1382 CLEANING PROCEDURES IN THE FACTORY/Types of Disinfectant

Types of Disinfectant ammonium compounds, amphoterics, biguanides, and acid anionics. J Fisher, Diversey Ltd, Riddings, UK This article is reproduced from Encyclopaedia of Food Science, Physical and Chemical Properties Food Technology and Nutrition, Copyright 1993, Academic Press. Oxidizing Disinfectants

Background Halogens Chlorine and iodine have been used as 0007 terminal disinfectants for many years. More recently, 0001 In food factories, the detergent stage is normally bromine and chlorine dioxide have been introduced. followed by a disinfecting stage. The detergent stage is required to remove all the soil, leaving a chemically Chlorine Chlorine was first used as a gas for fumi- 0008 clean surface. The disinfectant stage is used as an gation in hospitals in 1791, but this application has extra guarantee of cleanliness and to prevent recon- one obvious drawback – chlorine gas is toxic. Active tamination in some cases. It does not compensate for chlorine is available from two types of material: a bad detergent stage or badly designed process or cleaning equipment. 1. Inorganic compounds containing hypochlorite 0009 ions either as a liquid, e.g., sodium hypochlorite Disinfection (NaOCl), or as a powder, e.g., chlorinated triso- dium phosphate 0002 The definition of disinfection taken from BS5283 ððNa PO :11H OÞ NaOCl, NaClÞ: (1986) states ‘The destruction of microorganisms, 3 4 2 4 but not usually bacterial spores. It does not neces- 2. Powdered organic chlorine release agents, e.g., 0010 sarily kill all microorganisms but reduces them to a trichloroisocyanurate (Figure 1). level acceptable for a defined purpose, for example a In solution, both types hydrolyze to produce hypo- level which is harmful neither to health nor to the chlorous acid and/or hypochlorite ions, depending on quality of perishable goods.’ The acceptable level of the pH. microbial contamination on a surface or piece of equipment has to be determined; obviously, no patho- Acid Alkaline À gens should be found. (See Spoilage: Bacterial Spoil- Cl2 Ð HOCl Ð OCl age; Molds in Spoilage; Yeasts in Spoilage.) Chlorine gas Hypochlorous acid Hypochlorite ion 0003 The state of sterility is defined as free from all living In the food industry, sodium hypochlorite is used as a microorganisms. This is not achievable in the food general-purpose disinfectant. It is most stable in a factory by using acceptable chemicals (‘acceptable’ slightly alkaline solution, and it is for this reason that meaning safe for humans, plant materials and prod- the concentrate is supplied stabilized with sodium ucts). hydrocide at a pH of up to 12. An in-use solution of 0004 Disinfectants are used after the detergent applica- between 50 and 300 p.p.m. will have a pH between 7 tion in cleaning-in-place (CIP) operations where the and 9. The optimum pH for disinfection is pH 5.0, but term ‘terminal sterilant’ may be used. They are also used after hand cleaning. Equipment should be left in a soak bath until it is ready to be used, thus ensuring CI that it remains free from recontamination. 0005 There are a wide range of disinfectants available. N The choice of disinfectant depends on the user’s O O requirements, the type of processing and cleaning C C equipment, the method of use, and, to some extent, the personal preference of the user.

N N Types of Disinfectant CI CI C

0006 Disinfectants can be split into two broad groups, oxidizing and nonoxidizing. Oxidizing disinfectants O include the halogens, chlorine, iodine, bromine, Figure 1 Trichloroisocyanuric acid. Reproduced from Cleaning fig0001 and chlorine dioxide, and oxygen-releasing materials Procedures in the Factory: Types of Disinfectant, Encyclopaedia of such as peracetic acid and hydrogen peroxide. Food Science, Food Technology and Nutrition, Macrae R, Robinson Nonoxidizing disinfectants are as follows: quaternary RK and Sadler MJ (eds), 1993, Academic Press. CLEANING PROCEDURES IN THE FACTORY/Types of Disinfectant 1383

the solution is less stable. Below pH 5.0, chlorine gas Iodophors have a broad antimicrobial spectrum 0017 will be produced. that is similar to hypochlorite, although they are less 0011 Applications for sodium hypochlorite in the food active against bacterial spores. In common with industries are CIP, soak, and spray. Sodium hypo- sodium hypochlorite, they are fast-acting but are chlorite has many advantages: it is nonfoaming; it is more expensive. Iodophors are used in soak baths not affected by water hardness; it does not leave an and spray application at up to 10 p.p.m. available active residue, and it has a wide antimicrobial spec- iodine. In solution, iodophors are yellow-brown in trum, which includes activity against bacterial spores color. This color can be an advantage: in a soak and viruses. It is also fast-acting and cheap. bath application, the color indicates the presence of 0012 However, it also has numerous disadvantages: it iodine; the in-use solutions are unstable, so that as the can be corrosive to a wide range of components, iodine dissipates, the solution will become colorless. including stainless steel; it is irritating to the skin Staining may be a problem, especially with some 0018 and eyes; the in-use solution is unstable; it is inacti- plastics, and this may also result in taint problems. vated by organic materials, and it may give rise to Iodophors can be corrosive; it is therefore necessary taint problems. to ensure that the correct dilution is used; otherwise, damage to plant and personnel may occur.

0013 Chlorine dioxide Chlorine dioxide (ClO2) is an un- stable and toxic gas that is soluble in water. When Bromine Bromine itself is not used as a disinfectant, 0019 chlorine dioxide is generated in solution, as shown mainly because of its handling difficulties. Bromo- below, it is a very effective water disinfectant at point chlorodimethylhydantoin is supplied as a powder or of use. a solid. In solution, it releases hypobromous and hypochlorous acids. 5NaClO2 þ 4HCl Ð 4ClO2 þ 5NaCl þ 2H2O:

Chlorine dioxide at use concentrations (0.5–1 p.p.m.) Oxygen-releasing compounds 0020 0020 overcomes some of the disadvantages of hypochlorite Peracetic acid Peracetic acid was introduced in in that it is nontainting, noncorrosive, and nontoxic. 1955. The material is supplied as an equilibrium mix- Its sole use at present is in water disinfection. ture:

CH3Cð¼¼ OÞOOH þ H2O Ð CH3Cð¼¼ OÞOH 0014 Iodine Iodine itself is not very soluble in water, and Peracetic acid Water Acetic acid the vapor is irritating to the eyes, making it difficult to þH2O2: handle. Iodine is a very reactive element, and it is this Hydrogen peroxide reactivity that makes it a good disinfectant. 0015 Iodine compounds used in the food industry con- It is soluble in water and is completely biodegradable, tain iodine complexed with polyvinylpyrrolidone and breaking down to harmless products: other surface active agents, usually in an acid solu- 2CH Cð¼¼ OÞOOH ! 2CH Cð¼¼ OÞOH þ O tion. These are known as iodophors and were first 3 3 2 introduced in 1949. As supplied, peracetic acid is corrosive and has a very 0016 The complexes formed between iodine and carrier irritating smell, similar to vinegar; because of these molecule are water-soluble and overcome the hand- properties, it is unpleasant to handle, and manual use ling difficulties of iodine whilst retaining the disin- is not recommended. It is suitable for CIP, as it is fecting power. On dilution, the iodophors release nonfoaming. iodine gradually, and it is the free iodine that acts as Peracetic acid is a highly reactive material. As an 0021 the disinfecting agent. The optimum pH for microbial in-use solution, it is not very stable and will react with activity is pH 5.0. organic materials. Peracetic acid may attack plant materials, such as rubber gaskets, and at higher con- Acid Alkaline À À centrations, corrosion may be a problem. I2 Ð HOI Ð OI Ð IO : Peracetic acid has a wide antimicrobial spectrum, 0022 Greatest Some Inactive Inactive which includes bacterial spores and viruses. This ac- activity activity tivity is fast and is maintained at temperatures lower The surface-active agents provide better wetting than ambient. and organic soil penetration, thus making iodophors less affected by soil than hypochlorite. The choice of Hydrogen peroxide Hydrogen peroxide (H2O2) 0023 surface-active agent may lead to foam generation in was introduced as a disinfectant in 1887. It is supplied applications such as CIP. in solution, which has a tendency to decompose: 1384 CLEANING PROCEDURES IN THE FACTORY/Types of Disinfectant

derivatives of guanidine, a naturally occurring sub- 2H O ! 2H O þ O : 2 2 2 2 stance found in vegetables such as turnips and cereals: Manual use of hydrogen peroxide is not recom- mended, but it is used in spray applications such as NH aseptic packaging. Hydrogen peroxide is both bac- tericidal and fungicidal. Some bacteria and fungi are C less sensitive because of catalase activity, which des-

troys H2O2. Hydrogen peroxide is slow-acting, so H2NNH2 that a long contact time or elevated temperature is required for effective disinfection. Biguanides are usually supplied as polymers in the salt form, mostly as the hydrochloride. Optimum activity Nonoxidizing Disinfectants liesbetweenpH3.0andpH9.0.BelowpH3.0,activityis suppressed, whilst above pH 9.0, they are precipitated. 0024 Quaternary ammonium compounds Quaternary They are cationic in nature but are not regarded as 0030 ammonium compounds (QACs) were first introduced surface-active. Biguanides do not foam and are, there- in 1917 and are probably the best known cationic fore, suitable for CIP; they may also be used for soak surface-active agents. Their general formula is as and manual cleaning. They are noncorrosive but taint follows: may be a problem if not properly rinsed. The in-use + solution is stable but is affected by organic soil and, to R1 R2 some extent, by hard water. Most biguanides have equal antibacterial activity 0031 − N X against Gram-positive and Gram-negative microor- ganisms. They are less effective against molds and R4 R3 yeasts, and are ineffective against bacterial spores and viruses. X is usually a halide but sometimes a sulfate ion. R1, R2,R3, and R4 may be a variety of alkyl or aryl Amphoterics Amphoterics have been in use as dis- 0032 groups. infectants since the early 1950s. They are based on a 0025 QACs are generally poor detergents but good wet- substituted amino acid, usually glycerine. The term ting agents. In solution, they ionize to produce a ampholyte is often used to describe them because in cation, the substituted nitrogen part of the molecule, solution they ionize to produce cations, anions, or which provides the surface-active property. The zwitterions, depending on the pH: length of the carbon chain in the R groups affects þ the disinfectant ability; usually, C8 to C18 are the most effective. RÀ N H2ÀCH2ÀCH2ÀCð¼¼ OÞOH Acid cation 0026 The surface-active nature of these molecules tends þ À to make them too high-foaming for CIP use, but they RÀ N H2ÀCH2ÀCH2ÀCð¼¼ OÞO can be used for soak and manual cleaning at 200– Zwitterion 400 p.p.m. active. The optimum activity is around À neutral pH, but QACs are active between pH 3.0 and R À NHÀCH2ÀCH2ÀCð¼¼ OÞO : 10.0. Activity may be inhibited by water hardness. Alkaline anion 0027 QACs are noncorrosive and are stable at in-use Only certain amphoterics have a disinfecting ability dilution. Their major disadvantages are that they are and surface activity. The disinfecting ability appears affected by organic soil and that they tend to cling to to increase with the increase of basic groups. surfaces, so that they may be difficult to rinse off, Amphoterics tend to beviscousliquids that are freely 0033 resulting in possible taint problems. soluble in water. They are generally too high-foaming 0028 The antimicrobial range of QACs is less than that for use in CIP,but are suitable for soak, spray, and hand of the oxidizing disinfectants. They are less effective use. Amphoterics are equally effective against Gram- against Gram-negative bacteria than against Gram- negative and Gram-positive bacteria; they are less ef- positive bacteria. They also have limited activity fective against yeasts and molds, and have very little against bacterial spores and very little activity against effect against bacterial spores and viruses. The opti- viruses. To be effective against yeasts and molds, a mum activity lies between pH 3.0 and 9.0. higher concentration is required. Properties such as soil tolerance and corrosion vary 0034 with the amphoteric concerned. Corrosion is not 0029 Biguanides Biguanides with antimicrobial activity usually a problem. The in-use solution, usually were first reported in 1933. The biguanides are 1000 p.p.m. active, is stable. CLEANING PROCEDURES IN THE FACTORY/Overall Approach 1385

0035 Acid anionics The active molecule in acid anionics For the quaternary ammonium compounds, the 0042 varies considerably. There are two main types: those biguanides and the amphoterics, it would be neces- based on carboxylic acids, which include fatty acids sary to know the specific active molecule to be able to and derivatives, and those based on anionic surfac- quantify these activities in effluent. The active content tants combined with mineral acid. could then be determined by HPLC. 0036 Acid anionics tend to be formulated products with Acid anionics can be detected in the effluent by 0043 additions to aid activity or solubility. Properties will determining the anionic content. vary with product, but they tend to have some deter- gent and wetting ability. The higher-foaming products Comparison with Steam are unsuitable for CIP, so that their general use is for spray. They are not suitable for hand use, since a pH of There is no chemical suitable for use as a disinfectant 0044 2 is required for optimum antimicrobial activity. in the food factory that can compete with steam. It 0037 The antimicrobial activity is against Gram- is effective against bacteria, molds, yeasts, bacterial negative and Gram-positive bacteria, but they are spores, and viruses. It is not affected by soil and hard less effective against bacterial spores and viruses. water. There are no corrosion or stability problems, Certain carboxylic acid types are active against yeasts and it leaves no residues. The drawbacks are that it and molds. Both types are affected by organic soil and cannot be used with heat-sensitive plant materials, water hardness, but again, both properties will vary and it needs careful use to avoid human contact. with the product. The in-use solutions are stable. See also: Effluents from Food Processing: On-Site Processing of Waste; Disposal of Waste Water; Effluent Problems Composition and Analysis; Spoilage: Bacterial Spoilage; Molds in Spoilage; Yeasts in Spoilage 0038 The oxidizing disinfectants are degraded very easily by organic soil to ineffective products. Peracetic acid and hydrogen peroxide break down to the products Further Reading that have been described earlier. Block S (1977) Disinfection, Sterilisation and Preservation. 0039 The breakdown products from the halogens vary Philadelphia, PA: Lea & Febiger. with pH of the effluent, but in general, halide ions will Hugo WB (1971) Inhibition and Destruction of the Micro- be produced. The halogens should not be mixed with bial Cell. London: Academic Press. acid products, as chlorine will react with organic Hugo WB (1991) A brief history of heat and chemical chemicals to produce organo-chloro compounds, preservation and disinfection. Journal of Applied Bac- which may be carcinogenic. The nonoxidizing disin- teriology 71: 9–18. fectants in modern products tend to consist of bio- Sykes G (1972) Disinfection and Sterilisation (ICMSF) degradable compounds. The cationic products will International Commission on Microbiology Specifica- adsorb on to organic material. The biguanides are tion for Foods. London: Chapman & Hall. incompatible with alkaline chemicals and will form a precipitate. (See Effluents from Food Processing: On-Site Processing of Waste; Disposal of Waste Water; Composition and Analysis.) Overall Approach Analysis of Disinfectants in Waste Water H M J van Eijk and F A Majoor, Unilever Research 0040 Obviously, detection will tend to depend on the con- Vlaardingen, Vlaardingen, The Netherlands centration of disinfectant present. The oxidizing dis- Copyright 2003, Elsevier Science Ltd. All Rights Reserved. infectants are unlikely to be detected. Halide ions can be detected but cannot be identified as coming from the disinfectant. 0041 Using an available chlorine probe, chlorine may Background be detected up to 200 p.p.m., but because of the Plant and equipment is generally cleaned for one of 0001 presence of organic material and other chemicals, two reasons. the presence of available chlorine may not be detected. As with chlorine, available iodine can be detected using 1. Microbiological 0002 a probe, but iodine is converted very quickly to iodide. . defined by required final product microbio- 0003 The breakdown products of peracetic acid and hydro- logical quality. gen peroxide are unlikely to be detected. 2. Process 0004