but has little influence on protein composition. The exception to this is in very late lactation where stage of lactation and low ME intake can interact to reduce the casein fraction and increase the whey fraction in milk and, consequently, reduce the yield of cheese per unit of milk. Milk and dairy products could also provide significant amounts of Se, as selenoproteins, in human diets. Feeding organic Se supplements to dairy cows grazing pastures that are low in Se may also benefit cow health. Research into targetted feeding strategies that make use of feed supplements including oil seeds, vegetable and fish oils, and organic Se supplements would increase the management options available to dairy farmers for the production of milks that differ in their composition. Given appropriate market signals, milk could be produced with lower concentrations of fat or higher levels of unsaturated fats, including CLA, and/or high concentrations of selenoproteins. This has the potential to allow the farmer to find a higher value market for milk and improve the competitiveness of the dairy manufacturer by enabling better matching of the supply of dairy products to the demands of the market.

The composition of milk fat

Bovine milk contains about 3.5 to 5% total lipid, existing as emulsified globules 2 to 4 microns in diameter and coated with a membrane derived from the secreting cell. In homogenized milk, the coat is mostly casein. About 98% or more of the lipid is triacylglycerol, which is found in the globule. Phospholipids are about .5 to 1% of total lipids, and sterols are .2 to .5%. These are mostly located in the globule membrane. Cholesterol is the major sterol at 10 to 20 mg/dl. Data are presented on the membrane and the emulsion. Bovine milk contains substantial quantities of C4:0 to C10:0, about 2% each of C18:2 and trans-C18:1, and almost no other long-chain polyunsaturated fatty acids. The fatty acid composition is not altered by ordinary changes in diet. The triacylglycerol structure is unique, with much of the C4:0 to C10:0 at sn-3. The effects of milk cholesterol and fatty acids on human blood cholesterol levels and nonnutritive roles of some microlipids are discussed.

Lipid metabolism in anaerobic ecosystems

In anaerobic ecosystems, acyl lipids are initially hydrolyzed by microbial lipases with the release of free fatty acids. Glycerol, galactose, choline, and other non-fatty acid components released during hydrolysis are fermented to volatile fatty acids by the fermentative bacteria. Fatty acids are not degraded further in the rumen or other parts of the digestive tract but are subjected to extensive biohydrogenation especially in the rumen. However, in environments such as sediments and waste digestors, which have long retention times, both long and short chain fatty acids are beta-oxidized to acetate by a special group of bacteria, the H2-producing syntrophs. Long chain fatty acids can also be degraded by alpha-oxidation. Biotransformation of bile acids, cholesterol, and steroids by intestinal microorganisms is extensive. Many rumen bacteria have specific growth requirements for fatty acids such as n-valeric, iso-valeric, 2-methylbutyric, and iso-butyric acids. Some species have requirements for C13 to C18 straight-chain saturated or monoenoic fatty acids for growth.

Biotransformation of Unsaturated Long-Chain Fatty Acids by Eubacterium lentum

Eubacterium lentum (33 strains) isomerized the 12- cis double bond of C 18 fatty acids with cis double bonds at C-9 and C-12 into an 11- trans double bond before reduction of the 9- cis double bond. The 14- cis double bond of homo-γ-linolenic acid was isomerized by 29 strains into a 13- trans double bond. The same strains isomerized the 14- cis double bond of arachidonic acid into a 13- trans double bond and then isomerized the 8- cis double bond into a 7- trans double bond; the 13- cis double bond of 10- cis , 13- cis -nonadecadienoic acid was isomerized into a 12- trans double bond. None of these isomerization products was further reduced. Studies with resting cells showed optimal isomerization velocity at a linoleic acid concentration of 37.5 μM; higher concentrations were inhibitory. The pH optimum for isomerization was 7.5 to 8.5. The isomerase was inhibited by the sulfhydryl reagents iodoacetamide, bromoacetate, and N -ethylmaleimide and by the chelators EDTA and 1,10-phenanthroline.