Abstract:
Consumer interest in convenience foods is expected to continue growing world-wide due to the ever-busy lifestyle and urbanization. The challenge has been the nutritional shortcomings linked with convenience foods such as higher glycaemic index values since they are extruded from sifted cereals which are very high in starch, but low other nutrients. Thus, the objective of this study was to innovatively develop a high protein and high dietary fibre instant flour from composite blends of rice (OF)/ZL1 sativa), sorghum (Sorghum bicolor) and bamboo (Yushania alpina) shoots. First stage was to fonnulate blends from the three ingredients by optimization of protein, fibre and other nutrients using the Mixture Design Analysis (MDA) modelling approach. Second stage was to detennine the effect of extruder ingredient variables: feed blending, feed moisture and feed rate on the resultant products physico-chemical and shelf-life properties. Optimization modelling by MDA was by use of Minitab® software. Processing employed a factorial design where five blends (l00:0:0, 70:30:0, 60:30:10, 55:30:15 and 50:27:23 for rice, sorghum and bamboo shoot flour (BSF) respectively, on dry weight basis)), three levels of water addition (15, 20 and 25 kg/h) and two feed rates (1,800 and 2,100 kg/h) were used. A single screw dry extruder with barrel temperature of 250°C and screw speed of 1,480 rpm were used. The dry extrudates were milled to particle size of 0.2 um to obtain instant flour. Rice was rich in carbohydrates at 77.7%, BSF were richest in protein and fibre at 27.2% and 23.66%, respectively, while sorghum had the highest total phenolic and condensed tannins of 45.51 (mg GAE/kg) and 2.51 (mg CE/g), respectively. Optimization showed that increasing the amounts of BSF and sorghum in rice resulted in significant increase in all nutritional components of resultant blends. Optimum blend was established to have a ratio of 50:27:23 for rice, sorghum and BSF, respectively, with 13.4% protein, 6.2% fibre and 3.9% total minerals. Extrusion increased total phenolics and in-vitro protein digestibility by 96.3 and 36.9%, respectively in instant flour as compared to their respective raw blends. Extrusion reduced dietary fibre and condensed tannins by 14.9 and 88.7%, respectively. Increasing BSF in feed blends significantly caused increase in carbohydrates by 0.3-4.0% and fat by 0.01-0.2% while reducing protein loss from 1.4% to 0.03% and increasing fibre loss from 0.03% to 2.4%. Water addition rate caused significant increase of carbohydrates but reduced the loss of fibre and increased loss of fat. Feed rate only significantly affected carbohydrates. Hence, the findings of this study for the first time demonstrate that sorghum and bamboo shoots offer potential for development of novel and nutritious instant flour that can meet diverse consumer needs.
