FTIR of the lipid fraction as a potential marker for monitoring the time and temperature history of frozen hake (Merluccius merluccius, L.) muscle

Abstract

Mid infrared spectroscopy has been proven a useful technique to analyze the lipid deterioration process in frozen fish muscle. Previous results at -10 ºC showed that the intensity of the free fatty acid carboxylic band ¿(C=O) measured by ATR FTIR spectroscopy could be used for monitoring the development of lipid hydrolysis in hake lipids. Also, the disappearance of the ¿as(PO2-) of the phospholipids was observed. The high correlation of free fatty acids with instrumental texture suggested that this fraction could be used to evaluate quality changes of frozen stored lean species such as hake. Given that the rate of muscle deterioration is highly sensitive to freezing temperature and storage time, in this work we aimed at modeling the time and temperature changes of the lipid fraction of hake muscle. Fillets of a total of 190 hake (Merluccius merluccius, L.), stored at -10, -20, -30 or -80 ºC for up to 150 weeks were used in the experiment. Lipids were extracted from the muscle and analyzed by ATR FTIR spectroscopy. Three spectral regions corresponding to the ¿(C-H) groups (3100-2750 cm-1), the ester and carboxylic ¿(C=O) groups (1800-1670 cm-1), and the ¿as(PO2-) of the phospholipids (1330-1127 cm-1) were analyzed separately. Principal Component Analysis showed that in all three spectral ranges 3 PC were sufficient to explain at least 95 % of the total variance. The first principal component (PC1) of both the 3100-2750 cm-1 and 1800-1670 cm-1 regions, and PC2 of the 1330-1127 cm-1 region showed a strong time temperature dependence. The best time and temperature model was attained with the changes occurring in the region corresponding to the phosphorous moiety of the phospholipids with a coefficient of determination (R2) of 0.98. Modeling of the results obtained by FTIR keep a close relationship with other physical chemical quality parameters which suggests the potential of this technique for the authentication of frozen storage time and temperature in fishery products.