ORIGINAL ARTICLE Economical glucoamylase production by alginate-immobilized Thermomucor indicae-seudaticae in cane molasses medium P. Kumar and T. Satyanarayana Department of Microbiology, University of Delhi South Campus, Benito Juarez Road, New Delhi, India Introduction Glucoamylase is one of the most important enzymes in starch industry involved primarily in the production of glucose (Ford 1999; Reilly 1999). Starting from the non- reducing end of the starch molecule, it hydrolyses all a-1,4 glycosidic bonds consecutively while cleaving a-1,6 bonds at a slow rate to produce b-d-glucose (Meagher and Reilly 1989). Glucose being an essential substrate for numerous fermentation processes, glucoamylase extends its applications to a number of other food and beverage industries (Crabb and Shetty 1999; Polakovic and Bryjak 2004). Although glucoamylases have been reported from a wide variety of micro-organisms, the huge industrial demand is fulfilled by the filamentous fungi. Glucoamylase for industrial applications is produced from Aspergillus and Rhizopus spp. in submerged fer- mentation at 30–35°C, using corn and corn-steep liquor in the production medium (Nigam and Singh 1995). A number of different glucoamylase production media have been formulated (Haasum et al. 1991; Pedersen Keywords Ca 2+ -alginate, cane molasses, glucoamylase, response surface methodology, Thermomucor indicae-seudaticae. Correspondence T. Satyanarayana, Department of Microbiology, University of Delhi South Campus, Benito Juarez Road, New Delhi-110 021, India. E-mail: tsnarayana@gmail.com 2007 ⁄ 0210: received 12 February 2007, revised 17 May 2007 and accepted 21 May 2007 doi:10.1111/j.1472-765X.2007.02201.x Abstract Aims: 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. Methods and Results: The culture variables for glucoamylase production were optimized by ‘one-variable-at-a-time’ strategy and response surface methodo- logy (RSM). A high glucoamylase titre was attained when 40 alginate beads (c. 5 · 10 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 0Æ25%) resulted in 1Æ8-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 labor- atory air-lift bioreactor. Conclusions: 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. Significance and Impact of the Study: The cost of glucoamylase produced in cane molasses supplemented with ammonium nitrate was considerably lower (€1.43 per million U) than in synthetic medium containing sucrose and yeast- extract (€35.66 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. Letters in Applied Microbiology ISSN 0266-8254 392 Journal compilation ª 2007 The Society for Applied Microbiology, Letters in Applied Microbiology 45 (2007) 392–397 ª 2007 The Authors