The effects of processing methods on the levels of lysine, methionine and the general acceptability of ogi processed using starter cultures.

Batches of ogi were produced from maize flour slurry, dehulled maize grains and whole maize grains using Saccharomyces cerevisiae and Lactobacillus brevis as starter cultures. Fermentation over time showed that dehulled maize grains inoculated with the starter cultures and processed whole maize grains requiring steeping led to higher acid production than fermentation with dry-milled maize slurry. Ogi from dehulled maize grains inoculated with starter cultures showed the highest levels of lysine and methionine. Steeping grains encouraged a stronger ogi aroma than fermentation of maize flour slurry alone. Lactobacillus brevis contributed most to the taste of ogi. Fermentation with starter cultures showed good prospects for improving the lysine and methionine levels of ogi.

Evaluation of lysine and methionine production in some Lactobacilli and yeasts from ogi.

Lysine and methionine producing cultures of Lactobacillus and yeasts in batch fermentation of ogi were selected by growth in the presence of the analogues, S-2-aminoethyl]-L-cysteine (thialysine) and ethionine respectively. The study shows that 42.5% of the Lactobacillus and 83.3% of the yeast isolates tested were capable of lysine production while 25.0% of the Lactobacillus and 87.8% of the yeast isolates produced methionine. The lysine and methionine yields of Lactobacillus were significantly (P <0.01) higher than that of yeasts. The majority of the yeast isolates excreted most of the lysine and methionine produced. More lysine was produced than methionine in all tested isolates.

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

As a 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-producing Lactobacillus strain as the starter culture. The survival of an enterotoxigenic Escherichia coli strain was investigated in the naturally fermented food and in food fermented with the starter bacteriocin-producing Lactobacillus strain. An inhibition of E. coli was observed within 2 h of incubation in 'ogi' fermented with the bacteriocin producing strain. After 6 h, the viable count of E. coli in locally fermented 'ogi' was log 6.41 (2.54 X 10(6) CFU/mL), whereas in 'ogi' fermented with the bacteriocin producer it was reduced to log 1.70 (0.5 x 10(2) CFU/mL). Comparison of the shelf life of 'agidi' prepared from the naturally fermented food with that 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.

Studies on bacteriocinogenic Lactobacillus isolates from selected Nigerian fermented foods.

Ten bacteriocin-producing (bacteriocinogenic) Lactobacillus isolates obtained from three Nigerian fermented foods namely: kenkey, ogi and wara were tested against the following indicator organisms: Lactobacillus plantarum and food borne pathogens comprising enterotoxigenic Escherichia coli, enterohaemorrhagic Escherichia coli, Serratia, Pseudomonas, Vibrio cholerae, Aeromonas sobria, Aeromonas cavice, Salmonella typhimurium, Plesiomonas shigelloides and Staphylococcus aureus. All the bacteriocinogenic Lactobacillus were found to inhibit L. plantarum while some inhibited some of the food borne pathogens listed above. The antimicrobial activities of bacteriocins from L. plantarum KKY12 and L. casei OGM12 were caused by proteins detectable in the culture liquids. They are designated Plantacin N and Caseicin A and they have narrow antimicrobial spectra. Plantacin N from L. plantarum KKY12 was active against L. plantarum, Pseudomonas, Aeromonas sobria and Aeromonas cavice whereas Caseicin A from L. casei OGM12 inhibited L. plantarum, enterotoxigenic Escherichia coli and Vibrio cholerae. Caseicin A is stable at 121 degrees C/15 mins, and both are inactivated by proteolytic enzymes. The bacteriocinogenic properties of the local isolates of Lactobacillus can help to reduce hygienic risk and the spoilage of fermented foods.

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

Fourteen of 200 Lactobacillus isolates from African fermented foods, viz. 'wara', 'kenkey', 'ugba', 'ogi', 'kunuzarki', 'fufu' and 'iru' were found to produce bacteriocins against L. 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 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.

Root exudates in relation to growth and nitrogenase activity of Rhizobium japonicum.

Root exudates of cowpea and soybean were collected in aerated water cultures. The ability of these exudates to support nitrogenase activity of R. japonicum was studied on defined media. When a complete nitrogenase-inducing medium was supplemented with concentrated root exudate, there was an increased nitrogenase activity. When the cowpea root exudate was substituted for glutamine or sodium succinate in the medium, nitrogenase activity was not detected. Growth was good when the root exudate was substituted for sodium succinate but was poor when the exudate replaced glutamine. There was nitrogenase activity in R. japonicum when the cowpea root exudate was substituted for arabinose in the 20E medium. Gas chromatographic analyses of cowpea root exudates revealed that ribose, arabinose, glucose, and sucrose were the main constituents. The significance of this finding in the asymbiotic nitrogen fixation by Rhizobium spp. is discussed.