Effect of soaking and extrusion on functional and pasting properties of cowpeas flour

Cowpea (Vigna anguiculata) is a leguminous crop that is widely grown and consumed in Asia and Africa as a major source of dietary protein. This study investigated the effect of varying extrusion conditions (temperature and moisture content) on the functional and pasting properties of cowpea flour. Particle size distribution, functional and pasting properties of cowpeas flour were determined. Moisture content had a significant effect on the functional and pasting properties of cowpeas flour followed by temperature. Increasing moisture content from 10% to 15%, increased the bulk density from 0.4 to 0.5, Oil Absorption Capacity 149 to 238, Water Absorption Capacity 407 to 422, Swelling Power 4.6 to 4.9, Water Absorption Index 3.9 to 4.2, as well as Peak & Breakdown viscosities. On the other hand, reducing the moisture content decreased Water Solubility Index (WSI) from 31 to 21. Lower extrusion temperature increased all the functional properties except WSI along with pasting properties namely Peak, Final and setback viscosities. Higher extrusion temperature increased WSI, breakdown, peak time, and pasting temperature. The results suggest that variation of extrusion conditions can be used to modify the functional and pasting properties of cowpea flour to suit different applications

Performance Evaluation of a Locally Fabricated Hammer Mill

The performance of a hammer mill fabricated in Uganda was evaluated and the optimal performance conditions were determined. The evaluation was done with screen hole diameters (S) of  1.5, 2.0, and 3.0 mm, hammer tip speeds (H) of 68.12, 81.81, 102.17 m s-1 and hammer thicknesses (T) of 4.0, 5.0, and 6.0 mm for determination of energy consumption and final particle size (GMD) using a modified central composite (CCD) split-plot experimental design. Screen hole diameter and hammer thickness had significant effects on energy consumption (p<0.05). S and H had a significant effect on GMD but with T did not have a significant effect on GMD. S and H had significant effects on both GMD and energy consumption. Quadratic effect of T, interaction effects of TH and HS also had significant effects on energy consumption. The hammer mill was most efficient with a hammer thickness of 5 mm, hammer tip speed of 83.57 m s-1 and screen hole diameter of 2.16 mm, both for energy consumption and flour GMD. The achieved impact energy calculated per unit mass, were 0.8144 kWh t-1, 1.1748 kWh t-1 and 1.832 kWh t-1 for tip speed settings of 68.12, 81.81, and 102.17 m s-1 respectively. Impact energy supplied did not have an effect on GMD. Hammer mill settings obtained should be tested on other grains

Viscoelastic properties of sweet potato complementary porridges as influenced by endogenous amylases

Sweet potato (Ipomoea batatas L.) roots contain amylolytic enzymes, which hydrolyze starch thus having the potential to affect the viscosity of sweet potato porridges provided the appropriate working conditions for the enzymes are attained. In this study, the effect of sweet potato variety, postharvest handling conditions, freshly harvested and room/ambient stored roots (3 weeks), and slurry solids content on the viscoelastic properties of complementary porridges prepared using amylase enzyme activation technique were investigated. Five temperatures (55°C, 65°C, 70°C, 75°C, and 80°C) were used to activate sweet potato amylases and the optimum temperature was found to be 75°C. Stored sweet potato roots had higher soluble solids (⁰Brix) content in the pastes compared to fresh roots. In all samples, activation of amylases at 75°C caused changes in the viscoelastic parameters: phase angle (tan δ) and complex viscosity (η*). Postharvest handling conditions and slurry solids content significantly affected the viscoelastic properties of the porridges with flours from stored roots yielding viscous (liquid‐like) porridges and fresh roots producing elastic (solid‐like) porridges. Increase in slurry solids content caused reduction in the phase angle values and increase in the viscosity of the sweet potato porridges. The viscosity of the porridges decreased with storage of sweet potato roots. These results provide a possibility for exploiting sweet potato endogenous amylases in the preparation of complementary porridges with both drinkable viscosities and appropriate energy and nutrient densities for children with varying energy needs

Production of organic flavor compounds by dominant lactic acid bacteria and yeasts from Obushera, a traditional sorghum malt fermented beverage

Single and mixed starter cultures of lactic acid bacteria (LAB): Weissella confusa MNC20, Lactobacillus plantarum MNC21, Lactococcus lactis MNC24 and Lactobacillus fermentum MNC34 and yeasts: Issatchenkia orientalis MNC20Y and Saccharomyces cerevisiae MNC21Y were used to produce Obushera, a fermented sorghum beverage. Microbial counts, pH, sugars, organic acids, and volatile compounds in starter culture and spontaneous fermentations were monitored during 48 hrs. Maximum counts of LAB (8.4–9.4 log cfu g−1) and yeasts (7.5 ± 0.1 cfu g−1) starter cultures were attained in 6–48 hrs. Weissella confusa, Lc. lactis, and Lb. fermentum showed possible acid sensitivity while I. orientalis produced surface films. LAB starter cultures and their combinations with S. cerevisiae lowered pH from 5.83 to <4.5 (3.50–4.13) in a shorter time (12 hrs) than spontaneous fermentations (24 hrs). Lactococcus lactis and W. confusa metabolized glucose the fastest (p < .05) during the first 6 hrs. Lactobacillus fermentum, Lb. plantarum, and S. cerevisiae utilized glucose and maltose concurrently. Lactobacillus plantarum and S. cerevisiae additionally utilized fructose. S. cerevisiae metabolized sugars the fastest (p < .05) during the first 12–24 hrs. Lactobacillus plantarum and W. confusa produced the highest (p < .05) amounts of lactate (5.43 g kg−1) and diacetyl (9.5 mg kg−1), respectively. LAB also produced acetate, ethanol, acetaldehyde, acetone, and acetoin. Coculturing LAB with S. cerevisiae reduced (p < .05) lactate and diacetyl yield. Yeasts produced high amounts of acetaldehyde and methyl alcohols. Issatchenkia orientalis produced higher (p < .05) amounts of 2‐methy‐1‐propanol and 3‐methyl‐1‐butanol than S. cerevisiae. Combinations of LAB with S. cerevisiae produced a profile flavor compounds close to that of spontaneously fermented Obushera. These combinations can be adopted for controlled fermentation of Obushera and related fermented cereal products

Effect of Preparation Conditions on Protein Secondary Structure and Biofilm Formation of Kafirin

Various extraction and drying conditions for the isolation of kafirin from dry-milled, whole grain sorghum have been investigated, with a view to optimizing extraction of the protein for commercial food coatings and packaging films. The addition of sodium hydroxide to an aqueous ethanol extractant increased the yield and solubility of kafirin. Subsequent heat drying at 40 °C was shown to cause the kafirin to aggregate as indicated by an increase in intermolecular ß-sheets. Extraction of the flour using ethanol (70%, w/w) with 0.5% (w/w) sodium metabisulfite and 0.35% (w/w) sodium hydroxide at 70 °C followed by freeze-drying of the protein was found to produce a yield of 54% kafirin with good film-forming properties. The kafirin films were assessed for their sensory properties, tensile strength, strain, and water vapor permeability. Fourier transform infrared spectroscopy was used to study the secondary structure of the extracted kafirins. The best films were made with kafirin containing a large proportion of nativelike a-helical structures with little intermolecular ß-sheet content as indicated by the Fourier transform infrared reflectance peak intensity ratios associated with these secondary structures. The principal factor affecting the secondary structure of the protein appeared to be the temperature at which the protein was dried. Heat drying resulted in a greater proportion of intermolecular ß-sheets. Any industrial-scale extraction must therefore minimize protein aggregation and maximize native a-helical structures to achieve optimal film quality