Nutrient and Anti-nutrient Contents of Aspergillus niger -Fermented Cassava Products (Flour and Gari)

Abstract

Pure strain of Aspergillus niger was isolated and cultured using potato dextrose agar and broth, respectively. This was subsequently used to ferment six portions of 1 kg each of cassava pulp for 72 h. Three portions of the fermented cassava were each sieved and fried in a hot pan to gari, while the other three portions were each sun-dried and milled to cassava flour, the forms in which cassava products are popularly consumed in Nigeria. The results of the proximate analysis revealed that there was a significant increase ( P<0.05) in the protein content (flour (12.2±0.2%) gari (7.3±0.1)) determined by micro-Kjeldhal method as well as the fat content (flour (5.7±0.1%), gari (4.0±0.3%)) of the Aspergillus niger -fermented cassava products compared with unfermented and wildly fermented cassava products. However, there was no significant increase ( P>0.05) in the ash and crude fibre contents. The protein and fat contents were significantly higher ( P<0.05) in the cassava flour than the gari. The mineral composition (Na, K, Ca, Zn, Fe and Mg) of the products was considerably low, though gari had higher Na, K, Ca and Zn than the flour. The Aspergillus niger- fermented cassava products had very low cyanide (flour (9.1±0.2 mg/kg), gari (4.1±0.2 mg/kg)) and tannin (0.2%) contents. The gari had a significantly lower ( P<0.05) cyanide content than flour, while there was no significant difference ( P<0.05) in the tannin content. The results of the present study show that Aspergillus niger, a cheap, non-pathogenic saprophyte, has the capability to increase the nutritional potential of cassava products by increasing the protein and fat contents and decreasing the level of cyanide and tannin (anti-nutrients) present in them.