Physical methods to control microbial growth part 3 | Factors influence the effectiveness of antimicrobial treatment.

 

Physical methods to control microbial growth part 3 | Factors influence the effectiveness of antimicrobial treatment.

Physical methods to control microbial growth part 3

7: Osmotic Pressure

The large amount of salts and sugars in foods is used to create a hypertonic environment and to increase osmotic pressure.

Plasmolysis:

As water move out from the cell, cell membrane shrinks away from cell wall. Cell may not die, but generally stops growing.

Yeasts and molds: they are more resistant to high osmotic pressures.

Staphylococci spp. that lives on skin are resistant to some extend to high osmotic pressure.

8: Radiations

There are three types of radiation kill microbes:

1. Ionizing Radiations:

Gamma rays, electron beams, X rays, or higher energy rays. They have short wavelengths (less than 1 nanometer).  Dislodge electrons from ions and form atoms.

They cause mutations in DNA and produce peroxides.

Used to sterilize disposable medical supplies and pharmaceuticals. Food industry is interested in making use of ionizing radiation.

Disadvantages:

They penetrate human tissues and may cause genetic mutations in humans.

2. Ultraviolet light (Nonionizing Radiation):

Its wavelength is longer than 1 nanometer. It damages DNA by producing thymine dimers. Due to dimers, mutations will occur. UV light is used to disinfect operating rooms, cafeterias, nurseries.

Disadvantages:

It damages skin and eyes.

It doesn’t penetrate paper, cloth and glass.

3. Microwave Radiation:

Their wavelength ranges from 1 millimeter to 1 meter. Water molecules absorb heat. They may destroy vegetative cells in moist foods. Bacterial endospores, which do not have water, are not destroyed by microwave radiation. Solid foods are unevenly penetrated by microwaves.

Factors influence the effectiveness of antimicrobial treatment.

1. Number of Microbes.

2. Type of Microbes: it is very difficult to destroy endospores. Vegetative pathogens differ widely in vulnerability to different methods of microbial control.

3. Environmental influences: Organic matters such as blood, saliva, feces, tends to inhibit antimicrobials, pH etc.

4. Time of Exposure: Chemical radiations and antimicrobials treatments are more effective at longer times. Longer exposure is compensated for lower temperatures in heat treatments.