Enzymatic Cleaning of Inorganic Ultrafiltration Membranes Fouled by Whey Proteins MARIA A. ARGU ¨ ELLO,SILVIA A Ä LVAREZ,FRANCISCO A. RIERA,* AND RICARDO A Ä LVAREZ Department of Chemical Engineering and Environmental Technology, University of Oviedo, C/Julia ´n Claverı ´a 8, 33006 Oviedo, Spain The aim of this work was to study the cleaning of inorganic membranes fouled with whey protein solutions using the enzymatic formulation Alcalase (Novo Nordisk A/S). Hydraulic and chemical methods were considered to characterize the cleanliness of the membranes. Cleaning efficiency was observed to be a function of the operating conditions. The operating conditions tested were the following: recycling versus non-recycling of permeate, pH of the cleaning solution, addition of alkali to regulate the pH, enzymatic agent concentration, and cleaning time. The best conditions to perform the cleaning were related to the best conditions to hydrolyze whey proteins in a discontinuous reactor using the same enzyme preparations. Very high cleaning efficiencies (>90%) were achieved in short operating times (20 min). However, residual matter was observed on the membrane surface. KEYWORDS: Inorganic membranes; enzymatic cleaning; whey protein solutions; cleaning efficiency INTRODUCTION The application of ultrafiltration (UF) and microfiltration (MF) in the food industry and particularly in the dairy industry has attracted increasing interest in recent years. These techniques are widely used for the concentration and separation of proteins from whey (1, 2). However, the main problem of membrane techniques is the reduction of permeate flux with time due to membrane fouling, which also produces changes in the selectiv- ity and decreases the overall process productivity. To maintain the membrane’s performance, it is necessary to periodically stop the process to clean the membrane. Cleaning consumes time, energy, chemicals, and water, thus increasing production costs. The optimization of cleaning parameters can save money and increase the membrane life. The cleaning step has to be effective, easy, and fast, with no risks for the membrane and the rest of the installation (3). Untill recently, very little attention had been paid to mem- brane cleaning. Also, cleaning sequences were almost identical for different types of membranes and feed solutions. In recent a few studies about the cleaning of membranes were published (4-6). Most of the protocols consisted of series of acid-alka- line cleaning cycles, although a few authors considered the possibility of using enzymatic formulations to clean organic membranes (7, 8). The utilization of enzymatic detergents presents several advantages over conventional ones such as the easier neutralization of cleaning effluents and their biodegrad- ability (9). Flux reduction during filtration is mainly due to two types of phenomena: concentration polarization and fouling. Con- centration polarization is considered to be a reversible phenom- enon, whereas fouling effects are characterized by an “irrevers- ible” decline in flux. Membrane fouling is due to the deposition and accumulation of particles on the membrane surface and/or the crystallization and precipitation of small molecules on the surface and within the membrane pores. The nature and extent of fouling depend on the characteristics of the solute and solute- membrane interactions (2). When dairy solutions are filtered, one of the main contributions to fouling is the adsorption of proteins on the membrane surface and into the membrane pores (10, 11). Therefore, a cleaning formulation able to degrade the proteins that constitute the deposits could be used for membrane cleaning after whey ultrafiltration. In a previous work by the authors (12) the protein hydrolysis ability of different commercial detergents was studied using a discontinuous reactor. Two enzymatic (P3-Ultrasil 62 and P3-Ultrasil 53) and two nonenzymatic (P3-Ultrasil 13 and P3-Ultrasil 10A) formulations supplied by Henkel Ibe ´rica, S.A. (Barcelona, Spain), were tested. It was concluded that only the enzymatic detergents were able to produce a significant hy- drolysis of whey proteins. The best results were achieved with P3-Ultrasil 62 (Henkel Ibe ´rica) at temperatures between 48 and 52 °C. Higher temperatures resulted in strong enzyme dena- turation, thus causing a dramatic decrease of the enzymatic activity. The maximum hydrolysis degree (∼20%) was reached in 20 min. pH was observed to decrease during the process due to the proteins hydrolysis (13). The optimum initial pH was within the range of 10.3-10.8, which led to an average pH of 9.5-10.0. In this work the utilization of the enzymatic formulation Alcalase to clean inorganic membranes used in the fractionation * Corresponding author (telephone + 34 985 103436; fax + 34 985 103434; e-mail FAR@sauron.quimica.uniovi.es). J. Agric. Food Chem. 2002, 50, 1951-1958 1951 10.1021/jf0107510 CCC: $22.00 © 2002 American Chemical Society Published on Web 02/26/2002