Optimization of Physical and Functional Properties of Sorghum-Bambara Groundnut Extrudates

Abstract

Blends of sorghum and Bambara groundnut flour at 90:10, 80:20 and 70:30 ratios respectively, were extruded at 20%, 22.5% and 25% moisture levels and 120 o C, 140 o C and 160 o C barrel temperatures using a single-screw extruder. Response surface methodology with central composite face-centered (CCF) design was used to model the viscosity, water absorption index (WAI) water solubility index (WSI), sectional expansion index (SEI), bulk density (BD), apparent specific volume (ASV) and mass flow rate of the extrudates. , and 1.19 to 2.3 g/s respectively. The R 2 values were 0.83, 0.71, 0.55, 0.61, 0.66, 0.77 and 0.61 respectively with a non-significant lack of fit; except for viscosity. Plots of residuals against fitted values showed that residuals were randomly scattered in all cases, thus validating the empirical models for the responses. The optimum amount of Bambara groundnut flour, feed moisture and extrusion temperature were established for viscosity, WAI, SEI, BD, ASV and MFR of the extrudates. Feed moisture had the most effect on extrudates functional and physical properties followed by extrusion temperature.

Evaluation of selected properties of gluten-free instant gruels processed under various extrusion-cooking conditions [pdf]

“…The influence of initial moisture content or raw materials on the bulk density values was significant (Table 2) and similar for both compositions: bulk density of the extrudates increased with the higher initial moisture content of raw materials with R 2 = 0.84 and 0.70 for 75:25 and 50:50 samples, respectively (Table 1). Low bulk density is preferred in infant and weaning foods (Gbenyi et al, 2016). The same conclusions were made by Ding et al (2006) for extruded wheat flour.…”

“…2b). A lower water absorption capacity is desirable for making thinner gruels (Gbenyi et al, 2016). Results presented by Trela and Mościcki (2007) showed a similar tendency; increasing WAI if the amount of rice was increased in the recipe from 27 to 67.5%, and if snack pellets were processed at 35% moisture.…”

“…Potato starch moistened to 18-30% and extruded with a single-screw extruder was characterized by similar properties: increasing moisture level of raw materials increased WAI of the extrudates (Mitrus et al, 2010). The WAI range reported by other authors depended on raw materials used, the type of extruder and processing conditions, and varied from 4.5 to 6.6 g•g -1 for gluten-free extrudates based on rice flour and from 3.6 to 5.6 g•g -1 for fiber-enriched extrudates (Stojceska et al, 2010) and from 5.3 to 6.2 g•g -1 for sorghum-bambara groundnut extrudates (Gbenyi et al, 2016). Similar results, varying from 5.6 to 6.4 g•g -1 were reported for WAI of corn extrudates with added broccoli and olive paste (Bisharat et al, 2015), but a WAI almost 50% lower was observed for extruded instant rice-soybean or rice-mung bean porridge, varying from 3.21 to 2.77 g•g -1 , which decreased when the amount of legumes was increased (Mayachiew et al, 2015).…”

“…Stojceska et al (2010) reported bulk density of extrudates ranging from 100 up to 250 kg•m -3 for gluten-free extrudates and even up to 630 kg•m -3 if some fruit or vegetable fibers were added to the recipe. Gbenyi et al (2016) reported a bulk density of extrudates from sorghum flour from 223 to 499 kg•m -3 if groundnut flour was addied. Fleischman et al (2016) found a bulk density of 300 kg•m -3 for waxy wheat flour extrudates, which increased to up to 800 kg•m -3 if 37.5% of the mixture was replaced by wheat bran.…”

“…The extrusion-cooking process is carried out in extruders, in which the main operative element is a screw or pair of screws fitted into a barrel (Mościcki et al, 2007). Food extrusion is a complex process because it requires continuous control of many different parameters to ensure that the products will have the desired characteristics and a balanced nutritional composition (Fleischman et al, 2016;Gbenyi et al, 2016;Mayachiew et al, 2015). Processing variables, i.e.…”