Research On Preservation Technology Of Pseudosciaena Crocea With Controlled Freezing-point And Modified Atmosphere Packaging

This thesis is focused on the fresh quality of cultured Pseudosciaena crocea, and its fluctuation under different storage temperature, and different modified atmosphere packaging at freezing-point, through organoleptic investigation and a series determination of fresh quality index such as TVB-N, TBARS, total bacteria amount and purge loss rate.1. The freezing-point of Pseudosciaena crocea is determined to be -1.38℃through DSC method, thus the freezing temperature is from -1.38℃to 0℃.2. The initial fresh quality of market-purchased Pseudosciaena crocea can meet the first class standard issued by Ministry of Agriculture.3. A comparison study of Chilling storage(4℃±1℃) and Freezing Storage(-0.5℃±0.3℃)is conducted with the assistance of fresh quality determination and organoleptic investigation, which proves that freezing point storage is a better way as a new-born low-temperature storage method. The microbes and enzyme activities are restrained and depressed by freezing point storage, which can meet the second class fresh quality standard with a prolonged preservation for 2 days.4. Different modified atmosphere packaging at freezing-point (-0.5℃±0.3℃)are carried out (60%CO₂+20%O₂+20% N₂, 100%CO₂, and vacuum), in order to evaluate the fresh quality of Pseudosciaena crocea. The vacuum package method is less effective for fresh quality preservation than the other two methods, the storage of which, under the second fresh quality standard, can reach 14 days; while the other two methods can prolong the storage for 7 days by complying with the same fresh quality standard.5. API20E method is employed to characterize and determinate the initial bacterial flora of fresh Pseudosciaena crocea and the spoilage bacterial flora at chilling storage, freezing storage, vacuum-packaged, and 100% CO₂ packaged storage, respectively. Biochemical reactions prove that the initial bacterial flora is dominated by Enterobacteriaceae and Pseudosciaena crocea was polluted once harvested. The Enterobacteriaceae will survive as the dominant bacteria at freezing-point storage or modified atmosphere packaging without any pretreatment, and result in the spoilage of Pseudosciaena crocea by the end.