Identification of furan fatty acids in the lipids of common carp (Cyprinus carpio L.)

Highlights

• Lipid fractions and fatty acid composition of common carp tissues were studied.

• Triacylglycerols and monounsaturated fatty acids predominated in muscle.

• Polar lipids and polyunsaturated fatty acids predominated in male and female gonads.

• Eight furan fatty acids were identified in triacylglycerols of male gonad tissue.

• A less common furan fatty acid with even-numbered alkyl moiety was present.

Abstract

Fatty acid (FA) composition was analyzed in muscle and gonad tissues of marketed common carp (Cyprinus carpio). The extracted lipids were separated into four fractions: polar lipids (PL), diacylglycerols, free fatty acids and triacylglycerols (TAG) using thin layer chromatography. FA content within the lipid fractions was determined by gas chromatography with flame ionization detector (GC/FID). The muscle lipids consisted primarily of TAG (96.9% of total FA), while PL were the major component of both male (67.6%) and female gonad (58.6%) lipids. Polyunsaturated fatty acids predominated in PL of all tissues (52.2–55.8% of total FA); monounsaturated fatty acids were the most abundant FA group in TAG of muscle (51.8%) and female gonads (47.8%) whereas high proportion of furan fatty acids (F-acids) (38.2%) was detected in TAG of male gonads. Eight F-acids were identified by gas chromatography–mass spectrometry (GC/MS) in male gonad samples, including less common 12,15-epoxy-13,14-dimethylnonadeca-12,14-dienoic acid with even-numbered alkyl moiety.

Introduction

Furan fatty acids (F-acids) are widespread naturally occurring heterocyclic compounds. They are characterized by a furan ring, which is substituted with an unbranched fatty acid chain (typically with 7, 9, 11 or 13 carbons) in the α-position whereas the α′-position usually carries a propyl or pentyl moiety (Fig. 1). The β-/β′-positions of the furan ring are either both occupied by methyl groups or methyl is found only in the β-position adjacent to the fatty acid chain.

F-acids are generated in plants, algae (Batna, Scheinkonig, & Spiteller, 1993) and marine bacteria (Shirasaka, Nishi, & Shimizu, 1997), while other organisms accumulate these specific fatty acids in tissues after a nutritional intake (Spiteller, 2007). F-acids have been reported as minor constituents in a variety of living organisms (Spiteller, 2005), including aquatic organisms. A number of food samples and products of both plant and animal origin have also been examined for the presence of F-acids (Boselli et al., 2000, Vetter et al., 2012). Compared with other foods, fish are a particularly rich source of F-acids (Vetter et al., 2012).

Positive effect of the consumption of fish and fish oils on human health is well known. Numerous studies confirmed the reduction of the incidence of many diseases including cardiovascular diseases, cancer, inflammatory and autoimmune diseases as well as psychiatric and mental illnesses (Kris-Etherton et al., 2002, Saravanan et al., 2010, Simopoulos, 2002). The health benefits are ascribed to the presence of polyunsaturated fatty acids (PUFA) of the n-3 family, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Nevertheless, several studies have recognized a possible active role of F-acids (Okada et al., 1996, Pacetti et al., 2010, Spiteller, 2005, Spiteller, 2007, Teixeira et al., 2013, Wakimoto et al., 2011). It has been proposed (Okada et al., 1996) that F-acids with the electron-rich furan ring may be a part of the antioxidative protection mechanisms of highly unsaturated compounds, such as PUFA. F-acids may inhibit the progression of non-enzymatic lipid peroxidation reactions (Spiteller, 2007) that seem to be responsible for aging and age dependent diseases. More recently, Teixeira et al. (2013) showed that F-acids efficiently rescue the brain cells death which can be induced by the oxidative stress. Wakimoto et al. (2011) reported in vivo activity of F-acids, confirming that these minor components in the lipid extract of the New Zealand green-lipped mussel have exhibited more potent anti-inflammatory activity than EPA. Pacetti et al. (2010) demonstrated a positive correlation between total F-acids and EPA contents in the fillet of six fish species from the Adriatic Sea.

Freshwater fish can also serve as an important source of nutritionally valuable fatty acids (Ackman, 2002) but still only limited information on F-acids content in their tissues has been available. Common carp, Cyprinus carpio, has been one of the widely cultured freshwater species due to its fast growth rate and easy cultivation (Guler, Kiztanir, Aktumsek, Citil, & Ozparlak, 2008). Nevertheless, existing information (Glass et al., 1977, Gunstone et al., 1978, Ishii et al., 1988a) on F-acids level in this species has been fractional.

The aim of our study was to examine the fatty acid composition of different edible parts of common carp (muscle, male and female gonad tissues) with special attention to F-acids and their distribution within the lipid fractions.