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Abstract

The aim of this study was to determine the optimum levels of nutrients for the production of phytase by heat stressed Rhizopus oryzae in submerged fermentation. Plackett-Burman design (PBD) was initially adopted for evaluating the medium components (mannitol, K2HPO4, Na2HPO4 and sodium phytate) affecting the phytase production most. The optimum levels were estimated using the steepest ascent (descent) method followed by central composite design (CCD) of response surface methodology (RSM). The interactive effects of phosphorus sources on phytase yield were determined to be significant. Application of Genetic Algorithm (GA)/Nelder-Mead downhill simplex (NMDS) with RSM model was proved to be more efficient approach for optimization of phytase production by Rhizopus oryzae. A 7.95-fold increase in phytase production (12640 ± 1450 Ul-1) was achieved at the GA-predicted optimum concentration of (gl-1); mannitol 22.8, K2HPO4 5.18, Na2HPO4 3.25, and sodium phytate 9.68, compared with the phytase yield before optimization (1589 ± 135 Ul-1). In the bioreactor studies, the enzyme yields were sustainable to that of the shake flask; however, the time required for maximum phytase production was significantly reduced (288h to 96h), resulting in an increase in productivity by 3.32-fold. An unusual stability of phytase at low pH and at physiological temperature (39°C) further demonstrates the potential of this enzyme in food and feed applications.

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