Modification of cassava and cowpeas flours and their use in flatbread (Chapati) making

Abstract

Gluten in wheat accounts for the visco-elastic behavior of dough used for making leavened bread. Although making bread takes advantage of gluten in wheat to provide a visco-elastic dough, the need for gluten is not as critical in flat breads such as chapatti, as it is in volume pan loaves of bread. Therefore, in chapatti, alternative non-gluten proteins can be used to provide the nutritional and functional properties provided by gluten. This research used extrusion technology to modify the functional and pasting properties of cassava and cowpeas flours for flat bread (chapatti) making in Uganda. The effect of extrusion on functional, pasting and dough properties of cassava and cowpeas were investigated. The study explored the potential of using wheat, native cassava (NC) and modified cassava and cowpeas flours in various proportions for chapatti making and determined the textural and sensory properties of the chapatti. Fresh cassava roots of NAROCASS1 variety were peeled, washed, grated, and dried at 50 oC for about 3 hours 40 minutes . Dry seeds of Secow2 cowpeas were soaked for 72 hours to loosen the test from the cotyledons, dehulled, and dried at 50 oC for about 3 hours.. After drying, both cassava and cowpeas were milled and modified by extrusion at constant screw speed (40rpm) but varying feed moisture content (40% to 10%), and temperature (60 and 70 oC). The functional properties Bulk Density (BD), Water Absorption Capacity (WAC), Oil Absorption Capacity (OAC), Swelling Power (SP), Water Absorption Index (WAI) & Water Solubility Index (WSI) and particle size distribution were determined using standard methods. Pasting properties (peak viscosity, breakdown, final viscosity, setback, and pasting temperature) were determined using the Rapid Visco Analyzer (RVA). The dough and textural properties were determined using the mixolab and texture analyzer, respectively. Sensory analysis was conducted by both trained and untrained panelists using the 9 point hedonic scale Extrusion moisture content (MC) had a significant (0.05%) effect on the properties of high quality cassava flour (HQCF). WAC increased from 245% to 732%, SP from 3.4 g/g to 7.2 g/g, and WAI from 3.0% to 3.3% after extrusion at 40% MC. While at lower MC levels, BD increased from 0.7 g/ml to 0.8 g/ml for the non-extruded and 30% MC; OAC from 215% to 253% for the non-extruded and 10% MC; WSI from 6.0% to 56% for the non-extruded and 20% MC respectively. MC had a significant (0.05%) effect on the functional and pasting properties of cowpeas flour (p<0.05) followed by temperature. Increasing MC from 10% to 15%, increased BD from 0.4 to 0.5, OAC 149 to 238, WAC 407 to 422, SP from 4.6 to 4.9, WAI from 3.9 to 4.2, as well as Peak (158.7-185) & Breakdown viscosities (86.5-121.3. On the other hand, reducing the moisture content decreased WSI from 31 to 21. MC improve the finctional and pasting properties of cassava and cowpeas flour and enable them to form a consistant dough which was used to make chapatti. Blending cassava and cowpeas flours showed a significant (0.05%) effect on the functional and pasting properties of flours. Increment in the proportion of extruded cowpeas flour in composite blends increased BD from 4.7-5.2g/ml, WAC 609- 628%, OAC 202-224%, WAI 3.5-3.8% while increment of extruded cowpeas substitution reduced SP from 6.3-5.8 g/g and WSI 43-40-43%. The pasting temperature increased from 50-53 oC with a increment in the proportion of extruded cowpeas flour while the rest of the pasting properties reduced as the proportion of extruded cowpeas flour was increased. Mixolab results showed an increase in water absorption (125.5%) for 100% extruded cassava flour but a decrease in water absorption (74.5 oC) for native cassava flour with a reduction in maximum torque from 1.3 Nm to 1.1 Nm for 100% native and extruded cassava, respectively. The temperature at maximum torque force for native and extruded cassava flour reduced from 60.2 to 20.5 oC respectively. This measns that extrusion improved the properties of composite of cowpea and cassava flous and make them appropiate for chapatti making. Increasing the proportion of native cassava flour in the wheat-native cassava composite chapatti decreased the resistance to extension, and area under the curve but had no effect on the extensibility and yield. Increasing the proportion of extruded cassava flour in wheat decreased resistance to extension of chapatti but increased extensibility of the chapatti with no effect on yield. Increasing the proportion of extruded cassava flour for chapatti made from extruded cowpea-cassava composite flour decreased resistance to extension and area under the curve but increased the extensibility of the chapatti with no effect on yield which signifies soft and flexable chapatti which can be easily rolled Chapattis made from 80W:20EC and 80W:20NC were not distinguishable from those made from 100% wheat flour by the sensory panel. The sensory acceptability scores for chapattis made from 80W:20EC and 80W:20NC ranged from 6-8 (like slightly-like very much), while those for the chapattis made from 20CP:80EC ranged from 4-6 (dislike slightly to like slightly). The study, therefore, revealed that modification of cassava and cowpea flours improves chapatti making ability and improves the textural and sensory properties of the chapatti.