The composition and stability of lipids in meat products and a spectrofluorometric assay for malonaldehyde in biological tissues
A spectrofluorometric method for the determination of malonaldehyde in wet tissues which employes a malonaldehyde specific reagent, 4,4'-sulfonyldianiline, was developed. In this determination, malonaldehyde was reacted with 4,4'-sulfonyldianiline to form a fluorescent compound that can be measured at an excitation maximum of 475 nm and an emission maximum of 545 nm. Malonaldehyde was first extracted as an aqueous distillate from acidified muscle tissue and subsequently transferred from the aqueous solution into N,N-dimethylformamide. To achieve the transfer, an aliquot of the aqueous solution was mixed with dimethylformamide and the mixture made alkaline with 0.1N sodium hydroxide. Water was then removed from the mixture by fractional distillation. Under the alkaline condition (pH 11-12), malonaldehyde occurred in a non-volatile form and was retained in the dimethylformamide residue;The spectrofluorometric assay and the thiobarbituric acid (TBA) test gave similar results for the malonaldehyde content of raw and cooked turkey, beef and pork. However, the TBA test gave increasingly higher values for the cooked meats during storage than did the fluorometric assay. The SPF assay was at least 25x more sensitive than the TBA test;The effect of microwave energy on the stability and fatty acid composition of turkey, pork and beef lipids was also studied. For turkey and pork samples, the rate of lipid oxidation was significantly higher for microwave cooked than conventionally cooked samples. Cooking method did not significantly affect the rate of lipid oxidation in beef. Microwave cooking caused a significant increase in the unsaturated/saturated fatty acids (U/S) ratio for pork and turkey compared to conventional cooking. This increase in U/S ratio is probably responsible for the increased rate of lipid oxidation observed for microwave cooked samples. Trans fatty acids were not formed by microwave cooking in any meat samples;Formation of trans fatty acids by microorganisms during the fermentation of semi-dry summer sausages and natto (a fermented soy product) was studied. The organisms involved in these fermentations (Pediococcus, Micrococcus, and Bacillus subtilis) did not cause hydrogenation of the fatty acids, and hence, no trans fatty acids were detected.