Optimization of butylgalactoside synthesis by -galactosidase from Aspergillus oryzae Ali Ismail a , Michel Linder b , Mohamed Ghoul a, * a Laboratoire des Sciences du Ge ´nie Chimique, Centre National de la Recherche Scientifique-INPL, Vandoeuvre, France b Laboratoire de Physico-Chimie et Ge ´nie Alimentaire, Ecole Normale Supe ´rieur INPL, Vandoeuvre, France Received 29 July 1998; received in revised form 7 January 1999; accepted 10 February 1999 Abstract Response surface methodology (RSM) was used to optimize the enzymatic synthesis of butylgalactoside from lactose catalyzed by -galac- tosidase from Aspergillus oryzae. The empirical models developed by using RSM were adequate to describe relationships between the operating conditions (temperature, water-to-butanol volume ratio, lactose concentration, enzyme concentration) and the responses (butylgalactoside con- centration, conversion yield). Based on contour plots and canonical analysis, optimal conditions for maximizing butylgalactoside concentration were: temperature (45°C), water-to-butanol volume ratio (44%), lactose concentration (134 g/l), and enzyme concentration (1.5 g/l). Experimental data indicated that up to 24 g/l were produced at the optimum point. Maximum conversion yield of 79.5% was obtained at: temperature (46°C), water-to-butanol volume ratio (18%), lactose concentration (10 g/l), and enzyme concentration (1.5 g/l). The models were verified experimentally. Synthesis at a large scale was successful. © 1999 Elsevier Science Inc. All rights reserved. Keywords: Alkylglycosides; Butylgalactoside; -galactosidase; Doehlert matrix; Optimization; Response surface methodology 1. Introduction For several years, there has been a great interest in the enzymatic preparation of alkylglycosides [1–5]. These types of nonionic surfactants have several interesting properties in detergency, foaming, wetting, emulsification, and antimi- crobial effect [6,7]. Moreover, they can be used as raw materials for sugar fatty acid ester synthesis [8]. Produced from renewable agricultural resources, they are nontoxic, non-skin-irritating, and very biodegradable [7,9,10]. For these reasons, they have great potential application in many diversified areas such as the pharmaceutical, chemical, cos- metic, food, and detergent industries. Research efforts are mainly limited to alkylglycosides with high alkyl groups (C  6) having foaming properties. No in-depth attention is given to the synthesis of alkylgly- cosides produced from short alcohol (e.g. butanol). Never- theless, these molecules could be successfully used as flu- idifiers or emulsifiers or as substrates for sugar fatty acid ester synthesis [11–13]. A recent paper reported on the result of the synthesis of several butylglycosides by glycosidases [14]. The highest concentration of butylglycosides was obtained when lac- tose was used as a glycosyl donor. However, only limited data about the use of lactose for the synthesis of alkyl- glycosides are available [15,16]. Moreover, neither spe- cific information on the interaction effects of reaction parameters nor any detailed optimal conditions have been given. Response surface methodology (RSM) can evaluate the effects of multiple parameters, alone or in combination, on response variables [17]. It has been successfully ap- plied for optimizing conditions in food, chemical, and biological processes [18 –20] but has been rarely reported on for optimizing the enzymatic synthesis of alkylglyco- sides [21]. In this work, we perform the enzymatic synthesis of butyl- galactoside by -galactosidase from Aspergillus oryzae by using lactose as the glycosyl donor and butanol as the alcohol. The aim of this study was to investigate and optimize the process parameters by using RSM according to the Doehlert uniform shell design for four factors: temperature, water-to-butanol volume ratio, lactose, and enzyme concentrations. * Corresponding author. Tel.: +33-83-595-892; fax: +33-83-595-796. E-mail address: mohamed.ghoul@ensaia.inpl-nancy.fr (M. Ghoul) Enzyme and Microbial Technology 25 (1999) 208 –213 0141-0229/99/$ – see front matter © 1999 Elsevier Science Inc. All rights reserved. PII: S0141-0229(99)00028-9