This
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 reproduced, reviewed
or abstracted in part or in whole, or in
conjunction with other publications or research
work unless a written permission is obtained
from the Department. Acknowledgement is
required if other parts of this publication
are used.
Recently, salads have become
popular among consumers in Hong Kong. Many
different styles of salads are commercially
available in the market. In commercial settings,
salads are either freshly prepared at restaurants
or produced as pre-packaged food at food factories
for supplies to retail outlets. Some restaurants
have self-serve salad bars and food ingredients
displayed there may be of additional risk
of being contaminated by the patronizing customers.
In reviewing the microbiological surveillance
findings of 573 salad samples collected from
1999 through 2001 by the Food Surveillance
Programme, 10 (1.7%) out of 573 samples exceeded
the levels set out in the FEHD's Microbiological
Guidelines for Ready-to-eat Food in terms
of specific pathogens. Listeria monocytogenes
was isolated in 6 (1.0%) of these samples
and Salmonella spp. was isolated in the other
4 (0.7%) samples. With respect to hygienic
quality, during the past 3 years, 63 (24.9%)
out of 253 samples and 3 (1.3%) out of 239
samples were found unsatisfactory and exceeded
the hygienic quality level of Aerobic Colony
Count and E.coli (total) count respectively.
Salad preparation often involves handling
of pre-cooked or ready-to-eat ingredients
with little or no further cooking steps to
reduce the microbiological risk. Therefore,
improper handling of ingredients and contamination
after processing are the two main pathways
to contaminate the final products. Both the
trade and consumers are advised to take necessary
precautions to enhance food safety in preparation
and consumption of salads.
Risk Assessment Studies
Report No.9
Microbiological Risk Assessment
on Salads in Hong Kong
OBJECTIVE
The aim of this paper is to evaluate the microbiological
risk of salads in Hong Kong.
INTRODUCTION
2. Salads
are mixtures of minimally processed ready-to-eat vegetables[a]
with or without dressing[b]. Other common ingredients
are fruits, poultry, meat, seafood, egg, pasta, herbs,
nuts and cooked vegetables. Salads are usually
served cold.
3.
The ingredients for making salads usually impart fresh-like
quality characteristics. In addition to such
desirable quality, the consumption of fresh vegetables
and fruits is increasing as consumers strive to eat
healthy diets and benefit from the year-round availability
of these products that up until recently were considered
to be seasonal. Recently, salads have become
popular among consumers in Hong Kong. Many different
styles of salads are commercially available in the
market. Where restaurants served various kinds
of salads usually as appetizers, pre-packaged salads
supplied by food factories are also commonly available
in supermarkets and restaurants with take away service.
[a] Minimally processed ready-to-eat vegetables consist
of raw vegetables that have been washed, peeled,
sliced, chopped or shredded. [b] Typical salad dressings include mayonnaise, thousand
island sauce, French dressing, Italian dressing,
etc..
Production of Salads
4.
The production of salads includes steps in purchasing
and processing of raw materials, mixing of ingredients,
packaging, transportation and sale. The general
production of salads is illustrated in the flowchart
at Annex I.
5.
Major ingredients are minimally processed ready-to-eat
vegetables that have been washed, peeled, sliced,
chopped and shredded. Some of the raw materials,
like poultry, meat, seafood, egg and pasta have to
be cooked first. Others such as canned products,
herbs, nuts and dressings are usually readily available
for immediate use.
6.
Salads may be served with or without dressing depending
on consumers¡¦ preference. Some types of salads
consist of ingredients mixed with dressings.
Other types of salads, or in case of pre-packaged
salads, may contain ingredients only and a separate
package of dressing is available for consumers to
mix with the ingredients by themselves. Salad
dressings usually impart characteristic flavours and
may contribute some preservative effect to the product
to a certain extent.
7.
Large fast food chain stores usually purchase pre-prepared
raw materials which only required a mixing procedure
before serve. Other food premises may purchase
and prepare the salad ingredients by themselves.
8.
The finished products may be served on the premises.
Otherwise, the fresh-made salads may be packaged and
sold in restaurants with take-away service or packaged
in food factory and delivered to retail outlets or
supermarkets for sale.
9.
Some restaurants have self-serve salad bars where
customers can pick ingredients of their choice to
make up their own dishes. Food ingredients displayed
at self-serve salad bars may be of additional risk
of being contaminated by the patronizing customers.
Potential Microbiological Hazards
10.
Microbial pathogens associated with minimally processed
ready-to-eat vegetables include those occur naturally
in soil such as Listeria monocytogenes, Clostridium
perfringens, Bacillus cereus and those from faeces
of human or animal origin such as Salmonella
spp..1 The possible
sources of pathogens in these products include the
incoming raw vegetables themselves, the food handlers
and the processing environment. When vegetables
are chopped and shredded, the release of plant cellular
fluids provides a nutritive medium in which microorganisms
can grow. The high moisture content of fresh
vegetables, the lack of a lethal process to eliminate
microbial pathogens and the potential for time and
temperature abuse during preparation, distribution
and handling further intensify the risk of foodborne
illness.2
11.
Raw egg is known to be a source of Salmonella.
This pathogen may be introduced into the final product
if raw and unpasteurized eggs or egg products are
used to prepare salad dressings.
12.
As salad preparation often involves handling of pre-cooked
or ready-to-eat ingredients, good personal and environmental
hygiene practices should be observed to minimize the
chance of introduction of microbial hazards.
MICROBIOLOGICAL SURVEILLANCE ON
SALADS
13.
The Food and Environmental Hygiene Department (FEHD)
has a Food Surveillance Programme in place for food
surveillance and enforcement purposes. Food
samples were collected at every stage of the supply
process from the local market for chemical, microbiological
and radiological testing. Microbiological tests
were conducted by the Pathology Service of the Department
of Health. Microbiological examination results
of salads obtained in 1999 to 2001 were extracted
from the food surveillance database and were reviewed
and analyzed in the present study. The microbiological
tests included those for specific pathogens as well
as for hygienic quality.
14.
The results were evaluated based on the Microbiological
Guidelines for Ready-to-eat Food recommended by this
Department (Annex II).3
RESULTS
15.
From 1999 to 2001, a total of 573 salad samples were
taken for microbiological examination for specific
pathogens and hygienic indicator microorganisms.
Specific Pathogens
16.
¡§Specific pathogens¡¨ refer to bacteria that may cause
food poisoning or other illnesses. To safeguard
public health, salads should not contain specific
pathogens exceeding the levels as detailed in the
FEHD¡¦s Microbiological Guidelines for Ready-to-eat
Food (Annex II).3
17.
Ten (1.7%) out of 573 samples were found unsatisfactory
in terms of specific pathogens. The numbers
of unsatisfactory samples were 2 (1.2%) out of 169
samples in 1999, 7 (3.6%) out of 194 samples in 2000
and 1 (0.5%) out of 210 samples in 2001 respectively
(Table 1, Figure 1).
Table 1: Microbiological Surveillance Results of
Salads ¡V Specific Pathogens (1999 ¡V 2001)
Year
Total
Number of Sample
Number
of Unsatisfactory Sample (%)
1999
169
2
(1.2%)
2000
194
7
(3.6%)
2001
210
1
(0.5%)
1999
¡V 2001
573
10
(1.7%)
Figure 1: Microbiological Surveillance Results of
Salads ¡V Specific Pathogens (1999 ¡V 2001)
18.
As regards the types of pathogens isolated, Listeria
monocytogenes was detected in 6 of these samples,
whereas Salmonella spp. was isolated in the
other 4 samples (Table 2).
Table 2: Summary of Unsatisfactory Results ¡V Specific
Pathogens (1999 ¡V 2001)
Year
Pathogens
Isolated (Number of Samples)
1999
Salmonella spp. (1) Listeria monocytogenes (1)
2000
Salmonella spp. (2) Listeria monocytogenes (5)
2001
Salmonella spp. (1)
International Comparison
19.
Several studies in relation to the microbiological
status of salads and salad vegetables were reported
in a World Health Organization (WHO) review document
on fruits and vegetables eaten raw which was published
in 1998.4
The Public Health Laboratory Service (PHLS) of the
United Kingdom had also conducted a study in 2001
on the microbiological quality of retail-prepared
prepackaged ready-to-eat salad vegetables.5
Table 3 summarized the results of these studies.
Table 3: Summary of Studies on Microbiological
Status on Salad Conducted by Other Countries
Items
Country
Pathogen
Prevalence
Prepacked salads *
Northern Ireland
Listeria monocytogenes
3/21
(14.3%)
Salad vegetables *
Canada
Listeria monocytogenes
6/15
(40%)
Salad vegetables *
Germany
Listeria monocytogenes
6/163
(2.3%)
Salad vegetables *
Spain
Listeria monocytogenes
21/70
(30%)
Salad greens *
Egypt
Salmonella spp.
1/250
(0.4%)
Prepackaged ready-to-eat salad vegetables †
United Kingdom
Listeria monocytogenes Salmonella spp.
953/3851
(24.7%) 5/3851 (0.13%)
* Extracted from the WHO Review
Report of Fruits and Vegetables Eaten Raw. †Extracted from the PHLS study.
Hygienic Quality
20.
Hygienic quality of food is reflected by the Aerobic
Colony Count and E. coli (total) count.
Aerobic Colony Count (ACC)
21.
ACC is useful for indicating the overall microbiological
quality of a food product. Generally, it does
not relate to food safety hazards, but acts as an
indicator for food quality, shelf-life and post-heat
processing contamination. The quality level
of ACC for salad recommended by this Department is
not more than 106 colony-forming unit (cfu)
per gram of food (Annex II).3
22.
From 1999 to 2001, 253 salad samples were tested for
ACC and 63 (24.9%) had unsatisfactory levels.
The numbers of unsatisfactory samples were 18 (21.2%)
out of 85 samples in 1999, 16 (21.1%) out of 76 samples
in 2000 and 29 (31.5%) out of 92 samples in 2001 respectively
(Table 4, Figure 2).
Figure 2: Microbiological Surveillance
Result of Salads ¡V ACC (1999 ¡V 2001)
23.
A breakdown of the unsatisfactory results of ACC was
tabulated in Table 5.
Table 5: Breakdown of Unsatisfactory Results by Type
of Premises ¡V ACC (1999 ¡V 2001)
1999
2000
2001
No.
of samples taken
No.
of unsatisfactory sample (%)
No.
of samples taken
No.
of unsatisfactory sample (%)
No.
of samples taken
No.
of unsatisfactory sample (%)
Restaurant
64
14
(21.9%)
60
10
(16.7%)
70
26
(37.1%)
Others
21
4
(19.0%)
16
6
(37.5%)
22
3
(13.6%)
Total
85
18
(21.2%)
76
16
(21.1%)
92
29
(31.5%)
24.
The distribution of ACC in salads was studied (Figure
3). It is shown that 97 (38.3%) out of 253 samples
fall within values of log10 ACC range from
5.00 to 5.99, in which the upper range represents
the margin for satisfactory level.
Figure 3: Aerobic Colony Count of Salads (1999-2001)
25.
When the results are stratified by years, it can be
seen that the distribution patterns for the three
years are quite similar (Figure 4).
Figure 4: Distribution Curve of Aerobic Colony
Count of Salads (1999-2001)
E. coli (total) count
26.
The presence of E. coli in foods generally
indicates direct or indirect contamination from faecal
origin. Substantial numbers of E. coli
in food suggest a general lack of cleanliness in handling
and improper storage. Its presence does not
connote directly the presence of a pathogen, but implies
a certain risk that may present. The quality
level of E. coli recommended by this Department
for salad is a total count of not more than 100 cfu
per gram of food (Annex II).3
27.
During 1999 to 2001, 239 salad samples were tested
for E. coli and 3 (1.3%) were found unsatisfactory.
The numbers of unsatisfactory samples were 2 (2.4%)
out of 83 samples in 1999, 0 (0%) out of 66 samples
in 2000 and 1 (1.1%) out of 90 samples in 2001 respectively
(Table 6, Figure 5).
Table 6: Microbiological Surveillance Results of Salads
¡V E. coli (total) count
(1999 ¡V 2001)
28.
Listeria monocytogenes and Salmonella
spp. could be introduced by food handlers and cross-contamination
between ready-to-eat and raw items.
29.
Listeria monocytogenes was found in 6 of the
10 unsatisfactory samples for specific pathogens.
Listeria monocytogenes is naturally found in
soil and in decaying vegetables and can grow on salad
vegetables such as lettuce at temperatures as low
as 5¢XC.6,7
As for Salmonella, the possible routes of contamination
include direct contamination of the pre-harvested
vegetables or fruits from faeces of birds and animals,
the use of manure or sewage as fertilizer, or the
use of contaminated waters for irrigation of the crops.
Raw egg is also known to be a source of Salmonella.
This pathogen may be introduced into the final product
if raw unpasteurized eggs or egg products are used
to prepare salad dressings. Salmonella
may multiply in the finished products if ambient conditions
such as nutrient contents, pH value and water activity
favour their growth. It is therefore of paramount
importance to wash the salad vegetables thoroughly
to reduce the microbiological hazards. Proper
chilling of the salad items at 4¢XC or below is also
essential to reduce microbial growth. The risk
of Salmonella contamination by raw eggs can
be reduced by using pasteurized eggs or egg products
to prepare salad dressings.
30.
Reports of several overseas studies regarding the
microbiological quality of salads showed that the
prevalence of pathogens was variable. It has
been reported that the proportion of samples contaminated
with Listeria monocytogenes ranged from 2.3%
to 40%, and that contaminated with Salmonella
spp. ranged from 0.13% to 0.4%. Our local surveillance
results for Listeria monocytogenes compare
favorably with those from overseas, with local prevalence
of 1.0% (6 out of 573 samples) for Listeria monocytogenes
in salads during 1999 to 2001. For Salmonella
spp., the local prevalence was 0.7% (4 out of
573 samples), which is also comparable with overseas
findings.
31.
More than one-third (38.3%) of salad samples were
tested to have marginal levels of ACC (≥
105 to < 106 cfu) which are
approaching the unsatisfactory level. As ACC
is an indicator of overall hygienic quality of the
product, good hygiene practices that are essential
to improve the hygienic quality of salads should therefore
be strengthened.
32.
It is observed that there was an increase in unsatisfactory
rate with respect to ACC in 2001. Analysis revealed
that the increase was mainly contributed by samples
taken from restaurants. As a great variety of
foods were handled, processed and served by food handlers
at restaurants, it is likely that cross-contamination
between ready-to-eat and raw food items could contribute
to the higher levels of ACC.
33.
Samples found unsatisfactory with E. coli (total)
count might be due to faecal contamination of salad
crops. Such contamination might occur at the
pre-harvested stage by way of using manure as fertilizers
or using contaminated water for irrigation.
Faecal contamination might also be introduced by food
handlers if personal hygiene is not strictly observed.
34.
Vegetables and fruits which are subject to processes
such as peeling, slicing, chopping and shredding will
remove the natural protective barriers of the intact
plant and open the possibility for providing a suitable
medium for the growth of microorganisms. These
products are then eaten without a further heat processing
step. It is therefore of paramount importance
that these products should be washed thoroughly to
minimize the microbiological hazards. Disinfectants
may be applied to reduce the number of microorganisms
on foods. However, when such chemical is used,
the instructions from the suppliers of the disinfectants
must be followed to prevent any chemical hazard being
introduced into the final products.
35.
Acid salad dressings such as mayonnaise may contribute
some preservative effect to foods due to its relatively
low pH. However, such preservative effect will
depend on the initial contamination of the salad,
the pH, presence of nutrients (sugars), etc..
The concentration of acetic acid (from vinegar) and
the low pH of salad dressings are the major contributors
to their anti-microbial properties. In case
of mayonnaise, a total formula pH of less than or
equal to 4.1 is essential to inactivate Listeria
monocytogenes, Salmonella spp. in the dressing.8,9,10 However,
proper chilling of mayonnaise-based salad directly
after production is important to provide protection
against growth of microorganisms.11
To be on the safe side, it is recommended to use only
pasteurized eggs or egg products as an ingredient
to produce salad dressings.
36.
Food ingredients displayed at self-serve salad bars
may be of additional risk of being contaminated by
the patronizing customers. Storage temperature
of the ingredients should be kept at 4¢XC or below.
Sufficient numbers of tongs or ladles with suitably
long handles should be provided and they should be
replaced at a sufficient frequency (e.g. at 4 hours
interval). Contaminated tongs and ladles (e.g.
those dropped onto the floor) should be replaced with
clean ones immediately. The salad bar area should
be supervised by trained staff to prevent contamination
of foods by customers.
CONCLUSION & RECOMMENDATIONS
37.
To improve the hygienic quality of salads, good manufacturing
and handling practices should always be observed by
the trade especially for restaurants providing self-serve
salad bars. For consumers, they should observe
hygiene rules to minimize the potential microbiological
hazards. The followings are some recommendations.
Advice to Trade
(A) Handling of raw materials:
1. Purchase
raw materials from reputable and reliable suppliers.
2. Wash all
vegetables and fruits thoroughly.
3. Cook egg,
poultry, meat and seafood thoroughly.
4. Use pasteurized
eggs or egg products to prepare salad dressings.
5. Store salad
dressings at 4¢XC or below once their packages are
opened.
6. Avoid holding
chilled ingredients (e.g. meat, seafood, cut fruits
and vegetables) and finished products at above 4¢XC
for more than 2 hours.
(B) Self-serve salad bars
1. Display
salad ingredients in a proper manner and at 4¢XC
or below.
2. Provide
sufficient number of tongs or ladles with long handles
and replace them with clean ones when appropriate
(e.g. at 4 hour interval). Remove contaminated
tongs and ladles (e.g. those dropped onto the floor)
from the salad bar immediately.
3. Display
ingredients in small portions and avoid topping
up with fresh ones.
4. Discard
leftovers.
5. Supervise
the salad bar area by appropriately trained staff
to protect the food against contamination by customers.
(C) Hygienic practices:
1. Observe
good personal, food and environmental hygiene.
2. Prevent
cross-contamination.
Advice to Consumers
(A) Purchase
1. Buy salads
from reputable and reliable suppliers.
2. Check the
¡§use-by date¡¨ and pay attention to the storage temperature
of pre-packaged salads.
(B) Self-serve salad bars
1. Use appropriate
utensils for picking up ingredients and avoid direct
hand contacts.
2. Inform
restaurant staff if mis-handling of food at salad
bars is seen.
(C) Consumption
1. Consume
the salads as soon as possible.
2. If salads
are not consumed immediately, they (including home-made
ones) should be:
-
packed and stored at 4¢XC or below.
-
separated from raw food.
-
consumed within 1 to 2 days.
3. The elderly,
children, pregnant women and persons with lowered
immunity should be careful when choosing food especially
high risk food, such as salads.
REFERENCES
1.
International
Commission on Microbiological Specifications
for Foods. Vegetables and Vegetable
Products. In: Microorganisms in Foods
6 ¡V Microbial Ecology of Food Commodities.
London: Blackie Academic & Professional;
1998. p.215-251.
2.
Canadian
Food Inspection Agency. Code of Practice
for Minimally Processed Ready-to-Eat Vegetables.
3.
Food
and Environmental Hygiene Department.
Microbiological Guidelines for Ready-to-eat
Foods; February 2002.
4.
World
Health Organization. Surface Decontamination
of Fruits and Vegetables Eaten Raw: A Review;
1998.
5.
Advisory
Committee on the Microbiological Safety of
Food, the United Kingdoms. Microbiological
Status of Ready-To-Eat Fruit and Vegetables;
April 2002
6.
European
Commission. Report of the Scientific
Committee on Food ¡V Risk Profile on the Microbiological
Contamination of Fruits and Vegetables Eaten
Raw; April 2002.
7.
Adams
MR, Moss MO. Microbiology of Primary
Food Commodities. In: Food Microbiology.
Cambridge: The Royal Society of Chemistry;
1995. p.103-135.
8.
J.P.
Erickson, P. Jenkins. Comparative Salmonella
spp. and Listeria monocytogenes Inactivation
Rates in Four Commercial Mayonnaise Products.
Journal of Food Protection 1991;54(12):913-916.
9.
United
States Food and Drug Administration.
Guide To Inspections of Manufacturers of Miscellaneous
Food ¡V Dressing.
10.
O.P.
Snyder. Assuring Safety of Egg Yolk-Based
Sauces and Salad Dressings; 1998.
11.
B.M.
Lund, T.C. Baird-Parker, G.W. Gould.
Mayonnaise, Dressings, Mustard, Mayonnaise-based
salads and acid sauces. In: The Microbiological
Safety and Quality of Food Volume I.
Maryland, US: Aspen Publishers; 2000. p.807-835.
Annex I
Flow Chart of Salads
Production
Annex II
Microbiological Guidelines
for Salads
Hygienic quality
Aerobic
Colony Count (ACC)
≤
106 cfu/g
E.
coli (total)
≤
100 cfu/g
Food safety
Campylobacter
spp.
Absent
in 25g
E.
coli O157
Absent
in 25g
L.
monocytogenes
Absent
in 25g
Salmonella
spp.
Absent
in 25g
V.
cholerae
Absent
in 25g
V
parahaemolyticus
<103
cfu/g
S.
aureus
<
104 cfu/g
C.
perfringens
<
104 cfu/g
B.
cereus
<
105 cfu/g
This
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
reproduced, reviewed or abstracted in part or
in whole, or in conjunction with other publications
or research work unless a written permission
is obtained from the Department. Acknowledgement
is required if other parts of this publication
are used.
Recently, salads have become
popular among consumers in Hong Kong. Many different
styles of salads are commercially available
in the market. In commercial settings, salads
are either freshly prepared at restaurants or
produced as pre-packaged food at food factories
for supplies to retail outlets. Some restaurants
have self-serve salad bars and food ingredients
displayed there may be of additional risk of
being contaminated by the patronizing customers.
In reviewing the microbiological surveillance
findings of 573 salad samples collected from
1999 through 2001 by the Food Surveillance Programme,
10 (1.7%) out of 573 samples exceeded the levels
set out in the FEHD's Microbiological Guidelines
for Ready-to-eat Food in terms of specific pathogens.
Listeria monocytogenes was isolated in 6 (1.0%)
of these samples and Salmonella spp. was isolated
in the other 4 (0.7%) samples. With respect
to hygienic quality, during the past 3 years,
63 (24.9%) out of 253 samples and 3 (1.3%) out
of 239 samples were found unsatisfactory and
exceeded the hygienic quality level of Aerobic
Colony Count and E.coli (total) count respectively.
Salad preparation often involves handling of
pre-cooked or ready-to-eat ingredients with
little or no further cooking steps to reduce
the microbiological risk. Therefore, improper
handling of ingredients and contamination after
processing are the two main pathways to contaminate
the final products. Both the trade and consumers
are advised to take necessary precautions to
enhance food safety in preparation and consumption
of salads.
Risk Assessment Studies
Report No.9
Microbiological Risk
Assessment on Salads in Hong Kong
OBJECTIVE
The aim of this paper is to evaluate the microbiological
risk of salads in Hong Kong.
INTRODUCTION
2.
Salads are mixtures of minimally processed ready-to-eat
vegetables[a]
with or without dressing[b]. Other common ingredients
are fruits, poultry, meat, seafood, egg, pasta, herbs,
nuts and cooked vegetables. Salads are usually
served cold.
3.
The ingredients for making salads usually impart fresh-like
quality characteristics. In addition to such
desirable quality, the consumption of fresh vegetables
and fruits is increasing as consumers strive to eat
healthy diets and benefit from the year-round availability
of these products that up until recently were considered
to be seasonal. Recently, salads have become
popular among consumers in Hong Kong. Many different
styles of salads are commercially available in the
market. Where restaurants served various kinds
of salads usually as appetizers, pre-packaged salads
supplied by food factories are also commonly available
in supermarkets and restaurants with take away service.
[a] Minimally processed ready-to-eat vegetables consist
of raw vegetables that have been washed, peeled,
sliced, chopped or shredded. [b] Typical salad dressings include mayonnaise, thousand
island sauce, French dressing, Italian dressing,
etc..
Production of Salads
4.
The production of salads includes steps in purchasing
and processing of raw materials, mixing of ingredients,
packaging, transportation and sale. The general
production of salads is illustrated in the flowchart
at Annex I.
5.
Major ingredients are minimally processed ready-to-eat
vegetables that have been washed, peeled, sliced,
chopped and shredded. Some of the raw materials,
like poultry, meat, seafood, egg and pasta have to
be cooked first. Others such as canned products,
herbs, nuts and dressings are usually readily available
for immediate use.
6.
Salads may be served with or without dressing depending
on consumers¡¦ preference. Some types of salads
consist of ingredients mixed with dressings.
Other types of salads, or in case of pre-packaged
salads, may contain ingredients only and a separate
package of dressing is available for consumers to
mix with the ingredients by themselves. Salad
dressings usually impart characteristic flavours and
may contribute some preservative effect to the product
to a certain extent.
7.
Large fast food chain stores usually purchase pre-prepared
raw materials which only required a mixing procedure
before serve. Other food premises may purchase
and prepare the salad ingredients by themselves.
8.
The finished products may be served on the premises.
Otherwise, the fresh-made salads may be packaged and
sold in restaurants with take-away service or packaged
in food factory and delivered to retail outlets or
supermarkets for sale.
9.
Some restaurants have self-serve salad bars where
customers can pick ingredients of their choice to
make up their own dishes. Food ingredients displayed
at self-serve salad bars may be of additional risk
of being contaminated by the patronizing customers.
Potential Microbiological Hazards
10.
Microbial pathogens associated with minimally processed
ready-to-eat vegetables include those occur naturally
in soil such as Listeria monocytogenes, Clostridium
perfringens, Bacillus cereus and those from faeces
of human or animal origin such as Salmonella
spp..1 The possible
sources of pathogens in these products include the
incoming raw vegetables themselves, the food handlers
and the processing environment. When vegetables
are chopped and shredded, the release of plant cellular
fluids provides a nutritive medium in which microorganisms
can grow. The high moisture content of fresh
vegetables, the lack of a lethal process to eliminate
microbial pathogens and the potential for time and
temperature abuse during preparation, distribution
and handling further intensify the risk of foodborne
illness.2
11.
Raw egg is known to be a source of Salmonella.
This pathogen may be introduced into the final product
if raw and unpasteurized eggs or egg products are
used to prepare salad dressings.
12.
As salad preparation often involves handling of pre-cooked
or ready-to-eat ingredients, good personal and environmental
hygiene practices should be observed to minimize the
chance of introduction of microbial hazards.
MICROBIOLOGICAL SURVEILLANCE ON
SALADS
13.
The Food and Environmental Hygiene Department (FEHD)
has a Food Surveillance Programme in place for food
surveillance and enforcement purposes. Food
samples were collected at every stage of the supply
process from the local market for chemical, microbiological
and radiological testing. Microbiological tests
were conducted by the Pathology Service of the Department
of Health. Microbiological examination results
of salads obtained in 1999 to 2001 were extracted
from the food surveillance database and were reviewed
and analyzed in the present study. The microbiological
tests included those for specific pathogens as well
as for hygienic quality.
14.
The results were evaluated based on the Microbiological
Guidelines for Ready-to-eat Food recommended by this
Department (Annex II).3
RESULTS
15.
From 1999 to 2001, a total of 573 salad samples were
taken for microbiological examination for specific
pathogens and hygienic indicator microorganisms.
Specific Pathogens
16.
¡§Specific pathogens¡¨ refer to bacteria that may cause
food poisoning or other illnesses. To safeguard
public health, salads should not contain specific
pathogens exceeding the levels as detailed in the
FEHD¡¦s Microbiological Guidelines for Ready-to-eat
Food (Annex II).3
17.
Ten (1.7%) out of 573 samples were found unsatisfactory
in terms of specific pathogens. The numbers
of unsatisfactory samples were 2 (1.2%) out of 169
samples in 1999, 7 (3.6%) out of 194 samples in 2000
and 1 (0.5%) out of 210 samples in 2001 respectively
(Table 1, Figure 1).
Table 1: Microbiological Surveillance Results of
Salads ¡V Specific Pathogens (1999 ¡V 2001)
