C-13 NUCLEAR-MAGNETIC-RESONANCE MONITORING OF FREE FATTY-ACID RELEASEAFTER FISH THERMAL-PROCESSING

C-13 Nuclear magnetic resonance spectroscopy was applied to the study of lipid hydrolysis occurring during industrial canning of tuna (Thunn us alalunga). An increase in the free fatty acid (FFA) level was obser ved after cooking and sterilization, and a different FFA pattern was f ound when storage of the frozen raw material and thermal steps (cookin g and can sterilization) were compared. Lipolysis in raw muscle occurs preferentially in the sn-1 and sn-3 acyl positions of triacylglycerol s, with a consequent cleavage of saturated and monounsaturated fatty a cids. After thermal processing, an increase of docosahexaenoic acid (D HA) was found in the FFA fraction, as well as a relative decrease of t he peak intensity of DHA in the sn-2 position of triacylglycerols. Thi s finding indicates a different mechanism of FFA release during the fr ozen storage and thermal processing of raw fish.