Effect of different extent of protein oxidation on the frozen storage stability of muscle protein in obscure pufferfish (Takifugu obscurus)

The objective of this study was to explore frozen storage stability of muscle protein of the obscure pufferfish using a semi-model system based on light exposure (LE), oxygen concentration (OC), and multiple freeze-thaw cycles (FTCs). The dorsal muscle of fifteen frozen fish was cut into small pieces (2 cm × 1.5 cm × 1 cm) and divided into 4 groups stored in differing conditions: one was stored in light with 0% oxygen (L-0), one in light with 20% oxygen (L-20), one in dark with 0% oxygen (D-0), and one in dark with 20% oxygen (D-20). All were subsequently subjected to five FTCs. Protein oxidation (PO) levels, protein structure, and water states were all assessed. The results showed that both LE and OC could significantly accelerate sulfhydryl and tryptophan loss, in the order of L-20 > L-0 and D-20 > D-0 during FTCs. Changes of protein structure were in line with the extent of PO indicated by surface hydrophobicity and UV absorbance. An increased PO also affected the water states, with higher PO resulting in immobilized water being more tightly trapped within the protein. However, thawing loss was shown to be independent of PO and the structural changes of myofibrillar protein. •Light and oxygen could both accelerate PO during FTCs but through different pathways.•The conformational changes of MFP consistent with the extent of PO.•Immobilized water was more tightly trapped with the increased extent of PO.•The extent of PO has limited effect on thawing loss compared with mechanical damage.