Microbiology
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Item Tolerance of yeast to formic acid during ethanol fermentation(Bulgarian Society for Microbilogist, 2019) Afolabi, F. T.; Oduokpaha, G. E.; Onilude, A. A.This study was carried out to investigate the tolerance of yeasts isolated from some Nigerian traditional fermented foods to formic acid during laboratory-scale fermentation of ethanol. A total of 27 yeast strains were isolated from burukutu, ogi, kunu and palm wine. The yeasts were screened for formic acid tolerance using spot plate technique on two culture media. One strain was selected based on its ability to tolerate up to 15 mM concentration of formic acid on Yeast Extract Peptone Dextrose Agar and was further identified as Candida tropicalis strain IFM 63517. C. tropicalis was used for fermentation of ethanol with varying concentrations of formic acid, ethanol and residual glucose concentrations which were monitored at intervals. The total viable cell count was determined using plate count technique. The highest ethanol yield of 8.36% (v/v) with a residual glucose concentration of 0.33 g/L was obtained from 0 mM formic acid (control fermentation vessel) with a total viable cell count of 8.7x109 cfu/ml, while the lowest ethanol yield of 8.00% (v/v) with a residual glucose concentration of 0.14g/L was obtained from 15 mM concentration of formic acid with a total viable cell count of 6.1x109 cfu/ml. The yeast strain used in this work exhibited a high ethanol yield despite the presence of an inhibitory compound (formic acid) when comparing the ethanol yield at its tolerance threshold (15 mM of formic acid) to the control fermentation vessel without formic acid.Item Fermentation conditions and process optimization of citric acid production by yeasts(Conscientia Beam, 2018) Afolabi, F. T.; Adeyemo, S. M.; Balogun, H. O.The aim of this study was to isolate and screen citric acid producing yeasts using low cost substrates. Thirty three yeast isolates were obtained from pineapple, plantain and sugar cane waste and identified as; Saccharomyces cerevisiae, Schizosaccharomyces pombe, Candida tropicalis, Pichia guilliiermondii, Debaromyces sp., Candida parapsilosis, Candida rugosa, and Candida krusei. Candida tropicalis had zone of clearance of 49±2.1 mm in diameter, Pichia guilliermondii had 40±1.2mm. Saccharomyces cerevisiae produced citric acid with glucose with 105.0 mg/l. C. tropicalis yielded 132.2 mg/l with sodium nitrate. S. cerevisiae and C. tropicalis produced citric acid at pH 6 with 23.70mg/l and 23.80mg/l. P. gulliermondii at pH 4 produced 23.00mg/l. The temperature of 30°C favoured S. cerevisiae and C. tropicalis yielding 40.80mg/l and 39.80 mg/l. After extraction, the yield of the citric acid was 4.231g, 3g of which was recrystallized to yield 2.16g of pure citric acid resulting into 72% recovery. The result indicated that pineapple wastes, plantain wastes and sugarcane cane are potential sources of yeasts that can be used for the production of citric acid.Item Isolation and screening of phytate-degrading yeasts from cereals(Federal University Dutsin-Ma, 2025) Afolabi, F. T.; Gyegweh K. T.Application of phytase (myo-inositol hexakisphosphate phosphohydrolase) to catalyze the release of phosphate from phytates contained on grain-based feed has been used widely. This study was carried out to isolate, identify, screen and produce yeast phytase from cereals using submerged fermentation. Two hundred and twenty seven (227) yeast isolates were obtained from maize, sorghum and millet and identified based on various characteristics such as colony morphology, microscopy, biochemical tests, sugar fermentation tests and molecular analysis. The isolates were then screened for phytase production by growing them on Phytase Screening Medium (PSM) and observing the formation of a clear zone around their colonies, indicating their ability to degrade phytate. It was found that yeast species such as Pichia membranefaciens, Meyerozyma guilliermondii SWS81, Candida krusei, M. guilliermondii M122, Pichia fermentans, M. guilliermondii WM226 and Schwanniomyces occidentalis, were capable of phytate degradation. M. guilliermondii M122, M. guilliermondii SWS81, and M. guilliermondii WM226 with higher solubilizing indices (4.52 mm, 3.64 mm and 5.14 mm respectively) were selected for production and assay. The results showed that crude enzymes from these yeast strains had phytase activity ranging from 44.70 U/mL to 97.70 U/mL, making them potential supplements for animal feeds to improve nutritional status and combat environmental phosphorus pollution.Item Isolation and screening of phytate-degrading yeasts from cereals(Federal University Dutsin-Ma, 2025) Afolabi, F. T.; Gyegweh K. T.Application of phytase (myo-inositol hexakisphosphate phosphohydrolase) to catalyze the release of phosphate from phytates contained on grain-based feed has been used widely. This study was carried out to isolate, identify, screen and produce yeast phytase from cereals using submerged fermentation. Two hundred and twenty seven (227) yeast isolates were obtained from maize, sorghum and millet and identified based on various characteristics such as colony morphology, microscopy, biochemical tests, sugar fermentation tests and molecular analysis. The isolates were then screened for phytase production by growing them on Phytase Screening Medium (PSM) and observing the formation of a clear zone around their colonies, indicating their ability to degrade phytate. It was found that yeast species such as Pichia membranefaciens, Meyerozyma guilliermondii SWS81, Candida krusei, M. guilliermondii M122, Pichia fermentans, M. guilliermondii WM226 and Schwanniomyces occidentalis, were capable of phytate degradation. M. guilliermondii M122, M. guilliermondii SWS81, and M. guilliermondii WM226 with higher solubilizing indices (4.52 mm, 3.64 mm and 5.14 mm respectively) were selected for production and assay. The results showed that crude enzymes from these yeast strains had phytase activity ranging from 44.70 U/mL to 97.70 U/mL, making them potential supplements for animal feeds to improve nutritional status and combat environmental phosphorus pollution.Item Production and optimisation of citric acid by yeasts isolated from Kola nut pod husk.(Scholars Direct, 2022) Afolabi, F. T.; Akanbi, A. A.Citric acid is an organic acid commonly used in food, pharmaceutical, chemical industries.Citric acid is a weak acid found in nearly all tissues; both in plants and animal and it is generally regarded as safe. The work aimed to obtain yeast isolates capable of citric acid production from kola nut pod waste and to know optimum conditions that favour higher citric acid production. One hundred twenty seven (127) isolates were obtained out of which 46 were selected following primary screening for production of citric acid on compounded solid media. Nine (9) of these yeasts that had the highest potential for citric acid production having the largest acid production zones after primary and secondary screening were selected. KI8 identified as Candida rugosa, KI8 identified as Pichia kudriavzevii and KF16 identified as Rhodotorula rubra using molecular methods. Three (3) isolates with the highest citric acid were used for citric acid production and optimization. Box-Benkhen design was the statistical technique used for optimization of the experimental factors. Four factors:pH, carbon source (g/L), nitrogen source (g/L) and temperature were tested as the variables affecting citric acid production using Box-Benkhen design. The results showed that pH (5.0), glucose concentration (7.5 g/L), ammonium sulphate concentration of (1.5 g/L) and temperature (30 °C) were the best conditions for the highest yield of citric acid. The yield of citric acid yield was high at 17.8 g/L under the optimized conditions. Crude citric acid (4.00 g) was crystallized from the production medium. The citric acid recovered after recrystallization was 3.10%. The recovery was 78%. Hence, citric acid production through fermentation by yeasts can greatly increase acid availability for its various industrial applications.Item The effect of using biological treatment on microbial growth during the malting of sorghum(Science Domain international, 2021) Ayodeji, O. C.; Afolabi, F. T.; Abdulkadir, M.; Fasiku, O.Malting is an important industrial product with a huge market outlet. Sorghum grain carries a numerous and variable, microbial population that mainly consists of bacteria, yeasts, and filamentous fungi. Sorghum malt is heavily reliant on chemical control of moulds and coliforms. This research aimed at investigating ways of improving malt quality and safety, using starter cultures of lactic acid bacteria and yeast, during the steeping stage of malting. All the steep treatments contained a sizeable population of moulds, greater than 4logcfu/mL, at 0hrs of steeping. A 3Log decrease was recorded in the steep treatment containing only single culture of Lactobacillus plantarum All the steeping treatments achieved varying levels of anti-nutrient reduction. The Lactobacillus plantarum CLB8 steep reduced the phytate level by as much as 47% when compared to the phytate level in sorghum grain. The combined cultures of Lactobacillus plantarum CLB8 and Saccharomyces cerevisiaeCYT1 reduced the phytate content by as much as 40% when compared to the sorghum grain without treatment. When compared to the control steep, the Lactobacillus plantarum CLB8 steep improved the anti-nutrient degradation by 31%. The combined cultures of Lactobacillus plantarum CLB8 and Saccharomyces cerevisiae CYT1 reduced the phytate content by as much as 23% when compared with the control steep. The polyphenol content was reduced by about 46% in the Lactobacillus plantarum CLB8 steep and 29% in the combined cultures of Lactobacillus plantarum CLB8 and Saccharomyces cerevisiae CYT1 steep when compared to the polyphenol content in the whole sorghum grain. Only the Lactobacillus plantarum CLB8 steep had better polyphenol reduction than the control with a 9.6% reduction more than the control. It was concluded that lactic acid bacteria can be apply as a biological control organism in malting of grains.Item Tolerance of yeast to formic acid during ethanol fermentation(Bulgarian Society for Microbilogist, 2019) Afolabi, F. T.; Oduokpaha, G. E.; Onilude, A. A.This study was carried out to investigate the tolerance of yeasts isolated from some Nigerian traditional fermented foods to formic acid during laboratory-scale fermentation of ethanol. A total of 27 yeast strains were isolated from burukutu, ogi, kunu and palm wine. The yeasts were screened for formic acid tolerance using spot plate technique on two culture media. One strain was selected based on its ability to tolerate up to 15 mM concentration of formic acid on Yeast Extract Peptone Dextrose Agar and was further identified as Candida tropicalis strain IFM 63517. C. tropicalis was used for fermentation of ethanol with varying concentrations of formic acid, ethanol and residual glucose concentrations which were monitored at intervals. The total viable cell count was determined using plate count technique. The highest ethanol yield of 8.36% (v/v) with a residual glucose concentration of 0.33 g/L was obtained from 0 mM formic acid (control fermentation vessel) with a total viable cell count of 8.7x109 cfu/ml, while the lowest ethanol yield of 8.00% (v/v) with a residual glucose concentration of 0.14g/L was obtained from 15 mM concentration of formic acid with a total viable cell count of 6.1x109 cfu/ml. The yeast strain used in this work exhibited a high ethanol yield despite the presence of an inhibitory compound (formic acid) when comparing the ethanol yield at its tolerance threshold (15 mM of formic acid) to the control fermentation vessel without formic acid.Item Microbiological and physicochemical changes in palm wine subjected to spontaneous fermentation during storage(Conscientia Beam, 2019) Afolabi, F. T.; Owoola, T. A.This work aimed to isolate and identify yeasts obtained from palm wine subjected to spontaneous fermentation during storage. A total of forty (40) yeast isolates were from spontaneously fermented palm wine. The yeast counts obtained ranged from 5.46 x 104 cfu/ml at day one to 3.00 x 102 cfu/ml at day twenty-two. Saccharomyces cerevisiae was isolated at all stages of fermentation. The pH dropped from 3.70 at 24 hours to 3.37 at 360 hours. Total titratable acidity of the wine increased from 2.28% at 24 hours to 4.50% at 528 hours. Total sugar of the stored palm wine from decreased from 4.0211g/10 ml at 24 hours to 0.6417g/10 ml at 528 hours was observed. The reducing sugar content of the stored palm wine decreased from 13% at 24 hours to 0.960% at 456 hours was also observed. Ethanol content of the stored palm wine increased steadily from 21.06 mg/ml at 24 hours to 88.99mg/ml at 456 hours as the storage time increases. Palm wine whose storage time is not beyond 120 hours is not injurious to the health of consumers.Item Fermentation conditions and process optimization of citric acid production by yeasts(Conscientia Beam, 2018) Afolabi, F. T.; Adeyemo, S. M.; Balogun, H. O.The aim of this study was to isolate and screen citric acid producing yeasts using low cost substrates. Thirty three yeast isolates were obtained from pineapple, plantain and sugar cane waste and identified as; Saccharomyces cerevisiae, Schizosaccharomyces pombe, Candida tropicalis, Pichia guilliiermondii, Debaromyces sp., Candida parapsilosis, Candida rugosa, and Candida krusei. Candida tropicalis had zone of clearance of 49±2.1 mm in diameter, Pichia guilliermondii had 40±1.2mm. Saccharomyces cerevisiae produced citric acid with glucose with 105.0 mg/l. C. tropicalis yielded 132.2 mg/l with sodium nitrate. S. cerevisiae and C. tropicalis produced citric acid at pH 6 with 23.70mg/l and 23.80mg/l. P. gulliermondii at pH 4 produced 23.00mg/l. The temperature of 30°C favoured S. cerevisiae and C. tropicalis yielding 40.80mg/l and 39.80 mg/l. After extraction, the yield of the citric acid was 4.231g, 3g of which was recrystallized to yield 2.16g of pure citric acid resulting into 72% recovery. The result indicated that pineapple wastes, plantain wastes and sugarcane cane are potential sources of yeasts that can be used for the production of citric acid.