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AbstractsIn an attempt to account for carbonyls found in oxidized lipid systems, but not theoretically predicted from the decomposition of lipid hydroperoxides, a member from each of the monocarbonyl classes commonly observed in oxidizing lipids was oxidized at 45C in a Warburg apparatus and the carbonyl products studied. The carbonyl compounds used weren‐nonanal,n‐non‐2‐enal,n‐hepta‐2,4‐dienal andn‐oct‐1‐en‐3‐one. Nonanal was relatively stable to oxidation and was oxidized to nonanoic acid. Oct‐1‐en‐3‐one did not absorb oxygen during a 52‐hr period; however, the unsaturated aldehydes oxidized at faster rates than methyl linoleate or linolenate. Non‐2‐enal upon absorption of 0.5 mole of oxygen was oxidized almost quantitatively to non‐2‐enoic acid. Hepta‐2,4‐dienal was polymerized at 0.5 mole of oxygen uptake. In addition both of the unsaturated aldehydes produced shorter chain mono‐ and dicarbonyls as oxidative degradation products. The identification of these compounds helps to explain the presence of carbonyls in oxidizing lipids and model systems that are not accountable through the decomposition of theoretically predictable isomeric hydroperoxide esters. The relatively large yield of malonaldehyde from the oxidized dienal suggests that these carbonyls may serve as a major source of malonaldehyde in oxidizing diene esters. Significant quantities of malonaldehyde are not observed in methyl linoleate until late stages of oxidation, and the dienals formed through degradation of primary hydroperoxides may in turn oxidize to give malonaldehyde.

Immobilized lipase SP435 from Candida antarctica was used as a biocatalyst for the modification of the fatty acid composition of evening primrose oil by incorporating n-3 polyunsaturated fatty acid (PUFA) and eicosapentaenoic acid (EPA). Transesterification (ester-ester interchange) was conducted in organic solvent or without solvent, with EPA ethyl ester (EEPA) as the acyl donor. Products were analyzed by gas-liquid chromatography (GLC). After 24-h incubation in hexane, the fatty acid composition of evening primrose oil was markedly changed to contain up to 43% EPA. The amount of 18:2n-6 PUFA was reduced by 32%, and the saturated fatty acid content was also reduced. The effects of incubation time, molar ratio, enzyme load, and reaction medium on mol% EPA incorporation were also studied. Generally, as the incubation time (up to 24 h), molar ratio, and enzyme load increased, EPA incorporation also increased. Evening primrose oil, containing EPA and y-linolenic acid (18:3n-6) in the same glycerol backbone, was successfully produced and may be more beneficial for certain applications than unmodified oil.

The extent of protein-protein interactions in actomyosin solutions was measured as a change in light scattering absorbance of a solution undergoing change. The extent of the reaction registered as an increase in light scattering absorbance indicating an increase in the size of the macromolecules. In treatments where the extent of protein-protein interaction was extensive, film formation and/or precipitation of the macromolecules occurred. At constant protein concentration the kinetics of the reaction was dependent upon temperature, pH and the type of,actomyosin used. In general, the rate and maximum extent of change increased with increasing temperatures and decreasing pH. Below 40°C more change was generally observed in beef actomyosin solution compared to mackerel at the same temperature and pH. However, at higher temperatures, mackerel actomyosin often shows more change than beef under the same conditions. The shapes of the reaction curves were such that the slope of the steepest line that can be drawn from the origin to tangent the curve at the region where the change starts to taper off (the characteristic slope), was a good index of the rate of change and the maximum extent of interaction attained. Arrhenius-type plots of the characteristic slopes showed three possible mechanisms of change predominating within certain temperature ranges, as indicated by we& defined inflections in the curves, reflecting varying activation energies for the reactions. The three temperature zones are: below 40°C; between 40 and 60°C; and above 60°C. Below 40°C the rate and maximum extent of protein-protein interaction is very strongly temperature dependent.

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