Decreased gelling properties of protein in mirror carp (Cyprinus carpio) are due to protein aggregation and structure deterioration when subjected to freeze-thaw cycles

Abstract

The changes in the gelling property and structural integrity of mirror carp protein that was induced by freeze-thaw (F-T) cycles were discussed. The strength, whiteness and water-holding ability of myofibrillar protein (MP) gel, the solubility and Ca2+-ATPase activity of MP were all significantly reduced after 5 F-T cycles (P < 0.05). The transverse relaxation time peak (T2) of samples under repeated F-T cycles exhibited a significant redshift (P < 0.05). The MP film surface became rough and irregular, as observed using atomic force microscopy (AFM) during the multiple F-T cycles. Additionally, the state and the weight of molecular distribution evidenced that F-T cycles caused protein aggregation and mechanical damage. The alterations in primary, secondary and tertiary protein structure revealed that the protein structure integrity of fish was destroyed under repeated F-T cycles. These findings indicated that repeated F-T cycles should be avoided during the freezing storage of fish to improve gel quality and sustain protein structural integrity.