Effects of Cooking Methods on Lipids and Volatile Substances in Penaeus vannamei

In order to explore the mechanism of flavor differences, the effect of two cooking methods, namely steaming and microwaving on the lipid composition, the degree of lipid oxidation and hydrolysis, and volatile substances in Penaeus vannamei was studied. The results showed that the contents of total lipids as well as phospholipids, triglycerides, and free fatty acids in P. vannamei were significantly reduced after cooking (P < 0.05). The lipid composition differed between steamed and microwaved shrimp. Microwaved shrimp had higher phospholipid contents but lower free fatty acid contents than the steamed one. The content of saturated fatty acids decreased markedly whereas the content of unsaturated fatty acids increased significantly after cooking (P < 0.05), which may be related to the hydrolysis of phospholipids. Steaming and microwave heating accelerated the oxidation and hydrolysis of lipids, resulting in a significant increase in acid value and thiobarbituric acid reactive substances (TBARS) value (P < 0.05). The results of electronic nose analysis showed that the odor characteristics of fresh, steamed and microwaved shrimp were significantly different, and the odor of fresh shrimp changed more after microwave heating. Twenty-five volatile substances were isolated and identified from shrimp meat using gas chromatography-ion mobility spectrometry (GC-IMS). Among these compounds, 2,3-glutaraldehyde, 2-butanone, 2-methyl butyraldehyde, hexanal, 1-octen-3-one and glutaraldehyde were the major flavor substances in cooked shrimp meat and their contents were higher in the microwaved sample. Pearson correlation analysis showed that oxidative hydrolysis of lipids made an essential contribution to the flavor formation of cooked shrimp and the free fatty acids C_14:0, C_15:0, C_16:1, C_18:1n9c, C_18:2n6c and C_18:3n3 were closely related to the formation of the characteristic odors of shrimp meat.