Effects of different cooking methods on fatty acid profiles in four freshwater fishes from the Laurentian Great Lakes region
Introduction
Freshwater and marine fish are often considered to be a healthy component of the human diet, due to relatively high ratios of polyunsaturated to saturated fatty acids (PUFA:SAFA) compared to other animal food sources (Health Canada, 2011). In particular, fish contain high concentrations of n-3 long-chain PUFA (LC-PUFA), such as eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3). These fatty acids have been identified as essential elements of the human diet (Arts, Ackman, & Holub, 2001) because they cannot be synthesized in amounts adequate for optimal health (Gerster, 1998, Pawlosky et al., 2001). These essential n-3 fatty acids have been, and continue to be, investigated extensively in health studies, where the benefits of dietary consumption of n-3 LC-PUFA have been found in relation to cardiovascular disease, diabetes, inflammatory diseases, and neurological/neuropsychiatric disorders (Yashodhara et al., 2009).
Nutritional guidelines from various health agencies worldwide now provide recommendations for the dietary intake of EPA + DHA and/or n-3 fatty acids (e.g., European Food Safety Authority, 2012, Koletzko et al., 2008, Kris-Etherton et al., 2002, Simopoulos, 1989, U.K Scientific Advisory Committee on Nutrition, 2004). In addition, diets with n-3:n-6 ratios close to 1 (Simopoulos, 2002, Simopoulos, 2008) and PUFA:SAFA ratios >0.4 (Food and Agriculture Organization of the United Nations & World Health Organization, 1994) are also recommended for optimal health. Health Canada (2011) recommends the consumption of at least 150 g of cooked fish each week as part of a healthy diet.
In the Great Lakes region, ∼4.2 million adults consume at least one Great Lakes sport fish meal over the course of a year (Imm, Knobeloch, & Anderson, 2005). Recently, Neff et al. (submitted for publication) analysed fatty acid content in several important sport fish species from Lake Erie and found that eight of the analysed 15 species had an EPA + DHA content which met the recommended daily intake of 250 mg (European Food Safety Authority, 2012, Koletzko et al., 2008). In addition, all species analysed had optimal n-3:n-6 and PUFA:SAFA ratios (Neff et al., submitted for publication). These results further corroborate the conclusion that freshwater fish are a healthy dietary choice for human consumers. However, previous studies have also highlighted that fish fatty acid content can vary with a variety of factors, such as species, season, fish size, and geographical location (e.g., Snyder and Hennessey, 2003, Wang et al., 1990). In addition, the fatty acid content of raw, uncooked fish flesh may not be an accurate reflection of what is consumed by humans post-cooking.
Results from studies examining the effects of cooking on the fatty acid content of fish are variable, and overall suggest that both cooking method(s) and species influence whether an effect of cooking will be observed. Previous studies, covering a variety of fish species, have reported significantly lower EPA and DHA content after frying (e.g., Bakar et al., 2008, Candela et al., 1997, Candela et al., 1998, Gladyshev et al., 2006, Stephen et al., 2010, Türkkan et al., 2008). Additionally, some studies reported changes to the PUFA:SAFA and/or n-3:n-6 ratios after cooking (Candela et al., 1997, Candela et al., 1998). In contrast, a number of studies have reported no effects of various cooking methods on fish fatty acid composition (e.g., De Castro et al., 2007, Fajmonová et al., 2003) or attributed observed treatment effects to the incorporation of cooking oil (e.g., Larsen et al., 2010, Weber et al., 2008). Notably, most studies to date have examined marine species, often from fish farms, and no studies, to our knowledge, have examined the effects of different cooking methods on freshwater fish species from the Laurentian Great Lakes region.
In this study, four commonly consumed sport fish were collected from southern Ontario Great Lakes tributaries for a comparative analysis of fatty acid content after the application of three different cooking treatments. In particular, we highlight changes in the n-3 LC-PUFA, EPA and DHA, as well as in n-3:n-6 and PUFA:SAFA ratios.
Section snippets
Sample collection and preparation
A total of 21 individual fish were collected in 2010 and 2011 from southern Ontario river systems as a part of the Sport Fish Contaminant Monitoring Program of the Ontario Ministry of the Environment (Ontario Ministry of the Environment, 2013): Chinook salmon (Oncorhynchus tshawytscha, n = 5) from the Credit River, common carp (Cyprinus carpio carpio, n = 5) and white sucker (Catostomus commersonii, n = 2) from the Thames River, lake trout (Salvelinus namaycush, n = 4) from the Niagara River, and
Fatty acid content in raw fish
Fatty acid content (mg/100 g WW) in raw fillets varied by species. On a dry weight basis, lake trout had the highest content of EPA, DHA, n-3, n-6, SAFA, MUFA and PUFA, while walleye had the lowest EPA, n-6, SAFA, MUFA and PUFA content, and common carp the lowest DHA and n-3 content (Table S2). On a proportional basis, raw common carp fillets had the lowest beneficial fatty acids (e.g., EPA and DHA, as well as n-3 and PUFA), and the highest n-6, SAFA and MUFA (Table S3). Walleye had the highest
Discussion
Frying, baking or broiling does not appreciably affect levels of EPA and DHA, or total n-3 fatty acids, in Chinook salmon, common carp, lake trout or walleye (except for DHA in walleye). From a human health perspective, this is important as cooking fish does not reduce the amount of beneficial fatty acids consumed compared to what is contained in a raw fillet. However, there were differences in n-6, SAFA, MUFA and PUFA content, which could be important from a human health standpoint,
Acknowledgement
Thon Lin Ler of University of Toronto Mississauga assisted in data screening and preliminary data analysis for this work.
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Present address: Department of Chemistry and Biology, Ryerson University, 350 Victoria Street, Toronto, ON M5B 2K3, Canada.