Interface characterization and aging of bovine serum albumin stabilized oil-in-water emulsions as revealed by front-surface fluorescence.

This paper is devoted to the application of front-surface fluorescence to the study of aging and oxidation of oil-in-water emulsions. Emulsions with two oil droplet sizes were stabilized with bovine serum albumin (BSA) and stored at 37 or 47 degrees C. Lipid oxidation was demonstrated by measurement of hydroperoxides and headspace pentane. Front-surface fluorescence spectra (excitation wavelength = 355 nm) revealed gradual formation of oxidized lipid-protein adducts during the 4 weeks of storage. Fluorescence (excitation = 290 nm) of BSA tryptophanyl residues (Trp) declined during the first day of aging and then decreased slightly and linearly. Fourth-derivative Trp spectra exhibited peaks at 316 and 332 nm. Their evolution indicated that the ratio of Trp in hydrophobic environments to total Trp increased in small droplet emulsions. This suggests that, during lipid oxidation, the adsorbed and nonadsorbed protein underwent various degrees of Trp degradations, polymerization, and aggregation. Thus, front-surface fluorescence makes it possible to evaluate, noninvasively, protein modification and lipid oxidation end-products during processing and storage of food emulsions.

Crystal and molecular structure of a histo-blood group antigen involved in cell adhesion: the Lewis x trisaccharide.

This work describes the first crystal structure ever reported of a histo-blood group carbohydrate antigen: Le(x). This study provides a detailed description of the conformation of two crystallographic independent molecules in a highly hydrated environment along with their hydrogen bonding properties and packing features. Some interactions observed between adjacent trisaccharides can provide the basis for involvement of Le(x)-Le(x) interactions in cell-cell adhesion.

Computer modeling of the tetrasaccharide nystose.

Nystose, O-beta-D-fructofuranosyl-(2-->1)-O-beta-D-fructofuranosyl-(2-->1)- beta-D-fructofuranosyl alpha-D-glucopyranoside, was modeled with the rigid-residue program PFOS and with MM3. The three furanose rings of crystalline nystose trihydrate all are within the 1 kcal.mol-1 contour on an MM3 energy surface that was calculated with a dielectric constant of 4. The calculations showed that in the extended conformation found in the crystal, there was a small influence of the remainder of the residues on the conformation of any given disaccharide segment. Even accounting for intramolecular, interresidue forces, however, the central inulobiose and the sucrose linkages appear to be distorted. These discrepancies are apparently due to crystal packing forces and, for the sucrose linkage, miscalculation of the energy of an overlapping exoanomeric effect, as indicated by studies of a model miniature crystal. The different conformations of the central and terminal inulobiose linkages in the crystal show that conformations in higher oligosaccharides will not always correspond to the global minima on conformational maps for isolated disaccharides.