Optimization of enzymatic hydrolysis of fish soluble concentrate by commercial proteases Suthasinee Nilsang, Sittiwat Lertsiri, Manop Suphantharika, Apinya Assavanig * Department of Biotechnology, Faculty of Science, Mahidol University, Rama VI Road, Bangkok 10400, Thailand Received 11 May 2004; accepted 7 October 2004 Available online 30 November 2004 Abstract Fish protein hydrolysate (FPH) was produced from fish soluble concentrate (FSC), a by-product from canned fish industry, by using Flavourzyme TM and Kojizyme TM . Hydrolysis conditions were optimized by using a response surface methodology (RSM). The model equations were proposed with regard to the effects of temperature (T), time (t), and enzyme concentration (E) on the degree of hydrolysis (DH). The optimum values for Flavourzyme TM concentration, substrate concentration, temperature, and hydrolysis time were found to be 50 LAPU/g protein, 20% (w/w), 45 °C, and 6 h, respectively (LAPU; Leucine Aminopeptidase Unit). While those values for Kojizyme TM were 40 LAPU/g protein, 20% (w/w), 50 °C, and 6 h, respectively. Kojizyme TM enhanced the formation of some bitter-taste amino acids such as tryptophan during hydrolysis process whereas Flavourzyme TM did not. The spray-dried FPH pro- duced with Flavourzyme TM contained high protein content (66%). The bitterness of FPH was less than that of 1 ppm caffeine solution. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Fish protein hydrolysate; Fish soluble concentrate; Bitterness 1. Introduction Fish soluble is a by-product from canned tuna pro- cessing. It is made from tuna pressed liquids which is processed into a concentrated form of fish soluble con- centrate (FSC). This FSC contains high protein and amino acids contents, which are useful for aquaculture uses and animal feed. In order to increase the utilization of FSC, hydrolysis of protein with proteolytic enzymes can provide FSC into more marketable and value-added products of fish protein hydrolysate (FPH; Jeon, Byun, & Kim, 2000; Kristinsson & Rasco, 2000a; Liaset, Lied, & Espe, 2000; Liceaga-Gesualdo & Li-Chan, 1999; Shahidi, Han, & Synowiecki, 1995). Benjakul and Morrissey (1997) studied the produc- tion and composition of protein hydrolysate from Paci- fic whiting solid waste (PWSW) by using commercial enzymes Alcalase and Neutrase. The optimum condi- tions for PWSW hydrolysis were 20 AU Alcalase/kg, pH 9.5, 60 °C, and 1 h reaction time. Their hydrolysate had a high protein content and amino acids composition comparable to fish muscle. Gue ´rard, Dufosse ´, De La Broise, and Binet (2001) used Alcalase to hydrolyse pro- teins from tuna waste. Their studies revealed that the tuna protein hydrolysate performed effectively as a nitrogenous source in microbial growth media. The production of seafood flavors from under uti- lized fish species, using protein hydrolysis, is very chal- lenging in order to ensure a high organoleptic quality (Shahidi, 1998). An enzymatic process using specific protease has been developed to produce flavorants from seafood by-products (Baek & Cadwallader, 1995). How- ever, the hydrolysis of protein is often accompanied with 0260-8774/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2004.10.011 * Corresponding author. Tel.: +66 2 201 5300; fax: +66 2 354 7160. E-mail address: scaav@mahidol.ac.th (A. Assavanig). www.elsevier.com/locate/jfoodeng Journal of Food Engineering 70 (2005) 571–578