Kinetics of Total Volatile Basic Nitrogen and Trimethylamine Formation in Stored Rohu (Labeo rohita) Fish

Fish freshness estimation has been mostly studied in terms of total volatile basic nitrogen (TVB-N) and trimethylamine nitrogen (TMA-N) determination and partially addresses the kinetics, which limits its practical utility. In this study, TVB-N and TMA-N content of Rohu stored under limited refrigerated (5 and 0 degrees C) and frozen (-5 degrees C) conditions for 42 days showed an increasing trend, respectively. TVB-N and TMA-N formation in stored Rohu was higher at higher temperature and their initial and final values were found 4.57 +/- 0.321, 0.14 +/- 0.047 mg/100g and 46.56 +/- 0.994, 3.24 +/- 0.112 mg/100g, respectively. The volatile formations in Rohu at -5 degrees C were slow, as the frozen storage arrests the enzymatic and microbial activities in comparison to 0 degrees C and above. The kinetics of TVB-N and TMA-N were investigated using zero, first, and nth-order reaction model. First-order kinetics exhibited the best fit model for TVB-N (R-2 = 0.98; chi(2) = 0.045), whereas TMA-N formation showed nth-order kinetics (n = -0.4608, R-2 = 0.96, chi(2) = 0.028) as best fit model. The first-order kinetic reaction contributed activation energy of 58.16 kJ/mol for TVB-N and 10.86 kJ/mol for TMA-N. TVB-N and TMA-N formations were influenced by storage temperature and duration as expected. Kinetic parameters were also significantly (P <= 0.05) affected by storage temperatures.