ABSTRACT
Aims: 104 samples were collected from the west region and the coastal plain of Cameroon during two coffee campaigns, 2009 and 2010. Two coffee processes were evaluated (wet and dry processes) at different stages from harvesting to storage. Study Design: Food contaminants. Place and Duration of Study: Food Microbiology Laboratory, Department of Food Science and Nutrition (ENSAI) University of Ngaoundere; UMR 95 Qualisud, CIRAD of Montpellier, between May 2009 and September 2012. Methodology: Fungi profile was evaluated by direct plating techniques and identified using morphological and molecular tools. OTA levels were analyzed using HPLC technique after extraction and filtration using an immunoaffinity column. Results: Results obtained revealed an overall percentage of fungal contamination between 60-92% in 2009 and 70-90% in 2010. There was no ecological difference in the composition of ochratoxigenic species present in five sites. Coffee beans sampled in 2009 had a colonization incidence of 18-40% A. carbonarius, 12-22% A. niger, 3-15% A. ochraceus while those of 2010 had a colonization incidence of 15-30% A. carbonarius, 35- 40% A. niger, and 2-7% A. ochraceus. Fungal diversity was not correlated with the geographical origin, coffee cultivar and processing method. There was no difference between the processes studied in terms of occurrence of ochratoxigenic fungi. OTA levels were mostly below the recommended standards although some isolated cases of extreme contamination were observed in 2009. A higher level of OTA was detected in the presence of A. niger, A. carbonarius and A. ochraceus than when only A. niger was present. Conclusion: The important fungi with the potential to produce OTA in Cameroonian coffee beans are A. carbonarius and A. niger. These two species were predominant on each type of coffee beans. It was also observed that once a toxigenic strain was isolated from a coffee sample, the sample contained OTA.
ABSTRACT
Aim: To investigate increased thermal influence on morphology of Aspergillus carbonarius during RSDA production. Place and Duration of Study: Microbial fermentation Unit, Department of Microbiology, Faculty of Biological sciences, University of Nigeria, between July 2009 and August 2010. Methodology: In shake flask cultures thermal influence on A. carbonarius morphology and productivity investigated. Mycelial morphology was characterised by means of image analysis using as parameters, mean diameter, roughness, circularity and compactness of pellet. Thermal effect on amylase activity, total protein, biomass concentration and pH were also investigated. Results: Shifting the temperature from 27ºC to 37ºC significantly affected the morphological parameters of the pellets, but RSDA activity was not altered. The interesting thing about the morphology is the shearing off of the hairy part of the pellet at an increased temperature and subsequent agglomeration. At 27ºC the RSDA activity increased steadily with an optimum activity of 293U/ml at 96h and subsequently decreased to 75U/ml by the end of the fermentation. At 37ºC a maximum activity of 291U/ml was achieved at 72h of fermentation but this decreased to 87U/ml at the end of fermentation. Higher biomass concentration and total protein were obtained at 37ºC. The pH dropped from an initial of 5.0 to 3.0 and 2.5 for 27ºC and 37ºC temperature conditions respectively. Conclusion: Induced thermal increase resulted to changes in pellet morphology but raw starch digesting amylase activity was not altered.
ABSTRACT
Pectinase is one of the most important commercially synthesised enzyme having its application in several industrial sectors like food and beverages, fruit clarifications etc. A.carbonarius has the capacity to produce Exo-pectinase 50 U/ml by submerged fermentation process as per the previous study. The present study describes the improvement of previously identified fungal strain Aspergillus carbonarius for enhancement of pectinase production by inducing mutations using physical and chemical mutagens. Aiming to increase the potentiality in pectinase production, the parental strain was treated for three times with four mutagens - UV irradiation, Colchicine, Hydrogen peroxide and Ethidium bromide to obtain mutants. Mutants were selected based on higher enzyme activity, improved growth rates and varied morphology with increased pectinase production. All the surviving mutants were assessed quantitatively after first mutagenic treatment. The stability of the best mutants was tested by repeating the exposures for two times to obtain 3rd generation mutants. These mutants were tested quantitatively to assess the pectinase production. Of all the best mutants E8 showed maximum activity producing 65U/ml pectinase enzyme compared to wild and sister mutants. The wild strain of A. carbonarius is a low pectinase producing organism as per literature. This strain was successfully mutated to increase the productivity rate to 1.8 fold in comparison to wild strain. This overproduction and strain stability may be due to repeated mutagenic treatments.