Secretion of Methionine by Microorganisms Associated with Cassava Fermentation

Forty-six (46) bacteria were isolated from different sites associated with garri production from cassava: cassava pulp grated for garri production, grating machines, soil in the vicinity of the production of garri, and utensils involved in the processing of cassava into garri in several locations in Anambra State of Nigeria. Of these, Lactobacillus plantarum

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, Lactobacillus

sp., Leuconostoc

sp., Corynebacterium

sp. and Bacillus

sp. secreted methionine. The organisms were assessed for optimum methionine production at various levels of glucose, ammonium sulphate and varying mixtures of potassium hydrogen phosphate and di-potassium hydrogen phosphate. All the organisms required 10 g glucose for maximum methionine secretion. All the isolates required 20 g of (NH₄)₂SO₄/litre, except for Bacillus sp. which required as little as 5 g of (NH₄)₂SO₄/litre. The organisms' requirement for phosphate varied widely: the two lactobacilli required 0.5 g KH₂PO₄ and 1.5 g K₂HPO₄ per litre, Leuconostoc sp. and Bacillus sp. required 1.0 g KH₂PO₄ and 3.0 g K₂HPO₄ per litre. Lactobacillus spp. were the highest secreters of methionine, followed in that order by Leuconostoc sp., Corynebacterium sp. and Bacillus sp. The optimum period of incubation for the secretion varied from 48 h to 96 h, which is the period for cassava mash fermentation in garri production. The findings on Lactobacillus plantarum , Lactobacillus sp. and Leuconostoc sp. are of importance in any possible effort to increase the methionine content of garri. In this study the maximum quantities of methionine were secreted after 96 hours and 72 hours respectively by the lactobacilli and Leuconostoc sp. Since lactic acid bacteria are micro-aerophilic, it is suggested that lactic acid bacteria (the two lactobacilli and Leuconostoc sp.), which are the major organisms involved in cassava fermentation for garri production, may, in the less aerated environment of the cassava mash, produce more methionine and in shorter time, than observed under the aerobic conditions of this work.