Sunday, June 15, 2014

Food preservation technique using High Osmotic Pressure

By principle of osmosis, jams, jellies and pickles are preserved. The application of the principle of osmotic pressure can be used as an effective antimicrobial agent.
Bacteria reach osmotic equilibrium by two means:

1. In hypertonic environments the volume of the protoplasts will shrink, and
2. In hypotonic environments the rigid wall will resist increase in protoplasts volume at a limiting volume of water; equilibriums results from turgor against the wall.

Hypertonicity and process of salting are commonly used for inhibiting microbial growth in food preservation as an addition of sugar raises osmotic pressure of the food thus making it impossible for most microorganisms to grow.

The rigid walls present in bacteria cells enable most bacteria to tolerate even extremely dilute environments. Osmotic equilibrium is achieved by development of turgor pressure against the wall. The wall of gram-positive micrococci can withstand 22 atm of pressure.

Water is withdrawn from microbial cells when they are replaced in solutions containing large amounts of dissolved substances such as sugar or salt.

Although the walls of gram-negative rods have lower tensile strength, the wall is sufficiently strong to retain the turgor pressure if the cell is suspended in water.

The most commonly used osmotic agents are sucrose and sodium chloride. Other osmotic agents such as lactose, maltodextrin, ethanol, glucose, glycerine and corn syrups have been used.

Like dehydration, high osmotic pressure may inhibit microbial growth but it cannot be relied upon to kill microorganisms, yeasts and mould are relatively resistant to high osmotic pressure.
Food preservation technique using High Osmotic Pressure

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