Microbiology
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Item Screening and characterisation of yeast species for citric acid production using glycerol and agro-waste(The Nigerian Society for Microbiology (NSM), 2025) Afolabi, F. T.; Adeoye, A. E.The present study was aimed to isolate and screen yeast species for the production of citric acid using glycerol and agro-waste. Fruit samples (orange, lime, lemon and pineapple) were collected from Bodija market in Ibadan. The samples were subjected to microbiological and physicochemical analyses. A total of 43 yeast isolates were recovered from the fruit and 17 isolates had the potential to produce citric acid after screening. Yeast isolates were identified as: Candida tropicalis, Meyerozyma guilliermondii and Candida tropicalis2. The best incubation period for citric acid production by Candida tropicalis PiB10 was 120 hours (18.02 g/l), highest citric acid production (33.53 g/l) at pH 5.0, maximum citric acid production (20.84 g/l) was at 30°C, Glucose was the best carbon source, yielding 18.00 g/l of citric acid. Yeast extract was the best nitrogen source with citric acid production of 19.20 g/l and the highest production of 19.58 g/l at 200 rpm from glycerol. Meyerozyma guilliermondii LeB1 showed the highest citric acid production at 120 hours of incubation, yielding 17.02 g/l. The best pH was 5.5, yielding 35.90 g/l of citric acid. The best temperature was 30°C, with a production of 15.80 g/l, Glucose was also the preferred carbon source for this isolate, with a production of 20.13 g/l. Yeast extract was the best nitrogen source for Pichia guilliermondii LeB1, yielding 18.85 g/l. At 200 rpm from glycerol, the highest production was 22.37 g/l. This study demonstrated that Candida tropicalis, Meyerozyma guilliermondii and Candida tropicalis2 yielded high amount of citric acid using glycerol and agro-industrial wastes as substrates.Item Screening of yeasts obtained from different fermented foods for their ability to produce pectinase(Joanna Bródka, Poland, 2020) Afolabi, F. T.; Shitta Y. O.In the present study, Citrus pectin was used for the production of pectinase enzyme by yeast isolates using submerged fermentation. Fifty yeasts were isolated from different fermented foods and screened for their producing ability. Candida sp. OG2 and Candida tropicalis strain AUMC 10275 were the yeast isolates with the best potential of pectinase production. Fermentation parameters such as incubation period, pH, temperature, carbon and nitrogen source were optimized under submerged fermentation. The optimal conditions for pectinase production were found to be incubation time 48 hours, pH 6.0 and temperature 40°C. Citrus pectin best induced the production of pectinase while yeast extract/peptone (1:1) was the best source of nitrogen. Pectinase produced by Candida tropicalis strain AUMC 10275 was purified at 4.00 folds with a specific activity of 63.99 U/ml. The yeasts obtained from fermented foods have the ability to produce pectinase enzyme under optimized conditions and can be used for industrial purposes.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 Screening and characterisation of yeast species for citric acid production using glycerol and agro-waste(The Nigerian Society for Microbiology (NSM), 2025) Afolabi, F. T.; Adeoye, A. E.The present study was aimed to isolate and screen yeast species for the production of citric acid using glycerol and agro-waste. Fruit samples (orange, lime, lemon and pineapple) were collected from Bodija market in Ibadan. The samples were subjected to microbiological and physicochemical analyses. A total of 43 yeast isolates were recovered from the fruit and 17 isolates had the potential to produce citric acid after screening. Yeast isolates were identified as: Candida tropicalis, Meyerozyma guilliermondii and Candida tropicalis2. The best incubation period for citric acid production by Candida tropicalis PiB10 was 120 hours (18.02 g/l), highest citric acid production (33.53 g/l) at pH 5.0, maximum citric acid production (20.84 g/l) was at 30°C, Glucose was the best carbon source, yielding 18.00 g/l of citric acid. Yeast extract was the best nitrogen source with citric acid production of 19.20 g/l and the highest production of 19.58 g/l at 200 rpm from glycerol. Meyerozyma guilliermondii LeB1 showed the highest citric acid production at 120 hours of incubation, yielding 17.02 g/l. The best pH was 5.5, yielding 35.90 g/l of citric acid. The best temperature was 30°C, with a production of 15.80 g/l, Glucose was also the preferred carbon source for this isolate, with a production of 20.13 g/l. Yeast extract was the best nitrogen source for Pichia guilliermondii LeB1, yielding 18.85 g/l. At 200 rpm from glycerol, the highest production was 22.37 g/l. This study demonstrated that Candida tropicalis, Meyerozyma guilliermondii and Candida tropicalis2 yielded high amount of citric acid using glycerol and agro-industrial wastes as substrates.Item Screening and characterisation of yeast species for citric acid production using glycerol and agro-waste(The Nigerian Society for Microbiology (NSM), 2025) Afolabi, F. T.; Adeoye, A. E.The present study was aimed to isolate and screen yeast species for the production of citric acid using glycerol and agro-waste. Fruit samples (orange, lime, lemon and pineapple) were collected from Bodija market in Ibadan. The samples were subjected to microbiological and physicochemical analyses. A total of 43 yeast isolates were recovered from the fruit and 17 isolates had the potential to produce citric acid after screening. Yeast isolates were identified as: Candida tropicalis, Meyerozyma guilliermondii and Candida tropicalis2. The best incubation period for citric acid production by Candida tropicalis PiB10 was 120 hours (18.02 g/l), highest citric acid production (33.53 g/l) at pH 5.0, maximum citric acid production (20.84 g/l) was at 30°C, Glucose was the best carbon source, yielding 18.00 g/l of citric acid. Yeast extract was the best nitrogen source with citric acid production of 19.20 g/l and the highest production of 19.58 g/l at 200 rpm from glycerol. Meyerozyma guilliermondii LeB1 showed the highest citric acid production at 120 hours of incubation, yielding 17.02 g/l. The best pH was 5.5, yielding 35.90 g/l of citric acid. The best temperature was 30°C, with a production of 15.80 g/l, Glucose was also the preferred carbon source for this isolate, with a production of 20.13 g/l. Yeast extract was the best nitrogen source for Pichia guilliermondii LeB1, yielding 18.85 g/l. At 200 rpm from glycerol, the highest production was 22.37 g/l. This study demonstrated that Candida tropicalis, Meyerozyma guilliermondii and Candida tropicalis2 yielded high amount of citric acid using glycerol and agro-industrial wastes as substrates.Item Screening of yeasts obtained from different fermented foods for their ability to produce pectinase(Joanna Bródka, Poland, 2020) Afolabi, F. T.; Shitta Y. O.In the present study, Citrus pectin was used for the production of pectinase enzyme by yeast isolates using submerged fermentation. Fifty yeasts were isolated from different fermented foods and screened for their producing ability. Candida sp. OG2 and Candida tropicalis strain AUMC 10275 were the yeast isolates with the best potential of pectinase production. Fermentation parameters such as incubation period, pH, temperature, carbon and nitrogen source were optimized under submerged fermentation. The optimal conditions for pectinase production were found to be incubation time 48 hours, pH 6.0 and temperature 40°C. Citrus pectin best induced the production of pectinase while yeast extract/peptone (1:1) was the best source of nitrogen. Pectinase produced by Candida tropicalis strain AUMC 10275 was purified at 4.00 folds with a specific activity of 63.99 U/ml. The yeasts obtained from fermented foods have the ability to produce pectinase enzyme under optimized conditions and can be used for industrial purposes.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.