Abstract
The present investigation is aimed at assessing the suitability of cane molasses as a cheaper carbon and energy source for glucoamylase production using alginate-immobilized Thermomucor indicae-seudaticae. The culture variables for glucoamylase production were optimized by 'one-variable-at-a-time' strategy and response surface methodology (RSM). A high glucoamylase titre was attained when 40 alginate beads (c. 5x10(6) immobilized spores) were used to inoculate 50 ml of cane molasses (8%) medium in 250-ml Erlenmeyer flasks. Response surface optimization of fermentation parameters (cane molasses 7%, inoculum level 44 alginate beads per 50 ml of medium and ammonium nitrate 0.25%) resulted in 1.8-fold higher glucoamylase production (27 U ml(-1)) than that in the unoptimized medium (15 U ml(-1)). Enzyme production was also sustainable in 22 l of laboratory air-lift bioreactor. Cane molasses served as an excellent carbon and energy source for the economical production of glucoamylase, which was almost comparable with that in sucrose yeast-extract broth. The statistical model developed using RSM allowed determination of optimum levels of the variables for improving glucoamylase production. The cost of glucoamylase produced in cane molasses supplemented with ammonium nitrate was considerably lower (euro1.43 per million U) than in synthetic medium containing sucrose and yeast-extract (euro35.66 per million U). The reduction in fermentation time in air-lift bioreactor with sustainable glucoamylase titres suggested the feasibility of scale up of the process.
Published Version
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