Calcium activity versus "calcium threshold" as the key factor in the induction of yeast flocculation in simulated industrial fermentations

Abstract
Yeast flocculation is regulated by two parameters: the free-calcium activity and the "calcium threshold" or the quantity of calcium at which cells flocculate in a turbidimetric test. The study of the influence of different factors such as calcium concentration, pH, and chelating agents on flocculation has led us to put forward the following hypothesis. Flocculation occurs when the calcium threshold becomes equal to free-calcium activity, i.e., when the medium contains the exact quantity of calcium necessary for flocculation to occur. This hypothesis has been confirmed under standard laboratory culture conditions and in simulated industrial fermentations. Key words: flocculation, yeast, Saccharomyces cerevisiae, calcium induction.

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