Hydrogenation, fats fish oils

In this note the use of hydrogen in the fat hardening industry has been described with particular reference to the conversion of the unsaturated oleic and linoleic fatty acids into stearic acid However, what has been said in regard to diis matter is equally applicable to the conversion of olein and linolein into stearin, cotton-seed and most fish oils being quite easily converted into solid fats. 

At one time fish oils were low-cost industrial materials for the paint and linoleum industries. After World War II (WWII), these industries switched to chemicals and plastics, and therefore, much information in older books became obsolete by 1960. Hydrogenation of fats to produce margarines and shortenings, starting about 1900, led to improved oil refining and better quality and included whale oils when these animals were still plentiful. Two factors have recently impacted negatively on large-scale and continued use of marine oils in our food supply. 

Research on cis-trans isomerization (CTI) of lipid double bonds focused both on the conversion that occurs in some bacteria enzymatically and on trans isomers that are present in mammalian cells after a dietary supplementation of chemically modified fats [3,4]. It is known that cis/trans isomeric mixtures of fats result from vegetable and fish oils manipulated through partial hydrogenation or deodoriza-tion processes that are frequently utilized in the food industry. Nutritional and epidemiological studies revealed some harmful effects of these unnatural lipids for human health. However, it must be pointed out that in the chemical manipulation of oils the structures of trans fatty acid residues consist of geometrical and positional isomers with unshifted and shifted double bonds compared with the natural cis compounds. With the name trans lipids we indicate these unnatural geometrical and positional isomers. It has to be mentioned for clarity that there... 

Use Manuf soaps, oleomargarine, hydrogenated fats, lard substitute, glycerol, leather dressings, lubricants, cosmetics emollient also as salad and cooking oil packing fish. Pharmaceutic aid (solvent). 

Fish oils contain a wide range of fatty acids from C14 to C26 in chain length with 0-6 double bonds. The major acids include saturated (14 0, 16 0, and 18 0), monounsaturated (16 1, 18 1, 20 1, and 22 1) and n-3 polyene members (18 4,20 5,22 5, and 22 6). Fish oils are easily oxidized and are commonly used in fat spreads only after partial hydrogenation. However, they are the most readily available sources of n-3 polyene acids, especially, EPA and DHA, and with appropriate refining procedures and antioxidant addition these acids can be conserved and made available for use in food. The long-chain polyene acids are valuable dietary materials and there is a growing demand for high quality oil rich in EPA and DHA. °... 

Fig. 1. The concentration (mg/g wet weight) of the total cardiac lipids and the cardiac triglycerides of rats, pigs, and monkeys fed a low fat control diet (time 0) and diets to which a control oil (first bar) or a docosenoic acid containing oil (second bar) was added. The portion of triglycerides in the total lipids are indicated by a hatched bar wherever this information is available. Source of data rat (Kramer and Hulan, 1978 Kramer et al., 1979) pig, 1.4 weeks (Opstvedt et al., 1979), all other values (Kramer et a/., 1975) and monkey, 1 and 10 weeks (Beare-Rogers and Nera, 1972), all other values (Ackman, 1980). Erucic acid was the docosenoic acid in all studies except the monkey data from Ackman (1980) who fed partially hydrogenated fish oil containing mainly cetoleic acid.

Further interest in fish oils has been stimulated because of the association of the long-chain highly unsaturated acids, 20 5 and 22 6 with the alleviation of atherosclerosis (Dyerberg et ai, 1978 Barlow, 1980). Marine oils are however partially hydrogenated in order to obtain fats of adequate oxidative stability for conventional food application in margarine and shortenings. Industrial uses include soap, paints, varnishes, printing inks, leather treatment, water repellants and plasticizers. 

For TV analysis by gas-liquid chromatography (GLC) of fat to methyl esters (FAMEs) the official AOCS method prescribes the cyanopropylpolysilox-ane phase SP2340. The column should be 60 m x 0.25 mm fused silica with aim retention gap of si-lanized fused silica with a film thickness of 0.2 pm. Such columns will provide adequate separation of cis and trans FAME for most situations involving food fats (except fats containing hydrogenated fish oils). However, there is peak overlap and for exacting analyses, where information is required on the iso-... 

Fig. 1. Comparison of palmitate (P) and erucate (E) metabolism in isolated hepatocytes from rats fed different diets Low fat pellets (pellet), low fat pellets + 0.3% clofibrate (clof.), and high fat diets (30% of the calories) with peanut oil (peanut) ra eseed oil (rapeseed), and partially hydrogenated fish oil (fish). The rapeseed oil and the fish oil contained 11.5% C22 monounsaturated fatty acids. The isolated cells were incubated with 0.5 mAf (16- C)-palmitate or (14- C)-erucate for 30 min. The vertical hatching indicates erucic acid recovered in the cell lipids as shortened fatty acids...

Fig. 3. The activity of 2,4-dienoyl-CoA reductase in the hver of rats fed different fat diets 5% soybean oil (SO), 25% soybean oil (SO), 25% partially hydrogenated soybean oil (PHSO) 25% fish oil (FO), 25% partially hydrogenated fish oil (PHFO), or low fat pellets + 0.3% clofibrate...

Hydrogenation results in the production not only of saturated acids but also of trans acids. In addition a redistribution of double bonds within the fatty acid chain takes place, accounting for the presence in ruminant fats of vaccenic (trans-ll,18 l) and elaidic tmns-9,18 1) acids. A similar transformation occurs in the industrial hydrogenation of plant and fish oils. Partially hydrogenated vegetable oils, for example, commonly contain 3-5 g trans acids/100 g of the total fatty acids, and partially hydrogenated fish oils about 20 g. 

The nature of the dietary fat can have a profound effect on the composition of milk fat. Diets rich in acids up to palmitic generally increase the proportions of these acids in milk fat at the expense of the Cig adds. Dietary fats rich in saturated and unsaturated acids result in increased yields of oleic and stearic acids with associated decreases in shorter-chain acids, particularly palmitic acid. The secretion of Unoleic and linolenic acid or the longer-chain eicosapentaenoic or docosahexaenoic acids foimd in fish oils is little affected by diet owing to the extensive hydrogenation that occurs in the rumen and their preferential distribution in the phospolipid coating of the fat globules, which is considerably lower in milk than the triacylglycerols. 

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