Abstract
The aim of this work was to investigate the effect of ascorbic acid and a commercial bread improver on the physical quality of wheat-maize bread, and establish correlations between the physical properties of the bread and rheological properties of the dough. Wheat flour was substituted with 10, 20 or 30% maize flour and the farinograph and extensograph properties of the dough were evaluated. Farinograph water absorption, dough development time, dough stability and farinograph quality number decreased whereas the degree of softening increased with increasing substitution of wheat flour with maize flour. Extensograph dough energy, resistance to extension, extensibility and maximum resistance decreased with increasing substitution of wheat flour with maize flour. Ascorbic acid and commercial bread improver improved bread specific volume and form ratio; decreased crumb firmness, resilience and chewiness; and increased crumb springiness and cohesiveness. Farinograph water absorption and degree of softening; and extensograph energy, extensibility, maximum resistance and ratio number showed the highest number of significant correlations (P ≤ 0.01 or P ≤ 0.05) with the physical properties of wheat-maize bread. Key words: Bread, maize, wheat, rheology, texture profile analysis.  
Highlights
The unique dough-forming and breadmaking property of wheat is ascribed to gluten protein, which is formed when wheat flour is hydrated and subjected to mechanical shear
The water absorption of doughs made from wheat-maize flours tended to decrease with increasing substitution of wheat flour with maize flour
The changes in dough rheology were reflected in the physical properties of the wheat-maize breads, which declined with increasing substitution of wheat flour with maize flour
Summary
The unique dough-forming and breadmaking property of wheat is ascribed to gluten protein, which is formed when wheat flour is hydrated and subjected to mechanical shear. Substitution of wheat flour with non-wheat flour reduces the bread making potential of wheat flour due to dilution and disruption of the rheological and mechanical properties of gluten (Schoenlechner et al, 2013; Ribotta et al, 2005). Wheat production in sub-Saharan Africa remains insignificant relative to demand because of the unsuitable production environment (UNECA, 1998). Maize grows well in diverse agro-ecological zones and is an important source of macro- and micronutrients to millions of people in sub-Saharan Africa. Maize is principally used to make stiff or thin porridge (Onyango, 2014), potential exists to further increase its utilisation in processed foods such as bread (UNECA, 1998)
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