378 Modern Food Microbiology Table 15–1 Effect of Irradiation Temperature on D Values of Two Load Levels of C botulinum 33A in Precooked Ground Beef D (kGy) ◦ Temperature ( C) ∼5 × 10 Spores/Can ∼2 × 108 Spores/Can −196 −150 −100 −50 25 65 5.77 5.32 4.83 4.34 3.85 3.60 3.21 5.95 5.43 4.86 4.30 3.73 3.45 2.99 Note: Data are based on linear spore destruction Source: Grecz et al.27 reproduced by permission of National Research Council of Canada from Canadian Journal of Microbiology 17:135–142, 1971 Radappertization Radappertization of any foods may be achieved by application of the proper dose of radiation under the proper conditions The effect of this treatment on endospores and exotoxins of C botulinum is of obvious interest Type E spores have been reported to possess radiation D values on the order of 1.2–1.7 kGy.71 Types A and B spores were found by Kempe37 to have D values of 2.79 and 2.38 kGy, respectively Type E spores are the most radiation sensitive of these three types The effect of temperature of irradiation on D values of C botulinum spores is presented in Table 15–1: resistance increases at the colder temperatures and decreases at warmer temperatures.27 Different inoculum levels had no significant effect on D values whose calculations were based on a linear destruction rate D values of four C botulinum strains in three food products are presented in Table 15–2, from which it can be seen that each strain displayed different degrees of radiation resistance in each product Also, irradiation of cured meat products produced the lowest D values (The possible significance of this is discussed in Chapter 13 under nitrates and nitrites.) The minimum radiation doses (MRD) in kGy for the radappertization of nine meat and fish products are indicated below.3,13,35 With the exception of bacon (irradiated at ambient temperatures), each was treated at −30◦ C +10: Bacon Beef Chicken Ham Pork Shrimp Codfish cakes Corned beef Pork sausage 23 47 45 37 51 37 32 25 24–27 Radiation Protection of Foods, and Nature of Microbial Radiation Resistance 379 Table 15–2 Variations in Radiation D Values of Strains of C botulinum at 30◦ C in Three Meat Products D (kGy) Strain Number Codfish Cake Corned Beef Pork Sausage 33A 77A 41B 53B 2.03 2.38 2.45 3.31 1.29 2.62 1.92 1.83 1.09 0.98 1.84 0.76 Note: Computed by the Schmidt equation Source: Anellis et al.,3 copyright c 1972, American Society for Microbiology To achieve 12D treatments of meat products at about 30◦ C, the following kGy values are necessary:74 beef and chicken, 41.2–42.7; ham and codfish cake, 31.4–31.7; pork, 43.7; and corned beef and pork sausage, 25.5–26.9 Irradiation treatments of the types noted not make the foods radioactive.74 The radiation resistance of C botulinum spores in aqueous media was studied by Roberts and Ingram,72 and these values are considerably lower than those obtained in meat products On three type A strains, D ranged from 1.0 to 1.4; on two strains of type B, 1.0–1.1; on two strains of type E, 0.8–1.6; and the one type F strain examined by these authors showed a D value of 2.5 kGy All strains were irradiated at 18–23◦ C and an exponential death rate was assumed in the D calculations With respect to the effect of radiation on C perfringens, each of five different strains (types A, B, C, E, and F) was found to have D values between 1.5 and 2.5 kGy in an aqueous environment.72 The 12D values for strains of this organism were found to range between 30.4 and 41.4 kGy, depending upon the strain and method of computing 12D doses.8 Radiation D10 values for Listeria monocytogenes in mozzarella cheese and ice cream were found to be 1.4 and 2.0 kGy, respectively, with strain Scott A irradiated at 78◦ C.29 The respective calculated 12D values were 16.8 and 24.4 kGy To effect radappertization of ice cream and frozen yogurt, 40 kGy was sufficient but not for mozzarella or cheddar cheeses.30 The radappertization dose for Bacillus cereus in cheese and ice cream was 40–50 kGy As indicated in Figure 15–2, viruses are considerably more resistant to radiation than bacteria Sullivan et al found radiation D values of 30 viruses78 to range between 3.9 and 5.3 kGy in Eagle’s minimal essential medium supplemented with 2% serum The 30 viruses included coxsackie-, echo-, and poliovirus Of five selected viruses subjected to 60 Co rays in distilled water, the D values ranged from 1.0 to 1.4 kGy D values of coxsackievirus B-2 in various menstra at −30 and −90◦ C are presented in Table 15–3 The use of a radiation 12D process for C botulinum in meat products would result in the survival of virus particles unless previously destroyed by other methods such as heating Enzymes are also highly resistant to radiation, and a dose of 20–60 kGy has been found to destroy only up to 75% of the proteolytic activity of ground beef.48 When blanching at 64 or 70◦ C was combined with radiation doses of 45–52 kGy, however, at least 95% of the beef proteolytic activity was destroyed Radiation D values for a variety of organisms are presented in Table 15–4 The main drawbacks to the application of radiation to some foods are color changes and/or the production of off-flavors Consequently, those food products that undergo relatively minor changes in color and flavor have received the greatest amount of attention for commercial radappertization 380 Modern Food Microbiology Table 15–3 D Values of Coxsackievirus B-2 D (kGy) Suspending Menstrum Eagle’s minimal essential medium + 2% serum Distilled water Cooked ground beef Raw ground beef −30 ◦ C −90 ◦ C 6.9 — 6.8 7.5 6.4 5.3 8.1 6.8 Note: A linear model was assumed in D calculations Source: Sullivan et al.,78 copyright c 1973, American Society for Microbiology Bacon is one product that undergoes only slight changes in color and flavor development following radappertization Mean preference scores on radappertized versus control bacon were found to be rather close, with control bacon being scored just slightly higher.95 Acceptance scores on a larger variety of irradiated products were in the favorable range.35 Radappertization of bacon is one way to reduce nitrosamines When bacon containing 20 ppm NaNO2 +550 ppm sodium ascorbate was irradiated with 30 kGy, the resulting nitrosamine levels were similar to those in nitrite-free bacon.18 From a review of 539 D values obtained from 39 published papers, the most radiation resistant sporeformers noted were Geobacillus stearothermophilus and Clostridium sporogenes, while the most resistant nonsporeformers were Enterococcus faecium, Alcaligenes spp., and the Moraxella-Acinetobacter group.91 Overall, Gram-negative bacteria were more sensitive than Gram positives from published reports Table 15–4 Some Radiation D Values Reported Organism/Substance Bacteria Acinetobacter calcoaceticus Aeromonas hydrophila Bacillus pumilus spores, ATCC 27142 Arcobacter butzleri Bacillus cereus Campylobacter jejuni (5 strains) C jejuni Clostridium botulinum, type E spores C botulinum, type E Beluga C botulinum, 62A spores C botulinum, type A spores C botulinum, type B spores C botulinum, type F spores D (kGy) 0.26 0.14 1.40 0.27 1.485 0.175–0.235 0.19 1.1–1.7 0.8 1.0 2.79 2.38 2.5 Reference 87 60 87 10 42 10 19,46 48 48 27 27 48 continues Radiation Protection of Foods, and Nature of Microbial Radiation Resistance 381 Table 15–4 continued Organism/Substance D (kGy) Reference C botulinum A toxin in meat slurry C bifermentans spores C butyricum spores C perfringens, type A spores C sporogenes spores (PA 3679/S2 ) C sordellii spores Enterobacter cloacae Escherichia coli E coli 0157:H7 (gr beef, -20◦ C) E coli 0157:H7 (gr beef, 4◦ C) E coli O157:H7 (5 strains) Klebsiella pneumoniae Listeria monocytogenes L monocytogenes (mean of strains) L monocytogenes on beef at 5◦ C on beef at 0◦ C on beef at −20◦ C Moraxella phenylpyruvica M osloensis Pseudomonas putida P aeruginosa Salmonella Typhimurium S Enteritidis in poultry meat at 22◦ C in egg white at 15◦ C Salmonella sp Salmonellae spp.∗ S Mbandaka (alfalfa seeds, 20◦ C) Staphylococcus aureus (gr beef, 0◦ C) S aureus (gr beef, −20◦ C) Staphylococcus aureus S aureus ent toxin A in meat slurry Yersinia enterocolitica, beef, 25◦ C Y enterocolitica, ground beef at 30◦ C 36.08 1.4 1.5 1.2 2.2 1.5 0.18 0.20 0.98 0.39 0.241–0.307 0.183 0.42–0.55 0.35 0.42–0.43 ∼ 0.44 0.45 1.21 0.86 0.191 0.08 0.13 0.50 0.37 0.33 0.13 0.621–0.800 0.98 0.51 0.88 0.16 61.18; 208.49 0.195 0.388 73 48 48 48 48 48 87 87 80 80 42 61 32 83 83 83 62 42 62 87 61 54 54 87 81 80 80 87 73 16 16 Fungi Aspergillus flavus spores (mean) A flavus A niger Penicillium citrinum, NRRL 5452 (mean) Penicillium sp 0.66 0.055–0.06 0.042 0.88 0.42 70 75 75 70 87 Viruses Adenovirus (4 strains) Coxsackievirus (7 strains) Echovirus (8 strains) Herpes simplex Poliovirus (6 strains) 4.1-4.9 4.1–5.0 4.4–5.1 4.3 4.1–5.4 50 50 50 50 50 ∗ Five strains including serotypes Dublin, Enteritidis, and Typhimurium 382 Modern Food Microbiology Radicidation Irradiation at levels of 2–5 kGy has been found by many to be effective in destroying non-sporeforming and nonviral pathogens and to present no health hazard Kampelmacher36 notes that raw poultry meats should be given the highest priority because they are often contaminated with salmonellae and because radicidation is effective on prepackaged products, thus eliminating the possibilities of cross-contamination The treatment of refrigerated and frozen chicken carcasses with 2.5 kGy was highly effective in destroying salmonellae.53,54 A radiation dosage up to kGy (0.7 Mrad) has been approved by the World Health Organization (WHO) as being “unconditionally safe for human consumption”.19 When whole cacao beans were treated with kGy, 99.9% of the bacterial biota was destroyed, and Penicillium citrinum spores were reduced by about logs/g, and at a level of kGy, Aspergillus flavus spores were reduced by about logs/g.70 Fresh poultry, cod and red fish, and spices and condiments have been approved for radicidation in some countries (Table 15–5) Table 15–5 Some Food and Food Products Approved for Irradiation by Various Countries and by WHO Products Objective Potatoes Onions Garlic Mushrooms Wheat, wheat flour Dried fruits Cocoa beans Dry food concentrates Poultry, fresh Cod and redfish Spices/condiments Semipreserved meats Fresh fruits‡ Asparagus Raw meats Cod and haddock fillets Poultry (eviscerated) Shrimp Culinary prepared meat products Deep-frozen meals Papaya Shell eggs Fresh, tinned/liquid foodstuffs Sprout inhibition Sprout inhibition Sprout inhibition Growth inhibition Insect disinfestation Insect disinfestation Insect disinfestation Insect disinfestation Radicidation† Radicidation Radicidation Radurization Radurization Radurization Radurization Radurization Radurization Radurization Radurization Radappertization Radurization Radurization Radappertization ∗ Including WHO recommendations † For salmonellae ‡ Includes tomatoes, peaches, apricots, Source: Urbain89 and the literature Dose Range (kGy) 0.1–0.15 0.1–0.15 0.1–0.15 2.5 max 0.2–0.75 1.0 0.7 0.7–1.0 7.0 max 2.0–2.2 8.0–10.0 6.0–8.0 2.5 2.0 6.0–8.0 1.5 max 3.0–6.0 0.5–1.0 8.0 25.0 250 Gy 3.0 25.0 strawberries, cherries, grapes, and so forth Number of Countries∗ 17 10 1 1 1 1 ... essential medium supplemented with 2% serum The 30 viruses included coxsackie-, echo-, and poliovirus Of five selected viruses subjected to 60 Co rays in distilled water, the D values ranged from... radappertization 380 Modern Food Microbiology Table 15–3 D Values of Coxsackievirus B-2 D (kGy) Suspending Menstrum Eagle’s minimal essential medium + 2% serum Distilled water Cooked ground beef Raw... were reduced by about logs/g, and at a level of kGy, Aspergillus flavus spores were reduced by about logs/g.70 Fresh poultry, cod and red fish, and spices and condiments have been approved for