B.A. Anderson

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.

Calorimetric measurement of the heat of desorption of water vapor from amorphous and crystalline lactose

Abstract The heat required to release and vaporize bound H 2 O from crystalline α-lactose monohydrate and from lactose glass, as determined by differential scanning calorimetry is 12.3±0.7 and 10.8±0.5 kcal·mole −1 of H 2 O, respectively. Water vapor sorption by anhydrous α-lactose leads to the formation of the α-monohydrate. The isotherm, obtained gravimetrically for this process is Langmuir type. β-Lactose is completely non-hygroscopic below 97% relative humidity. Thereafter, it sorbs H 2 O rapidly to form a concentrated solution wherein the lactose is capable of mutarotation. Densites of lactose forms determined pycnometrically by helium displacement are: 1.535 g/cm 3 for α-lactose·H 2 O; 1.547 g/cm 3 for anhydrous α-lactose; and 1.576 g/cm 3 for β-lactose.

Lipids in foods: Problems and procedures in collating data

Reliable data on the quantities of individual fatty acids in all foods are needed. This article explains the program at Nutrient Data Research Center, USDA, designed to collate all available information concerning lipids and fatty acids in foods. It discusses the problems encountered in evaluating published data and emphasizes the need for full description of sample, i.e., full disclosure of production, processing, cooking treatments, and other factors influencing lipid composition. Typical examples of treatment parameters which affect lipids in foods are cited. Extraction methods are treated and the need for determination of the fatty acid content of extracted total lipids is emphasized. The criteria of good analyses and the commodities needing detailed analyses are included.

Contraction of dried casein particle surfaces effected by sequential H2O vapor sorption and desorption cycles

Abstract When casein micelles, isolated from milk by high-speed centrifugation, are washed with water and dehydrated by serial transfer through liquids of decreasing polarity before final solvent removal under vacuum, the resulting dry material has a specific surface area 10 times higher than washed micelles dried directly from aqueous systems by lyophilization. Subjecting the dried proteinaceous material to cyclic H 2 O vapor sorption and desorption resulted in contraction and loss in BET surface area as measured by low temperature N 2 adsorption. The observed surface area decrease is proportional to the amount of water sorbed by the casein before removal. The data indicate that the micelles in milk may be subject to shrinkage and loss of porosity during drying by procedures based on direct water vapor transfer.

Influence of dehydration method on the adsorption of benzene vapor by dried casein

Washed casein micelles were dehydrated by serial transfer through solvents of decreasing polarity followed by drying in vacuo. The product adsorbed approximately three times as much benzene as lyophilized casein for all PP0 values at 24 and 30°C. Adsorbed C5H6 molecules are very mobile on the surfaces of the lyophilized particles, −qst = 8.7 kcal/mole over the entire isotherm. However, much of the benzene is in a more tightly bound adsorbed state on solvent transfer dehydrated casein, with −qst gradually decreasing from a high of 20 kcal/mole to a constant value near 8 kcal/mole. Both types of casein adsorbed more C6H6 than anticipated from BET surface areas calculated from low temperature N2 adsorption data. The results suggest that the apolar amino acid residues of the casein subunits, which are normally squeezed into cavities in water according to theories of hydrophobic bonding, may be separated when water is replaced with a less polar solvent. Ultimately a porous dried product is thus obtained with localized binding sites for benzene, rather than hydrophobic regions in the macromolecule.

Hydrocarbon binding by particles of bovine casein

Abstract Casein, isolated from milk by high-speed centrifugation, was washed with water and dehydrated by serial transfer through liquids of decreasing polarity to provide a system consisting of protein dispersed in anhydrous, liquid hydrocarbon. Heats of fusion of solvents associated with casein were measured to determine how much hydrocarbon is free and can be frozen and what fraction is bound to the protein and immobilized. Ring substitution decreased binding in the aromatic compounds studied, i.e. : 8.4 mmoles benzene, 4.7 mmoles p -xylene, and 3.3 mmoles mesitylene bound per gram casein. Binding of even n-paraffins was significantly less than that of the aromatic compounds and decreased with increasing chain length, i.e. : 2.0 mmoles C 8 H 18 , 1.9 mmoles C 10 H 22 , 1.6 mmoles C 12 H 26 , 1.1 mmoles C 14 H 30 , and 1.0 mmoles C 16 H 34 bound per gram casein. The observation of unfreezable hydrocarbon indicates that some solvents, commonly considered as hydrophobic, attain preferred orientation at the protein-solvent interface.