O.B. Oyewole

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.

Lactic fermented foods in Africa and their benefits

Abstract Lactic acid fermentation is an important food processing technology in Africa. This technology is indigenous and is adaptable to the culture of the people. This paper reviews the different raw materials and microorganisms which are used in producing lactic fermented food products in Africa. The beneficial aspects of this technology for improving food safety in Africa as a low-cost method of food preservation and in improving the nutritional quality of the food raw materials are discussed. Areas of research needs to enhance further the benefits of this technology are highlighted.

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%.

Characteristics and significance of yeasts' involvement in cassava fermentation for 'fufu' production.

Six different strains of yeast, namely Candida krusei, C. tropicalis, Pichia saitoi, Saccharomyces cerevisiae, P. anomala and Zygosaccharomyces bailii were found present in cassava-fermenting water in the early part of the fermentation. The latter part of the fermentation was dominated in all cases by three strains of yeast namely C. krusei, C. tropicalis and Z. bailii. All the yeast strains exhibited amylolytic capabilities while none was able to produce cellulase. All the strains except Zygosaccharomyces spp. exhibited polygalacturonase activity, but only C. krusei was able to produce linamarase. In a study on the inter-relationships between C. krusei and Lactobacillus plantarum, the growth of the yeast strain was not enhanced in cassava by the presence of the lactic acid bacteria, but the growth of the L. plantarum strain was significantly enhanced when co-inoculated with C. krusei.

Effects of fermentation on the carbohydrate, mineral, and protein contents of cassava during “fufu” production

Abstract Investigations were carried out on the changes in the carbohydrate, mineral, and protein contents of cassava during the fermentation production of Wit, a pasty food material consumed in Africa with soup after cooking. Fermentation caused a reduction in the starch content. The total soluble and reducing sugar levels increased during the first 36 and 24 h, respectively, then fell in concentration for the remainder of the 96-h fermentation. The fermentation process caused an increase in the concentration of calcium (+12%) in cassava but reductions in the levels of magnesium (−53%), potassium (−71%), sodium (−68%), manganese (−60%), iron (−50%), copper (−7%), zinc (−85%), and phosphorus (−67%). Despite these losses, the fermented product, fufu, was found to contain appreciable quantities of calcium, magnesium, and potassium. The fermentation caused an overall 20% reduction in the protein content. The protein content which decreased during the first 72 h, showed a rapid increase during the last 24 h of the fermentation.

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.

Effect of lactic acid bacteria starter culture fermentation of cassava on chemical and sensory characteristics of fufu flour

The effects of lactic acid fermentation of cassava on the chemical and sensory characteristic of fufu flour were investigated. Two strains of Lactobacillus plantarum were used as starter cultures for the fermentation of cassava to fufu for 96 h. The resultant wet fufu samples were dried at 65oC in a cabinet dryer for 48 h and analyzed for chemical and sensory characteristics. Fermentation caused a high reduction in the protein content of cassava, which ranges between 1.26 ± 0.02% for cassava with starter culture SL 14, and 1.14 ± 0.04% for cassava with starter culture SL 19. However, the unfermented cassava fufu flour has the highest protein content; this shows the influence of fermentation in reducing the proximate composition of cassava. The values of the sugar, starch and amylose contents show similar trends. The sugar contents ranges between 5.21 ± 0.04 to 4.41 ± 0.0%, with the unfermented sample having the highest value. When subjected to sensory evaluation, the traditional and starterculture fermented cassava fufu flour were not significantly different in terms of color, odor, and texture, but the cassava fufu flour produced using starter culture SL19 had the highest overall acceptability (P<0.05).

Physicochemical and Functional Properties of Sour Starches from Different Cassava Varieties

This article reports our investigation on the effect of cassava varieties on the physicochemical and functional properties of sour starches. There were significant differences (P < 0.05) in the ash, pH, amylose, amylopectin, starch damage, total titratable acidity (TTA), sugar, and starch content but not moisture contents of various cassava sour starches. There were no significant differences (P > 0.05) in Water Absorption Capacity (WAC), swelling power, and solubility index, while significant differences were recorded in Least Gelation Concentration (LGC) and color at 5% level and granule size at P < 0.0001 for cassava sour starches. Peak viscosity values ranged from 333.17RVU (clone 4(2) 1425) to 380.75RVU (clone TME 1). There were significant differences (P < 0.05) in pasting properties except for pasting temperature and breakdown.

Production of Ogi from germinated sorghum supplemented with soybeans

Three varieties of sorghum grains were germinated before fermentation to Ogi . The protein and ash contents of Sorghum vulgare , Sorghum guineensis and Sorghum bicolor increased by 7.20 and 40.20%; 5.44 and 29.20%; and 4.00 and 42.18% respectively. Fermentation of the germinated grains however caused decreases in the protein, ash, fibre and fat contents. Supplementation of oven-dried (60%) powder with treated 30% (w/w) soyabeans flour yielded products of higher protein contents which ranges from 284% for Ogi made from S. vulgare, 270% for Ogi made from S. guineensis and 271% for Ogi made from S. bicolor. Similarly, supplementation of Ogi with 30% (w/w) soya-flour generally resulted in increase in fat contents (approx. 130%), ash (approx. 54.9%) and fibre (approx. 217%). A panel of evaluators showed greatest preference for soya- supplemented Ogi porridge made from S. vulgare, while soya-supplemented Ogi porridge from S. guineensis was the least acceptable. The soyasupplemented Ogi flour (moisture content 10%) kept well and retained their original flow- properties after twenty-one days of storage. Key words : Sorghum, germination, fermentation, soya-supplementation.

Bacterial species and mycotoxin contamination associated with locust bean, melon and their fermented products in south-western Nigeria

The microbiological safety of spontaneously fermented foods is not always guaranteed due to the undefined fermenting microbial consortium and processing materials. In this study, two commonly consumed traditional condiments (iru and ogiri) and their respective raw seeds (locust bean and melon) purchased from markets in south-western Nigeria were assessed for bacterial diversity and mycotoxin contamination using 16S rRNA gene sequencing and liquid chromatography tandem mass spectrometry (LC-MS/MS), respectively. Two hundred isolates obtained from the raw seeds and condiments clustered into 10 operational taxonomic units (OTUs) and spanned 3 phyla, 10 genera, 14 species and 2 sub-species. Bacillus (25%) and Staphylococcus (23.5%) dominated other genera. Potentially pathogenic species such as Alcaligenes faecalis, Bacillus anthracis, Proteus mirabilis and Staphylococcus sciuri subsp. sciuri occurred in the samples, suggesting poor hygienic practice during production and/or handling of the condiments. A total of 48 microbial metabolites including 7 mycotoxins [3-nitropropionic acid, aflatoxin B1 (AFB1), AFB2, beauvericin, citrinin, ochratoxin A and sterigmatocystin] were quantified in the food samples. Melon and ogiri had detectable aflatoxin levels whereas locust bean and iru did not; the overall mycotoxin levels in the food samples were low. There is a need to educate processors/vendors of these condiments on good hygienic and processing practices.