Q. Factors Affecting Water requirements of microorganisms?

Factors that may affect aw requirements of microorganisms include:

1. Kind of solute employed to reduce the aw: For some organisms, like molds, the lowest aw for growth is independent of the kind of solute used. For other organisms, however, lower limiting aw values differ from solute to solute. For example potassium chloride usually is less toxic than sodium chloride, and it in turn is less inhibitory than sodium sulphate. Thus, sodium sulphate at a lower concentration may be as effective in reducing aw as potassium chloride at a higher concentration.

2. Nutritive value of the culture medium: In general, the better the medium for growth, the lower the limiting aw permitting growth of microorganism.

3. Temperature: Most organisms have the greatest tolerance to low aw at about optimal temperatures.

4. Oxygen supply: Growth of aerobes takes place at a lower aw in the presence of air than in its absence, and the reverse is true of anaerobes.

5. pH: Most organisms are more tolerant of low aw at pH values near neutrality than in acid or alkaline media.

6. Inhibitors: The presence of inhibitors narrows the range of aw for growth of microorganism.