REPORT OF THE GREATER MANCHESTER/LANCASHIRE/PHLS
LIAISON GROUP SURVEY ON THE MICROBIOLOGICAL EXAMINATION
OF BOILED AND EGG FRIED RICE FROM CHINESE TAKEAWAY
PREMISES
K Williamson, G Allen, F J Bolton, PHLS North West FESL – Preston PHL.
Date of Report 24/01/00
Survey Code No. 904004
Introduction
Incidents of rice associated food poisoning have been linked to the practice of
preparing rice in bulk in advance, in anticipation of subsequent need. The traditional
practice in Chinese takeaway premises of boiling a large quantity of rice that is then
kept at room temperature before reheating was incriminated as the cause of several
food poisoning incidents in Lancashire and Greater Manchester.
Hence the purpose of this survey was to establish the microbiological quality of precooked rice awaiting reheating and rice sampled at the point of sale from Chinese
takeaway premises. In addition, the survey aimed to determine whether preparation
procedures produced a risk to health. In particular the practice of cooking rice and
storing it prior to final heating, and the use of shell eggs for egg fried rice was
investigated by enumeration and detection of Bacillus cereus and Salmonella
respectively.
Materials and Methods
Sample collection
This survey was carried out as part of the Greater Manchester FLG/Lancashire
FOG/Preston PHL sampling programme during April – August 1999. Samples
consisted of pre-cooked rice (stock rice) awaiting reheating or frying that were
collected from the food preparation area, and reheated (ready to eat) boiled or egg
fried rice from the point of sale, as if being purchased by the customer. Samples were
collected by local authority sampling officers between 6.00 pm and midnight in
accordance with the Food Safety Act of 1990 (Code of Practice No. 7 (1)). No
advance warning of the visit was given. In order to prevent bias, resulting from
samples being heated more thoroughly than usual prior to service, the point of sale
samples were purchased before the sampling officer disclosed their identity and
collected the precooked sample.
Samples were placed in a coolbox within 15 minutes and transferred to a monitored
refrigerator for overnight storage before submission to Preston PHL the following
day. Before leaving the premises, information relating to the preparation procedures
and processes was obtained by observation and completion of a standard
questionnaire (Appendix 1).
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Microbiological examination
A total of 647 samples of rice including 208 stock rice, 218 boiled rice and 221 egg
fried rice samples were submitted and examined from 24/26 authorities in Greater
Manchester and Lancashire as detailed in Appendix 1.
Samples were examined for aerobic colony count/g (ACC), Enterobacteriaceae/g, E.
coli/g, Staphylococcus aureus/g and Bacillus cereus and other Bacillus spp/g. The
stock and egg fried rice were also examined for Salmonella spp. All tests were
carried out according to UKAS approved PHLS-NW FESL methods.
Results
Microbiological results
Table 1.
Microbiological results of boiled rice (n = 218)
<10,<20,
<102,<103
o
ACC/g 30 C 72h
Enterobacteriaceae/g
E.coli/g
S.aureus/g
B.cereus/g
B.subtilis group/g
Table 2.
142
210
218
217
213
217
10-<102
102-<103
103-<104
104-<105
105-<106
106-<107
107
8
-
49
1
3
19
1
1
5
-
1
-
2
1
-
-
Microbiological results of egg fried rice (n = 221)
Detected
Not
detected
o
ACC/g 30 C 72h
Enterobacteriaceae/g
E.coli/g
S.aureus/g
B.cereus/g
B.subtilis group/g
Salmonella/25g
Table 3.
121
217
221
221
213
209
-
10-<102
102-<103
103-<104
104-<105
105-<106
106-<107
107
2
-
42
1
3
26
1
1
6
22
2
5
3
1
4
1
-
3
1
-
221
Microbiological results of stock rice (n = 208)
Detected
ACC/g 30oC 72h
Enterobacteriaceae/g
E.coli/g
S.aureus/g
B.cereus/g
B.subtilis group/g
Salmonella/25g
(KWKM004.doc)
<10,<20,
<102,<103
Not
detected
<10,<20,
<102,<103
71
130
181
207
200
197
-
10-<102
102-<103
103-<104
104-<105
105-<106
106-<107
107
16
8
-
27
11
9
1
4
34
12
7
2
8
21
12
1
2
13
14
1
1
20
8
1
2
-
22
5
-
208
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Table 4.
Relevant parameters2 in Category 3 of the PHLS microbiological
guidelines
Microbiological quality (cfu/g) unless stated
Satisfactory
Borderline
limit of
acceptability
Unsatisfactory
Unacceptable
potentially
hazardous
<105
105-<106
106
Not applicable
Enterobacteriaceae*
<100
102-104
104
Not applicable
E. coli
<20
20-<100
100-104
104
Staphylococcus aureus
<20
20-<100
100-104
104
<103
103-<104
104-<105
105
Not detected
in 25g
-
-
Detected in 25g
Aerobic colony
(30C/48h)
count
Bacillus cereus and
Bacillus subtilis group
Salmonella
* = proposed guideline
Table 5.
Microbiological quality of point of sale rice samples using PHLS
microbiological guidelines2
Type of rice
Satisfactory (%)
Borderline (%)
Unsatisfactory (%)
Unacceptable
(%)
Boiled
212 (97)
3 (1.5)
2 (1)
1 (0.5)
Egg Fried
199 (90)
8 (3.6)
11 (5)
3 (1.4)
Point of sale rice
The ACC exceeded 106/g in only 1.4% of point of sale samples. Bacillus subtilis
group and B. cereus were detected 104/g in 1.4% and 1.1% samples respectively.
Only 1 sample (0.2%) produced a Staphylococcus aureus count of >102/g. E. coli was
not detected in any of the 439 point of sale samples, and Enterobacteriaceae were not
detected in 97% of samples and none produced counts >104/g. Bacillus subtilis group
and B. cereus exceeded 104/g in 4.5% of egg fried rice samples and in only 0.4% of
boiled rice samples. Salmonella spp was not detected in any of the egg fried rice
samples.
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Based on category 3 of the PHLS microbiological guidelines for ready to eat foods
sampled at the point of sale (Table 4) (2), 98.6% of boiled rice and 93.6% of egg fried
rice were of acceptable microbiological quality (Table 5). Overall 4% of point of sale
rice samples were of unsatisfactory quality, with 0.9% being of unacceptable quality.
The unacceptable quality results were due to either B. cereus or Bacillus subtilis
group at 105/g. Egg fried rice produced three unacceptable results (1.4%) and boiled
rice one unacceptable result (0.4%).
Stock rice
Significantly more samples of precooked stock rice had a higher level of
contamination with E. coli (102) and Enterobacteriaceae (>104) compared with point
of sale cooked rice (Tables 1-3). E. coli 102 were present in 9% stock rice samples
compared to none detected in point of sale samples. Enterobacteriaceae (>104/g) were
present in 19% stock rice compared to none in point of sale samples.
Bacillus subtilis group and B. cereus exceeded 104/g in 1.4%and 1.0% of stock rice,
respectively compared to 2.7% and 1.8% in egg fried rice. B. subtilis group was not
detected at >104/g in boiled rice and B. cereus only detected in 0.4% of boiled rice at
this level.
Salmonella spp was not detected in any of the stock rice samples.
Questionnaire results
A copy of the questionnaire is available in Appendix 1.
Q1
The majority of stock rice (71%) did not contain egg product. Of the 23 stock
rice samples producing E. coli counts >100/g and/or Bacillus cereus/subtilis
>104/g 16(70%) contained egg product.
Q2
The majority of stock rice (85%) was sampled within 0-6 hours of initial
cooking.
Q3
The stock rice was stored: (n = 204)
Ambient
76 (37%)
Refrigerated
31 (15%)
Rice steamer
97 (48%)
Of the 23 stock rice samples producing E.coli counts >100/g and/or Bacillus
cereus/subtilis gp the majority 17(74%) were stored at ambient temperature, 4(17%)
were refrigerated and 2(9%) were stored in the steamer.
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Q4
The temperature of the stock rice at the time of sampling was:
Stock rice
storage
Ambient
n = 76
Refrigerated
n = 31
Rice steamer
n = 97
<5C
<8C
10C – 45C
30C – 40C
>63C
0
1
50
12
9
7
11
7
0
7
0
1
4
1
75
The above temperature bands in particular were selected for analysis on the basis that,
most species of bacteria do not grow at ideal refrigeration temperatures (0-5oC). The
legal standard for perishable food storage is < 8oC. Most food poisoning bacteria
grow in the range 10-45oC with the fastest growth rates being between 30 – 40oC.
Warm holding temperatures of >63oC are recommended.
The majority of rice stored within the growth range and optimum range occurred
when stored at ambient. Of the 23 stock rice samples producing E.coli counts >100/g
and/or Bacillus cereus/subtilis gp >104g the following storage method and
temperatures were observed:Stock rice
storage
Ambient
(n = 17)
Refrigerated
(n = 4)
Rice steamer
(n = 2)
<5C
<8C
10C – 45C
30C – 40C
>63C
0
0
11
0
1
1
2
1
0
0
0
0
0
0
2
Of the 17 ambient stored rice samples producing results of concern, 11 (65%) were
derived from a mesophilic growth range temperature (10oC – 450C)
Q5 The usual time for cooling stock rice after boiling, prior to refrigeration: (n = 30)
<1½h
15
<1½h – 4h
15
4 – 12h
0
>12h
0
Process information only, results not related to microbiological quality.
Q6
Is a new batch of boiled stock rice ever mixed with the remains of a previous
batch? (n=215)
No
190 (88%)
Yes
25 (11%)
Process information only, results not related to microbiological quality.
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Q7
How was the boiled rice served? (n=216)
Reheated
11(5%)
Freshly boiled
205(95%)
The majority of boiled rice samples (98%) were of acceptable microbiological quality,
hence results have not been related to method of serving.
Q8
What type of egg product is used in the egg fried rice process? (n=218)
Pasteurised
egg
-
Dried
powdered
-
Shell egg
191 (88%)
Pre-prepared
Shell egg mix
27 (12%)
Process information only, results not related to microbiological quality.
Q9
If shell eggs were used, where stored? (n=186)
Ambient
137 (74%)
Refrigerated
46 (26%)
Process information only, results not related to microbiological quality.
Q10 Where is the pre-prepared shell egg mix stored? (n=26)
Ambient
17 (65%)
Refrigerated
9 (35%)
Process information only, results not related to microbiological quality.
The following hygiene questions were not related to microbiological quality.
Q11
Are the refrigerator temperatures checked? (n=217)
Yes
183 (84%)
No
34 (16%)
Q12 Were the refrigerator temperature records available? (n=183)
Yes
52 (28%)
No
131 (72%)
Q13 Were the process temperatures of the rice checked?
Process
Boiling
n=8
Cooling
n=7
Storage
n=186
(KWKM004.doc)
Yes
21(10%)
No
197(90%)
4(2%)
183(98%)
30(16%)
156(84%)
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Q14 Were the process temperature records available?
Process
Boiling
(N=20
Cooling
N=4
Storage
N=26
Yes
2(10%)
No
180%)
0
4(100%)
7(27%)
19(73%)
Q15 Have any staff undergone food hygiene training within the last 3 years? (n=207)
Yes
94 (45%)
No
113 (55%)
Q16 Sampling officers opinion – were the staff aware of food safety risks associated
with the rocessing of egg fried rice/boiled rice? (n=207)
Yes
123(59%)
No
84(41%)
Conclusions
(1)
This survey indicated that most of the stock rice sampled from the
preparation area of chinese and takeaway establishments was of
acceptable microbiological quality.
(2)
This survey has shown that the overall microbiological quality of point
of sale rice samples in particular boiled rice was of good
microbiological quality.
(3)
Overall only 4% of point of sale rice samples were classified as
unsatisfactory. This suggests that preparation and storage practices of
premises associated with these samples could be improved.
(4)
The storage of stock rice at ambient temperature (37%) is of particular
concern, because there is a potential for significant growth of B.cereus
and production of heat stable emetic toxin. The majority of results of
concern were from stock rice stored at ambient temperature although
the number of B. cereus high counts (>104/g) was low in this study
(<1%).
(5)
Refrigeration or storage of stock rice in a steamer was effective in
reducing the number of samples observed in the 10C-45C growth
range at the time of sampling.
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(6)
The use of shell eggs in the preparation of egg fried rice (88%) and
ambient storage of eggs (74%) may be considered as potential risks for
Salmonella cross contamination. Pasteurised egg was not used at any
of the premises visited. However no Salmonella was isolated from the
egg fried rice or stock rice samples examined during this study.
(7)
The processing of point of sale rice subsequent to removal from the
stock indicated good practices as demonstrated by the reduction in
aerobic colony counts, Enterobacteriaceae and E.coli counts and
absence of Salmonella spp in egg fried rice.
(8)
There is a need to improve record keeping to support the temperature
monitoring of refrigerators. Process temperatures were not monitored
in the majority of cases and when carried out were infrequently
recorded.
(9)
Formal food hygiene training is not a legislative requirement and so the
55% having undergone no training within the last 3 years is a typical
expectation for this type of retail establishment. However the sampling
officers opinion that 41% of the Chinese takeaway staff were not aware
of the relevant food safety risks is of major concern. This indicates the
need for further education and review.
References
(1)
Ministry of Agriculture, Fisheries and Food. Department of Health,
Food Safety Act 1990, Code of practice No 7: Sampling for Analysis
and Examination. 1990. London H.M.S.O.
(2)
PHLS 1996. Microbiological Guidelines for Some ready to Eat Foods
sampled at the Point of Sale – an Expert opinion from the PHLS.
PHLS Microbiological Digest 13: 41-43
Acknowledgements
The authors would like to thank Andrea Lund (Tameside) and Richard Short (West
Lancashire) for their assistance in producing the questionnaire and protocol and for
their support and advice.
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APPENDIX 1
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(a)
Survey participants
(b)
Survey protocol
(c)
Survey questionnaire
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APPENDIX A
Survey – Participants
(A)
Authority
Number of
boiled rice
Number of egg
fried rice
Number of stock
rice
Total
number
of
samples
Barrow
Blackpool
Burnley
Chorley
Fylde
Hyndburn
Lancaster
Preston
RibbleValley
Rossendale
South Lakes
South Ribble
West Lancs
Wyre
Bolton
Bury
Manchester
Oldham
Rochdale
Salford
Stockport
Tameside
Trafford
Wigan
5
12
12
8
10
10
13
10
8
8
9
6
12
10
8
8
9
10
10
10
10
6
4
10
5
12
12
8
10
10
13
10
8
8
9
6
12
10
8
8
10
10
12
10
10
6
4
10
5
12
12
7
10
10
10
9
8
8
8
3
12
10
8
8
9
10
10
10
10
5
4
10
15
36
36
23
30
30
36
29
24
24
26
15
36
30
24
24
28
30
32
30
30
17
12
30
TOTAL
218
221
208
747
(B)
Survey Protocol
Available from FOG/FLG/PHL
(C)
Questionnaire
Available from FOG/FLG/PHL
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APPENDIX B
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APPENDIX C
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(KWKM004.doc)
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