ABSTRACT

Starches were isolated from two cultivars of Nigerian grown mungbeans (Vigna radiata L. Wilczek) (green improved and brown local cultivars), using three extraction methods (dil. alkaline -0.5% NaOH), cold water and warm water extraction methods) to obtain six native starch samples. The starch yield, isolation efficiency and total starches of samples were determined. Then, three highest yielding starches among the six native starches were further subjected to physical modification (annealing and heat-moisture treatments).  The native, modified starches and raw mungbean flour samples were analyzed for proximate composition, physicochemical properties, colour, particle size distribution, pasting and thermal properties using standard methods of analyses.  Furthermore, noodles were produced from the starches and flours and were evaluated for cooking qualities, textural and sensory properties (both dry and cooked noodles), using a commercial noodle as a control. The mungbean starch extraction residues obtained after starch extractions, were analyzed for phytochemicals, vitamin content and antioxidant activities. They were also used to partially substitute wheat flour for biscuit production and then evaluated for physical qualities, proximate composition, sensory properties and microbial load, using standard methods of analyses.  Results showed that the highest starch yield (43.44%) was obtained by alkaline extraction from green mungbean cultivar (AGS) while the cold water extraction method gave the highest yield (41.15%) for the brown mungbean cultivar (CBS) closely followed by the warm water-extracted brown mungbean starch (WBS), 40.45%. They had corresponding starch isolation efficiencies of 406.70%, 431.77% and 425.10% respectively. Total starch of 48.02-54.01% was obtained for the six native starches and there were no significant differences (P>0.05) among them. Proximate composition results showed that native starches had moisture content (8.51-10.44%), crude protein (0.03-0.51%), crude fat (0.79-1.44%) and ash (0.27-0.83%), indicating a high level of starch purity among samples. Raw green mungbean and brown flour (RGMF and RBMF) had significantly higher protein (26.52% and 27.77%) respectively, fat (3.53% and 3.22%) and ash (4.42% and 3.86%) than the native starches (0.30-0.43%), (0.79-1.44%) and (0.37-0.83) respectively and modified starches.  Significant differences (P<0.05) existed in the amylose (28.72-33.97%), amylopectin (66.55-71.28%), paste clarity (11.12-14.67%), iodine affinity (0.41-0.94ppm) and total sugar (18.29-18.63%) of all native starch samples. Annealed sample (CBS_ANN) had the highest peak viscosity (6702.33 RVU), trough (5145.67 RVU) and breakdown (1548.00RVU), Final Viscosity (7665.67 RVU) and setback (2519.00 RVU). Significant differences (P<0.05) existed among the phytochemicals of the starch extraction residues samples except for total flavonoids (1.19-1.48 mg/100g) and Total Phenolic Content (1.35-1.55 mg GAE/g). The antioxidant activity of sample AGMSR measured by DPPH was highest, 1.64 mg/ml while that measured by FRAP was highest in sample WGMSR (96.83µmol of Fe²⁺/g). Wheat flour substitution with mungbean flour reduced the Total Cooking Loss, rehydration and cooking time of noodles especially as substitution levels increased (2.04 – 0.00%), (325-201%) and (14.53-4.00min) respectively. Significant difference (P<0.05) existed in the textural properties of the noodle samples. Modification resulted in variation in transition temperatures and other thermal properties. Mungbean flour had higher transition temperatures than those of the starches. Therefore, this study has demonstrated that mungbeans have the potential to provide starches with useful characteristics for development of new food products in Nigeria.