Study On The Optimization Of Degreasing And Deodorizing Technology And The Flavors Of Pseudosciaena Crocea

Pseudosciaena crocea as a kind of marine fish has been farmed widely in China, but compared with wild Pseudosciaena crocea, there generally exist the problems of high fat content and strong fishy smell. So the degreasing and deodorizing technology of cultured Pseudosciaena crocea was the premise of its deep processing. This paper presented the optimized degreasing and deodorizing technology and then analyzed the key odor compounds and taste components changes of cultured Pseudosciaena crocea in the process.The confirmation of key odor compounds of cultured Pseudosciaena crocea. Volatile compounds from Pseudosciaena crocea were extracted and identified by headspace solid phase micro-extraction(HS-SPME) and gas chromatography-mass spectrometry(GC-MS). The relative odor activity value(ROAV) in association with odor threshold was applied to confirm the key odor compounds. The results indicated that the key odor compounds(ROAV≥1) of Pseudosciaena crocea were composed of Nonanal, Octanal, Trimethylamine, (E)-2-Octenal, Hexanal, Ethyl valerate, Heptanal, (Z)-4-Heptenal, (E, E)-2,4-Heptadienal, 1-Octen-3-ol, (E)-2-Hexenal, Decanal, Pentanal,3-Hexen-1-ol and 2-Pentylfuran. As a result of these compounds, cultured Pseudosciaena crocea presented the odor characteristic of lipid flavor, grass smell, fishy smell, earthy taste, fruity flavor and greasy flavor.The optimization of the degreasing technology. In consideration of the factors such as degreasing effect, cost, meat quality and taste during the degreasing process, the temperature was controlled at 25℃, pH of 9.4, the proportion of fish and water of 1:3. Through the response surface method, the suggested parameters for compound salt and alkaline lipase degreasing technology were the content of alkaline lipase 39.50 U/mL, the ratio of 0.27% NaHCO3/1.0% NaCl, degreasing time 67.62 min, and the degreasing rate was 40.32%. In addition, results showed that the intervention of ultrasonic can shorten the defatting time and improve the defatting rate, when ultrasonic power and time were 140 W and 45 min, the degreasing rate can be 49.13%.The protein loss rate was 21.46% when defatted by compound salt and alkaline lipase assisted with ultrasonic, comparing with 22.07% when defatted by compound salt and alkaline lipase only. The intervention of ultrasonic helped more saturated fatty acids(SFA) and polyunsaturated fatty acid(PUFA) being removed in the defatting process. GMP,IMP,Glu were of high TAVs greater than 1 before and after the degreasing process, which meant they had strong taste impacts on Pseudosciaena crocea. As the TAVs of AMP and Asp were lower than 1, they were likely to have insignificant contribution to the taste of Pseudosciaena crocea. The EUC was 7.19g MSG/l00g which meant the umami taste of Pseudosciaena crocea was very intense. In the process of defatting, before and after the intervention of ultrasonic the EUC was reducing to 4.48g MSG/l00g and 3.81g MSG/l00g respectively. The umami intensity of Pseudosciaena crocea was decreased after defatting but the variation between them was not significant. So the assist of ultrasonic was of great help to the degreasing of Pseudosciaena crocea.The changes of the key odor compounds of cultured Pseudosciaena crocea during the degreasing and deodorizing process. The intervention of ultrasonic during the defatting process had certain effect on reducing fishy smell. But Trimethylamine and (E, E)-2,4-Heptadienal which had important contribution to fishy smell can't be removed effectively. The organoleptic quality of Pseudosciaena crocea made different treatments for taking off fishy smell was judged synthetically with the method of the fuzzy mathematics, the result showed that the perilla juice was the best, followed by Oolong tea, ginger juice, Longjing tea and balck tea. The variation of the key odor compounds of Pseudosciaena crocea was detected by SPME-GC-MS. The result also showed that the perilla juice was the best deodorization method by comparing the peak area decreasing percentage of Trimethylamine, Heptanal, (Z)-4-Heptenal and (E, E)-2,4-Heptadienal which had relatively greater contribution to fishy flavor. The perilla juice had better effect on removing Trimethylamine, (Z)-4-Heptenal, (E)-2-Octenal, (E,E)-2,4-Heptadienal, Heptanal, Pentanal and 3-Hexen-l-ol.