Study On Changes Of Lipids And Their Control In Major Scallops From The Yellow Sea And The Bohai Sea During Aquaculture Purification And Storage

As a commercially important seafood species,scallop is a delicacy that contains various nutrinents and functional factors such as long chain omega-3 polyunsaturated fatty acids(n-3 LC-PUFA),and has high nutritional value and healthy function.The nutritional value of scallop is affected by harvest seasons.However,the study on seasonal variation of lipid components in scallop needs to be further clarified.Aquaculture purification is an indispensable step in the supply chain of shellfish,which has certain influence on nutritional quality,while researches on alteration of lipid componentsduring this process are currently limited.Scallop is rich in n-3 PUFA,and it is prone to oxidation during storage.Therefore,the control of quality deterioration of scallop during storage is crucial.In this study,the effects of the harvest season and aquaculture purification on the nutritional components of the scallops Patinopecten yessoensis and Chlamys farreri as well as the effects of different chitosan coatings on quality of scallop Chlamys farreri during refrigerated storage were measured to provide the theoretical basis for its deep processing and quality control.The live scallops Chlamys farreri and Patinopecten yessoensis with representive size were collected on February,April,June,August,October and December for measuring the contents of proximate compositon as well as lipid classes,phospholipid(PL)classes,FA composition and glycerophospholipid molecular species in order to reveal the effects of harvest seasons on the nutrient composition and lipid composition of scallops.Results showed that the contents of lipid,protein,carbohydrate and ash of the two scallops(freeze-dried samples)from different harvesting seasons were 3.80-5.09%,62.22-74.36%,6.73-13.25% and 6.09-8.62%,respectively.The nutrient compositions in adductor muscles of the two scallops were affected by different harvesting seasons.The highest and lowest contents of lipid and protein were presented in scallop samples harvested in winter and summer,respectively,whereas the polysaccharide content showed the opposite trend.Based on the results of the two scallops harvested in February,the lipids were rich in PL(84.67-85.10% of total lipid)and PUFA(58.76-59.12% of total fatty acids),especially eicosapentaenoic acid(EPA)and docosahexaenoic acid(DHA).Meanwhile,phosphocholine(PC,39.56-39.90 mol%)and phosphoethanolamine(PE,22.45-25.24 mol%)were the major phospholipid classes,while the molecular species of glycerophosphocholine(GPCho)and glycerophosphoethanolamine(GPEtn)that contain DHA and EPA accounted for about 45% and 80% of total molecular species,respectively,which indicating scallop is a dietary source of n-3 PUFA in PL form.Scallops harvested in different seasons have diverse lipid profile.From the perspective of lipid nutritional value,the samples harvested in February contained higher proportions of PL and PUFA but lower levels of cholesterol,IA and IT compared to the samples harvested in other seasons.Therefore,scallops harvested in February had better nutritional value in view of lipid.The changes of nutritional composition including lipid,protien,carbohydrate and ash contents as well as lipid profiles including lipid classes,PL classes,FA composition and glycerophospholipid molecular species of adductor muscle from scallop Patinopecten yessoensis of same harvest batch with representive size were determined during aquaculture purification in order to reveal the effects of aquaculture purification on the nutrient composition and lipid composition of scallops.Results showed that the adductor muscle of scallop Patinopecten yessoensis contained 77.60% of protein,6.84% of lipid,3.55% of carbohydrate and 17.21% of ash(percentage of dry weight)before aquaculture purification.The lipids were rich in PL(69.70% of total lipids)and PUFA(56.80% of total FAs),especially EPA(20.83% of total FAs)and DHA(32.18% of total FAs).With the extension of aquaculture purification,the lipid contents showed a slight decreasing trend and its decline rate was 5.35% after 6-day purification.The content of cholesterol(CHO)showed a decreasing trend and its decline rate was 17.83% whereas the content of PL displayed an increasing trend and the rising rate was 1.46%.The contents of PUFA,EPA and DHA all showed a slight downward trend and their decline rates were 8.42%,3.46% and 5.16%,respectively.The contents of PL molecular species containing EPA and DHA decreased slightly,but all the reduction rates were less than 9%.Taken together,industrialized aquaculture purification has little effect on the nutritional value of the scallop lipid.Effect of chitosan coating added with antioxidant of bamboo leaves(AOB)and potassium sorbate(PS)on qualities including total viable counts,total volatile basic nitrogen(TVB-N),peroxide value(POV),thiobarbituric acid reactive substance(TBARS),lipase activity as well as lipid profile including triacylglycerol(TAG),free fatty acid(FFA),PC and PE of scallop Chlamys farreri during refrigerated storage were evaluated.For the scallop samples with single chitosan coating,results showed that the total viable counts increased from 3.26 to 6.72 lg(CFU/g),the TVB-N values increased from 10.38 to 22.30 mg/100 g,lipase activity increased from 129.0 to 359.46 U/g,the POV value increased from 8.38 to 17.17 mmol/kg,the TBARS value increased from 1.16 to 2.23 mgMDA/kg,the PUFA content decreased from 7.61 to 4.04 mg/g,the TAG content decreased from 11.61 to 8.94 mg/g,the PC content decreased from 6.48 to 5.24 mg/g,the PE content decreased from 2.15 to 1.25 mg/g and the FFA content increased from 6.20 to 10.08 mg/g after 8 days’ refrigerated storage.The chitosan coating individually or combinatively added with AOB and PS can effectively inhibit the oxidation and hydrolysis of lipids and delay the deterioration of quality by inhibiting the increases of total viable counts,TVB-N,POV,TBARS and LPS activityas well as the decreases of PUFA,TAG,PC and PE.However,it showed no obvious synergistic effect with combinative ultization of AOB and PS.The present study systematically revealed the seasonal variation of nutrient compositions of scallops Patinopecten yessoensis and Chlamys farreri,illustrated the influence of aquaculture purification on nutritional quality of scallop Patinopecten yessoensis,and studied the control of deterioration of scallop Chlamys farreri during refrigerated storage by chitosan coatings with AOB and PS.This would provide the theoretical basis for deep processing,high value utilization,and quality control of scallop.