Studies on the microbiological, nutrient composition and antinutritional contents of fermented maize flour fortified with bambara groundnut (Vigna subterranean L)

Abstract

The nutrient composition, antinutritional factors and microflora in spontaneously fermenting maize flour fortified with bambara groundnut were examined over a period of 72 h. Titratable acidity as well as pH changes was obtained at 12 h interval during fermentation by adventitious microorganisms present in the fortified product. Results obtained showed that microflora gradually changed from gram negative enteric bacteria, molds, lactic acid bacteria and yeast to be dominated by gram positive lactic acid bacteria (LAB) and yeasts. All undesirable microorganisms such as coliforms and molds which were present at the start of fermentation were totally eliminated by 24 h of fermentation. Yeasts and LAB numbers in the fortified dough varied between 4.44 and 7.36 log cfu‑1. LAB number increased from 5.40 to 7.36 log cfu-1 during fermentation. Yeasts increased from 4.44 to 5.60 log cfu-1. The product pH decreased with concomitant increase in moisture, fat, ash, fibre and titratable acidity with increasing bambara groundnut addition. Bambara groundnut addition caused only minimal changes in the proximate composition with the exception of protein content, which increased remarkably from 18.40 to 21.68% with 30% bambara groundnut addition. Boiling, sprouting and fermentation significantly decreased the tannins and trypsin inhibitors levels. Boiling Bambara groundnut for 20 min before incorporation into the maize flour imparted a desirable flavour. Organoleptic evaluation revealed that the foods were well accepted. Based on the findings the application of bambara groundnut fortification to traditional foods can promote the nutritional quality of African maize - based traditional foods with acceptable rheological and cooking qualities. Key words: Spontaneous fermentation, fermented maize flour, Bambara groundnut fortification, micropopulation, nutrient quality, antinutritional factors, rheology.