Enhancing Composite Cassava Bread Quality - Effect of cassava pre-treatment and baking improvers

Doctoral thesis, 2015

Due to unfavourable climatic conditions, the production of wheat in Mozambique is not sufficient to satisfy national food industrial needs and substantial quantities must be imported at high cost. Bread is currently produced basically using wheat flour. Therefore, this thesis examined the partial replacement of wheat flour by cassava-maize flours in the Mozambican bread manufacturing context and looked for ways of improving bread quality at high wheat flour substitution. The effect of cassava pre-treatment (sun drying, roasting and fermentation), cassava level (20, 30 and 40%) and the addition of a baking improver, high methoxyl pectin (HM pectin) at two levels 1 and 3%, were evaluated for the bread quality parameters of loaf volume, crumb firmness, and crust colour. The loaf volume decreased by 20 to 30% in comparison with the wheat reference bread as a result of added cassava flour that had been pre-treated in different ways. Increasing the cassava level reduced the loaf volume except for bread with roasted cassava, which even increased in volume with the addition of high level HM pectin; the crumb firmness was higher in composite bread with sun-dried and fermented cassava flour compared with wheat bread, although the composite bread with roasted cassava flour with 3% HM pectin had a crumb firmness similar to wheat bread. Bread baked with roasted cassava flour also had a crust colour similar to wheat bread. The roasting pre-treatment of cassava flour along with baking improvers was indicated to have a good potential to improve the baking quality of composite cassava-maize-wheat breads. Two hydrocolloids, HM pectin and carboxymethylcellulose (CMC), were added alone or in combination with three different emulsifiers (DATEM, LC and SSL) in formulation of composite cassava-maize-wheat (ratio 40:10:50) breads in order to gain knowledge of their effect on bread quality characteristics. Each emulsifier was tested in combination with the hydrocolloids at the levels of 0.1, 0.3 and 0.5%, while hydrocolloids were used at the level of 3%. It was concluded that the hydrocolloids in combination with emulsifiers had a greater effect than hydrocolloids alone in increasing the specific volume (from 7.5 to 22%) and the brownness index (from 81.8 to 86.6%) and reducing the crumb firmness of the breads (from 14 to 36%). Two composite cassava-maize-wheat breads with either CMC/DATEM or HM pectin/LC, both at levels of 3/0.3%, were assessed for their acceptability and sensorial attributes among Mozambican consumers. The consumption pattern, willingness to buy and attributes of the composite breads were also collected. It was concluded that the optimized composite bread with 40% roasted cassava and CMC/DATEM was highly acceptable (score of 7.47 out of 9) and comparable to commercial wheat bread (score of 7.82 out of 9). Instrumental analysis of crust and crumb colour and firmness correlated highly with their perceived sensorial properties of its counterpart. Texture, moisture content and starch retrogradation (recrystallized amylopectin) of optimized composite bread were evaluated during storage up to four days under controlled conditions (23oC and 50% RH). In addition to the improvers used in the sensory analysis, monoglyceride (MG) was evaluated for its role on the bread quality during storage of those composite breads. DATEM and MG showed a softening effect, while the melting enthalpy was significantly lower in the composite bread with the hydrocolloids and emulsifiers compared to composite bread (without improvers).