Comparison of the gel-forming ability and gel properties of α-lactalbumin, lysozyme and myoglobin in the presence of β-lactoglobulin under high pressure

alpha-Lactalbumin (alpha-La) and lysozyme (LZM) each contain four disulfide bonds but no free SH group, whereas myoglobin (Mb) possesses no disulfide bond or free SH group. In this work, the pressure-induced gelation of alpha-La, LZM and Mb in the absence and in the presence of beta-lactoglobulin (beta-Lg) was studied. Solutions of alpha-La, LZM and Mb (1-24%, w/v) did not form a gel when subjected to a pressure of 800 MPa and circular dichroism analysis revealed that both alpha-La and LZM are pressure-resistant proteins. In the presence of beta-Lg (5%, w/v), however, a pressure-induced gel formed for alpha-La and LZM (each 15%, w/v) but not for Mb (15%, w/v). One- and two-dimensional SDS-PAGE demonstrated the disulfide cross-linking of proteins was responsible for the gelation. Although alpha-La and LZM are homologous and have the same disulfide bond arrangement, the texture and appearance of the gels formed from alpha-La/beta-Lg and LZM/beta-Lg were markedly different even when induced under the same experimental conditions. Microscopic analysis indicated that phase separation occurs during the gelation of LZM/beta-Lg but not during the gelation of alpha-La/beta-Lg. NMR relaxation measurement revealed that the association of water molecules with the protein matrix in the alpha-La/beta-Lg gel is tighter compared to that in the LZM/beta-Lg gel. These results indicate that the gel-forming ability of a globular protein under high pressure is related to the primary structure of the protein, and that the gel properties depend on the cross-linking reaction and on the phase behavior of protein dispersion under high pressure. (c) 2013 Elsevier Ltd. All rights reserved.