Nonthermal Decontamination of Raw and Processed Meat: Comparison
Please note this is a comparison between Version 1 by Rana Muhammad Aadil and Version 2 by Rita Xu.

Meat may contain natural, spoilage, and pathogenic microorganisms based on the origin and characteristics of its dietary matrix. Several decontamination substances are used during or after meat processing, which include chlorine, organic acids, inorganic phosphates, benzoates, propionates, bacteriocins, or oxidizers. Unfortunately, traditional decontamination methods are often problematic because of their adverse impact on the quality of the raw carcass or processed meat. The extended shelf-life of foods is a response to the pandemic trend, whereby consumers are more likely to choose durable products that can be stored for a longer period between visits to food stores. This includes changing purchasing habits from “just in time” products “for now” to “just in case” products, a trend that will not fade away with the end of the pandemic.

  • clean label foods
  • ozone
  • cold plasma

1. Introduction

Meat is high in protein, vitamins, and minerals, and it is one of the world’s most popular foods. Because of its intrinsic (nutrients, water availability, and pH) and extrinsic (transportation, processing, and storage) characteristics, meat is extremely susceptible to the development of pathogenic and spoilage microbes, for instance, Campylobacter spp., Escherichia coli, Salmonella spp., Staphylococcus aureus, lactic acid bacteria, and Pseudomonas spp. To guarantee food safety and conformity with quality requirements, all these microorganisms must be eliminated throughout industrial processing [1]. But in recent years, the safety of ready-to-eat (RTE) meats has been evaluated due to reported outbreaks that are associated with their consumption. During the repackaging of pasteurized meats, the core of the issue lies in post-process microbial contamination. Poultry and livestock producers can reduce the number of Salmonella (accounting for 31% of foodborne pathogenic deaths) that occur in animals before and during slaughter [2]. Besides, Listeria spp. grow during prolonged storage even at refrigeration temperatures (2–4 °C) [3]. This pathogen is sensitive to normal cooking, but it may contaminate the meat products after heating when exposed to the contaminated environment during cutting, slicing, and repackaging [4]. L. monocytogenes is of particular concern to meat and poultry products because it can grow in both raw and cooked meat [3]. This psychotropic Gram-positive pathogen causes a severe invasive disease called listeriosis. L. monocytogenes not only survive under a wide range of temperatures (1–45 °C) and pH (4.3–9.4), but it can also grow with water activity to a value of 0.92 and above. Furthermore, it can tolerate undesirable environmental conditions such as low-oxygen conditions, nitrite, and high salt content [3]. Food industries are putting efforts towards minimizing such post-process contamination and growth of pathogens by developing hurdle technologies [5]. Similarly, S. aureus can survive heat treatments and again can contaminate meat after cooking. Besides, the pre-and postslaughtering sources of S. aureus contamination include feed, feces, feathers, air, scald water and defeathering machines [6]. S. aureus has become a threat to public health because it can easily adapt to become methicillin-resistant S. aureus (MRSA), even during selective antimicrobial pressure, consequently causing staphylococcal foodborne illness that may lead to MRSA infection [7]. This opportunistic pathogen can grow in a wide range of temperatures, pH, and sodium chloride concentrations of up to 15% [8]. Raw and processed meat are the major food sources associated with food poisoning caused by S. aureus. The conventional techniques to evaluate the microbial safety of meat (i.e., culturing and biochemical testing) are time-consuming and labor-intensive [8].
Other thermal processing methods such as hot water and steam pasteurization [9], and chemical methods, for instance, lactic acid and sodium benzoate [10], trisodium phosphate and sodium hypochlorite [11], potassium sorbate [12], chlorine dioxide, and peroxyacetic acid [13], have been applied to reduce the bacterial counts in meat. For instance, Manzoor et al. [14] evaluated the effect of lactic acid spray (2–4%) on the microflora and shelf-life of buffalo meat displayed under modified atmospheric packaging. The aerobic plate count of sprayed carcasses and steaks was significantly lower than the unsprayed controls. Similarly, the bactericidal activity of lactic acid, levulinic acid, and sodium dodecyl sulfate was determined individually and in combination against Shiga toxin-producing E. coli (STEC) in pure culture conditions [15]. Results showed that the use of 3% lactic acid for 2 min in pure cultures reduced E. coli O26: H11, O45: H2, O111: H8, O103: H2, O121: H2, O145: NM, and O157: H7 populations by 2.1, 0.4, 0.3, 1.4, 0.3, 2.1, and 1.7 log CFU/mL, respectively. While the treatments of 0.5% levulinic acid, plus 0.05% sodium dodecyl sulfate, for less than 1 min reduced the populations of all STEC strains to undetectable levels [15]. In general, lactic acid concentrations less than 5% have not proven to be effective against Campylobacter in the form of a spray wash [16][17][16,17], even though levels of just 2% produced significant Salmonella reduction compared to other treatments [18]. The increased levels of to up to 8% caused considerable deterioration of the appearance of the carcasses, although the use of high acid concentration was beneficial for reducing the numbers of Campylobacter [16]. Changes in the texture and nutritional components may occur in meat owing to such processes [19][20][19,20]. In addition, chemical residues on meat surfaces cause health problems [21]. In the past, the poultry industry utilized 0.5–1 ppm chlorine and ice with a circulation system to lower chicken carcass temperature and bacterial load in the gizzard and intestine during the chilling process. This approach, however, may create cross-contamination in chiller tanks due to cycled poultry water. Chlorine and organic materials may react to generate halogenated organic compounds like chloroform, which relates to bladder and rectal cancer in humans. While considering the limitations and health concerns of chemical antimicrobial agents, it is necessary to seek other disinfectants or nonthermal technologies, such as ozone [22], high-hydrostatic pressure (HHP) [23][24][23,24], and cold plasma (CP) [25], as alternatives. Ozone gas, for instance, is one of the most potent oxidants known (for its use as a bactericide) because it can attack the cellular membrane of bacterial cells, leading to the lysis of cell structure and damage of DNA and proteins [26]. On the other hand, HHP, as a food preservation technology used for short-term treatment under high pressure, replaced the utilization of chemical preservatives or high temperatures [27]. Similarly, CP had been identified as a potential source of nitrite and its application in the meat industry as plasma-activated water is a great and efficient way of meat curing [28].

2. Nonthermal Decontamination Technologies

2.1. Ozonation

In recent years, ozone (a naturally occurring water-soluble triatomic gas that can act as a strong oxidizing agent) has been of great interest to the processing industry. Bacterial inactivation through cell wall disruption, or lysis by ozone, is faster than other disinfectants that require time to invade the cell membrane [29]. It is, therefore, a very effective germicide against viruses, bacteria, and spores. The two mechanisms of inactivation include: (i) sulfhydryl group and amino acids of enzymes, proteins, and peptides oxidized to smaller peptides and (ii) polyunsaturated fatty acids oxidized to acid peroxides, resulting in cell death [30]. The effect of ozone treatment operating conditions on several microorganisms’ reduction is presented in Table 1.
Table 1. Ozone applications to decontaminate meat and meat products.
The significant oxidative properties of ozone justify its use as a decontaminating agent as an alternative to conventional agents (50% more effective than chlorine) [34]. It is highly efficient in killing viruses, bacteria, and protozoa within a short contact time. Figure 1 shows the action mechanism of ozone imparting decontamination activity. Ozone has an oxidative potential of 2.07 V, which is nearly double the oxidizing potential of chlorine (1.36) and greater than the efficacy of peroxyacetic acid (1.81) [34]. The exclusion of heat generation during ozone treatment makes it adaptable for heat-sensitive foods [35]. The threshold limit of ozone exposure has usually been calculated as 8 h/day at 0.1 ppm (0.2 mg/m3). However, its oxidizing power may prove toxic for humans depending upon the exposure length and level of concentration (0.1–0.3 ppm) [29]. Since all the consumer demands are fulfilled by ozone treatment, it can therefore be regarded as a “greener” additive. Furthermore, no specific guidelines for foodstuff related to the dosage of ozone are given, and it can thus be used in compliance with current industry standards of good manufacturing practice [36].
Figure 1. Schematic presentation of decontamination using ozone.
Commercially, ozone is applied for industrial waste deodorization and drinking water disinfection. However, its food application has increased since 1997, when the Food and Drug Administration (FDA) designated it as generally recognized as safe (GRAS). In December 2001, the USDA’s Food Safety Inspection Service (FSIS) approved ozone as a suitable and safe ingredient used for the treatment of ready-to-eat (RTE) meat and poultry products just before packaging [37]. Ozonation safely oxidized the contaminants without affecting their quality and left no residues behind [38]. It is an ecofriendly approach to disinfecting a wide range of materials and replacing other chemical disinfectants, such as chlorine, salts, and acids [33]. Although many researchers have proposed that ozonized water effectively improved the chemical properties and safety of meat, there are, however, no specific guidelines for its usage [32]. Gaseous ozone provides an advantage over aqueous ozone by invading pathogens residing in inaccessible places [39]. According to Giménez et al. [33], the gaseous ozone pulses (duration ranging between 5 and 10 min) effectively control microbial flora in beef every 30 min for 5 h using 280 mg/m3, whereby these treatments enacted the reduction (of >1 log) of LAB, mesophilic, and Enterobacteriaceae. Furthermore, this reduced the inoculated L. monocytogenes (102 CFU g/tissue) to below the detection limit and restricted its growth for 16 days at 4 °C. However, ozone treatment intensities of >58.66 mg/min in beef samples with a concentration of 286 mg/m3 are harmful concerning lipid oxidation and surface discoloration. Similarly, more than 10 min of exposure results in rancidity and color loss. In addition, ozone is a nonradical derivative of ROS (reactive oxygen species), which initiates oxidation reaction in foods. The production of free radicals is closely coupled to myoglobin oxidation. Similar results were previously demonstrated by Muhlisin et al. [31]. In chicken and duck breast, gaseous ozone (10 × 10−6 kg O3/m3/h) suppressed coliforms, aerobic, and anaerobic bacteria effectively. However, oxidation by ozone action led to the irreversible damage of cellular proteins and fatty acids in the cell membrane [31]. In addition, continuous exposure to ozone gas might increase oxygen generation due to ozone degradation. Chicken breast meat showed acceptable thiobarbituric acid reactive substances (TBARS) values until up to 3 days, while duck meat TBARS values increased with undesirable browning. According to the authors, ozone and other ROS are powerful oxidants that induce myoglobin and lipid oxidation. Metmyoglobin is produced as a result of myoglobin oxidation, which leads to meat discoloration, i.e., lower redness. Furthermore, ozone oxidizing activity increases rancidity and modifies surface color, affecting red meat quality [31]. Ozone can decontaminate and protect meat surfaces against microbial spoilage. For instance, turkey breast meat treated with ozone (1 × 10−2 kg/m3, for up to 8 h) reduced 2.9, 2.3 and 1.9 log CFU/g of total aerobic mesophilic bacteria, Enterobacteriaceae, and yeast and mold, respectively [32]. Furthermore, the increased ozone treatment time enhanced the number of carbonyls, as well as the cooking yield and water-holding capacity, of turkey samples. It can be assumed that after ozonation, structural changes of protein increased both of these properties owing to the amount of water stored in both cooked and raw meat, as this is closely related to the proteinaceous substances in tissues. Probably, a thin layer forms on the meat surface with this restricting water loss due to the protein denaturation caused by pH reduction. In addition, a partially denatured protein film layer (rich in connective tissue) could result in lighter colors on meat surfaces. Recent trends in packaging showed a delay in meat spoilage that involves the combination of nonthermal treatment with vacuum or modified atmospheric packaging using the plastic materials alone or in combination. Gertzou et al. [29] used 2–10 mg/L ozone to treat fresh vacuum packaged chicken legs for 16 days at 4 °C. According to the authors, the lower concentration of ozone (5 or 10 mg/L) for 1 h resulted in a 0.5–1.0 log reduction of Pseudomonas and a total viable count when combined with vacuum packaging, whereas an increase in the intensity of gaseous ozone up to 10 mg/L resulted in >1.0 log cycles to the population of Enterobacteriaceae, lactic acid bacteria, and yeast and molds. Moreover, the shelf-life of vacuum-packaged ozonated chicken legs was extended to 6 days in comparison to single vacuum packaging. However, the physicochemical parameters noticeably varied depending on the intensity of the ozonation and storage period. In contrast, Zouaghi et al. [30] investigated that 0.6 ppm for 10 min was the best ozonation condition for maintaining the acceptable color, texture, and sensory quality of dried chicken breast fillets stored in modified atmosphere packaging with 80% N2 and 20% CO2 gas combination at room temperature. Cantalejo et al. [22] used the hurdle approach to preserve raw meat products by combining ozone and freeze-drying. However, the microorganisms’ growth ceased for a longer period in a well-lyophilized product due to lower water activity and residual humidity (<10%). Ozone treatment (0.6 ppm for 10 min) combined with lyophilization reduced total aerobic mesophilic bacteria (6.8 log CFU/g) and lactic acid bacteria counts (4.77 log CFU/g) with an extended shelf life of 8 months. Nevertheless, increasing ozone treatment intensity (concentration and time) decreased the aerobic mesophilic counts significantly. In contrast, four-month shelf-life stability was obtained for the lyophilized samples (alone). Furthermore, 0.4 ppm ozonation showed a negative effect on the chicken meat sample by increasing both chewiness and hardness, while lyophilized samples were susceptible to oxidation when stored in undesirable conditions, producing unwanted organoleptic characteristics [22]. These findings introduced the need for a suitable packaging hurdle for ozonated freeze-dried samples. The innovative nonthermal ozonation method is beneficial as it is cost-effective, chemical-free, and eco-friendly, as well as easy to use. However, ozone application in the meat industry is challenging because of its strong oxidative power, which might cause damage to the meat’s cellular proteins and fatty acids. Moreover, ozone is quite unstable, with even exposure to light potentially degrading it; hence, it cannot be stored [40]. Furthermore, ozone requires on-site generation, thus cutting the cost of control of chemical production. Ozone is water-insoluble; special mixers are therefore required to solubilize it, which also limits ozone application for the surface disinfection of fresh fruit and packaged food compared to microbial inactivation within the food samples. Furthermore, in comparison to other disinfection processes, the installation of ozone technology is highly complicated and demands a large capital investment. All these disadvantages limit ozone application in food industries. For that reason, further research is needed to overcome these limitations, as well as expand ozone technology utilization in the food industry.

2.2. High Hydrostatic Pressure (HHP)

HHP is a major trend in the food industry nowadays in terms of clean label technology. It is the most modern method of increasing the shelf stability of food products [41][42][41,42]. HHP is a response to the challenges faced by the industry and provides a competitive advantage, which is undoubtedly worth implementing sooner rather than later. According to Lee et al. [43], global revenues from the high-pressure food protection (i.e., HHP) market amounted to USD 1055 million in 2019 and will reach USD 2123 million in 2025, with a compound annual growth rate of 12.34% from 2021–2025. HHP can achieve food safety, inactivate pathogens, such as Salmonella, Listeria, and E. coli, and prevent recontamination, seeing as the packed product is virtually impossible to recontaminate. HHP reduces microorganisms or eliminates them and/or reduces chemical preservatives. Table 2 summarizes the range of parameters used in HHP to decontaminate meat and meat products. In general, HHP (a single step at 86,000 psi for 3 min) as a clean label (no preservatives) technology was able to effectively double the shelf-life of meat products, with the control product lasting for about 30 days compared to 60 days for the HHP product, concerning pathogen control.
Table 2. HHP applications to decontaminate meat and meat products.
Although the microbiological quality of poultry meat depends on several critical factors such as the physiological status of an animal, temperature, and other conditions during slaughter, HPP (for 10 min at 500 MPa) inhibited Salmonella ser. Enteritidis during 12 °C storage (0.48 log CFU/g) and extended the shelf-life of the chicken meat by 6 to 12 days [44]. Moreover, the population of Salmonella ser. Enteritidis remained below or near the detection limit during storage at 4 °C. According to the authors, the inactivation of Salmonella in HHP-treated samples was highly related to the product (raw material), as well as to the strains of Salmonella being inoculated. As compared to the control samples, HHP-treated samples showed unpredictable changes in the distribution and survival of the Salmonella strains at different inoculum levels and storage temperatures [44]. These results highlighted a potential mechanism involving the ecological modification of the food microbiota via different treatment conditions, which is crucial for designing and applying a new or different technology in the food industry. HHP (applied for 5 min at 400 MPa and 1 min at 500 MPa) not only lowered Salmonella spp. (>3 log units) populations in frozen fillets of chicken but also improved the color and texture profile, as compared to the control samples [45]. However, HHP at increased pressure (600 MPa) flattened and deformed the cells while increasing the holding times (5 min) and elongating the cellular tissues. Although changes in the textural profile of meat depend on the protein system, rigor state, and processing parameters (i.e., temperature, pressure level, and time), researchers have observed an increase in firmness and work area for the HHP-treated cooked chicken breast fillets, as compared to the control [45]. Additionally, no significant differences were found between Salmonella spp. counts for pressurized samples treated for 1 and 3 min and among the treatments of 5, 7 and 9 min, which indicated the fact that HHP treatments quickly destroy sensitive cells, while the remaining cells produce stress adaptation and higher resistance [45].