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MICROBIOLOGICAL FACTORS AFFECTING CANNED MEATS
MICROBIOLOGICAL FACTORS AFFECTING CANNED MEATS
Pages 4-37
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From page 4... ...
Chemical and Physical Factors Affecting the Thermal Resistance of Bacterial Spores HIROSHI SUGIYAMA The ability of the endospores of certain bacterial species to survive drastic heat treatment is the important factor in the heat preservation of foods. Numerous studies on the thermostability of bacterial spores have resulted in the accumulation of a mass of data; several reviews of this literature are now available (5, 40, 43)
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. Evidence has been adduced that the heat resistance of vegetative cells are not necessarily related to that of the spores; that is, the vegetative cells may be of relatively high thermal tolerance while that of the homologous spores may be low (52)
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What is the basis of the heat tolerance of bacterial spores? The most likely explanation would involve the change in the physio-chemical make-up of the vegetative cells in their transition into the spore state, resulting in a spore cytoplasm that becomes uniquely resistant to the thermal inactivation of its biological activities.
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. Conclusion From the brief review presented it is evident that a considerable amount of work has already been done on the thermal resistance of bacterial spores.
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A The water content of bacterial spores.
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E., and VINTON, C Bacteriological studies relating to thermal processing of canned meats.
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Factors Causing Sporulation and Vegetation of Spoilage Organisms in Canned Meats 0.
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It is still empirical so far as a knowledge of spore biology is concerned, and it will remain empirical until we fill in many of the gaps and expand our understanding of these critical cellular structures. We need to know why some bacteria, but not others, form spores; what conditions favor and what hinder spore formation; what promotes and what interferes with spore germination and subsequent growth; what is concerned in spore resistance to various adverse environmental conditions; what is the distribution of significant spore formers; what may be expected in the way of numbers in food for processing; and many other items of varying degrees of importance.
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From page 12... ...
Numerous workers have studied spore formation from vegetative cells and spore germination in the presence of one or more nutrient materials under conditions which would not support continued growth. An interesting observation regarding germination was made by Hills (7)
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This idea will be quickly dispelled if one makes spore percentage counts over a period of time. Some species are extremely reluctant to form spores, and even some strains of a species are poor spore formers, whereas other strains, incubated in parallel, regularly produce good spore crops.
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From page 14... ...
One series of experiments which may be mentioned briefly is that concerned with the water content of the substrate and spore germination, growth, and spore formation. A report on this phase of the research recently appeared in Food Research (19)
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Microorganisms Associated with the Spoilage of Thermal Processed Meats JOHN C AYRES The microorganisms which may ultimately contaminate and even decompose canned meat are disseminated in and on these products by diverse pathways.
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From page 16... ...
which indicates that the influence of relative humidity has little effect in delaying microbial growth on meat surfaces. Certainly, in a dry atmosphere the diffusion of water from the interior of meat helps to maintain a higher moisture content near the surface than is indicated by the relative humidity of the surrounding air.
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The 4 principal genera of low temperature bacteria comprising the initial flora were said to be: Achromobacter, 90%; Micrococcus, 7%; Flavobacterium, 3%; and Pseudomonas, less than 1%. In an earlier study, Empey and Vickery (9)
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as the causative agents in spoilage of canned meats. Information concerning the microorganisms causing spoilage of cured meats has been advanced by many investigators.
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From page 19... ...
tested sodium nitrite using a broader bacterial spectrum and found that the growth of the following genera at pH 5.7-6.0 was either inhibited or prevented by 0.02% NaNO2: Achromobacter, Flavobacterium, Pseudomonas, Micrococcus, Escherichia, Aerobacter and one species of Torula. Also, Tarr found that, in this pH range, sodium nitrite inhibited Clostridium botulinum, Clostridium sporogenes, Eberthella typhosa (Salmonella typhosa)
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Jensen (18) states: "During 2 decades of bacteriological control of canned meats, neither we nor any of our colleagues in this work have ever isolated a spontaneously occurring strain of Clostridium botulinum from canned meats." Insofar as the other mesophilic anaerobic spores are concerned, only limited numbers of these organisms have been encountered.
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Also, of 111 samplings from the 37 matched sets of knuckle, inside round, and outside round of cutter and canner grade beef, none of the putrefactive anaerobic spore counts exceeded 1.4 spores per gram (see Table 1)
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Co W 01 Z 4 O oo o Co K o o CO B: £ b U U oa t.
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It is not known whether this same condition prevails in the industry but, if it does, it would appear to indicate that it is possible to successfully utilize a thermal process known to be inadequate to destroy spores of some of the more heatresistant anaerobes. It is significant that viable organisms were found in cans from which no anaerobic spores were recovered.
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R Bacteriological studies relating to thermal processing of canned meats.
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E., and VINTON, C Bacteriological studies relating to thermal processing of canned meats.
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The group of canned meats specifically covered in this discussion are the pork luncheon meats. Even in this limited field there are complex bacteriological problems not fully understood.
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In the 1949 through 1952 period a process of F0=0.6 sterilized from 89% to 95% of the product with an apparent tendency for the percentage sterility to increase from year to year. The point b A thorough discussion of this method of expressing thermal processing results can be found in the Canned Food Reference Manual (14)
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From page 28... ...
Negative results in themselves are sometimes considered inconclusive, but additional evidence may be cited indicating that the methods are satisfactory. In other such processing and incubation tests on more complex canned meat products such as a liver loaf, spoilage was observed on the lower processing levels after prolonged incubation.
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The data show that apparently all viable organisms at all processing levels had lost their viability during the 51- to 87-month incubation period. These results were checked on the 1950-51 series of tests and checks made at more frequent time intervals in order to attempt to check the time when viability is apparently lost.
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When opened, typical putrefactive odors were present. Microscopic examination and subculturing demonstrated that a TABLE 4 EFFECT OF THERMAL PROCESSING LEVELS f Samples Positive for Viable Bacteria *
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From page 31... ...
3679. TABLE 6 TOTAL SPORE LOAD IN TRIMMINGS Range of Viable Spores after Pasteurization 0 to 10 11 to 100 over 100 Plant Samples Samples Per Cent Samples Per Cent Samples Per Cent 1951 A B 65 32 24 11 37 34 23 14 35 18 7 28 22 44 1952 A B 130 33 33 9 25 67 21 52 64 30 3 23 27 9 Total 260 77 30 125 48 58 22 31
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From page 32... ...
On the other hand these numbers are quite low compared to the levels normally used in inoculated pack studies. Discussion The purpose of the conventional thermal processing of canned meats is to destroy microbial life so that the product may be kept at ordinary storage temperatures without deterioration due to microbial action.
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From page 33... ...
indicate that spores of other common putrefactive anaerobes have a lower thermal resistance than Clostridium sporogenes. From these considerations it would seem that the required thermal processes could be drastically reduced if spores of P.A.
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Apparently from 26 to 31 months under such conditions is the normal period of loss of viability although 2 exceptions surviving a processing level of 0.2 were viable after 52 and 61 months. Summary and Conclusions The level of thermal processes required to reach sterility in cured canned luncheon meat products has been lowered in the past few years.
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R Bacteriological studies relating to thermal processing of canned meats.
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I Laboratory methods employed for studying thermal processes required to prevent bacterial spoilage of canned meats.
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From page 37... ...
Gross made an impressive point when he showed that even now a fairly large percentage -- from 40% to 60 % -- of the so-called pasteurized meat products that have been cooked at a relatively low temperature are sterile. I am sure if he dared, he could well go to his management and say, "Now, look and see what we have done.
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