The role of Bacillus species in the fermentation of cassava

Abstract

Cassava dough inoculum is added to grated cassava in order to achieve a modification of texture during fermentation into the fermented cassava meal, agbelima. The microflora of two different types of inocula and subsequently inoculated cassava mash at 0, 24 and 48 h of fermentation were examined in order to determine the mechanism responsible for the breakdown of cassava tissue. Bacillus spp. occurred in high numbers, 107–108 cfu g-1, in both types of inocula and persisted throughout the cassava dough fermentation. Bacillus spp. found were B. subtilis, B. mycoides, B. pumilus, B. cereus, B. amyloliquefaciens and B. licheniformis, with B. subtilis accounting for more than half of Bacillus isolates. All Bacillus isolates produced a wide spectrum of enzymes and showed similar enzymatic activities but only B. pumilus, B. licheniformis and B. amyloliquefaciens produced linamarase. Some isolates produced the tissue degrading enzymes polygalacturonase and pectin esterase and nearly all isolates hydrolysed starch. All isolates showed cellulase activity and were able to disintegrate cassava tissue. When cassava pieces were incubated in amylase, cellulase, pectin esterase and polygalacturonase solutions, only pieces in cellulase solution were dissolved revealing that the breakdown of cassava dough texture during fermentation with the inocula examined is brought about by Bacillus spp. through cellulase activity