| Pacific oyster(Crassostrea gigas)is an important economic shellfish in China.Especially in the coastal areas of shandong province,there has been a trend of oyster specialization,branding and integration,the nutritional and flavor quality of oysters has also attracted more and more attention from the public.Based on this background,this study took C.gigas populations in different regions of shandong province as research samples to explore the nutrition,flavor and feeding habits of C.gigas.The main research results are as follows:1.Composition of eukaryotes in C.gigas and correlation analysis with environmental factorsTo understand the characteristics of eukaryotic plankton community in mariculture of two sides of Shandong Peninsula,two representative locations were selected in the Kongtong Dao(KTD)area in Yantai of the northern Shandong peninsula,and the Donggang(DG)area in Rizhao of the southern Shandong peninsula.High-throughput sequencing technologies with 18 S rDNA V4 area as the target gene were used to study the diversity of eukaryotic phytoplankton in the two areas.Meanwhile,environmental factors(dissolved oxygen,ammonia nitrogen content,and other 10 physical and chemical indicators)were measured and correlated with the eukaryotic plankton data.A total of 455 species of plankton were identified,of which424 species in 36 categories were from KTD area,and 365 species in 34 categories from DG area.Chlorophyta and Diatomea were the most abundant phyla of phytoplankton in the two areas.In the KTD area,the monthly abundance of Chlorophyta was between3.0% and 21.3%,and that of Diatomea between 2.0% and 16.59%.In the DG area,the monthly abundance of Chlorophyta was between 2.0% and 12.3%,and that of Diatomea ranged from 2.0% to 47.0%.In addition,the dominant zooplankton species were arthropod in monthly abundance ranging from 6.0% to 38.9% and 7.6% to 48.6% in the two areas,respectively.Correlation analysis of environmental factors showed that water temperature,DO,pH value,silicate,nitrate,and other environmental factors were the main factors shaping the structure of the plankton community in the sea.This study may help understand the composition of bait for bivalve in KTD and DG aquaculture areas and its spatial and temporal variation,and could provide data support to coastal food network,ecological basic management,and shellfish aquaculture production.2.Nutritional quality analysis of different strains of C.gigas(1)The nutritional quality of several new Pacific oyster lines cultured in the sea areas of KTD and DG was tested.The gonad growth period of the Pacific oysters in March was investigated as follows: Luyi No.1 new line The(LY)and Rizhao population new lines(RZ)had higher glycogen content than other strains.Qingdao group new line(QD)total protein content was significantly higher than other strains.LY new line and control group(Control,C)total fat content was higher than other lines.Comparing the nutrient composition of the same line of oysters cultured in two sea areas of KTD and DG,it was found that the total protein content of Pacific oyster cultured in KTD sea area was higher than that of Pacific oyster cultured in DG sea area,while the Pacific oyster glycogen content and total fat content DG sea area were higher than KTD seaarea.Male-female differences: The comparison of nutrient composition between male and female individuals in the breeding period of May showed that the protein and glycogen content of male Pacific oysters was significantly higher than that of females;the female oysters had higher fat content than males.(2)Determination of fatty acid content in fresh Pacific oyster,and comparing the differences in fatty acid content of different cultivars of Pacific oyster: SFA content of RZ group and LY new line was significantly higher than other groups;QD population,Pacific oyster LY new line,Pacific oyster RZ group new line was higher than other strains,but the difference of EPA and DHA between different strains There was no obvious low;New oyster LY strain,control group,RZ group new line was higher than other strains.Comparing the fatty acid content of the same line of Pacific oyster cultured in two sea areas of KTD and DG,it was found that the SFA content of each line was generally higher than that of DG sea area.The content of unsaturated fatty acids(especially PUFA)in the same cultivars of the oysters cultured in the two seas was more significant.The difference between EPA and DHA,two different types of polyunsaturated fatty acids,was also significant.It was generally higher than the DG in the KTD.The characteristics of the sea.Male-female differences: SFA and MUFA content showed that the females of Pacific oyster were significantly higher than males,and the overall PUFA content showed the high male oysters.Fatty acid content after cooking: The oysters cultured in the seas of KTD and DG were basically the same before and after cooking.The Pacific oyster decreased in the content of SFA,MUFA and PUFA in March and July,and SFA in May.MUFA and PUFA content were all increased.After the cooking,the total amount of fatty acids decreased in March,and the changes in May and July were irregular.3.Analysis of the correlation between the determination and comparison of the flavor components of oyster and the composition of the diet(1)The content of taste components of fresh oysters in several new lines of KTD and DG were measured and the taste intensity value(TAV)was measured.The results showed that the content of main odorants in different oysters was in different strains and different culture areas.There are significant differences between different growing seasons;and in the unearthed samples of Pacific oysters cultured in the seas of the two places in March 2018,the glutamic acid and alanine taste intensity values are greater than 1,which is considered to be important for the Pacific oyster flavor.contribution.The content of the main taste nucleotides in the uncooked Pacific oyster samples was higher,and the TAV values were all greater than 1.It is believed that the three nucleotides of AMP,IMP and GMP make a significant contribution to the flavor of the Pacific oyster.(2)Analysis of the taste amino acid and nucleotide data of the cooked Pacific oysters.The results showed that the change of the content of each flavoring substance before and after cooking had a great influence on the taste of Pacific oysters.: After cooking,the amino acid content showed a general downward trend,and methionine was not detected after cooking.The amino acid taste intensity value decreased after cooking.In May,only the glutamic acid had a TAV value greater than 1,and the Pacific oysters of March and July had a TAV value of less than 1 after cooking.Comparing the nucleotide content and TAV value after cooking,it was found that the content of GMP,AMP and TAV of each cultivar increased after cooking,but the content of IMP and taste intensity decreased after cooking.(3)Spearman correlation analysis was carried out between eukaryotic planktondiversity data obtained by high throughput sequencing and oyster taste data(flavor amino acids and flavor nucleotides).Most flavor components were positively correlated with Streptophyllum,Cyclochaete,Noctiluca,Navigating Algae,Heterocapsa,Nudiflora,Telonema,Duboscquella and Ebria of the dinoflagellate phylum,and negatively correlated with Micrococcus,Microcystis,Flagellates,Symalgae.4.Determination and comparative analysis of odor components of Pacific oysterIn this study,the odor component of Pacific oyster was quickly determined by GC-IMS,and the difference of odor components before and after cooking was compared according to the fingerprint.64 odor components including alcohol,aldehyde,ketone,acid,ester,phenol,sulfur,etc.were determined,and the percentage difference of odor composition among multiple samples was analyzed.details as follows:(1)A comparison between the DG sea lines showed that the percentage of the odor components of the LY new line,1,2,4-trimethylbenzene and 3-pentanone,was 2.2and 3.2 times higher than that of the control group of the Pacific oyster in the March sample.The percentage of 1-heptanol,2,3-pentanedione and 3-penten-2-one in the component can reach 1.7 times that of the new LY strain;the LY new strain odor component 1-pentanol in the sample in May The percentage of isopropanol and trans,cis-2,6-nonadienal was 1.7 times higher than that of the Pacific oyster control group;the percentage of 3-pentanone in the odor component of the new LY oyster samples in July was up to Pacific oyster In the control group,2.5 times,the percentage of 1-octene-3-ol and(E)-2-octenal in the odor component of the Pacific oyster control group was 1.8 and1.7 times higher than that of the new Pacific oyster LY strain,respectively.Comparing the KTD sea line strains,it is found that the large difference in the percentage of odor components is mainly concentrated in the new LY oyster line and the control group in March 2018,and the ethyl acrylate and ethyl acetate in the odor component of the new LY line.The percentage of ester and 2,3-octanedione was 1.5-2.4 times that of the control group.(2)Comparing the new LY lines in DG and KTD sea areas,it is found that the percentage of heptaldehyde and hexanal in the odor component of the new LY sample in the DG sea area can reach 4.7,3.9 times of the KTD sea area,benzaldehyde and1-pentyl.The percentage of alcohol can reach 3 times that of KTD sea area.In the same period,the percentage of 3-methylbutyraldehyde in the new LY line of KTD sea area can reach 2 times of that in DG sea area;in the DG sea area,the odor component of LY new line sample in May is 3-e.The percentage of alken-2-one,2-hexenal,trans,cis-2,6-nonadienal and 2-hexen-1-ol acetate can reach 2-3 times that of KTD sea area,and KTD in the same period The percentage of ethanol in the new LY line of the sea can reach 4.2 times that of the DG sea area,the percentage of heptaldehyde can reach 2.7times of the DG sea area,and the percentage of 2-butanone,1-propanol and hexanal can reach 2.2 times that of the DG sea area.The percentage of 1-pentanol in the odor component of the LY new line sample in the DG sea area in July reached 2.5 times that of the KTD sea area,and the percentage of 2-hexenal in the new LY line of the KTD sea area reached 3.9 times that of the DG sea area.(3)The Pacific oyster cooked flavor substances exist obvious difference before and after,after cooked oysters emit more flavor substances,such as E,Z-2,6-nonyl diene aldehyde,2-phenyl ethanol,guaiacol,cyclohexanone,methyl sulfonium propionic aldehyde,benzene acetaldehy de,caprylic aldehyde,1-2-hexene-alcohol,2-nonyl ketone ketone,2-butanone,1-octene-3-alcohol,1-octene-3,3-methyl butyric acid,heptyl aldehyde ketone substances such as concentration increased;In addition,theconcentration of some substances decreased significantly after cooking,such as1-pentanol,2,3-pentanedione,2-propanol,dimethyl disulfide and so on.In cooked crassostrea gigas,alcohols,ketones,benzenes,acids and sulfurs were generally decreased,while aldehydes,esters,olefins and phenols were significantly increased. |
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