Chemical Engineering Science 56 (2001) 3401–3408 www.elsevier.nl/locate/ces Deactivation of lipase at gas–liquid interface in stirred vessel MadalasaMohanty a ,R.S.Ghadge a ,N.S.Patil a ,S.B.Sawant a ; * , J.B.Joshi a ,A.V.Deshpande b a Chemical Engineering Division, Department of Chemical Technology, University of Mumbai, Matunga, Mumbai 400 019, India b Applied Physics Division, Department of Chemical Technology, University of Mumbai, Matunga, Mumbai 400 019, India Received 4 August 2000; received in revised form 26 October 2000; accepted 8 December 2000 Abstract Deactivation of a lipase was investigated in a stirred vessel using two types of impellers, namely, six-bladed down-ow turbine and six-bladed straight turbine. The impeller speed was varied over the range of 16.67–33:33 rps with corresponding variation of the power consumption per unit volume from 1 to 70 kW= m 3 . Eect of enzyme concentration on the deactivation, under otherwise identical conditions, was also investigated. The enzyme underwent negligible deactivation in the absence of air–water interface. In the presence of the interface and for lower enzyme concentration, it showed rst order deactivation. The rst order deactivation constant was well correlated with the power consumption per unit volume and the gas hold-up. The rate of enzyme deactivation was decreased by the addition of polyethylene glycol into the enzyme solution. Steady-state uorescence studies were also done on the lipase during its deactivation. Based on this investigation, a strategy has been suggested for the improvements in the yield of enzymes in commercial production. ? 2001 Elsevier Science Ltd. All rights reserved. 1. Introduction Lipases, also known as glycerol ester hydrolase (EC 3.1.1.3), belong to the hydrolase enzyme class that catalyze the hydrolysis of triacylglycerols. Li- pases are widely distributed in various animals, plants and microorganisms. They have a vast po- tential for application in a number of industries due to their broad substrate specicity coupled with a high regio-, enantio- and= or fatty acid specicity for each substrate. These enzymes, especially those from microorganisms, have recently received in- creased attention because of their activity even in nearly anhydrous water immiscible organic solvents (Zaks & Klibanov, 1984). They can also be used for transesterication (Santaniello, Ferraboschi, & Grisenti, 1993; Cambou & Klibanov, 1984), ester- ication (Nakano, Kitahata, Tominaga, & Taken- ishi, 1991; Okumura, Iwai, & Tsujisaka, 1979), and resolution of racemic mixtures into optically active ∗ Corresponding author. Tel.: +91-022-414-5616; fax: +91-022-414-5614. E-mail address: sbs@udct.ernet.in (S. B. Sawant). alcohols or acids (Villeneuve & Foglia, 1997). An- other factor in favour of the use of lipases in industries is that they do not require any cofactor for hydroly- sis. The wide application of microbial lipases has at- tracted researchers to investigate the stability of the enzyme in varied environmental conditions like temper- ature, pH, metal ions, surfactants and solvents which may change the enzyme structure by creating an ad- verse environment in which the enzyme is not stable. Recent observations and studies (Lee & Choo, 1989; Stahmann, Boddecker, & Sahm, 1997; Elias & Joshi, 1997) reveal a lot of changes in enzyme structure due to hydrodynamic shear forces. More often, the loss in enzyme activity during production and recovery is at- tributed to some working parameters other than hydro- dynamic shear forces and the problems of low yield of enzymes during production and recovery remains un- solved. Recently, an investigation on fungal lipase has shown interfacial inactivation by stirring in the pres- ence of gas bubbles. It reveals the intensity to which these shear forces and gas–liquid interface can act ad- versely to disrupt the three-dimensional structure of enzymes (Stahmann et al., 1997). A comprehensive 0009-2509/01/$-see front matter ? 2001 Elsevier Science Ltd. All rights reserved. PII:S0009-2509(01)00020-3