Study On Change Of Lipids In Marine Fish During Frying Processing And Storage

Fish are important economic animals.In 2017,China's fish production reached 360.97million tons,accounting for 56%of the total output of marine aquatic products.Studies have shown that marine fish are rich in polyunsaturated fatty acids?PUFAs?,which can change the membrane fatty acid composition and membrane fluidity,which in turn affects ion channel activity;The n-3 polyunsaturated fatty acid?n-3 PUFA?is an essential fatty acid constituting cephalin,which promotes the uptake of taurine by nerve cells and has a brain-enhancing effect.However,it is prone to oxidation during processing and storage,causing spoilage and deterioration of aquatic products,and the food and economic value are adversely affected.In this paper,the lipid profiles of five marine fishes called Hexagrammos otakii,Sebastes schlegelii,Opium fish and Raja porosa were studied.The changes in lipids and major nutrientsof lipids in Hexagrammos otakii and Sebastes schlegelii during cold storage and the changes in lipids of Deep-fried processing of Hexagrammos otakii by Palm Oil and Soybean Oil were investigated.The present study provides a theoretical basis for improving the level of ice storage and frying techniques.In this paper,Hexagrammos otakii,Sebastes schlegelii,Opium fish and Raja porosaas the research object,the total lipids were extracted by methanol-chloroform?B-D?method,and the oil contents were 2.05,2.32,7.83 and 0.49%,respectively.The lipid composition was determined by Thin layer chromatography-flame ionization detection?TLC-FID?.The analysis showed that the four marine fish oils contained triglyceride?TAG?,polar lipid?PoL?,diacylglycerol?DAG?,monoglyceride?MAG?,cholesterol?CHO?and free fatty acids?FFA?,among which TAG and PoL contents were relatively higher,and the highest TAG content of Opium fishis 91.32%and the highest PoL content of Raja porosais 86.30%of total lipids,respectively.The phospholipid composition was determined by nuclear magnetic resonance spectroscopy(³¹P NMR).The analysis showed that the four marine fish phospholipids contained phosphatidylcholine?PC?,phosphatidylethanolamine?PE?,lysophosphatidylcholine,phosphatidylinositol,phosphatidylserine,phosphatidylglycerol,and glycerophosphatidic acid.Among which,PC and PE contents were relatively higher and the mole percentages?mol%?were 37.40-68.59 and 18.47-28.41,respectively.The fatty acid composition was determined by gas chromatography-mass spectrometry?GC-MS?.The analysis showed that the four marine fish PUFA accounted for 32.99-48.26%of total fatty acids,of which C20:5?n-3??EPA?and C22:6?n-3??DHA?were the predominant PUFA due to their higher concentrations.Hexagrammos otakii and Sebastes schlegelii were storaged at 4°C,and the physicochemical indexes as well as lipid changes of the samples were measured on 0,4,8,12,16,and 20 days to reveal quality changes.The results showed that both physical and biochemical changes occurred during ice storage.After storage,moisture,protein,ash and oil content decreased.PC,PE and TAG contents of Hexagrammos otakii decreased by 59.61%,49.63%and 46.10%,respectively.The corresponding values of Sebastes schlegelii decreased by 35.44%,32.37%and 23.24%,respectively,while the content of each free fatty acid?FFA?and the activities of lipases increased,indicating the occurrence of lipid hydrolysis.The ice storage increased peroxide value?POV?,thiobarbituric acid value?TBARS?as well as lipoxygenase activities of Hexagrammos otakii increased by 122.70%,252.38%and 96.0%,respectively.The corresponding values of Sebastes schlegelii increased by 115.26%,271.62%and 110.64%,but decreased the contents of fatty acids,indicating that lipids have oxidized.According to the rate of change of the above indicators in the two fish during ice storage,Sebastes schlegelii was more prone to spoilage,being less sensitive to hydrolysis and more sensitive to oxidation compared to Hexagrammos otakii.Hexagrammos otakii were fried in palm oil and soybean oil for 3 min and 6 min,respectively,and the physicochemical indexes as well as lipid changes of the samples were measured to reveal quality changes.The results showed that physical exchange and chemical reactions occur during frying processing,resulting in water loss,oil content increased,and nutrient composition changed.After fried in palm oil and soybean oil for 6 min,the sample AV decreased by 17.90%and 27.73%,respectively.TAG content increased by 146.00%and122.51%,the occurrence of physical exchange in frying processing was further proved.After fried in palm oil for 6 min,the SFAs and MUFAs contents of the samples increased by 22.47%and 21.60%,respectively,while the PUFAs content decreased by 42.17%.The fatty acids of soybean oil fried samples showed opposite trends,and SFAs and MUFAs decreased by 27.52%and 19.81%,respectively,while PUFAs increased by 44.16%,which was positively correlated with the fatty acid composition of palm oil and soybean oil,indicating that transesterification occurred during frying.After fried for 6 min,the PC content decreased by 41.32%and42.06%,and the PE content decreased by 35.21%and 34.51%,respectively,indicating that the lipid was hydrolyzed.The POV increased by 1.04 times and 1.68 times,and TBARS increased first and then decreased during the frying process,indicating that the lipid was oxidized during the frying process.In addition,after fried,the polyene index decreased,atherogenic index and thrombus formation index increased indicates that the frying process significantly reduces the nutritional value of the Hexagrammos otakii.