Qac

Acid-Anionics

Antimicrobial spectrum

Gram-positive bacteria

Gram-negative bacteria

Spores

Viruses

Low toxicity

Nonirritating to skin

Noncorrosive

Nonstaining

Stability during storage in hard water with organic matter

Use at temperatures

Mineral-protein films removed

Leaves no residues

Leaves no flavors or odors

Detergent-sanitizer

Self-indicating

Low cost

Note: Advantages attribute = -. disadvantageous attribute = -. "Only a problem if misused.

'Only some plastic materials and painted walls; staining of skin is temporary. cBy odor of available chlorine.

active agent, the resulting iodophor can be used as a detergent-sanitizer (Table 1). Diatomic iodine (I2) is highly bactericidal; hypoiodous acid (HOI) and the hypoiodite ion (10 ") are less bactericidal; the iodate ion (I0^~) is inactive.

Iodophors are generally used at 12.5-25.0 ppm; at these concentrations they are self-indicating, ie, the presence of available iodine is indicated by the amber color of the solution. They must be used at < 50°C to avoid the release of toxic iodine vapor. Iodophors are formulated with an acid, usually phosphoric acid, because they are more active at pH 3-5. They also solubilize and remove mineral and protein films from food-processing equipment (4).

Surface Active Agents (Surfactants)

These compounds are classified in three categories: (1) cat-ionic, (2) anionic, and (3) nonionic or amphoteric. All three categories have antimicrobial activity to varying degrees, depending on the specifics of molecular moiety and formulation with other ingredients to produce disinfectant or sanitizing compounds. Quaternary ammonium compounds (QACs), or quats, are cationic wetting agents or surfactants. The general chemical configuration of a QAC is

Ri R2

R4 R3

where R1; R2, R3, and R4 are covalently bound organic groups such as alkyl, methyl, benzyl, and cetylbenzyl. The H~ is a halogen, most often chlorine or occasionally bromide. These are synthesized compounds that are formed by reacting tertiary amines with quarterizing agents such as alkyl or cetyl halides. A wide array of groups may be substituted, and this may result in the formation of quaternaries with widely variable properties. The cation or positively charged proton of the molecule is microbiologi-cally active and lyophobic. The negatively charged halide is lyophilic. Because QACs are actively cationic, they are not compatible with detergents or other compounds that are anionic in solution. The chemical configuration for al-kyldimethylbenzylammonium chloride, one of the frequently employed quarternaries, is

Because of the great diversity of chemical composition with QACs, great variation in the antimicrobial activity may occur. Generalization is difficult with these compounds. QACs principally are antibacterial in activity. Often they are more effective against gram-positive bacteria than gram-negative bacteria, especially at alkaline pH. The antifungal activity of quaternaries is variable and depends on the moiety of the molecule of the specific QAC employed and the specific species of fungal organism(s) of concern. Some quaternaries are very effective fungicides, while others may be mediocre at best. Proper selection of

H"

these products for antifungal activity is necessary. The QACs are not considered to be effective agents for controlling either bacterial spores or fungal spores. They are variable as viricides, being moderately active against lipophilic viruses but not effective against hydrophilic viruses. In addition to molecular configuration, other factors have an influence on the antimicrobial activity of QACs. As stated previously, quaternaries at alkaline pH generally are more effective against gram-positive than gram-negative bacteria. However, there are complications, conflicts, and resistances related to the pH of solutions. Some gram-negative bacteria, such as Pseuomonas and Escherichia, show resistance to QACs at alkaline pH but may be much less resistant to neutral or slightly acid quaternary solutions. The effect of organic residues on antimicrobial effectiveness of QACs can be variable. To a large extent, the degree depends on the specific quaternary compound and the type of organic soil that may be present. In general, QACs are more stable to the presence of organic residues than hypochlorite and about equal to that of the iodophors. The activity of quaternary ammonium compounds may be affected by the presence of calcium and magnesium water-hardness salts in solutions. This effect varies with the quaternary compound employed. The QACs that are formulated with chelating agents, such as EDTA and/or se-questerants, have good tolerance to high levels of water-hardness salts. There is good agreement that the effectiveness of QACs increases as the solution temperature increases and that these compounds are more stable than both hypochlorite and iodophors at high temperatures (6).

The quaternaries have found use as sanitizing solutions for dairy and food equipment, skin antiseptics, and hospital sanitizing applications. Quaternary compounds may be combined with nonionic wetting agents and other detergent enhancers into detergent-sanitizer formulations for specific applications. If QACs are to be on sanitizing food-contact surfaces, they must be of a type and in a form that has FDA approval according to provisions of 21 CFR (7). Because of the great variability inherent to these products, it is imperative that they be selected after consultation with QAC manufacturers or suppliers who have been advised of the prevailing conditions under which the quaternary will be expected to perform. After this has been done, the selected product(s) should be used only under the explicit instructions that have been given.

The acid-anionic products are mixtures of anionic surfactant and an acid. Most frequently phosphoric acid is the acid employed. The chemical structure of the anionic surfactants usually is in the form of an alkyl aryl sulfonate. Some examples of these are dodecylbenzene sulfonic acid, sodium lauryl sulfate, sodium dioctylsulfosuccinate, and 1-octane sulfonate. For a more comprehensive list of anionics that have been approved for use in sanitizer solutions for application to food contact surfaces, refer to 21 CFR (7).

The antimicrobial activity of the acid-anionic sanitizers is most pronounced at low pH levels, with the pH range of 3.0 to 1.5 being the most optimal. At the recommended-use concentrations, for specific applications, they provide excellent antimicrobial activity against vegetative bacterial cells and most yeasts. Both bacterial spores and fungal spores show resistance to these products. At pH values above 3.5, the effectiveness of the acid-anionic sanitizers against gram-negative bacteria is reduced, and this becomes more pronounced with increasing pH. Water hardness at up to 1,000 ppm as CaC03 has not been shown to affect the antimicrobial activity of acid-anionics, but if the water-hardness level should be high enough to cause a rise in pH of a sanitizing solution above 3.5, then reduced sanitizing effectiveness could be anticipated. Because of their acidic reaction in solution, the acid-anionic surfactant sanitizers have found important applications for sanitizing both circulation cleaned-in-place (CIP) equipment and spray-cleaned tanks and vessels in dairy and beverage processing plants where mineral residuals may affect the sanitizing efficiency of the other types of cleaners. The acid-anionic sanitizers are more costly than hypochlorite, but they are less expensive than either the iodophors or the quaternary ammonium sanitizers (8).

Amphoteric surfactants are disinfectants that have been used in European and some other countries for more than 40 years. They have not received FDA approval in the United States for use as sanitizers on food contact surfaces. Most of the commercial amphoteric products are sold under the trade name Tego. They are termed amphoteric or ampholytic because in water solution they yield anions, cations, and zwitterions (dual-charged molecules). The chemical structure of amphoteric surfactants is a molecule composed of an amino acid, most frequently glycine, substituted with a long-chain alkyl amine group. Examples of the most frequently employed amphoterics include do-decylglycine, dodecylaminoethylglycine, and dodecyldi-aminoethylglycine. The amphoteric surfactants have been purported to be bactericidal, fungicidal, and viricidal and effective in the presence of soil, lipids, and proteins. The contact times required for effective microbial inactivation are longer than that for other more frequently used sanitizers. Because of their surfactant properties, the amphoteric sanitizers may adsorb on surfaces to form a film that is resistant to rinsing by water. This is an advantageous property when residual antimicrobial activity is desired but may be a disadvantage from the standpoint of possible sanitizer residuals in foods. The effect of organic residues on the antimicrobial of amphoteric surfactant sanitizers are contradictory. This has created a problem for their gaining acceptance and approval as sanitizers. The amphoteric sanitizers have been used as hand-wash disinfectants, floor-wash disinfectants, and food plant equipment sanitizers in European and some other countries (9).

The Peroxides

The two peroxides that are most frequently used for disinfection and sanitizing are hydrogen peroxide and per-oxyacetic acid (peracetic acid). Hydrogen peroxide at 3% concentration has been employed as a topical antiseptic and wound irrigation agent for many years. More recently, processes have been developed that allow the production of stable, highly concentrated solutions that may contain up to 90% hydrogen peroxide. This has resulted in the availability of hydrogen peroxide, of various grades and purity, that could be used for microbial control in the food, cosmetic and electronic industries. Hydrogen peroxide has shown effective antimicrobial activity against both non-spore-bearing and spore-bearing bacteria, yeasts, molds, and viruses. It is very effective against the anaerobes because they lack catalase enzyme, which hydrolyses hydrogen peroxide. Also, gram-negative bacteria are more easily inactivated by hydrogen peroxide than are gram-positive bacteria. Among the factors known to affect the antimicrobial activity of hydrogen peroxide are the concentration of chemical, pH, temperature, and presence of metallic salts. Hydrogen peroxide follows the classical relationship that the higher the concentration of chemical antimicrobial in solution, the more rapid the rate of microbial inactivation. Hydrogen peroxide is most active at acidic conditions; its activity is slower at neutrality and becomes progressively less active as the alkalinity of the solution increases. Temperature affects the action of hydrogen peroxide. In general, higher solution temperatures can result in lower concentrations and shorter contact times to obtain microbial inactivation. The presence of certain metallic salts or ions increases the antimicrobial effectiveness of hydrogen peroxide. These include copper, chromium, iron, and molybdenum. A good review on the antimicrobial activity of hydrogen peroxide has been presented by Turner (10).

In industrial applications, hydrogen peroxide has FDA approval for use as a sterilant of containers and equipment used in aseptic packaging of foods (7). For treatment of packaging rooms, 30 to 40% hydrogen peroxide for up to 30 minutes or more contact time at room temperature may be required; whereas at a temperature of 60 to 71°C, the sterilization contact time for containers may be reduced to seconds. Because of the potential hazard of hydrogen peroxide, it is important to insure that all necessary safety practices are in effect for handling and using this material to prevent serious harm to personnel. Hydrogen peroxide has shown promise as an agent for use in vapor-phase sterilization applications (11).

Peroxyacetic acid (peracetic acid) is an organic peroxide that has been used for practical microbial control. Peroxyacetic acid is a strong oxidizing agent that is soluble in water and has a characteristic pungent, vinegarlike odor. Concentrated solutions of peroxyacetic acid are highly unstable, particularly at high temperatures and in the presence of heavy metallic ions. Current commercially available products contain stabilizing ingredients, and they are safe to use. Typically these contain from 4 to 40% peroxyacetic acid. As with all chemicals, they must be handled, stored, and used according to specific label declarations and product safety data sheets for the product. Peroxyacetic acid is superior in action to hydrogen peroxide as an antimicrobial and has a broad spectrum of activity against both gram-positive and gram-negative bacteria, spore-bearing bacteria, and microbial spores. It has both fungicidal and viricidal activity at recommended conditions of use. The FDA allows the use of peroxyacetic acid sanitizing solutions on food-contact surfaces at a concentration of 100 to 200 mg/L (ppm) (7). The antimicrobial activity of peroxyacetic acid is affected by such factors as concentration, pH, and contact time. As is true with other chemical antimicrobials, higher concentrations of peroxyacetic acid in solution are more cidal than are lower concentrations, pro vided that all other factors are constant. With regard to pH, acid conditions are most optimal to inactivation of microbes, and as the pH increases above pH 7 to 8, there is decreasing cidal activity for a constant concentration of peroxyacetic acid in solution. As might be expected, the temperature of the solution affects the killing power of peroxyacetic acid at a given concentration. Increasing temperature improves the germicidal effect, but peroxyacetic acid retains some antibacterial activity at a temperature as low as 7°C. Because of this, peroxyacetic acid has an advantage over most other commonly used chemical sani-tizers for certain applications. Water-hardness minerals do not have a great effect on peroxyacetic acid, and it is not affected as adversely by organic residuals as are other oxidative sanitizers (12,13). As with all hazardous chemicals, necessary precautions are required when using this product. It is essential that personnel be made aware of these and that labeling directions and product safety instructions be followed precisely.

Phenols

Many phenolic compounds are strong germicides, but their potential for use in the food industry is limited by their odor and the possibility of causing off-flavors in foods. Their action involves cell lysis. Depending on concentration, phenols are either bactericidal or bacteriostatic. They have only limited activity against viruses, and they are not sporicidal. Halogenation of phenols increases their activity 3-30 times. Substitution in the para position is more effective than in the ortho position, substitution with two halogen atoms is more effective than one, and bromophe-nols are more active than chlorophenols (14). Chloroxy-lenol or para-chloro-meia-xylenol (PCMX), the active ingredient of Dettol, is a phenolic compound that can be used as a skin germicide.

Table 2 provides information on comparative information on some of the characteristics of the most common chemical sanitizers that have FDA (7) approval for no-rinse application on food-contact surfaces. Because of the wide variations in the formulation of commercial products, there may be anomalies from that normally expected. In all instances, the information and recommendations given by the manufacturers or supplies of commercial proprietary sanitizer products should be sought and followed explicitly for any application.

Many halogenated ftis-phenols (or phenylphenols) have considerable activity against bacteria and fungi, but they have low activity against pseudomonads (2). They are used as clinical disinfectants and in germicidal soaps, eg, hexa-chlorophene.

Hexachlorophene is not very volatile and lacks the unpleasant odor of phenols. It is more active against Grampositive than Gram-negative bacteria. It is bacteriostatic for Staphylococcus aureus at extremely low concentrations (0.05 /¿g/mL) and requires a suitable quenching agent to inactivate residues of the disinfectant so that its bactericidal activity can be accurately assessed (2). It was widely used as a skin antiseptic marketed as pHisoHex and in a wide range of over-the-counter (OTC) pharmaceutical and personal hygiene products. It can be absorbed through in-

Table 2. Comparative Characteristics of Different Sanitizers flamed and infant skin with the possibility of serious systemic toxicity (15). As a result, OTC products have generally been limited to 0.75% hexachlorophene. Higher concentrations are sold with medical prescription.

Restrictions on the use of hexachlorophene resulted in the development of a range of other disinfectants for use in germicidal soaps. For example, Irgasan DP 300, also known as triclosan, 2-4-4'trichlor-2'-hydroxy diphenyl ether is active against Gram-positive and Gram-negative organisms.

Other Antimicrobial Agents

Chlorhexidine is one of a family of JV1 ^-substituted big-uanides (2). Its use was licensed in the UK and Canada, but not in the United States.

Chlorhexidine is active against Gram-positive and Gram-negative bacteria; it has limited antifungal activity, but it is not active against acid-fast bacilli, bacterial spores, or viruses. However, some resistant pseudomonads can contaminate aqueous solutions of this compound. It is not compatible with anionic compounds. The digluconate salt is freely soluble in water; however, the diacetate and dihydrochloride salts are only poorly soluble. Alcoholic chlorhexidine or a 4% chlorhexidine detergent (Hibiscrub) are highly effective skin germicides (16).

The salicylanilides and carbanilides are families of antimicrobial chemicals (17). One of the more popular disinfectants among these chemicals is 3,4,4'-trichlorocarbani-lide. (TTC). It has been incorporated into soaps to give an antimicrobial product.

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