74 Modern Food Microbiology Table 4–7 Prevalence of Escherichia coli 0157:H7 and Related Pathogenic Serotypes in Some Fresh and Frozen Meat and Poultry Products, and Some Slaughter Animals and/or Their Products Product Chicken Ground beef Boneless beef Beef carcasses Beef carcasses Healthy cattle Downer cattle Steer/heifer carcasses Lamb/mutton Lamb carcasses Lamb products Sheep carcasses (frozen) Pork Retail meats Raw meats Cattle feces Beef carcasses, export only Cattle feed Calvesb , 3 to months Heifers, >6 months Beef products a Non-0157:H7 % Positive/No Tested Country Reference 0/36a 17/296 0/990 0.1/1,275 1.4/1,500 1.5/201 4.9/203 0.2/2,081 17/37 0.7/1,500 7.4/7,200 0.3/343 4/35a 12/91a 0.44/4,983 18/296 0.1/812 14.9/504 31.4/35 8.4/107 26.1/88 14.5/214 12.9/4,800 New Zealand United States Australia Australia United Kingdom United States United States United States New Zealand United Kingdom United Kingdom Australia New Zealand New Zealand United Kingdom United States Australia United States Japan Japan Japan Japan United Kingdom 16 154 141 141 27 19 19 178 16 27 27 179 16 16 27 154 141 36 98 98 98 98 27 Stx-producing strains; b Rectal stool samples Why bacteria grow faster in the meat-soy blends than in nonsoy controls is not clear The soy itself does not alter the initial biota, and the general spoilage pattern of meat-soy blends is not unlike that of all-meat controls One notable difference is a slightly higher pH (0.3–0.4 unit) in soy-extended products, and this alone could account for the faster growth rate This was assessed by Harrison et al.83 by using organic acids to lower the pH of soy blends to that of beef By adding small amounts of a 5% solution of acetic acid to 20% blends, spoilage was delayed about days over controls, but not all of the inhibitory activity was due to pH depression alone With 25% fat in the ground meat, bacterial counts did not increase proportionally to those of soy-extended beef.97 It is possible that soy protein increases the surface area of soy–meat mixtures so that aerobic bacteria of the type that predominate on meats at refrigerator temperatures are favored, but data along these lines are wanting The spoilage of soy-meat blends is discussed below For more information, see reference 39 Mechanically Deboned Meats When meat animals are slaughtered for human consumption, meat from the carcasses is removed typically by meat cutters However, the most economical way to salvage the small bits and pieces Fresh Meats and Poultry 75 of lean meat left on carcass bones is by mechanical means (mechanical deboning) Mechanically deboned meat (MDM) is removed from bones by machines The production of MDM began in the 1970s, preceded by chicken meat in the late 1950s, and fish in the late 1940s.53,58 During the deboning process, small quantities of bone powder become part of the finished product, and the 1978 U.S Department of Agriculture (USDA) regulation limits the amount of bone (based on calcium content) to no more than 0.75% (the calcium content of meat is 0.01%) MDM must contain a minimum of 14% protein and no more than 30% fat The most significant parametrical difference between MDM and conventionally processed meat relative to microbial growth is the higher pH of the former, typically 6.0–7.0.53,54 The increased pH is due to the incorporation of marrow in MDM Although most studies on the microbiology of MDM have shown these products to be not unlike those produced by conventional methods, some have found higher counts The microbiological quality of deboned poultry was compared to other raw poultry products, and although the counts were comparable, MPN coliform counts of the commercial MDM products ranged from 460 to >1,100/g Six of 54 samples contained salmonellae, four contained C perfringens, but none contained S aureus.137 The APC of handboned lamb breasts was found to be 680,000, whereas for mechanically deboned lamb allowed to age for week, the APC was 650,000/g.55 Commercial samples of mechanically deboned fish were found to contain tenfold higher numbers of organisms than conventionally processed fish, but different methods were used to perform the counts on fish frames and the mechanically deboned flesh (MDF146 ) These investigators did not find S aureus and concluded that the spoilage of MDF was similar to that for the traditionally processed products In a later study, MDM was found to support the more rapid growth of psychrotrophic bacteria than lean ground beef.149 Several studies have revealed the absence of S aureus in MDM, reflecting perhaps the fact that these products are less handled by meat cutters In general, the mesophilic biota count is a bit higher than that for psychrotrophs, and fewer Gram negatives tend to be found Field53 concluded that with good manufacturing practices, MDM should present no microbiological problems, and a similar conclusion was reached by Froning58 relative to deboned poultry and fish Hot-Boned Meats In the conventional processing of meats (cold boning), carcasses are chilled after slaughter for 24 hours or more and processed in the chilled state (postrigor) Hot boning (hot processing) involves the processing of meats generally within 1–2 hours after slaughter (prerigor) while the carcass is still “hot.” In general, the microbiology of hot-boned meats is comparable to that of cold-boned meats, but some differences have been reported One of the earliest studies on hot-boned hams evaluated the microbiological quality of cured hams made from hot-boned meat (hot-processed hams) These hams were found to contain a significantly higher APC (at 37◦ C) than cold-boned hams, and 67% of the former yielded staphylococci to 47% of the latter.145 Mesophiles counted at 35◦ C were significantly higher on hot-boned prime cuts than comparable cold-boned cuts, both before and after vacuumpackaged storage at 2◦ C for 20 days.101 Coliforms, however, were apparently not affected by hot boning Another early study is that of Barbe et al.,9 who evaluated 19 paired hams (hot and cold boned) and found that the former contained 200 bacteria per gram, whereas 220 per gram were found in the latter In a study of hot-boned carcasses held at 16◦ C and cold-boned bovine carcasses held at 2◦ C for up to 16 hours postmortem, no significant differences in mesophilic and psychrotrophic counts were found.96 Both hot-boned and cold-boned beef initially contained low bacterial counts, but after a 14-day storage period, the hot-boned meats contained higher numbers than the cold boned.59 These 76 Modern Food Microbiology investigators found that the temperature control of hot-boned meat during the early hours of chilling is critical and in a later study found that chilling to 21◦ C within 3–9 hours was satisfactory.60 In a study of sausage made from hot-boned pork, significantly higher counts of mesophiles and lipolytics were found in the product made from hot-boned pork than in the cold-boned product, but no significant differences in psychrotrophs were found.114 The effect that delayed chilling might have on the biota of hot-boned beef taken about hour after slaughter was examined by McMillin et al.125 Portions were chilled for 1, 2, 4, and hours after slaughter and subsequently ground, formed into patties, frozen, and examined No significant differences were found between this product and a cold-boned product relative to coliforms, staphylococci, psychrotrophs, and mesophiles A numerical taxonomy study of the biota from hot-boned and cold-boned beef at both the time of processing and after 14 days of vacuum storage at 2◦ C revealed no statistically significant differences in the biota.108 The predominant organisms, after storage, for both products were “streptococci” (most likely enterococci) and lactobacilli, whereas in the freshly prepared hot-boned product (before storage), more staphylococci and bacilli were found Overall, though, the two products were comparable Restructured lamb roast made from 10% and 30% MDM and hot-boned meat was examined for microorganisms; overall, the two uncooked products were of good quality.148 The uncooked products had counts