Microbiological and Biochcmical Changes in the Production of Akyeke -A Fermented Cassava product

ABSTRACT

Utilization of cassava, which contributes 22% of the gross agricultural product in Ghana, is limited by its high perisability, low protein content and toxicity due to the presence of the cyanogenic glucoside, linamarin and lotaustralin. Akyeke, a fermented and granulated, steamed-cooked cassava meal consumed extensively along the southwestern parts of Ghana is one of several products prepared from cassava in order to reduce postharvest loss of the crop. Fermenting grated cassava for 5-7 days with an inoculum, water is added several times to remove some amount of starch and colour from the fermented cassava mash, dewatered, sifted and sun dried before steaming. During fermentation, a breakdown of the texture of cassava dough occurs to give a smooth and non-rubbeiy texture. The microflora of Akyeke inoculum and the inoculated fermenting cassava dough were examined to determine microbial and biochemical changes associated with fermentation of cassava into Akyeke as well as detoxification of the product during fermentation. The microflora in Akyeke inoculum and during fermentation were dominated by Bacillus spp., lactic acid bacteria and yeasts.The Bacillus species identified were Bacillus subtilis, Bacillus licheniformis, Bacillus cereus, Bacillus pumilus and Corynebacterium. sp. Isolated lactic acid bacteria were Lactobacillusplantarium, Lactobacillus brevis, Lactobacillus fermentum, Lactobacillus salivarius and Leuconostoc mesenteroides at levels of 109 to 1010 in both laboratory and field samples. Yeasts species Candida Xropicalis, Candida krusei, Zygosaccharomyces florentinus and Geotrichum candidum. Bacillus sutilis, Candida Xropicalis and Zygosaccharomyces florentinus were found to be responsible for the disintegrated cassava tissues when plated directly on sterile cassava slices Titratable acidity expressed as lactic acid increased from 0.38%-0. 32% to 1.67%-l. 11 % after fermentation for field and laboratory samples respectively. pH dropped from 5.15 to 3.21 after fermentation. The large number of lactic acid bacteria, low pH and high acidity confirms the fermentation of cassava in the production of Akyeke to be lactic acid fermentation. There was substantial reduction of total cyanide from 69.3 and 110.3 mg/kg to 1.4 and 2.8 mg/kg for field and laboratory' samples respectively.