Study On The Frozen Technology And Related Quality Control Of Eriocheir Sinensis

Chinese mittern crab is popular among consumers,due to itstender texture,rich nutrition,and unique flavor.crabs are consumed freshly and alive,mainly in autumn and winter,so the overstock would cause great waste.study on the storage of crab is meaningful to the subsequent processing and the balance between supply and demand,consequently promoting the development of crab breeding industry.however,up to date,few reports were focused on the storage and quality control of crabs.In this paper,fresh crabs were treated with different freezing methods,including slow fridge freezing at-20oC,rapid freezing at-20oC,-40oC,-60oC and in liquid nitrogen respectively.Different freezing storage temperature(-20?,-30? and-40?)and the addition of quality improver were also studied to evaluate their effects on the quality.The aim of this study was to improve the quality of the crab after frozen storage and provide the theoretical basis and technical guidance for the processing and utilization of the crab.The main research results were given as follows:(1)During the frozen storage,the quality characteristics,was shown as that pH value,Ca2+-ATPase activity and total sulfhydryl content decreased,and MDA contents increased firstly and then decreased,while surface hydrophobicity increased continuously.The SDS-PAGE showed that that there were no significant difference in protein bands among different freezing rates after the fist one week.The bands of protein were weak significantly after 8 weeks.A new band at 100 ~ 130 kDa appeared in the-20oC slow freezing group after 18 weeks,which may be the cause of the degradation of MHC.Hardness,springiness and chewiness decreased during the storage.The change of each characteristic in the groups with rapid freezing methods was much slower than these in the slow fridge freezing group.Super-freezing,-60oC and liquid nitrogen freezing,were better than the moderate freezing,at-20oC and-40oC.But there's no significant difference between-60oC and liquid nitrogen.(2)Different freezing storage temperature(-20?,-30? and-40?)were used to evaluate their effects.During the storage time,The change tendency of the physical and chemical proporties of the crabs was similar,but the change rate was significantly different.The results showed pH value,Ca2+-ATPase activity and total sulfhydryl content were decreased during the frozen storage,while surface hydrophobicity increased.The SDS-PAGE showed that the lower the storage temperature was,the deeper the same band was low temperature had protective effect on myofibrillar protein.These changes in physical and chemical properties resulted in the deterioration of quality texture and other characteristics of the crab muscle.At the lower the storage temperature,the hardness,springness and chewiness were higher than those stored at the higher temperatures.The lower temperature can effectively inhibit the production of the total alkaloid content,putrescine,cadaverine and tyramine of crab muscle.Changes of each quality characteristic in the crab sample stored at-40? were significantly lower than those stored at-20?.(3)Arginine can be used as non-phosphate additive to increase the yield of crab and decrease the thawing and cooking loss.Use of arginine in combination of NaCl showed synergistic effect on the increase of water-holding capacity(WHC).The addition of Arg increased WHC,hardness,springiness,and chewiness.The treatment with 3% arginine caused a left shift of T22 ralaxation times.The samples treated with 2%arginine and 3%arginine had higher content of ?-helix,indicating that they had slighter protein denaturation than other treatments.DSC results showed that the sample with the treatment of 3% arginine had a higher transition temperature.(4)The texture,protein secondary structure,electron microscopy and flavor of fresh crab were compared between the groups with three treatments,slow-freezing group,quick-freezing group and quick-freezing with arginine.The results showed that the hardness,springness and chewiness with different treatments declined,compared with fresh group.The changes of the hardness,springness and chewiness of the group with arginine were relatively slight compared with the other two groups and could maintain good texture.Quick-freezing group had better texture characteristics than slow-freezing group,indicating that quick-freezing can improve the quality of crab.The group with arginine had higher ?-helix content than other groups.The changes in tissue microstructure of body,plier,and foot in the arginine-treated group were smaller.There were significant differences in the odor components among different treatments.The treatments with arginine and slow-freezing had larger effect on the flavor.The slow-freezing treatment had larger effect on plier of crabs,while arginine had larger effect on gonad.The group with the addition of arginine had a higher sensory score than the other groups in colour,odor,muscle texture and soup,mostly close to the fresh group.Results showed that the addition of arginine could improve the edibility and quality of frozen crab.