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Food Safety and Environmental Services
Food Equipment Cleaning and Sanitizing: Water Chemistry and Quality (Page 5)
Quaternary Ammonium Compounds (QACs)
The properties of these compounds depend upon the covalently bound alkyl groups (R groups), which can be highly diverse. Since QACs are positively charged actions, their mode of action is related to their attraction to negatively charged materials such as bacterial proteins. It is generally accepted that the mode of action is at the membrane function. The carbon length of R-group side chain is, generally, directly related with sanitizer activity in QACs. However, because of the lower solubility in QACs composed of large carbon chains, these sanitizers may have lower activity than short chain structures.
QACs are active and stable over a broad temperature range. Because they are surfactants, they possess some detergency. Thus, they are less affected by light soil than are other sanitizers. However, heavy soil dramatically decreases activity. QACs generally have higher activity at alkaline pH. While lack of tolerance to hard water is often listed as a major disadvantage of QACs when compared to chlorine, some QACs are fairly tolerant of hard water. Activity can be improved by the use of EDTA as a chelator. QACs are effective against bacteria, yeasts, mold, and viruses.
An advantage of QACs in some applications is that they leave a residual antimicrobial film. However, this would be a disadvantage in operations such as cultured dairy products, cheese, beer, etc. where microbial starter cultures are used.
QACs are generally more active against gram positive than gram negative bacteria. They are not highly effective against bacteriophages. Their incompatibility with certain detergents makes thorough rinsing following cleaning operations imperative. Further, many QAC formulations can cause foaming problems in CIP applications.
Under recommended usage and precautions, QACs pose little toxicity or safety risks. Thus, they are in common use as environmental fogs and as room deodorizers. However, care should be exercised in handling concentrated solutions or use as environmental fogging agents.
Like QACs, acid-anionic sanitizers are surface- active sanitizers. These formulations include an inorganic acid plus a surfactant, and are often used for the dual function of acid rinse and sanitization.
Whereas QACs are positively charged, these sanitizers are negatively charged. Their activity is moderately affected by water hardness. Their low use pH, detergency, stability, low odor potential, and non-corrosiveness makes them highly desirable in some applications.
Disadvantages include: relatively high cost, a closely defined pH range of activity (pH 2 to 3), low activity on molds and yeasts, excessive foaming in CIP systems, and incompatibility with cationic surfactant detergents.
Fatty Acid Sanitizers
Fatty acid or carboxylic acid sanitizers were developed in the 1980s. Typical formulations include fatty acids plus other acids (phosphoric acids, organic acids). These agents also have the dual function of acid rinse and sanitization. The major advantage over acid anionics is lower foaming potential. These sanitizers have a broad range of activity, are highly stable in dilute form, are stable to organic matter, and are stable to high temperature applications.
These sanitizers have low activity above pH 3.5 - 4.0, are not very effective against yeasts and molds, and some formulations lose activity at temperatures below 10°C (50°F). They also can be corrosive to soft metals and can degrade certain plastics, or rubber.
Peroxides or peroxy compounds contain at least one pair of covalently bonded oxygen atoms (-O-O-)and are divided into two groups: the inorganic group, containing hydrogen peroxide (HP) and related compounds; and the organic group, containing peroxyacetic acid (PAA) and related compounds.
Hydrogen peroxide (HP), while widely used in the medical field, has found only limited application in the food industry. FDA approval has been granted for HP use for sterilizing equipment and packages in aseptic operations.
The primary mode of action for HP is through creating an oxidizing environment and generation of singlet or superoxide oxygen (SO). HP is fairly broad spectrum with slightly higher activity against gram-negative than gram-positive organisms.
High concentrations of HP (5% and above) can be an eye and skin irritant. Thus, high concentrations should be handled with care.
Peroxyacetic Acid (PAA) has been known for its germicidal properties for a long time. However, it has only found food-industry application in recent years and is being promoted as a potential chlorine replacement. PAA is relatively stable at use strengths of 100 to 200ppm. Other desirable properties include: absence of foam and phosphates, low corrosiveness, tolerance to hard water, and favorable biodegradability. PAA solutions have been shown to be useful in removing bio-films.
While precise mode of action mechanisms have not been determined, it is generally theorized that the PAA reaction with microorganisms is similar to that of HP. PAA, however, is highly active against both gram- positive and gram-negative microorganisms. The germicidal activity of PAA is dramatically affected by pH. Any pH increase above 7-8 drastically reduces the activity.
PAA has a pungent odor and the concentrated product (40%) is a highly toxic, potent irritant, and powerful oxidizer. Thus, care must be used in its use.
A general comparison of the chemical and physical properties of commonly used sanitizers is presented in Table 3.
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