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Breadmaking properties of barley proteins Ho, Mary Kwok

Abstract

Similarities can be drawn between protein contents, solubility profile, remix loaf volume, and total sulfhydryl-disulfide contents of barley and wheat flours. However, the quantitative relat-ship between loaf volume and protein content or protein solubility distribution used for wheat flour did not apply to barley. Barley flour demonstrated very poor breadmaking ability and low loaf volume. Elution patterns from Sephadex G100 showed that the molecular weight of barley gluten was lower than wheat. Sephadex G150 elution profiles of barley and wheat glutelin gave two and three peaks respectively. The F₂ fraction of wheat glutenin, which differentiates the breadmaking potential of different wheat flours, was missing in barley. Turbidity studies on protein aggregation behavior revealed that barley proteins had a lower aggregation rate than wheat. Wheat gliadin gave the highest rate of aggregation, while hordein failed to aggregate. The alcohol soluble protein fraction of barley was capable of polymerization via disulfide bridges at low temperatures, which resulted in 'gluten' formation in vitro. Such a phenomenon was not observed in wheat. Addition of oxidizing agents did not improve the quality of barley dough. These suggested that the thiol and disulfide groups of barley are either very inaccessible, and/or different from wheat. Therefore, it is postulated that the Theologically effective sulfhydryl and disulfide groups in barley are inferior in quality and quantity than that of wheat. Amino acid analysis demonstrated that proteins of barley and wheat were different in structure and composition. The amount of glutamic acid in barley was only about 70fo that of wheat. Fluorescence quenching studies showed that hydrophobicity of wheat gluten was higher than barley. Barley is weak in the vital chemical forces which govern breadmaking potential, and furthermore there are numerous differences among functional proteins of these two cereals. These studies would provide some insights to their differences in physical properties and breadmaking potentials.

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