Structuring diluted wheat matrices: impact of heat moisture treatment on protein aggregation and viscoelasticity of hydrated composite flours

Abstract

The influence of heat-moisture treatment (HMT) and flour hydration (DY) on the restoration of dough viscoelasticity of wheat/non-wheat binary matrices was investigated by applying fundamental and empirical rheological procedures, and the protein structural reorganisation was monitored by measuring residual protein solubility in different media, and by assessing the accessibility of thiol groups inside the protein network. Single chestnut (CN), chickpea (CP), millet (MI) and teff (T) flour samples submitted to HMT (15% moisture content, 1 h and 120ºC) were blended with wheat flour at 10% (CN, CP) and 30% (MI, T) of replacement, and binary matrices hydrated at low (L), medium (M) and high (H) DY. Structuring ability of HMT was mainly observed in cereal flour blends (T, MI), where higher elastic moduli and lower loss tangent together with solid-like elastic structure over higher shear stress were observed as compared with treated non-cereal flour blends (CN. CP). Increased flour hydration significantly weakened blends structure, inducing a stepped decrease in dynamic moduli values particularly noticed in cereal blends at highest level of flour hydration, and a shift from elastic-like to viscous-like structure at lower shear stress in non-wheat cereal matrices. The formation of a protein network with reinforced compact structure associated to the presence or formation of intramolecular (CN, CP, T) and intermolecular disulphide bonds (CN, CP, MI, T), water soluble (CN, MI) and water insoluble aggregates (CP, T) is feasible to achieve with proteins of non-wheat flours submitted to HMT, particularly in high DY doughs. The lower the amount of free thiols in high molecular weight proteins encompassing high degree of crosslinking, corresponded to thermally treated samples (T, MI) blended at L and M hydration levels. For thermally treated samples, the lower the amount of free thiols in high molecular weight proteins encompassing high degree of crosslinking, corresponded to T and MI binary matrices blended at L and M hydration levels. These samples exhibited a solid-like elastic structure over higher shear stress and showed increased tolerance to stress/ strain before losing the structure.