《冷冻食品》（英文第二版） Part 14 Cleaning and disinfection.pdf_大学文库

398 Chilled foods or skin, have been dealt with under personal hygiene( Chapter 13). In this context. surface sanitation is undertaken to remove microorganisms, or material conductive to microbial growth. This reduces the chance of contamination by pathogens and, by reducing spoilage organisms, may extend the shelf-life of some products remove materials that could lead to foreign body contam provide food or shelter for pests. This also improves the quality of product by removing food materials left on lines that may deteriorate and re-enter subsequent production runs extend the life of, and prevent damage to equipment and services, provide a safe and clean working environment for employees and boost morale and present a favourable image to customers and the public. On audit, the initial perception of an untidy'or 'dirty' processing area, and hence a poorly managed operation is subsequently difficult to overcome 14.2 Sanitation principles Sanitation is undertaken primarily to remove all undesirable material (food esidues, microorganisms, foreign bodies and cleaning chemicals) from surfaces in an economical manner, to a level at which any residues remaining are of minimal risk to the quality or safety of the product. Such undesirable materia generally referred to assoil,, can be derived from normal production, spillages, line-jams, equipment maintenance, packaging or general environmental contamination (dust and dirt). To undertake an adequate and economic sanitation programme, it is essential to characterise the nature of the soil to be removed The product residues are readily observed and may be characterised by their chemical composition, e.g. carbohydrate, fat, protein or starch. It is also important to be aware of processing and/or environmental factors, however, the same product soil may lead to a variety of cleaning problems dependent primarily on moisture levels and temperature. Generally, the higher the product oil temperature(especially if the soil has been baked) and the greater the time period before the sanitation programme is initiated (i.e. the drier the soil becomes), the more difficult the soil is to remove e Microorganisms can either be incorporated into the soil or can attach to urfaces and form layers or biofilms. There are a number of factors that have been shown to affect attachment and biofilm formation such as the level and type of microorganisms present, surface conditioning layer, substratum nature and roughness, temperature, pH, nutrient availabil ity and time available. Several reviews of biofilm formation in the food industry have been published including Pontefract (1991), Holah and Kearney(1992), Mattila-Sandholm and Wirtanen (1992), Carpentier and Cerf (1993), Zottola and Sasahara(1994), Gibson et al

or skin, have been dealt with under personal hygiene (Chapter 13). In this context, surface sanitation is undertaken to: • remove microorganisms, or material conductive to microbial growth. This reduces the chance of contamination by pathogens and, by reducing spoilage organisms, may extend the shelf-life of some products. • remove materials that could lead to foreign body contamination or could provide food or shelter for pests. This also improves the appearance and quality of product by removing food materials left on lines that may deteriorate and re-enter subsequent production runs. • extend the life of, and prevent damage to equipment and services, provide a safe and clean working environment for employees and boost morale and productivity. • present a favourable image to customers and the public. On audit, the initial perception of an ‘untidy’ or ‘dirty’ processing area, and hence a ‘poorly managed operation’ is subsequently difficult to overcome. 14.2 Sanitation principles Sanitation is undertaken primarily to remove all undesirable material (food residues, microorganisms, foreign bodies and cleaning chemicals) from surfaces in an economical manner, to a level at which any residues remaining are of minimal risk to the quality or safety of the product. Such undesirable material, generally referred to as ‘soil’, can be derived from normal production, spillages, line-jams, equipment maintenance, packaging or general environmental contamination (dust and dirt). To undertake an adequate and economic sanitation programme, it is essential to characterise the nature of the soil to be removed. The product residues are readily observed and may be characterised by their chemical composition, e.g. carbohydrate, fat, protein or starch. It is also important to be aware of processing and/or environmental factors, however, as the same product soil may lead to a variety of cleaning problems dependent primarily on moisture levels and temperature. Generally, the higher the product soil temperature (especially if the soil has been baked) and the greater the time period before the sanitation programme is initiated (i.e. the drier the soil becomes), the more difficult the soil is to remove. Microorganisms can either be incorporated into the soil or can attach to surfaces and form layers or biofilms. There are a number of factors that have been shown to affect attachment and biofilm formation such as the level and type of microorganisms present, surface conditioning layer, substratum nature and roughness, temperature, pH, nutrient availability and time available. Several reviews of biofilm formation in the food industry have been published including Pontefract (1991), Holah and Kearney (1992), Mattila-Sandholm and Wirtanen (1992), Carpentier and Cerf (1993), Zottola and Sasahara (1994), Gibson et al. 398 Chilled foods

(1995)and Kumar and Anand, (1998). In general, however, biofilm formation is usually found only on environmental surfaces, and progression of attached cells through microcolonies to extensive biofilm is limited by regular cleaning and disinfection ibson et al.(1995)in studies of attached microorganisms in 17 different processing environments, recorded 79% of isolates as Gram negative rods, 8.6% Gram positive cocci, 6.5% Gram positive rods and 1.2% yeast strains. The most ommon organisms were Pseudomonas, Staphylococcus and Enterobacter spp Pseudomonads are environmental psychrotrophic organisms that readily attach to surfaces and are common spoilage organisms in chilled foods. Other commor Gram negatives that have been associated with surfaces are coliform organisms that are widely distributed in the environment and may also be indicators of inadequate processing or post process contamination. Staphylococci are associated with human skin and therefore their presence on surfaces may be as a result of transfer from food handlers. In addition, Mettler and Carpentier(1998) studied the microflora associated with the surfaces in milk, meat and pastry sites and concluded that the micro-flora was specific to the processing environment Bacteria adhering to the food product contact surfaces may be an important source of potential contamination leading to serious hygienic problems and economic losses due to food spoilage. For example, pseudomonads and many other Gram negative organisms detected on surfaces are the spoilage organisms of concern in chilled foods. The survival of organisms in biofilms may be a source of post process contamination, resulting in reduced shelf life of the oroduct. In addition, Listeria monocytogenes has been isolated from a range of food processing surfaces( Walker et al. 1991, Lawrence and Gilmore 1995 and Destro et al. 1996)and is usually looked for in high-risk processing areas via the company environmental sampling plan Following HACCP principles, if the food processor believes that biofilms are a risk to the safety of the food product, appropriate control steps must be taken. These would include providing an environment in which the formation of the biofilm would be limited, undertaking cleaning and disinfection programmes as required, monitoring and controlling these programmes to ensure their success during their operation and verifying their performance by a suitable(usually microbiological)assessment. Within the sanitation programme, the cleaning phase can be divided up into three stages, following the pioneering work of Jennings(1965) and interpreted by Koopal (1985), with the addition of a fourth stage to cover disinfection These are described below 1. The wetting and penetration by the cleaning solution of both the soil and the equipment surface. 2. The reaction of the cleaning solution with both the soil and the surface to facilitate: peptisation of organic materials, dissolution of soluble organics and minerals, emulsification of fats and the dispersion and removal from the surface of solid soil components

(1995) and Kumar and Anand, (1998). In general, however, biofilm formation is usually found only on environmental surfaces, and progression of attached cells through microcolonies to extensive biofilm is limited by regular cleaning and disinfection. Gibson et al.(1995) in studies of attached microorganisms in 17 different processing environments, recorded 79% of isolates as Gram negative rods, 8.6% Gram positive cocci, 6.5% Gram positive rods and 1.2% yeast strains. The most common organisms were Pseudomonas, Staphylococcus and Enterobacter spp. Pseudomonads are environmental psychrotrophic organisms that readily attach to surfaces and are common spoilage organsisms in chilled foods. Other common Gram negatives that have been associated with surfaces are coliform organisms that are widely distributed in the environment and may also be indicators of inadequate processing or post process contamination. Staphylococci are associated with human skin and therefore their presence on surfaces may be as a result of transfer from food handlers. In addition, Mettler and Carpentier (1998) studied the microflora associated with the surfaces in milk, meat and pastry sites and concluded that the micro-flora was specific to the processing environment. Bacteria adhering to the food product contact surfaces may be an important source of potential contamination leading to serious hygienic problems and economic losses due to food spoilage. For example, pseudomonads and many other Gram negative organisms detected on surfaces are the spoilage organisms of concern in chilled foods. The survival of organisms in biofilms may be a source of post process contamination, resulting in reduced shelf life of the product. In addition, Listeria monocytogenes has been isolated from a range of food processing surfaces (Walker et al. 1991, Lawrence and Gilmore 1995 and Destro et al. 1996) and is usually looked for in high-risk processing areas via the company environmental sampling plan. Following HACCP principles, if the food processor believes that biofilms are a risk to the safety of the food product, appropriate control steps must be taken. These would include providing an environment in which the formation of the biofilm would be limited, undertaking cleaning and disinfection programmes as required, monitoring and controlling these programmes to ensure their success during their operation and verifying their performance by a suitable (usually microbiological) assessment. Within the sanitation programme, the cleaning phase can be divided up into three stages, following the pioneering work of Jennings (1965) and interpreted by Koopal (1985), with the addition of a fourth stage to cover disinfection. These are described below. 1. The wetting and penetration by the cleaning solution of both the soil and the equipment surface. 2. The reaction of the cleaning solution with both the soil and the surface to facilitate: peptisation of organic materials, dissolution of soluble organics and minerals, emulsification of fats and the dispersion and removal from the surface of solid soil components. Cleaning and disinfection 399

400 Chilled foods 3. The prevention of redeposition of the dispersed soil back onto the cleansed surface 4. The wetting by the disinfection solution of residual microorganisms to facilitate reaction with cell membranes and/or penetration of the microbial cell to produce a biocidal or biostatic action. Dependent on whether the disinfectant contains a surfactant and the disinfectant practice chosen (i.e with or without rinsing), this may be followed by dispersion of the microorganisms from the surface of four major factors as described below. The combinations of these four factors vary for different cleaning systems and, generally, if the use of one energy source is restricted, this short-fall may be compensated for by utilising greater nputs from the others 1. mechanical or kinetic energy 2. chemical energy 3. temperature or thermal energy Mechanical or kinetic energy is used to remove soils physically and may include craping, manual brushing and automated scrubbing(physical abrasion)and pressure jet washing(fluid abrasion). Of all four factors, physical abrasion is regarded as the most efficient in terms of energy transfer(Offiler 1990), and the efficiency of fluid abrasion and the effect of impact pressure has been described by Anon.(1973)and Holah (1991). Mechanical energy has also been demonstrated to be the most efficient for biofilm removal (Blenkinsopp and Costerton 1991. Wirtanen and Mattila Sandholm 1993.1994 Mattila-Sandholm and Wirtanen 1992 and Gibson et al. 1999) e In cleaning, chemical energy is used to break down soils to render them sier to remove and to suspend them in solution to aid rinsability. At the time of writing, no cleaning chemical has been marketed with the benefit of aiding microorganism removal. In chemical disinfection. chemicals react with microorganisms remaining on surfaces after cleaning to reduce their viability The chemical effects of cleaning and disinfection increase with temperature in a linear relationship and approximately double for every 10oC rise. For fatty and oily soils, temperatures above their melting point are used, to break down and mulsify these deposits and so aid removal. The influence of detergency in cleaning and disinfection has been described by Dunsmore(1981), Shupe et al. (1982), Mabesa et al.(1982), Anderson et al.(1985) and Middlemiss et al. (1985). For cleaning processes using mechanical, chemical and thermal energies, generally the longer the time period employed, the more efficient he process. When extended time periods can be employed in sanitation programmes, e.g. soak-tank operations, other energy inputs can be reduced(e.g reduced detergent concentration, lower temperature or less mechanical brushing

3. The prevention of redeposition of the dispersed soil back onto the cleansed surface. 4. The wetting by the disinfection solution of residual microorganisms to facilitate reaction with cell membranes and/or penetration of the microbial cell to produce a biocidal or biostatic action. Dependent on whether the disinfectant contains a surfactant and the disinfectant practice chosen (i.e. with or without rinsing), this may be followed by dispersion of the microorganisms from the surface. To undertake these four stages, sanitation programmes employ a combination of four major factors as described below. The combinations of these four factors vary for different cleaning systems and, generally, if the use of one energy source is restricted, this short-fall may be compensated for by utilising greater inputs from the others. 1. mechanical or kinetic energy 2. chemical energy 3. temperature or thermal energy 4. time. Mechanical or kinetic energy is used to remove soils physically and may include scraping, manual brushing and automated scrubbing (physical abrasion) and pressure jet washing (fluid abrasion). Of all four factors, physical abrasion is regarded as the most efficient in terms of energy transfer (Offiler 1990), and the efficiency of fluid abrasion and the effect of impact pressure has been described by Anon. (1973) and Holah (1991). Mechanical energy has also been demonstrated to be the most efficient for biofilm removal (Blenkinsopp and Costerton 1991, Wirtanen and Mattila Sandholm 1993, 1994, Mattila-Sandholm and Wirtanen 1992 and Gibson et al. 1999). In cleaning, chemical energy is used to break down soils to render them easier to remove and to suspend them in solution to aid rinsability. At the time of writing, no cleaning chemical has been marketed with the benefit of aiding microorganism removal. In chemical disinfection, chemicals react with microorganisms remaining on surfaces after cleaning to reduce their viability. The chemical effects of cleaning and disinfection increase with temperature in a linear relationship and approximately double for every 10ºC rise. For fatty and oily soils, temperatures above their melting point are used, to break down and emulsify these deposits and so aid removal. The influence of detergency in cleaning and disinfection has been described by Dunsmore (1981), Shupe et al. (1982), Mabesa et al. (1982), Anderson et al. (1985) and Middlemiss et al. (1985). For cleaning processes using mechanical, chemical and thermal energies, generally the longer the time period employed, the more efficient the process. When extended time periods can be employed in sanitation programmes, e.g. soak-tank operations, other energy inputs can be reduced (e.g. reduced detergent concentration, lower temperature or less mechanical brushing). 400 Chilled foods

Cleaning and disinfection 401 Soiling of surfaces is a natural process which reduces the free energy of the system. To implement a sanitation programme, therefore, energy must be added to the soil to reduce both soil particle-soil particle and soil particle-equipment surface interactions. The mechanics and kinetics of these interactions have been discussed by a number of authors (Jennings 1965, Schlussler 1975, Loncin 1977, Corrieu 1981, Koopal 1985, Bergman and Tragardh 1990), and readers are directed to these articles since they fall beyond the scope of this chapter. In practical terms, however, it is worth looking at the principles involved in basic soil removal, as they have an influence on the management of sanitation programmes Soil removal from surfaces decreases such that the log of the mass of soil per nit area remaining is linear with respect to cleaning time(Fig. 14.1(a)and thus follows first-order reaction kinetics (Jennings 1965, Schlusser 1975). This approximation,however, is only valid in the central portion of the plot and, in practice, soil removal is initially faster and ultimately slower(dotted line in Fig 14.1(a)than that which a first-order reaction predicts. The reasons for this unclear, though initially, unadhered, gross oil is usually easily removed ( Loncin 1977)whilst ultimately, soils held within surface imperfections, or otherwise protected from cleaning effects, would be more difficult to remove(Holah and Routine cleaning operations are never, therefore, 100% efficient, and over a course of multiple soiling/cleaning cycles, soil deposits(potentially including microorganisms)will be retained. As soil accumulates, cleaning efficiency will decrease and, as shown in plot A, Fig. 14.1(b), soil deposits may for a period grow exponentially. The timescale for such soil accumulation will differ for all 品E0 Cleaning time→> Number of periodic cleans Fig 14.1 Soil removal and accumulation. (a) Removal of soil with cleaning time. Solid line is theoretical removal, dotted line is cleaning in practice.(b) Build up of soil(and/or microorganisms); A, without periodic cleans and b, with periodic cleans. (After Dunsmore et al. 1981)

Soiling of surfaces is a natural process which reduces the free energy of the system. To implement a sanitation programme, therefore, energy must be added to the soil to reduce both soil particle-soil particle and soil particle-equipment surface interactions. The mechanics and kinetics of these interactions have been discussed by a number of authors (Jennings 1965, Schlussler 1975, Loncin 1977, Corrieu 1981, Koopal 1985, Bergman and Tragardh 1990), and readers are directed to these articles since they fall beyond the scope of this chapter. In practical terms, however, it is worth looking at the principles involved in basic soil removal, as they have an influence on the management of sanitation programmes. Soil removal from surfaces decreases such that the log of the mass of soil per unit area remaining is linear with respect to cleaning time (Fig. 14.1(a)) and thus follows first-order reaction kinetics (Jennings 1965, Schlusser 1975). This approximation, however, is only valid in the central portion of the plot and, in practice, soil removal is initially faster and ultimately slower (dotted line in Fig. 14.1(a)) than that which a first-order reaction predicts. The reasons for this are unclear, though initially, unadhered, gross oil is usually easily removed (Loncin 1977) whilst ultimately, soils held within surface imperfections, or otherwise protected from cleaning effects, would be more difficult to remove (Holah and Thorpe 1990). Routine cleaning operations are never, therefore, 100% efficient, and over a course of multiple soiling/cleaning cycles, soil deposits (potentially including microorganisms) will be retained. As soil accumulates, cleaning efficiency will decrease and, as shown in plot A, Fig. 14.1(b), soil deposits may for a period grow exponentially. The timescale for such soil accumulation will differ for all Fig. 14.1 Soil removal and accumulation. (a) Removal of soil with cleaning time. Solid line is theoretical removal, dotted line is cleaning in practice. (b) Build up of soil (and/or microorganisms); A, without periodic cleans and B, with periodic cleans. (After Dunsmore et al. 1981). Cleaning and disinfection 401

402 Chilled foods processing applications and can range from hours(e.g. heat exchangers)to typically several days or weeks, and in practice is controlled by the application of a ' clean(Dunsmore et al. 1981). Periodic cleans are employed to return the surface-bound soil accumulation to an acceptable base level(plot B, ig. 14.1(b)and are achieved by increasing cleaning time and/or energy input, e.g. higher temperatures, alternative chemicals or manual scrubbing. A typical example of a periodic clean is the week-end clean down or ' bottoming 14.3 Sanitation chemicals In many instances, management view the costs of cleaning and disinfection as the price of the chemicals purchased, primarily because this is the only"invoice that they see. In reality, however, sanitation chemicals are likely to represent approximately only 5% of the true costs, with labour and water costs being the most significant. The purchase of a good quality formulated cleaning product, whilst being initially more expensive, will more than cover its costs by oth the standard of clean and cle Within the sanitation programme it has traditionally been recognised that cleaning is responsible for the removal of not only the soil but also the majority of the microorganisms present Mrozek(1982) showed a reduction in bacterial numbers on surfaces by up to 3 log orders whilst Schmidt and Cremling(1981) described reductions of 2-6 log orders The results of work at CCfrA on the assessment of well constructed and competently undertaken sanitation programmes on food processing equipment in eight chilled food factories is shown in Table 14.1. The results suggest that both cleaning and disinfection are equally responsible for reducing the levels of adhered microorganisms. It is important, therefore, not only to purchase quality cleaning chemicals for their soil removal capabilities but also for their potential for microbial removal Unfortunately no single cleaning agent is able to perform all the functions necessary to facilitate a successful cleaning programme; so a cleaning solution, or detergent, is blended from a range of typical characteristic components urfactants · inorganic alkalis Table 14.1 Arithmetic and log mean bacterial counts on food processing equipment before and after cleaning and after disinfection Before cleaning After cleaning After disinfection Arithmetic mean 867×104 2.5×103 g mean No of observations 3147

processing applications and can range from hours (e.g. heat exchangers) to typically several days or weeks, and in practice is controlled by the application of a ‘periodic’ clean (Dunsmore et al. 1981). Periodic cleans are employed to return the surface-bound soil accumulation to an acceptable base level (plot B, Fig. 14.1(b)) and are achieved by increasing cleaning time and/or energy input, e.g. higher temperatures, alternative chemicals or manual scrubbing. A typical example of a periodic clean is the ‘week-end clean down’ or ‘bottoming’. 14.3 Sanitation chemicals In many instances, management view the costs of cleaning and disinfection as the price of the chemicals purchased, primarily because this is the only ‘invoice’ that they see. In reality, however, sanitation chemicals are likely to represent approximately only 5% of the true costs, with labour and water costs being the most significant. The purchase of a good quality formulated cleaning product, whilst being initially more expensive, will more than cover its costs by increasing both the standard of clean and cleaning efficiency. Within the sanitation programme it has traditionally been recognised that cleaning is responsible for the removal of not only the soil but also the majority of the microorganisms present. Mrozek (1982) showed a reduction in bacterial numbers on surfaces by up to 3 log orders whilst Schmidt and Cremling (1981) described reductions of 2–6 log orders. The results of work at CCFRA on the assessment of well constructed and competently undertaken sanitation programmes on food processing equipment in eight chilled food factories is shown in Table 14.1. The results suggest that both cleaning and disinfection are equally responsible for reducing the levels of adhered microorganisms. It is important, therefore, not only to purchase quality cleaning chemicals for their soil removal capabilities but also for their potential for microbial removal. Unfortunately no single cleaning agent is able to perform all the functions necessary to facilitate a successful cleaning programme; so a cleaning solution, or detergent, is blended from a range of typical characteristic components: • water • surfactants • inorganic alkalis Table 14.1 Arithmetic and log mean bacterial counts on food processing equipment before and after cleaning and after disinfection Before cleaning After cleaning After disinfection Arithmetic mean 1.32106 8.67104 2.5103 log mean 3.26 2.35 1.14 No. of observations 498 1090 3147 402 Chilled foods

Cleaning and disinfection 40 inorganic and organic acids · sequestering agents For the majority of food processing operations it may be necessary, therefore employ a number of cleaning products, for specific operations. This requirement must be balanced by the desire to keep the range of cleaning chemicals on site to a minimum so as to reduce the risk of using the wrong product, to simplify the b of the safety officer and to allow chemical purchase to be based more on the economics of bulk quantities. The range of chemicals and their purposes is well documented(Anon. 1991, Elliot 1980, ICMSF 1980, 1988, Hayes 1985, Holah 1991, Koopal 1985, Russell et al. 1982)and only an overview of the principles is given here. Water is the base ingredient of allwet cleaning systems and must be of table quality. Water provides the cheapest readily available transport medium for rinsing and dispersing soils, has dissolving powers to remove ionic-soluble compounds such as salts and sugars, will help emulsify fats at temperatures above their melting point, and, in high-pressure cleaning, can be used as an abrasive agent. On its own, however, water is a poor wetting agent and cannot dissolve non-ionic compounds Organic surfactants(surface-active or wetting agents)are amphipolar and are omposed of a long non-polar(hydrophobic or lyophilic) chain or tail and a polar(hydrophilic or lyophobic) head. Surfactants are classified as anionic (including the traditional soaps), cationic, or non-ionic, depending on their ionic charge in solution, with anionics and non-ionics being the most common Amphipolar molecules aid cleaning by reducing the surface tension of water and by emulsification of fats. If a surfactant is added to a drop of water on a surface the polar heads disrupt the waters hydrogen bonding and so reduce the surface tension of the water and allow the drop to collapse andwet' the surface Increased wettability leads to enhanced penetration into soils and surface irregularities and hence aids cleaning action. Fats and oils are emulsified as the hydrophilic heads of the surfactant molecules dissolve in the water whilst the hydrophobic end dissolves in the fat. If the fat is surface-bound, the forces acting on the fat/water interface are such that the fat particle will form a sphere(to obtain the lowest surface area for its given volume) causing the fat deposit to roll-up' and detach itself from the surface. lkalis are useful cleaning agents as they are cheap, break down proteins through the action of hydroxyl ions, saponify fats and, at higher concentrations, may be bactericidal. Strong alkalis, usually sodium hydroxide(or caustic soda) exhibit a high degree of saponification and protein disruption, though they are corrosive and hazardous to operatives. Correspondingly, weak alkalis are less hazardous but also less effective. Alkaline detergents may be chlorinated to aid the removal of proteinaceous deposits, but chlorine at alkaline ph is not an effective biocide. The main disadvantages of alkalis are their potential to precipitate hard water ions, the formation of scums with soaps, and their poor disability

• inorganic and organic acids • sequestering agents. For the majority of food processing operations it may be necessary, therefore, to employ a number of cleaning products, for specific operations. This requirement must be balanced by the desire to keep the range of cleaning chemicals on site to a minimum so as to reduce the risk of using the wrong product, to simplify the job of the safety officer and to allow chemical purchase to be based more on the economics of bulk quantities. The range of chemicals and their purposes is well documented (Anon. 1991, Elliot 1980, ICMSF 1980, 1988, Hayes 1985, Holah 1991, Koopal 1985, Russell et al. 1982) and only an overview of the principles is given here. Water is the base ingredient of all ‘wet’ cleaning systems and must be of potable quality. Water provides the cheapest readily available transport medium for rinsing and dispersing soils, has dissolving powers to remove ionic-soluble compounds such as salts and sugars, will help emulsify fats at temperatures above their melting point, and, in high-pressure cleaning, can be used as an abrasive agent. On its own, however, water is a poor ‘wetting’ agent and cannot dissolve non-ionic compounds. Organic surfactants (surface-active or wetting agents) are amphipolar and are composed of a long non-polar (hydrophobic or lyophilic) chain or tail and a polar (hydrophilic or lyophobic) head. Surfactants are classified as anionic (including the traditional soaps), cationic, or non-ionic, depending on their ionic charge in solution, with anionics and non-ionics being the most common. Amphipolar molecules aid cleaning by reducing the surface tension of water and by emulsification of fats. If a surfactant is added to a drop of water on a surface, the polar heads disrupt the water’s hydrogen bonding and so reduce the surface tension of the water and allow the drop to collapse and ‘wet’ the surface. Increased wettability leads to enhanced penetration into soils and surface irregularities and hence aids cleaning action. Fats and oils are emulsified as the hydrophilic heads of the surfactant molecules dissolve in the water whilst the hydrophobic end dissolves in the fat. If the fat is surface-bound, the forces acting on the fat/water interface are such that the fat particle will form a sphere (to obtain the lowest surface area for its given volume) causing the fat deposit to ‘roll-up’ and detach itself from the surface. Alkalis are useful cleaning agents as they are cheap, break down proteins through the action of hydroxyl ions, saponify fats and, at higher concentrations, may be bactericidal. Strong alkalis, usually sodium hydroxide (or caustic soda), exhibit a high degree of saponification and protein disruption, though they are corrosive and hazardous to operatives. Correspondingly, weak alkalis are less hazardous but also less effective. Alkaline detergents may be chlorinated to aid the removal of proteinaceous deposits, but chlorine at alkaline pH is not an effective biocide. The main disadvantages of alkalis are their potential to precipitate hard water ions, the formation of scums with soaps, and their poor rinsability. Cleaning and disinfection 403

404 Chilled foods Acids have little detergency properties, although they are very useful in making soluble carbonate and mineral scales, including hard water salts and proteinaceous deposits. As with alkalis, the stronger the acid the more effective it is; though, in addition, the more corrosive to plant and operatives. Acids are not used as frequently as alkalis in chilled food operations and tend to be used Sequestering agents(sequestrants or chelating agents) are employed to prevent mineral ions precipitating by forming soluble complexes with them Their primary use is in the control of water hardness ions and they are added to surfactants to aid their dispersion capacity and rinsability. Sequestrants are most commonly based on ethylene diamine tetracetic acid (EDTA), which is expensive. Although cheaper alternatives are available, these are usually polyphosphates which are environmentally unfriendly A general-purpose food detergent may, therefore, contain a strong alkali to saponify fats, weaker alkali"builders'or" agents, surfactants to improve wetting, dispersion and rinsability and sequestrants to control hard water ions. In addition, the detergent should ideally be safe, non-tainting, non-corrosive, stable, environmentally friendly and cheap. The choice of cleaning agent will depend on the soil to be removed and on its solubility characteristics, and these are summar- ised for a range of chilled products in Table 14.2(modified from Elliot 1980 Because of the wide range of food soils likely to be encountered and fluence of the food manufacturing site(temperature, humidity, type of equipment, time before cleaning, etc. ) there are currently no recognised laboratory methods for assessing the efficacy of cleaning compounds. Food manufacturers have to be satisfied that cleaning chemicals are working appropriately, by conducting suitable field trials. Although the majority of the microbial contamination is removed by the cleaning phase of the sanitation Table 14.2 Solubility characteristics and cleaning procedures recommended for a rang of soil types Soil type Solubility characteristics Cleaning procedure Sugars, organic Mildly alkaline detergent High protein food Water-soluble Chlorinated alkaline detergent poultry, fish) Alkali-soluble Slightly acid-soluble Starchy foods, tomatoes, Partly water-soluble Mildly alkaline detergent fruits Alkali-soluble Fatty foods(fat, butter, Water-insoluble Alkaline-soluble Heat-precipitated water Water-insoluble Acid cleaner used on a hardness. milk stone Alkaline-insoluble protein scale Acid-soluble

Acids have little detergency properties, although they are very useful in making soluble carbonate and mineral scales, including hard water salts and proteinaceous deposits. As with alkalis, the stronger the acid the more effective it is; though, in addition, the more corrosive to plant and operatives. Acids are not used as frequently as alkalis in chilled food operations and tend to be used for periodic cleans. Sequestering agents (sequestrants or chelating agents) are employed to prevent mineral ions precipitating by forming soluble complexes with them. Their primary use is in the control of water hardness ions and they are added to surfactants to aid their dispersion capacity and rinsability. Sequestrants are most commonly based on ethylene diamine tetracetic acid (EDTA), which is expensive. Although cheaper alternatives are available, these are usually polyphosphates which are environmentally unfriendly. A general-purpose food detergent may, therefore, contain a strong alkali to saponify fats, weaker alkali ‘builders’ or ‘bulking’ agents, surfactants to improve wetting, dispersion and rinsability and sequestrants to control hard water ions. In addition, the detergent should ideally be safe, non-tainting, non-corrosive, stable, environmentally friendly and cheap. The choice of cleaning agent will depend on the soil to be removed and on its solubility characteristics, and these are summarised for a range of chilled products in Table 14.2 (modified from Elliot 1980). Because of the wide range of food soils likely to be encountered and the influence of the food manufacturing site (temperature, humidity, type of equipment, time before cleaning, etc.), there are currently no recognised laboratory methods for assessing the efficacy of cleaning compounds. Food manufacturers have to be satisfied that cleaning chemicals are working appropriately, by conducting suitable field trials. Although the majority of the microbial contamination is removed by the cleaning phase of the sanitation Table 14.2 Solubility characteristics and cleaning procedures recommended for a range of soil types Soil type Solubility characteristics Cleaning procedure recommended Sugars, organic acids, salt Water-soluble Mildly alkaline detergent High protein foods (meat, Water-soluble Chlorinated alkaline detergent poultry, fish) Alkali-soluble Slightly acid-soluble Starchy foods, tomatoes, Partly water-soluble Mildly alkaline detergent fruits Alkali-soluble Fatty foods (fat, butter, Water-insoluble Mildly alkaline detergent; if margarine, oils) Alkaline-soluble ineffective, use strong alkali Heat-precipitated water Water-insoluble Acid cleaner, used on a hardness, milk stone, Alkaline-insoluble periodic basis protein scale Acid-soluble 404 Chilled foods

Cleaning and disinfection 405 programme, there are likely to be sufficient viable microorganisms remaining on the surface to warrant the application of a disinfectant. The aim of disinfection is therefore to further reduce the surface population of viable microorganisms, via removal or destruction, and/or to prevent surface microbial growth during the inter-production period. Elevated temperature is the best disinfectant as it penetrates into surfaces, is non-corrosive, is non-selective to microbial types, is easily measured and leaves no residue ( Jennings 1965). However, for open surfaces, the use of hot water or steam is uneconomic, hazardous or impossible and reliance is, therefore, placed on chemical biocides Whilst there are many chemicals with biocidal properties, many common disinfectants are not used in food applications because of safety or taint problems, e.g. phenolics or metal-ion-based products. In addition, other disinfectants are used to a limited extent only in chilled food manufacture and/or for specific purposes, e.g. peracetic acid, biguanides, formaldehyde glutaraldehyde, organic acids, ozone, chlorine dioxide, bromine and iodine ompounds. Of the acceptable chemicals, the most commonly used products are chlorine-releasing components quaternary ammonium compound amphoterics quaternary ammonium/amphoteric mixtures Chlorine is the cheapest disinfectant and is available as hypochlorite (or occasionally as chlorine gas) or in slow releasing forms(e.g. chloramines, dichlorodimethy hydantoin). Quaternary ammonium compounds ( Quats o DACs)are amphipolar, cationic detergents, derived from substituted ammonium salts with a chlorine or bromine anion and amphoterics are based on the amino acid glycine, often incorporating an imidazole group In a( CCFRA) survey undertaken of the UK food industry in 1987, of 145 applications of disinfectants 52% were chlorine based, 37% were quaternary ammonium compounds and 8% were amphoterics. Of these biocides there were respectively, 44, 30 and 8 branded products used. In a(CCFRA)European survey of 1993, the most common disinfectants used in the Uk and Scandinavian countries were QACs for open surfaces and peracetic acid and chlorine for closed, liquid handling surfaces. The survey also showed that open surfaces were usually cleaned with alkaline detergents which were foamed and then rinsed with medium pressure water(250psi)and closed systems were CIP cleaned with caustic followed by acidic detergents with a suitable rinse in- between. A survey of the approved disinfectant products in Germany (DVG listed) in 1994 indicated that 36% were QACs, 20% were mixtures of QACs with aldehydes or biguanides and 10% were amphoterics(Knauer-Kraetzl 1994). More recently the synergistic combinations of QACs and amphoterics have been explored in the UK and these compounds are now widely used in The characteristics of the most commonly used are 143. The properties of QAC/amphoteric mixes will be lar to their parent compounds with often enhanced microorganism contr

programme, there are likely to be sufficient viable microorganisms remaining on the surface to warrant the application of a disinfectant. The aim of disinfection is therefore to further reduce the surface population of viable microorganisms, via removal or destruction, and/or to prevent surface microbial growth during the inter-production period. Elevated temperature is the best disinfectant as it penetrates into surfaces, is non-corrosive, is non-selective to microbial types, is easily measured and leaves no residue (Jennings 1965). However, for open surfaces, the use of hot water or steam is uneconomic, hazardous or impossible, and reliance is, therefore, placed on chemical biocides. Whilst there are many chemicals with biocidal properties, many common disinfectants are not used in food applications because of safety or taint problems, e.g. phenolics or metal-ion-based products. In addition, other disinfectants are used to a limited extent only in chilled food manufacture and/or for specific purposes, e.g. peracetic acid, biguanides, formaldehyde, glutaraldehyde, organic acids, ozone, chlorine dioxide, bromine and iodine compounds. Of the acceptable chemicals, the most commonly used products are: • chlorine-releasing components • quaternary ammonium compounds • amphoterics • quaternary ammonium/amphoteric mixtures. Chlorine is the cheapest disinfectant and is available as hypochlorite (or occasionally as chlorine gas) or in slow releasing forms (e.g. chloramines, dichlorodimethylhydantoin). Quaternary ammonium compounds (Quats or QACs) are amphipolar, cationic detergents, derived from substituted ammonium salts with a chlorine or bromine anion and amphoterics are based on the amino acid glycine, often incorporating an imidazole group. In a (CCFRA) survey undertaken of the UK food industry in 1987, of 145 applications of disinfectants 52% were chlorine based, 37% were quaternary ammonium compounds and 8% were amphoterics. Of these biocides there were, respectively, 44, 30 and 8 branded products used. In a (CCFRA) European survey of 1993, the most common disinfectants used in the UK and Scandinavian countries were QACs for open surfaces and peracetic acid and chlorine for closed, liquid handling surfaces. The survey also showed that open surfaces were usually cleaned with alkaline detergents which were foamed and then rinsed with medium pressure water (250psi) and closed systems were CIP cleaned with caustic followed by acidic detergents with a suitable rinse inbetween. A survey of the approved disinfectant products in Germany (DVG listed) in 1994 indicated that 36% were QACs, 20% were mixtures of QACs with aldehydes or biguanides and 10% were amphoterics (Knauer-Kraetzl 1994). More recently the synergistic combinations of QACs and amphoterics have been explored in the UK and these compounds are now widely used in chilled food plants. The characteristics of the most commonly used are compared in Table 14.3. The properties of QAC/amphoteric mixes will be similar to their parent compounds with often enhanced microorganism control. Cleaning and disinfection 405