Effect of Low Temperature Plasma Sterilization on Myosin Degradation and Related Cathepsin Activity of Oncorhynchus mykiss

To clarify the mechanism of the effect of low temperature plasma sterilization on the degradation of Oncorhynchus mykiss and related cathepsin activity, Oncorhynchus mykiss fillets were treated with 70 kV dielectric barrier discharge low temperature plasma (DBD) sterilization and storage under ice temperature for 8 d. Changes in texture, TCA soluble peptides, amino acid nitrogen, myofibrillar fragmentation index (MFI) of Oncorhynchus mykiss fillets from different storage days were analyzed, and the activities of cathepsin B, D, and L in the fillets and their degradation effects on myosin were explored. The binding of the main active substance NO₃⁻ produced by DBD sterilization with cathepsin was further analyzed through molecular dynamics simulation. The results showed that 70 kV DBD treatment had no significant effect on the hardness and elasticity of Oncorhynchus mykiss fillets during early storage (P>0.05), and the reduction of hardness and elasticity was delayed during the storage. It also delayed the increase of TCA soluble peptides, myofibrillar fragmentation index (MFI), and amino acid nitrogen content. The activity of cathepsins B and L were significantly inhibited (P<0.05), and the degradation of myosin light chain MLC-2 fragment was slowed. The activity of cathepsin B, D and L was significantly reduced after DBD sterilization (P<0.05). Molecular dynamics simulations showed that the binding free energies of cathepsin B, D and L with NO₃⁻ were −10.937, −5.0555, and −19.112 kcal/mol, respectively, and the hydrogen bonding frequencies of cathepsin B, D, and L with NO₃⁻ were 13.56%, 15.02%, and 31.23%, respectively, indicating stronger hydrogen bonding between NO₃⁻ and cathepsin L. The degradation of fish protein and activity of cathepsin could be delayed by DBD sterilization, and the texture of fish fillet was maintained. The greatest effect on cathepsin L was shown by the active ingredient NO₃⁻ produced by DBD sterilization, which could exist in a stable way in its active center and had low binding free energy.