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The effect of pretreatment methods (soaking in water, potassium metabisulphite solution, and blanching) and drying methods (sun and oven) on some quality attributes of flour from ten varieties of sweet potato roots were investigated. The quality attributes determined were chemical composition and functional properties. Data obtained were subjected to descriptive statistics, multivariate analysis of variance, and Pearson's correlation. The range of values for properties of sweet potato flour were: moisture (8.06–12.86 ± 1.13%), starch (55.76–83.65 ± 6.82%), amylose (10.06–21.26 ± 3.92%), total sugar (22.39–125.46 ± 24.68 μg/mg), water absorption capacity (140–280 ± 26), water solubility (6.89–26.18 ± 3.80), swelling power (1.66–5.00 ± 0.50), peak viscosity (24.50–260.92 ± 52.61 RVU), trough (7.08–145.83 ± 34.48 RVU), breakdown viscosity (11.00–125.33 RVU), final viscosity (10.21–225.50 ± 60.55 RVU), setback viscosity (3.04–92.21 RVU), peak time (6.07–9.06 min) and pasting temperature (69.8–81.3°C). Variety had a significant (P < 0.001) effect on all the attributes of sweet potato flour. Pretreatment did not significantly (P > 0.05) affect moisture, fat and lightness (L*). Drying method did not significantly (P > 0.05) affect fiber and L*. The interactive effect of variety, pretreatment and drying method had a significant (P < 0.001) effect on all the attributes except fat and fiber. Total sugar correlated significantly (P < 0.01) with water solubility (r = 0.88) of the flour samples. Variety was a dominant factor influencing attributes of sweet potato flour and so should be targeted at specific end uses.

“Amala” is a generic term in Nigeria, used to describe a thick paste prepared by stirring flour (“elubo”) from yam, cassava or unripe plantain, in hot water, to form a smooth consistency. In order to overcome its high perishability and increase the utilization of sweet potato roots, three varieties of sweet potato roots were processed into flour using two methods. The interactive effect of variety and the processing method had a significant effect (P < 0.05) on all the functional properties of the flour except yellowness, setback viscosity, and peak time. Acceptable sweet potato “amala” with average sensory acceptability score of 7.5 were obtained from yellow-fleshed varieties irrespective of the processing method. Flour that produced acceptable “amala” were characterized by lower values of protein (2.20–3.94%), fiber (1.30–1.65%), total sugar (12.41–38.83 μg/mg), water absorption capacity (168–215 g/100 g), water solubility (8.29–14.65%), swelling power (0.52–0.82 g/g), and higher peak time (6.9–8.7 min).

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Pasting properties of flour prepared from 12 diverse cowpea varieties as affected by dry and wet decortication processes were determined using a Brabender viscoamylograph. Dry decorticated flour (DDF) was prepared from seeds wetted, dried, and mechanically dehulled; wet decorticated flour (WDF) was prepared from seeds soaked, manually decorticated, dried, and milled to flour. No pasting peak was obtained during heating of flour slurry to 95°C for both DDF and WDF for all cowpea varieties. WDF samples had higher paste viscosities than DDF samples. Presoaking of seeds (2, 4, 8, or 16 h) affected paste viscosities, especially hot paste viscosity (HTPV), and particle size distribution. Maximum HTPV and highest quantities of medium-size particles (mesh 40-80, 0.42-0.177 mm) were attained with flour prepared from seeds presoaked for 4 h. Presoaking for more than 4 h did not yield further increase in HTPV. Cowpea flour with at least 65% of medium-size particles exhibited the best hydrothermal properties, leading to increased rate of moisture absorption and higher HTPV during aqueous heating of slurry.

Effects of frying treatments on texture (hardness) and colour parameters (L,a,b,ΔE) during deep fat frying of yellow fleshed cassava root slices (TMS 01/1371) were investigated. Slices (dimension of 40 mm × 25 mm × 3 mm) were divided into three portions and subjected to vacuum frying (fresh slices) and atmospheric frying (fresh and predried slices) and equivalent thermal driving forces (ETDF) of 60°C, 70°C, and 80°C were maintained during frying. The quality attributes investigated were best preserved in vacuum fried chips. The overall colour change in chips fried under vacuum conditions at 118°C and 8 min was the least (21.20) compared to fresh and atmospherically predried ones (16.69 and 14.81, resp.). A sharp reduction in the breaking force was obtained for all frying treatments after 8 min and this effect was the least in vacuum fried chips. First-order kinetics modeled the changes in quality attributes for all the temperatures investigated. Rate constants k (min−1) obtained for vacuum frying were almost equal to that of atmospheric frying while activation energies for hardness and colour change were 53.30 and 467.11 KJ/mol, respectively. Quality attributes studied were best preserved during vacuum frying.

Two flavoured extruded products were developed by co-extruding yam grits (750 µm) obtained from white yam (Dioscorea rotundata) and bambara groundnut flour (250 µm) in 160:40 respectively obtained from white bambara groundnut with added flavouring agents of salt (1% -3%) and sugar (4% -6%) in the feed blends at screw speed of 70 rpm, 17.5%, feed moisture and at the barrel temperature of 145˚C. The extruded products were packaged in low density polyethylene bag (0.02 µm gauge size) and stored at room temperature (28˚C ± 2˚C) and at refrigeration temperature (9˚C ± 2˚C) for a period of twenty weeks. The microbiological changes in the extruded products as determined by the total plate under both storage conditions showed that maximum total plate counts were 0.5 × 10 4 and 5.4 × 10 4 cfu/g at 9˚C ± 2˚C and 28˚C ± 2˚C respectively. Nutritional evaluation studies of extrudates were comparable (p ≥ 0.05) with standard casein diet with minimum crude protein content of 13.51% providing 1707.2 KJ energy per 100g of diet and supported weight gain and growth of laboratory animals.

The thermal properties of 12 varieties of cowpea flour were studied by differential scanning calorimetry (DSC). Flour samples were prepared to a paste of 60% moisture content and sealed in standard DSC pans. Samples were scanned at a heating rate of 5 degrees C/min over a scan range of 40- 130 degrees C. Samples exhibited single major endotherms, which occurred over varied temperatures. The transition enthalpy (deltaH) ranged between 1.4 J/g and 4.7 J/g. Transition onset (T(o)) and transition peak (T(p)) temperatures ranged between 75-78 degrees C and 78-82 degrees C,respectively. All the DSC parameters measured varied significantly among the varieties. The transition enthalpy (deltaH) was the most discriminating parameter and accounted for 80% of the total variance. The major chemical components of cowpea flour, starch amylose and protein are significant predictors of deltaH. Protein denaturation appears to be a significant modification which occurs during processing of cowpea seeds to flour. The transition enthalpy deltaH could become an important functional index of cowpea flour when related to some quality parameters in products that contain the flour.