Vibrational spectroscopic analysis of hake (Merluccius merluccius L.) lipids during frozen storage

► Fish lipids extracted from hake muscle have been spectroscopically characterised. ► Lipid hydrolysis in hake muscle is an important event related to quality changes. ► Changes in the phospholipids-PO2− group could be related with membrane deterioration and associated to texture changes in hake. ► The ATR-FTIR ν(CO) band of carboxylic acid can be used as a marker for monitoring frozen storage time at this temperature. Vibrational spectroscopy (mid FTIR and FT-Raman) was used to monitor lipids extracted from hake fillets during frozen storage. Kramer shear resistance was used as a marker of texture changes and lipid damage was also investigated by following the development of conjugated dienes and free fatty acids by spectrophotometric methods. Results show that the intensity of the free fatty acid carboxylic ν(CO) band measured by ATR-FTIR spectroscopy can be used for monitoring the development of lipid hydrolysis in hake lipids. Changes in the Raman ν(CC) stretching region (1658cm−1 band), partially attributed to conjugated dienes development, were the only observed spectroscopic alterations related to lipid oxidation of hake lipids during frozen storage at −10°C. The high correlation of free fatty acids with instrumental texture and the disappearance of the νas(PO2−) band are consistent with membrane lipid hydrolysis being one of the factors directly related with toughening of lean fish flesh.