The effect of natural antioxidants on haemoglobin-mediated lipid oxidation during enzymatic hydrolysis of cod protein Sigrun M. Halldorsdottir a,b,⇑ , Hordur G. Kristinsson a,c , Holmfridur Sveinsdottir a , Gudjon Thorkelsson a,b , Patricia Y. Hamaguchi a a Matis, Vinlandsleid 12, 113 Reykjavík, Iceland b University of Iceland, Department of Food Science and Nutrition, School of Health Sciences, Saemundargotu 2, 101 Reykjavík, Iceland c University of Florida, Department of Food Science and Human Nutrition, 359 FSHN Building, Newell Drive, Gainesville, FL 32611-0370, USA article info Article history: Received 7 January 2013 Received in revised form 14 March 2013 Accepted 25 March 2013 Available online 16 April 2013 Keywords: Fish protein hydrolysates Enzyme hydrolysis Lipid oxidation Natural antioxidants abstract Heating and changes in pH often practised during fish protein hydrolysis can cause lipid oxidation. The effect of natural antioxidants towards haemoglobin-mediated lipid oxidation during enzymatic hydroly- sis of cod proteins was investigated. Different variants of a washed cod model system, containing differ- ent combinations of haemoglobin and natural antioxidants (L-ascorbic acid and Fuscus vesiculosus extract), were hydrolysed using Protease P ‘‘Amano’’ 6 at pH 8 and 36 °C to achieve 20% degree of hydro- lysis. Lipid hydroperoxides and thiobarbituric acid reactive substances (TBARS) were analysed periodi- cally during the hydrolysis process. The in vitro antioxidant activity of the final products was investigated. Results indicate that oxidation can develop rapidly during hydrolysis and antioxidant strat- egies are preferable to produce good quality products. Oxidation products did not have an impact on the in vitro antioxidant activity of the hydrolysates. The natural antioxidants inhibited oxidation during hydrolysis and contributed to the antioxidant activity of the final product. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Recently, the consumer awareness of natural bioactive ingredi- ents has significantly increased indicating a place for bioactive fish peptides on the market. Studies have shown that fish peptides pos- sess antioxidant activity (Halldorsdottir et al., 2011; Wu, Chen, & Shiau, 2003). Antioxidant compounds can act as health protecting factors and can also be a useful tool for food preservation to retard negative effects of oxidation. However, oxidation can be a problem during the processing of fish protein material when the aim is to yield bioactive peptides with properties such as antioxidant. Cold water fish muscle is rich in polyunsaturated fatty acids and several very potent pro-oxidants such as haemoglobin and iron (Hultin, 1994). These muscle constituents interact before, during and after enzymatic hydrolysis processing and oxidation products may be carried over into the final fish protein product (Kristinsson, 2007). During hydrolysis key pro-oxidants like haem proteins are hydrolyzed, thus releasing haem which can cause extensive oxida- tion. This can have a detrimental impact on the protein hydrolysate products in terms of off-flavors and odours thus surpassing the consumer threshold of acceptance. Moreover, oxidation can have an effect on functionality, e.g. loss of solubility (Ladikos & Lougo- vois, 1990) and possibly on the bioactivity of the protein hydroly- sate products. To overcome this problem, efforts must be made to understand the oxidative mechanisms during and after hydrolysis. The use of natural antioxidants is expected to address the problem of oxidation during hydrolysis by enhancing oxidative stability during the process. Incorporation of synthetic antioxidants has been shown to reduce oxidation during hydrolysis of fish protein (Yarnpakdee, Benjakul, Nalinanon, & Kristinsson, 2012). However, natural antioxidants are more favourably accepted than synthetic antioxidants (Shi, Noguchi, & Niki, 2001) and their use has grown greatly in the past years while use of synthetic antioxidants is declining. Polyphenols from natural sources have been shown to be effective in reducing post-harvest spoilage in fish (Banerjee, 2006). Research on phenolic compounds extracted from Icelandic brown algae, Fucus vesiculosus have shown very promising results in in vitro antioxidant activity studies (Wang et al., 2012). More- over, they have shown a great potential to inhibit Hb-mediated li- pid oxidation in a washed cod model (WCM) system and in fish protein isolate during storage (Wang et al., 2010). Ascorbic acid is also a naturally occurring compound with antioxidant properties that is commonly used as an antioxidant food additive (Frankel, 2007). As the function of antioxidants depends on the environmen- tal conditions as well as the pro-oxidants present it is important to 0308-8146/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodchem.2013.03.101 ⇑ Corresponding author at: Matis, Vinlandsleid 12, 113 Reykjavík, Iceland. Tel.: +354 4225000/+354 8651704; fax: +354 4225001. E-mail addresses: sigrun.m.halldorsdottir@matis.is, sigrunha@hi.is (S.M. Halldorsdottir). Food Chemistry 141 (2013) 914–919 Contents lists available at SciVerse ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem