Ricinoleic acid transformations

Finally, the yeast Yarrowia lipolytica is able to transform ricinoleic acid (12-hydroxy oleic acid) into y-decalactone, a desirable fruity and creamy aroma compound however, the biotransformation pathway involves fi-oxidation and requires the lactonisation at the CIO level. The first step of fi-oxidation in Y. lipolytica is catalysed by five acyl-CoA oxidases (Aox), some of which are long-chain-specific, whereas the short-chain-specific enzymes are also involved in the degradation of the lactone. Genetic constructions have been made to remove these lactone-degrading activities from the yeast strain [49, 50]. A strain displaying only Aox2p activity produced 10 times more lactone than the wild type in 48 h but still showed the same growth behaviour as the wild type. 

Fig. 8. (A) X-ray diffraction spectra (unit, nm) and (B) polarized Fourier transform-infrared spectra of the four polymorphs in ricinoleic acid (SRS).

Traditional fermentation using microbial activity is commonly used for the production of nonvolatile flavor compounds such as acidulants, amino acids, and nucleotides. The formation of volatile flavor compounds via microbial fermentation on an industrial scale is still in its infancy. Although more than 100 aroma compounds may be generated microbially, only a few of them are produced on an industrial scale. The reason is probably due to the transformation efficiency, cost of the processes used, and our ignorance to their biosynthetic pathways. Nevertheless, the exploitation of microbial production of food flavors has proved to be successful in some cases. For example, the production of y-decalactone by microbial biosynthetic pathways lead to a price decrease from 20,000/kg to l,200/kg U.S. Generally, the production of lactone could be performed from a precursor of hydroxy fatty acids, followed by p-oxidation from yeast bioconversion (Benedetti et al., 2001). Most of the hydroxy fatty acids are found in very small amounts in natural sources, and the only inexpensive natural precursor is ricinoleic acid, the major fatty acid of castor oil. Due to the few natural sources of these fatty acid precursors, the most common processes have been developed from fatty acids by microbial biotransformation (Hou, 1995). Another way to obtain hydroxy fatty acid is from the action of LOX. However, there has been only limited research on using LOX to produce lactone (Gill and Valivety, 1997). 

With the expansion of the textile industry, other surfactants besides soap began to achieve importance. For example, industry a surface-active product, produced by sulfonation of castor oil, possesses outstanding properties. Under the name of turkey red oil , it is still in use today. It was found that the sulfuric acid semi-ester of the OH-group of ricinoleic acid was the surface-active moiety in this material. At first, the carboxylic group of the ricinoleic acid was transformed into an ester to avoid forming insoluble salts from the water hardness. Later, Bertsch logically arrived at the use of fatty alcohols instead of ricinoleic acid as suitable hydrophobic starting materials. 

Dehydration of a suitable precursor at high temperature under vacuo initially yielded a polyester (8), upon which pyrolysis afforded the trans-9,trans-11-18 2 isomer. For this procedure ricinoleic acid was first elaidinized, which means a transformation of the ds- double bond into a trans- double bond (9). The so formed ricinelaidic acid was then heated under vacuum at 235°C. Intermolecular esterification (estolide formation) yielded polyesters with a molecular weight of 1500 to 1600. Pyrolysis and simultaneous distillation furnished a crude product, which was recrystallized in 95% ethanol to furnish the desired trans-9,trans-W- % 2 isomer in a 35% yield. 

Most contributions to the preparation of macromolecular materials derived from vegetable oils involve at least a modicum of chemical transformation, if not major modifications. The pancity of studies associated with their direct exploitation is due to the intrinsic mechanistic limitations of these pristine structures (with the possible exception of castor oil and ricinoleic acid) in terms of constructing as wide a variety of materials as required by the vast array of polymer applications. 

Table 1 shows the polymorphic behavior of the three TAG in which the saturated fatty acid at the the in-1 and in-2,3 positions is stearic and the sn-2 acid varied from oleic (SOS), ricinoleic (SRS) to linoleic (SLS). As a reference, a typical feature of polymorphic transformation of SOS from a to 3j forms through y, P and P2 is illustrated in Table 1 (10). As briefly mentioned in die previous section, one of the unique polymorphic properties in SOS is that the chainlength structure converted from DCL (a) to TCL (y, P, P2, and Pj), and the subcell structures of stearic and unsaturated acid leaflets in the TCL polymorphs changed in different manners. This transformation behavior is caused by the steric hindrance of steric and unsaturated acid chains, as well as by the structural stabilization of the aliphatic chains and glycerol groups altogether, as briefly summarized in the following.

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