Protein changes in shrimp (Metapenaeus ensis) frozen stored at different temperatures and the relation to water-holding capacity

To study the effects of freezing temperature on muscle proteins, shrimp (Metapenaeus ensis) were frozen stored at either ?18 or ?60 °C up to 90 and 210 days. Shrimp frozen at ?18 °C had higher thawing and compression loss and poor myofibril water-holding capacity compared with those frozen at ?60 °C. In terms of protein characteristics, shrimp frozen at ?18 °C had higher levels of carbonyls and reduced sulphhydryls. Moreover, the shrimp frozen at ?18 °C had higher surface hydrophobicity and reduced Ca²⁺-ATPase activity, indicating increased protein denaturation. Proteomics revealed that seventy-five proteins were classified as differentially abundant proteins (DAPs) following freezing. There were sixty-four DAPs in the F18-CON comparison group (shrimp frozen at ?18 °C vs. control) and thirty-two DAPs in the F60-CON comparison group (shrimp frozen at ?60 °C vs. control), suggesting that freezing at ?18 °C results in more DAPs than freezing at ?60 °C. A comparison between F18 and F60 revealed that ribosomal proteins (L44, L7a) and heat shock protein 21 were downregulated in F18. These results increase our understanding of the variable quality associated with shrimp frozen at different temperatures.