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is a publication of the Food and Public Health
Branch of the Food and Environmental Hygiene
Department of HKSAR Government. Under no circumstances
should the research data contained herein be
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Correspondence:
Risk
Assessment Section
Food and Environmental Hygiene Department
43/F, Queensway Government Offices,
66 Queensway, Hong Kong.
MICROBIOLOGICAL
RISK
ASSESSMENT OF SIU-MEI
AND LO-MEI
IN HONG KONG
Abstract
Siu-mei
and lo-mei are specially processed meat, poultry
and offal products in Chinese cuisines. By definition,
siu-mei would have been roasted at temperature
over 200¢XC in the preparation. Lo-mei are braised
and soaked in large volume of seasoning sauce
for a period of time for flavour enrichment.
In both, roasting and cooking are the critical
steps to destroy the microorganisms present
in raw food. However, microbiological hazards
might be introduced after heat treatment. Physical
properties, namely pH value, salinity value,
water activity, nutrient value, and the ambient
environment such as relative humidity, temperature
and gaseous atmosphere, are factors influencing
the microbial growth in siu-mei and lo-mei.
In 2000, out of the total 596 samples, the overall
unsatisfactory rate of hygienic quality was
2.2% and the unsatisfactory rate of pathogenic
contamination was 0.8%. The hygienic quality
of siu-mei was better at an unsatisfactory rate
of 1% (4 out of 406 samples), as compared with
4.7% (9 out of 190 samples) of lo-mei. As far
as specific pathogens were concerned, Salmonella
spp. was found in 2 sui-mei (roasted pork and
BBQ pork) and 1 lo-mei (steamed plain chicken);
S. aureus was found in 1 siu-mei (BBQ
pork) and in 1 lo-mei (steamed plain chicken).
Post contamination and prolonged storage at
ambient temperature might be the main contributing
factors.
Microbiological
Risk Assessment of Siu-mei and Lo-mei in Hong Kong
INTRODUCTION
Siu
mei and lo mei¡]¿N¨ý³¿¨ý¡^are general terms covering
a wide range of processed meat and poultry products
in the Chinese cuisines. They are often treated
as a group and considered high-risk items in terms
of microbiological risks. However, upon closed examinations,
it is identified that their characteristics are
very different.
Objective
This
paper evaluates the microbiological hazards associated
with consumption of siu-mei and lo-mei, examines
the local food surveillance findings for the period
of 2000, identifies the critical control points
in the manufacturing practices and recommends
improvement measures to the trade.
Definitions
Though
a traditional Chinese food originated from Guandong,
there is no documented definition for the terms
"siu-mei" and "lo-mei". A review on their generic
production procedures and way of consumption provides
some insights on the classification. The following
definitions are suggested and used in this paper.
Lo-mei
is the foodstuff that has been soaked or immersed
in large volume of seasoning sauces prior to cooking.
Some lo-mei items may be braised again after cooking
and/or at the time of serving. Food groups that
are commonly used to produce lo-mei include poultry
meat¡]¶Q¦mÂû¡B³aªoÂû¡B³¿¤ôÃZ¡B³¿¤ôÂûž]¤ÎÂûÁl¡^,
red meat¡]³¿¤ô¤û á^and offal products¡]Âû¸z¡BÃZ¸z¡B¥Í¸z¡^.
Legal
provision
Siu-mei
and lo-mei are classified as restricted food under
Schedule 2 of the Food Business Regulation of the
Public Health and Municipal Services Ordinance,
Cap. 132. Manufacturing and sale of siu-mei and
lo-mei in Hong Kong are subject to licensing control.
A specific licence or endorsement must be obtained
for the siu-mei and lo-mei business.
As
of March 2001, some 1,700 food premises are allowed
to sell siu-mei and lo-mei. The operators should
comply with and observe the relevant licensing requirements
and conditions, and maintain their premises in satisfactory
hygienic conditions. These licensing requirements
and conditions basically require the vendors to
put in place appropriate hygienic measures in the
establishment for proper handling of food. For instance,
there should be separate food preparation tables
for siu-mei and lo-mei. The finished products should
be displayed in an isolated showcase for sale. In
addition, hand-washing facilities including soap
and clean water supply should be provided for the
food handlers. Health inspectors carry out regular
checks to monitor compliance to these licensing
requirements and conditions.
MANUFACTURING
PRACTICE OF SIU MEI AND LO MEI
The
key steps of preparing siu-mei and lo-mei are illustrated
in the schematic diagrams at Figure
1 and Figure 2 respectively.
The raw ingredients of siu-mei are either fresh
or frozen meat or poultry. They have to undergo
pre-roasting preparation including defrosting, washing,
marinating, and even pre-cooked. Roasting is the
critical step to cook siu-mei products. At a temperature
of 200¢XC or above, almost all microbiological hazards
would be eliminated. The products are then cooled,
delivered and displayed for sale.
As
for lo-mei, the main step involved is the use of
marinade to impart the special taste and texture
of meat and offal. The meat and offal are first
cooked with seasoning sauce or water, and then braised
in the sauce for a period of time to enrich their
flavour. The finished products can be served hot
or cold. If it is served cold, chilling should take
place at the time of braising. Pig knuckle¡]âÀ¿á¡^is
an example of lo-mei served cold.
MICROORGANISMS
OF PUBLIC HEALTH CONCERN
Some
microorganisms, such as Campylobacter spp.,
Salmonella spp., Clostridium botulinum,
Clostridium perfringens and Bacillus cereus,
are the normal floras naturally present in raw meat
and offal (1). Some could also
be introduced during food preparation, such as Staphylococcus
aureus. However, whether such organisms may
persist in siu-mei and lo-mei is the combined results
of the physical properties of siu-mei and lo-mei
and the ambient environment.
Physical
Properties of Siu-mei and Lo-mei
Nature
of food plays key role in affecting activities of
the microbes, like growth, stasis and death (2).
The most important physical properties that can
affect microbial growth in food are pH value, salinity
value (salt content), water activity (aw)
and nutrient value. There is scarce documentation
about these properties of siu-mei or lo-mei in the
literature. However, basing on the understanding
of the food preparation steps of siu-mei and lo-mei,
it is recognized that most of them have relatively
high salinity level and low water activity as compared
with other meat and poultry products. One study
conducted by the Department of Health Services in
the State of California, USA in 1990 reported that
the water activity (aw) of skin of roasted
pig was low at a range of 0.72 to 0.81 (3).
Low water activity would put some microorganisms
at a competitive disadvantage and have difficulties
to grow. Such inherent properties offer some protective
effects to siu-mei and lo-mei against microbiological
hazards.
Environmental
Factors
In addition, the characteristics of the ambient
environment, including relative humidity, temperature
and gaseous atmosphere, can influence the growth
of microorganisms (2, 4).
Water activity in food could be increased when placed
in an environment with a high relative humidity.
In addition, warm storage temperature, such as room
temperature, is the other factor affecting the bacterial
levels. All these contribute to a favourable environment
for microbial growth.
MICROBIOLOGICAL
QUALITY OF SIU-MEI & LO-MEI IN HONG KONG
The
Food and Environmental Hygiene Department has conducted
a surveillance on siu-mei and lo-mei available on
the market for microbiological risk assessment.
All samples are assessed for the hygienic quality
and pathogenic contamination. The results of 2000
are analyzed and compared with the Department's
Microbiological Guidelines for Ready-to-eat Foods.
The unsatisfactory microbiological criteria for
siu-mei and lo-mei are shown in Annex
1.
A
total of 596 samples were taken for microbiological
examinations. Of these, 406 (68%) and 190 (32%)
samples were siu-mei and lo-mei respectively. Details
are shown in Table 1.
Hygienic
Quality
The
hygienic quality of siu-mei was better as compared
with lo-mei. The unsatisfactory rate for siu-mei
was lower at 1% as compared with lo-mei which was
at 4.7%. Of the 13 unsatisfactory samples, nearly
70% were lo-mei.They were steamed plain chicken
(3 samples), pig knuckle (2 samples), cooked chicken
(1 sample), red meat (1 sample), lo shuo goose (1
sample), and duck gizzard (1 sample). The remaining
ones were siu-mei samples including 2 roasted pork
, 1 BBQ pork and 1 mixed dish of rice with chicken
and BBQ pork.
Presence
of specific Pathogens
Of
the 406 siu-mei samples examined, 3 samples (0.7%)
were found to contain unsatisfactory level of pathogens.
Salmonella spp. was present in 1 roasted
pork and 1 BBQ pork. In addition, excessive amount
of S. aureus was detected in another BBQ pork sample.
Of
the 190 samples of lo-mei tested, 2 samples (1.1%)
were found to contain unsatisfactory amount of pathogens.
Two steamed plain chickens were found unsatisfactory
due to presence of Salmonella spp. in a sample
and excessive amount of S. aureus in the
other.
DISCUSSIONS
Comparing
the hygienic quality of siu-mei and lo-mei, the
unsatisfactory rates of lo-mei were obviously higher
than that of siu-mei. There were two possible reasons.
First, the quality of lo-mei seasoning sauce from
different food premises may vary a lot and some
may provide favourable medium for microbial growth
due to prolonged storage time. Second, lo-mei would
have higher water activity as it is soaked in a
sauce for a longer time. This may flavour the microbial
growth.
Of all lo-mei products, the hygienic quality of
steamed plain chicken was relatively poorer. Inadequate
cooking, improper handling and poor personal hygiene
might be the main contributing factors. In general,
steamed plain chicken is usually not thoroughly
cooked and displayed at ambient temperature for
a long period of time. Before consumption, reheating
is commonly not applied at all.
Of all samples taken in 2000, two specific pathogens,
unsatisfactory level of Salmonella spp. and
S. aureus were isolated in the food samples.
Both bacteria can be readily destroyed by heat treatment.
The steps of roasting and cooking in siu-mei and
lo-mei production could have eliminated these microbiological
hazards theoretically. Post-heat treatment contamination
was the most likely reason for introduction of such
microbiological hazards from the environment, other
raw or cooked food and food handlers to siu-mei
and lo-mei products. Salmonella spp. is commonly
transmitted due to poor food and environmental hygiene.
S. aureus is the normal flora found in hands
and noses; and poor personal hygiene is the main
concern.
To
further improve these situations, we have identified
the following handling practices at siu-mei and
lo-mei shops that might have contributed to introduction
of microbiological hazards:
(a)
siu-mei and lo-mei are often stored at room temperatures
within the danger zone of 4-60¢XC, which are warm
beds for growth of micro-organisms;
(b)
they are often handled by bare hands, and occasionally
the same staff may handle siu-mei and lo-mei products
with other foodstuffs and cash;
(c)
leftover without adequate reheating may be sold;
and
(d)
to attract customers, some vendors defy the sanitary
requirement and expose siu-mei and lo-mei in open
air without cover.
Among
the above, improper handling procedure and sub-optimal
storage conditions could be the main factors contributing
to the introduction and perpetuation of specific
pathogens. To improve the situation, application
of HACCP principles in manufacturing practices
is the key to successful microbiological risk
management.
CONCLUSION
AND RECOMMENDATIONS
Siu-mei and lo-mei are two distinct types of food
preparation. Roasting and cooking are the critical
steps in the production to destroy the bacteria.
This study showed that the hygienic quality of lo-mei
is less satisfactory than siu-mei, especially the
steamed plain chicken. For pathogenic contamination,
Salmonella spp. and S. aureus are
the organisms of concern. Post-heat treatment contamination
is the main route to introduce microbiological hazards.
In addition, prolonged storage time at ambient temperature
is flavourable for the microbial growth. In view
of these, we recommend the application of HACCP-based
safety plan to control siu-mei and lo-mei.
The following critical control measures at the key
steps of preparation are recommended to the trade.
(a)
Purchasing
Buy
raw materials from such as raw meat and offal
from approved and reliable sources.
Inspect the incoming goods and documents before
acceptance to verify that there is no sign or
indication of contamination or damage to the
goods.
Appropriate
and clean vehicles should be used to transport
the siu-mei and lo-mei. During transportation,
siu-mei and lo-mei should be properly protected
to avoid cross contamination.
(b) Preparation
Raw
and cooked meats should be handled with separate
utensils to avoid cross contamination.
The demand of siu-mei and lo-mei should be carefully
estimated to avoid over-production. This can
prevent prolonged storage duration of siu-mei
and lo-mei displayed at ambient temperatures.
Observe
good personal hygiene. Refrain from smoking,
eating or playing with their hair during preparation.
Open wound should be covered.
Wash
hand thoroughly with soap and water before and
after handling siu-mei and lo-mei.
Siu-mei and lo-mei should be thoroughly cooked.
(c)
Display and Storage
Store raw and cooked meats separately.
Siu-mei
and lo-mei should be stored and displayed in
an insect- and dust-proof showcase.
Food, other than siu-mei and lo-mei, especially
raw food such as seafood and Chinese preserved
sausage, should not be stored in showcase for
siu-mei and lo-mei.
Equipment including trays, towels, chopping
boards and knives should be maintained in hygienic
conditions and regularly cleansed or regularly.
Different
staff should be deployed for handling cash and
food.
Consumers are advised to take note of the following
as food safety measures.
(a) Patronize clean and well-maintained food premises
(b)
Observe whether food handlers follow good personal
hygiene. They should not be smoking, playing with
their hair or have any open wounds
(c)
Observe whether the siu-mei and lo-mei are covered
or displayed in insect- and dust-proof showcase
(d)
Observe whether raw food is placed in the siu-mei
and lo-mei showcase
(e)
Consume siu-mei and lo-mei as soon as possible
(f)
Store the leftover in a refrigerator and reheat
them thoroughly before consumption
REFERENCE
1.
ICMSF. Microorganisms in Foods 6 - Microbial Ecology
of Food Commodities. Blackie Academic & Professional.
London. 1998.
2.
Adams, MR and Moss, MO. Food Microbiology. The Royal
Society of Chemistry. London. 1995.
3.
York, GK. Microbial Evaluation of Chinese-style Roasted,
Whole Pig. Jointed project conducted by Department
of Health Services, State of California, and Department
of Food Science and Technology, University of California.
1990.
4.
Garbutt, J. Essential of Food Microbiology. Arnold.
London. 1997.
Figure
1: Flow diagram of siu-mei production
Figure
2: Flow diagram of lo-mei production
Table
1: Results of microbiological examination of siu-mei
and lo-mei in 2000
Unsatisfactory
results
Total
no. of sample
Hygieneic
quality(Unsatisfactory rate)
Presence
of Pathogens(Unsatisfactory rate)
Remarks
Siu-mei
406
4
(1.0%)
3
(0.7%)
Salmonella
spp.
(Roasted pork ; BBQ pork)
S.
aureus (Roasted pork)
Lo-mei
190
9
(4.7%)
2
(1.1%)
S.
aureus
(Steamed plain chicken x 2)
Total
596
13
(2.2%)
5
(0.8%)
----
Annex
1
FEHD
Microbiological Guidelines for Ready-to-eat Food *
Unsatisfactory
Hygienic quality (for Siu-mei and Lo-mei):
Last
review date: 19-01-2005