Water Migration and Quality Change of Prawn Preserved under Controlled Freezing-point Storage Combined with Low Frequency Electric Field Technology

To study the feasibility of shelf life extending for prawns preserved through controlled freezing-point storage combined with low frequency electric field technology. A low frequency electric field was applied on controlled freezing-point storage to keep fresh of prawns (LFEF+CFPS). During storage, the total viable count (TVC) and total volatile basic nitrogen (TVB-N) content of prawn were monitored, and the microstructure changes were analysed. Moreover, the water migration and change of prawn meat and head were studied by the low field nuclear magnetic resonance (LF-NMR) technology, respectively. Meanwhile, the CFPS was used as control. The results showed that: Storage of 9^th day, the TVC and TVB-N content of the LFEF+CFPS group began to show significantly lower than those of control group (P<0.05). Furthermore, the TVC in the LFEF+CFPS group was one order of magnitude under the control group at 12^th day. Its TVB-N content was 36% lower than the control group at 11^th day (P<0.05), and with the shelf life of more than 13 days. Compared with the loose structure of the control group, microstructure change of prawn in LFEF+CFPS group was significantly samller. LF-NMR technology also showed that, water migration from immobilized water to free water in prawn head was significantly inhibited by LFEF from storage of 7^th day. Slower water diffusion was also found in MRI. As the decay rate in prawn meat was lower than that in prawn head, there was no apparent water migration in prawn meat of LFE+CFPS group within 15 days. LFEF was contributive to delay the corruption in prawn and prolong its shelf life for 3~5 days during CFPS.