Correlation of Product Quality of Extruded Sorghum Products to Extent of Starch Gelatinization 1
A comparison was made of extrudes made from pure sorghum flour (Ll87), wheat flour (biscuit) and composites of the two flours containing various percentages of sorghum. The different parameters which were contrasted included expansion and density, mechanical strength (shear) and colour. Correlation of these properties to the extent to which starch was gelatinized at the extrusion temperature was made. Amount of gelatinized starch was monitored by Direct Scanning Calorimetry (D.S.C) in conjunction with Scanning Electron Microscopy (S.E.M). Results indicated that there is a direct relationship between extent of product expansion and extent of gelatinization, loss of shear with extent of gelatinization; increase in expansion with increased moisture content for sorghum products and-decrease of colour (tannin content) with increased gelatinization. The ability of wheat and sorghum to gelatinize at different temperatures was identified as the main setback to production of good composite extrudes.
Key words: Sorghum, wheat, extrusion, Direct Sc,mning Calorimetry (D.S.C), Scanning Electron Microscopy (S.E.M)