Effect of germination and roasting on the proximate, mineral and anti-nutritional factors in finger millet (Eleucine coracana), cowpeas () and orange maize (Zea mays)

Abstract

Finger millet (Eleucine coracana), cowpea (Vigna unguiculata), and bio-fortified vitamin A “orange” maize (Zea mays) are three nutrient  dense crops currently being promoted in Zimbabwe. The effect on nutrient content of processing these specific crop varieties has not  been investigated. Therefore, this study was designed to determine the effects of germination and roasting on the proximate, mineral,  and antinutritional factors in finger millet, cowpeas and orange maize. Finger millet grains were germinated for 48hrs, cowpeas and  orange maize for 24hrs, at room temperature (20-23oC). Both raw and processed samples were dried and milled into flour for the  determination of proximate and mineral and anti-nutritional composition. Protein content of finger millet increased significantly after  processing from 6.53±0.25 mg/100 g to 11.27±0.15 mg/100 g in germinated finger millet flour (P<0.05). Germination of finger millet  resulted in significantly increased minerals (mg/100 g); calcium from 345.53±0.55 to 352.63±0.21, zinc from 3.59±0.15 to 8.71±0.01, sodium from 49.89±0.16 to 57.78±1.20 and iron content from 3.75±0.05 to 4.52±0.01 whilst magnesium and potassium decreased significantly  from 198.09±0.07 to 69.08±0.06 and 487.08±0.03 to 144.78±0.27 respectively. Processing of cowpeas resulted in slight but significant  increase in protein content (20.47±0.21 to 28.50±0.10), increased calcium (138.18±0.12 to 148.18±0.12 mg/100 g), magnesium (14.23±2.00 to 19.18±0.31 mg/100 g), potassium (232±4.00 to 443.41±0.02 mg/100 g) and iron (4.85±0.03 to 4.86±0.04 mg/100 g). Conversely zinc and  sodium decreased from 4.5±0.30 to 2.9±0.10 mg/100 g and 31.85±0.03 to 11.64±0.02 mg/100 g, respectively. Notably for orange maize,  protein content did not change from 10.06±0.04 to 10.04±0.04 g/100 g before and after processing. Calcium increased from 47.02±2.82 to  57.99±8.85 (mg/100 g), magnesium from 90.91±0.11 to 108.30±0.53 (mg/100 g), potassium from 2.13±0.04 to 4.33±0.25 (mg/100 g),  sodium from 0.50±0.02 to 0.70±0.02 (mg/100 g) and iron from 0.50±0.02 to 1.25±0.05 (mg/100 g). Zinc decreased from 6.2±0.2 to 3.53±0.55  (mg/100 g). Tannins, oxalates and phytates decreased significantly after processing of all three crops. Results showed that  germination and roasting increased the nutritional profile and decreased anti-nutrient content in finger millet, cowpeas and orange  maize. Therefore, it is important to consider germinating and roasting these grains during processing to increase the nutritional potential  of the end food product. Further studies are required to investigate the decrease in some nutrients after germination and  roasting and possibly establish optimum processing parameters for improved nutrient profile of these food crops.