Multi-objective optimization in Aspergillus niger fermentation for selective product enhancement |
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Authors: | Chaitali Mandal Ravindra D Gudi G K Suraishkumar |
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Institution: | (1) Department of Chemical Engineering, IIT Bombay, 400 076 Powai, Mumbai, India;(2) Biotechnology Department, IIT Madras, 600 036 Chennai, India |
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Abstract: | A multi-objective optimization formulation that reflects the multi-substrate optimization in a multi-product fermentation
is proposed in this work. This formulation includes the application of ε-constraint to generate the trade-off solution for
the enhancement of one selective product in a multi-product fermentation, with simultaneous minimization of the other product
within a threshold limit. The formulation has been applied to the fed-batch fermentation of Aspergillus niger that produces a number of enzymes during the course of fermentation, and of these, catalase and protease enzyme expression
have been chosen as the enzymes of interest. Also, this proposed formulation has been applied in the environment of three
control variables, i.e. the feed rates of sucrose, nitrogen source and oxygen and a set of trade-off solutions have been generated
to develop the pareto-optimal curve. We have developed and experimentally evaluated the optimal control profiles for multiple
substrate feed additions in the fed-batch fermentation of A. niger to maximize catalase expression along with protease expression within a threshold limit and vice versa. An increase of about
70% final catalase and 31% final protease compared to conventional fed-batch cultivation were obtained. Novel methods of oxygen
supply through liquid-phase H2O2 addition have been used with a view to overcome limitations of aeration due to high gas–liquid transport resistance. The
multi-objective optimization problem involved linearly appearing control variables and the decision space is constrained by
state and end point constraints. The proposed multi-objective optimization is solved by differential evolution algorithm,
a relatively superior population-based stochastic optimization strategy. |
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Keywords: | |
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