Development and evaluation of a starter culture for the industrial production of gari

Gari starter cultures (Gastat) were developed by mixing pure single strains of the organisms that ferment cassava. They were propagated and maintained as granules on dried cocoyam slurry. The cultures were tested for fermentative and acid-producing activity. The acidity produced at 30°C varied from 0.07% to 0.85% lactic acid with maximum levels occurring after 48 h. High levels of reducing sugar were produced during the first 24 h. The amounts produced were about 50% more than those from the self-inoculated cassava. The quality of the gari produced by the starter cultures was good and well accepted. The texture was similar to that produced by natural fermentation. These results highlight the possibility of using starter cultures in the large-scale production of gari.     

Predation byCheilomenes vicina [Coleoptera: Coccinellidae] on the cowpea aphid,Aphis craccivora [Homoptera: Aphididae]: Effect of prey stage and density

Consumption of larvae and females ofAphis craccivora Koch by 1st and 4th larvae and adults ofCheilomenes vicina (Muls.) was studied under fluctuating temperature (24–30°C). The early aphid instars were consumed in significantly greater numbers than later instars and females. The feeding rates ofC. vicina were significantly positively correlated with the population density of prey. The number of prey consumed daily by each predator stage tested, increased more steeply at lower than at higher prey densities, exhibiting thus the type 2 functional response

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Résumé Consommation des larves et des ♀ d'Aphis craccivora par les11^e stades, les 4^e stades et les adultes deCheilomenes vicina a été étudiée à une température variant de 24 à 30°C. Les jeunes stades du puceron sont consommés en nombre plus grand significativement que les derniers stades et les ♂. Les taux d'alimentation deC. vicina manifestent une corrélation hautement significative avec la densité de population de la proie. Le nombre de proies consommées quotidiennement par chaque stade considéré du prédateur augmentait plus brusquement aux faibles qu'aux fortes densités de proies, manifestant ainsi chez le prédateur le type 2 de réponse fonctionnelle.

     

Characterization of the solid-state fermentation of cassava

The solid-state fermentation of cassava (Mannlhot esculenta Crantz) was characterized by determining pH and biological oxygen demand (BOD). The results showed a strong association (=0.73) between pH of the fermenting slurry and that of the waste llquor. BOD of the liquor decreased as fermentation progressed. After 96 h fermentation, BOD was about 6×10² mg/l. Progress of cassava fermentation can probably be determined indirectly by following the changes in the pH and BOD profiles of the liquor.

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Résumé La fermentation en milleu solide du manioc (Mannihot esculenta Crantz) a été caractérisée en déterminant le pH et la demande biolgique en oxygène (DBO). Les résultats montrent une forte corrélation (=0.73) entre le pH de la pâte en fermentation et celui de la liquer résiduaire. La DBO de la liqueur décroît au fur et à mesure que la fermentation progresse. Après 96hh de fermentation, la DBO était de 6×10² mg/l. L'avancement de la fermentation du manioc peut probablement être déterminée indirectement ectement en sulvant l'évolution des profiles en pH et en DBO de la liqueur.

     

Physical properties of pectic polysaccharidases ofPseudomonas solanacearum from Nigeria

Pseudomonas solanacearum (obtained from Nigeria) produced certain pectic polysaccharidases when grown in aerobic batch cultures containing pectic substances. The pH optima of the enzymes were different. The optimum for polygalacturonase EC 3.2.2.15 was 5.5, and for pectate lyase EC 4.2.99.3 it was 8.5. The -1,4-glycosidic bonds between galacturonide units were cleaved at random, indicating the endo character of the enzymes. The pectic polysaccharidases were purified by (NH₄)₂SO₄ fractionation and by electrofocusing. Highest polygalacturonase activity and pectate lyase activity were obtained in the fractions at 41%–60% and 61%–80% (NH₄)₂SO₄ saturation, respectively. Polygalacturonase was resolved into two components with isoelectric points of 5.0 and 7.5; the isoelectric point of pectate lyase was 8.1.     

Post-processing microflora and the shelf stability of gari marketed in Port Harcourt

Gari was examined for its post-processing microbial content. Aerobic mesophilic bacteria and fungi were isolated from all samples. The total viable bacterial counts ranged from 2.0 × 10² to 8.0 × 10⁴ cfu/g. Fungal counts ranged from 1.0 × 10² to 1.5 × 10⁴ cfu/g. The total viable counts of fresh samples were much lower than those of market and packaged samples. Bacillus, Micrococcus and Proteus spp. were the bacteria isolated, Aspergillus niger, Aspergillus flavus and Penicillium spp. the fungi. Food borne parasites and pathogens such as Staph. aureus and Clostridium perfringens were not found. The gari samples were quite stable, having a shelf life of 3–6 months. The water activities of the samples ranged from 0.52 to 0.68. Based on the microbial counts of the samples, the critical upper limit for the safety of gari was set at 10⁴ cfu/g dry sample.     

Post-processing microflora and the shelf stability of gari marketed in Port Harcourt

Gari was examined for its post-processing microbial content. Aerobic mesophilic bacteria and fungi were isolated from all samples. The total viable bacterial counts ranged from 2.0 X 10(2) to 8.0 X 10(4) cfu/g. Fungal counts ranged from 1.0 X 10(2) to 1.5 X 10(4) cfu/g. The total viable counts of fresh samples were much lower than those of market and packaged samples. Bacillus, Micrococcus and Proteus spp. were the bacteria isolated, Aspergillus niger, Aspergillus flavus and Penicillium spp. the fungi. Food borne parasites and pathogens such as Staph. aureus and Clostridium perfringens were not found. The gari samples were quite stable, having a shelf life of 3-6 months. The water activities of the samples ranged from 0.52 to 0.68. Based on the microbial counts of the samples, the critical upper limit for the safety of gari was set at 10(4) cfu/g dry sample.     

Microbial degradation and utilization of cassava peel

Cassava peel was readily degraded and utilized by a strain ofRhizopus growing in a solid-state fermentation. Growth was maximal at 45°C and was proportional to the degree of hydrolysis of the peel. The yield of biomass, as weight of dry mycellum from the reducing sugars of the peel, was 51%. After 72 h fermentation, the peel contained 76% moisture, 6% cellulose, 7% hemicellulose and 0.4% ash and the protein content had increased from 5.6% to 16%. These results suggest a possible economic value of cassava peel in the production of fungal biomass and feedstock.

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Résumé Les pelures de manioc sont aisément dégradées et utilisées par une souche deRhizopus croissant en milieu solide. La croissance est maximale à 45°C et est proportionnelle au degré d'hydrolyse des pelures. Le rendement en biomasse, en poids de mycelium sec à partir des sucres réducteurs des pelures, est de 51%. Après 72 heures de fermentation, les pelures contiennent 76% d'humidité, 6% de cellulose, 7% d'hémicelluloses et 0.4% de cendres. Le contenu en protéines augmente de 5.6 à 16%. Ces résultats suggèrent une valorisation potentielle économique des pelures de manloc dans la production de biomasse et de substrat longique.

     

Fermentation of cassava peels for the production of cellulolytic enzymes

Cassava peels were used as a substrate for the production of cellulolytic enzymes. Under solid substrate fermentation conditions and a Rhizopus sp., thermostable cellulolytic enzymes were produced. Optimal production temperature and pH were 45°C and 5.6 respectively. Kinetic studies of the enzymes showed that the cellulase C₁ activity was optimal at pH 5.0 and 50°C, whereas that of cellulase C_x was optimal at pH 7.0 and 60°C. The enzymes degraded ca 44% of sorghum grains in 6 h, thus suggesting a possible use in saccharification processes. The results also showed the possibility of re-cycling cassava peels as a cheap substrate for the enzyme industry. and accepted 6 June 1989     

Effect of some plant extracts on two coccinellid predators of the cowpea aphid,Aphis craccivora (Hom.: Aphididae)

This study was conducted to examine the effects of some aphicidal biologically active plant compounds on the natural enemies of the cowpea aphid,Aphis craccivora Koch. In the laboratory, acetone extracts ofCymbopogon citratus (DC) Stapf.,Momordica charantia L.,Zingiber officinale Rose andAframomum melegueta (Rose) K. Schum, were tested for toxicity to two coccinellid species,Cheilomenes lunata (Fabricius) andCheilomenes vicina (Mulsant) predaceous on the aphid. All the extracts were highly ovicidal to eggs of the two coccinellid predators. None of the extracts caused mortality of eitherC. lunata orC. vicina fourth-instar larvae after 24 h. Larvae treated with the extracts consumed fewer aphids in 24 h than untreated larvae. Ability to pupate was also significantly reduced in larvae treated with the extracts. No morphological deformities were observed in adults emerging from treated larvae.     

Modelling of the rate data from the fermentation of cassava slurry

Data from analyses of the fermentation of cassava slurry were used to derive kinetic constants for the rate of hydrolysis of bound cyanide, formation of free cyanide, pH change and fermentation. The pseudo-kinetic constant for the decay of bound cyanide was 1·6 times 10^-2/h and 2·5/h for free cyanide. Under the experimental conditions, the concentration of bound cyanide at any time during fermentation was 22·65e^-0·016tμg/g, where t is time in h. The fermentation rate constant was determined as 2·2871 times 10¹⁹. Based on the empirical expressions of the rate data, it is believed that rate constants of the intrinsic parameters of fermentation of systems similar to cassava slurry could be determined.