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The temperatures and ages of packs of beef displayed in multi-shelf retail cabinets
Food Control 14 (2003) 145–151 www.elsevier.com/locate/foodcont
The temperatures and ages of packs of beef displayed in multi-shelf retail cabinets C.O. Gill b
a,*
, T. Jones a, A. Houde b, D.I. LeBlanc c, K. Rahn d, R.A. Holley e, R. Starke
f
a Agriculture and Agri-Food Canada, Lacombe Research Centre, 6000 C & E Trail, Lacombe, AB, Canada T4L 1W1 Agriculture et Agroalimentaire Canada, St-Hyacinthe Centre de Recherche, 3600 Boul. Casavant ouest, St-Hyacinthe, Quebec, Canada J2S 8E3 c Agriculture and Agri-Food Canada, Food Research Centre, Pavillion Jacqueline-Bouchard, Universite de Moncton, Moncton, New Brunswick, Canada E1A 3E9 d Health Canada Guelph Laboratory, 110 Stone Road West, Guelph, Ontario, Canada N1G 3W4 e Department of Food Science, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2 f Agriculture and Agri-Food Canada, Kentville Research Centre, 32 Main Street, Kentville, Nova Scotia, Canada B4N 1J5
Received 23 March 2002; received in revised form 18 June 2002; accepted 25 June 2002
Abstract The temperatures and ages of 5389 packs of beef in 10 multiple shelf display cabinets were determined. The median temperature of the packs in each cabinet was <4 °C. The maximum temperatures of the packs in six cabinets were >7 °C. All packs in three cabinets were 6 2 days old. The percentages of packs older than 2 days were <1% in three cabinets, about 40% in three cabinets and about 70% in one cabinet. Both aggregated data and data for individual cabinets indicated that, generally, older packs were cooler than newer, packs at the backs of shelves were cooler than packs at the fronts, and packs on intermediate shelves were cooler than packs on bottom or top shelves. The aggregated data also indicated that the temperatures of packs did not differ at different times of the day, or at different positions along cabinets; and that packs in lower layers were generally cooler than packs in top layers. However, the findings for individual cabinets were that packs in nine cabinets had different median temperatures at different times of the day, that temperature gradients existed along five cabinets; and that temperatures of packs in different layers did not differ. Consideration of only aggregated data from surveys may lead to some erroneous conclusions about display cabinet performances. Crown Copyright Ó 2002 Published by Elsevier Science Ltd. All rights reserved. Keywords: Beef; Retail display; Temperatures; Pack ages
1. Introduction It is often suggested that retail display is the weakest link in the cold chain for the distribution of raw, chilled meat (James, 1996). Moreover, various studies have indicated that the temperatures of displayed product have not changed over many years, which implies that industrial and regulatory initiatives aimed at reducing the temperatures of chilled foods on display have been ineffective (Greer, Gill, & Dilts, 1994; Torstveit & Magnussen, 1998). In contrast, a recent survey of the temperatures and ages of beef displayed at 41 Canadian retail stores indicated that the control of product temperatures had improved in the past few years (Gill et al.,
*
Corresponding author. Tel.: +1-403-782-8113; fax: +1-403-7826120. E-mail address: [email protected] (C.O. Gill).
2002). However, some findings from that survey were counter intuitive and/or contradictory to previous reports (Bøgh-Sorensen & Olsson, 1990; Brolls, 1986; LeBlanc, Stark, MacNeil, Goguen, & Beaulieu, 1996) in that the survey data suggested that there was no effect of refrigeration equipment defrosting on product temperatures, no variation of temperatures along the lengths of cabinets, higher temperatures of product on bottom and top than on other shelves of cabinets, and cooling rather than warming of product during display. Such unexpected findings might reflect improved designs of newer display cabinets and/or better management of cabinets in response to continuing concerns about the microbiological safety of raw meat (Likes, 1996). Those findings might, however, have arisen as artifacts of data having been collected from packs in cabinets at conveniently located stores, with packs being selected on the basis of generalized assumption about the management and performances of cabinets that
0956-7135/02/$ - see front matter Crown Copyright Ó 2002 Published by Elsevier Science Ltd. All rights reserved. PII: S 0 9 5 6 - 7 1 3 5 ( 0 2 ) 0 0 0 5 8 - 0
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might be erroneous for any particular cabinet. If the unexpected findings were artifactual, then the apparent indications of improvement may also be so. Therefore, to clarify the findings of the previous survey, and to better relate the temperatures and ages of displayed beef overall to the conditions of meat in different display cabinets, the temperatures and ages of retail packs of beef in each of a further 10 display cabinets at Canadian retail stores were examined.
2. Materials and methods 2.1. Selection of packs Retail packs of beef were selected for examination from a display cabinet at each of 10 retail stores. Packs were selected without regard to the form of the meat, steak, roast or ground, that each contained. The cabinets from which packs were selected were all used to display only beef. Each cabinet had three or more, open shelves, with a bottom, horizontal shelf about twice the width of the upper shelves which sloped downward from back to front. The bottom shelves of cabinets typically measured about 350 80 cm (L W ). Each of the stores was visited on nine occasions, with three visits at each of three times of the day which were within 1 h of store opening, between 12:00 and 14:00 h, and within 1 h before the store closed. On each occasion, packs were selected for examination from each layer of packs on each shelf, from the left side, middle and right side of the front, centre line and back of the shelf (Fig. 1). Thus, nine packs were selected for examination from each complete layer on each shelf. For partial layers a pack from each of the positions that was filled was examined. 2.2. Determination of temperatures and ages of packs Temperatures were measured using a thermistor probe designed for surface measurements (400 Series, Cat. No. E-08431-50; Cole-Parmer, Anjou, QC, Canada) connected to a digital thermometer (Traceablee; Control Co., Friendswood, TX, USA). For each measurement, the probe was placed with the tip at the center of the upper surface of the selected pack. An adjacent pack was inverted over the probe when the selected pack was in the single or upper layer of packs on a shelf, or the pack above replaced when the selected pack was in a lower layer of packs. The temperature displayed 2 min after the placing of the probe was recorded. In addition to the temperature, the packed-on or best-before date given on the label of each selected pack was recorded. For each store where best-before dates were used, explanation of the relationship between the best-before
Fig. 1. The front left (FL), middle (FM) and right (FR); centre line left (CL), middle (CM) and right; and back left (BL), middle (BM) and right (BR) positions on cabinet shelves from which retail packs were selected for determination of their surface temperatures and identification of their ages.
date and the time of preparation of retail packs of each type of product was obtained. 2.3. Analysis of data Descriptive statistics for data sets were obtained using Microsoft Excel, version 4, statistical functions (Microsoft Corp. Redmond, WA, USA). Sets of data were tested for normal distribution using the WilkShapiro test (Shapiro, 1990) in the UNIVARIATE procedure of SAS, version 6 (SAS Institute Inc., Cary, NC, USA). Median values for sets of data were separated using the Kruskal–Wallis test (Conover, 1971) in the NPARIWAY procedure of SAS, version 6 (SAS Institute Inc.).
3. Results The numbers of packs examined at each store ranged from 385 to 738, for a total of 5389 packs (Table 1). The median temperatures for packs at different stores ranged from 1.9 to 4 °C. The maximum temperatures were >4 °C at all the stores, and >7 °C at six of the stores. The median ages of displayed packs were 0 day at six stores, but 2 or 3 days at the other four stores. The minimum age of packs at all stores was 0 day. The maximum ages of packs were 6 2 days at three stores and P7 days at three stores also. Overall about 80% of the selected packs were 62 days old, but the percentages of packs of those ages
C.O. Gill et al. / Food Control 14 (2003) 145–151
147
Table 1 Temperatures and ages of retail packs in a multiple shelf display cabinet devoted to beef at each of 10 retail stores Store
No. of packs
Temperature (C°)
Age (days)
Median
Mean
Maximum
Median
Mean
Maximum
1 2 3 4 5 6 7 8 9 10
616 738 645 482 654 533 492 385 457 387
1.9 2.0 2.3 2.5 2.6 2.8 3.1 3.1 3.5 3.8
1.9 2.1 2.1 2.5 2.6 2.7 3.0 3.2 3.6 4.0
Minimum 2.0 1.2 1.8 1.2 1.5 0.1 1.0 0.3 0.5 0.4
8.2 6.8 7.4 5.6 8.1 6.8 6.6 9.5 10.6 8.6
2 0 0 2 0 3 0 0 0 2
2.2 0.5 0.3 2.3 0.3 3.0 0.6 0.3 0.5 2.2
6 4 8 6 2 7 5 1 2 7
All
5389
2.7
2.6
2.0
10.6
1
1.2
8
temperature range at the same store were not normally distributed (P < 0:05). Overall, the median age of the packs in each 2 °C temperature range was 1 day, except for the <1% of product of temperature >8 °C for which the median age was 0 days. However, at only one store were the warmest packs of a median age significantly less (P < 0:05) than those of cooler packs. Twenty of 30 sets of temperatures collected at different times of day from packs at each store were not normally distributed (P < 0:05; Table 4). The three sets of combined data for each time of day were not normally distributed (P < 0:05). The median values for the sets of temperatures obtained for the combined data for packs at all stores at each time of the day were not significantly different (P > 0:05). However, for seven stores, the median value for temperatures of packs at
ranged from 28% to 100% at different stores (Table 2). Twenty one of 43 sets of temperatures for packs of the same age at the same store were not normally distributed (P < 0:05). The median temperature of packs that were examined on the days they were prepared were significantly higher (P < 0:05) than the median temperature of packs that were 1 or 2 days old at four stores. At the other stores there was no consistent increase or decrease of median temperature with time on display. Overall, the temperatures of about 18% of the packs were P 4 °C, but the percentages of packs of those temperature ranged from about 6% to about 44% at different stores (Table 3). Also, the temperatures of 1.3% of the packs were P7 °C, but the percentages of packs at those temperatures ranged from 0% to 4.4% at different stores. All sets of ages for packs in the same 2 °C
Table 2 Percent fractions and median temperatures of retail packs of different ages in a multiple shelf display cabinets devoted to beef at each of 10 retail stores Store
Age (days) 0
1
2
3
4
5
6
Fractions (%)
Temperature (°C)
Fractions (%)
Temperature (°C)
Fractions (%)
Temperature (°C)
Fractions (%)
Temperature (°C)
Fractions (%)
Temperature (°C)
Fractions (%)
Temperature (°C)
Fractions (%)
Temperature (°C)
1 2 3 4 5 6 7 8 9 10
11.9 60.4 75.3 11.2 73.9 3.0 52.8 70.4 60.8 14.7
1.7B 2.2B 2.4B 2.4AB 2.7A 2.4A 3.0A 3.5B 3.5B 4.0A
14.6 33.1 24.0 22.2 25.8 18.2 34.6 29.6 30.0 16.0
2.0BC 2.0B 1.6A 2.7BC 2.5A 2.4A 3.5B 2.2A 3.7B 4.1A
31.5 6.2 0.3 26.8 0.3 6.6 11.8 –b 9.2 24.3
1.4A 1.4A –a 2.0A –a 2.2A 3.2AB
2.1BC –a
2.8 –b –b 10.0 –b 5.1 0.2 –b –b 5.7
2.7BC
3.5A
0.8 –b –b 4.1 –b 8.4 0.4 –b –b 1.8
3.0BC
3.7A
15.9 0.1 –b 7.5 –b 9.3 –b –b –b 13.4
2.3C
2.5A 3.6A
22.6 0.1 –b 18.3 –b 39.4 0.8 –b –b 24.0
3.7A
All
45.0
2.7CD
24.9
2.6B
11.2
2.1A
9.9
3.1E
5.4
2.7BCD
1.4
2.6BCD
2.6B 3.2B –a
a
3.3BC 2.7A
4.6B 2.8DE
Median temperatures in the same row with the same letter are not significantly different (P > 0:05). a Insufficient packs for estimation of a median temperature. b Less than 0.1% of packs of the indicated age.
2.1
2.6B 1.6A –a
3. 5C 1.6A –a
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Table 3 Percent fractions and median ages of retail packs of different temperature ranges in a multiple shelf display cabinet devoted to beef at each of 10 retail stores Store
Temperature (°C) 60
0.1–2.0
2.1–4.0
4.1–6.0
6.1–8.0
>8.0
Fractions (%)
Age (days)
Fractions (%)
Age (days)
Fractions (%)
Age (days)
Fractions (%)
Age (days)
Fractions (%)
Age (days)
1 2 3 4 5 6 7 8 9 10
9.3 11.8 10.7 3.5 5.5 0.8 2.6 2.9 0.2 0.8
2B 1B 0B 2A 0A 3A 0A 0AB 2A 3A
46.3 38.3 32.6 31.6 27.1 26.1 26.0 26.5 15.5 6.2
2BC 0AB 0AB 2A 0A 3A 0A 0B 1A 2A
38.1 37.9 49.9 53.3 54.4 58.5 43.9 40.0 48.4 49.0
3C 0A 0B 2A 0A 3A 0A 0A 0A 2A
4.7 11.2 6.7 11.5 11.8 12.9 25.6 26.8 29.3 36.4
3BC 0AB 0B 2A 0A 3A 1A 0A 0A 2A
1.3 0.6 0.2 –a 10.7 1.7 1.4 2.3 4.6 6.2
1AB 1AB 0AB
All
5.5
1A
29.2
1A
47.2
1A
16.0
1A
0A 3A 1A 0AB 0A 2A
1.7
Fractions (%) 0.3 –a –a –a 0.2 –a –a 1.8 2.0 1.3
1A
0.4
Age (days) 0A
0A
0AB 0A 2A 0A
Median ages in the same row with the same letter are not significantly different (P > 0:05). a No packs in the temperature range.
Table 4 The effects of the time of day on the temperatures of retail packs in a multiple shelf display cabinet devoted to beef at each of 10 retail stores Store
Temperature (°C) Median a.m.
Store
Maximum noon
p.m.
a.m.
noon
Table 5 The effects of the levels of shelves on the median temperatures of retail packs in a multiple shelf display cabinet devoted to beef at each of 10 retail stores
p.m.
1 2 3 4 5 6 7 8 9 10
1.6A 2.5B 2.3B 2.3A 2.5A 2.8B 2.3A 4.0B 3.1A 4.0B
2.5B 2.3B 2.3B 2.5A 2.8B 3.1C 3.0B 2.9A 3.3A 4.2B
1.8A 1.2A 2.0A 2.8A 2.7B 2.5A 4.0C 2.8A 4.3B 2.3A
4.4 6.3 7.4 5.6 5.1 5.3 5.6 9.3 6.8 7.1
8.2 6.8 7.2 5.3 8.1 6.8 5.6 9.5 7.0 8.6
5.1 5.0 6.8 5.1 5.2 4.8 6.6 6.8 10.6 6.5
1 2 3 4 5 6 7 8 9 10
All
2.6A
2.7A
2.6A
9.3
9.5
10.6
All
Median temperature in the same row with the same letter are not significantly different (P > 0:05).
one time differed significantly (P < 0:05) from the median temperatures at other times, while for two stores all three median values differed significantly (P < 0:05) from one another. At eight stores, the maximum temperature at one time of the day was P1 °C more than the maximum temperatures at other times. Thirty four of the 50 sets of temperatures for packs on shelves at different levels were not normally distributed (P < 0:05; Table 5). The six sets of combined data for packs on shelves at each level were not normally distributed (P < 0:05). Overall, the median temperature for packs on the sole sixth shelf was significantly higher (P < 0:05) than the median temperature for packs on other shelves; while the median temperature for packs on the bottom shelves was significantly higher
Temperature (°C) Shelf 1a
Shelf 2
Shelf 3
Shelf 4
Shelf 5
Shelf 6
2.5D 2.6C 2.7C 3.1C 3.1C 3.1C 3.7B 3.8C 4.7B 4.5B
1.7B 1.6A 1.7A 2.4B 2.9BC 1.5A 2.8A 3.2B 3.0A 3.4A
0.8A 1.3A 2.1AB 2.0A 1.8A 2.8B 2.5A 3.1B 2.9A 3.7A
2.0C 2.1B 2.3B –b 1.6A 3.1C 2.6A 2.3A 3.7B –b
–b 2.1B 2.4B –b 2.7B –b 4.0B 2.7AB –b –b
–b –b –b –b 3.7D –b –b –b –b –b
3.2D
2.3A
2.3A
2.5B
2.7C
3.7E
Median temperatures in the same row with the same letter are not significantly different (P > 0:05). a The bottom shelf is designed shelf 1. b No shelf at the level.
(P < 0:05) than the median temperatures for packs on all other shelves except the sixth. The median temperature of the packs on the bottom or top shelf was significantly higher (P < 0:05) than the median temperatures for packs on other shelves at 6 and 1 stores, respectively. At three stores, the median temperatures of packs on top and bottom shelves were similar, and significantly higher (P < 0:05) than the medium temperatures of packs on other shelves. Packs in upper, second, third or fourth layers were about 62%, 29%, 8% or 1% of the total packs examined. Packs in fifth or sixth layers were together only 0.1% of the total. Twenty of the 37 sets of temperatures for packs in different layers at each store were not normally
C.O. Gill et al. / Food Control 14 (2003) 145–151 Table 6 The effects of the layering of packs on the median temperatures of retail packs in a multiple shelf display cabinet devoted to beef at each of 10 retail stores Store
Temperature (°C) Layer 1a
Layer 2
Layer 3
Layer 4
Layer 5
Layer 6
1 2 3 4 5 6 7 8 9 10
2.1C 2.1A 2.3A 2.5A 2.7A 2.8A 3.2B 3.1A 3.6B 3.8A
1.8B 2.1A 2.2A 2.5A 2.6A 2.6A 2.6A 3.6A 3.2A 3.8A
1.5A 1.7A 2.1A 2.6A 2.5A 3.0A 4.0d AB 2.5b A 3.8AB 4.6d A
0.0b A 2.2A –c 2.3d A 2.0b A 3.5d A –c 5.2b A 6.5b B –c
–c 0.5b A –c –c –c –c –c –c –c –c
–c 0.3b A –c –c –c –c –c –c –c –c
All
2.8D
2.5B
2.3A
2.5CD
0.5b CD
0.3b C
Median temperatures in the same row with the same letter are not significantly different (P > 0:05). a The top layer is designed layer 1. b The number of packs was <10. c No layer of packs at the level. d The number of packs was P 10 < 20.
distributed (P < 0:05; Table 6). The sets of combined data for packs in each of layers 1, 2 and 3 were not normally distributed (P < 0:05). Overall, median temperatures for packs in second and third layers were significantly lower (P < 0:05) than median temperature for packs in other layers. However, at each of seven stores there was no significant difference (P > 0:05) between the median temperatures of packs in different layers; and at only one store was the median temperature of packs in the first layer significantly higher (P < 0:05) than the median temperatures of packs in other layers. Thirty-five of the 90 sets of temperatures for packs at different positions on shelves at each store were not
149
normally distributed (P < 0:05). Eight of the nine sets of combined data for packs at each of the different positions on shelves were not normally distributed (P < 0:05). Overall, the median temperatures for packs at the fronts of cabinets were significantly higher (P < 0:05) than the median temperatures for packs along the midline, and the median temperatures of those latter packs were significantly higher (P < 0:05) than the median temperatures for packs at the backs of cabinets (Table 7). Similarly, at each store, median temperatures for packs at the front of the cabinet were significantly higher (P < 0:05) than median temperatures for packs at the back. Overall, the median temperatures of packs at the middle of the fronts or centre lines of cabinets were significantly less (P < 0:05) than the median temperatures of packs at the fronts or at the centre lines on the left and right or the right sides (Table 7). At each of two stores, the median temperatures of packs at the midline of the cabinet were significantly less (P < 0:05) than the median temperatures of packs on the left and right sides. At each of three other stores, the median temperature of packs on the left or right side of the cabinet were significantly less (P < 0:05) than the median temperature of packs on the other side. At the remaining five stores, no temperature gradients along the cabinets were apparent although there were significant differences (P < 0:05) between the median temperatures of packs at different positions in each cabinet.
4. Discussion Because many of the data sets were not normally distributed, sets were compared by reference to their
Table 7 The effects of the positions of packs on shelves on the median temperatures of retail packs in a multiple shelf display cabinet devoted to beef at each of 10 retail stores Store
Temperatures (°C) Front
Centre line
Back
Left
Middle
Right
Left
Middle
Right
Left
Middle
Right
1 2 3 4 5 6 7 8 9 10
2.7D 3.6E 3.2E 3.2D 2.7CD 2.8D 3.3BC 4.5D 4.4F 4.3CD
2.0C 3.1D 2.7D 3.0D 3.2DE 3.1D 4.1D 3.2C 4.1EF 4.7D
2.6D 2.8D 3.1E 3.7E 3.3E 3.2D 4.5D 5.0D 3.0C 3.8AB
2.0C 1.7C 2.2C 2.1C 2.4B 2.5BC 2.3AB 3.0C 4.1DEF 3.5AB
1.2AB 2.0C 1.7BC 2.0BC 2.5BC 3.1CD 3.5C 1.6B 3.7CDE 4.1BC
2.0C 1.1B 1.9C 2.9D 2.8CD 2.9CD 3.3C 3.8C 2.6B 4.0BC
1.3AB 1.5B 1.1AB 1.5AB 1.2A 2.1A 1.7A 2.0B 3.5CD 3.4A
0.8A 1.1B 0.6A 1.3A 2.0B 2.8CD 2.8BC 1.1A 3.1C 3.5AB
1.6BC 0.7A 1.2AB 2.1C 2.0B 2.3B 2.4AB 3.1C 1.9A 3.2AB
All
3.3E
3.1D
3.3E
2.5BC
2.4B
2.6C
1.8A
1.7A
2.0A
Median temperatures in the same row with the same letter are not significantly different (P > 0:05).
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C.O. Gill et al. / Food Control 14 (2003) 145–151
median values, which were separated by the non-parametric, Kruskal–Wallis test. In the previous survey of packs of beef in 41 retail cabinets, the median temperatures of packs in 24 of the cabinets were <4 °C, but the maximum temperatures were P4 and P7 °C in 38 and 20 cabinets, respectively. (Gill et al., 2002). In this survey, the median temperatures of packs in all 10 cabinets were <4 °C, but the maximum temperature were P4 and P7 °C in 10 and 6 cabinets, respectively. Also, in this survey, the percentages of packs at temperatures >4 and >7 °C were about 50% and 30% respectively of the fractions of packs found to be of those temperatures in the previous survey. Thus, the data indicate that the temperatures of packs in the 10 multiple shelf cabinets were within the same range but shifted downwards as compared with the temperatures of packs examined in the previous survey. The ages of the packs in the two surveys were similar, with >80% of packs examined in each being 62 days old. Moreover, in both surveys few packs older than 2 days were found in about half the display cabinets. The numbers of packs from each cabinet that were examined in the first survey were insufficient to establish the distribution of pack ages in cabinets where packs older than 2 days were found. In the second survey, four cabinets contained substantial numbers of packs older than 2 days. The percentages of older packs were between 40% and 45% in three of those cabinets, and about 75% in the fourth cabinet. Prolonged residence of packs in display cabinets seems intrinsically undesirable, as some, all be it small fractions of packs will evidently experience abusive temperatures during display in even the best of cabinets. Investigation of the factors that lead to prolonged display of chilled beef at some stores would then seem desirable, to identify possible means of reducing the times for which product is displayed, and so reducing potential exposure to abusive temperatures. In the previous survey it was found that older packs tended to be cooler than newer packs, while older packs were found to be cooler than newer packs at four stores in this survey. It therefore appears that there may be a tendency for product to warm during the preparation or other handling of retail packs at some stores. Such warmed product would appear to cool during subsequent display, so the preparation and handling of retail packs before display, rather than display per se, could sometimes be the weakest link in the cold chain for chill beef. As warm product can be expected to cool only slowly in display cabinets (Bøgh-Sorensen & Bertelsen, 1988), action to assure that retail packs are at temperatures <4 °C before they are placed on display would be desirable. In both surveys, the combined data from all cabinets indicated that packs at the fronts of shelves were warmer than packs at the back, and that packs on bottom and top shelves were warmer than packs on
intermediate shelves. The findings for individual cabinets in this survey were similar. Therefore, findings elsewhere of product on bottom shelves being cooler than product on higher shelves (Bøgh-Sorensen & Olsson, 1990) are apparently not applicable to chilled beef displayed in Canada. The contradictory findings probably reflect differences of cabinet designs. Investigation of means of avoiding substantial differences in temperature between packs on different shelves and between packs at the front and back of any shelf would seem desirable. In both surveys, the combined data from all cabinets indicated little difference in the temperatures of packs at different times of the day, no differences in the temperatures of packs at different positions along the lengths of cabinets, and lower temperatures of packs in lower layers than in the top layers. However, the findings for individual cabinets in this survey were contradictory to those implications of the combined data in that distinct differences in pack temperature at different times of the day were apparent in nine of the 10 cabinets, temperature gradients from sides to centres or along cabinet lengths were apparent in five cabinets, and temperatures of packs in different layers were similar in nine cabinets. The finding of different temperatures for packs at different times of the day was to be expected, because of warming of cabinet air during the cyclic defrosting of refrigeration equipment (Brolls, 1986). The finding of temperature gradients within some cabinets was also to be expected, because various factors intrinsic as well as extrinsic to a cabinet can affect the distribution of refrigerated air along its length (Malton, 1980). However, that no temperature gradients along their lengths were found in half the cabinets indicates the possibility of such temperature gradients being avoidable in all. The finding for most cabinets of packs in all layers being of similar temperatures was unexpected, as warming of product in top layers by radiant heating or draughts of warm air entering cabinets have been reported (BøghSorensen & Olsson, 1990), while any product above a cabinet load line will be markedly warmer than product below it (Woolfe, 1988). The findings for the individual cabinets therefore suggest that packs of beef are usually not stacked above loading lines, and that the radiant or other heating of packs in upper layers may be of much less importance than some have suggested. The discrepancies between some of the conclusions that can be drawn from combined data or data from individual cabinets demonstrates that the consideration of combined data alone can be sometimes misleading. Therefore, in surveys of the temperatures of product in commercial facilities and systems, the detailed examination of product in some facilities or systems that are seemingly representative of those being considered would be desirable, to avoid the drawing of erroneous conclusions from aggregated data.
C.O. Gill et al. / Food Control 14 (2003) 145–151
Acknowledgements We thank the management and staff of the retail stores involved in this study for facilitating and assisting with the collection of data from displayed product. However, the companies involved with the study wish to remain anonymous. Funding for the study was provided by the Canadian CattlemenÕs Association, the Beef Information Centre, and the Matching Investment Initiative Fund of Agriculture and Agri-Food Canada.
References Bøgh-Sorensen, L., & Bertelsen, G. (1988). Temperatures in the chill chain for meat products. In Cold chains in economic perspective (pp. 99–103). Paris: International Institute of Refrigeration. Bøgh-Sorensen, L., & Olsson, P. (1990). The chill chain. In T. R. Gormley (Ed.), Chilled foods; the state of the art (pp. 245–267). London: Elsevier Applied Science. Brolls, E. K. (1986). Factors affecting retail display cabinets. In Meat chilling (pp. 325–333). Paris: International Institute of Refrigeration. Conover, W. J. (1971). Practical nonparametric statistics (pp. 229–237). New York: Wiley.
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Gill, C. O., Jones, T., LeBlanc, D. I., Rahn, K., Holley, R. A., Starke, R., & Houde, A. (2002). Temperatures and ages of packs of beef in Canadian display cabinets. Meat Science, 62, 139–144. Greer, G. G., Gill, C. O., & Dilts, B. D. (1994). Evaluation of the bacteriological consequences of the temperature regimes experienced by fresh chilled meat during retail display. Food Research International, 27, 371–377. James, S. (1996). The chill chain ‘‘from carcass to consumer’’. Meat Science (suppl. 43), S203–S216. LeBlanc, D. I., Stark, R., MacNeil, B., Goguen, B., & Beaulieu, C. (1996). Perishable food temperatures in retail stores. In New developments in refrigeration for food safety and quality (pp. 72–81). Paris: International Institute of Refrigeration. Likes, P. W. (1996). New developments in display cabinets and refrigeration systems. In New developments in refrigeration for food safety and quality (pp. 153–157). Paris: International Institute of Refrigeration. Malton, R. (1980). Displaying wrapped meat in refrigerated cabinets: the problems. Meat (U.K.), 53, 37–43. Shapiro, S. S. (1990). How to test normality and other distributional assumptions (pp. 21–33). Milwaukee: American Society for Quality Control. Torstveit, A. K., & Magnussen, O. M. (1998). Temperature conditions in refrigerated counters in Vest Agder, Norway. In Hygiene, quality and safety in the cold chain and air conditioning (pp. 237–241). Paris: International Institute of Refrigeration. Woolfe, M. (1988). The economic consequences of legislation in the cold chain in the UK. In Cold chains in economic perceptive (pp. 85– 89). Paris: International Institute of Refrigeration.
The temperatures and ages of packs of beef displayed in multi-shelf retail cabinets C.O. Gill b
a,*
, T. Jones a, A. Houde b, D.I. LeBlanc c, K. Rahn d, R.A. Holley e, R. Starke
f
a Agriculture and Agri-Food Canada, Lacombe Research Centre, 6000 C & E Trail, Lacombe, AB, Canada T4L 1W1 Agriculture et Agroalimentaire Canada, St-Hyacinthe Centre de Recherche, 3600 Boul. Casavant ouest, St-Hyacinthe, Quebec, Canada J2S 8E3 c Agriculture and Agri-Food Canada, Food Research Centre, Pavillion Jacqueline-Bouchard, Universite de Moncton, Moncton, New Brunswick, Canada E1A 3E9 d Health Canada Guelph Laboratory, 110 Stone Road West, Guelph, Ontario, Canada N1G 3W4 e Department of Food Science, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2 f Agriculture and Agri-Food Canada, Kentville Research Centre, 32 Main Street, Kentville, Nova Scotia, Canada B4N 1J5
Received 23 March 2002; received in revised form 18 June 2002; accepted 25 June 2002
Abstract The temperatures and ages of 5389 packs of beef in 10 multiple shelf display cabinets were determined. The median temperature of the packs in each cabinet was <4 °C. The maximum temperatures of the packs in six cabinets were >7 °C. All packs in three cabinets were 6 2 days old. The percentages of packs older than 2 days were <1% in three cabinets, about 40% in three cabinets and about 70% in one cabinet. Both aggregated data and data for individual cabinets indicated that, generally, older packs were cooler than newer, packs at the backs of shelves were cooler than packs at the fronts, and packs on intermediate shelves were cooler than packs on bottom or top shelves. The aggregated data also indicated that the temperatures of packs did not differ at different times of the day, or at different positions along cabinets; and that packs in lower layers were generally cooler than packs in top layers. However, the findings for individual cabinets were that packs in nine cabinets had different median temperatures at different times of the day, that temperature gradients existed along five cabinets; and that temperatures of packs in different layers did not differ. Consideration of only aggregated data from surveys may lead to some erroneous conclusions about display cabinet performances. Crown Copyright Ó 2002 Published by Elsevier Science Ltd. All rights reserved. Keywords: Beef; Retail display; Temperatures; Pack ages
1. Introduction It is often suggested that retail display is the weakest link in the cold chain for the distribution of raw, chilled meat (James, 1996). Moreover, various studies have indicated that the temperatures of displayed product have not changed over many years, which implies that industrial and regulatory initiatives aimed at reducing the temperatures of chilled foods on display have been ineffective (Greer, Gill, & Dilts, 1994; Torstveit & Magnussen, 1998). In contrast, a recent survey of the temperatures and ages of beef displayed at 41 Canadian retail stores indicated that the control of product temperatures had improved in the past few years (Gill et al.,
*
Corresponding author. Tel.: +1-403-782-8113; fax: +1-403-7826120. E-mail address: [email protected] (C.O. Gill).
2002). However, some findings from that survey were counter intuitive and/or contradictory to previous reports (Bøgh-Sorensen & Olsson, 1990; Brolls, 1986; LeBlanc, Stark, MacNeil, Goguen, & Beaulieu, 1996) in that the survey data suggested that there was no effect of refrigeration equipment defrosting on product temperatures, no variation of temperatures along the lengths of cabinets, higher temperatures of product on bottom and top than on other shelves of cabinets, and cooling rather than warming of product during display. Such unexpected findings might reflect improved designs of newer display cabinets and/or better management of cabinets in response to continuing concerns about the microbiological safety of raw meat (Likes, 1996). Those findings might, however, have arisen as artifacts of data having been collected from packs in cabinets at conveniently located stores, with packs being selected on the basis of generalized assumption about the management and performances of cabinets that
0956-7135/02/$ - see front matter Crown Copyright Ó 2002 Published by Elsevier Science Ltd. All rights reserved. PII: S 0 9 5 6 - 7 1 3 5 ( 0 2 ) 0 0 0 5 8 - 0
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C.O. Gill et al. / Food Control 14 (2003) 145–151
might be erroneous for any particular cabinet. If the unexpected findings were artifactual, then the apparent indications of improvement may also be so. Therefore, to clarify the findings of the previous survey, and to better relate the temperatures and ages of displayed beef overall to the conditions of meat in different display cabinets, the temperatures and ages of retail packs of beef in each of a further 10 display cabinets at Canadian retail stores were examined.
2. Materials and methods 2.1. Selection of packs Retail packs of beef were selected for examination from a display cabinet at each of 10 retail stores. Packs were selected without regard to the form of the meat, steak, roast or ground, that each contained. The cabinets from which packs were selected were all used to display only beef. Each cabinet had three or more, open shelves, with a bottom, horizontal shelf about twice the width of the upper shelves which sloped downward from back to front. The bottom shelves of cabinets typically measured about 350 80 cm (L W ). Each of the stores was visited on nine occasions, with three visits at each of three times of the day which were within 1 h of store opening, between 12:00 and 14:00 h, and within 1 h before the store closed. On each occasion, packs were selected for examination from each layer of packs on each shelf, from the left side, middle and right side of the front, centre line and back of the shelf (Fig. 1). Thus, nine packs were selected for examination from each complete layer on each shelf. For partial layers a pack from each of the positions that was filled was examined. 2.2. Determination of temperatures and ages of packs Temperatures were measured using a thermistor probe designed for surface measurements (400 Series, Cat. No. E-08431-50; Cole-Parmer, Anjou, QC, Canada) connected to a digital thermometer (Traceablee; Control Co., Friendswood, TX, USA). For each measurement, the probe was placed with the tip at the center of the upper surface of the selected pack. An adjacent pack was inverted over the probe when the selected pack was in the single or upper layer of packs on a shelf, or the pack above replaced when the selected pack was in a lower layer of packs. The temperature displayed 2 min after the placing of the probe was recorded. In addition to the temperature, the packed-on or best-before date given on the label of each selected pack was recorded. For each store where best-before dates were used, explanation of the relationship between the best-before
Fig. 1. The front left (FL), middle (FM) and right (FR); centre line left (CL), middle (CM) and right; and back left (BL), middle (BM) and right (BR) positions on cabinet shelves from which retail packs were selected for determination of their surface temperatures and identification of their ages.
date and the time of preparation of retail packs of each type of product was obtained. 2.3. Analysis of data Descriptive statistics for data sets were obtained using Microsoft Excel, version 4, statistical functions (Microsoft Corp. Redmond, WA, USA). Sets of data were tested for normal distribution using the WilkShapiro test (Shapiro, 1990) in the UNIVARIATE procedure of SAS, version 6 (SAS Institute Inc., Cary, NC, USA). Median values for sets of data were separated using the Kruskal–Wallis test (Conover, 1971) in the NPARIWAY procedure of SAS, version 6 (SAS Institute Inc.).
3. Results The numbers of packs examined at each store ranged from 385 to 738, for a total of 5389 packs (Table 1). The median temperatures for packs at different stores ranged from 1.9 to 4 °C. The maximum temperatures were >4 °C at all the stores, and >7 °C at six of the stores. The median ages of displayed packs were 0 day at six stores, but 2 or 3 days at the other four stores. The minimum age of packs at all stores was 0 day. The maximum ages of packs were 6 2 days at three stores and P7 days at three stores also. Overall about 80% of the selected packs were 62 days old, but the percentages of packs of those ages
C.O. Gill et al. / Food Control 14 (2003) 145–151
147
Table 1 Temperatures and ages of retail packs in a multiple shelf display cabinet devoted to beef at each of 10 retail stores Store
No. of packs
Temperature (C°)
Age (days)
Median
Mean
Maximum
Median
Mean
Maximum
1 2 3 4 5 6 7 8 9 10
616 738 645 482 654 533 492 385 457 387
1.9 2.0 2.3 2.5 2.6 2.8 3.1 3.1 3.5 3.8
1.9 2.1 2.1 2.5 2.6 2.7 3.0 3.2 3.6 4.0
Minimum 2.0 1.2 1.8 1.2 1.5 0.1 1.0 0.3 0.5 0.4
8.2 6.8 7.4 5.6 8.1 6.8 6.6 9.5 10.6 8.6
2 0 0 2 0 3 0 0 0 2
2.2 0.5 0.3 2.3 0.3 3.0 0.6 0.3 0.5 2.2
6 4 8 6 2 7 5 1 2 7
All
5389
2.7
2.6
2.0
10.6
1
1.2
8
temperature range at the same store were not normally distributed (P < 0:05). Overall, the median age of the packs in each 2 °C temperature range was 1 day, except for the <1% of product of temperature >8 °C for which the median age was 0 days. However, at only one store were the warmest packs of a median age significantly less (P < 0:05) than those of cooler packs. Twenty of 30 sets of temperatures collected at different times of day from packs at each store were not normally distributed (P < 0:05; Table 4). The three sets of combined data for each time of day were not normally distributed (P < 0:05). The median values for the sets of temperatures obtained for the combined data for packs at all stores at each time of the day were not significantly different (P > 0:05). However, for seven stores, the median value for temperatures of packs at
ranged from 28% to 100% at different stores (Table 2). Twenty one of 43 sets of temperatures for packs of the same age at the same store were not normally distributed (P < 0:05). The median temperature of packs that were examined on the days they were prepared were significantly higher (P < 0:05) than the median temperature of packs that were 1 or 2 days old at four stores. At the other stores there was no consistent increase or decrease of median temperature with time on display. Overall, the temperatures of about 18% of the packs were P 4 °C, but the percentages of packs of those temperature ranged from about 6% to about 44% at different stores (Table 3). Also, the temperatures of 1.3% of the packs were P7 °C, but the percentages of packs at those temperatures ranged from 0% to 4.4% at different stores. All sets of ages for packs in the same 2 °C
Table 2 Percent fractions and median temperatures of retail packs of different ages in a multiple shelf display cabinets devoted to beef at each of 10 retail stores Store
Age (days) 0
1
2
3
4
5
6
Fractions (%)
Temperature (°C)
Fractions (%)
Temperature (°C)
Fractions (%)
Temperature (°C)
Fractions (%)
Temperature (°C)
Fractions (%)
Temperature (°C)
Fractions (%)
Temperature (°C)
Fractions (%)
Temperature (°C)
1 2 3 4 5 6 7 8 9 10
11.9 60.4 75.3 11.2 73.9 3.0 52.8 70.4 60.8 14.7
1.7B 2.2B 2.4B 2.4AB 2.7A 2.4A 3.0A 3.5B 3.5B 4.0A
14.6 33.1 24.0 22.2 25.8 18.2 34.6 29.6 30.0 16.0
2.0BC 2.0B 1.6A 2.7BC 2.5A 2.4A 3.5B 2.2A 3.7B 4.1A
31.5 6.2 0.3 26.8 0.3 6.6 11.8 –b 9.2 24.3
1.4A 1.4A –a 2.0A –a 2.2A 3.2AB
2.1BC –a
2.8 –b –b 10.0 –b 5.1 0.2 –b –b 5.7
2.7BC
3.5A
0.8 –b –b 4.1 –b 8.4 0.4 –b –b 1.8
3.0BC
3.7A
15.9 0.1 –b 7.5 –b 9.3 –b –b –b 13.4
2.3C
2.5A 3.6A
22.6 0.1 –b 18.3 –b 39.4 0.8 –b –b 24.0
3.7A
All
45.0
2.7CD
24.9
2.6B
11.2
2.1A
9.9
3.1E
5.4
2.7BCD
1.4
2.6BCD
2.6B 3.2B –a
a
3.3BC 2.7A
4.6B 2.8DE
Median temperatures in the same row with the same letter are not significantly different (P > 0:05). a Insufficient packs for estimation of a median temperature. b Less than 0.1% of packs of the indicated age.
2.1
2.6B 1.6A –a
3. 5C 1.6A –a
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C.O. Gill et al. / Food Control 14 (2003) 145–151
Table 3 Percent fractions and median ages of retail packs of different temperature ranges in a multiple shelf display cabinet devoted to beef at each of 10 retail stores Store
Temperature (°C) 60
0.1–2.0
2.1–4.0
4.1–6.0
6.1–8.0
>8.0
Fractions (%)
Age (days)
Fractions (%)
Age (days)
Fractions (%)
Age (days)
Fractions (%)
Age (days)
Fractions (%)
Age (days)
1 2 3 4 5 6 7 8 9 10
9.3 11.8 10.7 3.5 5.5 0.8 2.6 2.9 0.2 0.8
2B 1B 0B 2A 0A 3A 0A 0AB 2A 3A
46.3 38.3 32.6 31.6 27.1 26.1 26.0 26.5 15.5 6.2
2BC 0AB 0AB 2A 0A 3A 0A 0B 1A 2A
38.1 37.9 49.9 53.3 54.4 58.5 43.9 40.0 48.4 49.0
3C 0A 0B 2A 0A 3A 0A 0A 0A 2A
4.7 11.2 6.7 11.5 11.8 12.9 25.6 26.8 29.3 36.4
3BC 0AB 0B 2A 0A 3A 1A 0A 0A 2A
1.3 0.6 0.2 –a 10.7 1.7 1.4 2.3 4.6 6.2
1AB 1AB 0AB
All
5.5
1A
29.2
1A
47.2
1A
16.0
1A
0A 3A 1A 0AB 0A 2A
1.7
Fractions (%) 0.3 –a –a –a 0.2 –a –a 1.8 2.0 1.3
1A
0.4
Age (days) 0A
0A
0AB 0A 2A 0A
Median ages in the same row with the same letter are not significantly different (P > 0:05). a No packs in the temperature range.
Table 4 The effects of the time of day on the temperatures of retail packs in a multiple shelf display cabinet devoted to beef at each of 10 retail stores Store
Temperature (°C) Median a.m.
Store
Maximum noon
p.m.
a.m.
noon
Table 5 The effects of the levels of shelves on the median temperatures of retail packs in a multiple shelf display cabinet devoted to beef at each of 10 retail stores
p.m.
1 2 3 4 5 6 7 8 9 10
1.6A 2.5B 2.3B 2.3A 2.5A 2.8B 2.3A 4.0B 3.1A 4.0B
2.5B 2.3B 2.3B 2.5A 2.8B 3.1C 3.0B 2.9A 3.3A 4.2B
1.8A 1.2A 2.0A 2.8A 2.7B 2.5A 4.0C 2.8A 4.3B 2.3A
4.4 6.3 7.4 5.6 5.1 5.3 5.6 9.3 6.8 7.1
8.2 6.8 7.2 5.3 8.1 6.8 5.6 9.5 7.0 8.6
5.1 5.0 6.8 5.1 5.2 4.8 6.6 6.8 10.6 6.5
1 2 3 4 5 6 7 8 9 10
All
2.6A
2.7A
2.6A
9.3
9.5
10.6
All
Median temperature in the same row with the same letter are not significantly different (P > 0:05).
one time differed significantly (P < 0:05) from the median temperatures at other times, while for two stores all three median values differed significantly (P < 0:05) from one another. At eight stores, the maximum temperature at one time of the day was P1 °C more than the maximum temperatures at other times. Thirty four of the 50 sets of temperatures for packs on shelves at different levels were not normally distributed (P < 0:05; Table 5). The six sets of combined data for packs on shelves at each level were not normally distributed (P < 0:05). Overall, the median temperature for packs on the sole sixth shelf was significantly higher (P < 0:05) than the median temperature for packs on other shelves; while the median temperature for packs on the bottom shelves was significantly higher
Temperature (°C) Shelf 1a
Shelf 2
Shelf 3
Shelf 4
Shelf 5
Shelf 6
2.5D 2.6C 2.7C 3.1C 3.1C 3.1C 3.7B 3.8C 4.7B 4.5B
1.7B 1.6A 1.7A 2.4B 2.9BC 1.5A 2.8A 3.2B 3.0A 3.4A
0.8A 1.3A 2.1AB 2.0A 1.8A 2.8B 2.5A 3.1B 2.9A 3.7A
2.0C 2.1B 2.3B –b 1.6A 3.1C 2.6A 2.3A 3.7B –b
–b 2.1B 2.4B –b 2.7B –b 4.0B 2.7AB –b –b
–b –b –b –b 3.7D –b –b –b –b –b
3.2D
2.3A
2.3A
2.5B
2.7C
3.7E
Median temperatures in the same row with the same letter are not significantly different (P > 0:05). a The bottom shelf is designed shelf 1. b No shelf at the level.
(P < 0:05) than the median temperatures for packs on all other shelves except the sixth. The median temperature of the packs on the bottom or top shelf was significantly higher (P < 0:05) than the median temperatures for packs on other shelves at 6 and 1 stores, respectively. At three stores, the median temperatures of packs on top and bottom shelves were similar, and significantly higher (P < 0:05) than the medium temperatures of packs on other shelves. Packs in upper, second, third or fourth layers were about 62%, 29%, 8% or 1% of the total packs examined. Packs in fifth or sixth layers were together only 0.1% of the total. Twenty of the 37 sets of temperatures for packs in different layers at each store were not normally
C.O. Gill et al. / Food Control 14 (2003) 145–151 Table 6 The effects of the layering of packs on the median temperatures of retail packs in a multiple shelf display cabinet devoted to beef at each of 10 retail stores Store
Temperature (°C) Layer 1a
Layer 2
Layer 3
Layer 4
Layer 5
Layer 6
1 2 3 4 5 6 7 8 9 10
2.1C 2.1A 2.3A 2.5A 2.7A 2.8A 3.2B 3.1A 3.6B 3.8A
1.8B 2.1A 2.2A 2.5A 2.6A 2.6A 2.6A 3.6A 3.2A 3.8A
1.5A 1.7A 2.1A 2.6A 2.5A 3.0A 4.0d AB 2.5b A 3.8AB 4.6d A
0.0b A 2.2A –c 2.3d A 2.0b A 3.5d A –c 5.2b A 6.5b B –c
–c 0.5b A –c –c –c –c –c –c –c –c
–c 0.3b A –c –c –c –c –c –c –c –c
All
2.8D
2.5B
2.3A
2.5CD
0.5b CD
0.3b C
Median temperatures in the same row with the same letter are not significantly different (P > 0:05). a The top layer is designed layer 1. b The number of packs was <10. c No layer of packs at the level. d The number of packs was P 10 < 20.
distributed (P < 0:05; Table 6). The sets of combined data for packs in each of layers 1, 2 and 3 were not normally distributed (P < 0:05). Overall, median temperatures for packs in second and third layers were significantly lower (P < 0:05) than median temperature for packs in other layers. However, at each of seven stores there was no significant difference (P > 0:05) between the median temperatures of packs in different layers; and at only one store was the median temperature of packs in the first layer significantly higher (P < 0:05) than the median temperatures of packs in other layers. Thirty-five of the 90 sets of temperatures for packs at different positions on shelves at each store were not
149
normally distributed (P < 0:05). Eight of the nine sets of combined data for packs at each of the different positions on shelves were not normally distributed (P < 0:05). Overall, the median temperatures for packs at the fronts of cabinets were significantly higher (P < 0:05) than the median temperatures for packs along the midline, and the median temperatures of those latter packs were significantly higher (P < 0:05) than the median temperatures for packs at the backs of cabinets (Table 7). Similarly, at each store, median temperatures for packs at the front of the cabinet were significantly higher (P < 0:05) than median temperatures for packs at the back. Overall, the median temperatures of packs at the middle of the fronts or centre lines of cabinets were significantly less (P < 0:05) than the median temperatures of packs at the fronts or at the centre lines on the left and right or the right sides (Table 7). At each of two stores, the median temperatures of packs at the midline of the cabinet were significantly less (P < 0:05) than the median temperatures of packs on the left and right sides. At each of three other stores, the median temperature of packs on the left or right side of the cabinet were significantly less (P < 0:05) than the median temperature of packs on the other side. At the remaining five stores, no temperature gradients along the cabinets were apparent although there were significant differences (P < 0:05) between the median temperatures of packs at different positions in each cabinet.
4. Discussion Because many of the data sets were not normally distributed, sets were compared by reference to their
Table 7 The effects of the positions of packs on shelves on the median temperatures of retail packs in a multiple shelf display cabinet devoted to beef at each of 10 retail stores Store
Temperatures (°C) Front
Centre line
Back
Left
Middle
Right
Left
Middle
Right
Left
Middle
Right
1 2 3 4 5 6 7 8 9 10
2.7D 3.6E 3.2E 3.2D 2.7CD 2.8D 3.3BC 4.5D 4.4F 4.3CD
2.0C 3.1D 2.7D 3.0D 3.2DE 3.1D 4.1D 3.2C 4.1EF 4.7D
2.6D 2.8D 3.1E 3.7E 3.3E 3.2D 4.5D 5.0D 3.0C 3.8AB
2.0C 1.7C 2.2C 2.1C 2.4B 2.5BC 2.3AB 3.0C 4.1DEF 3.5AB
1.2AB 2.0C 1.7BC 2.0BC 2.5BC 3.1CD 3.5C 1.6B 3.7CDE 4.1BC
2.0C 1.1B 1.9C 2.9D 2.8CD 2.9CD 3.3C 3.8C 2.6B 4.0BC
1.3AB 1.5B 1.1AB 1.5AB 1.2A 2.1A 1.7A 2.0B 3.5CD 3.4A
0.8A 1.1B 0.6A 1.3A 2.0B 2.8CD 2.8BC 1.1A 3.1C 3.5AB
1.6BC 0.7A 1.2AB 2.1C 2.0B 2.3B 2.4AB 3.1C 1.9A 3.2AB
All
3.3E
3.1D
3.3E
2.5BC
2.4B
2.6C
1.8A
1.7A
2.0A
Median temperatures in the same row with the same letter are not significantly different (P > 0:05).
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median values, which were separated by the non-parametric, Kruskal–Wallis test. In the previous survey of packs of beef in 41 retail cabinets, the median temperatures of packs in 24 of the cabinets were <4 °C, but the maximum temperatures were P4 and P7 °C in 38 and 20 cabinets, respectively. (Gill et al., 2002). In this survey, the median temperatures of packs in all 10 cabinets were <4 °C, but the maximum temperature were P4 and P7 °C in 10 and 6 cabinets, respectively. Also, in this survey, the percentages of packs at temperatures >4 and >7 °C were about 50% and 30% respectively of the fractions of packs found to be of those temperatures in the previous survey. Thus, the data indicate that the temperatures of packs in the 10 multiple shelf cabinets were within the same range but shifted downwards as compared with the temperatures of packs examined in the previous survey. The ages of the packs in the two surveys were similar, with >80% of packs examined in each being 62 days old. Moreover, in both surveys few packs older than 2 days were found in about half the display cabinets. The numbers of packs from each cabinet that were examined in the first survey were insufficient to establish the distribution of pack ages in cabinets where packs older than 2 days were found. In the second survey, four cabinets contained substantial numbers of packs older than 2 days. The percentages of older packs were between 40% and 45% in three of those cabinets, and about 75% in the fourth cabinet. Prolonged residence of packs in display cabinets seems intrinsically undesirable, as some, all be it small fractions of packs will evidently experience abusive temperatures during display in even the best of cabinets. Investigation of the factors that lead to prolonged display of chilled beef at some stores would then seem desirable, to identify possible means of reducing the times for which product is displayed, and so reducing potential exposure to abusive temperatures. In the previous survey it was found that older packs tended to be cooler than newer packs, while older packs were found to be cooler than newer packs at four stores in this survey. It therefore appears that there may be a tendency for product to warm during the preparation or other handling of retail packs at some stores. Such warmed product would appear to cool during subsequent display, so the preparation and handling of retail packs before display, rather than display per se, could sometimes be the weakest link in the cold chain for chill beef. As warm product can be expected to cool only slowly in display cabinets (Bøgh-Sorensen & Bertelsen, 1988), action to assure that retail packs are at temperatures <4 °C before they are placed on display would be desirable. In both surveys, the combined data from all cabinets indicated that packs at the fronts of shelves were warmer than packs at the back, and that packs on bottom and top shelves were warmer than packs on
intermediate shelves. The findings for individual cabinets in this survey were similar. Therefore, findings elsewhere of product on bottom shelves being cooler than product on higher shelves (Bøgh-Sorensen & Olsson, 1990) are apparently not applicable to chilled beef displayed in Canada. The contradictory findings probably reflect differences of cabinet designs. Investigation of means of avoiding substantial differences in temperature between packs on different shelves and between packs at the front and back of any shelf would seem desirable. In both surveys, the combined data from all cabinets indicated little difference in the temperatures of packs at different times of the day, no differences in the temperatures of packs at different positions along the lengths of cabinets, and lower temperatures of packs in lower layers than in the top layers. However, the findings for individual cabinets in this survey were contradictory to those implications of the combined data in that distinct differences in pack temperature at different times of the day were apparent in nine of the 10 cabinets, temperature gradients from sides to centres or along cabinet lengths were apparent in five cabinets, and temperatures of packs in different layers were similar in nine cabinets. The finding of different temperatures for packs at different times of the day was to be expected, because of warming of cabinet air during the cyclic defrosting of refrigeration equipment (Brolls, 1986). The finding of temperature gradients within some cabinets was also to be expected, because various factors intrinsic as well as extrinsic to a cabinet can affect the distribution of refrigerated air along its length (Malton, 1980). However, that no temperature gradients along their lengths were found in half the cabinets indicates the possibility of such temperature gradients being avoidable in all. The finding for most cabinets of packs in all layers being of similar temperatures was unexpected, as warming of product in top layers by radiant heating or draughts of warm air entering cabinets have been reported (BøghSorensen & Olsson, 1990), while any product above a cabinet load line will be markedly warmer than product below it (Woolfe, 1988). The findings for the individual cabinets therefore suggest that packs of beef are usually not stacked above loading lines, and that the radiant or other heating of packs in upper layers may be of much less importance than some have suggested. The discrepancies between some of the conclusions that can be drawn from combined data or data from individual cabinets demonstrates that the consideration of combined data alone can be sometimes misleading. Therefore, in surveys of the temperatures of product in commercial facilities and systems, the detailed examination of product in some facilities or systems that are seemingly representative of those being considered would be desirable, to avoid the drawing of erroneous conclusions from aggregated data.
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Acknowledgements We thank the management and staff of the retail stores involved in this study for facilitating and assisting with the collection of data from displayed product. However, the companies involved with the study wish to remain anonymous. Funding for the study was provided by the Canadian CattlemenÕs Association, the Beef Information Centre, and the Matching Investment Initiative Fund of Agriculture and Agri-Food Canada.
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