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A new search for thermotolerant yeasts, its characterization and optimization using response surface methodology for ethanol production.

Arora R, Behera S, Sharma NK, Kumar S - Front Microbiol (2015)

Bottom Line: After optimization using Face-centered Central Composite Design (FCCD), the growth parameters like temperature and pH were found to be 45.17°C and 5.49, respectively for K. marxianus NIRE-K1 and 45.41°C and 5.24, respectively for K. marxianus NIRE-K3.Further, batch fermentations were carried out under optimized conditions, where K. marxianus NIRE-K3 was found to be superior over K. marxianus NIRE-K1.Ethanol yield (Y x∕s ), sugar to ethanol conversion rate (%), microbial biomass concentration (X) and volumetric product productivity (Q p ) obtained by K. marxianus NIRE-K3 were found to be 9.3, 9.55, 14.63, and 31.94% higher than that of K. marxianus NIRE-K1, respectively.

View Article: PubMed Central - PubMed

Affiliation: Biochemical Conversion Division, Sardar Swaran Singh National Institute of Bio-Energy Kapurthala, India ; I.K Gujral Punjab Technical University Kapurthala, India.

ABSTRACT
The progressive rise in energy crisis followed by green house gas (GHG) emissions is serving as the driving force for bioethanol production from renewable resources. Current bioethanol research focuses on lignocellulosic feedstocks as these are abundantly available, renewable, sustainable and exhibit no competition between the crops for food and fuel. However, the technologies in use have some drawbacks including incapability of pentose fermentation, reduced tolerance to products formed, costly processes, etc. Therefore, the present study was carried out with the objective of isolating hexose and pentose fermenting thermophilic/thermotolerant ethanologens with acceptable product yield. Two thermotolerant isolates, NIRE-K1 and NIRE-K3 were screened for fermenting both glucose and xylose and identified as Kluyveromyces marxianus NIRE-K1 and K. marxianus NIRE-K3. After optimization using Face-centered Central Composite Design (FCCD), the growth parameters like temperature and pH were found to be 45.17°C and 5.49, respectively for K. marxianus NIRE-K1 and 45.41°C and 5.24, respectively for K. marxianus NIRE-K3. Further, batch fermentations were carried out under optimized conditions, where K. marxianus NIRE-K3 was found to be superior over K. marxianus NIRE-K1. Ethanol yield (Y x∕s ), sugar to ethanol conversion rate (%), microbial biomass concentration (X) and volumetric product productivity (Q p ) obtained by K. marxianus NIRE-K3 were found to be 9.3, 9.55, 14.63, and 31.94% higher than that of K. marxianus NIRE-K1, respectively. This study revealed the promising potential of both the screened thermotolerant isolates for bioethanol production.

No MeSH data available.


3-D plot of maximum specific growth rate as a function of temperature and pH (A) K. marxianus NIRE-K1 (B) K. marxianus NIRE-K3.
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Figure 8: 3-D plot of maximum specific growth rate as a function of temperature and pH (A) K. marxianus NIRE-K1 (B) K. marxianus NIRE-K3.

Mentions: The value of coefficient of variation (CV = 5.16 and 6.31% for K. marxianus NIRE-K1 and NIRE-K3) was low due to the small residue between actual and predicted maximum specific growth rate. Also, to measure the adequate precision of the model and reliability of the experimental part, ratio of signal to noise is determined, where a ratio greater than 4 is desirable (Montgomery, 2001). In the present study, the ratio of 41.292 and 37.079 in case of K. marxianus NIRE-K1 and NIRE-K3 indicates an adequate signal to use the model for prediction purposes. Figures 6A,B show the diagnostic plots between the experimental and predicted values for K. marxianus NIRE-K1 and NIRE-K3, respectively, wherein all the points lie along the diagonal line, again indicating a good fit for both the models. Contour and three dimensional plots for isolates K. marxianus NIRE-K1 and NIRE-K3 have been shown in Figures 7, 8, respectively. The interaction between the variables is indicated by the shape of the contour plot. Strong interactions between the variables are indicated by the elliptical plots whereas circular plots indicate weaker interactions (Prakash et al., 2008). However, the plots of both the isolates were found to be elliptical (Figure 7). In three dimensional plots, (Figure 8), the convex response surface suggested well-defined optimum variables (temperature and pH) and maximum specific growth rate increased to the peak with the increase of temperature and pH up to 45°C and 5.5 for both the isolates which declined beyond the values.


A new search for thermotolerant yeasts, its characterization and optimization using response surface methodology for ethanol production.

Arora R, Behera S, Sharma NK, Kumar S - Front Microbiol (2015)

3-D plot of maximum specific growth rate as a function of temperature and pH (A) K. marxianus NIRE-K1 (B) K. marxianus NIRE-K3.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4555967&req=5

Figure 8: 3-D plot of maximum specific growth rate as a function of temperature and pH (A) K. marxianus NIRE-K1 (B) K. marxianus NIRE-K3.
Mentions: The value of coefficient of variation (CV = 5.16 and 6.31% for K. marxianus NIRE-K1 and NIRE-K3) was low due to the small residue between actual and predicted maximum specific growth rate. Also, to measure the adequate precision of the model and reliability of the experimental part, ratio of signal to noise is determined, where a ratio greater than 4 is desirable (Montgomery, 2001). In the present study, the ratio of 41.292 and 37.079 in case of K. marxianus NIRE-K1 and NIRE-K3 indicates an adequate signal to use the model for prediction purposes. Figures 6A,B show the diagnostic plots between the experimental and predicted values for K. marxianus NIRE-K1 and NIRE-K3, respectively, wherein all the points lie along the diagonal line, again indicating a good fit for both the models. Contour and three dimensional plots for isolates K. marxianus NIRE-K1 and NIRE-K3 have been shown in Figures 7, 8, respectively. The interaction between the variables is indicated by the shape of the contour plot. Strong interactions between the variables are indicated by the elliptical plots whereas circular plots indicate weaker interactions (Prakash et al., 2008). However, the plots of both the isolates were found to be elliptical (Figure 7). In three dimensional plots, (Figure 8), the convex response surface suggested well-defined optimum variables (temperature and pH) and maximum specific growth rate increased to the peak with the increase of temperature and pH up to 45°C and 5.5 for both the isolates which declined beyond the values.

Bottom Line: After optimization using Face-centered Central Composite Design (FCCD), the growth parameters like temperature and pH were found to be 45.17°C and 5.49, respectively for K. marxianus NIRE-K1 and 45.41°C and 5.24, respectively for K. marxianus NIRE-K3.Further, batch fermentations were carried out under optimized conditions, where K. marxianus NIRE-K3 was found to be superior over K. marxianus NIRE-K1.Ethanol yield (Y x∕s ), sugar to ethanol conversion rate (%), microbial biomass concentration (X) and volumetric product productivity (Q p ) obtained by K. marxianus NIRE-K3 were found to be 9.3, 9.55, 14.63, and 31.94% higher than that of K. marxianus NIRE-K1, respectively.

View Article: PubMed Central - PubMed

Affiliation: Biochemical Conversion Division, Sardar Swaran Singh National Institute of Bio-Energy Kapurthala, India ; I.K Gujral Punjab Technical University Kapurthala, India.

ABSTRACT
The progressive rise in energy crisis followed by green house gas (GHG) emissions is serving as the driving force for bioethanol production from renewable resources. Current bioethanol research focuses on lignocellulosic feedstocks as these are abundantly available, renewable, sustainable and exhibit no competition between the crops for food and fuel. However, the technologies in use have some drawbacks including incapability of pentose fermentation, reduced tolerance to products formed, costly processes, etc. Therefore, the present study was carried out with the objective of isolating hexose and pentose fermenting thermophilic/thermotolerant ethanologens with acceptable product yield. Two thermotolerant isolates, NIRE-K1 and NIRE-K3 were screened for fermenting both glucose and xylose and identified as Kluyveromyces marxianus NIRE-K1 and K. marxianus NIRE-K3. After optimization using Face-centered Central Composite Design (FCCD), the growth parameters like temperature and pH were found to be 45.17°C and 5.49, respectively for K. marxianus NIRE-K1 and 45.41°C and 5.24, respectively for K. marxianus NIRE-K3. Further, batch fermentations were carried out under optimized conditions, where K. marxianus NIRE-K3 was found to be superior over K. marxianus NIRE-K1. Ethanol yield (Y x∕s ), sugar to ethanol conversion rate (%), microbial biomass concentration (X) and volumetric product productivity (Q p ) obtained by K. marxianus NIRE-K3 were found to be 9.3, 9.55, 14.63, and 31.94% higher than that of K. marxianus NIRE-K1, respectively. This study revealed the promising potential of both the screened thermotolerant isolates for bioethanol production.

No MeSH data available.