Free fatty acids membrane separation

Recently, polymeric ultrafiltration membranes were used for degumming crude soybean oil and removing phospholipids from the crude oil/hexane miscella (168). Crude soybean oil also can be de-acidified by methanol extraction of the free fatty acids and the extract separated into fatty acids and solvent by a membrane filter (169). A surfactant-aided membrane degumming also has been applied to crude soybean oil, and the degummed oil contained 20-58 ppm of phosphorus (170). Supercritical carbon dioxide extraction was shown to be an effective means of degumming (171). In this process, soybean oil countercurrently contacted supercritical carbon dioxide at 55 MPa and 75°C. The phosphorus content of the oil was reduced from 620 ppm to less than 5 ppm. Ultrasonic degumming was also successfully used to reduce the gum content of soybean oil (172). 

The commercial membrane separation processes are offered in the areas of nitrogen production and waste treatment applications (1). Developing membrane applications in oil milling and edible oil processing are (1) solvent recovery, (2) degumming, (3) free fatty acid removal, (4) catalyst recovery, (5) recovery of wash water from second centrifuge, (6) coohng tower water recovery, (7) protein purification, and (8) tocopherol separation. 

Triacylglycerols are dominant and constitute about 98% of milk fat, together with small amounts of di- and monoacylglycerols and free fatty acids. Small quantities of phospholipids, cholesterol, and cholesterol esters are also present as well as the fat-soluble vitamins A, D, and E. Lipid molecules in milk associate to form large spherical globules, which are surrounded by a phospholipid layer, the globule membrane, from the proteins in the milk. This membrane stabilizes the hydrophobic lipid in the aqueous phase of the milk. The emulsion must be broken and the protein film removed before the fat can be separated and determined volumetrically. 

In another study, Snape and Nakajima [3], using membrane separation for lipids classes in hydrolyzed sunflower oil, observed that free fatty acids permeated the membrane and preferentially concentrated in the permeate, while triglycerides were retained. Mono- and diglycerides showed intermediate behavior that is, they were equally distributed between permeate and retentate. 

Neutral fats and phospholipids can also be separated by dialysis (van Beers et al. 1958, Eberhagen and Betzing 1962). Phosphatides aggregate in non-polar solvents whereas neutral lipids do not. Therefore only cholesterol esters, glycerides, free fatty acids, and free cholesterol pass through a rubber membrane in petroleum ether solution. The duration of dialysis depends on the pore size of the membrane. Contamination by soluble rubber components should be prevented by prewashing the membranes. 

Ethanol and choline glycerolipids were isolated from calf brain and beef heart lipids by PTLC using silica gel H plates. Pure ethanol amine and choline plasmalogens were obtained with a yield of 80% [74]. Four phosphohpid components in the purple membrane (Bacteriorhodopsin) of Halobacterium halobium were isolated and identified by PTLC. Separated phosphohpids were add-hydrolyzed and further analyzed by GC. Silica gel G pates were used to fractionate alkylglycerol according to the number of carbon atoms in the aliphatic moiety [24]. Sterol esters, wax esters, free sterols, and polar lipids in dogskin hpids were separated by PTLC. The fatty acid composition of each group was determined by GC. 

The main occurrence of free sterols Is In the cytoplasmic membrane, where they Interact with other lipids and proteins. Two modes of action for sterols In membranes are proposed. One Is the so called bulk menfl>rane function, l.e., the Interaction with phospholipids and the spatial separation of these charged molecules [13]. The other role Is a cofactor function for the Incorporation of unsaturated fatty acids Into lipids [14]. 

Note that we have invoked lipase action several times but we have referred each time not to lipase, but to a lipase. This is because it is a different lipase each time. They all carry out the same chemical job, but they have to work in different places under different conditions - the intestinal one is a secreted enzyme working free in the intestinal juice, whereas the lipase at the surface of adipose tissue is a membrane-bound enzyme. Similarly, the lipases of adipose tissues are tailored for their separate jobs by being structured to respond to different physiological regulatory signals. Thus, the lipase involved in fatty acid mobilisation, for instance, is known as hormone-sensitive lipase . 

Turning our attention to the aorta, let us see in which cellular subtraction fatty acid synthesis occurs. The enormous technical problem of making aortic homogenates has retarded the study of cell-free systems. Ideally one would like to be able to separate the aortic layers so that intima, media, and adventitia could be studied separately, but this has not yet been possible. Simply to obtain sufficient and viable cell-free preparations from this very tough tissue has been very difficult. The shear forces required to break up aortic strips are so great that the generated frictional heat is disastrous to many enzymes and to delicate membranes sensitive to mechanical and thermal trauma (e.g., mitochondria). 

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