ELUCIDATING THE STRUCTURAL CHANGES OF SOYBEAN BETA-CONGLYCININ AT THE OIL-WATER INTERFACE

Soy proteins are among the most used plant-derived food proteins in human nutrition for their interesting nutritional proprieties. They reportedly exhibit hypocholesterolemic effects and prevent cardiovascular diseases, and their physicochemical proprieties are exploited for their use as food ingredients. beta-conglycinin constitutes 30% of total soybean proteins. Beta-conglycinin is a glycosilated hetero-trimer composed randomly by three different subunits: alpha, alpha’ and beta. The alpha and alpha’subunits are composed by two different domains: the core region and the extension region. The beta subunit only contains the core region. beta-conglycinin readily adsorbs at the interface of an oil-water emulsion with homogenization, but very little is understood yet on the details of the structural changes at the interface. These changes may affect the biological activity of beta-conglycinin, including allergenicity and bioavailability. The aim of this work is to study the structural changes of beta-conglycinin at the oil-water interface. Fluorescence spectroscopy was used to evaluate tertiary structural changes in beta-conglycinin stabilized emulsions. Mass spectroscopy was utilized for a preliminary identification of the peptides released after tryptic digestion of beta-conglycinin alone and at the emulsion interface. Beta-conglycinin undergoes a structural change at the oil-water interfaces. In fact, the fluorescence spectra of the protein in beta-conglycinin stabilized emulsion are red-shifted compared with the fluorescence spectra of the native protein. In particular, beta-conglycinin tryptophans seem to increase their exposure to solvent water when the protein interacts with the oil surface. Tryptophans in the mature form of beta-conglycinin are present only in the in the N-terminal extension regions, the least hydrophobic areas, of alpha and alpha’ subunits. After emulsion digestion with trypsin, some peptides were released into the aqueous phase, including the tryptophan containing regions in the extension domains. Large peptides from the core region are released as well. These peptides come from the least hydrophobic regions of this domain. In conclusion, it is possible to hypothesize that the core regions of the beta-conglycinin subunits interact with the oil phase, whereas the extension regions of the alpha and alpha’subunits protrude in the aqueous medium. Our proteolysis data also suggest that the core domain is oriented with its least hydrophobic regions exposed to the water.