W.L. Dunkley

Initiation of lipid peroxidation by a reduced metal ion

Abstract Ferrous iron was more effective than ferric in the initiation of peroxidation of heterogeneous linoleatc at 30 °C. The oxidation observed for ferric catalysis was autocatalytic in nature. Ferrous iron caused a linear uptake of oxygen, except in the more dilute solutions in which the reaction was first linear and subsequently autocatalytic. The results are considered in relation to a hypothesis that the reduced ion is involved in initiation of lipid peroxidation. It is proposed that a perhydroxyl radical is produced by the reduced metal ion. The hypothesis is discussed in relation to other systems.

Measurement oftrans and other isomeric unsaturated fatty acids in butterand margarine

A procedure is described for gas liquid chromatographic determination of cis andtrans isomers of unsaturated fatty acids after fractionation of the saturated, monenoic, dienoic, and polyenoic fatty acid methyl esters by argentation thin layer chromatography. To test its reliability, the procedure was used for quantitative measurement of transisomers of unsaturated fatty acids in a known mixture of simple triglycerides containing saturated fatty acids from 4:0 to 24:0 andcis andtrans isomers of 14:1. 16:1, 18:1, and 18:2. Results of the analyses of five margarine and five butter samples are presented, together with results of infrared spectrophotometric analyses fortrans fatty acid concentrations, ultraviolet spectrophotometric analyses for conjugated fatty acid concentrations, and enzymatic analyses forcis-cis-methylene interrupted fatty acid concentrations. The combined argentation thin layer and gas Chromatographic procedure is suitable for determination of the principal fatty acids in complex food lipids such as milk fat.

Composition of milk fat globules with increased linoleic acid.

Abstract and SummaryComparisons were made of the composition and distribution of the lipids in fat globules from conventional milks and polyunsaturated milks produced by cows fed protected lipid supplement. Washed creams were prepared from the milks of three individual cows fed a conventional ration, and three fed a protected sunflower-soybean supplement rich in linoleic acid. The washed creams were fractionated by treatment with sodium deoxycholate and centrifugation. Each washed cream and four fractions (designated as outer globule membrane, inner membrane, pellet, and globule core) were analyzed for protein, lipid, phospholipid, cholesterol, tocopherols, carotenoids, and fatty acid composition. The outer and inner membrane fractions were further fractionated into neutral and polar (phospholipid) lipid classes by thin layer chromatography. For both types of washed cream the approximate weight distribution of total solids was: outer membrane, 1%; inner membrane, 2%; pellet, 0.1%; and core, 96%. The percentages of protein, phospholipid, cholesterol, and carotenoids were all lower in the polyunsaturated than in the conventional creams. In the polyunsaturated creams, the percentages of both saturated and unsaturated C18 acids were higher, and of acids of C16 and shorter chain length lower, than in the conventional creams. The phospholipids in the outer and inner membranes from the polyunsaturated milks had larger proportions of linoleic acid than did the phospholipids from the conventional milks. However, this increase in unsaturation was less than that of the core neutral lipids. Pancreatic lipase hydrolysis of the core fractions showed that the increased linoleic acid was introduced preferentially at the 2-position of the triglycerides. In general, the observed changes in physical properties and in susceptibility of polyunsaturated milk to the development of oxidized flavor are consistent with the differences in the relative proportions of the various classes of lipids in the conventional and polyunsaturated milks.