12 Reducing pathogen risks in MAP-prepared produce D O Beirne and G. A. Francis, University of Limerick, Ireland 12.1 Introduction Modified atmosphere packaged(MAP) prepared fresh produce provides substrates and environmental conditions conducive to the survival and growth of microorganisms. Minimal processing treatments such as peeling and slicing disrupt surface tissues, expose cytoplasm and provide a potentially richer source of nutrients than intact produce(Brackett, Barry-Ryan and O'Beirne 1998, 2000). This, combined with high Aw and either close to neutral (vegetables) or low acid(many fruits) tissue pH, facilitate microbial growth ( Beuchat, 1996) These products can harbour large and diverse populations of microorganisms, and counts of 10-10 CFU/g are frequently present. Most bacteria present are Gram-negative rods, predominantly Pseudomonas, Enterobacter or Envinia species(Brocklehurst et al, 1987, Garg et al., 1990; Magnuson et al., 1990 Manvell and Ackland, 1986; Marchetti et al, 1992; Nguyen-the and Prunier 1989). The organisms present and counts are affected by product type and torage conditions Lactic acid bacteria have been detected in mixed salads and grated carrots, and may predominate in salads when held at abuse(30C) temperatures(Manvell and Ackland, 1986). Yeasts commonly isolated include Cryptococcus, Rhodotorula, and Candida(Brackett, 1994). Webb and mundt ( 1978)surveyed 14 different vegetables for moulds. The most commonly isolated genera were Aureobasidium, Fusarium, Mucor, Phoma, RhiZopus, and Penicillium A number of important human pathogens can also be found in MAP prepared roduce. Their presence is a consequence of contamination during agricultural production(mainly from contaminated seed, soil, irrigation water, and air)
12.1 Introduction Modified atmosphere packaged (MAP) prepared fresh produce provides substrates and environmental conditions conducive to the survival and growth of microorganisms. Minimal processing treatments such as peeling and slicing disrupt surface tissues, expose cytoplasm and provide a potentially richer source of nutrients than intact produce (Brackett, 1994; Barry-Ryan and O’Beirne, 1998, 2000). This, combined with high Aw and either close to neutral (vegetables) or low acid (many fruits) tissue pH, facilitate microbial growth (Beuchat, 1996). These products can harbour large and diverse populations of microorganisms, and counts of 105 –107 CFU/g are frequently present. Most bacteria present are Gram-negative rods, predominantly Pseudomonas, Enterobacter or Erwinia species (Brocklehurst et al., 1987; Garg et al., 1990; Magnuson et al., 1990; Manvell and Ackland, 1986; Marchetti et al., 1992; Nguyen-the and Prunier, 1989). The organisms present and counts are affected by product type and storage conditions. Lactic acid bacteria have been detected in mixed salads and grated carrots, and may predominate in salads when held at abuse (30ºC) temperatures (Manvell and Ackland, 1986). Yeasts commonly isolated include Cryptococcus, Rhodotorula, and Candida (Brackett, 1994). Webb and Mundt (1978) surveyed 14 different vegetables for moulds. The most commonly isolated genera were Aureobasidium, Fusarium, Mucor, Phoma, Rhizopus, and Penicillium. A number of important human pathogens can also be found in MAP prepared produce. Their presence is a consequence of contamination during agricultural production (mainly from contaminated seed, soil, irrigation water, and air), 12 Reducing pathogen risks in MAP-prepared produce D. O’Beirne and G. A. Francis, University of Limerick, Ireland
232 Novel food packaging techniques during harvesting and manual preparation(human contact) or during machine processing and packaging(contaminated work surfaces/packaging materials/ equipment). Cross-contamination by end-users after pack opening can also By extending shelf-life and protecting product quality, MAP prepared produce systems can provide sufficient time for pathogens to grow to significant numbers on otherwise acceptable fresh foods(Berrang et al, 1989b). The risk of food poisoning is greatest in products eaten raw without any further preparation While the food safety record of these products is good, a comprehensive understanding of the implications of this technology for pathogen survival and growth is required in order to optimise production systems and to inform HACCP protocols. The effects of MAP technology on the survival and growth of non-pathogens and on the interaction between pathogens and non-pathogens also important(Francis and O Beirne, 1998b). Non-pathogens are both potential competitors of pathogens and important indicators of product spoilage While considerable progress has been made in the past decade in our understanding of the safety of these novel and complex food systems there are still significant gaps in knowledge requiring further research 12.2 Measuring pathogen risks A range of pathogens have been isolated from raw produce(Brackett, 1999, Francis et al, 1999) and foodborne infections have been linked to the consumption of raw vegetables and fruits (Tables 12.1 and 12.2). While pathogens have also been isolated from MAP prepared produce(see Table 12. 1) relatively few foodborne infections have been directly linked with this range of oducts. those that have been linked include an outbreak of botulism ultimately linked to an MaP dry coleslaw product( Solomon et al., 1990)and a Salmonella Newport outbreak linked to ready-to-eat salad vegetables(PHLS 2001). There was also an outbreak of shigellosis linked to shredded lettuce (Davis et al., 1988)though exactly how this product was packaged is unclear Increasing consumption of fresh produce in the United States has been paralleled by an increase in produce-linked food poisoning outbreakS(NACMCF, 1999) Contributory factors include the increased range and diversity of products available to consumers and the elimination of seasonality by almost year-round availability of many commodities. This diversity and availability has been achieved by increased globalisation of the produce trade, and has brought with it new food safety risks and challenges. While the main pathogens of concern are still non-proteolytic Clostridium botulinum, Listeria monocytogenes, Yersinia enterocolitica and Aeromonas hydrophila, there are important emerging threats from viral and protozoan pathogens There are a number of difficulties in estimating the magnitude of the true microbial risk from fresh produce and MAP fresh produce. Studies where samples of produce are examined for the presence of pathogens are, of necessity
during harvesting and manual preparation (human contact) or during machine processing and packaging (contaminated work surfaces/packaging materials/ equipment). Cross-contamination by end-users after pack opening can also occur. By extending shelf-life and protecting product quality, MAP prepared produce systems can provide sufficient time for pathogens to grow to significant numbers on otherwise acceptable fresh foods (Berrang et al., 1989b). The risk of food poisoning is greatest in products eaten raw without any further preparation. While the food safety record of these products is good, a comprehensive understanding of the implications of this technology for pathogen survival and growth is required in order to optimise production systems and to inform HACCP protocols. The effects of MAP technology on the survival and growth of non-pathogens and on the interaction between pathogens and non-pathogens is also important (Francis and O’Beirne, 1998b). Non-pathogens are both potential competitors of pathogens and important indicators of product spoilage. While considerable progress has been made in the past decade in our understanding of the safety of these novel and complex food systems there are still significant gaps in knowledge requiring further research. 12.2 Measuring pathogen risks A range of pathogens have been isolated from raw produce (Brackett, 1999; Francis et al., 1999) and foodborne infections have been linked to the consumption of raw vegetables and fruits (Tables 12.1 and 12.2). While pathogens have also been isolated from MAP prepared produce (see Table 12.1) relatively few foodborne infections have been directly linked with this range of products. Those that have been linked include an outbreak of botulism ultimately linked to an MAP dry coleslaw product (Solomon et al., 1990) and a Salmonella Newport outbreak linked to ready-to-eat salad vegetables (PHLS, 2001). There was also an outbreak of shigellosis linked to shredded lettuce (Davis et al., 1988) though exactly how this product was packaged is unclear. Increasing consumption of fresh produce in the United States has been paralleled by an increase in produce-linked food poisoning outbreaks (NACMCF, 1999). Contributory factors include the increased range and diversity of products available to consumers and the elimination of seasonality by almost year-round availability of many commodities. This diversity and availability has been achieved by increased globalisation of the produce trade, and has brought with it new food safety risks and challenges. While the main pathogens of concern are still non-proteolytic Clostridium botulinum, Listeria monocytogenes, Yersinia entercolitica and Aeromonas hydrophila, there are important emerging threats from viral and protozoan pathogens. There are a number of difficulties in estimating the magnitude of the true microbial risk from fresh produce and MAP fresh produce. Studies where samples of produce are examined for the presence of pathogens are, of necessity, 232 Novel food packaging techniques
Reducing pathogen risks in MAP-prepared produce 233 limited in size and may not accurately reflect global contamination levels. In than those showing their presence, and this may distort the true picture. A recent examination of 127 fresh produce items from the Washington DC area Thunberg et al, 2002)showed low levels of contaminati Salmonella Campylobacter contamination, and seven samples positive for L nocytogenes. On the other hand, food poisoning incidents related to fresh produce may be under-reported. By comparison with those linked to meat and poultry, outbreaks related to produce do not have the same pathogen and product characteristics which assist in recognition, investigation, and reporting (NACMCF, 1999). For example, the short shelf-lives, complex distribution and universal consumption of fresh produce make produce-implicated outbreaks more difficult to pin down. Even when produce is almost certainly implicated, the exact point of contamination is difficult to prove beyond doubt. Of 27 examples of produce-linked food poisoning outbreaks considered by NACMCF, investigators had definitively identified the point of contamination in only two The main pathogens of concern in MAP produce are discussed below, focusing on sources and levels of contamination, and their likely health risk to consumers 12. 2.1 Listeria monocytogenes L. monocytogenes is a Gram-positive rod which causes several diseases in man including meningitis, septicaemia, still-births and abortions(ICMSF, 1996). It is considered ubiquitous in the environment, being isolated from soil, faeces, sewage, silage, manure, water, mud, hay, animal feeds, dust, birds, animals and man(Al-Ghazali and Al-Azawi, 1990, Gunasena et al., 1995, Gray and Killinger, 1966; Nguyen-the and Carlin, 1994; Welshimer, 1968) Contamination of vegetables by L. monocytogenes may occur through agricultural practices, such as irrigation with polluted water or use of contaminated manure(Nguyen-the and Carlin, 1994; Geldreich and Bordner 1971). It may also occur during processing(see Section 12.3.3).L monocytogenes has been isolated from minimally processed vegetables at rates ranging from 0%(Farber et al, 1989, Fenlon et al, 1996, Gohil et al., 1995: Petran et al, 1988)to 44%(Arumugaswamy et al., 1994, Beckers et al., 1989 Doris and Seah, 1995, Harvey and Gilmour, 1993; Mac Gowan et al., 1994 McLauchlin and gilbert, 1990; Sizmur and Walker, 1988; Velani and roberts 1991). In France(Nguyen-the and Carlin, 1994)and Germany(Lund, 1993) levels of>10 CFU/g are unacceptable, while in the UK and USA the organism must be absent in 25g Of particular concern is the organism's ability to grow at refrigeration temperatures; the minimum temperature for growth is reported to be -04C (Walker and Stringer, 1987). It is also facultatively anaerobic, capable of survival/growth under the low O2 concentrations within MA packages of prepared vegetables. While counts generally remain constant at 4C(Farber et al., 1998), they can increase to high numbers at mild abuse temperatures( 8C)
limited in size and may not accurately reflect global contamination levels. In addition, surveys showing the absence of pathogens may receive less attention than those showing their presence, and this may distort the true picture. A recent examination of 127 fresh produce items from the Washington DC area (Thunberg et al., 2002) showed low levels of contamination, no Salmonella or Campylobacter contamination, and seven samples positive for L. monocytogenes. On the other hand, food poisoning incidents related to fresh produce may be under-reported. By comparison with those linked to meat and poultry, outbreaks related to produce do not have the same pathogen and product characteristics which assist in recognition, investigation, and reporting (NACMCF, 1999). For example, the short shelf-lives, complex distribution and universal consumption of fresh produce make produce-implicated outbreaks more difficult to pin down. Even when produce is almost certainly implicated, the exact point of contamination is difficult to prove beyond doubt. Of 27 examples of produce-linked food poisoning outbreaks considered by NACMCF, investigators had definitively identified the point of contamination in only two. The main pathogens of concern in MAP produce are discussed below, focusing on sources and levels of contamination, and their likely health risk to consumers. 12.2.1 Listeria monocytogenes L. monocytogenes is a Gram-positive rod which causes several diseases in man including meningitis, septicaemia, still-births and abortions (ICMSF, 1996). It is considered ubiquitous in the environment, being isolated from soil, faeces, sewage, silage, manure, water, mud, hay, animal feeds, dust, birds, animals and man (Al-Ghazali and Al-Azawi, 1990; Gunasena et al., 1995; Gray and Killinger, 1966; Nguyen-the and Carlin, 1994; Welshimer, 1968). Contamination of vegetables by L. monocytogenes may occur through agricultural practices, such as irrigation with polluted water or use of contaminated manure (Nguyen-the and Carlin, 1994; Geldreich and Bordner, 1971). It may also occur during processing (see Section 12.3.3). L. monocytogenes has been isolated from minimally processed vegetables at rates ranging from 0% (Farber et al., 1989; Fenlon et al., 1996; Gohil et al., 1995; Petran et al., 1988) to 44% (Arumugaswamy et al., 1994; Beckers et al., 1989; Doris and Seah, 1995; Harvey and Gilmour, 1993; MacGowan et al., 1994; McLauchlin and Gilbert, 1990; Sizmur and Walker, 1988; Velani and Roberts, 1991). In France (Nguyen-the and Carlin, 1994) and Germany (Lund, 1993) levels of >102 CFU/g are unacceptable, while in the UK and USA the organism must be absent in 25g. Of particular concern is the organism’s ability to grow at refrigeration temperatures; the minimum temperature for growth is reported to be ÿ0.4ºC (Walker and Stringer, 1987). It is also facultatively anaerobic, capable of survival/growth under the low O2 concentrations within MA packages of prepared vegetables. While counts generally remain constant at 4ºC (Farber et al., 1998), they can increase to high numbers at mild abuse temperatures (8ºC), Reducing pathogen risks in MAP-prepared produce 233
Table 12.1 Occurrence of pathogens on minimally processed produce Vegetable Number(and % Country and Reference Listeria monocytogenes 4/5(80%) Malaysia Arumugaswamy et al., 1994 Coleslaw 2/50(4%) Singapore Doris and Seah. 1995 Harvey and gilmour, 1993 Pre-packed mixed salads 3/21(14.3%) Northern Ireland United Kingdo Sizmur and Walker. 1988 Chopped lettuce 5/39(13%) sumeru et al. 1997 Cut and packaged 3/120(2.5%) Szabo et al. 2000 Prepared mixed ve 8/42(19%) Velani and Roberts. 1991 Fresh cut salad vegetables l1/25(44%) Beckers et (<10-g present Chicory salads Nguyen-the and Carlin, 1994 (<1/g present) l26(3.8%) United Kingdom Mac Gowan et al. 1994
Table 12.1 Occurrence of pathogens on minimally processed produce Vegetable Number (and %) Country and Reference of positive samples comments Listeria monocytogenes Cucumber slices 4/5 (80%) Malaysia Arumugaswamy et al., 1994 Bean-sprouts 6/7 (85%) Malaysia Arumugaswamy et al., 1994 Coleslaw 2/92 (2.2%) Canada Schlech et al., 1983 2/50 (4%) Singapore Doris and Seah, 1995 3/39 (7.7%) United Kingdom MacGowan et al., 1994 Harvey and Gilmour, 1993 Pre-packed mixed salads 3/21 (14.3%) Northern Ireland 4/60 (6.7%) United Kingdom Sizmur and Walker, 1988 Chopped lettuce 5/39 (13%) Canada Odumeru et al., 1997 Cut and packaged lettuce 3/120 (2.5%) Australia Szabo et al., 2000 Prepared mixed vegetables 8/42 (19%) United Kingdom Velani and Roberts, 1991 (contamination during processing suspected; <200/g present) Fresh cut salad vegetables 11/25 (44%) The Netherlands Beckers et al., 1989 (<102/g present) Chicory salads (8.8%) France Nguyen-the and Carlin, 1994 (<1/g present) Prepared vegetables 1/26 (3.8%) United Kingdom MacGowan et al., 1994
Processed vegetables and salads (13%) United Kingdom McLaughlin and gilbert. 1990 Cut lettuce 66/120(55% australia Szabo et al 2000 Salad mix 12/12(100%) Marchetti et aL. 1992 Prepared salads Fricker and Tompsett, 1989 E. coli o157: H 0/63(0%) Lin et al. 1996 Clostridium botulinum MAP Salad mix 2/35000.6%) Lilly et al, 1996 MAP cabbage US Lilly et al, 1996 MAP green pepper l/201(0.5% Lilly et al, 1996 Salmonella spp Salad mix l/59(06%) E Sadik et aL. 1985 Tamminga et al. 1978 Yersinia spp 71/120(59% australia Szabo et al. 2000 Brocklehurst et aL. 1987 Mushroom 3/200(1.5%) United States Doyle and Schoeni. 1986
Processed vegetables and salads (13%) United Kingdom McLaughlin and Gilbert, 1990 Aeromonas spp. Cut lettuce 66/120 (55%) Australia Szabo et al., 2000 Salad mix 12/12 (100%) Italy Marchetti et al., 1992 Prepared salads (21.6%) UK Fricker and Tompsett, 1989 E. coli O157:H7 Salad mix 0/63 (0%) US Lin et al., 1996 Clostridium botulinum MAP Salad mix 2/350 (0.6%) US Lilly et al., 1996 MAP cabbage 1/337 (0.3) US Lilly et al., 1996 MAP green pepper 1/201 (0.5%) US Lilly et al., 1996 Salmonella spp. Salad mix 1/159 (0.6%) Egypt Saddik et al., 1985 Endive 2/26 (7.7%) Netherlands Tamminga et al., 1978 Yersinia spp. Cut and packaged lettuce 71/120 (59%) Australia Szabo et al., 2000 Prepacked salads 3/3 (100%) UK Brocklehurst et al., 1987 Campylobacter jejuni Mushrooms 3/200 (1.5%) United States Doyle and Schoeni, 1986