Walter Bushuk Graduate Research Award in Cereal Protein Chemistry - Cross-linking of gluten, globular proteins and mixtures thereof in aqueous ethanol and water

Network formation between proteins determines processability and end product quality of many food products. The structure of wheat-based food is mainly impacted by gluten proteins (e.g. in bread and pasta) and in some cases also by albumins and globulins (e.g. in cake and egg noodles). Protein aggregation is triggered by chemical forces between amino acid side chains and its immediate environment. Food systems often contain water and sometimes also alcohols. This study compared the impact of both solvents on heat-induced aggregation and polymerization of various food proteins. In a first part, wheat gliadin, bovine serum albumin (BSA) and soy glycinin, were heated in water and 50% (v/v) ethanol. Extracts of the unheated and heated model proteins in sodium dodecyl sulfate containing media were then analyzed using size exclusion HPLC. Isolated gliadin polymerized in water but not in 50% (v/v) ethanol. In water, cross-linking of gliadin, which lacks free sulfhydryl (SH) groups was initiated by β-elimination reactions. Ethanol appeared to slow down these reactions. In 50% (v/v) ethanol, BSA already denatured at room temperature and the increased exposure of free SH groups led to covalent polymerization through SH-disulfide interchange reactions. Soy glycinin, which had a low level of free SH groups, polymerized to a larger extent in water than in 50% (v/v) ethanol. Possibly, the few SH groups originating from -elimination reactions in 50% (v/v) ethanol were rapidly consumed in oxidation reactions which terminated disulfide cross-linking. In a second part, interactions and reactions between different protein types (albumins, globulins, prolamins) were investigated. Gliadin-BSA and gliadin-glycinin mixtures polymerized to a larger extent in water than in 50% (v/v) ethanol. Globular proteins and gliadin influenced each other’s behavior in both media. During heating in water, more gliadin was incorporated in the protein network of the mixture than in that of isolated gliadin. In 50% (v/v) ethanol, gliadin slightly slowed down the polymerization of both glycinin and BSA. In a third part, it was shown that pretreatment of isolated proteins with aqueous ethanol induced conformational changes which affected subsequent cross-linking of protein mixtures in water.status: publishe