Proliferation of Yeasts and Molds in Low Moisture Foods

In foods of low water activity, yeasts and molds proliferate by changing their internal cell moisture concentration form high to low water activity. To do this, they synthesize some water binding molecules (solutes) which can be used at their discretion to trap water from the surrounding environment. The trapped water is then used for biochemical reactions required for growth. E.g. of these solutes include glycerol, glucose, sucrose and sorbitol.
The presence of these compounds also decreases the water activity of the fungi cells, thereby buffering them and enabling equilibrium between the cells and the environment. Increase in solute concentration and decrease in water activity of the cells allow the movement of water from the environment into the cell, thereby enabling growth and proliferation of the yeast and mold.