0361-3hSXiXS $3.00 + 0.w Pergamon Press Ltd. ENGINEERING ASPECTS OF FLUIDIZED BED REACTOR OPERATION APPLIED TO LACTASE TREATMENT OF WHOLE WHEY C. Metzdorf, P.-F. Fauquex, E. Flaschel, A. Renken Institute of Chemical Engineering Swiss Federal Institute of Technology, CH-1015 Lausanne ABSTRACT An interesting possibility for the use of lactoserum in human nutrition is the hydrolysis of lac- tose to glucose and galactose, sugars which exhibit a better digestibility, a higher solubility, and which have a greater sweetening power than lactose. The hydrolysis is catalyzed by an enzyme, the p-galactosidase which, due to its high price, must be used continuously, preferentially in immobilized form. The enzyme used for these studies has been immobilized on silica gel precoated with chitosan. When whole whey or partially deproteinized whey is treated, a fluidized bed reactor seems to be the most appropriate to circumvent problems with protein adsorption and reactor plugging. However the fluidization of fine particles with a small density difference between the solid and the liquid may give rise to stability problems. In order to prevent unstable operation of the fluidized bed, the reactor has been equipped with special internals. They impose a radial distri- bution of the liquid and the solid phase and increase the linear velocity required to achieve a given expansion by a factor of five. Besides the resulting high solids content, the back-mixing of the liquid decreasessignificantly when static mixer-packings are used. KEYWORDS Liquid/solid fluidized beds; static mixers; expansion; backmixing; scale-up; lactose; lactase immobilization. INTRODUCTION Whey represents the bulky by-product of the cheese industry. Although it is of high nutritional value, whey has not found much application in food industry, a market with high potential demand. An extended use for nutritional purposes is prevented due to the unfavourable properties of the main whey constituant, the lactose. One possibility to circumvent this problem is given by the hydrolysis of lactose to glucose and galactose, sugars which exhibit a better digestibility, a higher solubility and which have a greater sweetening power than lactose. The lactose hydrolysis is catalysed by enzymes known as lactases (p-galactosidases). Since the productivity/price ratio for lactases is still rather low, they have to be recovered. In consequence, it is generally aimed at using the enzyme in continuous processes in immobilized form.