Modelling the kinetics of biomass and lactic acid production during Rohu fish pickle fermentation

Abstract

Fish pickle was prepared from Rohu (Labeo rohita) by fermentation for 15 days and the changes in biomass growth, lactic acid production, and pH were evaluated. The data obtained were fitted in two most widely accepted microbial growth models: Modified Gompertz, and Logistic model and three well known lactic acid production models: Luedeking-Piret, Monteagudo et al., and Balannec et al. model for lactic acid fermentation. Model constants and coefficients were determined by a nonlinear regression method. All the models were validated using statistical parameters namely, coefficient of determination (R2), root mean square error (RMSE), reduced chi-square (χ2) and the reduced sum of squares (RSS). The results revealed that the viable cell counts increased from 0.91×107 cfu/ml to 9×109 cfu/ml after nine days of fermentation. The lactic acid increased by about 11.6 times in 12 days and remained constant for the rest of the fermentation period. The pH decreased from 6.5 to 4.2 on the 15th day of fermentation and then increased slightly till the final day of fermentation. The Logistic model and Luedeking-Piret model were best fitted to describe the biomass growth and lactic acid production by LAB during the fermentation period of pickle. The growth-associated and non-growth associated coefficients were determined to be 0.813 and 0.005, respectively. Based on these estimated parameters, it is concluded that lactic acid production in the fish pickle was a mixed type.