Bacteria vs. Acids

[tatsunaku]

Why is it that a cutting board smeared with lunch meat can be sanitized by weaker acids better than the stronger acids?

(weaker acids as in vinegar/grapefruit juice)
(stronger acids as in lemon juice/lime juice)

Grapefruit has more sugar than lemon or lime. So, can I assume that sugar has anti-bacterial properties?

[Borek]

Quite the contrary, sugar will make most bacteria to grow faster.

[Monique]

What does an acid have to do with sugar content? And where did you get the information that weaker acids are stronger sanitizers than stronger acids?

[iansmith]

Quite the contrary, sugar will make most bacteria to grow faster.

Not entirely true. High concentrations will prevent the growth of bacteria and other micro-organisms by removing water. Jams is an example of preserving food using a high sugar concentration.

[Borek]

Not entirely true. High concentrations will prevent the growth of bacteria and other micro-organisms by removing water. Jams is an example of preserving food using a high sugar concentration.

Right, I was a little bit too general. But in the case described sugars will be in low concentrations.

[gravenewworld]

Why are weak acids weak?


Because they don't dissociate completely. Strong acids like HCl completely dissociate. Bacteria can absorb the undissociated forms of acids where then inside the bacterial cell they dissociate, lower the pH, and kill the bacteria. Strong acids are already dissociated and can't be absorbed by the bacteria which is why weaker acids are better for their sanitizing properities.

[Borek]

That's assuming that the acid molecule has to enter bacteria cell to kill it. My bet is that in pH low enough bacteria will be killed just by the effects of the cell wall protonation.