FTIR spectral changes of lipids extracted from hake (Merluccius merluccius, L.) muscle stored at various freezing temperatures

Abstract

Free fatty acids formed by hydrolysis of triglycerides and phospholipids and lipid oxidation products have been reported as factors affecting the quality parameters of lean fish muscle. The progressive decrease in the intermyofibrillar space observed morphologically in hake and cod suggests that membrane lipid degradation may be one of the factors directly related with toughening of lean fish flesh and therefore, the lipid fraction in this lean fish is important, not only due to changes occurring on the lipids themselves, but also as drivers of toughening of frozen fish. In this sense it is important to further characterize the changes occurring in this fraction in conditions well known to render different textural deterioration rates. Mid infrared spectroscopy is a useful analytical technique to characterize edible oils and to investigate the lipid deterioration process. The objective of this work was to investigate lipid changes by ATR-FTIR spectroscopy from hake fillets stored at different temperatures (-10 to -80 ºC) for up to 150 week so that a wide variability of toughening of hake was achieved. The intensities of the free fatty acid carboxylic ¿(C=O) band at 1712 cm-1 confirmed the strong temperature-dependence of lipid hydrolysis. Moreover, intensity decreasing of the phospholipid ¿as(PO2-) vibrational mode near 1231 cm-1 and the C-N asymmetric stretching motion in the (CH3)3N+ moiety of phosphatidylcholine (970 cm-1) was observed the longer the storage time and the higher the temperature. These results suggest that most of the hydrolysis occurs in phospholipid fraction. The importance of lipid hydrolysis and fat content were discussed in the light of the time and temperature conditions subjected to the hake muscle.