Commercial Production of CLA

COMMERCIAL PRODUCTION OF CLA 15 TABLE 3. Summary of Solvents Used in CLA Production. 

The most attractive method for production of pure 9,ll-c,t-CLA is through the dehydration of ricinoleic acid. Synthesis from this relatively inexpensive starting material has proven elusive as it is difficult to control the formation of dehydration products (124). Synthesis of 9,ll-c,t-CLA from ricinoleic acid has been reported (125), which, although an efficient reaction, uses expensive elimination reagents such as l,8-diazobicyclo-(5,4,0)-undecene. For most applications, the high cost of the elimination reagent increases the production cost beyond the level at which commercial production of CLA is economically viable. 

At the same time, research is still needed to improve the commercial production of CLA. Although the content of desirable isomers in commercial CLA products has improved, there is still a demand for highly enriched or pure 9,1 l-cis-, trans-octadecadienoic acid products. The kinetic control of CLA synthesis will allow the development of CLA products that are virtually free of isomers other than 9,11-ct and 10,12-tc. Kinetic control of reactions requires exceedingly rapid analytical techniques that can be applied inexpensively and onhne or virtually online. 

Commercial processes for the synthesis of any compound of economic value is normally proprietary information and the commercial methods of CLA production are no exception. The process by which each brand of commercial CLA is synthesized is not known by the authors of this review. Therefore, this review is directed at the patent literature on CLA synthesis, major problems encountered in CLA synthesis, and analysis of CLA from commercial suppliers. 

If commercial CLA is to be synthesized from a fatty acid, it must be recognized that commercial fatty acids are generally not intended for use in the production of CLA. Commercial fatty acids are usually produced by the reaction of water (steam) and TAG oil at high temperatures in a continuous reaction (Reaction 1). 

Ssebo, A. Commercial Production of Conjugated Linoleic Acid (CLA). Lipid Technol. Newsletter Feb. 2001 9-13 (2001). 

Quantitative isomerization of oils containing polyunsaturated fatty acids in monohydric and polyhydric alcohols was described in 1941 (6). A detailed procedure using ethylene glycol is described in a patent from 1996 (11). Ethylene glycol has not been used commercially for production of CLA for consumer safety reasons. Propylene glycol has therefore been selected by several producers who independently developed proprietary procedures (12,13). KOH was selected as catalyst because of its high solubility compared with NaOH. Reaction temperatures are typically 130-180°C, and times of reaction are from 3 to >24 h. The quantity of KOH... 

Given the current widespread interest in reducing cancer, obesity, and other maladies, there is considerable interest in the use of the CLAs, either as a mixture or in the form of individual isomers, as beneficial dietary adjuncts. Cow s milk, beef tallow, and products made from them are natural sources of CLA. However, CLA is also readily synthesized in high yield in the laboratory from vegetable oils that are rich in linoleic acid, such as sunflower and safflower. The resulting synthetic product has CLA levels of about 80%, not the 0.3-0.5% (fat basis) found in beef tallow and dairy products (176). As a result, except for studies of the specific effects of foods containing CLA, vegetable oil is the typical source of CLA in contemporary studies and in commercial dietary supplements. This trend will probably continue. 

Industrial conjugated linoleic acid (CLA) is a poorly defined blend of compounds (102). Early commercial syntheses focused on maximizing total CLA content. Many early products were rich in CLA but contained a number of positional isomers. Market demand has now shifted for a product that contains two predominant isomers, specifically 9,ll-c,t-octadecadienoic acid and 10,12-tc-octadecadienoic acid. It is not surprising that alkali isomerization produced some undesirable positional isomers of CLA. In 1970, Mounts and Dutton (103) had shown unequivocally that when potassium t-butoxide was used, at least four positional isomers of CLA were produced. It was not until 1997, after the use of CLA as a dietary supplement... 

The raw material for CLA production must be a material that is rich in linoleic acid. This product could be in the triacylglycerol form, fatty acids or fatty acid esters. The concentration of CLA in the final product is directly dependent on the level of linoleic acid in the starting material. The highest level of linoleic acid available from botanical sources is not available in commercial products. Extraction and refining equipment would be required to obtain oils with the highest linoleic acid levels. Table 1 lists the commercial and noncommercial sources of oil and fatty acids that are known to be rich in linoleic acid and their availability as TAGs and fatty acids. 

Another possible means of formation of CLA is via enzymatic processes of fermentation. Elevated CLA levels were reported several times in fermented milk products related to raw milk (Aneja Murlhy, 1990 Jiang et al., 1997 Shantha, Ram, O Leary, Hicks, Decker, 1995), whereas others found no differences (Boylston Beitz, 2002 Lin et al., 1995 Shantha et al., 1995) in fat basis. However, it seems that commercially used dairy starter bacteria have only a minor contribution to the CLA level of the fermented product (Salamon, Loki, Csap6-Kiss, Csapd, 2009 Sieber et al., 2004), while the use of suitable strains may lead to favourable results. 

Research to determine the benefits of CLA for humans will present a unique challenge in the next few years. It will certainly require the improved and complementary methods of CLA and trans FA analysis to evaluate the biological effects of dietary supplements to determine the true effects of CLA in humans. In some studies the presence of CLA in human bodies and those produced by bacteria in the gut may need to take into consideration. The CLA research to date in humans has focused mainly on the effects of rl0,fl2-18 2 rather than on c9,t 1-18 2, the major CLA isomer present in the milk and meat of ruminants. This would appear to be due to the readily available source of commercial CLA preparations compared to pure c9,tl 1-18 2. Commercial CLA preparations consist of an equal mixture of t 0,c 2-18 2 and c9,rl 1-18 2. On the other hand, the rl0,cl2-18 2 isomer is generally present only in trace amounts in milk fats, while some ruminant fats may contain more of the CLA isomers. The true response, if any, of c9,fl 1-18 2 in humans remains to be determined. Several cohort studies have shown a significant reduction in risk factors associated with the consumption of diets high in dairy products and certain types of cancers but not with others. It remains to be seen if the benefits were due to c9,rl 1-18 2, other components in dairy products, or synergistic processes. Regardless of whether CIA s apparent benefits can be translated to humans, it is likely that CLA, as a model test object, will be used in the future in many more studies related to major maladies such as cancer, atherosclerosis, diabetes, etc. 

Fig. 4.17. Partial GC chromatogram of four commercially available milk fats, one from Korea (DHA-enriched milk fat also known as Einstein milk courtesy Dr. In-Hyu Bae, Sunchon, Korea), one from Ontario (Dairy Oh product marketed by Neilson Inc., ON), and one from the UK (Naturally Spreadable salted butter marketed by Marks and Spencer, London, UK). Two experimental milk fats are included from studies conducted at the University of Guelph in which fish meal (105) or Ca salt of CLA (sample courtesy M. Sippel and Dr. J.P. Cant) was supplemented in cow feeding studies.

Much of the safety support comes from the fact that CIA is already consumed in the human diet, especially in ruminant derived products, without apparent adverse effects. However, the isomeric composition of naturally occurring CLA is different from the CIA available as food supplements. Ruminant meat and dairy products contain mainly the cis-9,trans- 1 CLA isomer, whereas commercial CLA preparations generally contain equal proportions of the cts-9,trans- and the trans-l0,cis-l2 CLA isomer. There is a growing body of evidence that these two isomers have very distinct biological functions (1). In addition, the intake of CLA from natural dietary sources was calculated to range from 150—400 mg/day (2, 3), whereas the recommended intake for commercial CLA supplements varies from 1 to 3.4 g/day. The safety assessment of CLA based on the natural occurrence in the diet is therefore limited. 

Fig. 3.3. Partial silver-ion high-performance liquid chromatography profile of (A) the methyl esters of a commercial CLA isomer mixture, (B) the l2-iso-merized product of (A), and (C) the l2-isomerized product of (A) co-injected with cheese total lipid fatty acid methyl esters. Ultraviolet detection at 233 nm. (Published with permission from Ref. 14 and redrawn from original.)...

More research is required. A better understanding of the regiodistribution of CLA isomers in TAG formulations has potential applications in the labeling of commercial CLA-containing products and, perhaps more importantly, in the development of a better understanding of TAG structure as it relates to FA absorption and utilization in living systems (70). 

Several papers have reported the preparation of CLA isomers labeled with carbon isotopes. In aU cases, the labeled carbon atom was located on the carboxylic position. It should also be pointed out that recent preparations of unlabeled (9Z,llE) and (10 ,12 conjugated linoleic acid isomers in their highly purified form were accomplished by alkaline isomerization of (9Z,12Z) linoleic acid followed by selective lipase-catalyzed fractionation (16-18). These procedures may be used for the production of labeled (9Z,llE) and (10E,12Z) CLA because analogs of hnoleic acid labeled with carbon 13 or carbon 14 are commercially available. 

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