Phenolic Compounds and Plant Phenolic Extracts as Natural Antioxidants in Prevention of Lipid Oxidation in Seafood: A Detailed Review Sajid Maqsood, Soottawat Benjakul, Aisha Abushelaibi, and Asifa Alam Abstract: Lipid oxidation is the principal cause of quality loss in seafood, which is known to contain high amounts of polyunsaturated fatty acids. Such quality deterioration, associated with the development of off-flavor as well as lowering of nutritive value, can be retarded by incorporation of additives having antioxidative properties. The use of synthetic antioxidants has long been practiced in retarding lipid oxidation. However, due to the potential health concerns of synthetic antioxidants, polyphenolic compounds, which are found in different plants and their manufactured by-products, have been used as an alternative natural antioxidants to retard lipid oxidation in different seafood systems. Both pure phenolic compounds and crude plant phenolic extracts have been successfully used in delaying oxidation in fish muscle, fish oil, and fish oil-in-water emulsions. This article reviews in detail the phenolic antioxidants and their natural sources as well as focuses on the role of pure phenolic compounds and crude plant phenolic extracts on the prevention of lipid oxidation in different seafood systems. Keywords: lipid oxidation, fish mince, fish oil, oil-in-water emulsion, phenolic compounds, plant extracts Introduction Seafood contains high amounts of nutritionally important omega-3 polyunsaturated fatty acids (PUFAs) such as eicosapen- taenoic acid (EPA, C20:5 n-3) and docosahexaenoic acid (DHA, C22:6 n-3). Intake of these PUFAs is believed to have benefi- cial effects on human health (Lee and Lip 2003). However, the presence of high amounts of PUFAs in seafood products makes them more prone to lipid oxidation. This is related to the devel- opment of an offensive odor and loss in quality (Frankel 1998). Moreover, the presence of heme pigments (myoglobin [Mb] and hemoglobin [Hb]) and trace amounts of metallic ions like iron and copper makes the fish more susceptible to lipid oxidation (Hsieh and Kinsella 1989). Hb acts as an important catalyst for lipid oxidation in fish. Hb may be a source of activated oxygen because of Hb autoxidation. In addition, protein releases heme iron which promotes the lipid oxidation (Richards and Hultin 2002). Lipid oxidation can be enhanced by reduced pH and might be enhanced because of intensified autoxidation of Hb at decreased pH (Tsuruga and others 1998). Oxidation can also cause other detrimental effects such as vitamin devastation, discoloration, and loss of essential fatty acids, leading to organoleptic breakdown and MS 20140544 Submitted 4/2/2014, Accepted 7/23/2014. Authors Maqsood and Abushelaibi are with Dept. of Food Science, College of Food and Agriculture, United Arab Emirates Univ., Al-Ain, 15551, United Arab Emirates. Author Benjakul is with Dept. of Food Technology, Faculty of Agro-Industry, Prince of Songkla Univ., Hat Yai, Songkhla, 90112, Thailand. Author Alam is with Sustainable Development Study Center (SDSC), Government College Univ., Lahore, 54000, Pakistan. Direct inquiries to author Sajid (E-mail: sajid.m@uaeu.ac.ae). a decline in nutritive value (Sherwin 1978). To decelerate such a quality loss due to lipid oxidation, synthetic antioxidants have been widely utilized in the past to retard lipid oxidation in seafood (Boyd and others 1993). Nevertheless, the uses of synthetic an- tioxidants have raised concerns about possible toxicity and food safety (Maqsood and others 2013). Therefore, the practice of using natural antioxidants is being increasingly adopted as an effective methodology for the control of lipid oxidation and restraining its harmful outcomes. Focusing on the increasing demand for food products without synthetic additives, much effort is being diverted toward the discovery of antioxidants from natural sources such as phenolic compounds. Many phenolic compounds and plant phe- nolic extracts have successfully demonstrated the retarding effect on lipid oxidation in different seafoods. The antioxidant effects of various plant extracts, as well as individual phenolic compounds, have been evaluated and tested in different seafood model systems. Plant polyphenolics are the compounds holding one or more phenolic rings and are derived from the secondary metabolism of plants (Parr and Bolwell 2000). Phenolic compounds are present in several foods and drinks of plant origin, for example, veg- etables, fruits, coffee (Clifford 1999), tea (Lakenbrink and others 2000), beer, wine, and chocolate (Hollman and Katan 1999) (Ta- ble 1). In addition to being present in many foods naturally, phe- nolic compounds can be extracted from their respective sources and thereafter can be added to some foods for their coloring properties and for their antioxidant effects (Maqsood and others 2013). Several studies have illustrated the effectiveness of using pure phenolic compounds for preventing lipid oxidation in differ- ent seafood systems. Moreover, plant extracts rich in polyphenolic C  2014 Institute of Food Technologists ® doi: 10.1111/1541-4337.12106 Vol. 13, 2014  Comprehensive Reviews in Food Science and Food Safety 1125