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I know that salt is used as preservative as it dehydrates microbes. Is there any other advantage like - altering pH or inactivating microbial enzymes ?

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salt cannot change pH directly. Dehydration which causes the loss of bulk water can alter the pH and also affect protein activity. –  WYSIWYG Nov 13 '13 at 4:58

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High salt environments are strongly hypertonic and disrupt the osmotic gradients of cells. Excess salt gets forced in (disrupting function) and cell water gets drawn out.

In simpler terms, it dehydrates them.

This link has more info regarding what is required to live in high salt environments (and by corollary, why organisms without such features die):

http://en.wikipedia.org/wiki/Halophile

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Another factor involved is the effect that high salt concentrations have on the 3-D structure of proteins. At higher than "normal" concentrations of salt, many proteins will fold differently and no longer be in their "active" form. Since all biological reactions involve enzymes, which are protein, you can see why this unfolding might be problematic.

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Salt draws water out of cells via the process of osmosis. Essentially, water moves across a cell membrane to try to equalize the salinity or concentration of salt on both sides of the membrane. If you add enough salt, too much water will be removed from a cell for it to stay alive or reproduce. Organisms that decay food and cause disease are killed by a high concentration of salt. A concentration of 20% salt will kill bacteria. Lower concentrations inhibit microbial growth, until you get down to the salinity of the cells, which may have the opposite and undesirable effect of providing ideal growing conditions! Salt can also be used when you are preserving a product via fermentation. The salt will inhibit the growth of moulds and yeasts. While some moulds and yeast are certainly needed during the fermentation process, by using small amounts of salt, it is possible to regulate and stabilise this process.

It is only possible to do this though if you are using salt that does not contain ‘free-flowing’ agents or iodine.

Refer to :https://suite.io/rachel-tsoumbakos/xpx288 for details.

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