Sterilizing effect of dense phase carbon dioxide on dominant spoilage bacteria from shrimp and its mechanism

Abstract: Dense phase carbon dioxide (DPCD) is a non-thermal pasteurization method that affects microorganisms and enzymes through molecular effects of CO2 under pressures below 50MPa and temperature below 60℃. The DPCD sterilization technique could be one of the most promising techniques for sterilizing foods without exposing them to adverse effects of heat, thereby retaining their fresh physical, nutritional, and sensory qualities. In order to investigate the sterilization effect and mechanism of aquatic product spoilage bacteria induced by dense phase carbon dioxide (DPCD), using a strain of Litopenaeus vannamei dominant spoilage bacteria (Chryseobacterium sp. LV1) as the research object, the effects of temperature (30-55℃), pressure (5-25 MPa), time (5-60 min) on sterilization were studied and the changes of Chryseobacterium sp. LV1 physicochemical properties were analyzed before and after DPCD treatment. The results showed that DPCD had a good bactericidal effect on Chryseobacterium sp. LV1. The sterilization effect is enhanced with increasing temperature, pressure and time, and the sterilization effect of supercritical CO2 was better than that of subcritical CO2. Under DPCD conditions of 45℃/15 MPa /30 min or 55℃/15 MPa /30 min, the total bacterial count decreased by 5 logs; the pH value of the bacterial suspension decreased from 6.97 to 5.58 and 5.56; the content of extracellular protein increased from the initial 78.69 to 151.91 and 157.40 μg/mL; and the absorbance value from 200 to 800 nm increased. These results indicated that DPCD could result in intracellular protein and nucleic acid leakage of Chryseobacterium sp. LV1 because of permeability changes in its cell membrane. The SDS-PAGE electrophoretogram of Chryseobacterium sp. LV1 proteins showed that DPCD could reduce the solubility of Chryseobacterium sp. LV1 soluble protein because of soluble protein denaturation. The results detected by the API ZYM system kit showed that DPCD could inactivate 14 enzymes related to the metabolism of Chryseobacterium sp. LV1. The agarose gel electrophoretogram of Chryseobacterium sp. LV1 DNA showed that DPCD could not degrade the DNA of Chryseobacterium sp. LV1. Therefore, changes in the physicochemical properties of Chryseobacterium sp. LV1 induced by DPCD may be one of the main mechanisms of DPCD sterilization. The research results will provide a reference for the application of DPCD in the processing of shrimp.