Resumen de Modelling of lactic fermentation of carrot slices in salted brines
R.M. Nabais, Francisco Xavier Malcata
Increases in suspended biomass and variation in the concentrations of reducing sugars, salt, and lactic acid in brine containing sliced carrots were followed for a period of several days. A tentative unstructured, unsegregated model for the metabolism of suspended Lactobacillus plan tarum coupled with Fick's second law of diffusion for the transport of solutes within the carrot material was postulated. This general model was fitted by non-linear multiresponse regression analysis to an extensive set of experimental data encompassing several processing temperatures and initial brine concentrations. Maximum specific growth rates decreased with initial sodium chloride (NaCl) concentration and were maximal at ca 30°C leading to a peak concentration of reducing sugars in the brine. The lag phase of microbial growth in the brine is apparently disguised by the lag phase of sugar leaching from the carrots into the brine. Lactic acid was confirmed to be a growth-associated product. Intrinsic diffusivities of the various compounds considered ranged up to ca 10-11 m2/s, and varied with temperature according to the Arrhenius law; the maximum activation energy was at ca 8% (w/v) NaCl. The work developed is useful for the simulation and eventual optimization of pickled carrot manufacture.
