Study On The Off-flavor Compounds Character Of Sturgeon And Their Relationship With Lipid Oxidation

Sturgeon has a high economic value which fresh is rich in nutrition. But due to the unreasonable industry structure, the development and utilization of sturgeon resources are not sufficient. Off-flavor is an important factor that restricts the development of sturgeon. Therefore, this paper determines the characteristics of sturgeon off-flavor and odor compounds by SPME-GC/MS. The major flavor compounds and its correlation with quality indices during storage in sturgeon fresh are analyzed. In addition, this paper studies preliminary the source of off-flavor compounds and the oxidation of unsaturated fatty acids to provide theoretical basis for aquatic products processing and quality management. The main research content and results are as follows:(1) The volatile flavor components in different parts (ventral fresh, tergal fresh, tail fresh, gill, skin and liver) of sturgeon are detected by SPME-GC/MS. The main fishy odor components in sturgeon are short-chain linear saturated or unsaturated aldehydes from C6to C10, unsaturated alcohols (1-octen-3-ol) and ketones (2,3-octanedione); fresh sturgeon is mainly characterized by grassy, fruity and fishy odor, the earthy and metallic odor is weak. Off-flavor is strong in skin and gill.(2) The changing of quality indices and off-flavor in ventral fresh, tergal fresh and tail fresh are analyzed during freezing (-18℃) and chilling (4℃) storage. TVB-N values are increasing during chilling storage days and the fish fresh is deteriorating fast. The freezing fresh TVB-N values growth slowly. TBARS values are rising during storage. TBARS values growth faster in the last3days of chilling storage. The activity of LOX enhances at the initial stage and then weakens during chilling storage and it is weakening during the freezing experiment. Freezing storage may passivate the LOX. UFAs content is dropping during freezing and the chilling storage losses more. The grassy, fishy and rancid odor enhances while the off-flavor compounds are increasing during storage.(3) Volatile compounds contributing to the characteristic odor of sturgeon fresh in freezing and chilling storage are analyzed by principal component analysis (PCA) and the relationships of principal volatile components from PCA and quality indices are studied by correlation analysis using SPSS software. The results show that off-flavor compounds including short-chain (C6-C9) saturated and unsaturated aldehydes,1-penten-3-ol and2,3-octanedione dominate the variance of volatile compounds in sturgeon during storage which are the first PC. The off-flavor is stronger in chilling storage than freezing storage. The first PC is highly correlated with TVB-N, TBARS and UFAs. The off-flavor compounds may come from fresh spoilage and fatty acids oxidation. Compared with the chilling samples, the variance of off-flavor compounds from freezing samples has higher correlation with LOX. Fruity and planty medium-chain saturated or unsaturated aldehydes (2-undecenal and dodecanal) are the second PC. They do not have significant influence to the variance of fresh flavor during storage. TVB-N values show high correlation with PC2.(4) The sturgeon fresh is separated into several components by organic solvent: protein components, soluble components, phospholipids components and triglyceride components. Then the volatile flavor compounds derived from the fresh components are identified. The results indicate that the off-flavor compounds are produced by lipids (especially phospholipids) mainly. Alcohols are present in large quantities in the proteins samples. The samples of proteins and phospholipids contain most of ketones. The experiment modeling the UFAs oxidation catalyzed by LOX and autoxidation states that the LOX from sturgeon can catalyze the oxidation of arachidonic acid obviously. C6-C10aldehydes is the main products of the UFAs oxidation. The n-6UFAs make the most important contribution to the off-flavor compounds. Hexanal and nonanal are present at the high level in the oxidation of n-6and n-9UFAs and LOX is an important catalyst for them.2-alkenals arise from the oxidation of n-6UFAs and they are catalyzed hardly by LOX excepted for2,4-heptenal.2,4-heptadienal is aggrandized by LOX and2,4-nonadienal generated from the autoxidation of UFAs mainly. Other2,4-alkadienals is present at the low level.2,3-octanedione can be found most in the samples of n-9UFAs catalyzed by LOX. The unsaturated alcohols formed from the samples of arachidonic acid with LOX.