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, 64 (7), 2616-23

Modeling of Growth of Lactobacillus Sanfranciscensis and Candida Milleri in Response to Process Parameters of Sourdough Fermentation

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Modeling of Growth of Lactobacillus Sanfranciscensis and Candida Milleri in Response to Process Parameters of Sourdough Fermentation

MG Gänzle et al. Appl Environ Microbiol.

Abstract

We investigated the effect of the ecological factors pH, temperature, ionic strength, and lactate, acetate, and ethanol levels on Candida milleri and two strains of Lactobacillus sanfranciscensis, organisms representative of the microflora of sourdough. A mathematical model describing the single and combined effects of these factors on the growth of these organisms was established in accordance with the following criteria: quality of fit, biological significance of the parameters, and applicability of the in vitro data to in situ processes. The growth rates of L. sanfranciscensis LTH1729 and LTH2581 were virtually identical under all conditions tested. These organisms tolerated >160 mmol of undissociated acetic acid per liter. Growth occurred in the pH range of 3.9 to 6.7 and was completely inhibited by 4% NaCl. C. milleri had a lower optimum temperature for growth (27 degreesC) than the lactobacilli. The growth of the yeast was not affected by pH in the range of 3.5 to 7, and up to 8% NaCl was tolerated. Complete inhibition of growth occurred at 150 mmol of undissociated acetic acid per liter, but acetate at concentrations of up to 250 mmol/liter exerted virtually no effect. The model provides insight into factors contributing to the stability of the sourdough microflora and can facilitate the design of novel sourdough processes.

Figures

FIG. 1
FIG. 1
Effect of temperature on the μmax values for L. sanfranciscensis LTH2581 (A) and LTH1729 (B) and C. milleri LTH H198 (C). The solid and dashed lines represent growth rates predicted with models 1a and 1b, respectively. Error bars indicate the standard deviations from the means of two independent experiments. The shaded area represents the range commonly encountered during sourdough fermentations.
FIG. 2
FIG. 2
Effect of pH on μmax values for L. sanfranciscensis LTH2581 (○) and LTH1729 (▵) and C. milleri LTH H198 (□) (A) and effect of NaCl addition expressed as ionic strength on the growth of L. sanfranciscensis LTH2581 and C. milleri LTH H198 (B). The lines represent the predicted growth rates. Error bars indicate the standard deviations from the means of three independent experiments. The shaded areas represent the ranges commonly encountered during sourdough fermentations.
FIG. 3
FIG. 3
Effect of ethanol (A), acetate (B), and lactate (C) on μmax of L. sanfranciscensis LTH2581 (○) and C. milleri LTH H198 (□). The lines represent the growth rates predicted with model 4. Error bars indicate the standard deviations from the means of three independent experiments. The shaded areas represent the ranges commonly encountered during sourdough fermentations.
FIG. 4
FIG. 4
Three-dimensional plot of observed growth rates (•) versus surfaces of predicted growth rates. Observed growth rates are taken from data subsets for the evaluation of combined effects; calculated growth rates were extrapolated with the models describing single effects. (A) L. sanfranciscensis LTH2581; (B) C. milleri LTH H198.
FIG. 5
FIG. 5
Plot of observed growth rates versus growth rates predicted with the model for the combined effects. (A) L. sanfranciscensis LTH2581; (B) C. milleri LTH H198.

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