A novel model for continuous fermentation process for Worcestershire sauce production using a trickle bed bioreactor

Abstract

The mass balances of sugar and ethanol were computed on the assumption that the trickle bed bioreactor used was a continuous-flow stirred-tank reactor (CSTR), and simulation of the steady ethanol concentration at various dilution rates was performed using a modified Contois equation. The equation proposed here represents the conventional Contois equation as a particular equation of the modified formula ( m=1.0). The stability of the continuous fermentation in the production of Worcestershire sauce was evaluated, and this process was kinetically analyzed using the modified Contois equation. Neither decrease in yeast activity nor clogging with growth yeasts was observed in the trickle bed bioreactor with comb-shaped ceramic carriers during the fermentation period (about 6 months). From the results of the evaluation of mixing conditions this bioreactor can be regarded as a combination of a plug flow reactor (PFR) in the ceramic part, and a CSTR in the retention part. However, the trickle bed bioreactor could function as a CSTR having the same capacity as the actual volume of the retention part for the fermentation contribution rate of each part of the bioreactor. The observed ethanol concentration and productivity at the steady states were almost the same as the values calculated using the material balance equations of the sugar concentration and the ethanol concentration in a CSTR and the modified Contois equation with m=6.0. Thus, the modified Contois equation ( m=6.0) has been proposed as a design equation for a fermentation process for Worcestershire sauce production. When the modified Contois equation was applied to an acetic acid fermentation process and a plant tissue culture the observed product concentrations at each dilution rate were similar to the calculated values. It has been proved that the modified Contois equation is applicable not only to an alcohol fermentation process for Worcestershire sauce production but also to other fermentation processes and growth reactions.