The Effect of Nitrate and Nitrite on the Microbial Flora of Wiltshire Bacon after Maturation and Vacuum-packed Storage

Unsmoked Wiltshire bacon was produced with and without nitrate and with different concentrations of nitrite. Micrococci, Moraxella spp. and Moraxella -like organisms were the most common bacteria on the bacon after maturation when there was little difference between the microflora of the various back bacon. Collar bacon cured without nitrate carried much higher numbers of Moraxella spp. than that cured with nitrate. Micrococci and lactic acid bacteria usually predominated after vacuum-packed storage. Inclusion of nitrate in the cure increased the numbers of micrococci but did not reduce stability on storage. The highest numbers of lactic acid bacteria were present on bacon containing the lowest initial concentration of nitrite (34 parts/10⁶) and it is thought that nitrite may delay the souring which these bacteria cause in vacuum-packed bacon.     

Chemical and Microbiological Changes during Storage of Vacuum Packed Sliced Bacon

Summary: The micro-ecology of block cured, sliced, vacuum packed bacon has been studied during storage at 20 and 30°; high salt (8–12% NaCl, based on the aqueous phase) and low salt (5–7% NaCl) bacon were used. The dominant flora of all samples during the first 9 days' storage comprised catalase positive cocci. They persisted in the high salt bacon but, under lower salt conditions, group D streptococci and motile lactic acid bacteria became dominant.
Of the chemical changes studied, proteolysis, lipolysis and reduction of nitrate and nitrite were due largely to coagulase negative subgroup II staphylococci. Micrococci which predominated at 20° were capable of reducing nitrate to nitrite but of only slightly increasing free amino or fatty acids.
Inoculation of low count bacon with subgroup II staphylococci confirmed that this group was responsible for putrefaction in low salt bacon stored at temperatures above 20°. Similarly micrococci which tend to delay spoilage did not contribute much to the off odours and it was thought that the heterofermentative catalase negative organisms could contribute to typical sour spoilage.     

A Proteus inconstans which Produces 'Cabbage Odour' in the Spoilage of Vacuum-packed Sliced Bacon

The isolation and identification of a species of Proteus inconstans capable of producing 'cabbage odour' spoilage of sliced vacuum-packed bacon are described. Gas chromatographic-mass spectrometric analysis indicated that the odoriferous compound was methane thiol. Data are presented on the effect of the pH and salt level on the growth of the organism in laboratory media and the production of methane thiol in bacon.     

Microbial Progression in Sliced Vacuum Packaged Bacon at Refrigeration Temperatures

S ummary . Three hundred and forty eight strains of micro-organisms were isolated from packaged bacon which had been cured by one or other of 2 methods (A and B) and stored at 0–10° for 7 weeks. Before storage, Micrococcus sub-group 7 (47%) and coryneform bacteria (33%) were the principal contaminants of bacon cured by method A and Micrococcus subgroup 1 (20%) and Microbacterium thermosphactum (21%), in bacon cured by method B. After 7 days at 0°, coagulase negative staphylococci accounted for 10 and 33% of the microflora in bacon A and B, respectively: other organisms were micrococci, 60% (A) and 25% (B); corynebacteria, 20% (A) and 12·5% (B), yeasts ( Torulopsis candida and T. dattila ) 5% (A) and 29% (B). In the following month at 10°, Micrococcus sub-group 5 was the dominant (43–88%) contaminant of bacon B; the incidence of Streptococcus Group N ranged from 27–36% and that of unidentified lactic acid bacteria from 23–32%. Towards the end of storage, the order of dominance was Micrococcus sub-group 3 (38–58%) and atypical streptobacteria (38%) in A; Streptococcus Group N (42%) and Gram positive rods (5–20%) in B. Staphylococci tended to die out during storage of bacons cured by the 2 methods and coagulase positive staphylococci were not isolated.     

The Occurrence and Significance of Pseudomonas in Wiltshire Bacon Brines

Pseudomonas spp. in Wiltshire bacon cover brines taken from seven bacon factories were enumerated at regular intervals over six months. There were differences between factories as assessed by the geometric mean counts (12–2907/ml) or by the percentage of samples exceeding 10₃/ml (0–75%). Heavy pseudomonad contamination of brines was associated with large populations of Pseudomonas spp. on fresh pork carcasses and vice versa. The curing of defrosted pork carcasses also led to high Pseudomonas spp. counts in brines. The average time for 90% reduction in a Pseudomonas population in brine was 35 d. These data can aid interpretation of the Pseudomonas count of bines when it is used as a part of microbiological quality control. A set of advisory standards proposed.     

Effect of Sodium Nitrite on Toxin Production by Clostridium botulinum in bacon

Pork bellies were formulated to 0, 30, 60, 120, 170, or 340 μg of nitrite per g of meat and inoculated with Clostridium botulinum via pickle or after processing and slicing. Processed bacon was stored at 7 or 27 C and assayed for nitrite, nitrate, and botulinal toxin at different intervals. Nitrite levels declined during processing and storage. The rate of decrease was more rapid at 27 than at 7 C. Although not added to the system, nitrate was detected in samples during processing and storage at 7 and 27 C. The amount of nitrate found was related to formulated nitrite levels. No toxin was found in samples incubated at 7 C throughout the 84-day test period. At 27 C, via pickle, inoculated samples with low inoculum (210 C. botulinum per g before processing and 52 per g after processing) became toxic if formulated with 120 μg of nitrite per g of meat or less. Toxin was not detected in bacon formulated with 170 or 340 μg of nitrite per g of meat under these same conditions. Toxin was detected at all formulated nitrite levels in bacon inoculated via the pickle with 19,000 C. botulinum per g (4,300 per g after processing) and in samples inoculated after slicing. However, increased levels of formulated nitrite decreased the probability of botulinal toxin formation in bacon inoculated by both methods.     

Characteristics of Staphylococci and Micrococci isolated in a Bacon Curing Factory

S ummary . The majority of 164 strains of staphylococci and micrococci isolated from fresh pork, curing brines and bacon fell into Shaw subgroups 2 and 3. The strains were tolerant to nitrite, but this was toxic in high concentration, particularly at low pH. Although arginine was attacked by many strains, there was little decarboxylase or deaminase activity with the other amino acids tested. The heat resistance of the strains was generally < 30 min at 60°. The lipolytic activity of the bacon isolates was studied using tributyrin, lard, butter, triolein and palm kernel oil as substrates. The hydrolysis of tributyrin occurred with a number of strains in the presence of 5% of salt, 2% of potassium nitrate and 100 p of sodium nitrite/m and at 4°.     

Microbiological and Chemical Changes in Lean Wiltshire Bacon During Aerobic Storage

Total microbial growth and chemical changes in aerobically stored bacon lean were found to fall into 2 phases. Phase 1: there was an increase in total microbial load to c . 10⁹/g, during which most of the nitrate was broken down and there was an accumulation of nitrite. Phase 2: the microbial load increased further to c . 10¹⁰/g and during this time most of the accumulated nitrite was broken down to unknown products, so that at the end of the experiments most of the nitrate and nitrite had disappeared from the bacon.
The most important types of micro-organisms isolated from the bacons were Micrococcus , yeasts, Vibrio, Acinetobacter, Alcaligenes and Arthrobacter-Corynebacterium. The latter 3 types appeared to be associated with phase 2 changes.     

QTL mapping for growth and carcass traits in an Iberian by Landrace pig intercross: additive,dominant and epistatic effects

Results from a QTL experiment on growth and carcass traits in an experimental F2 cross between Iberian and Landrace pigs are reported. Phenotypic data for growth, length of carcass and muscle mass, fat deposition and carcass composition traits from 321 individuals corresponding to 58 families were recorded. Animals were genotyped for 92 markers covering the 18 porcine autosomes (SSC). The results from the genomic scan show genomewide significant QTL in SSC2 (longissimus muscle area and backfat thickness), SSC4 (length of carcass, backfat thickness, loin, shoulder and belly bacon weights) and SSC6 (longissimus muscle area, backfat thickness, loin, shoulder and belly bacon weights). Suggestive QTL were also found on SSC1, SSC5, SSC7, SSC8, SSC9, SSC13, SCC14, SSC16 and SSC17. A bidimensional genomic scan every 10 cM was performed to detect interaction between QTL. The joint action of two suggestive QTL in SSC2 and SSC17 led to a genome-wide significant effect in live weight. The results of the bidimensional genomic scan showed that the genetic architecture was mainly additive or the experimental set-up did not have enough power to detect epistatic interactions.     

Pathological Lesions in Swine at Slaughter

The influence of environment on animal health was studied in 40 bacon herds. These herds delivered approx. 11,000 baconers annually to the slaughter-house. The data from the meat inspection was studied in connection with the environmental recordings, and the relationship between 18 lesions and 20 environmental factors were estimated by statistical methods. The data was collected in the period 1975–1977. The influence of environmental factors upon the prevalence of different lesions showed considerable variation. Ten environmental factors were significantly associated with pleurisy and tail lesions (cannibalism). On the other hand none of the environmental factors bore any significant relation to atrophic rhinitis, pericarditis, peritonitis, perihepatitis, polyarthritis, arthritis and claw lesions. Eight environmental factors influenced the proportion of healthy animals. The recorded environmental factors influenced the overall health situation to a varying degree. For example, design of pen walls, insulation of pen floors, occasional use of supplementary feed and free access to drinking water were related to 5–7 lesions, while the nature of the concentrate (meal/pellets) had no significant influence. The study indicated that many details in environment and management could be of importance to the health of bacon pigs. However, statistical analysis also showed that production systems had a considerably stronger influence upon the health situation than any of the “pure” environmental factors – even when these factors were added.     

METHODS FOR THE ISOLATION OF FAECAL STREPTOCOCCI (LANCEFIELD GROUP D) FROM BACON FACTORIES

SUMMARY: Two methods have been developed for isolating and enumerating group D faecal streptococci from localities such as bacon factories where they are heavily outnumbered by other organisms. The first depends on presumptive counts in a Lab-Lemco-peptone-glucose broth (pH 6·0) containing 0·1% of thallous acetate with confirmation by streaking on tetrazolium agar. The other method involves direct plating on tetrazolium-glucose agar (pH 6·0) containing 0·1% of thallous acetate. On the tetrazolium medium differentiation can be made between Streptococcus faecalis and its variants zymogenes and liquefaciens and the other group D organisms, Strep. faecium, Strep. durans and Strep. bovis .     

Characterization of production of cholesterol oxidases in three Rhodococcus strains

The production of cholesterol oxidase in two strains of Rhodococcus equi No. 23 from butter, and Rhodococcus sp. No. 33 from bacon, which had properties on biochemical and physiological tests almost similar to the strains of R. equi , was compared with that of the type strain (ATCC 6939) of R. equi. The intensity of cholesterol oxidase activity, both extracellular and membrane-bound, from the three strains was in the order No. 23, ATCC 6939 and No. 33. More extracellular enzyme was produced by strain No. 23 than by the other two strains. Halo formation on the agar medium containing cholesterol depended on the conversion of cholesterol to 4-cholesten-3-one by the extracellular cholesterol oxidase.     

Characterization of production of cholesterol oxidases in three Rhodococcus strains

The production of cholesterol oxidase in two strains of Rhodococcus equi No. 23 from butter, and Rhodococcus sp. No. 33 from bacon, which had properties on biochemical and physiological tests almost similar to the strains of R. equi, was compared with that of the type strain (ATCC 6939) of R. equi. The intensity of cholesterol oxidase activity, both extracellular and membrane-bound, from the three strains was in the order No. 23, ATCC 6939 and No. 33. More extracellular enzyme was produced by strain No. 23 than by the other two strains. Halo formation on the agar medium containing cholesterol depended on the conversion of cholesterol to 4-cholesten-3-one by the extracellular cholesterol oxidase.     

Radiation Sterilization of Bacon for Military Feeding

Sliced, cured bacon, packed in cans and seeded with 6 × 10⁵ spores per can of Clostridium botulinum strains 33A or 41B, or with 3 × 10⁶ spores per can of strains 36A, 12885A, 9B, or 53B, was irradiated to various dose levels with γ radiation. Evidence provided by swelling, toxicity, and recoverable C. botulinum with 2,200 inoculated, irradiated cans demonstrated that: (i) 4.5 Mrad were more than adequate as a sterilization dose; (ii) the experimental minimal sterilizing dose was 2.0 Mrad, and the theoretical 12-log reduction dose was 2.65 or 2.87 Mrad depending on the method of calculation; (iii) some spoilage occurred at dose levels below 2.0 Mrad; (iv) all visible spoilage of irradiated bacon was due to strains 33A and 12885A only, whose D values were, respectively, 0.141 and 0.177 Mrad based on spoilage data, and 0.221 and 0.188 Mrad, respectively, when based on recovery data; (v) toxic cans did not always result in swelling, nor did swollen cans always produce toxic spoilage; and (vi) viable C. botulinum can exist for at least 8 months in storage at 30 C without producing visible or toxic spoilage at doses below 2.0 Mrad.     

A numerical taxonomic study of lactic acid bacteria from vacuum-packed beef, pork, lamb and bacon

S haw B. G. & H arding C harmaigne D. 1984. A numerical taxonomic study of lactic acid bacteria from vacuum packed beef, pork, lamb and bacon. Journal of Applied Bacteriology 56 , 25–40.
A numerical taxonomic study using 79 unit characters has been performed on 100 isolates of lactic acid bacteria from refrigerated vacuum-packed beef, pork, lamb and bacon. Three clusters were observed at 78% S which contained all the strains apart from three unidentifiable streptobacteria, one Leuconostoc , and one strain of Pediococcus pentosaceus . One cluster (III) consisted of only one strain of Leuc. paramesenteroides and six unidentifiable Leuconostoc strains. The two largest clusters (I and II) were both composed entirely of streptobacteria. Cluster I contained 31 strains (G + C content 33–2–36–9 moles %) which were not identifiable with any described species. Cluster II contained 57 strains (G + C content 40–7–43–7 moles %) which were provisionally identified with Lactobacillus sake or Lact. bavaricus according to the lactic acid isomer produced. The division of nearly all the streptobacteria into two clearly defined clusters has resolved problems which have existed in the classification of lactic acid bacteria from vacuum-packed meat.     

Simultaneous determination of seven nitroimidazole residues in meat by using HPLC-UV detection with solid-phase extraction

A method was developed for the determination of the seven nitroimidazoles including metronidazole (MNZ), ronidazole (RNZ), dimetridazole (DMZ), tinidazole (TNZ), ornidazole (ONZ), secnidazole (SNZ) and the common metabolite of RNZ and hydroxydimetridazole (DMOHZ) in poultry and pork muscles by high-performance liquid chromatography (HPLC) with ultraviolet detection (UV). After extraction with ethyl acetate and evaporation, the nitroimidazoles were redissolved in ethyl acetate and purified using strong cation exchange (SCX) solid-phase extraction (SPE) column. The HPLC separation was carried through on a C(18) bonded silica column with a deionized water-methanol-acetonitrile mobile phase using a gradient elution procedure. The limit of detection of all the seven nitroimidazoles was 0.2 microg/kg. The recoveries of the seven nitroimidazoles for chicken, pork and bacon samples spiked with 1-20 microg/kg were in the range of 71.4-99.5%. The linearity is satisfactory with a correlation coefficient of >0.998 at concentrations ranging from 0.7 to 60 microg/kg. The relative standard deviations of 10 measurements for spiked chicken, pork and bacon samples at the concentration of 1 and 20 microg/kg were in the range of 6.2-13.9% and 4.0-8.7%, respectively. The intra-day precision (n=5) for nitroimidazoles residues in chicken spiked at 20 microg/kg is 6.9%, and the inter-day precision for 5 days (n=25) is 11%. The method is capable of identifying nitroimidazole residues at > or =0.7 microg/kg levels and was applied in the determination of nitroimidazole residues in meat sample.     

Polymorphism of sorbitol dehydrogenase and 6-phosphogluconate dehydrogenase in swine (Sus scrofa)

More than 300 kidneys from the local bacon factory were investigated and it was shown that the enzyme sorbitol dehydrogenase (EC 1.1.1.14) exhibits a genetically determined polymorphism. While homozygous individuals yield only a single enzyme band after starch gel electrophoresis, heterozygotes show multiple bands.
On the same material also 6-phosphogluconate dehydrogenase (EC 1.1.1.44) and lactate dehydrogenase were investigated, the former showed also clear genetic variants while the latter appeared only in one form.
Gene frequencies for different breeds and types of pigs are given and the results discussed.     

The Use of Gallamycin for Controlling Infectious Atrophic Rhinitis in Bacon Pigs

The use of Gallamycin to control nasal deterioration and permit increased growth rates in bacon type pigs was studied. Litters were randomly divided according to sex into treatment and control groups. Animals were treated by injection with 2.5 mgm of Gallamycin per pound liveweight at weekly intervals commencing during the first through the fifth week of age. Treatments ceased during the eighth week of age. Gallamycin treatment did not reduce significantly the percentage of nasal turbinate degeneration nor increase the rate of gain per day of treatment compared with control animals within litters. Possible explanations of results obtained are hypothesized.     

Aflatoxin Production in Meats. I. Stored Meats

Aflatoxins were produced on fresh beef (in which bacterial spoilage was delayed with antibiotics), ham, and bacon inoculated with toxinogenic fungi and stored at 15, 20 and 30 C. Meats stored at 10 C were spoiled by bacteria and yeast before detectable levels of aflatoxins were produced. High levels of aflatoxins were formed in meats stored at 20 C; one sample supported the production of 630 mug of aflatoxins per g of meat, the major portion (580 mug) of which was aflatoxin G(1). Meats stored below 30 C developed higher levels of aflatoxin G(1) than B(1), but at 30 C Aspergillus flavus produced equal amounts of B(1) and G(1), whereas A. parasiticus continued to produce more G(1) than B(1).     

THE DISTRIBUTION AND SIGNIFICANCE OF DIFFERENT SPECIES OF FAECAL STREPTOCOCCI IN BACON FACTORIES

SUMMARY: A survey has been made of the numbers and types of group D faecal streptococci in three bacon factories. Although Streptococcus faecium , normally present in the gut of the pig and isolated from spoiled canned hams, was found, it was often outnumbered by Strep. faecalis , an indicator of human faecal contamination which is rare in the pig. The rôle of these two organisms in ham spoilage is discussed. The value of thallous acetate-tetrazolium-glucose agar for isolating and distinguishing these organisms has been demonstrated, and it is suggested that the method may have more general application where it is necessary to differentiate between faecal streptococci of human and animal origin.