Abstract
In this study, the effects of frozen (−18 °C) storage time on molecular weight, size distribution, conformation, free amino groups and free sulfhydryl groups of gluten were studied by small-angle X-ray scattering (SAXS), multi-angle laser light scattering (MALLS) in conjunction with a size exclusion chromatography (SEC) and spectrophotometrically. The results showed that the gluten dissolved in 50 mM acetic acid appeared to be similar to quasi-spherical of the chain conformation and the slope of theconformation plot decreased during the storage. Both the molecular weight and radius of gyration of the frozen gluten decreased with the storage time showing a depolymerization in the high molecular weight fraction of gluten (105 Da ~ 109 Da). Therefore, at constant molecular weight the change of the chain conformation did not show a clear correlation with the storage time. The free amino groups content changed little and the free sulfhydryl groups content of the gluten increased from 9.8 μmol/g for the control to 12.87 μmol/g for 120-day-stored gluten, indicating that the water redistribution and ice recrystallization lead to the breakage of the disulphide bonds and may be one of the reasons for the depolymerization of gluten polymer.
Highlights
The frozen food market has grown steadily in recent years due to the convenience and high quality of frozen foods
Southan and MacRitchie proved that the properties of dough such as tensile strength were determined by a fraction of polymer with Mw above a certain critical value (1 × 106 Da) and the molecular weight distribution (MWD) of this fraction [1]
This postulation was further supported by the fact that the scattered intensity at zero angle, I(0) of the small-angle X-ray scattering (SAXS) data listed in Table 1, which is related to the Mw of the solutes in solution [7,12], decreased with the frozen storage time
Summary
The frozen food market has grown steadily in recent years due to the convenience and high quality of frozen foods. It was reported that the molecular weight (Mw) and distribution of the wheat gluten protein complexes are related with dough texture and baking properties. With the development of the corresponding instrumentation new methods have recently become widely used to detect the molecular weight and distribution, e.g., Kuktaite et al [4] and Gupta et al [5] used size-exclusion high-performance liquid chromatography (SE-HPLC) to investigate the change of size distribution in the gluten during dough processing. The objective was to further investigate the effect of prolonged frozen storage on the solution conformation, Mw and size distribution of the gluten by the SAXS and SEC-MALLS techniques
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