Structural changes of hake (Merluccius merluccius L.) fillets: Effects of freezing and frozen storage

Structural changes in hake (Merluccius merluccius L.) fillets as affected b y freezing method and frozen storage temperature have been studied through Raman spectroscopy and related to changes in texture and functionality. Cha nges in protein secondary structure were observed due to storage temperatur e, accompanied by changes in apparent viscosity and shear resistance. Sampl es at -10 degrees C showed greater structural alteration than at -30 degree s C in terms of increase of beta-sheets at the expense of a-helices. An inc rease of unordered protein structure was found only in samples stored at -1 0 degrees C. Exposure of buried tryptophan residues was observed at both st orage temperatures. The decrease of the delta CH2 band upon storage suggest ed an increase of hydrophobic interactions of aliphatic residues. Except fo r liquid air frozen fillets, all samples showed a decrease of the vO -H/vC- H band ratio compared to the fresh ones, this decrease being higher the har sher the conditions.