Microbial Studies and Biochemical Characteristics of Controlled Fermented Afiyo- a Nigerian Fermented Food Condiment from Prosopis africana (Guill and Perr.) Taub

Abstract

One hundred and fifteen bacterial strains isolated from fermenting Prosopis africana during a controlled production of okpehe, a Nigerian food-seasoning condiment most popular among the middle belt states of Nigeria were characterized as Bacillus subtilis, Bacillus pumilus, Bacillus licheniformis, Bacillus megaterium, non-sporing Staphylococcus species and Escherichia coli according to their differences in morphological, microscopic and biochemical characteristics using the bacterial taxonomic tools. There was no isolation of fungi throughout the fermentation period. The biochemical changes and enzymatic activities in fermenting okpehe mash were investigated. Reducing sugars increased from 2.0 mg g^-1 to 11.6 mg g^-1 during the first 2 days of fermentation but subsequently decreased to 7.8 mg g^-1 at day 6 while total soluble sugars decreased from 13.4 mg g^-1 at day 1 to 5.8 mg g^-1 at day 6. The most significant biochemical activity during the fermentation was the rapid and steady increase in the quantity of free amino acids throughout the fermentation period from 43.7 mg g^-1 - 70.0 mg g^-1. Proteinase activities increased from 0.51 – 0.71 U ml^-1. Alpha-amylase activities were not consistent but had their peaks at days 1 and 3, while lipase activities were maximal at days 3 and 5 of fermentation. The role of each associated bacteria in the fermenting okpehe indicated B. licheniformis, B. megaterium and Bacillus subtilis as the most active bacteria involved in the controlled fermentation without masking the fermented cotyledons after 3-6 months storage, but smoking as post fermentation treatment changed the colour of the condiment from dark brown to black.