Mechanisms For The Formation Of Fishy Odor In Tilapia And Research On Deodorization Technology

Tilapia is recommended by FAO to breed worldwide and has a broad prospect ofdevelopment and utilization. The objection of this paper is to use tilapia as raw material tostudy the volatile compositions of different tissues, mechanism of fishy odor development anddeodorization methods, aiming to provide theoretical guidance for tilapia processing andquality management.Volatile compositions of tilapia and fishy odor development in the muscle were studied.Investigations were carried out to extract the volatile compounds in tilapia using solid phasemicroextraction (SPME). Volatile compositions of tilapia were analyzed by gaschromatography and mass spectrometry (GC-MS). A total of35,35and38volatilecomponents were identified in the muscle, head and skin of tilapia, respectively. Aldehydesand alcohols were the most dominant volatiles in tilapia, as they accounted for the largestproportion. Hexanal, heptanal, nonanal,1-octen-3-ol, E, E-2,4-nonenal were potent odorantson the basis of relative odor activity values (ROAVs). Within these, nonanal, octanal andE-octenal were the most powerful contributors to the fishy odor of Tilapia，along with hexanaland1-octen-3-ol.Lipid oxidation in tilapia muscle during storage was monitored by measuring CD(conjected diene), PV (peroxide value), and TBARS (thiobarbituric acid reactive substances)values. The increase in CD was observed in tilapia muscle up to12days of iced storage. Theincrease in PV was noticeable within the first3days of iced storage. After3days of icedstorage, a gradual decrease in PV was found in tilapia muscle. Slight decreases in PV duringstorage suggested that hydrogen peroxide generated by fatty acid oxidation degradated intosecondary products, such as low molecular alcohols, aldehydes. A continuous increase ofTBARS in tilapia muscle was observed throughout the iced storage of12days. Increases inTBARS formation indicated that lipid oxidation became more pronounced as storage timeincreased, which contributed to the deterioration and unacceptability of tilapia. Lipidhydrolysis occurred in tilapia muscle during iced storage. FFA (free fatty acid) content intilapia muscle increased as the storage time increased. At the end of storage period, lipidhydrolysis occurred to a great extent as evidenced by the highest FFA content obtained inmuscle. After9d, increase of TVBN (total volatile basic nitrogen) values showed thatmicrobial spoilage have occured in fish. Sensory evaluation scores and TBARS valuesshowed good correlations, which can be presumed that the development of off-odor in tilapiamuscle during12days of iced storage were mainly attributed to lipid oxidation. Research on deodorization methods for tilapia muscle was carried out respectively usingphysical method (embedding by β-CD and absorption by active carbon), chemical method(using citric acid and CaCl2to extract and dissolve fishy odorants) and biological method(yeast fermentation, dried yeast alcohol dehydrogenase extract, commercial alcoholdehydrogenase). One factor experiments and orthogonal tests were carried out to determinethe optimum deodorization conditions of each method. Considering TBARS values andsensory evaluation results, dried yeast alcohol dehydrogenase extract, commercial alcoholdehydrogenase could effectively lower the level of fishy odor intensity and TBARS valus offish, further indicating that the key fishy odorants of tilapia muscle were composed by lowmolecular alcohol and aldehyde. On the basis of single deodorization method, results of dualcombination of different methods showed that CaCl2-citric acid combined with eachbiological method had better deodorization effect than other combination.