RESUMO

Raw yam (Dioscorea rotundata) flour was cooked and extruded in a Brabender single-screw laboratory scale extruder. Response surface methodology using an incomplete factorial design was applied with various combinations of barrel temperature [100, 125, 150 degrees C], feed moisture content [18, 22, 26%] and screw speed [100, 150, 200 rpm]. Initial viscosity at 30 degrees C, water solubility index, expansion and hardness were determined. The highest values of initial viscosity were at the highest barrel temperatures and the highest moisture contents. At high feed moisture content and high barrel temperatures the yam extrudate flour showed the greatest values of water solubility index. The physical properties of the extruded product showed that at high temperature the lower the moisture content the greater the expansion index. Hardness was influenced directly by moisture content and inversely by extrusion temperature. The extrusion of yam flour led to the production of snacks and pre-gelatinized flours of diverse properties. Also extruded yam flour can be successfully used in the preparation of 'futu' (pre-cooked compact dough), a yam-based food, popular in Western Africa.

Assuntos

Farinha/análise , Solanaceae/química , Fenômenos Químicos , Físico-Química , Manipulação de Alimentos , Indústria Alimentícia , Dureza , Solubilidade , Viscosidade

RESUMO

Whole, ground and abrasively dehulled grains from both normal (H-34 and H-34) and quality protein (QPM and QPMa) maize were mixed with water contents of 70, 95 and 100 g kg-1 and calcium hydroxide concentrations of 0.0, 0.3, 0.5 and 2.0 g kg-1 and heated (operating frequency 2.450 MHz, high-power setting) for 10, 15 and 20 min in a commercial microwave oven. The cooked grain was then oven dried and milled to obtain nixtamalised maize flour (NMF). The protein contents and test weights of QPM were higher than for the normal hybrids. The highest yields of masa and tortillas were found for the normal hybrids, and these samples did not show significant differences, as compared with the commercial nixtamalised flour (CNMF) used as control, with respect to masa firmness and adhesiveness and tortilla tensile strength. The cutting force of tortillas from hybrid H-30 and QPM did not show significant differences from the control. The highest values of tortilla rollability were found for the control followed by hybrid H-34. The values of residual cooking liquor for microwave-heated samples were lower than for the control. Ground or dehulled maize grain gave sticky masa and poor mechinical characteristics. Tortillas from whole grain showed good characteristics of texture and consistency of masa, and the tortillas were subjectively similar in colour, flavour and rollability to the tortillas prepared with CNMF. These results indicate a potential use of microwave energy to produce NMF for tortillas and derivatives. © 2000 Society of Chemical Industry.