Influence of yeast extract concentrationon batch cultures of Lactobacillus helveticus: growth and production coupling |
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Authors: | Amrane A. Prigent Y. |
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Affiliation: | (1) Départment Chimie, Université de Rennes I, Laboratoire des Procédés de Séparation (Unité associée INRA), IUT, BP 1144, 35014 Rennes Cedex, France |
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Abstract: | Lactobacillus helveticus was cultivated batchwise on whey permeate supplemented with 2–30g yeast extract l-1. For low supplementation levels, growth was slow, and a long maintenance phase in the absence of any cell autolysis was observed. When the yeast extract concentration was increased, growth time increased slightly; under these circumstances, a large increase of maximum biomass concentration was recorded, indicating a clear nitrogen source starvation at low supplement concentration. At the same time the length of the maintenance phase decreased; for a 30gl-1 supplementation, it vanished and a death phase was observed instead: this behaviour highlighted a shift from nitrogen to carbon source starvation. For more and more supplemented media, the final lactic acid concentration was constant, while fermentation time decreased significantly; a growth-associated production phase was followed by a maintenance production phase. The part played by the former mecha nism was under tight control of yeast extract concentration: for 30gl-1 supplementation, 83% of total lactic acid was provided by a growth-linked production process. |
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Keywords: | Growth and production coupling lactic acid bacteria yeast extract |
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