Processed Meats and Seafoods 105 own biota B thermosphacta has been found by many investigators to be the most predominant spoilage organism for sausage The changes that fresh meat bacteria bring about as processed meats undergo souring are unlikely to occur in the latter since many members of the fresh meat Gram-negative biota are unable to proliferate at the lower aw and pH of processed meats Even in fresh meats, definitive spoilage changes affecting structural proteins not occur until APC is in the 109 to 1010 range54 Although mold spoilage of these meats is not common, it can and does occur under favorable conditions When the products are moist and stored under conditions of high humidity, they tend to undergo bacterial and yeast spoilage Mold spoilage is likely to occur only when the surfaces become dry or when the products are stored under other conditions that not favor bacteria or yeasts Two types of greening occur on stored and processed red meats: one caused by H2 O2 and the other by H2 S The former occurs commonly on frankfurters as well as on other cured and vacuumpackaged meats It generally appears after an anaerobically stored meat product is exposed to air Upon exposure to air, H2 O2 forms and reacts with nitrosohemochrome to produce a greenish oxidized porphyrin.73 H2 O2 may accumulate when heating if nitrite destroys catalase, and the peroxide reacts with meat pigments to form choleglobin, which is green Greening also occurs from growth of causative organisms in the interior core, where the low oxidation–reduction (Eh) potential allows H2 O2 to accumulate Weissella viridescens is the most common organism in this type of greening, but leuconostocs, Enterococcus faecium, and Enterococcus faecalis are capable of producing greening of products Greening can also be produced by H2 O2 producers such as Lactobacillus fructivorans and Lactobacillus jensenii W viridescens is resistant to >200 ppm NaNO2 , and it can grow in the presence of 2–4% NaCl but not in 7%.73 W viridescens has been recovered from anaerobically spoiled frankfurters and from both smoked pork loins and frankfurter sausage stored in atmospheres of CO2 and N2 In spite of the discoloration, the green product is not known to be harmful if eaten The second type of greening occurs generally on fresh red meats that are held at 1–5◦ C and stored in gas-impermeable or vacuum-packaging containers; it is caused by H2 S production H2 S reacts with myoglobin to form sulphmyoglobin (Table 5–2) This type of greening does not usually occur when meat pH is below 6.0 The organism responsible in one study was thought to be Pseudomonas mephitica71 but in another study of DFD meats, S putrefaciens was the H2 producer.37 In the latter, greening occurred even with glucose present, and it could be prevented by lowering pH to below 6.0 H2 S-producing lactobacilli were recovered from vacuum-packaged fresh beef and found to produce H2 S in the pH range of 5.4–6.5.81 Only slight greening was produced, and the H2 S was from cysteine, a system that was plasmid borne The organism reached × 107 /cm2 after days, and ultimately reached about 108 /cm2 at 50◦ C No offness of vacuum-packaged sliced luncheon meat was observed when another lactobacillus attained 108 /cm2 At least one strain of Lactobacillus sakei has been shown to produce H2 S on vacuum-packaged beef; and the effect of pH and glucose on production is presented in Table 5–3.26 The investigators found that greening by L sakei was not as intense as that caused by S putrefaciens and that it occurred only after about weeks at 0◦ C Further, the lactobacillus produced H2 S only in the absence of O2 and utilizable sugars No greening was observed when films with an O2 transmission rate of ml O2 /m2 or 300 ml O2 /m2 were used, but it did occur with films that had O2 transmission rates between 25 and 200 ml/m2 /24 hours.26 Visible greening was seen only on samples packaged in films with O2 transmission rates of 100 and 200 ml/m2 /24 hours and only after 75 days’ storage With meat in the pH 6.4–6.6 range, H2 S was detected when cell numbers reached 108 /g A yellow discoloration of vacuum-packaged luncheon-style meat was caused apparently by Enterococcus casseliflavus The discoloration appeared as small spots on products stored at 4.4◦ C, and 106 Effects of reagents as in in large excess Effect of H2 S and oxygen on myoglobin Effect of hydrogen peroxide on myoglobin or oxymyoglobin; effect of ascorbic or other reducing agent on oxymyoglobin Effect of reagents as in in excess Combination of metmyoglobin with excess nitrite Effect of heat, denaturing agents on myoglobin, oxymyoglobin; irradiation of globin haemi chromogen Effect of heat, denaturing agents on myoglobin, oxymyoglobin, metmyoglobin, haemochromogen Effect of heat, salts on nitric oxide myoglobin Reduction of metmyoglobin; deoxygenation of oxymyoglobin Oxygenation of myoglobin Oxidation of myoglobin, oxymyoglobin Combination of myoglobin with nitric oxide Mode of Formation Intact Intact Intact Intact Intact Intact Intact Intact but reduced Intact but reduced Porphyrin ring opened Porphyrin ring destroyed; chain of porphyrins Fe2+ Fe3+ Fe3+ Fe3+ Fe2+ Fe3+ Fe2+ Fe3+ Fe2+ or Fe3+ Fe3+ Fe absent Intact State of Haematin Nucleus Fe2+ State of Iron Source: Reprinted with permission from R.A Lawrie, Meat Science, copyright c 1966, Pergamon Press 12 Bile pigments 11 Verdohaem Nitric oxide haemochromogen Sulphmyoglobin 10 Choleglobin Globin haemi chromogen Globin haemochromogen Oxymyoglobi n Metmyoglobin Nitric oxide myoglobin Metmyoglobin nitrite Myoglobin Pigment Table 5–2 Pigments Found in Fresh, Cured, or Cooked Meat Absent Denatured Denatured Denatured Denatured Denatured Denatured Native Native Native Native Native State of Globin Yellow or colorless Green Green Green Bright red Brown Dull red Red Bright red Brown Bright red Purplish red Color Processed Meats and Seafoods 107 Table 5–3 Effect of Meat pH and Glucose on Hydrogen Sulfide Production by a Pure Culture of Lactobacillus sakei L13 Growing under Anaerobic Conditions at 5◦ C on Beef Hydrogen Sulfide Production Days pH 5.6–5.7 pH 6.4–6.6 pH 6.4–6.6 with 250 µg Glucose per Gram of Meat 11 15 18 21 −∗ − − − +† + − +‡ + + + + − − − − +‡ + ∗ Each treatment done in triplicate − = All three tubes negative; + = all three positive † One tube out of three positive ‡ Two tubes out of three positive Source: Egan et al.26 it was fluorescent under long-wave ultraviolet light.10 Between and weeks were required for the condition to develop, and the responsible organism survived 71.1◦ C for 20 minutes but not 30 minutes In addition to 4.4◦ C, it occurred also at 10◦ C but not at 20◦ C or above Although tentatively identified as E casseliflavus, the causative organism did not react with Group D antisera The other yellow-pigmented enterococcal species is E mundtii; and both are discussed further in Chapter 20 A summary of several spoilage conditions of processed meats is presented in Table 5–4 Table 5–4 Summary of Some Microbial Spoilage Conditions of Processed Meats Condition Products Affected Greening Reference vacuum-packaged bologna Vacuum-packaged beef Fresh red meats DFD meats Wieners, bologna Vacuum-packaged luncheon meats Cured meats Sausage Vacuum-packaged meats Vacuum-packaged meats Greening Greening Greening Greening/sliminess Yellowing Black spot Souring “Blown pack” General spoilage Etiology C viridans Reference 48 L sakei P mephitica, S putrefaciens S purefaciens W viridescens E casseliflavus 26 41, 71 37 Many 101 C nigrificans B thermosphacta C frigidicarnis, C gasigenes L algidus; L fuchuensis 36 66 9, 10 57, 79 108 Modern Food Microbiology BACON AND CURED HAMS The nature of these products and the procedures employed in preparing certain ones, such as smoking and brining, make them relatively insusceptible to spoilage by most bacteria The most common form of bacon spoilage is moldiness, which may be due to Aspergillus, Alternaria, Fusarium, Mucor, Rhizopus, Botrytis, Penicillium, and other molds (Table 5–1) The high fat content and low aw make it somewhat ideal for this type of spoilage Bacteria of the genera Enterococcus, Lactobacillus, and Micrococcus are capable of growing well on certain types of bacon such as Wiltshire, and E faecalis is often present on several types Vacuum-packaged bacon tends to undergo souring due primarily to micrococci and lactobacilli Vacuum-packed, low-salt bacon stored above 20◦ C may be spoiled by staphylococci.92 Cured hams undergo a type of spoilage different from that of fresh or smoked hams This is due primarily to the fact that curing solutions pumped into the hams contain sugars that are fermented by the natural biota of the ham and also by those organisms pumped into the product in the curing solution, such as lactobacilli The sugars are fermented to produce conditions referred to as “sours” of various types, depending on their location within the ham A large number of genera of bacteria have been implicated as the cause of ham sours, among which are Acinetobacter, Bacillus, Pseudomonas, Lactobacillus, Proteus, Micrococcus, and Clostridium Gassiness is not unknown to occur in cured hams where members of the genus Clostridium have been found In their study of vacuum-packed sliced bacon, Cavett13 and Tonge et al.92 found that when highsalt bacon was held at 20◦ C for 22 days, the catalase-positive cocci dominated the biota, whereas at 30◦ C the coagulase-negative staphylococci became dominant In the case of low-salt bacon (5–7% NaCl versus 8–12% in high-salt bacon) held at 20◦ C, the micrococci as well as E faecalis became dominant; at 30◦ C the coagulase-negative staphylococci as well as E faecalis and micrococci became dominant In a study of Iberian dry-cured hams, over 97% of the isolates were staphylococci with the four predominant species being S equorum, S xylosus, S saprophyticus, and S cohnii.77 Interestingly, one S xylosus isolate hybridized with a DNA probe for staphylococcal enterotoxins C and D, but the investigators noted that probe-positive isolates not always produce enterotoxins In a study of lean Wiltshire bacon stored aerobically at 5◦ C for 35 days or 10◦ C for 21 days, Gardner35 found that nitrates were reduced to nitrites when the microbial load reached about 109 /g The predominant organisms at this stage were micrococci, vibrios, and the yeast genera Candida and Torulopsis Upon longer storage, microbial counts reached about 1010 /g with the disappearance of nitrites At this stage, Acinetobacter, Alcaligenes, and Arthrobacter-Corynebacterium spp became more important Micrococci were always found, whereas vibrios were found in all bacons with salt contents >4% In a study of Italian dry fermented sausages, the most frequently isolated staphylococci were S xylosus followed by S saprophyticus, S aureus, and S sciuri.34 S xylosus appears to be the most frequently isolated from several Italian dry sausages In Iberian dry cured hams, the two predominant organisms in the ripening process are Staphylococcus equorum and S xylosus, and both are believed to contribute to product flavor Safety Overall, fermented meat products have a long history of safety throughout the world This is not to imply that they are never the vehicles of foodborne illness outbreaks, but when such incidents have occurred they have been sporadic Several outbreaks of illness occurred in the United States in the 1990s involving fermented meat products as vehicles As a consequence, the USDA mandated a log10 Processed Meats and Seafoods 109 reduction in the number of pathogens, especially E coli 0157:H7, in the manufacture of dry and semidry fermented sausages As a result, a number of studies have been conducted on the efficacy of domestic and commercial processing to achieve the pathogen reduction goal An outbreak of E coli 0157:H7 from dry-cured salami occurred in the states of California and Washington in 1994, and there were 23 victims.15 Following this outbreak, a series of studies were conducted on the conditions of pepperoni manufacture that are needed to effect a log reduction in numbers of specific pathogens Using a 5-strain cocktail of E coli 0157:H7 at a level of ≥ × 107 /g, it was found that the traditional nonthermal process destroyed only about log units/g and that in order to effect a log 5–6 reduction, postfermentation heating to an internal temperature of 63◦ C instantaneous or 53◦ C for 60 minutes was necessary.46 In a more extensive study, pepperoni sticks were fermented at 36◦ C and 85% relative humidity (RH) to a pH ≤4.8 and then dried at 13◦ C and 65% RH to a moisture/protein ratio of ≤1.6:1.29 The five-strain pathogen mixture was reduced only about log units To achieve a log reduction, storage for at least weeks at ambient temperature in air was necessary for sliced pepperoni In another study, a >log decrease in E coli 0157:H7 could be achieved by fermentation at 41◦ C to a pH of 4.6 or 5.0 and postfermentative heating of summer sausage chubs to an internal temperature of 54◦ C for 30 minutes.12 In a similar study of pepperoni manufacture and storage with S Typhimurium DT104, it was found that this pathogen is more sensitive to destruction than E coli 0157:H7 and thus methods that will reduce the latter by log are more than adequate for the former.52 The fate of S aureus in country-cured hams was investigated by the spraying of fresh hams with four strains at levels of log10 8.57 and log10 8.12 followed by curing, cold smoking, and aging After months of aging, S aureus was below detectable levels by plating, although some cells were recovered by enrichment.74 Sodium nitrite was employed in some cures and aw was controlled with 4.45 or 3.37% NaCl Forty percent of the inoculated and 50% of controls contained enterotoxin following the aging period SEAFOODS Fish and Shellfish As used in this chapter, the term seafood covers fish, shellfish, and mollusks from all waters–fresh, marine, warm, or cold In general, the biota of a fresh seafood animal is reflective of the waters from which it is taken As is the case for meat animals, the inner tissues of a healthy fish are sterile With fish, the microbial biota is found generally in three places: the outer slime, gills, and the intestines of feeding fish Fresh or warm-water fish tend to have a biota that is composed of more mesophilic Gram-positive bacteria than cold-water fish, which tends to be largely Gram negative (the indigenous bacterial biota of marine water is Gram negative) The organisms that make up the biota of seafoods are listed in Table 5–5, and what is known about their interplay in bringing about the spoilage of these products is discussed in the section on spoilage of fish and shellfish Microorganisms As noted above, the overall sanitary quality of the waters from which these animals are taken is key to the overall microbial quality of finished products Beyond the water source, microbes are picked up at various processing steps such as peeling, shucking, evisceration, breading, and the like ... Fresh, Cured, or Cooked Meat Absent Denatured Denatured Denatured Denatured Denatured Denatured Native Native Native Native Native State of Globin Yellow or colorless Green Green Green Bright red Brown... Yellow or colorless Green Green Green Bright red Brown Dull red Red Bright red Brown Bright red Purplish red Color Processed Meats and Seafoods 107 Table 5–3 Effect of Meat pH and Glucose on Hydrogen... Intact Intact Intact Intact Intact Intact Intact Intact but reduced Intact but reduced Porphyrin ring opened Porphyrin ring destroyed; chain of porphyrins Fe2+ Fe3+ Fe3+ Fe3+ Fe2+ Fe3+ Fe2+ Fe3+