QUANTITATIVE HIGH-RESOLUTION C-13 NMR ANALYSIS OF LIPIDS EXTRACTED FROM THE WHITE MUSCLE OF ATLANTIC TUNA (THUNNUS-ALALUNGA)

Lipids extracted from albacore tuna (Thunnus alalunga) were studied us ing high-resolution C-13 nuclear magnetic resonance (NMR) spectroscopy . Simultaneous quantitative determination of free fatty acids, lipid c lasses, and fatty acids alpha-beta positional distribution in triacylg lycerols was obtained. Glyceride and phospholipid composition was stud ied using glyceryl resonances. Lipids extracted from fresh white muscl es of Atlantic tuna had a different triacylglycerol and phospholipid c ontent, related to fish weight. Free fatty acid carbonyl resonances we re detected at the lower, field of the C-13 NMR carbonyl region and us ed for its quantitative determination. NMR data agreed with those obta ined using UV spectrophotometry, showing that NMR is a suitable method to follow lipolytic alterations. The careful study of glyceryl and ca rbonyl resonances also leads to the direct determination of fatty acid alpha-beta distribution in triacylglycerols. The quantitative analysi s of fatty acid composition and distribution was then achieved, and re sults obtained using high-resolution NMR were in good agreement with t hose obtained by gas chromatography. Polyunsaturated fatty acids showe d a preferential location in the beta-acyl position, whereas monounsat urated fatty acids were found preferentially esterified in the alpha-p osition. The method may be used to monitor the composition and changes in fish lipids and oils during processing or storage.