Effect of Konjac Glucomannan Combined with Tea Polyphenols on Freeze-thawed Carp Surimi

In order to resist quality deterioration caused by repeated freeze-thaw cycles during frozen storage, 1% konjac glucomannan (KGM) combined with 0.02% tea polyphenols were added as antifreeze protectants. This study investigated the protective effects on the protein structure (particle size, potential, hydrophobicity, Fourier transform infrared spectrum, tryptophan fluorescence spectrum, scanning electron microscopy) and oxidation (carbonyl group content, sulfhydryl group content) of frozen carp surimi after multiple freeze-thaw cycles (0, 1, 3, 5). The results showed that the addition of KGM and tea polyphenols had a protective effect on the aggregation of protein particle size, prevented the increasing particle size, delayed the increased in hydrophobicity of myofibrillar proteins (MP) (P<0.05), weakened the flocculation state of MP solution, and improved its stability (P<0.05). The addition of KGM and tea polyphenols also slowed the decrease of β-fold content in surimi caused by freeze-thaw cycles (P<0.05), inhibited the transformation of β-fold to α-helix (P<0.05), and effectively prevented secondary structure degradation in surimi proteins. In the fluorescence spectrum test, the addition of KGM and tea polyphenols effectively inhibited hydrogen bond rearrangement and protein conformational changes induced by freezing and thawing of surimi (P<0.05). Microscopic analysis showed that KGM penetrated the muscle fiber pores, bonded with protein and water molecules, controlled ice crystal growth within the muscle fiber pores, and stabilized protein structure. Furthermore, the addition of KGM and tea polyphenols significantly inhibited the increase in carbonyl content and the decrease in sulfhydryl content (P<0.05), and effectively inhibiting proteins oxidation (P<0.05). In conclusion, the addition of KGM and tea polyphenols to frozen surimi reduced the deterioration of protein structure caused by repeated freeze-thaw cycles and effectively inhibited protein oxidation in carp surimi, thus improving the quality of repeatedly frozen and thawed surimi.