MODELLING THE KINETICS OF BIOMASS AND LACTIC ACID PRODUCTION DURING ROHU FISH PICKLE FERMENTATION

Abstract

The study was conducted to prepare Rohu fish pickle and changes in its cell growth and multiplication and lactic acid production during fermentation. The obtained data were used to determine the best fit model describing pH, acidity and LAB growth. Fish Pickle was prepared from Rohu fish which was washed, made into fillets and then cut into small pieces using sharp knife. The pieces were marinated, fried in mustard oil, added other ingredients and finally heated till vinegar absorbed. During packing care was taken to see that there was layer of oil over the contents in the bottles. During the fermentation period of 16 days, changes in biomass, titratable acidity and pH were evaluated. The data obtained were then applied to three well known lactic acid production models and two most accepted growth models for lactic acid fermentation. Model constants and coefficients were determined by nonlinear regression method. All the models were validated using statistical parameters in MS-excel 2016 namely; coefficient of determination (R2), root mean square error (RMSE), reduced chi-square (χ2), reduced sum of squares (RSS) and relative deviation modulus (RDM). The experiment results revealed that the viable cell counts increased from 0.91×107 cfu/ml to 9×109 cfu/ml after 9 days of fermentation. The lactic acid increased by about 11.6 times in 12 days and remained constant for rest of the fermentation period. Unlike this, pH decreased from 6.5 to 4.2 on the 15th day of fermentation and then increased slightly till the last day of fermentation which is due to growth kinetics of bacteria. Logistic model and Luedeking- Piret model were best fitted to describe growth and lactic acid production by LAB during the fermentation period of pickle respectively. The growth associated and non growth associated coefficients were determined to be 0.813 and 0.005 respectively. Based on these estimated parameters, it was noticed that lactic acid production in pickle was mixed type.