Effect of dextrans of differing molecular weights on the rheology of wheat flour doughs and the quality characteristics of pan and Arabic breads

Dextrans (alpha-1-6-D-glucans) with weight-average molecular weights (Mw) ranging from 10 to 500 kDa were used at a rate of 20 g kg-1 (flour basis) in order to modify doughs made from flour of the Australian hard-grained wheat cultivars Banks, Sunco and Hartog. Doughs containing dextran fractions with Mw below 100 kDa showed significant (P less than or equal 0.01) reductions in Farinograph maximal consistency and significant increases in Farinograph development time. Additions of dextrans also resulted in significant increases in maximal resistance and significant reductions in extensibility when doughs were subjected to Extensograph testing. After addition of dextran fractions with Mw of 100 kDa or less, there were significant reductions in loaf volumes in pan bread of the cultivar Hartog manufactured by a rapid dough system and in pan bread of the cultivars Banks and Hartog made by a fermented dough system. Arabic bread supplemented with dextrans had poorer internal and keeping qualities, and reduced bread surface area, leading to significantly decreased quality scores. These observations are discussed in relation to possible interactions between neutral polysaccharides and other flour components.