Studies On Tdentify, Analysis And Removal Technologies Of Off-Odors In Silver Carp

Silver carp(Hypophthalmichthys molitrix)is widely raised in China, due to its quick growth and resistance to stress, diseases, and the annual production reached 5 million tons in 2009. However, the development of silver carp surimi is limited due to its fishy off-odors. The main content of the present study include the detection of off-odors in silver carp,the formation mechanism of off-odors and the methods of deodorization. The main research content are following:1.The optimized conditions of solid phase micro-extraction(SPME) for volatiles in silver carp were:divinyl benzene/Carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fiber, extration time 50min, extraction temperature 60℃,the ratios of saturated salt water and fish 7:3,desorption time 5min. The results showed that the methods of SPME were effective in extracting volatiles in Silver carp.The volatiles of silver carp mince were detected by simultaneous distillation extraction and gas chromatography mass chromatography (SDE-GC-MS).The results showed that hexane extraction is better than dichloromethane extraction, and the column of 60m DB-5MS for separation and detection for off-odors was better than the column of 30m DB-5MS's.2.The extraction effect for larger molecular weight substances of SDE was better than the extraction effect of SPME, and the method of SPME is suitable for extraction of some small molecules, especially aldehydes and alcohols.The off-odors in silver carp mince were extracted using SPME combined with SDE and detected by gas chromatography-mass chromatography, and the effect were better than SPME's or SDE's alone.3.The off-odor compounds in silver carp were detected using SPME and GC-MS. The types of volatiles in the gills were more than other tissues and the number of off-door compounds was 52,and the number of volatiles in scales, viscera and mince was 40,35 and 33 respectively. The main off-odor compouds in silver carp were hexanal, benzaldehyde, 1-octen-3-ol,octanal, nonanal and 2,4-decadienal.The main reaction products of arachidonic acid and lipoxidase were analyzed by GC-MS,and the main reaction products were hexanal, 1-octen-3-ol,2-octenal,2-nonenal and 2,4-decadienal. These compouds were the main off-odors compouds, and the enzyme avtivity of gill was stronger than other tissues in silver carp.4. The internal standard analysis of Gsm and 2-Mib in water and zebrafish was established. The recovery of Gsm and 2-Mib in water were 97.2%±1.4%-109.9%±4.2% and 88.5%±7.5%-101.6%±1.3% respectively, and the recovery of Gsm and 2-Mib in zebrafish were 78.5%±3.8%-87.2%±1.7% and 88.3%±2.3%-91.4%±5.3% respectively. The concentrations of Gsm-and 2-Mib in east lake were determined using the above method, and the concentration range of Gsm and 2-Mib in east lake were 1.67 ng/L-5.37 ng/L and 15.26 ng/L-29.68 ng/L respectively. The enrichment and resolve of Gsm and 2-Mib were studyed, when the zebrafish was exposed in the presence of Gsm and 2-Mib in water, Gsm and 2-Mib rapidly enriched to zebrafish. The higher of concentration of Gsm and 2-Mib in water, the higher of concentration of Gsm and 2-Mib in zebrafish. The concentration of Gsm-2-Mib in zebrafish were slower decreased with shimizu on storage time.The results showed that the off-odor substances in environment breathe into fish by gill and skin and accumulate in fish leading to strong off-odors in fish.5.The production mechanism of off-odor compounds have intenal and external causes.The formation mechanism of off-odors in fish were fish's own endogenous enzyme degradated the unsaturated fatty acids producing odor compounds.The off-odor substances in environment breathe into fish by gill and skin and accumulation in fish. These forms lead to strong off-odor in fish and affect the development of silver carp in industry.6.The better treatment deodorization conditions were identified in single factor and orthogonal test. The optimum deodorization conditions of activated carbon were: absorption temperature 60℃,absorption time 30min and the amount of activated carbon 1.5%.The optimum deodorization conditions of yeast were:fermentation temperature 40℃,fermentation time 60min and addition of yeast 1.0%.The optimum deodorization conditions of tea polyphenol were:reaction temperature 20℃,reaction time 50min and addition of tea polyphenol 1.0g/kg. The optimum deodorization cond-itions of ginger and cooking wine were reaction tempera-ture 40℃,reaction time 40 min and addition of ginger and cooking wine 2.5%.The effect of deodorization was evaluated by sensory evaluation and GC-MS and electronic nose,and the results of deodorization were satisfactory.7.Various methods of deodorization were combinated. The results showed that the combination of ginger and cooking and tea polyphenol were best, and the results of sensory evaluation are consistent with the results of GC-MS and electronic nose.The nutrition and health indicators were in line with national standards.