Changes in nutritious component and water molecule of peeled shrimp during dense phase carbon dioxide treatment

Abstract: Dense phase carbon dioxide (DPCD) is a non-thermal processing technology, which affects microorganisms and enzymes through molecular effects of CO2 under pressures below 50 MPa and 60℃. DPCD has had less of a significant effect on the quality of food and has been applied to the process of meats, vegetables, seeds and food powders, fruits, spices and herbs, and fish. Currently, most of research are more focused on microorganisms and enzymes that are inactivated by DPCD. However, some research indicated that DPCD has an effect on the quality of meat and its products, mainly related to muscle pH value, color, water holding capacity, texture, etc. The nutritional composition of meat and its products also has a decisive effect on their qualities. Water is the highest content in meat and its products composition. Water can directly affect color, tenderness, juiciness, flavor, and the processing characteristics of meat and its products. Water content and its distribution showed dynamic changes in the processing and storage of meat and its products, which is an important factor in determining quality and shelf life. Litopenaeus vannamei is a favorite of consumers in aquatic products due to tender meat and high nutritional value. In our previous study, Litopenaeus vannamei was treated for sterilization and inactivation of polyphenol oxidase by DPCD. In order to further investigate the effect of DPCD on shrimp muscle quality, peeled shrimp were used as the studied object. The effects of temperature (35-55℃), pressure (5-25 MPa), and time (10-60 min) on nutritious components and water molecules of shrimp muscle were studied. The results showed as follows: when using the untreated peeled shrimp, the content of nutritious components (moisture, crude protein, crude fat, and ash), especially fat, significantly decreased (P<0.05) after DPCD treatment. With the increasing of DPCD treatment intensity, fat was extracted and water was dried out by DPCD. Partially ionized minerals and small molecular compounds containing nitrogen (e.g. free amino acids) were carried out with CO2 in the unloading process. While using the untreated peeled shrimp, the contents of myofibrillar and sarcoplasmic protein decreased significantly (P<0.05) and the content of insoluble protein increased significantly (P<0.05) with exposure to time, temperature, and pressure when DPCD was increasing. The reason for that was myofibrillar and sarcoplasmic protein were denatured and transformed to insoluble protein by DPCD. The results of low field nuclear magnetic resonance (LF-NMR) showed that peeled shrimp contained four kinds of water molecules with different mobility. With exposure to time, temperature, and pressure when DPCD was increasing, the degree of freedom of bound water increased while the degree of freedom of immobilized water and free water decreased. Nonetheless, the content of bound water and free water increased significantly (P<0.05) while the content of immobilized water decreased significantly (P<0.05), when the peeled shrimp was treated for 30 min at 15 MPa and 55℃ of DPCD. Microorganism and PPO from Litopenaeus vannamei were inactivated, but the content of moisture, crude protein, crude fat, and ash decreased by 7%、3%、25%, and 11%, respectively. Sarcoplasmic and myofibrillar protein were denatured, and the free water ratio increased significantly (P<0.05). The research results will provide a reference for the application of DPCD in shrimp processing.