S. A. Odunfa

African fermented foods

Fermented foods constitute a significant component of African diets. Many fermented foods are known, some serve as main course meals, others as beverages while others are highly prized food condiments. Those which serve as main meals and beverages are usually products of carbohydrate-rich raw materials. Some of the most important ones in this group include ‘gari’ from cassava, ‘ogi’ and ‘mahewu’ from maize and ‘kaffir’ beer from sorghum. Those which serve as food condiments are usually made from the fermentation of protein rich seeds. These include ‘iru’ from African locust bean; ‘ugba’ from African oil bean and ‘ogiri’ from melon seeds among others. All are known to be good sources of proteins and vitamins.

Microbiological changes during the traditional production of ogi-baba, a West African fermented sorghum gruel

The micro-organisms responsible for the spontaneous acidic fermentation in ogi-baba , a fermented sorghum gruel, were investigated. The ogi-baba was produced in the traditional way. The micro-organisms present in the unfermented grains at the initial stage of steeping were various species of Aspergillus and Penicillium fungi as well as bacteria of the following genera — Bacillus, Lactobacillus and Streptococcus . As the steeping progressed, the microbial population consisted of Lactobacillus, Streptococcus, Leuconostoc and a yeast, Debaryomyces hansenii . Of these, Lactobacillus plantarum and Streptococcus lactis were predominant. At the souring stage. S. lactis and another yeast, Candida krusei , were the dominant micro-organisms. Throughout the fermentation the titratable acidity increased, thereby resulting in a gradual fall in pH. The dissolved oxygen during the steeping also fell from 28 % saturation to 2/sd1 % saturation within 48 h.

Microbiological studies on cassava fermentation for ‘lafun’ production

Abstract The microorganisms involved in the traditional fermentation of cassava for ‘lafun’ production were investigated. The microorganisms isolated during the fermentation include Bacillus sp., Leuconostoc sp., Klebsiella sp., Corynebacterium sp., Lactobacillus sp., Candida sp., Aspergillus sp., and Geotrichum sp. The moulds disappeared within the first 36h of fermentation. Bacillus sp. which were present at the beginning of fermentation decreased drastically as fermentation progressed. The yeasts appeared between 24–48h of the fermentation and increased rapidly. The lactic acid bacteria were implicated throughout the duration of the fermentation. Bacillus sp., Corynebacterium sp., Candida sp. and the lactic acid bacteria were considered to play important roles. The titratable acidity of the steeping water and tubers increased rapidly reducing the pH to below 4·0. The temperature of the steeping water varied between 30–32°C and usually not above the ambient. The moisture content of the fermenting tubers increased from 65% to 70% within the first 36 h and was never below 60% during the steeping period. The post-fermentation sun-drying reduced the moisture content to 12–15%.

Assessment of a bacteriocin-producing Lactobacillus strain in the control of spoilage of a cereal-based African fermented food.

As part of a program to develop starter cultures aiding in the spoilage control and sanitation of African fermented foods, a cereal-based food (‘ogi’ and its solid form ‘agidi’ or ‘eko’) was prepared using a bacteriocin-producingLactobacillus strain as the starter culture. The survival of an enterotoxigenicEscherichia coli strain was investigated in the naturally fermented food and in food fermented with the starter bacteriocin-producingLactobacillus strain. An inhibition ofE. coli was observed within 2 h of incubation in ‘ogi’ fermented with the bacteriocin producing strain. After 6 h, the viable count ofE. coli in locally fermented ‘ogi’ was log 6.41 (2.54×106CFU/mL), whereas in ‘ogi’ fermented with the bacteriocin producer it was reduced to log 1.70 (0.5×102 CFU/mL). Comparison of the shelf life of ‘agidi’ prepared from the naturally fermented food with that fermented with the bacteriocin-producing starter culture showed that the latter had a better shelf life (kept for 11 d before spoilage occurred as compared with 7 d for the natural one). The results are discussed in terms of the potential of bacteriocin-producing cultures in the control and retardation of spoilage and food-forne infections in some African fermented foods.

Microbial assessment and quality evaluation of ogi during spoilage

The changes during the fermentation of ogi, a cereal-based traditional lactic acid-fermented weaning food were studied up to the spoilage stage. Ogi off-odour was first noticed at the fourth day of fermentation (including 24 h steeping). Yeast isolates such as Candida valida, C. krusei, Geotrichum candidum and bacteria like Lactobacillus brevis, L. plantarum, Pediococcus pentosaceus, Bacillus subtilis, Brevibacterium linens, Br. oxydans and other two Brevibacterium spp. dominated the fermenting mash at the spoilage stage. The brevibacteria contributed most significantly to ogi off-odour. Ogi samples inoculated with lactic acid bacteria increased acidity and product acceptability over the time of fermentation. The pH, titratable acidity, dissolved hydrogen sulphide and the presence of brevibacteria appear as good indices for monitoring spoilage. Hydrogen sulphide (H2S) levels appear to be the most useful of the parameters studied. No coliforms and clostridia were identified during spoilage.

Extracellular enzyme activities during cassava fermentation for ‘fufu’ production

Amylase and pectin methyl esterase activities increased rapidly during the early period of the fermentation of cassava for ‘fufu’ production, attaining their peak activities after 12 and 24h, respectively. Cellulase activity was lower and approximately constant for most of the fermentation period.

Plasmid profiles of bacteriocin-producing Lactobacillus isolates from African fermented foods.

Fourteen of 200Lactobacillus isolates from African fermented foods,viz. ‘wara’, ‘kenkey’, ‘ugba’, ‘ogi’, ‘kunuzarki’, ‘fufu’ and ‘iru’ were found to produce bacteriocins againstL. plantarum and only three bacteriocinogenic isolates inhibited some of the food pathogens. Plasmid analysis of the 14 bacteriocin-producing lactobacilli showed that only 5 isolates harbored plasmids ranging in size from 3.1 to 55.5 kb.

Extracellular proteinases ofBacillus spp. isolated from fermented African locust bean,Iru

Abstract Extracellular proteinase production by seven strains ofBacillus subtilis group isolated from fermented African locust bean was compared. The seven strains, which were designated BS1, BS2, BS3, BL1, BL2, BL4 and BP2, showed significant differences (α = 0·05) in extracellular proteinases production. The order of proteolytic activity (in descending order) of the strains in nutrient broth medium containing African locust bean was: BL2 > BP2 > BS2 > BL4 > BS3 > BL1 > BS1. The proteinases of strains BL2 were purified and characterized by ammonium sulphate precipitation, ion-exchange chromatography. Three proteinases (serine proteinase, neutral proteinase and an esterase) were identified with MW of 18·2–19·7, 22·6 and 33·5 kDa, respectively. The serine proteinase was highly hydrophobic while the esterase was characterized by low specific activity.

Bacteria involved in the deterioration of Nigerian palm oil under storage

Abstract The percentage of lipolytic bacterial colonies in samples of good-grade palm oil varied from zero to 26%, while in the deteriorated oil it was from 52–73%. The organisms isolated and their percentage frequencies were Bacillus subtilis, 43%; B. pumilus, 31%; B. laterosporus 14%; B. megaterium, 6%; and B. brevis 6%. B. subtilis and B. pumilus were the only species with pronounced lipolytic activities. Over the range 25–40°C, temperature had a profound effect on the lipolytic activities of these two species. The deterioration of the palm oil was ascribed to improper processing which leaves traces of water in the oil and also to post-processing contamination from the use of previously used containers and from unhygienic handling during transport and marketing.