Effect of frozen storage on physico-chemistry of wheat gluten proteins: Studies on gluten-, glutenin- and gliadin-rich fractions

In this study, the effect of frozen storage on chemical and physical properties of wheat gluten-, glutenin- and gliadin-rich fractions was evaluated. Chemical changes were studied by size-exclusion (SE) and reversed-phase (RP) high-performance liquid chromatography (HPLC), thiol (SH) measurement, sodium dodecyl sulphate poly-acrylamide gel electrophoresis (SDS-PAGE), circular dichroism (CD) spectroscopy and Fourier transform infrared (FTIR) spectroscopy. Physical properties were determined by dynamic rheological measurements. During the frozen storage, depolymerization of glutenin macropolymer (GMP) was observed by SE-HPLC in gluten- and glutenin-rich fractions with a higher depolymerization rate of GMP in gluten-rich fraction, this further suggested that gliadin might have the potential to disaggregate the GMP. The depolymerization effects led to the major variation of thiol content. The results of SE-HPLC were also in accordance with that of the SDS-PAGE profiles of gluten and glutenin-rich fractions. No aggregation behavior was observed for α-gliadin and γ-gliadin containing cysteine in gluten- and gliadin-rich fractions, leading to the constant content of thiol content of gliadin during the frozen storage. The results of combined CD spectroscopy and FTIR spectroscopy indicated non-covalent interactions were also affected. Significant loss of elastic modulus (G′) and viscous modulus (G″) to gluten- and glutenin-rich fractions were detected with the increasing storage except that no apparent changes occurred in gliadin-rich fractions, suggesting that variation of glutenin functionality was quite important for that of gluten. Moreover, highly significant negative correlations between the content of SDS-soluble glutenin and data of G′ were found in gluten- and glutenin-rich fractions suggested depolymerization of GMP was the main indicator of deterioration of gluten and glutenin during the frozen storage.