The efficacy of cleaning products on food industry surfaces.

Introduction

The incidence of foodborne illness in Australia is estimated at an average of 4.2 million cases each year; approximately 11,500 people succumb to foodborne illnesses in Australia each day (Food Standards Australia New Zealand, 2002). These figures equate to 220 cases per 1,000 persons in the population, compared with 190 cases per 1,000 in New Zealand and the United Kingdom and 175 cases per 1,000 in the United States. The estimated cost to the Australian community is over $2.6 billion each year. Although food-poisoning incidence rates are growing, less than 1 percent of cases are reported in notification schemes (Food Standards Australia New Zealand, 2002).

Changing eating habits mean that Australians are spending 30 percent of their food budget on dining out and take-out, and about 60 to 80 percent of foodborne illness are acquired from the food service industry (Food Standards Australia New Zealand, 2002). Various common bacteria are implicated in food poisoning because of their presence in large numbers in raw food and on kitchen surfaces and equipment, or because of bacterial survival during food preparation or recontamination of food after cooking (Angelillo, Viggiani, Greco, & Rito, 2001).

There is evidence that the survival and transfer of pathogenic bacteria via environmental surfaces are important (Humphrey, Martin, & Whitehead, 1994; Nastov, Tan, & Dingle, 2002). The kitchen environment is a vehicle of infection both for personnel and for the public. Unclean kitchen surfaces and equipment can harbor infective bacteria, which can contaminate food (Rusin, Orosz-Coughlin, & Gerba, 1998). Bacteria from raw meat and poultry can also be passed to cooked foods. Dust and soil containing dried organisms can lead to the proliferation of bacteria and contamination of foods.

Some of the pathogenic bacteria that cause food poisoning include Bacillus cereus, Campylobacter jejuni, Escherichia coli, Listeria monocytogenes, Salmonella species, Staphylococcus aureus, and Yersinia enterocolitica. Staphylococcus aureus is considered both a pathogen and an indicator of unhygienic food handling (Buckle et al., 1989). It may cause an intoxication disease within four to six hours, and symptoms of diarrhea and vomiting may last six to eight hours. Infection usually occurs in the kitchen from infected people who have cuts, abrasions, or lesions or from people who are nasal carriers (Angellilo et al., 2001). Food preparation areas with crevices and cracks tend to harbour staphylococci (Collins, Lyne, & Grange, 1995).

Escherichia coli can grow in food and on inadequately cleaned surfaces associated with food processing. It may enter the kitchen in raw foods and contaminate cooked foods via hands, surfaces, and kitchen equipment that have been used for both raw foods and cooked foods. Hence, the presence of E. coli is indicative of unhygienic food preparation. Infection may lead to symptoms that include prolonged diarrhea, severe abdominal pain, and mucosal damage (Buckle et al., 1989; Heritage, Evans, & Killington, 1999).

The hygiene status of food surfaces is essential for the production of high-quality safe food. Cleaning is either conducted automatically with clean-in-place systems or conducted manually depending on the nature of the surface. Two considerations are essential when surfaces are being cleaned: 1) cleaning to remove product residues and 2) sanitizing to destroy microorganisms (Health Department of Western Australia, 2000; Standards Australia, 2001). Inadequate cleaning may constitute a direct risk to the quality and safety of the foods that come in contact with the unclean surface (Patel, 1994).

Food Standards Australia and New Zealand have implemented preventive measures in the form of food safety programs based on the hazard analysis critical control point (HACCP) system. These programs ensure that the food industries minimize the potential for food contamination by implementing two food safety strategies. First, hazards are controlled by time, pH, temperature, and water activity of food. Second, personal hygiene, cleaning, and sanitizing are addressed (Angelillo et al., 2001; McSwane, & Linton, 2000).

According to the Health Department of Western Australia (2000) effective cleaning can be achieved through a four-stage process:

1. Preparation--remove dirt and food particles.

2. Cleaning--wash with hot water at 140[degrees]F (60[degrees]C) and detergent, and rinse with clean water.

3. Sanitizing--wash with hot water at 167[degrees]F (75[degrees]C) for at least one minute or apply a sanitizer as directed on the label.

4. Air-drying--leave benches, counters, and equipment to air-dry.

Compliance with these processes reduces the spread of pathogenic bacteria. It ensures that the premises are clean and sanitary and that high-quality safe foods are produced.

The objective of the study reported here was to investigate the effectiveness of different cloths and sanitizing methods for sanitizing surfaces in the food industry according to the standards of the Health Department of Western Australia. More specifically, the study examined whether use of fiber cloths sanitized with hot water at 167[degrees]F (75[degrees]C) resulted in concentrations of S. aureus and E. coli similar to those achieved with generic cloths sanitized with hot water at 167[degrees]F (75[degrees]C) or chemical sanitizers. The effectiveness of air-drying in maintaining low concentrations of bacteria also was investigated.

Methods

Preparation of Bacterial Suspensions

Gram-positive bacteria Staphylococcus aureus ATCC 25923 were grown in 100 milliliters (mL) of brain heart infusion broth (Amyl Media Pty. Ltd., Dandenong, New South Wales [NSW]) at 99[degrees]F [+ or -] 36[degrees]F (37[degrees]C [+ or -] 2[degrees]C) for 24 hours. Gram-negative bacteria Escherichia coli UB 1301 were grown in 100 mL of Lauryl tryptose broth (Amyl Media Pty. Ltd., Dandenong, NSW) at 99[degrees]F [+ or -] 36[degrees]F (37[degrees]C [+ or -] 2[degrees]C for 18 hours. These culture conditions were found to yield approximately 1[0.sup.9] colony-forming units per milliliter (CFUs/mL).

Preparation of Neutralizer

The neutralizer was adapted from methods described in the Australian Standards (Standards Australia, 1988). Two grams of sodium thiosulfate (Analytical Reagent, Univar, APS Ajax Finechem, Auburn, NSW); 100 mL of lecithin/Tween 80 emulsion containing 2 percent volume/volume (v/v) soybean lecithin (Naytura[TM], Yennora, NSW) in a 3 percent v/v aqueous solution of Tween 80 (Merck Pty. Ltd., Kisyth, Victoria) was added to 1 L of 0.1 percent peptone water. The neutralizer was autoclaved for 20 minutes at 200 kilopascals (kPa).

Neutralizer Verification

A suspension of the test organism containing 1[0.sup.9] CFUs/mL was used to verify the inactivation effect of the neutralizer. A 0.5-mL aliquot of a commercial-grade quaternary ammonium compound (QAC) or hypochlorite sanitizer was added to 9 mL neutralizer. After 15 seconds, 1 mL of the test organism was added to the solution, and the solution was shaken on a mechanical shaker for 10 seconds. One mL and 0.1 mL triplicate samples were plated at two minutes, one hour, and six hours using plate count agar (Oxoid Ltd., Basingstoke, UK).

[FIGURE 1 OMITTED]

A 1-mL aliquot of the test organism was added to 9.5 mL of neutralizer but no sanitizer. The solution was mixed and triplicate samples were plated as previously described. The plates were incubated at 99[degrees]F [+ or -] 36[degrees]F (37[degrees]C [+ or -] 2[degrees]C) for 24 hours (Standards Australia, 1992). When the plates showed no differences in the number of CFUs per milliliter, the neutralizer was considered effective.

Preparation and Inoculation of Surfaces

A food-grade stainless-steel kitchen bench top, Grade 304 (AvestaPolarit Pty. Ltd., Canning Vale, Western Australia), was marked with squares that were 5 centimeters (cm) by 10 cm. The surfaces were sanitized according to a validated cleaning protocol (Moore & Griffith, 2002). Initially they were disinfected for five minutes with a commercial-grade heavy-duty chlorinated sanitizer before being rinsed with boiling water. The surfaces were then thoroughly cleaned with commercial-grade detergent and boiling water. They were rinsed three times with boiling water to remove all detergent residues. All surfaces were left to air-dry for one hour at room temperature (Moore & Griffith).

[FIGURE 2 OMITTED]

A 0.1-mL aliquot of either S. aureus or E. coli was inoculated and spread evenly onto a 50-c[m.sup.2] surface (Moore & Griffith, 2002). The surfaces were allowed to air-dry for a further hour until no visible liquid remained on the surface.

Preparation of Cloths

The fiber cloths that were tested included kitchen fiber cloths and all-purpose fiber cloths (ENJO Pty. Ltd., Willeton, Western Australia). These cloths have longer fibers than do generic cloths and are statically charged to enhance the removal of dirt and dust from surfaces. The generic cloths that were tested included antibacterial cloths and cleaning cloths (Homebrand, Yennora, NSW). All cloths were divided into 310-c[m.sup.2] portions and autoclaved for 20 minutes at 200 kPa.

Microbiological Sampling of Surfaces

Positive-control assays were conducted by inoculation of bacteria on the surfaces without use of a cloth to sanitize the surface. Negative-control assays were performed on surfaces that were not inoculated with bacteria but were sanitized with a cloth.

The cloths were soaked in hot water at 167[degrees]F (75[degrees]C) for one minute or a generic-brand commercial-grade chemical sanitizer such as QAC or hypochlorite for six minutes. Sanitizers were applied according to the manufacturers' recommended in-use concentrations. After the 50-c[m.sup.2] surface was wiped four times with a cloth, a sterile cotton-tip swab was moistened with sterile 0.1 percent peptone water containing neutralizer, and the surface was swabbed. The swab was placed into 9 mL of 0.1 percent peptone water and neutralizer, and was cultured on plate count agar. The bacterial samples were incubated at 99[degrees]F [+ or -] 36[degrees]F (37[degrees]C [+ or -] 2[degrees]C) for 24 [+ or -] 2 hours.

The wet-surface tests were performed immediately after the surfaces had been wiped with a cloth, while they were still wet. Dry-surface tests were performed after the surfaces had been left to air-dry at room temperature for one hour.

Statistical Analyses

Statistical analyses of the bacterial concentrations were conducted with SPSS 10.0 for Windows (SPSS, Inc., Chicago, Illinois). The concentrations of bacteria were transformed to logarithmic values (lo[g.sub.10]) to achieve a normal distribution. Analyses that were performed included mean concentrations and the two-tailed paired t-tests with a confidence interval of 95 percent.

Results

Sanitizing the stainless-steel kitchen surfaces with each of the cloth-sanitizer combinations resulted in the removal of all vegetative bacteria. After the stainless-steel kitchen surfaces were left to air-dry for one hour, the overall concentrations of Gram-negative E. coli found on the surfaces were higher than the concentrations of Gram-positive S. aureus (Figure 1, Figure 2).

The kitchen fiber cloths and the all-purpose fiber cloths gave lower concentrations of both species of bacteria than did the antibacterial cloths and cleaning cloths sanitized with hot water at 167[degrees]F (75[degrees]C) (Figure 1, Figure 2).

Overall, use of the QAC sanitizer resulted in the lowest concentrations of bacteria on the stainless-steel kitchen surfaces. The kitchen fiber cloths sanitized with hot water at 167[degrees]F (75[degrees]C) did not result in significantly different concentrations of S. aureus than did the antibacterial cloths (p = .144) and the cleaning cloths (p = .297) sanitized with QAC (Figure 1). These results were consistent for E. coli for both the antibacterial cloths (p = .120) and the cleaning cloths (p = .062) sanitized with QAC (Figure 2).

Significant differences in the concentrations of S. aureus and E. coli were found on the surfaces cleaned by the all-purpose fiber cloths sanitized with hot water at 167[degrees]F (75[degrees]C) and the QAC sanitizer on the antibacterial cloths and cleaning cloths (p < .050). The QAC sanitizer on the generic cloths gave lower concentrations of both bacteria on the stainless-steel kitchen surfaces (Figure 1, Figure 2).

Use of the hypochlorite-sanitized cloths resulted in the highest concentrations of bacteria on the stainless-steel kitchen surfaces (Figure 1, Figure 2). The concentrations of S. aureus were significantly lower for the kitchen fiber cloths sanitized with hot water at 167[degrees]F (75[degrees]C) than for the generic cloths (p < .050) sanitized with hypochlorite (Figure 1). The concentrations of E. coli also were significantly lower for the kitchen fiber cloths sanitized with hot water at 167[degrees]F (75[degrees]C) than for the cleaning cloths sanitized with hypochlorite (p < .050) (Figure 2).

Use of the all-purpose fiber cloths sanitized with hot water at 167[degrees]F (75[degrees]C) resulted in significantly lower concentrations of S. aureus (p = .003) and E. coli (p < .050) on the stainless-steel kitchen surfaces than did use of the cleaning cloths sanitized with hypochlorite.

Discussion

Sanitizing the stainless-steel kitchen surfaces with the different cloths and hot water at 167[degrees]F (75[degrees]C) or a chemical sanitizer such as QAC or hypochlorite removed all traces of vegetative bacteria but not spores. Bacterial spores can remain dormant on surfaces for long periods of time, and with suitable conditions of food, temperature, and moisture they may germinate and actively grow, resulting in concentrations of bacteria present on the surface after air-drying (Figure 1, Figure 2).

The concentrations of S. aureus and E. coli on the stainless-steel kitchen surfaces after use of the kitchen fiber cloths were significantly lower than the concentrations present after use of the all-purpose fiber cloths (Figure 1, Figure 2). According to the general instructions for the fiber cloths, the kitchen fiber cloths are specifically designed for cleaning the kitchen environment. These cloths have longer fibers so that they can effectively trap and remove organic and grease materials. In contrast, the all-purpose fiber cloths have shorter fibers and can be used on any surface to stop bacterial growth and reduce unpleasant smells (ENJO, 2002).

The results for the concentrations of Gram-negative E. coli followed a pattern that was homogeneous with the pattern of results for the concentrations of Gram-positive S. aureus on the stainless-steel kitchen surfaces (Figure 1, Figure 2). The overall concentrations were lower for Gram-negative bacteria than for Gram-positive bacteria. Some bacteria require B vitamins in low quantities, and most natural foods contain these vitamins, which allows the bacteria to synthesize their essential requirements. Gram-positive bacteria, however, are less able to synthesize materials and need to be supplied with one or more of these compounds before they can grow (Jay, 1992). Thus, concentrations of E. coli on the stainless-steel kitchen surfaces were higher than concentrations of S. aureus (Figure 1, Figure 2).

The fiber cloths sanitized with hot water at 167[degrees]F (75[degrees]C) achieved better results--lower concentrations of bacteria on the surfaces--than did the antibacterial cloths and the cleaning cloths that were sanitized with the same sanitizer (Figure 1, Figure 2). This result clearly demonstrates that for compliance with the Health Department of Western Australian standards, the fiber cloths performed better on stainless-steel kitchen surfaces than did the generic cloths sanitized with hot water at 167[degrees]F (75[degrees]C).

The performance of the kitchen fiber cloths sanitized with hot water at 167[degrees]F (75[degrees]C) was similar to that of QAC on the antibacterial cloths (S. aureus: p = .144; E. coli: p = .120) and cleaning cloths (S. aureus p = .297; E. coli p = .062). This result suggests that the kitchen fiber cloths sanitized with hot water at 167[degrees]F (75[degrees]C) could be used as an alternative to generic cloths sanitized with the chemical QAC for the removal of bacteria from stainless-steel kitchen surfaces, despite the lower concentrations obtained by QAC.

Use of kitchen fiber cloths resulted in lower concentrations of bacteria than did use of generic cloths sanitized with hypochlorite. The concentrations were only significantly different, however, in comparison with use of the antibacterial cloths and cleaning cloths to remove S. aureus and use of the cleaning cloths to remove E. coli. This result indicates that the kitchen fiber cloths sanitized with hot water at 167[degrees]F (75[degrees]C) also could be used as an alternative to the generic cloths sanitized with hypochlorite; the concentrations of bacteria on the surfaces after use of the kitchen fiber cloths were significantly less (p < .050) than those found after use of the generic cloths.

Although the concentrations of S. aureus and E. coli found on the stainless-steel kitchen surfaces were higher for the all-purpose fiber cloths sanitized with hot water at 167[degrees]F (75[degrees]C) than for the QAC sanitizer, the concentrations were relatively similar to those found after use of generic cloths sanitized with hypochlorite (Figure 1). For both S. aureus (p = .030) and E. coli (p < .050), there were significant differences between results from the all-purpose fiber cloths sanitized with hot water at 167[degrees]F (75[degrees]C) and the results from the cleaning cloths sanitized with hypochlorite; the concentrations of bacteria on the stainless-steel kitchen surfaces were higher for the cloths sanitized with hypochlorite. These results indicate that the all-purpose fiber cloths sanitized with hot water at 167[degrees]F (75[degrees]C) were as effective at removing Gram-positive and Gram-negative bacteria from stainless-steel kitchen surfaces as were generic cloths sanitized with hypochlorite. Compared with other sanitizers, hypochlorite sanitizers have disadvantages: They cause corrosion of metallic equipment and are inactivated by most organic materials (Hobbs & Gilbert, 1981). Therefore, on stainless-steel surfaces it would be preferable to use all-purpose fiber cloths sanitized with hot water at 167[degrees]F (75[degrees]C) rather than hypochlorite sanitizer. In general food preparation areas and food industries that are prone to S. aureus contamination from dairy products such as custards, trifles, creams, and cheeses, the all-purpose fiber cloths could be used to limit the amount of bacteria present.

Conclusions

Fiber cloths could have an effective role in limiting the concentrations of bacteria on food industry surfaces. This method is both inexpensive and environmentally friendly. For removal of Gram-positive and Gram-negative bacteria, kitchen fiber cloths sanitized with hot water at 167[degrees]F (75[degrees]C) performed similarly to generic cloths sanitized with QAC. Therefore, this method could be used as a chemical-free, nontoxic alternative. The all-purpose fiber cloths had a sanitizing performance consistent with the results observed for the antibacterial cloths and cleaning cloths sanitized with hot water at 167[degrees]F (75[degrees]C) and the cleaning cloths sanitized with hypochlorite. These results suggest that the all-purpose fiber cloths sanitized with hot water could be used as an alternative in food industries that are using generic cloths sanitized with hot water or hypochlorite.

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Fairuz Lalla

Peter Dingle, Ph.D.

Corresponding Author: Peter Dingle, Senior Lecturer in Health and the Environment, School of Environmental Science, Murdoch University, Murdoch WA 6150, Australia. E-mail: [e-mail].