Effective Concentration of Salt on the Microbial Growth



Effective Concentration of Salt on the Microbial Growth

Introduction

All organisms with a semipermeable membrane are subject to osmotic pressure, or the effect of water moving in and out of the cell. Bacteria have a cell membrane and a cell wall. Bacteria must live in an aqueous (watery) environment. Most often this is a hypotonic environment, in other words, the concentration of water outside the cell is greater than the concentration of water inside the cell. This causes the net movement of more water into the cell than outside. If the bacterium did not have a cell wall, this could cause the cell to burst. (In fact, many antibiotics work by causing an ineffective cell wall to be made, which allows the bacterial cell to burst under water pressure). [1] So why does salt work as a preservative? Because when the outside environment around a cell is salty, then the concentration of water in the solution is less than inside the cell and water tends to leave the cell. This causes the cell to dehydrate, which eventually kills the cell. By subjecting bacteria to a salty environment, it keeps them from growing. Some bacteria however, have adapted to living in salty environments, such as Staph. bacteria a common skin inhabitant. [2] Your skin tends to be salty-this is one way your body protects you against bacteria on your skin. But even Staph can't live in highly salty surroundings, such as salted foods like ham, etc.

Aim

My intent is to determine the effective concentration of natural food preservative (salt) on the microbial growth.

Hypothesis

I expect that as the concentration of the salt increases the microorganisms grow on food will decreases. Null Hypothesis: There is no link between the concentration of salt and the effects it has on the growth of the bacteria.

Discussion

Most fresh foods, such as fresh meat, vegetables, and fruits, have awvalues that are close to the optimum growth level of most microorganisms (0.97 - 0.99). [3]The aw can be manipulated in foods by a number of means, including addition of solutes such as salt or sugar, physical removal of water through drying or baking, or binding of water to various macromolecular components in the food. Weight for weight, these food components will decrease aw in the following order: ionic compounds > sugars, polyhydric alcohols, amino acids and other low-molecular-weight compounds > high-molecular-weight compounds such as cellulose, protein or starch. It is well known that groups of microorganisms have pH optimum, minimum, and maximum for growth in foods. [4] As with other factors, pH usually interacts with other parameters in the food to inhibit growth. The pH can interact with factors such as aw, salt, temperature, redox potential, and preservatives to inhibit growth of pathogens and other organisms. The pH of the food also significantly impacts the lethality of heat treatment of the food. Less heat is needed to inactivate microbes as the pH is reduced.[5]

The major groups of microorganisms based on their relationship ...