Studies On The Effect Of Ultrasonic Assisted Freezing On The Ice Crystals And The Ouality Chaneges In Fenneropenaeus Chinensis

Due to the specific characteristics of its meat,especially the tender flesh,high protein and low fat,the Fenneropenaeus chinensis is popular among consumers and became an important fishery economic product in China.But the special habitat environment and high water physiological characteristics have a strong negative impact on the storage of this shrimp.This study focused on the optimization of Fenneropenaeus chinensis by ultrasonic assisted freezing(UF)to improve the quality of the shrimp.The shrimp samples were treated by UF,immersion freezing(IF)and refrigerator freezing(RF)respectively and the connection between the changed of ice crystals and moisture of tissue during freezing process was investigated.The relationship of quality change and ice crystals in tissue by different frozen methods for different days were also discussed.The main results were as follows:1.Different ultrasonic parameters had great impact on Fenneropenaeus chinensis meat.Single factor results showed that UF went the shortest time through the zone of maximum ice crystal formation,when the temperature reached 0?,power of 270 w,function time of 5 s on/3 s off for the shrimp sample,the intermediate values of 3 conditions were obtained by single factor experiment,time of the zone of maximum ice crystal formation was set as the response value.The design of response surface optimization analysis revealed the optimal parameters of frozen,which is temperature of 0.13 ?,power of 191.97 W,action time of 4.92 s on/3 s off.Under the optimal condition,it took 101.541s to go through the zone of maximum ice crystal formation.Further experiments verified the optimal ultrasonic parameters for Fenneropenaeus chinensis treated by UF,the zone of maximum ice crystal formation was 106.000 s,the relative error was 2.99%,suggesting a good reference value to the ultrasonic assisted frozen Fenneropenaeus chinensis.The comparison of the histologic of it after optimal UF and non-ultrasonic immersion freezing shown that the ice crystal of Fenneropenas chinensis was smaller with UF,which was better than non-ultrasonic immersion freezing.2.The formation of ice crystals and the change of moisture of Fenneropenaeus chinensis treated by UF,IF or RF,and the effects of different exposure time were investigated.The results showed that the time passing through the zone of maximum crystallization was 130 s for UF,which was much faster than that of IF or RF.The minimal tissue destruction was observed for samples treated by UF with the minimum diameter of crystal of 46.81?m.Compared with other groups,samples treated by UF had a higher water holding capacity and a lower dehydration.Furthermore,the results of Pearson analysis indicated that there was an extremely significant correlation between ice crystals area and the moisture content for all the tested groups,and a significant correlation between the roundness and moisture content also existed in samples treated by UF,no correlation was discovered in those treated by IF or RF yet.3.The ice crystals increased gradually in persistent frozen storage after the treatment with different freezing,and the TVB-N value increased continuously.The TVB-N value of UF,IF and RF were smaller than 25.000 mg/100 g in 60 d,which was a grade,with the TVB-N value for UF<IF<RF.The content of salt soluble protein gradually decreased during the storage period.The preservation results of the salt soluble protein for samples treated by UF after 60 d was better than that of IF for 20 d,RF over 35 d.Moreover,the activity of Ca2+-ATPase increased with storage time and gradually decreased after reaching the maximum in 15 d,IF and UF were relatively slow,and Ca2+-ATPase activity was resemblance at 60 d.In addition,TBA value for the 3 groups resemblance at early storaged and increased gradually with the storage time.There was RF significantly higher than UF and IF,and UF slightly smaller than IF when it came to 60 d.The pH value decreased with extension of storage,and the pH value decreased to 6.42?6.57 with a trend of UF>IF>RF.The water holding capacity decreased as well,it reduced by 24.5%after UF,and lost about 41.9%after RF at 60 d.At the end of frozen storage,sensory evaluation value of the UF treated group fall slightly,followed by that of IF and RF was down to 6.43 in 60 d.