Single and mixed starter culture fermentation of Oso (fermented seeds of Cathormion altissimum)
Oso is a fermented food made from spontaneous fermentation of Cathormion altissimum seeds. It is a local staple food of the people of Yewa in Ogun state. The lack of consistency in the product due to uncontrollable fermentation process remains a challenge, hence the objective of this study. 38 strains of micro-organisms, of which 15 Bacillus subtilis strains, 10 Bacillus licheniformis strains, ten Staphylococcus aureus strains and three Leuconostoc mesenteroides involved in the spontaneous fermentation of Oso, were tested for suitability as starter cultures. Enzyme activities using the plate assay method and APIZYM kit (Biomerieux, France) were used to determine the suitability of the strains for use as starter cultures. The quality of the starter culture fermented sample was measured based on the sensory evaluation test. The toxigenic potential of the selected strains were carried out by haemolytic test on sheep blood agar. Protease activities ranged from 9.5 to 20.9 mm. Out of the 14 combinations of starters, single and mixed strains, only five of the combinations (BS, BL, BS+BL, BS+BL+LM, BS+BL+SA+LM) were accepted based on results of sensory evaluation. The five combinations of starters (BS, BL, BS+BL, BS+BL+LM, BS+BL+SA+LM) and the spontaneously fermented sample were not significantly different (P > 0.05). They were rated the same and the best. The sample fermented with only the Bacillus subtilis and the one fermented with only Bacillus licheniformis were not significantly different (P > 0.05). Results of the present investigation indicate the potential of single and mixed strains of micro-organisms as starter culture for the fermentation of Oso.
Keywords: starter culture, APIZYM kit, toxigenic potentials, enzyme, sensory evaluation