Modeling of total volatile basic nitrogen and thiobarbituric acid of silver carp dried in cold-air dryer with heat pump

Abstract: The quality and flavor of dried fish products tend to be affected by dry conditions. A high drying temperature will lead to the propagation of microorganisms, the oxidation of fat, and the increase of the content of total volatile basic nitrogen (TVB-N) in fish. A cold-air dryer with a heat pump can be used to keep the quality and flavor of dried fish stable, and to reduce drying energy consumption, in which the lower temperature source is used to heat the drying air with the help of a compressor. The drying medium of air in this technique is not in contact with the outside environment, so that the oxidation of nutrients and propagation of microorganisms are effectively avoided To realize the characteristics of fish products dried by cold air in a dryer with a heat pump, and determine the effects of the cold wind drying process parameters on the dried fish quality, silver carp was used as the drying material and tested by a uniform design of experiments of U10*(103). TVB-N and the value of thiobarbituric acid (TBA) for oxidation of fat was investigated as the criteria of quality of dried silver carp in the conditions of different cold air drying process parameters. The drying air temperature(x1) was 8, 11, 14, 17, 20, 23, 26, 29, 32, and 35℃, the by-pass air ratio (x2) was 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0, and the air velocity (x3) was 0.3, 0.45, 0.6, 0.75, 0.9, 1.05, 1.2, 1.35, 1.5, and 1.65 m/s, respectively. The value of TVB-N of 10 experiments was 36.12, 34.72, 34.44, 31.64, 47.04, 35.28, 42.00, 52.92, 97.44, and 85.40 mg/100g, and the value of TBA was 4.32, 4.65, 3.68, 3.36, 4.74, 3.59, 6.67, 6.53, 7.96, and 10.58 mg/kg respectively. By SPSS analysis, the regression equations of TVB-N (mg/100g) and TBA value (mg/kg) was Y1=80.364-4.629x1+0.150x12-11.813x3, Y2=7.854-0.535x1+0.017 x12, respectively. The results show that the fit of the regression equations are good. The drying temperature was the main factor that had an effect on TVB-N and TBA. However, the effects of the by-pass air ratio and air velocity were not significant. The optimal parameters of the silver carp drying process were determined as temperature 15.5℃, air velocity 1.65m/s, and by-pass air ratio 0.6. The results can provide references for the industrial production of silver carp dried in a cold-air dryer with a heat pump.