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Comparison of estimation capabilities of response surface methodology (RSM) with artificial neural network (ANN) in lipase-catalyzed synthesis of palm-based wax ester.

Basri M, Rahman RN, Ebrahimpour A, Salleh AB, Gunawan ER, Rahman MB - BMC Biotechnol. (2007)

Bottom Line: The actual experimental percentage yield was 84.6% at optimum condition, which compared well to the maximum predicted value by ANN (83.9%) and RSM (85.4%).The order of effective parameters on wax ester percentage yield were; respectively, time with 33.69%, temperature with 30.68%, amount of enzyme with 18.78% and substrate molar ratio with 16.85%, whereas R2 and AAD were determined as 0.99998696 and 1.377 for ANN, and 0.99991515 and 3.131 for RSM respectively.Though both models provided good quality predictions in this study, yet the ANN showed a clear superiority over RSM for both data fitting and estimation capabilities.

View Article: PubMed Central - HTML - PubMed

Affiliation: Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia. mahiran@science.upm.edu.my

ABSTRACT

Background: Wax esters are important ingredients in cosmetics, pharmaceuticals, lubricants and other chemical industries due to their excellent wetting property. Since the naturally occurring wax esters are expensive and scarce, these esters can be produced by enzymatic alcoholysis of vegetable oils. In an enzymatic reaction, study on modeling and optimization of the reaction system to increase the efficiency of the process is very important. The classical method of optimization involves varying one parameter at a time that ignores the combined interactions between physicochemical parameters. RSM is one of the most popular techniques used for optimization of chemical and biochemical processes and ANNs are powerful and flexible tools that are well suited to modeling biochemical processes.

Results: The coefficient of determination (R2) and absolute average deviation (AAD) values between the actual and estimated responses were determined as 1 and 0.002844 for ANN training set, 0.994122 and 1.289405 for ANN test set, and 0.999619 and 0.0256 for RSM training set respectively. The predicted optimum condition was: reaction time 7.38 h, temperature 53.9 degrees C, amount of enzyme 0.149 g, and substrate molar ratio 1:3.41. The actual experimental percentage yield was 84.6% at optimum condition, which compared well to the maximum predicted value by ANN (83.9%) and RSM (85.4%). The order of effective parameters on wax ester percentage yield were; respectively, time with 33.69%, temperature with 30.68%, amount of enzyme with 18.78% and substrate molar ratio with 16.85%, whereas R2 and AAD were determined as 0.99998696 and 1.377 for ANN, and 0.99991515 and 3.131 for RSM respectively.

Conclusion: Though both models provided good quality predictions in this study, yet the ANN showed a clear superiority over RSM for both data fitting and estimation capabilities.

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Three dimensional plot showing the effect of amount of enzyme, temperature and their mutual effect on the synthesis of wax esters. Other variables are constant: molar ratio palm oil:oleyl alcohol, 1:3 and incubation time, 5 h.
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Figure 5: Three dimensional plot showing the effect of amount of enzyme, temperature and their mutual effect on the synthesis of wax esters. Other variables are constant: molar ratio palm oil:oleyl alcohol, 1:3 and incubation time, 5 h.

Mentions: Figure 3 shows the three dimensional plots as function of time, temperature and interaction on wax ester synthesis at substrate molar ratio 1:3 and amount of enzyme of 1.50%. The percentage yield increased with an increase in incubation time. Reaction with temperature 50°C and time 7.5 h, led to the maximum percentage yield (over 80%). The percentage yield was increased from 40 to 50°C and decreased thereafter up to 60°C. The increase in percentage yield is an indication of the conformational change indicating greater unfolding of the enzyme at 50°C than at 30 and 60°C [25]. The effect of varying substrate molar ratio and reaction temperature on alcoholysis at constant reaction time (5 h), and amount of enzyme at 1.50% is as shown in Figure 4. Figure 5 represents the effect of varying amount of enzyme and reaction temperature on alcoholysis at 5 h and substrate molar ratio of 1:3. The typical plots are dome shaped. Many lipase-catalyzed esterification systems exhibit this type of plots [26]. In this type of plot, while in one axis there is a linear increase in alcoholysis, in the other axis there is increase only up to an extent, which decreases thereafter. This indicates that a critical temperature is involved up to which alcoholysis is favored and it is not so after that critical temperature. However percentage yield was lower at 55°C. Meanwhile, the low percentage yield at high substrate molar ratios (Figure 4) indicated that alcohols are terminal inhibitor of lipases and their effects could increase at high temperatures. Harikrisna et al. suggested that high temperature has reduced the operational stability of the enzyme [27]. Chiang et al. had reported an increase in temperature up to 55°C resulted in less alcoholysis at any given amount of enzyme because of the inactivation of enzyme at temperature over 55°C [11].


Comparison of estimation capabilities of response surface methodology (RSM) with artificial neural network (ANN) in lipase-catalyzed synthesis of palm-based wax ester.

Basri M, Rahman RN, Ebrahimpour A, Salleh AB, Gunawan ER, Rahman MB - BMC Biotechnol. (2007)

Three dimensional plot showing the effect of amount of enzyme, temperature and their mutual effect on the synthesis of wax esters. Other variables are constant: molar ratio palm oil:oleyl alcohol, 1:3 and incubation time, 5 h.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2211475&req=5

Figure 5: Three dimensional plot showing the effect of amount of enzyme, temperature and their mutual effect on the synthesis of wax esters. Other variables are constant: molar ratio palm oil:oleyl alcohol, 1:3 and incubation time, 5 h.
Mentions: Figure 3 shows the three dimensional plots as function of time, temperature and interaction on wax ester synthesis at substrate molar ratio 1:3 and amount of enzyme of 1.50%. The percentage yield increased with an increase in incubation time. Reaction with temperature 50°C and time 7.5 h, led to the maximum percentage yield (over 80%). The percentage yield was increased from 40 to 50°C and decreased thereafter up to 60°C. The increase in percentage yield is an indication of the conformational change indicating greater unfolding of the enzyme at 50°C than at 30 and 60°C [25]. The effect of varying substrate molar ratio and reaction temperature on alcoholysis at constant reaction time (5 h), and amount of enzyme at 1.50% is as shown in Figure 4. Figure 5 represents the effect of varying amount of enzyme and reaction temperature on alcoholysis at 5 h and substrate molar ratio of 1:3. The typical plots are dome shaped. Many lipase-catalyzed esterification systems exhibit this type of plots [26]. In this type of plot, while in one axis there is a linear increase in alcoholysis, in the other axis there is increase only up to an extent, which decreases thereafter. This indicates that a critical temperature is involved up to which alcoholysis is favored and it is not so after that critical temperature. However percentage yield was lower at 55°C. Meanwhile, the low percentage yield at high substrate molar ratios (Figure 4) indicated that alcohols are terminal inhibitor of lipases and their effects could increase at high temperatures. Harikrisna et al. suggested that high temperature has reduced the operational stability of the enzyme [27]. Chiang et al. had reported an increase in temperature up to 55°C resulted in less alcoholysis at any given amount of enzyme because of the inactivation of enzyme at temperature over 55°C [11].

Bottom Line: The actual experimental percentage yield was 84.6% at optimum condition, which compared well to the maximum predicted value by ANN (83.9%) and RSM (85.4%).The order of effective parameters on wax ester percentage yield were; respectively, time with 33.69%, temperature with 30.68%, amount of enzyme with 18.78% and substrate molar ratio with 16.85%, whereas R2 and AAD were determined as 0.99998696 and 1.377 for ANN, and 0.99991515 and 3.131 for RSM respectively.Though both models provided good quality predictions in this study, yet the ANN showed a clear superiority over RSM for both data fitting and estimation capabilities.

View Article: PubMed Central - HTML - PubMed

Affiliation: Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia. mahiran@science.upm.edu.my

ABSTRACT

Background: Wax esters are important ingredients in cosmetics, pharmaceuticals, lubricants and other chemical industries due to their excellent wetting property. Since the naturally occurring wax esters are expensive and scarce, these esters can be produced by enzymatic alcoholysis of vegetable oils. In an enzymatic reaction, study on modeling and optimization of the reaction system to increase the efficiency of the process is very important. The classical method of optimization involves varying one parameter at a time that ignores the combined interactions between physicochemical parameters. RSM is one of the most popular techniques used for optimization of chemical and biochemical processes and ANNs are powerful and flexible tools that are well suited to modeling biochemical processes.

Results: The coefficient of determination (R2) and absolute average deviation (AAD) values between the actual and estimated responses were determined as 1 and 0.002844 for ANN training set, 0.994122 and 1.289405 for ANN test set, and 0.999619 and 0.0256 for RSM training set respectively. The predicted optimum condition was: reaction time 7.38 h, temperature 53.9 degrees C, amount of enzyme 0.149 g, and substrate molar ratio 1:3.41. The actual experimental percentage yield was 84.6% at optimum condition, which compared well to the maximum predicted value by ANN (83.9%) and RSM (85.4%). The order of effective parameters on wax ester percentage yield were; respectively, time with 33.69%, temperature with 30.68%, amount of enzyme with 18.78% and substrate molar ratio with 16.85%, whereas R2 and AAD were determined as 0.99998696 and 1.377 for ANN, and 0.99991515 and 3.131 for RSM respectively.

Conclusion: Though both models provided good quality predictions in this study, yet the ANN showed a clear superiority over RSM for both data fitting and estimation capabilities.

Show MeSH