| Antarctic krill(Euphausia Superba),which is rich in resources with large catch and rich nutritional value,is an important part of marine fishery resources.Shrimp meal is one of the most important processed products of Antarctic krill.Its processing process mainly includes cooking,separation,drying,pulverization and packaging.Among them,heat treatment mainly involves cooking and drying.Heat treatment will cause the loss of nutrients and the destruction of active substances,especially heat-sensitive substances such as astaxanthin.Because of its poor structural stability,heat-sensitive substances is easy to degrade and isomerize under high temperature conditions.Thus,heat treatment is the most important processing step to determine the quality of shrimp meal.In order to grasp the flow path of the main nutrients such as protein and lipid during the processing of shrimp meal,as well as the changes in the content,structure and antioxidant activity of the main active substances such as astaxanthin,frozen Antarctic krill was used as the experimental material in this study,using the processing technology of Antarctic krill → flowing water freezing → draining → cooking →drying → crushing and sieving → shrimp meal to process it into shrimp meal.The changes in the content of nutrients and the loss of fatty acids,astaxanthin and other active substances would be measured to analyze the flow paths and reasons of the main substances and to compare the composition changes of unsaturated fatty acids in each processing stage and to analyze the influence of heat treatment on the composition of fatty acids.The structural changes and antioxidant properties of astaxanthin in different processing stages would be compared to analyze the correlation between the structure and functional activity of astaxanthin.The main results are as follows:(1)The flow direction of the main nutrient active substances in Antarctic krill during heat treatment.The water lost 8.49% during the cooking process and 63.5%during the drying process,mostly in the form of evaporation;the protein lost 1.12%during the cooking process,of which 0.87% went to the cooking liquid,and the lost part was mainly water-soluble protein.The drying process Loss of 6.05%;lipid content decreased by 1.11% and 1.61% during cooking and drying respectively;astaxanthin was affected by heat treatment,and the content of astaxanthin decreased by 21.9 and 36.6mg/kg after cooking and drying,respectively;2.85% and 0.85% respectively during drying.(2)Effects of heat treatment on fatty acid composition and astaxanthin structure during processing of Antarctic krill meal.The GC method was used to analyze the change of fatty acid composition.After cooking and drying,it was found that the content of polyunsaturated fatty acids decreased from 45.57% to 43.65%,and the relative content of EPA decreased by 0.41% and 1.16% during the cooking and drying process,respectively.There was little change during the process,and the decrease was0.68% during the drying process.The structure of astaxanthin was analyzed by HPLC.The content of astaxanthin in the raw material of Antarctic krill was 110.6 mg/kg,of which all-trans structure astaxanthin accounted for 90.7%,13-cis astaxanthin and 9-cis astaxanthin accounted for 4.7% and 4.6%,respectively.After cooking and drying,all-trans astaxanthin accounted for 76.3% and 72.2%,respectively.13-cis astaxanthin accounted for 76.3% and 72.2%.Astaxanthin accounted for 19.9% and 21.9%respectively,and 9-cis-astaxanthin accounted for 3.9% and 5.9% respectively;the 3S,3’S,3S,3’R,The contents of the three optical isomers of 3R and 3’R were 16.8,17.9 and72.1 mg/kg,12.0,25.5 and 55.3 mg/kg after cooking,and 2.8,8.1 and 12.4 mg/kg after drying.(3)Comparison of antioxidant activity of astaxanthin in different processing stages of Antarctic krill meal.Taking Vc as a reference,the antioxidant activity of Antarctic krill astaxanthin in different processing stages was determined by DPPH method,hydroxyl radical method and total antioxidant capacity method(FRAP).The ability of astaxanthin to scavenge DPPH free radicals was significantly stronger than that of Vc(P<0.05);in terms of scavenging hydroxyl radicals,the antioxidant capacity of astaxanthin after cooking and drying was stronger than that of astaxanthin in raw materials(P<0.05);In the FRAP iron reduction experiment,the astaxanthin after cooking and drying also showed higher reducing ability.Based on the results of in vitro antioxidant experiments,the order of in vitro antioxidant activities of krill astaxanthin and Vc in three processing stages is: after drying > after cooking > after thawing > Vc.The results showed that the heat treatment in the processing of Antarctic krill meal had a greater impact on the nutritionally active substances in Antarctic krill.1.In terms of content: the loss of water,protein,polyunsaturated fatty acids and astaxanthin mainly occurs in the drying stage,the loss in the cooking stage is relatively small,the loss of lipids in the cooking and drying processes is similar,and the drying is slightly higher than that in the cooking.The loss of ash mainly occurs in the cooking stage,and the loss in the drying process is relatively small;the main substances lost in the cooking process are mostly water-soluble substances,which mainly flow to the cooking liquid,and a small part of the loss is caused by biochemical reactions.Except for evaporation,the remaining losses are mostly caused by biochemical reactions.2.In terms of composition and structure: During the processing of shrimp meal,the proportion of polyunsaturated fatty acids(EPA,DHA)in fatty acids decreased due to thermal oxidative decomposition;the geometric structure of astaxanthin in Antarctic krill was all-trans.Mainly,isomerization mainly occurs in the cooking stage.After heat treatment,part of the trans-astaxanthin is converted into cis-astaxanthin.The optical structure of astaxanthin in Antarctic krill is mainly 3R,3’R,and the isomerization is mainly Occurs in the drying stage;Antarctic krill astaxanthin has good antioxidant capacity(better than Vc),and the antioxidant capacity of each processing stage is significantly different.Compared with krill raw materials,the antioxidant capacity of astaxanthin after cooking and drying is enhanced.This study preliminarily grasped the content changes and flow paths of main substances during the processing of Antarctic krill meal,analyzed the reasons for the changes and the main influencing factors,compared the differences in antioxidant activity of astaxanthin in each processing stage,and analyzed the correlation structure and the functional activity of astaxanthin.It can provide theoretical basis and technical reference for the subsequent optimization of the processing process and parameters of Antarctic krill meal and It has a very positive significance for improving the quality of shrimp meal and promoting the high-quality utilization of Antarctic krill resources. |
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