Cleaning and disinfection J. Holah, Campden and Chorleywood Food Research Association 14.1 Introduction Chapter 13 has outlined the concept of hygienic designand hygienic practices'in controlling the safety of chilled food products. This chapter deals with hygienic practices, specifically those related to cleaning and disinfection Contamination in food products may arise from four main sources: the constituent raw materials, surfaces, people (and other animals) and the air Control of the raw materials is addressed elsewhere in this book and is the only non-environmental contamination route. Food may pick up contamination as it is moved across product contact surfaces or if it is touched or comes into contact ith people(food handlers)or other animals(pests). The air acts as both a source of contamination, i.e. from outside the processing area, or as a transport medium, e.g. moving contamination from non-product to product contact surfaces Provided that the process environment and production equipment have been hygienically designed( Chapter 13), cleaning and disinfection (referred to together as'sanitation)are the major day-to-day controls of the environmental routes of food product contamination. When undertaken correctly, sanitation programmes have been shown to be cost-effective and easy to manage, and, if diligently applied, can reduce the risk of microbial or foreign body contamination. Given the intrinsic demand for high standards of hygiene in the production of short shelf-life chilled foods, together with pressure from customers,consumers and legislation for ever-increasing hygiene standards, sanitation demands the same degree of attention as any other key process in the manufacture of safe and wholesome chilled foods This chapter is concerned with the sanitation of "hard surfaces only equipment, floors, walls and utensils-as other surfaces, e.g. protective clothing
14.1 Introduction Chapter 13 has outlined the concept of ‘hygienic design’ and ‘hygienic practices’ in controlling the safety of chilled food products. This chapter deals with hygienic practices, specifically those related to cleaning and disinfection. Contamination in food products may arise from four main sources: the constituent raw materials, surfaces, people (and other animals) and the air. Control of the raw materials is addressed elsewhere in this book and is the only non-environmental contamination route. Food may pick up contamination as it is moved across product contact surfaces or if it is touched or comes into contact with people (food handlers) or other animals (pests). The air acts as both a source of contamination, i.e. from outside the processing area, or as a transport medium, e.g. moving contamination from non-product to product contact surfaces. Provided that the process environment and production equipment have been hygienically designed (Chapter 13), cleaning and disinfection (referred to together as ‘sanitation’) are the major day-to-day controls of the environmental routes of food product contamination. When undertaken correctly, sanitation programmes have been shown to be cost-effective and easy to manage, and, if diligently applied, can reduce the risk of microbial or foreign body contamination. Given the intrinsic demand for high standards of hygiene in the production of short shelf-life chilled foods, together with pressure from customers, consumers and legislation for ever-increasing hygiene standards, sanitation demands the same degree of attention as any other key process in the manufacture of safe and wholesome chilled foods. This chapter is concerned with the sanitation of ‘hard’ surfaces only – equipment, floors, walls and utensils – as other surfaces, e.g. protective clothing 14 Cleaning and disinfection J. Holah, Campden and Chorleywood Food Research Association
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