Effect of kappa-carrageenan oligosaccharides on myofibrillar protein oxidation in peeled shrimp (Litopenaeus vannamei) during long-term frozen storage

Protein oxidation during chilling and frozen storage has recently attracted great attention due to its consequences on protein solubility and functionality. In this study, the effects of kappa-carrageenan oligosaccharides on myofibrillar protein oxidation in peeled shrimp (Litopenaeus vannamei) during frozen storage were investigated by assessing the content of the carbonyls, total sulfhydryl, dityrosine, and surface hydrophobicity. We also examined the means of antioxidant activity in vitro, degradation of muscle proteins, and integrity of tissue structure. Our data revealed that in vitro carrageenan oligosaccharides exhibited good capacities of OH center dot, O-2(-center dot), and DPPH center dot scavenging and Fe2+-chelating activity. Chemical analyses showed that frozen storage increased susceptibility of myofibrillar proteins to frozen oxidation. We found that the incorporation of carrageenan oligosaccharides during the treatment of the shrimp prior to frozen storage significantly decreased the formation of protein carbonyl and dityrosine, lowered the changes in myofibrillar surface hydrophobicity, and maintained a higher total sulfhydryl content when compared with the water-treated samples (control). Additionally, the results of protein degradation and tissue structure confirmed that these antioxidant oligosaccharides exhibited marked effects on stability of muscle proteins and effectively inhibited the degradation/oxidation of muscle proteins during frozen storage. Overall, the contribution of the antioxidant activities played an important role in cryoprotective effects of carrageenan oligosaccharides on frozen shrimp. Further application of these findings might maintain better quality and extend the commercialization of refrigerated products.