-L. wrote:
> Bob (this one) wrote:
>
>>Water activity is ubiquitous in human life. But a single factor as
>>explanation for such complex conditions is not sufficient.
>>
>>>Sorry Bob ...we may differ in our opinions regarding the relevance of
>>> water activity in the general food processing...
>>
>>No, I don't think we do. I understand that water activity is a crucial
>>issue. But it's not the only issue.
>>
>>Pastorio
>
>
> I was a molecular biologist for 15 years and have had advanced
> coursework in micro, mycology and molecular biology, to name a few. I
> have never heard of "water activity" as being a factor to be considered
> in whether or not an organism will culture on a particular medium.
> Must be a food science term he's hung up on,

It is. It's essentially an index about how much water is available to
colonizing organisms. Not how much water is in the particular food, but
how much of it isn't bound. In food science, the lower the index number
(ranges from 0.0 [no water] to 1.00 [water]), the less water there is
for the metabolic needs of any critters; so reduced viability for
culturing in food products. Points to shelf life and storage
requirements. High water activity and low pH means refrigeration.

"Control of water activity (rather than water content) is very important
in the food industry as low water activity prevents microbial growth
(increasing shelf life), causes large changes in textural
characteristics such as crispness and crunchiness (e.g. the sound
produced by 'crunching' breakfast cereal disappearing above about aw =
0.65) and changes the rate of chemical reactions (increasing hydrophobe
lipophilic reactions but reducing hydrophile aqueous-diffusion-limited
reactions)."
<http://www.lsbu.ac.uk/water/activity.html>

> or something (honestly I
> have never encountered the term.) His entire diatribe seems pretty
> simplistic and, frankly, dumb, to me, as so many factors need to be
> considered - pH, available sugars, carbs sources, salt concentration,
> light, heat, aeration, etc.

Exactly. That's why I said there needs to be more consideration than
merely water activity.

Pastorio