Transesterification reaction variables that affect yield and purity of the product esters from cottonseed, peanut, soybean and sunflower oils include molar ratio of alcohol to vegetable oil, type of catalyst (alkaline vs acidic), temperature and degree of refinement of the vegetable oil. With alkaline catalysts (either sodium hydroxide or methoxide), temperatures of 60 C or higher, molar ratios of at least 6 to 1 and with fully refined oils, conversion to methyl, ethyl and butyl esters was essentially complete in 1 hr. At moderate temperatures (32 C), vegetable oils were 99% transesterified in ca. 4 hr with an alkaline catalyst. Transesterification by acid catalysis was much slower than by alkali catalysis. Although the crude oils could be transesterified, ester yields were reduced because of gums and extraneous material present in the crude oils.

Canola oil triacylglycerols from genetically modified canola lines {InterMountain Canola Co., Cinnamlnson, NJ) have been evaluated for their photooxidative and autoxidative stabilities, as influenced by their fatty acid compositions and their triaeylglycerol compositions and structures. Purified canola oil triacylglycerols were oxidized in duplicate in fluorescent light at 25~ and in the dark at 60~ under oxygen, and their oxidative deterioration with time was monitored by determining eolorimetric peroxide values. Also monitored with time, oxidation products were determined by reversed-phase high-performance liquid chromatography with ultraviolet absorbance detection. Total volatiles, generated by thermal decomposition of the oxidized triacylglycerols, were quantitated by static-headspace gas chromatography. These experimental parameters were statistically correlated with predicted oxidizability, fatty acid composition, position of fatty acids on glycerol carbons and triaeylglyeerol composition. Oxidative de terioration of canola triacylglycerols correlated negative ly with oleic acid composition, with oleie add content at carbon 2 and with trioleoylglycerol content of the oil. Deterioration was positively correlated with the amount of linolenic acid on nonspecific locations on glycerol cap bons 1,2 and 3, the amount of linoleic acid on glycerol cap bon 2 and with sn~)leoyllinoleoyllinolenoyl glycerol content. Differences in character or quantity of volatile product and triacylglycerol hydroperoxides were low, whether generated during autoxidation or photooxidation of the canola triacylglycerols.

The oxidative stability of soybean oil triacylglycerols was studied with respect to composition and structure. Crude soybean oils of various fatty acid and triacylglycerol composition, hexane~extracted from ground beans, were chromatographed to remove non-triacylglycerol components. Purified triacylglycerols were oxidized at 60~ in air, in the dark. The oxidative stability or resistance of the substrate to reaction with oxygen was measured by determination of peroxide value and headspace analysis of volatiles of the oxidized triacylglycerols (at less than 1% oxidation). The correlation coefficients (r) for rates of peroxide formation (r = 0.85) and total headspace volatiles (r = 0.87) were related positively to oxidizability. Rate of peroxide formation showed a positive correlation with average number of double bonds (r = 0.81), linoleic acid (r = 0.63), linolenic acid (r = 0.85). Rate of peroxide formation also showed a positive correlation with linoleic acid (r = 0.72) at the 2-position of the glycerol moiety. A negative correlation was observed between rate of peroxide formation and oleic acid (r = --0.82). Resistance of soybean triacylglycerols to reaction with oxygen was decreased by iinolenic (r = 0.87) and increased by oleic acid (r = --0.76)-eontalning triacylglycerols. Volatile formation was increased by increased concentration of linolenic acid at exterior glycerol carbons 1,3 and by linoleic acid at the interior carbon 2. Headspace analysis of volatiles and highperformance liquid chromatography of hydroperoxides indicated that as oxidation proceeded there was a slight decrease in the linolenic acid-derived hydroperoxides and an increase in the linoleic acid~ierived hydroperoxides. The oxidative stability of soybean oil triacylglycerols with respect to composition and structure is of interest to the development of soybean varieties with oils of improved odor and flavor stability.