Download ICoMST 2016 LSaucier corrected document 160419

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Microbial spoilage, quality and safety within the context of meat sustainability
Linda Saucier
Department of Animal Science, Institute of Nutrition and Functional Foods, Faculty of
Agricultural and Food Science, Université Laval, Quebec City, Québec, Canada, G1V 0A6
Prof. Linda Saucier PhD, agr, chm
Départment des sciences animales
Faculté des sciences de l’agriculture et de l’alimentation
Université Laval
Pavillon Paul Comtois, local 4203
2425 rue de L’Agriculture
Québec (Québec) G1V 0A6
Canada
Tel.: 418-656-2131 | 6295
Fax: 418-656-3766
E-mail: [email protected]
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ABSTRACT
Meat is a nutrient-dense food that provides ideal conditions for microbes to grow
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and defines its perishable nature. Some organisms simply spoil it while others are a threat
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to our health. In either case, meat must be discarded from the food chain and, being
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wasted and consequently an environmental burden. Worldwide, more than 20% of the
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meat produced is either lost or wasted. Hence, coordinated efforts from farm to table are
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required to improve microbial control as part of our effort towards global sustainability.
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Also, new antimicrobial systems and technologies arise to better fulfill consumer trends
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and demands, new lifestyles and markets, but for them to be used to their full extent, it is
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imperative to understand how they work at the molecular level. Undetected survivors,
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either as injured, dormant, persister or viable but non-culturable (VBNC) cells,
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undermine proper risk evaluation and management.
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Keywords: Feeding strategies, Meat safety, Meat spoilage, Microflora management,
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Near-death physiology, Survivors
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1.
Introduction
Even if Lutz, Sanderson & Scherbov (2001) predicted that the world population
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should stop growing by the end of the century, our number is expected to reach 9.6
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billion by 2050. Demand for animal-based proteins will continue to rise, but to an extent
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that will vary from country to country according to various factors such as geography,
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culture, etc. (Sans & Combris, 2015). A fair part of our food supply will keep travelling
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the world, but parallel to this, the need to maintain viable agricultural social communities
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and to buy locally are still very much present. Food security during pandemic outbreaks
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(e.g., Ebola in West Africa) and related land biosecurity protocols remind us that no one
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should solely depend on others to feed its people. More than ever, agriculture and food
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production remain vital economic activities.
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Integration of agri-food activities from farm to table has closely linked
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commercial partners and it takes, in this continuum, only one intermediate performing
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poorly to destroy the efforts of a whole sector of activities. These interactions have
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fostered traceability protocols, but also liability to one another. Consumer trends and
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demands continue to drive the food industry whether as mass productions or niche
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markets (Table 1). Challenges reside in designing safe food without compromising
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quality and shelf life while responding to consumers’ demands for minimally processed
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foods with fewer additives, but that remain easy to prepare. Development of novel
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strategies and antimicrobial systems therefore requires thorough knowledge of the
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physiological response expressed by microorganisms to be controlled.
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Safety of our meat supply could be challenged in various ways. Except for
chemical contaminants build up through reaction with meat constituents (e.g.,
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nitrosamine), chemical contaminants are likely to remain at the same level or to decay
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with time. This is a major distinction compared to microbial contaminants that have the
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potential to increase in numbers if the conditions allow growth to occur or resume. With
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respect to meat sustainability, it can be improved by increasing productivity, but
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reduction of waste and spoilage is also part of the solution. In this context, microbial
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control is a major issue. Novel interventions need to be integrated from farm to table and
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based on a thorough understanding of microbe near-death physiology at the molecular
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level. In this context, examples of effective microbial control are presented here.
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2.
Economic burden of safety, waste, and spoilage
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WHO (2015) reported 420-960 million foodborne illnesses and 310,000 to
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600,000 deaths in 2010 representing 25-46 million Disability Adjusted Life Years
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(DALYs); amongst the culprits, namely Salmonella Typhi and non-typhoidal Salmonella
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enterica, Campylobacter spp. Taenia solium, enteropathogenic Escherichia coli, hepatitis
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A virus, norovirus and aflatoxin. In terms of food waste, FAO (2011) indicates that 1.3
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billion tons of food are lost or wasted every year. With respect to meat, more than 20% of
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the 263 million tons of meat produced worldwide do not reach consumption, which
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represents 75 million bovines raised for nothing (FAO, 2016). Animal products,
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including meat, are nutrient dense, but highly perishable food commodities. In order to
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reduce waste, spoilage, recalls linked to contamination with pathogens, etc. innovative
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and effective strategies to improve microbial control have to emerge in order to improve
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our sustainability towards meat and meat products. These new approaches may also
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include tighter management systems. For example, Moisson Beauce, which is a non-for-
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profit organization, helps people living with difficult socio-economic situations. It carries
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many activities like a food bank, reinsertion programs, etc. In partnership with a grocery
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chain, they have implemented a meat recuperation program in order to reduce waste and
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to provide beneficiaries with more nutritious foods (Fournier, 2015). In this case, meat is
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frozen before the best before date and processed in provincially inspected kitchens before
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being served to beneficiaries of charitable organizations. Alternatively, meat could be
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sold at some point at a discount price before the end of shelf life. But if the product is not
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handled properly by the consumer, poor eating experience and safety issues may arise.
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3.
Microbial control begins at the farm
With the exception of lymph nodes, muscles of healthy animals contain little to no
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microorganisms (Huffman, 2002). Hence, the animal health status prior to slaughter is
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paramount in securing meat quality and safety. On top of veterinary surveillance,
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biosecurity measures at the farm must be established to protect the animal from diseases
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and contamination by undesirable organisms. Obviously, reducing risk of economic
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losses caused by animal death and herd dissemination is the logical reason to embark on a
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biosecurity program. On top of biosecurity protocols, many producer associations have
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developed a HACCP system at the farm. Although, these tend to be more of type 2
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(minimizing microbial growth) than actual type 1 (procedures where cell counts are
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reduced, in order to prevent or eliminate hazards), they are deemed valuable with respect
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to microbial safety (Gill, 2000).
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Free-range farming is seen as a less intensive system for animal production, but it
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does, nonetheless, require stockmanship to be done properly and effectively with respect
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to welfare and productivity. Furthermore, higher incidence of parasitic infection was
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reported when pigs are raised with access to outdoor facilities compared to more
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conventional production systems (Eijck & Borgsteede, 2005). So, parameters such as
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quality of pastures, feed, water facilities, pest and wildlife control, etc. remain important
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to control disease and contamination that will lead to increased mortality, loss of
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productivity and more carcass waste. Couple of years ago, pork producer associations in
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Canada have promoted less severe cooking for whole muscle cuts as “pink cooking” for
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customers to enjoy a more pleasing eating experience. It was deemed safe considering the
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microbial quality achieved by producers but such practices would not be recommended
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for free-range pigs as less severe cooking can lead to safety issues when incidence of
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parasites is increased. Much to proof that new intervention must be studied thoroughly to
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avoid introducing unsuspected risks.
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Before being transported to slaughter houses, animals are submitted to a feed
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withdrawal to reduce problems associated with motion/transport sickness, notably nausea,
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vomiting, diarrhea, known to favour contamination to spread between them, but also
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losses (death or non-ambulatory; Bradshaw et al., 1996; Isaacson et al., 1999; Ritter et al.,
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2006). Pre-slaughter fasting is now a standard procedure and parameters for its proper
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application vary not only amongst species but also amongst producers. That is why it is
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deemed preferable to refer to fasting efficacy rather than fasting time. Conversely, a too
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long fasting will affect animal welfare, as hunger makes them more irritable; fights are
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more frequent leading to bruises on the carcasses. When they are properly fasted, the
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volume of the gastro-intestinal (GI) tract is reduced along with risks of perforation during
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evisceration as well as carcass and equipment contamination.
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Excessive feed withdrawal will also have a negative effect on carcass yield. With
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pork, it takes four to eight hours before nutrients gets absorbed by the small intestine and
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nine hours to reach blood stream. Hence, it takes 10 to 12 h before the feed consumed
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materialized into carcass gain (Faucitano et al., 2010b). Undigested material left in the
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digestive tract is an unnecessary expense for the producer and represents an extra waste
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to manage at slaughter (Murray, 2001). Effective feed withdrawal reduces the incidence
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of Pale, Soft and Exudative (PSE) meat. If unduly extended, muscle reserves will get
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exhausted leading to Dark, Firm and Dry (DFD) meat (Faucitano et al., 2010b). Its high
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pH favours microbial growth, leads to early spoilage of the meat and reduces shelf life.
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Furthermore, hungry animals may drink more in order to reduce discomfort and water fill
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up the stomach (Saucier et al., 2007), which is counterproductive with respect to reducing
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GI tract volume (Rabaste et al., 2007).
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Many factors are susceptible to influence meat quality including pre-slaughter
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stress, truck design, seasons, roads, animal density, duration of transport, feed
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withdrawal, etc. (Faucitano & Schaefer, 2008; Weschenfelder et al., 2012, 2013a, 2013b).
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In fact, stress inflicted on animals before slaughter may interfere with their health and
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welfare leading to poor meat quality and microbial contamination (Faucitano et al.,
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2010b). After death, muscles remain metabolically active until reserves are exhausted in
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anaerobic conditions since breathing has ceased. If the animal is submitted to a prolonged
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stress before slaughter (e.g., long transport), reserves will get exhausted prior to
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slaughter, limited production of lactic acid will occur and ultimate pH (pHu) after 24 h of
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chilling will be higher leading to DFD meat. This higher pH is favourable for microbial
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growth (Faucitano et al., 2010a), the meat will spoil faster and shelf life will be reduced.
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However, when pH is higher, myofibrillar proteins are far from their isoelectric point
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producing a net charge causing repulsion between the fiber networks. Water then has
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more space and meat retaining it will have a dry appearance. This improved retention
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leads to reduced cooking losses, better yield and quality in processed meat (Interbev,
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2006).
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If stress is inflicted shortly before slaughter (e.g., use of electric prod), it leads to
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poor quality PSE meat as well as low cooking yield although its low pH refrain microbial
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growth compared to DFD meat. More recently, intermediate quality classes have been
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defined in pork, namely, Red, Soft and Exudative (RSE) and Pale, Firm and Non-
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exudative (PFN). Much remains to be unveiled with respect to this newly suggested
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classification, but we have demonstrated that, after DFD, RSE meat spoils the fastest
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(Faucitano et al., 2010a). So, proper pre-slaughter management is important to control
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contamination and to obtain quality meat with optimized shelf life.
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Improving quality and shelf life while reducing waste
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Many small fruits (e.g., cranberry, strawberry, etc.) and plants (e.g., tea leaves,
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onions, etc.) contain large amounts of phenolic compounds, including ellagic and gallic
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acids, which are known for their antimicrobial and antiviral activity in vitro as well as in
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vivo (Buzzini et al., 2008; Leusink et al., 2010; Rozoy et al., 2013). Cranberry is very rich
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in proanthocyanidins, which have inhibitory effects on Staphylococcus aureus and
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Escherichia coli growth in meat (Daglia, 2012) and lipid oxidation in fresh turkey and
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ground pork meat (Lee, Reed & Richards et al., 2006; Raghavan & Richards, 2006).
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Essential oils from herbs and spices also demonstrate antimicrobial (Oussalah et al.,
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2007) and antioxidant properties (Botsoglou et al., 2002, 2003, 2004). However, when
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directly applied to meat, organoleptic concerns arise.
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It is well documented that feed supplementation with vitamin E improves the
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oxidative stability of meat (Schaefer et al., 1995). Addition to feed is more effective than
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on meat (Mitsumoto et al., 1993; Houben & Gerris, 2002; Lahucky et al., 2010) and its
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action is immediate upon surface exposition to air. By a similar feeding strategy, Soultos
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et al. (2009) demonstrated that adding oregano oil to the diet of rabbits reduced total
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mesophilic aerobes, Pseudomonas spp. and Enterobacteriaceae of the carcass after 12
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days of refrigeration under aerobic conditions. As well, Fortier, Saucier & Guay (2012)
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improved the microbial quality of pork meat when rations were supplemented with
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oregano oil and cranberry pulp. The idea here is not to feed farm animals with fruits and
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plants, but rather with feed enriched with bioactive compounds extracted from plant by-
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products to improve meat quality and shelf life. Effective use of polyphenols and other
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bioactive molecules aligns with a global vision for sustainable agriculture and economic
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efficiency.
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5.
Microflora management
One technology that has ship-shaped meat microbial shelf life in the past few
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decades is most certainly modified atmosphere packaging. Without any additives or other
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interventions, but simply by changing composition of the gaseous environment around
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the meat, we have been able to modulate its microflora in order for less spoiling lactic
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acid bacteria to prevail over psychrotrophic Pseudomonas, provided that the cold chain is
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maintained throughout storage and transport (Saucier, 1999). So, this fine-tuning of
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microbial ecology has led us to keep the microorganisms that we want, at the level that
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we want, and with the timing that we want. Rather than having a “bazooka” approach,
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where everything is wiped out, a more targeted “sniper” one eliminating the bad and
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leaving the good microbes to thrive has proved to be beneficial. In any case, microbial
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void created by reducing or eliminating endogenous microflora is at risk to be
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recontaminated and recolonized by opportunistic organisms at post treatment.
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In 2008, the Canadian meat processing industry was shaken by a listeriosis
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outbreak where elderly people actually died. Luncheon meat had been contaminated with
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Listeria monocytogenes from a biofilm found on a slicer (Weatherill, 2009). This incident
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has led to the implementation of new reforms including approval of two antimicrobials
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for processed meat (sodium acetate and sodium diacetate) and new regulations with
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respect to microbial control on surfaces near or touching meats got implemented. One of
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the hypotheses proposed to explain the presence of L. monocytogenes in meat plants fits
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with the improvement of sanitation, where only psychrotrophs like L. monocytogenes can
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survive in cold processing rooms. Drains are difficult to decontaminate since water and
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organic matter are constantly being flushed through them. Zhao et al. (2006) reported that
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Listeria sp. can reach 3.6 to 7.5 CFU/1000 cm2 in drains of poultry processing plants and
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that use of Lactococcus lactis subsp. lactis with Enterococcus durans at 107 CFU/mL in
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an enzyme-foam-based cleaning agent can reduce Listeria sp. population after four weeks
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of treatment. Similarly, a commercial biological product design to control odors in grease
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traps and drain was tested for its ability to exert a competitive exclusion on Listeria
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innocua (Fig. 1). Even the way plant activities are laid out will influence the spread of
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contamination. Lundén et al. (2003) reported that facilities with more compartmentalized
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activities are less susceptible to contamination spread compared to large processing
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rooms.
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6.
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New technologies to improve meat quality and processing efficiency
Biological control using bacteriophages infecting and killing undesirable bacteria
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have been studied against Pseudomonas in meat (Geer & Dilts, 1990). It was soon
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realized while controlling a wide group of bacteria, such as members of a whole genus,
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host range coverage and specificity were important criteria. Although the use of cocktails
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provides a larger host range and reduces the emergence of phage resistant clones, better
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success was obtained when phages were used to target specific bacterial species such as
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E. coli O157:H7 (Table 2; Saucier, Moineau & Fairbrother, 2001), L. monocytogenes
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(Hagens & Loessner, 2014) and Brochothrix thermosphacta (Greer & Dilts, 2002). To be
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effective, lytic, not temperate, phages must be used and since most bacterial viruses only
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multiply in viable and active cells, growth limiting conditions, such as refrigeration,
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reduce its efficacy. Transducing phages are to be avoided since genetic material could be
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transferred from cell to cell. Furthermore, contact between phages and bacteria should be
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optimized otherwise high titers of phages are necessary to provide a significant effect.
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Commercial phage preparations are available, notably Listex™ consisting of a broad
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range phage, P100, and ListShield, a cocktail of phages (Hagens & Loessner, 2014).
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Phage-encoded enzymes, such as endolysins, have been also tested as anti-
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microbiological agents against Listeria biofilm, although their stability remains an issue.
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The absence of the outer membrane in Gram positive organisms allows its application
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externally on Listeria.
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High efficiency meat tenderizers as well as brine or marinade injectors have been
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developed to improve eating qualities of less noble cuts. By piercing meat surface with
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blades or needles, it compromises its integrity allowing microorganisms on the surface to
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penetrate the core of the muscle similarly to ground beef. It was only a matter of time
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before meatborne outbreaks got linked to such process. Indeed in 2012, 18 cases of
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Escherichia coli O157 were linked to such products in Canada (Catford et al., 2013) and
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prompted the implementation of guidelines for mandatory labelling to provide proper
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cooking information (Health Canada, 2014). So, on the package of non-intact muscles, it
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must be indicated: “mechanically tenderized”, “cook to a minimum internal temperature
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of 63°C (145°F)” and, in the case of steak, “turn steak over at least twice during
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cooking”. Gill et al. (2014) demonstrated that if steak is turned twice or more while being
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cooked to 63°C, a 5 Log reduction is obtained. Again, this emphasizes the need to study
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thoroughly the behavior of microorganisms in food systems when new technologies are
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introduced and to establish their efficacy and safety. Apart from the O157 serotype, other
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Shiga-toxin producing E. coli (STEC) namely, O26, O45, O103, O111, O121, O145,
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commonly referred to as the “Big Six”, are now considered adulterants in meats and must
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be controlled as well.
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7.
Efficacy of antimicrobial systems and cell physiology
Various antimicrobial systems are used to control microorganisms in food, including
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meat, and heat treatments are amongst the oldest and the most widely studied. Métris et
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al. (2008) demonstrated that recovery time increases with severity of heat treatment. Cell
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recovery and growth have been traditionally used to assess severity and efficacy of
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antimicrobial systems (e.g., commercial sterility of canned food). For recovery and
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detection to happen, however, survivor cells must be able to grow and form colonies on
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culture media. Injured cells do not grow on selective media (Oliver, 2005; Li et al.,
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2014). To be detected, they must deal first with their injuries in non-selective growth
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conditions. Stress, including commonly used food preservatives, can induce a viable but
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non-culturable (VBNC) state (Oliver, 2010; Li et al., 2014). Contrary to injured cells,
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those in VBNC state cannot grow on any media (Oliver, 2005; Li et al., 2014) but they
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remain metabolically active whereas dormant cells are not (Pinto, Santos & Chambe,
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2015). As stated by Li et al. (2014), little is known about the genetic control of these
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VBNC cells and their age also influences resuscitation time, which can take days or years
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depending on strains and conditions. Furthermore, they are known to be more resistant to
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physical and chemical stresses (Li et al., 2014). VBNC state is seen as an adaptive
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strategy to survive longer under unfavourable conditions. Also, persister cells have been
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described as a subpopulation of phenotypic non-growing variants associated with
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antibiotic resistance (Yamaguchi & Inouye, 2011; Li et al., 2014; Leung, Dufour &
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Lévesque, 2015). Through a toxin-antitoxin (TA) system, they control cellular growth
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and death that can lead to a “dormant” state. Under stress, induced proteases eliminate the
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less stable antitoxin and free the toxin. There are three groups of TA systems (I, II and
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III) based on the antitoxin function and they have been identified in many bacteria;
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E. coli K12 is known to have 36 TA systems (Yamaguchi & Inouye, 2011). Survivors,
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either as injured, dormant, persister or VBNC cells, can resuscitate when the conditions
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are right, notably during storage and transport. So, there is always a possibility that those
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conditions favouring resuscitation may not be known, and risks associated with
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undetected survivors remain; they could be dangerous if they are pathogenic and ingested
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(Olivier, 2010, Rowan, 2004). The efficacy of antimicrobial systems is traditionally
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evaluated by cell enumeration on solid growth medium during challenge studies. Hence,
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when viable cells cannot grow to be detected, we overestimate the efficacy of
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antimicrobial treatments indicating that other markers should complement cell count
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enumeration to assess risk properly.
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In order to survive, microorganisms react to antimicrobial systems used to control
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them and initiate a variety of physiological responses to modify metabolic activity
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(transcriptome, proteome, etc.), cell structure (e.g., membrane fluidity) or genetic make-
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up. For example, when exposed to antibiotics, cells can develop tolerance or acquire
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resistance at genetic level, depending on concentration of antibiotics encountered.
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General, as well as specific, stress responses have been described in many organisms
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(Storz & Hengge-Aronis, 2000; Dodd & Aldsworth, 2002; Jones, 2012). The general
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stress response, under the control of  factor RpoS in E. coli, leads to cross protection
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against other stresses (Lemay et al., 2000; Blackman, Park & Harrison, 2005; Jones,
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2012). At the molecular level, stress proteins, induced by sub-lethal heat treatment, have
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been described in several eukaryotes and prokaryotes. The stress response associated with
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heat shock can also be induced by other factors (ethanol, UV, DNA-gyrase inhibitors) in
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E. coli and many proteins induced by various stresses have already been identified (Storz
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& Hengge-Aronis, 2000; Jones, 2012). Organism survival to an inhibitory treatment, such
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as heat or acid, can be improved by prior exposure to sub-lethal conditions (Storz &
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Hengge-Aronis, 2000; Seyer et al., 2003; Jones, 2012). Interestingly, heat shock proteins
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protect E. coli cells against freezing but not chilling conditions (Chow, & Tung, 1998).
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Using reporter gene assays, Purushottam et al. (2005) demonstrated that cold
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temperatures (5°C) prevent induction of the general stress genes uspA and rpoS upon
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osmotic shock. Similarly, in starved E. coli O157:H7 cells, the GrpE general stress
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protein is most abundant at 5°C, whereas UspA is most abundant at 37°C. Bacteria also
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sense and communicate (e.g., quorum sensing, “scout”/suicide hypothesis) their exposure
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to stresses (Leung, Dufour & Lévesque, 2015; Pinto, Santos & Chambe, 2015). For
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example, upon alkali or acid exposure, extracellular induction components are produced
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and can act as alarmones to warn unstressed cells to prepare for the upcoming danger
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(Lazim & Rowbury, 2000; Rowbury & Goodson, 2005; Li et al., 2014; Leung, Dufour &
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Lévesque, 2015,). Stress-inducible alarmones are small signaling molecules that diffuse
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readily and can be activated by more than one stress (Leung, Dufour & Lévesque, 2015).
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The level of (p)ppGpp is also involved in RpoS transcription (Jones, 2012). So far,
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research on bacterial stress responses have focused on the period when physiological
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changes are at their peak and geared towards survival (Storz & Hengge-Aronis, 2000).
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DnaK is a chaperone protein implicated in the folding of nascent polypeptides, repair of
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denatured proteins, and degradation of non-functional ones (Georgopoulos, & Welch,
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1993); it represents 1% of the total proteins under optimal growth conditions. It is also
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known as a heat shock protein which may increase up to 13% of the total proteins when
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cells are grown at 30°C and then exposed to 42°C (Herendeen, VanBogelen, Nedhardt,
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1979). Residual DnaK after heating was found to be necessary for cell recovery, and
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additional DnaK was produced during the recovery process. Furthermore, resistance to
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the same lethal heat treatment was better in cells that went to a recovery process than in
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exponentially growing cells as if, through some epigenetic process, daughter cells
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remembered the stress their mother cells were exposed to (Seyer et al., 2003). Real-time
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PCR measurement of heat shock gene expression also indicated that dnaK and groEL
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mRNA levels decreased significantly above 60°C to become similar to control cells at
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37°C suggesting that above 60°C, cells’ ability to adapt to heat treatment declined and the
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treatment begins to be effective (Guernec, Robichaud-Rincon & Saucier, 2013). Hence,
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as stress severity approaches cell death, stress response drops, suggesting a shift towards
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a “near-death physiology state” (Seyer et al., 2003; Guernec, Robichaud-Rincon &
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Saucier, 2013). In practice, this means that for heat treatment to be effective, it must be
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severe enough to avoid bacterial stress response and adaptation.
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Processed meat cooking (e.g., ham, bologna, etc.) aims to control non-spore
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formers. Therefore, the product is not sterile and must be kept refrigerated to secure a
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decent shelf life that reaches 30 days under modified atmosphere packaging (e.g.,
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vacuum), depending on the product and its formulation. Historically, processed meat
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products are cooked to a temperature of 71°C at their geometric center to be considered
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effective and should provide a 6.5-log reduction of Salmonella in meat products that do
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not contain poultry, and a 7-log for those that do (Martin, 1984, Sallami et al., 2006).
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However, an extremely heat-resistant E. coli has been isolated from a beef processing
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facility (Dlusskaya, McMullen, & Gänzel, 2011). Heat resistance is associated with a
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14 kb genomic island containing 16 predicted open reading frames which share >99%
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sequence identity with sequence in Cronobacter sakazakii and Klebsiella pneumonia
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known to be linked to heat resistance (Mercer et al., 2015). Our microarray results reveal
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that although cells of E. coli K12 treated at 58 or 60°C for a pasteurization value (PV) of
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3 min could not resume growth after treatment, their gene expression was significantly
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different from those treated at a core temperature of 71°C (Fig. 2). In fact, eight genes
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were still expressed differentially between treatments (Guernec, Robichaud-Rincon &
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Saucier, 2013). The biological significance of the presence of those transcripts remains to
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be tested since residual metabolic activity does not necessarily mean viability. For
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instance, when an animal is slaughtered, eviscerated and carcass dressing is completed,
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muscle cells remain metabolically active until cellular reserves are exhausted, even
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though there is no more vascular circulation. So, it is important to discriminate when
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bacteria are still fighting adverse conditions and when residual metabolic activity is
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sustained beyond cell survival ability. Membrane integrity has been suggested as a key
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component to assess viability and cell wall strengthening by increased peptidoglycan
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cross-linking has been observed in VBNC cells (Li et al., 2014).
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Working with a food matrix is complex and a whole array of antimicrobial
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systems is used in carcass dressing (e.g., organic acid showers (1.5% lactic or acetic
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acid), carcass pasteurization, cold storage, etc.) and during meat processing (e.g., nitrite,
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acidification/fermentation, drying, salt content, etc.). This multitude of processes can
386
actually lead to various cross protections (Lemay et al., 2000; Li et al., 2014). Our
387
previous work (Lemay et al., 2000), on different antimicrobial systems applied in
388
different sequences, like it is often seen in industrial food preparation (e.g., chilling after
389
cooking), indicates that cells survive better after exposure to a sub-lethal osmotic shock
390
(NaCl) followed by an acid stress (lactic or glutamic acid), compared to reverse order.
391
Lowest survival is obtained when treatments are applied simultaneously. Hence, the
392
sequence of events during food processing is important and will influence both the
393
overall efficacy of treatments and the level of microbiological control obtained.
394
Furthermore, using irradiation treatments (0.3 kGy) applied at different rates (8x10-2 and
395
3x10-3 KGy/min) on E. coli cells, we demonstrated that treatment applied at a slower rate
396
initiated a stronger stress response (Saucier et al., 2012). Even though a lot is known
397
about individual hurdles, little physiological information is available with respect to
398
various combinations, sequences and rates of application in real food/meat systems.
399
As the industry thrives to provide both good quality and safe foods, and to answer
400
consumers’ demands, it is important to acquire the necessary knowledge and tools to
401
improve our understanding of near-death physiology in order to sustain the vitality of our
402
agri-food sector. A new technology or antimicrobial system cannot be used to its full
403
potential if we do not understand how it works. Such knowledge is important for
404
improving food safety and product quality, and to reduce economic losses in the agri-
405
food industry due to microbial spoilage, loss, waste as well as recalls.
406
407
408
8.
Conclusion
Nature is resilient and all living organisms thrive to survive. Survival strategies
409
and physiological make up do exist, and continue to evolve, even amongst
410
microorganisms and these pose challenges in terms of risk assessments related to safety.
411
So, when we abuse our agricultural resources to a point of no return, it is a sign that we
412
have went too far. Ocean garbage patches, the recurrent presence of smog in major cities,
413
the recent burst of toxic mining waste in Brazil are all signs that we are running towards a
414
wall. It is not a matter of if, but when, and at what speed we are getting there. Economic
415
growth based on demography and productivity alone no longer holds. Agricultural
416
sustainability, wise natural resources management, reduction of waste will have to
417
become part of the equation.
418
419
420
Acknowledgements
This review manuscript and associated presentation at the 62nd International
421
Congress on Meat Science and Technology in Bangkok, Thailand are dedicated to the
422
memory of a colleague and dear friend Dr. C.O. Gill (1943-2014) Research Scientist at
423
the Lacombe Research Centre, Agriculture and Agri-Food Canada.
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425
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Figure Captions
Fig. 1. Competitive exclusion study between a commercial biological product
containing a live non-pathogenic consortium of bacteria designed for odour
treatment of grease trap and drain in agri-food facilities against Listeria
innocua at Log103 CFU/ml of each. Cell enumeration (Log10 CFU/ml) was
performed over time after incubation in Brain Heart Infusion at 10°C with or
without agitation (WA and NA, respectively).
Fig.1 Hierarchical clustering of differential gene expression upon various heat
treatments. Only E. coli cells heated at 58°C PV2 were able to resume growth.
Pasteurisation value (PV) is defined as the time needed at a given temperature
to control the reference organism, here Enterococcus faecalis (D value of 2.95
min at 70°C and z value of 10°C).
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Table 1
Consumer trends and demands as defined by Fread (2014).
Designations
Foodies
702
Description
curious, variety of foods, pleasure
Healthies
healthy foods, more natural, less preservative
Greenies
socially responsible (ethic, environment)
Speedies
convenient food, minimal preparation
Cheapies
value-conscious, limited spending
Newbies
immigrant with “culinary culture”