Phlorotannin Extracts from Ascophyllum nodosum Inhibited Proteases Activities and Structural Changes from Apostichopus japonicus

Fresh Apostichopus japonicas (A. japonicas) are easy to autolyze through the actions of endogenous proteases under certain circumstances, further inducing a decline in A. japonicas product quality and business value. To solve this serious problem in the A. japonicas industry, we investigated the inhibition of phlorotannin extracts (PhTE) on the activities and structural changes of crude endogenous proteinase (CEP) from A. japonicas. The results of enzyme activity and SDS-PAGE indicated that PhTE could inhibit enzyme activity in a dose dependent manner. Analysis of multiple spectroscopic methods, scanning electron microscopy, and differential scanning calorimetry indicated that PhTE promoted the cross-linking and aggregation of CEP and increased the particle size of the enzyme, thus changing the structure of the enzyme protein and decreasing the thermostability of protease. In conclusion, PhTE might be an effective inhibitor on endogenous proteinase in A. japonicas, which opened up a new way to prevent the A. japonicas autolysis.