Change And Its Control Of Lipids In Oyster(Crassostrea Talienwhanensis) During Hot Air Drying Process

Oyster,as a commercially important seafood species,the output of oysters in China reached 4.88 million tons in 2017,occupying the highest level of shellfish products.Studies have shown that oyster is a delicacy that contains various nutritional and functional factors such as polyunsaturated fatty acids in phospholipid mode(PL-PUFA),and has high nutritional value and healthy function.The nutritional value of oyster is affected by harvest seasons.However,the study on seasonal variation of lipid components in oyster needs to be further clarified.Drying is one of the main process modes to prolong the shelf-life of shellfish,which has certain influence on its nutritional quality,while researches on alteration of lipid components during this process are currently limited.Oyster is rich in n-3 PUFA,and it is prone to oxidation during drying process and lead to deterioration of dry products quality.Therefore,the control of quality deterioration of oyster during drying process is crucial.In this paper,the effects of the harvest season on the nutritional components and lipid profile of the oyster(Crassostrea talienwhanensis)as well as the change rules and control methods of lipids of oyster during hot air drying process were analyzed to provide the theoretical basis for its deep processing and quality control.The live oyster(Crassostrea talienwhanensis)was collected on February,April,June,August,October and December for measuring the contents of protein,fat,total carbohydrate,ash as well as lipid classes,phospholipid(PL)classes,fatty acid(FA)composition and glycerophospholipid molecular species to reveal the effects of harvest seasons on the nutritional composition and lipid composition of oyster.Results showed that the contents of protein,fat,total carbohydrate and ash of oyster from different harvesting seasons were37.42%-60.04%,9.48-13.98%,5.95-20.84%and 8.57-13.06%,respectively.The highest and lowest contents of lipid and total carbohydrate occurred in oyster samples harvested in winter and summer,respectively.For oyster harvested in different seasons,triglyceride(TAG)and polar lipid(PoL)were the majority of the total lipids,which accounted for 39.56-84.49%and11.46-52.12%of the total lipids,respectively.Phosphatidylcholine(PC,43.89-50.26 mol%)and phosphatidylethanolamine(PE,36.77-43.13 mol%)were the major phospholipid classes.The lipids of oyster were rich in PUFA(39.04-48.77%of total fatty acids),especially C20:5(n-3)(EPA)and C22:6(n-3)(DHA).Direct injection electrospray tandem mass spectrometry(ESI-MS/MS)was used to determine the molecular species of glycerophospholipid(GP)including glycerophosphocholine(GPCho),glycerophosphoethanolamine(GPEtn),lycerophosphoserine(GPSer)and glycerophosphoinositol(GPIns)in the lipid of oyster.More than 270 molecular species were deduced.The main molecular species were rich in DHA and EPA,indicating that oyster is an important dietary source of PL-n-3 PUFA.Oysters harvested in different seasons have diverse lipid profile.Among which,the samples harvested in February contained higher levels of PUFA(48.77%of total fatty acids)and PoL(52.12%of total lipids)and lower level of atherogenic index(IA,0.29),and the molecular species of GPCho that contain EPA and DHA accounted for 75.24%of total molecular species.Therefore,oyster Crassostrea talienwhanensis harvested in February had better nutritional value in view of lipid.After boiling for 15 minutes,Crassostrea talienwhanensis were processed by hot air drying at 70? and 90?,respectively.The changes of moisture contents,peroxide value(POV),thiobarbituric acid value(TBARS)as well as lipid profiles including lipid classes,fatty acid(FA)composition as well as the contents of TAG,free fatty acid(FFA),PC and PE were determined during drying process to reveal the effects of drying process on the lipid composition of Crassostrea talienwhanensis.Results showed that the contents of lipids,TAG,FFA,PC and PE of fresh Crassostrea talienwhanensis were 12.03%,32.76 mg/g,7.49 mg/g,4.20 mg/g and 4.21 mg/g,respectively.POV and TBARS values of fresh Crassostrea talienwhanensis were 0.43 g/100g and 8.82 mg MDAeq/kg,respectively.The lipids of fresh Crassostrea talienwhanensis were rich in PUFA(49.67%of total fatty acids).After boiling for15 min,the contents of TAG,PC,PE and PUFA were decreased to 29.45 mg/g,2.62 mg/g,1.86 mg/g and 47.19%,respectively,while POV,TBARS and FFA contents were increased to0.50 g/100g,9.74 mg MDAeq/kg and 14.52 mg/g,respectively.After drying process,the contents of FFA and saturated fatty acid(SFA)were increased,while the contents of TAG,PC,PE and PUFA were decreased,and there was a positive correlation between drying temperature and the increase of FFA and SFA as well as the decrease of TAG and PUFA.The above results showed that the lipids of oyster were hydrolyzed and oxidized during drying process,so drying process can influence the nutritional value of the oyster lipid.Crassostrea talienwhanensis was treated with water,gallic acid and propylgallate after boiling for 15 min,and then were processed by hot-air drying at 55 ~oC.The changes of moisture content,POV,TBARS and lipid profiles including FA composition as well as the contents of TAG,FFA,PC and PE were determined,respectively,after 0,5,10,15 and 20 h of drying process to reveal the effects of different antioxidants on lipids of Crassostrea talienwhanensis during drying process.Results showed that the contents of PC,PE and TAG of the blank control group were decreased by 48.50%,57.67%,76.31%,respectively,while the TBARS value and FFA content of the blank control group were increased by 82.81%and50.31%,respectively,after drying process.This indicates that the oyster lipids had been oxidized and hydrolyzed during drying process.The POV,TBARS and FFA content of the antioxidant treated groups were lower than those of the blank control group,while the contents of PC,PE and TAG of the antioxidant treated groups were higher than those of the blank control group.The above results indicated that gallic acid and propylgallate could inhibit the oxidation of lipids during the drying process of Crassostrea talienwhanensis,and the inhibitory effect of propylgallate was more impressive.The present study systematically revealed the seasonal variation of nutrient compositions as well as the influence of drying process on lipid profiles of Crassostrea talienwhanensis,and studied the control of quality deterioration of Crassostrea talienwhanensi during drying process by antioxidants.This would provide the theoretical basis for deep processing and quality control of oyster.