| Bighead carp(Aristichthys nobilis) is one of important species of freshwater fish in China because of its large output, low prices, and rich nutritional value. Currently, the research foundation of nutritional properties, quality variation and quality control of bighead carp is weak. The present thesis investigated seasonal variations of fatty acid profile in different tissues of bighead carp and compared fatty acid profile of muscle, brain and eyes of seven freshwater fish; determined the quality changes of bighead carp at different temperature storages; established quality predictive models for bighead carp; applicated the general stability index (GSI) method to predict quality deterioration in bighead carp heads during storage at different temperatures; evaluated the effects of low concentration of salt and sucrose on the quality of bighead carp fillets stored at4℃and the effects of different freezing treatments on the biogenic amine and quality changes of bighead carp heads during ice storage. The results show as follows:(1) The fatty acid composition of farmed bighead carp varied significantly with seasons and tissues. Significantly higher SEPA+DHA (%) was recorded in all tissues in summer (June) when compared with those of the other three seasons (p<0.05). the fatty acid composition of the filter-feeder fish (silver carp and bighead carp) was distinct from the other five species. The percentage of DHA+EPA is higher in the muscle of seven freshwater fish than the eyes and brain.(2) Sensory quality exceeded the acceptability limit with the score of18on the10th day of storage at4℃while it get little odorous scent with the score of15on the35th day of storage at-3℃. pH value reach the minimum,6.81and6.76after4days at4℃and10days at-3℃, respectively. Drip loss was2.80%after8days at4℃and5.18%after10days at-3℃. Cooking loss at-3℃exceed the values at4℃after4days. After being stored for35days at-3℃, the value of TVB-N reached13.52%mg/100g, and the value of4℃on the8th day was18.96mg/100g, both belong to the secondary freshness limit. TBA values of bighead carp were0.61mg/kg and0.78mg/kg on the8th day at4℃and on the35th day at-3℃, respectively. They are still within the limit value of2.00mg/kg. The K value were64.51%and74.37%at35th day at-3℃and at8th days at4℃, respectively. The results indicated that the shelf life is8days and35days at4℃and-3℃, respectively. Storage of-3℃can extend the shelf life markedly compared to4℃. However, as ice crystals grew, both of drip loss and cooking loss were larger at-3℃than those at4℃.(3) Quality predictive models of bighead carp fillets based on sensory score, K value, TVB-N and TACs are B Sensory score=B Sensory scoreO-1.16X1015t exp (-78173.65/RT), BK value=BK valueO+1.36X1015t exp (-76212.28/RT), BTVB-N=BTVB-NO+2.60X1014t exp (-75925.44/RT) and BTAc=BTAcO+4.05X1019t exp (-106532.40/RT), respectively.(4) The established model based on GSI is GSI=1-1.14×1015t exp (-85613.38/RT) and it could effectively predict the freshness of bighead carp heads.(5) No significant differences were observed between T1and T2for sensory score and EC (p>0.05). Brining treatments predominantly decreased chemical changes, reflected in TVB-N and pH, retarded water loss and discolor-ation, inhibited bacterial growth and increased the overall sensory quality of fish, compared to untreated fillets.(6) No significant differences were observed among Tl(-40℃for3month), T2(-40℃for12hours then-18℃3month) and T3(-18℃for3month) for drip loss, cooking loss and EC (p>0.05). T2showed lower TACs, pH value, TBA and TVB-N than T3did. Significant lower value of spermine and spermidine were observed in T1, T2and T3than those of control group (fresh) from9th to18th day (p <0.05). Drip loss was significantly correlated with TBA, pH value, TVB-N, and TACs in groups Tl, T2and T3(p<0.05). |
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