Preservative+Efficacy

Danny O'Shea and James Hargens

Project Proposal: Topic: At what point does salt prevent the growth of bacteria Chemistry Concept: How much salt does it take to prevent the growth of bacteria - Growth is affected by osmosis and diffusion Hypothesis: There will be a certain concentration of salt that will prevent the growth of bacteria. Journal Articles: [|Salt as a Food Preservative M. Ingram, A. G. Kitchell] [|Derivatives of Sorbic Acid as Food Preservatives John A Troller, Robert A Olsen] Lab Procedure: Swipe agar dishes with bacterial cultures. Then treat each with different concentrations of salt. After time has passed see which have bacterial growth and which do not. Apparatus and Chemicals Needed: Agar plates, salt, water, scales, bacteria, microscope. **I have ordered e. coli bacteria - gram negative strain** Safety Information: Must be careful to only get the known bacteria in the culture, otherwise there could be growth of harmful bacteria and fungi from the air in the room. Other Information: Based off of lab preformed a few years ago. Attempting to narrow range to find a more exact concentration of salt it takes to prevent the bacterial growth.

Abstract:

**Concentration of Sodium Chloride Necessary to Prevent Growth of //Escherichia Coli.//**
 * Danny O’Shea, James Hargens.** This lab attempted to find the concentration of sodium chloride (NaCl), commonly known as table salt, necessary to prevent the growth of //Escherichia coli// bacteria//.// To do this agar plates were made and then a culture of the bacteria was streaked across the surface. Once it was streaked paper disks that had been dipped into solutions varying in molarity from 2.00 to 5.00 molar NaCl and a control of 0.00 M were placed on the surface, without giving the bacteria a chance to grow. The procedure failed to find any solution that would prevent bacterial growth, likely due to either resistance, or diffusion of the dissolved NaCl through the agar, reducing the concentration. For the reason a second procedure was used, this procedure placed the //E. coli// into nutrient broths of the different concentrations. This forced the bacteria to grow in the desired concentration. After growth in the broth samples were streaked onto agar plates. High concentrations of salt should be able to kill bacteria because it increases the concentration of solutes outside the cell, causing water to diffuse out of the bacteria through osmosis. The ability of the salt to prevent the growth of bacteria is important in the preservation of food. Bacteria can be dangerous as some strains cause illness in humans. Finding the threshold that prevents the growth of bacteria is important as insufficient levels will allow bacterial growth, but too high of levels are wasteful, expensive, and can affect the flavor of the food. This lab found that the threshold for concentration of NaCl necessary to prevent the growth of //E. coli// is at or below 2.50 molar.

Key Terms: //Escherichia coli,// Sodium Chloride, Agar Plates, Molarity, Preservative, Food Preservation, Osmosis

Audio:media type="file" key="Hargens O'Shea Abstract Recording.wav" width="300" height="50"

 Plate after growth trial 1:   Plate Trial 2: 