Abstract
In this study, seventeen (17) composite blends of broken rice fractions and full-fat soybean, formulated using response surface methodology and central composite design within a range of barrel temperatures (100-140 °C), initial feed moisture content (15-25%) and soybean composition (8-24%), were extruded with a twin-screw extruder and the expansion and color indices were optimized. The results indicated a significant (p<0.05) effect of extrusion conditions on the responses. Fitted predictive models had coefficients of 88.9%, 95.7%, 97.3%, 95.4% and 95.2%, respectively, for expansion index, bulk density, lightness, redness and yellowness. The p-value and lack-of-fit tests of the models could well explain the observed variability and therefore could be used to establish production setting for the twin-screw extruder. The optimum extrusion conditions were found to be 130 °C (barrel temperature), 20% (feed moisture level) and 23% feed soybean composition and optimum responses in terms of bulk density, expansion index, lightness, redness and yellowness chroma indices were 0.21 g cm -3 , 128.9%, 17.1, 3.13 and 24.5 respectively. This indicates that optimum conditions can be established in twin-screw extrusion cooking of broken rice fractions and full-fat soybean composite blends that can result in product of low bulk and maximum expansion with a satisfactory light yellow product color that can be used to produce products that valorize broken rice and reduce qualitative postharvest loss.
Highlights
Rice (Oryza sativa L.) is an important source of food for a large number of the population in subSaharan Africa (SSA), its production and utilization is an important economic program for most governments in the region
These observations are similar to those reported by Nwabueze (2007), that thin-smooth to thin-fine-smooth extrudates were obtained when African bread fruits blended with soybean and yellow maize were extruded at a higher moisture level
In the reports of Agbisit, Alavi, Cheng, Herald, and Trater (2007), Yagci and Gogus (2008), it had been demonstrated that variation of feed moisture content and temperature during extrusion cooking affected the degree of expansion through transformation of the extrusion matrix, leading to differences in void space formation of puffed products
Summary
Rice (Oryza sativa L.) is an important source of food for a large number of the population in subSaharan Africa (SSA), its production and utilization is an important economic program for most governments in the region. Research investment for the reduction of postharvest losses has resulted in increased interest in the utilization of rice flour from low grade broken rice fractions for the production of value added products Extrusion cooking technology and blends of cereals and legumes have been used in several parts of Africa to produce products that are nutrient dense, consumer acceptable, with improved physical and functional qualities (Danbaba et al, 2017; Filli, 2011, 2016; Gogoi, Oswalt, & Choudhury, 1996). To maximize the use of EC in new food product development, it is important to be able to alter process conditions to produce consumer acceptable products, improved physical and functional properties, minimized cost of production by adopting low-cost raw materials, maintained
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