The effect of heat on wheat gluten and the involvement of sulphydryl-disulphide interchange reactions

Abstract

The baking performance of gluten declined progressively on heating and most of its functionality was destroyed by 75°C. This was accompanied by a decreased extractability of the gluten proteins in an SDS buffer, and chromatographic examination of the SDS-extracted proteins showed that glutenin proteins were affected predominantly. Extractability of gliadin proteins in aqueous propan-l-ol was unaffected by heating at temperatures up to 75°C but decreased markedly after heating at 100°C. Electrophoresis showed that the gliadin patterns were essentially unaltered up to 75°C but at 100°C ω-gliadins dominated the patterns. Both the change in propanol extractability at 100°C and the alteration in the gliadin pattern were reversed by including dithioerythritol in the extradant. Total free sulphydryl groups were measured and these were esssentially constant irrespective of temperature. However, there was a progressive shift of free sulphydryl groups from an SDS-extractable to an SDS-insoluble form. Chromatographic examination showed that free sulphydryl groups were found predominantly in glutenin aggregates of lowest molecular weight and in gliadins; sulphydryl groups in these glutenin species were particularly involved in the changes occurring at 55–75°C. These data indicate that there are heat-induced alterations in gluten proteins at temperatures above 55°C, which appear to be involved in the loss of functionality (baking performance) on heating. It is postulated that the glutenin proteins are unfolded on heating up to 75°C and that this facilitates sulphydryl/disulphide interchange between exposed groups. The protein is then ‘locked’ into the denatured state on cooling due to this disulphide bond rearrangement. At temperatures above 75°C the gliadin proteins are also affected, involving similar mechanisms.