A Study On The Structure Distribution Of Carotenoids In Algae,Shrimps,Crabs And Fishes And The Isomerization Of Astaxanthin

Compared with wild aquatic animals,farmed shrimps,crabs,and fishes commonly suffer from a series of problems,such as weak radiation resistance,poor immunity and disease resistance,reduced fertility and hatchability,dark luster,poor color,and rough texture or fragrant umami,poor taste and low nutrition,easy to disease in the breeding process and can easily lead to reduced yield or even no harvest,seriously affecting the nutritional quality of aquatic products,sales prices and production.At present,the specific causes and mechanisms that have led to the above-mentioned common problems have not yet been clarified.It is speculated that there may be a significant relationship between the significant changes in the composition of feeding foods and natural foods in the aquaculture process.For example,the lack of important functional metabolites?such as carotene and its derivatives,polyunsaturated fatty acids,functional glycoproteins,etc.?which cannot be synthesized de novo by animals and can only taken from food.Whether this is the case,it still needs strict system evaluation.Taking the carotenoids?especially astaxanthin and its isomers?as the breakthrough and based on the literature review,this paper chooses shrimps,Chinese mitten crabs,rainbow trout and Haematococcus pluvialis as the main research subjects and studies the structure and distribution characteristics of carotenoids and the isomerization of astaxanthin and the following issues are addressed.First,screening and establishment of sample pretreatment optimization methods suitable for the analysis of astaxanthin isomers;secondly,using the large scale photobioreactor and continuous monitoring,the seasonal fluctuations of astaxanthin content and isomer composition of in outdoor industrialization platforms were detail studied.Meanwhile,the basic characteristics of carotenoids,particularly astaxanthin and its isomers of the main shrimp species in China including Penaeus monodon,Fenneropenaeus chinensis,Litopenaeus vannamei,Exopalaemon carinicauda and Trachysalambria curvirostris were determined.The differences in the main carotenoid characteristics of wild-type Exopalaemon carinicauda and its red mutants were compared.The effects of carotenoid-enriched feeds on the Eriocheir sinensis's shell color and gonadal development were explored.In addition,the effect of feeding on rainbow trout with H.pluvialis residue was analyzed,and the quality of the product such as meat quality and coloring were improved.The purpose is to solve common problems in aquaculture and provide detailed basic,prospective and applied data.The main results are as follows:1.The pretreatment methods for the detection of astaxanthin and its isomers were optimized and compared.It found that the optimal conditions for enzymolysis was adding 0.67 units/mL cholesterol esterase under 37°C for 75 min.and the recovery of free astaxanthin was 92.95%;the optimal conditions for saponification was adding 0.021mol/L NaOH under 5°C for 90 min and the recovery of free astaxanthin was only 48.37%.Compared the recovery of free astaxanthin and stability of astaxanthin geometrical isomers,between enzymolusis and saponification,enzymolysis induced little degradation and isomerization of astaxanthin,thus hydrolysis the astaxanthin esters by cholesterol esterase before HPLC analysis was a reliable method for samples which contained astaxanthin esters.2.By tracking the changes of astaxanthin accumulation and isomers composition of H.pluvialis in different bioreactors,strains and seasons during large-scale clutivation,we found that:?1?The astaxanthin accumulation in tubular photobioreactor was siginificantly higher than that in open race pond,wheas there were no significant differences in isomers composition.?2?The astaxanthin accumulation and isomers composition were similar among H₂,H₃ and H₆.?3?Astaxanthin content and isomers composition were remarkable correlated with the five abiotic parameters?daily average termperature,daily maximum temperature,daily minimum temperature,temperature difference and daily total solar radiation?.Astaxanthin content was high,whereas the proportion of all-trans was relatively low under high temperature,strong light and large temperature difference conditions.On the contrary,lower astaxanthin content and higher all-trans astaxanthin proportion were observed under low temperature,weak light and small temperature difference conditions.3.The carotenoids in different body parts of five commercial shrimps in China,P.monodon,F.chinensis,L.vannamei,E.carinicauda and T.curvirostris were compared.We found that:the carotenoid level varies greatly depending on the species and the body part sampled.Astaxanthin,mainly esterified but also unesterified,was the predominant carotenoid.All-trans-astaxanthin was the predominant geometrical isomer and 9-cis and 13-cis were the major cis isomers.With regard to stereoisomers,only?3S,3'S?and?3S,3'R?-astaxanthin were observed in E.carinicauda where?3'S,3'S?-astaxanthin contributed more than 96%to the total astaxanthin content.In contrast,all three possible stereoisomers were detected in P.monodon,F.chinensis,L.vannamei and T.curvirostris.New breed of Exopalaemon carinicauda which named‘Kesuhong-1'has a significant higher content of carotenoids compared to the conventional ones.The notable red body color,which was mainly contributed by flesh instead of shell.The astaxanthin accumulated in‘Kesuhong-1'was in free form,but the major geometric and optical isomers of astaxanthin of it was similar to the conventional shrimp.4.Feeding trials in Chinese mitten crabs with H.pluvialis formula feed showed that:dietary supplement with broken H.pluvialis dry powder had significant effects on the accumulation of carotenoid in ovary,hepatopancreas,carapace and epidermis of Chinese mitten crabs.There was a clear dose-effect relationship between the carotenoid content deposited in tissues and the addition amount of H.pluvialis astaxanthin in feed.Esterfied astaxanthin were only found in epidermis.All-trans-astaxanthin was predominant in all tissues,but there were differences in the dominant cis-isomers in different tissues.In the ovary,the 15-cis was the dominant cis isomer,and the 13-cis was the dominant isomer in the carapace and epidermis.Pure?3S,3'S?-astaxanthin from H.pluvialis can stably deposit in the ovaries of crabs without epimerization,whereas in the epidermis and carapace,significant epimerization?S to R?occurred,especially in the carapace,there was a clear discrepancy with the?3S,3'S?-astaxanthin.5.Feeding trials in rainbow trout with H.pluvialis residue formula feed found that astaxanthin from H.pluvialis can replace synthetic astaxanthin as a source of coloring pigment for rainbow trout.The results showed that esterified astaxanthin from H.pluvialis was de-esterfying after absorb by rainbow trout,and the proportion of geometric isomers of astaxanthin were also changed.All-trans-astaxanthin was more likely to accumulate in rainbow trout's muscle tissue.As for cis astaxanthin,13-cis was more likely to deposit in rainbow trout than 9-cis isomer.Rainbow trout could deposit three different optical isomers in its muscles,but was more inclined to deposit?3S,3'S?-astaxanthin.The pure?3S,3'S?-astaxanthin in the H.pluvialis could steadly deposit in rainbow trout without epimerization.In summary,carotenoids and their oxidized derivatives,astaxanthin,were widely distributed in aquatic products such as algae,shrimp,crab,and fish,and could be transmitted and deposited step by step through the food chain.In this process,isomerization of astaxanthin was ocurred.and the color and nutritional quality of aquaculture animals were improved.