Robert Ndjouenkeu

Production and partial characterization of a thermostable amylase from ascomycetes yeast strain isolated from starchy soils

An amylolytic yeast strain was isolated from starchy soils (flour mills environment, flour market, cassava farms after harvesting and transformation of tubers) and its enzyme productivity and activity evaluated. The enzyme synthesis was optimum at 30°C when initial pH of fermentation medium was 4.5. After extraction and partial purification, the enzyme remained stable in a range of temperature and pH between 20°C-60°C and 2-8 pH respectively. The optimum enzyme activity was displayed at 70°C and pH 5.5 and 6.5. The thermostability of the enzyme was comparable to that of amylases from bacteria. Key Words: Amylolytic yeast, amylase activity, thermostable amylase. African Journal of Biotechnology Vol.4(1) 2005: 14-18

Effect of cooking methods and rigor state on the composition, tenderness and eating quality of cured goat loins

Abstract Six Grassland African Dwarf goats were slaugtered in this study. Longissimus dorsi muscle samples were removed from 10 to 12 kg goat carcasses. Two equal roasts were obtained from each loin. From each animal, the four roasts were cured and three cooking methods were applied to pre- and one post-rigor loins. Effects of cooking methods and rigor state on composition, tenderness and eating parameters of cured loins were determined. The method of cooking had no significant effect (P

Nutrient content of complementary foods based on processed and fermented sorghum, groundnut, spinach, and mango

Background Many African mothers use gruels made of maize and sorghum as complementary foods for their infants because they cannot afford the cost of nutritionally superior commercial weaning foods. Objective To improve the nutritional quality of traditional sorghum gruels used as complementary foods for children between six months and five years in the northern part of Cameroon. Methods Sorghum grains were processed by dehulling, sprouting, dehulling and cooking, and sprouting and cooking, then fermented using Saccharomyces cerevisae and tested for nutritional quality. The processed samples were analyzed for their nutrient composition and the digestibility of proteins and carbohydrates. Results The resulting products showed a significant reduction in antinutritional factors (e.g., phenolic compounds and phytates). In addition, germination improved the in vitro digestibility of proteins and carbohydrates. These effects were enhanced by fermentation of the resulting sorghum flour, regardless of how grains were pretreated, although the protein and mineral content remained low. Use of a composite flour made from pretreated sorghum, groundnut, spinach, and mango improved the protein, mineral, and vitamin A and C content of the gruels. Fermentation of composite flours resulted in an improvement in the protein content. Conclusions This study, conducted under local conditions and using local technology, describes an opportunity for improving the quality of complementary foods using local ingredients.

Air Drying Behaviour of Fresh and Osmotically Dehydrated Onion Slices (Allium cepa) and Tomato Fruits (Lycopersicon esculentum)

Onion slices (0.5 cm thick) and tomato fruits, fresh and osmotically dehydrated in sugar (600 g/l), salt (300 g/l) or mixed salt and sugar (45/15, w/w) solutions, were air dried at 60°C and drying constants determined. The air drying occurred in two falling rate periods, characterised each by a drying constant. The drying rate and the moisture diffusivity of osmosed samples were higher than that of fresh samples. The overall drying behaviour of osmosed onion slices was not influenced by osmotic conditions (solution and time), while the drying behaviour of osmosed tomato samples depended on osmotic solution and pre-treatment time. 15 minutes and 20 hours of pre osmosis seemed more convenient before drying of onion slices and tomato respectively. In this respect, the structural modification of cells of tomato membrane during extended pre treatment seemed to explain the variation in the drying behaviour.

Mise en evidence de la biodisponibilité du calcium et du magnésium au cours de la fermentation du lait par des bactéries lactiques isolées du lait caillé de zébu

Resume Fermentation of skim milk by wild Streptococcus thermophilus and Lactobacillus bulgaricus , isolated from Cameroonian traditional fermented zebu milk showed high solubilisation of calcium and magnesium, indicating an excellent bioavailability of these minerals. Combination of the bacteria strains, while performing a high level of mineral solubilisation, appears less efficient than individual strains. These results suggest that scientific and technological characterisation of the bacteria from traditional source is important, in order to determine their contribution to the quality of traditional fermented milk. Des souches sauvages de Streptococcus thermophilus et de Lactobacillus bulgaricus , isolees du lait caille de zebu Camerounais, ont ete utilisees pour fermenter du lait UHT ecreme. Le dosage du calcium et du magnesium solubles dans les laits fermentes obtenus montre, quelle que soit la souche bacterienne, une augmentation de la solubilite de ces mineraux, donc de leur biodisponibilite. L’association des deux souches, tout en maintenant un niveau eleve de solubilisation des mineraux, apparait moins performante que les souches en culture individuelle. L’efficacite de ces souches sauvages vis-a-vis de la biodisponibilite des mineraux justifient l’interet de leur caracterisation biochimique afin de mieux preciser leur contribution a la qualite des laits fermentes locaux.

Microbial interactions for enhancement of α-amylase production by Bacillus amyloliquefaciens 04BBA15 and Lactobacillus fermentum 04BBA19

Interactions occurring between Saccharomyces cerevisiae and two thermostable α-amylase producing strains (Bacillus amyloliquefaciens 04BBA15 and Lactobacillus fermentum 04BBA19) were analyzed by comparing their growth patterns obtained in isolation with those obtained in mixture. The difference between the patterns was assessed using analysis of variance (ANOVA) in order to measure how much the growth of an organism was affected by other. The results showed two types of interactions in mixed culture; commensalism between S. cerevisiae and B. amyloliquefaciens 04BBA15 and mutualism between S. cerevisiae and L. fermentum 04BBA19. In mixed culture, the α-amylase production increased significantly compared to that observed in monoculture (P < 0.05). Response surface optimization of fermentation parameters in mixed cultures (initial yeast to bacteria ratio 1.125, temperature 33.5 °C, pH 5.5) resulted in about 1.8 fold higher enzyme production than that observed in the unoptimized fermentation.

Effect of Different Carbon Sources on Biosurfactants’ Production by Three Strains of Lactobacillus spp.

The potential of three indigenous bacterial strains (Lactobacillus delbrueckii N2, Lactobacillus cellobiosus TM1, and Lactobacillus plantarum G88) for the production of biosurfactants using sugar cane molasses or glycerol as substrates was investigated through emulsifying, surface tension, and antimicrobial activities. The different biosurfactants produced with molasses as substrate exhibited high surface tension reduction from 72 mN/m to values ranged from 47.50 ± 1.78 to 41.90 ± 0.79 mN/m and high emulsification index ranging from 49.89 ± 5.28 to 81.00 ± 1.14%. Whatever the Lactobacillus strain or the substrate used, the biosurfactants produced showed antimicrobial activities against Candida albicans LV1, some pathogenic and/or spoilage Gram-positive and Gram-negative bacteria. The yields of biosurfactants with molasses (2.43 ± 0.09 to 3.03 ± 0.09 g/L) or glycerol (2.32 ± 0.19 to 2.82 ± 0.05 g/L) were significantly (p < 0.05) high compared to those obtained with MRS broth as substrate (0.30 ± 0.02 to 0.51 ± 0.09 g/L). Preliminary characterization of crude biosurfactants reveals that they are mainly glycoproteins and glycolipids with molasses and glycerol as substrate, respectively. Therefore, sugar cane molasses or glycerol can effectively be used by Lactobacillus strains as low-cost substrates to increase their biosurfactants production.

Optimization of drying parameters for mango seed kernels using central composite design

BackgroundThe combined effect of drying temperature and time was evaluated on residual water content, yield of oil extraction, total phenolic compounds and antioxidant activity of seed kernel from a Cameroonian local variety of mango (Local Ngaoundere). Response surface methodology (RSM) using central composite design (CCD) as tool, was used to develop, validate and optimize statistical models in order to establish the impact of the drying parameters (temperature and time) either alone or in combination.ResultsIt was shown that drying temperature individually in its first order (X1) contributed 30.81, 21.11, 41.28 and 33.24% while drying time individually in its first order (X2) contributed 39.91, 15.12, 29.92 and 25.87% for residual water content, yield of oil extraction, total phenolic components and antioxidant activity respectively. The increase of drying temperature increased antioxidant activity while the other physicochemical characteristics such as water content, yield of oil extraction and total phenolic components decreased. Concerning drying time, only water content was reduced with an increase of that factor. The synergetic effect of drying temperature and time was effective only for antioxidant activity. A compromise for optimization were then fixed for water content ≤ 10% w/w; oil content ≥ 9% w/w; total polyphenols ≥ 1 mg/g and antioxidant activity ≥ 1000 mg AAE/100 g DM. A simulation for optimization gave, for 60 H and 60°C for drying time and temperature respectively permitted to obtain 4.10% w/w, 9.53% w/w, 1340.28 mg AAE/100 g DM and 1.16 mg/g for water content, oil content, antioxidant activity and total polyphenols respectively.ConclusionsThe physicochemical characteristics studied was globally influenced by the chosen factors (drying time and temperature).

Production and Partial Characterization of an Extracellular Thermophile Alkaline Protease from a Selected Strain of Bacillus sp Isolated from Abattoir Soil in the North Region of Cameroon

The present study aims at screening and isolates thermostable alkaline protease producing bacteria from soil sample in the northern part of Cameroon, and characterizes their enzyme. Samples of soil were collected from four (04) North Cameroonian towns (Ngaoundere, Garoua, Figuil and Maroua). Six (06) isolates showed important proteolytic activity on skim milk agar. The strain N2.3.5 from Ngaoundere showed the largest hydrolysis halo (24 mm) and was selected for protease production. The partial identification of strain N2.3.5 through morphological and biochemical characterization enabled us to classify it as belonging to the genus Bacillus sp. The growth of the strain N2.3.5 and its enzyme production profile showed that the growth of the bacteria was a diauxic type, and that the protease production was not directly associated with the microbial growth. In a medium composed of soya flour, corn flour, yeast extract and at alkaline pH, following the monitoring of each of these parameters by a complete factorial experimental design, the pH value of 10 was found to be significant for an optimal growth. Meanwhile, the corn flour, the soya flour and the yeast extract did not have a consequent influence on the protease production by the bacteria, under the chosen experimental conditions. The extracellular protease produced by Bacillus sp N235 was partially purified using a precipitation with ammonium sulphate, a dialysis and a gel filtration on sephadex G-75. A specific activity of 1516.7 U/mg and a purification yield of 37.63% were obtained. The partially purified enzyme was able to maintain its activity after been heat-treated at 80°C for 30 min. The maximal activity was exhibited at temperature of 80°C and to a pH 12. The enzyme activity and stability was enhanced in presence of the Ca2+.

Valorisation of crude earth as sustainable building material: a case of international cooperation in the Logone Valley (Chad–Cameroon)

Deforestation is one of the most dramatic threats to environmental equilibrium and food safety in many regions of the world, and particularly in sub-Saharan Africa. It is enhanced by many kinds of human activities, among which is the earth brick-firing process that needs large amounts of wood for attaining and maintaining temperatures required during this process. In order to reduce deforestation, the present study investigated from different points of view the potential of crude earth to be used as building material, taking as a case study the Logone Valley located at the border between Chad and Cameroon. First, an on-site investigation was made to verify the state-of-the-art of brick production technologies and to evaluate their impact on the environment. Subsequently, morphological and geotechnical analyses on soil samples collected from different sites of the Logone Valley were carried out, to evaluate their suitability to brick production. Finally, a pilot plant for crude earthen brick production was set, particularly based on a new press designed for this purpose.