Biochemical Engineering Journal 27 (2006) 287–294 Optimization of lipase production in a triple impeller bioreactor Meenal S. Puthli, Virendra K. Rathod, Aniruddha B. Pandit ∗ Mumbai University Institute of Chemical Technology, Chemical Engineering Division, Matunga, Mumbai 400019, India Received 9 July 2004; received in revised form 3 August 2005; accepted 3 August 2005 Abstract The fermentation kinetics for the synthesis of lipase by Candida rugosa has been studied in a batch system in a 2 l batch bioreactor. The studies illustrated the influence of gas–liquid mass transfer coefficient on the cell growth and hence the lipase production. In order to maintain sufficient oxygen concentration for the optimum cell growth and lipase activity, fermentation has been carried out using triple impeller system at an operating speed of 600 rpm (optimum operating speed as found in the earlier work) and at different aeration rates. Gas-flow rate of 50.34 cc/s has been observed to be optimum. Under optimized conditions of the bioreactor, cell production was enhanced and the lipase activity increased by 2.5 folds. The Monod’s kinetics was fitted to the data of the operating parameters to understand the cell growth and substrate consumption. Luedking and Piret model was applied to the data to determine the relationship between the cell growth and lipase production. The lipase production was found to be microbial growth associated function. © 2005 Elsevier B.V. All rights reserved. Keywords: Bioreactor; Gas–liquid mass transfer; Fermentation; Triple impeller; Aerobic process; Growth kinetics 1. Introduction Candida cylindracea (now named Candida rugosa) is recognized to be a good producer of lipase [1–3]. Lipase produced by Candida rugosa has been one of the most widely used enzymes in research owing to its high activity in hydrolytic reactions as well as synthetic chemistry. Research on lipases is focused particularly on structural characteriza- tion, elucidation of mechanism of action, kinetics of lipase catalyzed reactions, sequencing and cloning of lipase genes and general characterization of its performance. In compari- son with this effort, very little literature is available about the effect of different fermentation conditions, the relationship between the processes involved in the consumption of the substrate and the lipase production and the development of lipase bioreactor system for a commercial use [4]. Microbial lipase fermentations are affected by the medium pH, tempera- ture, medium composition, inoculation volume, aeration and agitation and many other factors related to bioreactor design such as impeller configuration, impeller spacing, impeller diameter, distance of the impeller from the bottom of biore- ∗ Corresponding author. Tel.: +91 22 24145616; fax: +91 22 24145614. E-mail address: abp@udct.org (A.B. Pandit). actor, H/T ratio, etc. Vadehra and Harmon [5] and Alford and Smith [6] observed that a presence of air was essential for lipase production by Staphylococcus aureus. Similar reports indicating the necessity of the aeration and agitation for lipase production are available in the literature though using differ- ent strains [7–10]. The initial shake flask study of Candida rugosa suggested that there should be an optimum balance between the aeration and agitation for maintaining proper oxygen concentration for the good growth of the Candida rugosa and the lipase activity [11]. Shaken flask appears to be a simple technique, however it can present a number of experimental difficul- ties [12–13] indicating that agitation is a preferable alterna- tive. In the case of stirred bioreactors also, multiple impeller bioreactors are now becoming important due to efficient gas distribution, higher gas phase residence time, increased gas hold-up, superior liquid flow (plug flow) characteristics and lower power consumption per impeller as compared to the single impeller systems resulting into a substantial savings in the operational costs. The increase in the number of energy dissipation points due to redistribution, results into a higher volumetric gas–liquid mass transfer coefficients [14]. The aim of the present work was to determine the optimum oxygen tension favourable for the growth of Candida rugosa and the 1369-703X/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.bej.2005.08.016