Study On EPA And DHA Enrichment Processes In Sardine Oil

Sardine is a pelagic fish in offshore warm water.It has high oil content and is rich in polyunsaturated fatty acid(PUFA),especially eicosapentaenoic acid(EPA)and docosahexaenoic acid(DHA),so it has great economic value as raw materials for the production of fish oil products.However,the EPA and DHA content of sardine oil without enrichment and purification can not meet the market demand.Therefore,the EPA and DHA enrichment processes of sardine oil were studied,and the impacts on fatty acid composition and volatile components of the obtained fish oil samples were analyzed,which were of great significance for the production of high-content EPA and DHA sardine oil products and meeting market demand.Based on the analysis of the raw material,the refined sardine oil was used to be converted into ethyl ester type,and then enriched with EPA and DHA in ethyl ester oil by urea complexation.The analysis of fatty acid composition and volatile component of the fish oil samples treated by these two processes was respectively carried out.Finally,on the basis of ethyl esterification and urea complexation processes,EPA and DHA were further enriched by molecular distillation,and the quality of molecular distillation oil was analyzed by physicochemical indexes,fatty acid composition and volatile components.The main findings are as follows:The quality of the raw material,ie,refined sardine oil,was analyzed by measuring physicochemical indexes,fatty acid composition and volatile components,and using relative odor activity value(ROAV).The results showed that the acid value,peroxide value and iodine value of refined sardine oil reached the standard of refined fish oil specified in fish oil industry standard SC/T 3502-2016.The distribution of fatty acids in refined sardine oil ranged from C12 to C22,and the relative content of PUFA accounted for 26.66%,of which the total amount of EPA and DHA was 23.41%.It could be seen that refined sardine oil could be used as raw material for producing high-content EPA and DHA fish oil products.A total of 35 volatile components in refined sardine oil were identified by headspace solid phase microextraction-gas chromatography-mass spectrometry(HS-SPME-GC-MS).The main flavor components determined by the ROAV method were nonanal,hexanal,undecanal,2-nonanone,and ethylbenzene,so that the fish oil exhibited a fatty taste,a fishy smell,a fragrance,and the like.The ethyl esterification process of refined sardine oil was studied by alkali catalysis.The effects of anhydrous ethanol dosage,NaOH dosage,reaction time and reaction temperature on the yield of ethyl ester were investigated.Fatty acid composition and volatile components of the ethyl ester oil obtained under the optimal process conditions were analyzed.The results were as follows:The optimum ethyl esterification process parameters were determined by response surface methodology,which were anhydrous ethanol dosage 60 g,NaOH dosage 1.2 g,reaction time 75 min and reaction temperature 50 ?,and through three times parallel test,average yield of ethyl ester reached 88.12%.15 kinds of fatty acids were detected in the ethyl ester oil obtained by the optimum ethyl esterification process.The total content of saturated fatty acids(SFA)was the highest,reaching 37.42%,mainly palmitic acid and myristic acid;the total content of EPA and DHA was 25.25%,accounting for 82.44%of PUFA.A total of 41 volatile components were identified in ethyl ester oil,and the content of esters was the highest.The content of tetradecanoic acid,ethyl ester reached 31.98%,which was the highest volatile component and showed a certain oily smell.Therefore,the optimum ethyl esterification process obtained by the single factor and response surface optimization experiments could effectively convert the refined sardine oil into ethyl ester type,which laid a foundation for the enrichment and purification of EPA and DHA.Enrichment of EPA and DHA in ethyl ester oil was carried by urea complexation process.The effects of urea-to-ester ratio,inclusion temperature,alcohol-to-urea ratio and inclusion time on the relative content of EPA and DHA were investigated.The impacts of the optimal urea complexation process on the fatty acid composition and volatile components of fish oil were analyzed.The results were as follows:The optimal process parameters were obtained by response surface method,which were urer-to-ester ratio 3.5:1,inclusion temperature 0 ?,alcohol-to-urea ratio 2.6:1,inclusion time 1.2 h.In the urea complexation oil obtained under the optimal process conditions,the total content of EPA and DHA reached 78.12%,and the content of SFA and Monounsaturated fatty acid(MUFA)was significantly lower than that of ethyl ester oil.A total of 33 volatile components were detected in the urea complexation oil,among which the content of hexadecanoic acid,ethyl ester was the highest,occupying 27.31%,and the volatile components exerting important influence on the flavor formation of urea complexation oil were mainly aldehydes,which accounted for 6.49%.Therefore,the optimal urea complexation process obtained by the single factor and response surface optimization experiments could greatly increase the EPA and DHA contents in fish oil.The refined sardine oil was treated by ethyl esterification and urea complexation process,and then subjected to molecular distillation to obtain a final fish oil product.The quality of molecular distillation oil was analyzed by measuring the physicochemical indexes,fatty acid composition and volatile components and combining ROAV method.The results showed that the peroxide value,acid value and iodine value of the molecular distillation oil reached the first-grade refined fish oil standard specified in the fish oil industry standard SC/T 3502-2016.5 kinds of fatty acids were detected in molecular distillation oil,namely oleic acid,eicosenoic acid,docosapentaenoic acid,EPA and DHA.The total content of EPA and DHA was 88.90%,which was 65.49%higher than that of raw oil.33 kinds of volatile components were identified in molecular distillation oil,among which the content of esters was still the highest;the main flavor components of molecular distillation oil were determined by ROAV method,which were hexanal,(Z)-3-hexenal,octanal,(E,E)-2,4-heptadienal,hexanoic acid,ethyl ester,heptanoic acid,ethyl ester,2-pentyl-furan,octanoic acid,ethyl ester,so that the fish oil presented a certain fishy smell,grassy taste,scorch aroma,fatty taste,fruity,sweet wine,green bean flavor,etc.Therefore,molecular distillation could further increase the EPA and DHA contents in sardine oil,so that the quality of the final fish oil products met market requirements.