John L. Weihrauch

Lipid conversion factors for calculating fatty acid contents of foods

Abstract and SummaryThe U.S. Department of Agriculture is searching the world literature published since 1960 for data on food lipids and their fatty acid composition. These data are being used to update and expand the national tables of food composition and to establish a computerized nutrient data bank. Customarily, investigators report fatty acid data in terms of weight percent of total methyl esters. For the benefit of users of nutrient tables, relative amounts of com-ponent fatty acid esters should be converted to grams fatty acid (as free acid) per 100 grams food. For this purpose, conversion factors, defined as the weight of fatty acids in 1 gram of fat, were derived for various food products. Derivation of, and basis for, factors and their application are described for selected food products. Variables affecting factors are also dis-cussed. Investigators should include, in reports on fatty acid composition of foods, information on total lipid content and on the fatty acid content of the lipid. The latter values are readily obtained by a saponification procedure, complete acid hydrolysis, or if desired, by lipid class analysis.

Phospholipid content of foods

The content of total lipids and total and component phospholipids in ca. 140 foods was compiled in response to frequent requests for data by researchers in nutrition and medicine, and to fill the appar-ent need for a reliable up-to-date tabulation of recent data. Eggs, organ meats, lean meats, fish, shellfish, cereal grains and oilseeds are good sources of phospholipids, especially the choline phosphatides: phosphatidylcholine, sphingomyelin and lysophosphatidylcholine. Leafy vegetables, fruiting parts, roots and tubers are, with few ex-ceptions, relatively poor dietary sources of total lipids and phospho-lipids. Foods or tissues in which the phospholipids perform similar functions also have similar relative phospholipid distributions. The data were tabulated by food group in separate tables with appropri-ate discussion. The use of conversion factors for calculating the total and individual phospholipids, sources of error, and research needs are discussed.

Composition of Selected Dietary Fats, Oils, Margarines, and Butter

Fats and oils provide the most concentrated source of energy in the diet, about 9 kcal/g. Animal tissues, dairy products, and oils extracted from certain seeds contribute most of the fat in the diet (see Table I). The source, chemical nature, and processes that fats and oils are subjected to before they reach the market shelf are important aspects of the study of lipids. A fat is distinguished from an oil by its solid state at a particular temperature, usually room temperature. Some oils are winterized to remove triglycerides that would cause the oil to solidify in the refrigerator; other oils are lightly hydrogenated to convert highly unsaturated fatty acids to more saturated acids to prevent the development of off-flavors and rancidity.

Methods for the isolation and characterization of constituents of natural products: XV. Application of a periodic acid column for locating double bond position

Abstract The ability of a microcolumn of periodic acid impregnated on magnesium sulfate to effect oxidation of ethylenic unsaturation was studied. The aldehyde, produced on the hydrocarbon side of the double bond in 30–40% yield, was converted to a 2,4-dinitrophenylhydrazone on a microderivatizing column and identified by thin-layer chromatography. The method was applied to unsaturation in fatty acids, their methyl esters, alcohols, aldehydes, and colored derivatives of the latter two classes. Double bonds in a variety of positions in the chain were successfully located, but terminal unsaturation or unsaturation with a methyl group on either carbon of the double bond could not be characterized. The procedure was routinely run on 25 μg but can still be successfully executed on 5 μg of a pure compound.

Methods for the isolation and characterization of constitutents of natural products: XII. A chromic acid column procedure for the quantitative oxidation of secondary alcohols at the micromole level

Abstract A two-phase column procedure for the quantitative oxidation of saturated secondary alcohols to the corresponding ketone is described. Aqueous chromic acid on a column of Celite and a CCl 4 solution of the alcohol comprise the system. The method is well-suited for the oxidation of secondary alcohols at the micro- and even submicromole level.

Methods for the isolation and characterization of constituents of natural products: XVIII. A micro-bisulfite column for extracting aldehydes and certain ketones

Abstract A procedure using a sodium bisulfite-Celite column was modified for extraction of micromole amounts of aldehydes and certain ketones from nonaqueous solution. Quantitative removal of saturated and unsaturatcd normal chain aliphatic and aromatic aldehydes takes place rapidly, but under the same conditions aldehydes branched on the alpha carbon atom fail to extract quantitatively or at all. Acetone, cyclopentanone and cyclohexanone were removed quantitatively hut higher members in both classes were not. Vicinal diketones were extracted quantitatively. A scaled-down version conducted in a melting point capillary and suitable for microliter volumes containing microgram amounts of carbonyls also was tested.

Methods for the isolation and characterization of constituents of natural products: XVI. Quantitative microdetermination of diols as bis-esters of pyruvic acid 2,6-dinitrophenylhydrazone: Separation from monohydric alcohol derivatives and resolution of an homologous series

Abstract A quantitative colorimetric method is described for the acylation of micro- and submicromole amounts of dihydric alcohols as bis-esters of pyruvic acid 2,6-dinitrophenylhydrazone. The bis-esters which are obtained exclusively, can be cleanly and quantitatively separated from a complex mixture of monohydric alcohol derivatives on an alumina column. Separation of an homologous series of terminal diol derivatives by thin-layer partition chromatography is also described.

Methods for the isolation and characterization of constituents of natural products: XIV. Use of iodine monochloride for detecting unsaturation in microgram quantities of colored derivatives

Abstract A procedure is described for detecting unsaturation in the parent compound of colored derivatives at the microgram level using iodine monochloride. Included in the study were the 2,4-dinitrophenylhydrazone derivatives of carbonyl compounds, the 2,6-dinitrophenylhyrazone derivatives of pyruvic acid esters of alcohols, the α-methyl-2,4,6-trinitrophenylhydrazone derivatives of alkoxyacetaldehyde compounds, the 2,6-dinitrophenylhydrazone derivatives of pyruvamides and the N-2,4-dinitrophenylethanolamine esters of fatty acids. Compounds which add iodine monochloride are sufficiently retarded on thin-layer partition plates to be classified as unsaturated. Carbonyl derivatives in which the double bond or bonds are conjugated with the hydrazone linkage and certain carbonyl compounds containing a double bond β,γ to the hydrazone linkage fail to be detected.

Methods for the isolation and characterization of constituents of natural products: XI. Preparation of the 2,4-dinitrophenylhydrazone derivatives of fatty acid esters of glycolaldehyde and separation of an homologous series by thin-layer partition chromatography

Abstract An homologous series of the 2,4-dinitrophenylhydrazone derivatives of the glycolaldehyde esters of fatty acids have been prepared. The derivatives are all solids having an absorption maximum at 350 mμ (CHCl3) and a molar extinction coefficient near 20,000. Neutral and alkaline thin-layer partition chromatographic procedures and a thin-layer, silver-ion adsorption system are described for resolving the derivatives.