Effect of pretreatment on lipid oxidation and fishy odour development in protein hydrolysates from the muscle of Indian mackerel Suthasinee Yarnpakdee a , Soottawat Benjakul a,⇑ , Hordur G. Kristinsson b,c , Sajid Maqsood d a Department of Food Technology, Faculty of Agro-Industry, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand b Matis – Icelandic Food and Biotechnology R & D, Vinlandsleid 12, Reykjavik IS-113, Iceland c Department of Food Science and Human Nutrition, University of Florida, Gainesville, FL 32611, USA d Department of Food Science, Faculty of Food and Agriculture, UAE University, P.O. Box 17551, Al-Ain, United Arab Emirates article info Article history: Received 29 February 2012 Received in revised form 1 June 2012 Accepted 3 July 2012 Available online 15 July 2012 Keywords: Indian mackerel Lipid oxidation Fishy odour Protein hydrolysate Fortification abstract Impact of different pretreatments on chemical compositions of Indian mackerel mince was studied. Mince prepared using washing/membrane removal/alkaline solubilisation process (W–MR–Al) contained the lowest remaining myoglobin and haem iron content and also showed the lowest total lipid and phospholipid contents. When mince and W–MR–Al were hydrolysed using Alcalase for up to 120 min, a higher degree of hydrolysis (DH) was found in W–MR–Al after 30 min of hydrolysis. Furthermore, hydrolysate from W–MR–Al had lower peroxide value (PV), thiobarbituric acid reactive substances (TBARS) and non-haem iron content throughout hydrolysis period (P < 0.05). When hydrolysate powder produced from mince and W–MR–Al (0–0.3% w/v) were fortified in milk, the former resulted in the lower likeness score (P < 0.05) at all levels used. The addition of the latter, for up to 0.2%, had no effect on like- ness of all attributes, compared with milk without fortification (P > 0.05). Therefore, the appropriate pre- treatment of mince yielded hydrolysate with lower fishy odour. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Proteins from seafood resources are well balanced with regard to their amino acid composition. Enzymatic hydrolysis is a process that has been developed some time ago to convert proteins into more marketable and acceptable forms. Numerous fish protein hydrolysates have been reported to possess antioxidative activities and various other bioactive properties such as those from brown- stripe red snapper (Khantaphant, Benjakul, & Ghomi, 2011), ornate threadfin bream (Nalinanon, Benjakul, Kishimura, & Shahidi, 2011), round scad (Thiansilakul, Benjakul, & Shahidi, 2007) and mackerel (Wu, Chen, & Shiau, 2003). Due to their functional properties, fish protein hydrolysates have been used in foods. With their excellent interfacial properties, they may have the potential use as emulsify- ing ingredients in a variety of products, e.g. dressing, margarine and meat batter (Kristinsson, 2007). In addition, Khan et al. (2003) used fish scrap protein hydrolysate as the cryoprotectant to prevent protein denaturation of lizardfish surimi during frozen storage at 25 °C. However, a major problem connected to hydro- lysate preparation from fish flesh is the presence of pro-oxidants such as haem proteins and unstable lipid substrates (Raghavan, Kristinsson, & Leeuwenburgh, 2008b). Lipid oxidation generally contributes to the development of undesirable odour, especially fishy odour (Maqsood & Benjakul, 2011). This offensive odour lim- its the use of fish protein hydrolysates, particularly in foods or drinks which have a light odour or smell. Fatty fish have been known to contain high levels of myoglobin, other haem proteins, low molecular weight (LMW) transition me- tal complexs and lipoxygenases in their dark muscle (Chaijan, Ben- jakul, Visessanguan, & Faustman, 2005; Thiansilakul, Benjakul, & Richards, 2011). Furthermore, phospholipid membranes are be- lieved to be the key substrate for lipid oxidation due to their highly unsaturated fatty acid composition (Liang & Hultin, 2005). Con- tamination of pro-oxidants and oxidised lipids in mince can have a great impact on functionality and antioxidative properties of pro- tein hydrolysates (Raghavan & Kristinsson, 2008a). Haem proteins in the raw material can also become oxidised during the hydrolysis process, thereby promoting lipid oxidation and development of unpleasant odours/flavours (Raghavan et al., 2008a). Therefore, the removal of pro-oxidants and lipids could be a promising means to alleviate such problems occurring in hydrolysates from fatty fish flesh. Khantaphant et al. (2011) reported that pretreatment of fish mince also affected antioxidative activity of the resulting fish pro- tein hydrolysate. One recent successful method to recover fish proteins is the pH shift method, where the fish proteins are separated and recovered from other undesirable components (i.e. lipids, connective tissue, skin and bones) by their pH-dependent solubility properties (Kris- tinsson, Theodoure, Demir, & Ingadottir, 2005). In brief, fish muscle 0308-8146/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodchem.2012.07.037 ⇑ Corresponding author. Tel.: +66 66 7428 6334; fax: +66 66 7455 8866. E-mail address: soottawat.b@psu.ac.th (S. Benjakul). Food Chemistry 135 (2012) 2474–2482 Contents lists available at SciVerse ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem