Spectrophotometric determination of small proportions of polyunsaturated constituents in fatty materials

Abstract

Summary Existing ultraviolet spectrophotometric methods have been modified for application primarily to the detection and estimation of low proportions of conjugated and nonconjugated unsaturated constituents in fats, oils, and soaps. The method is applicable also to fatty materials having high proportions of these constituents. Modifications include corrections for absorption by interfering substances, use of alkaline glycerol as an isomerization medium in the analytical procedure, and correction of absorption data on the isomerized product for absorption by conjugated constituents in the material before isomerization. The presence of small proportions of highly unsaturated conjugated and nonconjugated compounds is established in lards, tallows, tallow soaps, and highly purified esters and acids. Tall oil fatty acids are shown to contain approximately 10% of conjugated diene acids and a small amount of linolenic acid.

Standardization of spectrophotometric methods for determination of polyunsaturated fatty acids using pure natural acids

“…Brice et al (3,4,5,6) improved the sensitivity and accuracy in respect to determination of small proportions of the conjugated and noneonjugated acids by proposing measurement of absorption before and after isomerization in KOH-glycerol, a medium more transparent than KOH-ethylene glycol in air, and by applying corrections for preformed conjugation and extraneous background absorption. Beadle and Kraybill (2) extended it to include determination of araehidonic acid.…”

CONSTITUTION OF THE LIPID FROM STORED FLORIDA VALENCIA ORANGE JUICEa

“…The acids were eluted from the column with several combinations of solvents, as shown in Table I. Since the highly colored constituent had been removed from fractions A and B, these fractions were combined, and the combined fraction, which had an iodine number of 96.85, Wijs 30 min., was examined spectrophotometrically by the method of Brice, Swain, Schaeffer, and Ault (2). Also examined spectrophotometrically were the mixed fatty acids containing the colored constituent.…”

“…The long mathematical form given by Brice et al (2) was used in calculating the nonconjugated constituents. It can be seen from the results in Table 2 that there is very little difference in the composition of the chromatographed acids and the mixed acids containing the colored constituent.…”

Fat Rancidity in Eviscerated Poultry

“…Induction periods of the skin fat were determined as previously described by Schreiber et al (1947). The composition of the mixed fatty acids of the samples was determined by spectrophotometric analysis according to the method of Brice et al (1945), and the iodine values (Wijs solution) were determined according to the method of Yasuda (1931). The phospholipid content in milligrams per gram of the fat extracted from the skin was determined as described by Gortner (1945).…”