MICROBIOLOGICAL AND BIOCHEMICAL-CHARACTERIZATION OF CASSAVA RETTING, A TRADITIONAL LACTIC-ACID FERMENTATION FOR FOO-FOO (CASSAVA FLOUR) PRODUCTION

The overall kinetics of retting, a spontaneous fermentation of cassava roots performed in central Africa, was investigated in terms of micro bial-population evolution and biochemical and physicochemical paramete rs, During the traditional process, endogenous cyanogens were almost t otally degraded, plant cell walls were lysed by the simultaneous actio n of pectin methylesterase and pectate lyase, and organic acids (C-2 t o C-4) were produced, Most microorganisms identified were found to be facultative anaerobes which used the sugars (sucrose, glucose, and fru ctose) present in the roots as carbon sources, After 24 h of retting, the fermentation reached an equilibrium that was reproducible in all t he spontaneous fermentations studied, Lactic acid bacteria were largel y predominant (over 99% of the total flora after 48 h) and governed th e fermentation, The epiphytic flora was first replaced by Lactococcus lactis, then by Leuconostoc mesenteroides, and finally, at the end of the process, by Lactobacillus plantarum. These organisms produced etha nol and high concentrations of lactate, which strongly acidified the r etting juice, In addition, the rapid decrease in partial oxygen pressu re rendered the process anaerobic, Strict anaerobes, such as Clostridi um spp., developed and produced the volatile fatty acids (mainly butyr ate) responsible, together with lactate, for the typical flavor of ret ted cassava. Yeasts (mostly Candida spp.) did not seem to play a signi ficant role in the process, but their increasing numbers in the last s tage of the process might influence the flavor and the preservation of the end products.