D. Harrington

The relationship between hide cleanliness and bacterial numbers on beef carcasses at a commercial abattoir

Cattle were visually inspected in the lairage of a commercial abattoir and assigned to a category ranging from 1 (very clean) to 5 (very dirty) depending on the observed cleanliness of the hide. Animals from categories 2, 3 and 5 were slaughtered and total viable counts (TVCs) enumerated at five sites (hock, brisket, cranial back, bung and inside round) on the subsequent carcasses. The TVCs at the hock were significantly higher on category 5 than on category 2 carcasses (P < 0·05). Similarly, TVCs at the brisket were significantly higher on categories 3 and 5 than on category 2 carcasses (P < 0·05). There were no differences in counts among the categories at any of the other sites. The TVCs averaged over the five carcass sites were higher for category 5 than for category 2 carcasses (P < 0·05). The TVCs at the brisket were significantly higher than all other sites (P < 0·01). In general, carcasses from category 2 animals slaughtered in a batch with dirtier animals (categories 3 and 5) did not have higher TVCs than carcasses of category 2 animals slaughtered at the beginning of the day in the absence of dirtier animals. The introduction of improved hygienic practices during the dehiding of category 4 animals resulted in reduced TVCs at the brisket (P < 0·001).

Washing and chilling as critical control points in pork slaughter hazard analysis and critical control point (HACCP) systems

Aims: The aim of this research was to examine the effects of preslaughter washing, pre‐evisceration washing, final carcass washing and chilling on final carcass quality and to evaluate these operations as possible critical control points (CCPs) within a pork slaughter hazard analysis and critical control point (HACCP) system.

Studies to determine the critical control points in pork slaughter hazard analysis and critical control point systems.

Aerobic mesophilic counts (AMC), coliform (CC) and coliform resuscitation counts (CRCs) were obtained by swabbing 50 cm(2) areas at three sites (ham, belly and neck) on pig carcasses, after each of seven stages of the slaughter/dressing process (bleeding, scalding, dehairing, singeing, polishing, evisceration and chilling). In most cases, there were no statistical differences (P>0.05) among the counts derived by these three methods. Reductions in counts at individual sites were observed after scalding (3.5 log(10) cfu cm(-2)), and singeing (2.5 log(10) cfu cm(-2)). Increases in counts at individual sites were observed after dehairing (2.0 log(10) cfu cm(-2)) and polishing (1.5 log(10) cfu cm(-2)). The incidence of Salmonella on pig carcasses was also obtained by swabbing the outside surfaces of 100 half carcasses. Information on the incidence of Salmonella in scald tank water (108 samples) was also investigated. Carcass swabs and scald tank water were examined for the presence of Salmonella using standard enrichment methods. Salmonella were detected on 31% of carcasses immediately after bleeding, 7% of carcasses immediately after dehairing and evisceration, and 1% of carcasses immediately after scalding. Serovars included Salmonella Typhimurium, Salmonella Hadar, Salmonella Infantis and Salmonella Derby. No Salmonella were recovered from samples of scald tank water. The impact of pig slaughter/dressing processes on carcass microbiology and their potential use as critical control points (CCPs) during pork production are discussed.

Thermal inactivation of Listeria monocytogenes and Yersinia enterocolitica in minced beef under laboratory conditions and in sous‐vide prepared minced and solid beef cooked in a commercial retort

D‐values were obtained for Listeria monocytogenes and Yersinia enterocolitica at 50, 55 and 60 °C in vacuum‐packed minced beef samples heated in a laboratory water‐bath. The experiment was repeated using vacutainers, which allowed heating of the beef to the desired temperature before inoculation. D‐values of between 0·15 and 36·1 min were obtained for L. monocytogenes. Pre‐heating the beef samples significantly affected (P < 0·05) the D60 value only. D‐values for Y. enterocolitica ranged from 0·55 to 21·2 min and all the D‐values were significantly different (P < 0·05) after pre‐heating. In general, the D‐values obtained for core inoculated solid beef samples were significantly higher (P < 0·05) than those generated in minced beef when heated in a Barriquand Steriflow commercial retort.

The Effect of Vacuum and Modified Atmosphere Packaging on the Shelf-life of Lamb Primals, Stored at Different Temperatures

Lamb primals (shoulders) were vacuum packaged or packaged in modified atmospheres containing 80% O(2)/20% CO(2), 50% CO(2)/50% N(2) or 100% CO(2), and stored at 5 or 0 °C. They were examined microbiologically at 7 day intervals for total counts obtained under (1) aerobic, (2) CO(2) enriched or (3) anaerobic conditions; B. thermosphacta; pseudomonad and Enterobacteriaceae counts. Off-odour assessments were also carried out at these times. In general, there were no significant differences between the total counts obtained from the different incubation conditions in any of the atmospheres. The only exception was noted in 80% O(2)/20% CO(2) at 5 °C. Significant differences between atmospheres for the total counts were observed at 0 °C only. In the case of B. thermosphacta, the pseudomonads and the Enterobacteriaceae, differences between atmospheres were noted at 5 and 0 °C. In general, vacuum packs and 80% O(2)/20% CO(2), and the two high CO(2) atmospheres fell into distinct groups. Storage temperature had a significant effect on all three counts. The relationship between bacterial counts and time was modelled using regression analysis. Data from total counts gave the equations of best fit. Significant differences between atmospheres in terms of off-odour production were observed at 5 °C only. The effect of temperature on off-odour production was significant in all atmospheres except 100% CO(2). A scheme was devised based on the growth of different groups of organisms which facilitated comparisons between studies on packaged meats. The results of the present work and that of others are discussed in relation to the different growth patterns which developed with packaging treatments and storage temperature.

Survival and growth of Aeromonas hydrophila on modified atmosphere packaged normal and high pH lamb

The growth of A. hydrophila on normal pH (5.5-5.8) and high pH ( > 6.0) lamb stored under modified atmospheres was examined. Lamb pieces and mince, inoculated with A. hydrophila were packaged in air, vacuum pack, 80% O2/20% CO2, 50% CO2/50% N2, or 100% CO2 and stored at 5 or 0 degrees C for up to 42 days. Samples were examined for the survival and/or growth of A. hydrophila by enrichment in alkaline peptone water and/or direct plating on starch ampicillin agar. The pH of each sample was estimated. On lamb pieces and mince of normal pH, A. hydrophila numbers decreased during storage at 5 and 0 degrees C under all the packaging conditions. The organism was not detected after 21 days storage. In contrast, A. hydrophila numbers were maintained or increased on high pH lamb under most storage regimes. Storage at 5 degrees C allowed significant increases in A. hydrophila numbers on high pH lamb under all the atmospheres, except 100% CO2. In lamb held at 5 degrees C under 100% CO2 for up to 42 days, A. hydrophila was recovered from most samples, although cell numbers decreased during storage. After storage at 0 degrees C, A. hydrophila was recovered from high pH packs stored under all atmospheres. Significant increases in cell numbers were only observed in minced lamb of high pH stored under air or vacuum. The pH values of lamb pieces and mince held at 5 or 0 degrees C under any of the packaging atmospheres did not change in a uniform manner during storage.

Thermal resistance of wild‐type and antibiotic‐resistant Listeria monocytogenes in meat and potato substrates

Aims: This study aimed to elucidate the relationship, if any, between the acquisition/possession of antibiotic resistance in strains of Listeria monocytogenes and the resistance of such strains to heat stress.

Investigations on the growth of Listeria monocytogenes on lamb packaged under modified atmospheres

The growth of Listeria monocytogenes in air and modified atmosphere packaged lamb pieces and mince, stored at 5 or 0°C was investigated at 42 days. The modified atmospheres included: (i) vacuum pack; (ii) 80% O 2 /20% CO 2 ; (iii) 50% CO 2 /50% N 2 ; and (iv) 100% CO 2 . On lamb pieces at 5°C, growth of L. monocytogenes occurred in air and all the modified atmospheres, except 100% CO 2 . L. monocytogenes growth on minced lamb at 5°C was reduced compared with lamb pieces. Growth did not occur in vacuum packaged mince or in an atmosphere containing 100% CO 2 . At 0°C, growth of the organism was completely inhibited on pieces and mince in all the modified atmospheres tested and in air. It was noted that pH did not increase or decrease in a regular manner throughout the storage period. Thus pH was eliminated as a factor controlling the growth of L. monocytogenes on modified atmosphere packaged lamb.

Growth of Yersinia enterocolitica O:3 on modified atmosphere packaged lamb

The growth of pathogenic Yersinia enterocolitica serotype 0:3 was investigated on lamb pieces and lamb mince, packaged in air and a range of modified atmospheres, at 5 or 0° C. The modified atmospheres investigated were: (i) vacuum pack; (ii) 80% O 2 /20% CO 2 ; (iii) 50% CO 2 /50% N 2 ; and (iv) 100% CO 2 . Y. enterocolitica 0:3 counts were examined at 28 days in each of the atmosphere/temperature combinations. Growth of Y. enterocolitica 0:3 occurred on lamb pieces stored at 5° C in air and all the modified atmospheres tested. On lamb pieces stored at 0° C, pathogen growth was noted in air, vacuum packs and 50% CO 2 /50% N 2 . In all atmospheres except air, growth of Y. enterocolitica 0:3 on minced lamb at 5 and 0° C was reduced compared to growth on lamb pieces. At 5° C on minced lamb, growth of the organism occurred in air, vacuum packs and 50% CO 2 /50% N 2 . However, at 0° C, growth was observed in air only. An atmosphere containing a high O 2 concentration was inhibitory to the growth of Y. enterocolitica 0:3. In addition, the combination of a high CO 2 (100%) atmosphere and low temperature (0° C) was inhibitory to growth.

Comparison of selective and non‐selective enrichment media in the detection of Listeria monocytogenes from meat containing Listeria innocua

G. DUFFY, D. WALSH, J.J. SHERIDAN, C.M. LOGUE, D. HARRINGTON, I.S. BLAIR AND D.A. MCDOWELL. 2001.