There is considerable interest in changing the composition of oilseed plants through plant breeding and genetic engineering (Greiner 1990). This may involve increasing or decreasing the total lipid in the seed or the composition of the lipid. Modern plant breeding is largely empirical and produces large numbers of plants whose oilseed composition must be evaluated. For example, two plants may be crossed and give rise to many offspring that are a genetic mixture of the two parents (Graef et al. 1988). Each of the offspring may differ genetically, and those with interesting oilseed compositions must be identified. Or, a batch of seed may be treated with a chemical or physical agent to induce mutations (Hammond and Fehr 1985). The surviving seed will give rise to plants that may have random mutations and must be evaluated to identify those with interesting compositions. In these situations plant breeders turn to those skilled in oilseed analysis, and close cooperation between breeder and analyst is needed for success.

Organization of Rapid Analysis of Lipids in Many Individual Plants

Various oil-accumulating yeasts were tested for their ability to produce lipase and live on fats and oils as carbon sources. Of these,Candida lipolytica seemed most promising, and the possibility was explored of modifying fats and oils by fermenting them withC. lipolytica and extracting the modified oil deposited in the yeast cells. Oxygen was required for the growth of yeast on fats and oils, but unless the oxygen level was controlled at a low value after cell populations peaked, most of the substrate oil was converted to citrates rather than accumulating as oil. Oil accumulation byC. lipolytica from a corn oil substrate was slightly depressed by excess nitrogen in the medium. The yeasts were able to use about 18 g/l of oil in 72 hr. At substrate oil levels greater than 18 g/l, the dry yeasts were 60% oil, and about 45–57% of the substrate oil was recovered as yeast oil. The fatty acid composition of the yeast oil was quite similar to that of the substrate oil under optimum conditions of deposition. Sterols, but not tocopherols, were transferred from the substrate to the yeast oil.Candida lipolytica oil was high in free fatty acids. The greatest potential for biomodification by fermentation withC. lipolytica seems to be in altering glyceride structure.

Biomodification of fats and oils: Trials withCandida lipolytica

Phospholipid (PL) fatty acid composition and stereospecific distribution of 25 genetically modified soybean lines with a wide range of compositions were determined by gas chromatography and phospholipase A2 hydrolysis. Pl contained an average of 55.3% phosphatidylcholine, 26.3% phosphatidylethanolamine, and 18.4% phosphatidylinositol. PL class proportions were affected by changes in overall fatty acid composition. PL fatty acid composition changed with oil fatty acid modification, especially for palmitate, stearate, and linolenate. Stereospecific analysis showed that saturated fatty acids were primarily located at the sn-1 position of all PL, and changes of the saturates in PL were largely reflected on this position. Oleate was distributed relatively equally between the sn-1 and sn-2 positions. Linoleate was much more concentrated on sn-2 than on sn-1 position for all PL. Linolenate was distributed relatively equally at low concentration but preferred sn-2 position at high concentration.

Phospholipid fatty acid composition and stereospecific distribution of soybeans with a wide range of fatty acid composition

Efforts to improve the composition of soybean oil by breeding the beans for low linolenic acid in the oil have continued since 1968. This paper reports recent work using hybrid crosses and induced mutations. No lines are yet available that contain oil having less than 3% linolenic acid.

Improving the fatty acid composition of soybean oil

The positional selectivity of several commercial lipases was reevaluated from the point of view of synthetic utility. A 1,2-diglyceride was synthesized, and exposed to typical conditions of lipase-catalyzed hydrolysis (without the enzyme). Little, or no, acyl migration was observed. The recovery of oleic acid from several lipase-catalyzed hydrolyses of 1(3)-palmitoyl-2-oleoyl-3(1)-stearoyl glycerol (POS) reported here, therefore, must be regarded as due to the presence of the lipases themselves. This could limit the use of such catalysts in schemes requiring high selectivity for the primary positions of triglycerides. Fatty acid selectivity data of the enzymes studied also are presented.

Evaluation of lipase selectivity for hydrolysis

A rapid method for the stereospecific analysis of triglycerides based on enzymatic hydrolysis on thin layer plates was applied to a number ofGlycine max, Glycine soya, Avena sativa andAvena sterilis strains. The percentage of each fatty acid on thesn-1,sn-2- andsn-3-positions was linearly related to the total percentage of the fatty acid in the triglyceride. Large deviations from the common triglyceride pattern were not found.

E. G. Hammond

Papers

Stereospecific analysis of triglycerides of Glycine max, Glycine soya, Avena sativa and Avena sterilis strains.