Oct-1-en-3-one and the more potent octa-l,cis-5-dien-3-one have been identified as being responsible for the metallic odour which developed when a model system containing butterfat, a-tocopherol and cupric palmitate was allowed to oxidise at 35°C for 35 h. These vinyl ketones were synthesised, their mass and n.m.r. spectra determined, and odour descriptions and odour thresholds assessed. Octa-1 ,cis-5-dien-3-one in aqueous solution could be detected at a dilution of 1 in 10l2. Its metallic odour was also described as like geranium leaves. Oct-1-en-3-one (detectable at 1 in 1010 dilution) was described as mushroom like at low concentrations and only exhibited a metallic odour at higher concentrations. Both compounds had an odour threshold concentration about five hundred times greater in groundnut oil than in water. The significance of these compounds is discussed with reference to the published literature and their formation from (n -3) and (n -6) polyenoic fatty acids.

The methyl ester of individual positional isomers of linoleate hydroperoxide were prepared by an enzymic oxidation of linoleate. On injection onto a gas chromatographic column they were thermally decomposed and the resulting volatile components analyzed. The major (67-80% yield on a molar basis) cleavage products were found to be hexanal, methyl octanoate, 2,4-decadienal isomers, and methyl 9-oxononanoate. Both the 9 and 13 isomers of linoleate hydroperoxide gave rise to these same four compounds, an observation suggesting carbon-oxygen scission in their decomposition. This was confirmed by using very pure individual isomers obtained by high performance liquid chromatography. The involvement of an isomerization reaction of the hydroperoxides is discussed.

The changes occurring in sunflower seed oil under simulated frying conditions and during potato chip frying were monitored. The changes monitored were in: (a) fatty acid composition, (b) triglyceride content, (c) octanoate content, (d) titratable acidity, and (e) colour. To simulate frying conditions either argon or air, with or without steam, was bubbled through the hot oil. For the frying of potato chips, two methods of frying were used, viz continuous frying throughout 1 day and intermittent frying over a total of 10 days. It was found that whenever the hot oil was exposed to air, whether during simulated frying or the frying of potato chips, there was evidence of oxidative deterioration. Steam appeared to have an antioxidant effect in the simulated frying experiments. In all experiments the molar yield of acidity was comparable in magnitude with that of the octanoate. The correlation of octanoate production with the losses of linoleate and triglyceride is discussed.

Iodine values, melting (slip) points and fatty acid analyses for back (' bung') and perinephric (kidney) fats from 114 pure and cross-bred pigs are reported.In most cases the effects of breed were small, but half-Hampshire crosses showed a high proportion of pigs producing abnormally soft and highly unsaturated fats, though others were normal.Although a general correlation existed between iodine value and melting-point the relationship broke down in some cases, and the ratio of monoene to saturated fatty acids of carbon chain length 16 and 18 is suggested as a better chemical index of softness due to causes other than dietary lipid.