Processing Environments: Effective Use of Chlorine

by Shelly McKee

Auburn University Department of Poultry Science

Introduction

This provides information regarding the use of chlorine and chlorine-based compounds to achieve safety for food contact surfaces.

Chlorine is a widely distributed element that is not found in its free state, but exists primarily in combination with sodium, calcium, potassium, and magnesium. Commercially, sodium and calcium are generally combined with chlorine to produce hypochlorites which are more convenient to use than other forms of chlorine such as chlorine gas. With the emerging use of hypochlorites (note: chlorine and hypochlorites will be used as interchangeable terms; however, the most prevalent form of chlorine for food industry use is in the form of hypochlorites) in water treatment systems and as disinfectants, chlorine and chlorine based compounds gained widespread acceptance as effective sanitizers. Chlorinated tap water used is usually at a concentration of 1-3 ppm.

Chlorine use as cleaning and sanitizing agents in food processing facilities

Chlorine is often used as a cleaning and/or sanitizing agent for equipment, product contact surfaces, and hand wash stations in food processing facilities. Cleaning and sanitizing are two separate yet related processes. Cleaning removes visible soil and/or food particles from the equipment and physically reduces the microbial load. As a cleaning agent, chlorine is very effective in removing protein residues and to a lesser extent, carbohydrate residues from surfaces. The efficacy of chlorine as a bactericidal agent is affected by pH of the solution and the amount of organic material present during cleaning or sanitizing. Specifically, the efficacy of chlorine in lowering bacterial levels decreases with increasing pH and increasing organic load. During cleaning, organic loads are usually high and alkaline (high pH) detergents are often used; therefore, chlorine would function as a cleaning compound instead of a bacteria reducing compound.

Secondary to its cleaning effectiveness is the ability of chlorine to reduce bacteria levels. When chlorine is used to reduce bacteria levels it is typically applied as a sanitizer to equipment after cleaning. The Code of Federal Regulations define sanitization as follows:

21 CFR 110.3 (o) “Sanitize” means to adequately treat food-contact surfaces by a procedure that is effective in destroying vegetative cells of microorganisms of public health significance, and in substantially reducing numbers of other undesirable microorganisms, but without adversely affecting the product or its safety for the consumer.

When sodium hypochlorite is used as sanitizer, USDA requires that chlorine concentrations in solution be no less than 50 ppm and no greater than 200 ppm (USDA, 1981). A number of factors have an impact on the effectiveness of the sanitizer including concentration of sanitizer, duration of contact, temperature, and pH. When using chlorine or chlorine based compounds as sanitizers it is critical that the surface to be treated has been washed and rinsed thoroughly to remove organic materials that would interfere with the bactericidal properties of chlorine. In addition, when using chlorine as a sanitizer it is important that the pH is <5 to improve its germicidal properties. Because high pH reduces the efficacy of chlorine, chlorine sanitizers should not be combined with alkaline compounds. In addition, surfaces should be rinsed thoroughly after using and alkaline detergent during washing so that residuals of the cleaning solution do not increase the pH of the sanitizing solution.

In addition to pH, temperature is also a very critical factor in determining bactericidal efficacy. As the temperatures of wash water decreases so does the bactericidal effect of the solution. Therefore, as a cleaning agent it is recommended that processors use levels of 200 ppm chlorine plus an anionic detergent (pH>10, 40-50°C) followed by a rinse then a sanitizer application with 200 ppm chlorine. These levels were established early from work that determined the break-point chlorination which refers to the chlorination beyond water demand resulting in residual free available chlorine. In addition, this level (200 ppm) of chlorination was deemed safe for use at these levels. The minimum concentrations of chlorine are dependent on the temperature of the water being used. If the water temperature is less than 37°C, then a minimum of 100 ppm chlorine is required for sanitizing. When water temperatures range from 37-50°C, then the minimum concentration of chlorine required is 50 ppm. At water temperatures exceeding 50°C, the minimum concentration of chlorine required is 25 ppm.

Bactericidal Properties of Chlorine

The disinfecting efficiency of chlorine is dependent on the amount hypochlorous acid (HOCl) present. Hypochlorous acid is formed when chlorine is added to water and equilibrium is established giving the formula:

Cl₂ + H₂O <--> HOCl + H⁺ + Cl^-

The usual reactant behavior of HOCl with organic molecules is for the chlorine atom to become free to react with compounds that possess unpaired electrons, such as amine-N or aromatic double bonds. As the pH increases, hypochlorous acid disassociates thereby increasing the formation of OCl-which is less effective as a bactericidal agent.

Chlorine is an oxidizing agent, and it is through its ability to oxidize compounds that it derives its germicidal activity. The proposed mechanisms mentioned were alteration of the cell membranes, oxidation of cellular protoplasm, precipitation of bacterial proteins, formation of toxic chloramines within the cells, oxidation of cellular protoplasm, and prevention of enzyme regeneration. The bactericidal effect of aqueous chlorine solution is attributed to hypochlorous acid (HOCl). It is important to monitors the free chlorine levels because organic matter causes the loss of chlorine.

Specifically, chlorine is an –SH reactor or in other words it oxidizes thiol groups. Because of its ability to oxidize thiol groups, chlorine effectively disrupts the cell wall of gram positive bacteria and the outer membrane of gram negative bacteria. In addition, chlorine is able to oxidize thiol groups of enzymes in the cytoplasmic membrane of bacteria and oxidize thiol groups of enzymes and proteins with in the cytoplasm of the bacterial cell.

Calculating Chlorine Levels in Cleaning and Sanitizing Solutions

Chlorine concentrations exceeding 200 ppm chlorine are excessive. According to USDA regulations, maximum levels should not exceed 200 ppm. Increasing the concentration of chlorine and organic compounds such as in wastewater and effluents from various treatment facilities result in the formation of many different chlorine compounds. To minimize risk to the environment, food manufacturers should apply chlorine judiciously to minimize chlorine waste in food production while producing foods that are safe from microbial contamination.

Example Usage Calculations

I. Calculation for 200 ppm (0.02% Chlorine) Solution from Standard Bleach

1. Start with Standard Bleach is 5.25% (0.0525) Sodium Hypochlorite (NaCIO)

2. Sodium Hypochlorite is 47.62% (0.4762) Chlorine

3. To calculate the amount of Chlorine in Standard Bleach

0.0525 (sodium hypochlorite) times 0.4762 (percentage of chlorine in sodium hypochlorite equals 0.025 or 2.5%

4. Calculate Y, The ratio of final solution volume-to-standard bleach volume required to achieve a solution of 200 ppm chlorine concentration:

Y = (the amount of chlorine in bleach) / (desired solution chlorine concentration)

Y = 2.50% / 0.02% = 125 to 1.0

A 125 unit volume of 200 ppm final solution will consist of 124 units water and 1.0 units of standard bleach, a 124 to 1.0 ratio of water-to-standard bleach.

5. Calculate X, the ratio of standard bleach volume-to-final solution volume required to achieve a solution of 200 ppm chlorine concentration:

X = (desired solution chlorine concentration) / (the amount of chlorine in bleach)

X = 0.02% / 2.50% = 0.008 (0.80%) to 1.0

A 125 unit volume of 200 ppm final solution will consist of 0.8% bleach (1.0 units) and 99.2% water (124 units), a .0081 to 1 ratio of standard bleach-to-water.

II. Calculation for 200 ppm (0.02% Chlorine) Solution from Sodium Hypochlorite (47.62% chlorine)

1. Calculate Y, The ratio of final solution volume-to-sodium hypochlorite volume required to achieve a solution of 200 ppm chlorine concentration

Y = (the amount of chlorine in sodium hypochlorite) / (desired final solution chlorine concentration)

Y = 47.62% / 0.02% = 2,381 to 1.0

A 2,381 unit volume of 200 ppm final solution will consist of 2,380 units water and 1.0 units of sodium hypochlorite, a 2,380 to 1.0 ratio of water-to-sodium hypochlorite

2. Calculate X, the ratio of sodium hypochlorite volume-to-final solution volume required to achieve a solution of 200 ppm chlorine concentration

X = (desired solution chlorine concentration) / (amount of chlorine in sodium hypochlorite)

X = 0.02% / 47.62% = 0.0004 (0.040%) to 1.0

A 2,381 unit volume of 200 ppm final solution will consist of 0.040% sodium hypochlorite (1.0 units) and 99.6% water (2,371.376 units), a .000402 to 1 ratio of sodium hypochlorite-to-water.