Microbiological, physicochemical and nutritional changes of millet for Koko production under different nixtamalisation conditions

Abstract

Koko is a traditional fermented cereal gruel made from millet. Nixtamalisation is a traditional process by which cereals are cooked and steeped in lime. The microbiological and physicochemical changes of the millet used for koko production under different nixtamalisation conditions were investigated. The lactic acid bacteria isolated from the fermenting samples comprised Lactobacillus plantarum, Lactobacillus fermentum, Lactobacillus brevis, Pediococcus acidilactici and two genera of yeasts, namely Candida and Saccharomyces. There was a reduction in pH in all the samples; the spontaneous sample had the least of pH 3.9 at 72 h while the highest of pH 11.5 was observed in the 1.5% nixtamalised sample at 0h. The titratable acidity increased from 0.000mg/ml at 0h to 0.008mg/ml after 72 h at 0.75% nixtamalisation concentration. Selection was based on the proximate analyses of the fermenting samples. Nixtamalised samples at 1% and 1.5% had the highest crude fibre content (0.13% and 0.11%) and ash content (0.28% and 0.26%) respectively. Lactobacillus fermentum K048 (L.f) and Pediococcus acidilactici K1.548 (P.a) were selected as starter cultures. The controlled fermentation with starter cultures L.f + P.a had the highest crude protein content of 1.70% while the least of 0.39% was observed in 1.5% nixtamalised sample without starter culture. Sensory evaluation shows that controlled fermentation of 1.5% nixtamalised sample using L. fermentum K048 had the best general acceptability. Nixtamalisation made milling easier during processing by softening and swelling of the grains while inoculation with starter cultures enhanced the nutritional qualities of the grains for koko production.

Keywords: Millet, nixtamalisation, koko, physicochemical, proximate analysis