Pilot plant recovery of catheptic proteases from surimi wash water Christina A. Mireles DeWitt * , Michael T. Morrissey Oregon State University Seafood Laboratory, 2001 Marine Dr., Astoria, OR 97103-3427, USA Received 30 October 2000; received in revised form 20 September 2001; accepted 20 September 2001 Abstract Recovery of bioactive compounds, such as proteolytic enzymes, from waste streams is a means to both recuperate value and reduce environmental pollution. Previously optimized lab-scale parameters for the recovery of a stable crude protease fraction from Pacific whiting (Merluccius productus) surimi wash water were tested using pilot plant equipment. Pretreatment of surimi wash water with 60 °C heat, acidification to pH 6, and centrifugation doubled ultrafiltration membrane flux and significantly improved protease purity by reducing a majority of the 35–205 kDa proteins. Concentrated crude protease obtained from wash water contained predominantly cathepsin L activity. Enzyme purity was increased about 100-fold, and yield was approximately 80%. Stability (frozen and freeze-dried protease) was maintained for 9 weeks at )80 °C. Freeze-dried preparations were also stable for 9 weeks at 4 and )15 °C. Successful application of pilot plant conditions allows for sufficient production of protease for further investigations into their applicability. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Enzyme recovery; Enzyme stability; Ultrafiltration; Seafood waste; Protease; Surimi wash water 1. Introduction The production of surimi, a product obtained from minced fish flesh that is washed with water, from Pacific whiting (Merluccius productus) results in utilization of approximately 26% of the original raw material (Toyoda et al., 1992). This means that about 80% of the product is considered waste or potential by-product material. In Oregon, surimi-processing facilities ship their solid waste for conversion to fish meal, pet foods, hydroly- sates, and fertilizer. Soluble wastes from surimi wash water are returned to the environment either by direct discharge into the Columbia River or shipped and sprayed over farmers’ fields. Increasing concerns about the negative impact of direct wastewater discharge has led to research in protein recovery from surimi wash water. As opposed to the traditional conversion of seafood waste into fertilizer or animal feeds/diets, more novel approaches to waste management and by-product uti- lization involve the identification and recovery of useful biochemical compounds. Perhaps the best example in the food industry concerning recovery and utilization of by-products from waste streams involves whey, a func- tional protein and by-product of cheese or casein pro- duction. Liquid whey contains 0.8–0.9% protein (Charles and Radjai, 1977; Modler et al., 1980; Shay and Wegner, 1986). The protein composition in surimi wash water is between 0.85% and 1.5% protein (Huang and Morrissey, 1998). As a result, liquid whey makes a sat- isfactory model when considering the effect of various treatments on protein reduction and/or concentration in surimi wash water. Whey protein is typically modified or concentrated by one of the five processes (Grindstaff, 1974): gel filtration, electrodialysis, polyphosphate pre- cipitation, heat coagulation, and ultrafiltration (Stribley, 1963; Hidalgo et al., 1973; Zall, 1992; Morr, 1976). Ul- trafiltration is the system of choice when it comes to producing a concentrate with good functional proper- ties. Ultrafiltration works by passing low molecular weight products (lactose, salts, water) while retaining high molecular weight products such as protein (Horton et al., 1972). An early problem with ultrafiltration in- volved severe fouling of membranes. However, devel- opment of chemical and heat stable polysulphone membranes has increased the feasibility of this tech- nology (Morr, 1976). A system described by Crocco (1975) was capable of processing 40,000 lbs of whey per hour into whey protein concentrate. Although the vast majority of protein recovery liter- ature originates from whey reclamation efforts, several Bioresource Technology 82 (2002) 295–301 * Corresponding author. Tel.: +1-405-744-6616; fax: +1-405-744- 7390. Present address: Oklahoma State University, 104 Animal Science, Stillwater, OK 74078-6051, USA. E-mail address: dewittc@okstate.edu (C.A. Mireles DeWitt). 0960-8524/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S0960-8524(01)00178-X