Microwave Thawing Characteristics Of Minced Antarctic Krill(Euphausia Superba)

Antarctic krill(Euphausia superba),living in high-latitudes and low-temperature area,is a commercially important marine organism in the Antarctic Ocean and is also considered the largest animal protein resource in the world.Because of its unique structure and degradation characteristics,further processing and cooking of Antarctic krill must be done by thawing,therefore,thawing processing of Antarctic krill will be hot topics of discussion by scholars.Microwave thawing is a convenient,safe and emerging food processing method,thus,the application of food thawing and heating using microwave method is widely concerned.Nowadays,it is a crucial problem that uneven heating during microwave thawing,and the changes of multiple freezingthawing cycles,heating rate and food composition could affect temperature distribution during microwave processing,thereby,the quality of foodstuff could be changed.Based on the reasons above,according to multiple freezing-thawing cycle times,additives types and content and temperature distribution,the effects on physicochemical properties,ATP degradation products,amino acid content and dielectric properties of Antarctic krill were studied during microwave thawing.Moreover,the reliability of the numerical simulation in temperature distribution was confirmed using COMSOL Multiphysics software.The main contents and conclusions are as follows:1.Based on the index of quality loss,pH,ATP degradation products and amino acid content,the changes of flavoring components and food quality of Antarctic krill were studied,and the effects of multiple freezing-thawing cycle times on dielectric properties during microwave processing.Results showed that quality loss and pH of minced Antarctic krill rose with the increase of multiple freezing-thawing cycle times.Compared to the change of ATP degradation products and amino acid content,in the range of twice cycles,delicious nucleotides content is higher than others and the flavoring amino acid content keep constant.When the cycles times is more than two times,delicious nucleotides content deceased gradually while bitter nucleotides content increasing significantly,and the bitter amino acid content showed a trend of increasing.Besides,the polarity and nonpolar amino acid content may affect dielectric properties of Antarctic krill.Generally,in the small range of freezing-thawing cycles,the flavor,quality and thermal properties keep a good level.2.Dielectric properties of Antarctic krill and white shrimp were measured across the microwave frequency range 300 to 3000 MHz in a temperature range of-20 to 20 °C.To shorten thawing time,the effects of salt,sucrose and moisture contents on dielectric properties at 915 and 2450 MHz were also studied during microwave thawing(MT)and microwave heating(MH).The change in sucrose content had a smaller effect on dielectric properties of Antarctic krill,and only addition of salt had a significant influence(p < 0.05)on dielectric properties during MT.The synergistic effect of salt and sucrose also affects dielectric properties and penetration depth of Antarctic krill,suggesting that MT and MH can be applied to the processing of freshwater and oceanic shrimp,and that addition of only salt or the salt-sucrose mixture can further quicken thawing and heating rates to optimize the industrial processing of shrimp.3.Using COMSOL Multiphysics software,the electromagnetic and temperature distribution of Antarctic krill were simulated and calculated during microwave thawing.The predicted temperature simulation was developed,and the reliability of simulation was also confirmed.Results indicate that thawing time shortened significantly when salt and sucrose were simultaneously added to the samples.Besides,the center temperature and temperature distribution within cross-section of Antarctic krill and white shrimp confirmed effects of various additives on dielectric properties.Due to microwave penetration performance and metal reflection effect,temperature distribution of cylindrical minced Antarctic krill shown uneven characteristic.When the microwave processing time was 130 s,there is the highest temperature at centre and the lowest temperature at edges in cross –section of samples.Moreover,the temperature distribution of samples with kinds of additives shown a significant difference.The simulated results is a good agreement with the experimental results,so the numerical model by COMSOL Multiphysics could predict the temperature distribution within the samples during microwave thawing.