Modification of the Low-Molecular Weight Basic Albumin Fraction From Rapeseed (Brassica Napus L.) by Acetylation Part 1. Chemical and Physicochemical Aspects

Abstract

The chemical and physicochemical changes of the low‐molecular weight basic albumin fraction from rapeseed, as a function of degree of acetylation, were studied using amino and ester groups analyses, PAGE electrophoresis, isoelectric focusing, viscometry, circular dichroism and fluorescence spectroscopy. The surface hydrophobicity was evaluated by means of the ANS fluorescence probe technique. The protein was readily acetylated at the amino groups by addition of acetic anhydride. Acetylation of amino acid hydroxyl groups was significantly slower and proceeded in the presence of an excess of the reagent after the amino groups had already been blocked. Acetylation resulted in protein species with isoelectric points at pH 7.6, 6.6, 5.95 and 5.4. The intrinsic viscosity of the native protein fraction dropped from 0.159 dlg−1 to 0.038 dlg−1 at a moderate degree of modification. The secondary structure of the protein, characterized by a content of 40–45% helix conformation, was not significantly influenced by acetylation. Modification did not result in wavelength shifts of the peaks in the near ultraviolet CD and fluorescence spectra. However, the negative ellipticities in the 250–270 nm region of the CD spectrum increased markedly with increasing degree of acetylation. The surface hydrophobicity increased linearly with the amount of acetyl groups introduced into the protein.

Heat‐induced gelation of rapeseed proteins: Effect of protein interaction and acetylation

“…These data point to considerable changes in the globulin spatial structure, whereas that of napin changed only slightly owing to stabilization by disulfide bridges. A marked increase of the surface hydrophobicity at high degrees of acetylation, which has been observed for napin (23) and faba bean 11S globulin (24), can also be assumed for the rapeseed globulin component. In the latter, the hydrophobicity increase should be due both to the attachment of hydrophobic acetyl residues and to intrinsic factors that became evident by exposing buried hydrophobic residues after unfolding of the protein.…”

“…Although there is a lack of detailed information on conformational changes of the rapeseed globulin cruciferin after acetylation, the existing knowledge on structural changes in succinylated cruciferin (22) and acetylated napin (23), as well as those in acetylated plant globulin homologous to cruciferin (24), may be used to interpret the functionality of acetylated rapeseed protein isolates. These data point to considerable changes in the globulin spatial structure, whereas that of napin changed only slightly owing to stabilization by disulfide bridges.…”

Rapeseed Proteins for Paperboard Coating

“…Studies on the influence of the blocking degrees have shown a direct dependence of the ratio of the amount of reagents to reactive groups. By modification of rapeseed albumin, an N-blocking degree of 98 % could be obtained with a molar ratio of acetic anhydride to all reactive groups of 1.1 [9]. On the other hand, acetylation of rapeseed globulin and rapeseed protein isolates lead to N-blocking of 62 % and > 80 %, respectively, with a mass ratio of 0.20 g acetic anhydride per g protein [26,27].…”

Some Physicochemical and Interfacial Properties of Native and Acetylated Legumin from Faba Beans (Vicia faba L.)

“…The vicilin content amounted to e4% as determined with SDS-polyacrylamide gel electrophoresis by Schwenke et al (1994). Legumin acetylation was performed according to the procedure of Schwenke et al (1989). The legumin samples were dialyzed against distilled water and freeze-dried just after preparation.…”