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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 reproduced, reviewed,
or abstracted in part or in whole, or in conjunction
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Correspondence:
Risk
Assessment Section
Food and Environmental Hygiene Department
43/F, Queensway Government Offices,
66 Queensway, Hong Kong.
An
Evaluation on the Use of Preservatives and Colouring Matter
in Lap-mei
-Surveillance Findings 1999-2000-
AbstractThe addition of nitrate and/or
nitrite to meats and poultry at low concentrations
has been a common method of preservation for centuries.
In curing of Lap-mei, referring to traditional Chinese
preserved meat products, nitrate/nitrite is essential
not only its provision of unique characteristic in
colour and taste, but more important, is its anti-microbial
properties against bacteria growth and spore formation
especially Clostridium botulinum.
However, nitrites may react with other substances
found in meat forming nitrosamines, compounds that
may cause human cancer. Thus, application of
nitrate/ nitrite in curing is strictly controlled
to the amount required to achieve the intended effect
only. We reviewed the Lap-mei surveillance from
1999-2000 to examine this chemical hazard. Of
the 130 samples collected throughout this period,
there were 69 tested samples on nitrate and nitrite
respectively. Three were found to exceed the
permitted level of sodium nitrate, representing a
non-compliance rate of 4.3%. These samples were
all preserved sausages collected in 1999. There
were another 168 tests conducted on non-permitted
preservatives, all of them were proved satisfactory.
Test results on the colouring matter were also reviewed
in this report, one of the 62 tested samples was detected
with non-permitted colouring matter, resulting in
1.6% non-compliance rate.
Meat
Curing in Chinese cuisine A
Risk Assessment on Lap-mei Introduction
1. Meat
curing is a food technology widely employed to maintain
the quality of meat for prolonged duration in the days without
refrigeration. As a matter of fact, the use of salt, sodium
chloride, to preserve meat is a practice with a long history.
It was an incidental finding that the presence of sodium
nitrate as an impurity in crude salt could give the treated
meat an attractive red or pink colour. These lead to the
later use of nitrate in meat preservation and subsequently
led to the development of modern meat curing. [1]
2.
There is also a type of traditional Chinese meat curing
similarly using salt and sodium nitrate to a product called
Lap-mei. Like the western meat curing, Lap-mei has
lost its importance as meat preservation due to the availability
of industrial and domestic refrigerators. Instead,
it provides choices of wider varieties in distinct colour
and flavour to the consumers nowadays.
Purpose
3.
In this risk assessment study, we review the manufacturing
process of Lap-mei to identify possible hazards, examine
the surveillance results and assess the potential risks
related to consumption of Lap-mei. Recommendations
would be made to the trade and the consumers.
Lap-Mei
¡V definition and characteristics
4.
Historically, Lap means ¡§ritual¡¨ in old Chinese,
it was very often that surplus meat after the ritual would
be cured for use in times of scarcity. In Chinese
tradition, they are usually prepared around the time of
December of lunar calendar (or in Chinese ¡§Lap-Yue¡¨)
as one of the delicacies to cerebrate the Spring Harvesting
Festival, and therefore named as such.
5.
There are three types of Lap-mei available on the local
market. They are preserved Chinese sausages, preserved
pork, and preserved ducks. These are characterized
by their unique appearance, texture, and taste where are
the results of the respective curing formulation.
6.
The principal approach in producing Lap-mei is similar to
the standard curing practice documented in the Western reference
literatures. For instance, the meat or poultry are
subject to the treatment of curing ingredients, which typically
consist of salt, sugar, wine, and sodium nitrate/nitrite.
The relative proportion of the curing ingredients may differ
with the nature of meat and type of products involved.
Food additives may be added to improve the quality of the
final product.
7.
The curing process of Lap-mei is summarized in a schematic
diagram at Figure 1. The process
involves five main steps. The raw materials, usually
meat or duck, are cleaned and appropriately cut. They
are then immersed in curing ingredients and mixed either
manually or mechanically. The curing ingredients,
that is, salt, sugar, wine, and nitrate diffuse into the
meat and poultry. The mixture of meat and curing ingredients
may be placed in chillers overnight to allow stabilization
and thorough distribution. Some manufacturers may
have cuisine with other flavouring agents such as spices
or soya sauces. Furthermore, food additives such as
colouring matter may be added to make the products better
looking.
8.
The meat, poultry, or sausages, after well soaked in the
curing ingredients have to be dried such that the moisture
content of finished products comes down to 25% or even lower.
In the past, the meat or poultry are most often air-dried.
The products would be hung to allow gradual reduction in
the moisture. However, air-drying is seldom employed
in the present days. Reasons are the space required
for loading, the unpredictable climates, and the process
being relatively time-consuming.
9.
In industrial setting, hot air-drying is the preferred method.
The pieces of meat are placed in air-conditioned chamber
at temperature range between 35¢XC-40¢XC. The choice
of temperature and duration combination also depends on
the characteristics of the meat or poultry pieces under
processing. Usually three to four days of hot air-drying
are sufficient for preserved sausages weighing about 500kg.
Functions
of the Curing Ingredients used in Lap-mei
10.
Typical curing ingredients in the preparation of Lap-mei
include salt, nitrate and nitrite, sugar, and wine.
Salt is known to have preservation effects and also serves
flavouring purpose. The level of salt is usually less
than 3%.
11.
Sugar and wine both give special flavour to the finished
products. Sugar has the effect of colour stabilization
whereas wine has a mild preservative effect.
12.
Nitrates and nitrites have a unique place in meat curing.
They are important from a food safety perspective that they
have anti-microbial functions especially on Clostridium
botulinum and the inhibition of toxin production.
13.
Clostridium botulinum is a gram-positive, spore-forming,
anaerobic rod that can cause fatal infection. It is
well known to exist in anaerobic conditions, thus, vacuum-packaged
foods such as bacon and canned processed meat are capable
of supporting growth and toxin production by Clostridium
botulinium strains without causing noticeable off-odors.
In preserved meat especially meat sausages, spores of the
bacteria can germinate, grow and produce toxin under conditions
of abused temperatures. Clostridium botulinum can
grow at water activity of 0.94 and above.
14.
Nitrates and nitrites have other important technical functions.
First, they fix the colour of cured meat at red-pink by
stabilizing the haem in myoglobin through the formation
of nitrosomyoglobin. Second they can delay the process
of oxidative rancidity and hence prevent the development
of warmed-over flavour. This is an undesirable oxidized
flavour that may gradually develop during prolonged storage
of meat.
Health
Implications of the Nitrate/nitrite
15.
Nitrites are the compounds that are of more human health
concern. Nitrates at the levels commonly present in
food are not toxic to humans but serve as the reservoir
for conversion to nitrite by the intestinal flora.
Nitrate per se has a relatively low toxicity.
16.
Accidental poisoning by significant amount of nitrite can
cause methaemoglobinaemia when the iron in haemoglobin is
oxidized from the ferrous Fe(II) to the ferric Fe(III) form.
Methaemoglobin loses its ability to bind oxygen and causes
hypoxia in the affected individuals. The condition
is characterized by headache, weakness and breathlessness,
and a bluish discolouration of the skin and mucous membranes
called cyanosis. Methaemoglobinaemia resulting from
exposure to food contaminated with nitrite has been extremely
rare.
17.
The development of methaemoglobinaemia is determined by
the ingested dose and individual susceptibility. Infants
are particularly susceptible to nitrite-induced methaemoglobinaemia
because fetal haemoglobin converts to methemoglobin more
easily. In addition, infants have a low concentration
of the reducing enzyme such that methemoglobin is not converted
back to hemoglobin as readily. For mild cases of methaemoglobinaemia,
the patients usually recover without specific treatment.
18.
At present, there is no evidence to show an association
between nitrate and nitrite exposure and risk of cancer
in humans. Nevertheless, they can combine with amines
or amides in food to form N-nitrosocompounds, nitrosamines
and some of these have been shown to be carcinogenic in
experimental animals and epidemiologically implicated carcinogenicity.[2]
19.
The matter has been reviewed by International Agency for
Research on Cancer (IARC), which confirmed that these N-nitroso-compounds
are reasonably anticipated to be a human carcinogen based
on sufficient evidence of carcinogenicity in experimental
animals.[3],[4],[5]
20.
In reviewing of the previous evaluations, toxicological
and epidemiological data, Joint FAO/WHO Expert Committee
on Food Additive (JECFA) in 1995, concluded that nitrate/nitrite
as food additive, an acceptable daily Intake (ADI) of 0-3.7
mg/kg body weight per day[6] and 0-0.06 mg/kg body weight per day respectively[7] (as expressed in ion form) was
allocated.
Local
Situation
21.
As listed under the Preservatives in Food Regulations in
Hong Kong, made under section 55 of Public Health and Municipal
Services Ordinance (Cap. 132), preservative means any substance,
which is capable of inhibiting, retarding or arresting the
process of fermentation, acidification or other deterioration
of food or masking any of the evidence of putrefaction but
this term does not include substances added to food for
maintaining or improving nutritional qualities or any permitted
antioxidant, permitted colouring matter, common salt (sodium
chloride).
22.
The permitted preservatives for use in foods are stipulated
in the First Schedule to the Preservatives in Food Regulations,
which specify the permitted preservatives for use in specified
foods, as well as the respective maximum permitted levels.
Surveillance
Findings of ¡§Lap-mei¡¨ 1999-2000
23.
The surveillance results from 1999-2000 were reviewed to
examine the potential hazards related to preservatives and
colouring matter in locally available Lap-mei.
Results
24.
There were 130 Lap-mei samples sent to Government Laboratory
for testing on preservatives and colouring matter.
The methods used included High Performance Liquid Chromatography
(HPLC) and Thin Layer Chromatography (TLC).
25.
Of all these samples, 118, 5 and 7 was preserved sausage,
preserved pork and preserved duck respectively. They
were examined for sodium nitrate, sodium nitrite, non-permitted
preservatives and colouring matter.
26.
The results were compared against the statutory specifications
stipulated in the Preservative in Food Regulations in Food
Regulations and Colouring Matter in Food Regulations made
under the Public Health and Municipal Services Ordinance
(Cap.132).
Sodium
nitrate/nitrite
27.
Of 69 samples examined for nitrate and nitrite, three samples
of preserved sausages taken in 1999 were found to exceed
the permitted level of sodium nitrate, resulting in non-compliance
rate of 4.3%. The levels reported were 990ppm, 1000ppm
and 1100ppm.
Table 1- Results of sodium nitrate
and nitrite obtained from Lap-mei samples.
Year
Sodium
Nitrate
Sodium
Nitrite
No.
of Sample
No.
of Unsatisfactory Samples (%)
No.
of Sample
No.
of Unsatisfactory Samples (%)
1999
42
3
(7.1%)
42
0%
(0%)
2000
27
0
(0%)
27
0%
(0%)
Total
69
3
(4.3%)
69
0%
(0%)
Other
Preservatives
28.
We also conducted 168 tests on the non-permitted preservatives
such as benzoic acid, sorbic acid, hydroxybenzoate, sulphur
dioxide and boric acid. None of the samples
were found to have used preservatives that were not appropriate
for Lap-mei.
Colouring
Matter
29.
As for colouring matter, one out of 62 tested samples was
detected with an industrial dye namely Crocein Scarlet 7B,
resulting in 1.6% non-compliance rate. This incriminated
samples was a preserved sausage that taken in 1999.
30.
There were 26 samples containing permitted coloring matter.
Of these detectable samples, the most commonly used permitted
coloring matter was Ponceau 4R which gives a red colour.
Discussion
and Conclusions
31.
The above analyses revealed that the inappropriate use of
non-permitted preservatives in Lap-mei has not been a practice.
Nevertheless, excessive use of sodium nitrate and unlawful
use of coloring matter are notable in the past three years.
It is therefore the misuse of these substances remains a
concern.
32.
To prevent nitrite-induced intoxication and to minimize
the extent of exogenous nitrosamines formation in cured
meats such as Lap-mei, manufacturers are liable to assure
their products contain no more than the permitted levels
of sodium nitrate and /or nitrite in order to reduce the
residual nitrites in food.
33.
To this end, a standardized measurement is of importance.
In a typical traditional Lap-mei production, nitrate/nitrite
is added in a household utensil such that variation may
occur according to the experience of personnel.
Recommendation
Advice
To Trade
34.
The use of preservatives should be appropriate in accordance
with good manufacturing practice (GMP) such that they are
of food grade and be prepared and handled as food ingredient.
The amount added to food should be appropriate to fulfill
their intended purposes.
35.
To further enhance the safety of Lap-mei, the trade is recommended
to adopt the following measures during preparation and storage:
(a)
Mix the curing agents well and ensure they are evenly distributed;
(b)
Lap-mei should be adequately dried under natural or artificial
conditions; and
(c)
Store finished products under cool and dry conditions.
Advice
To Public
36.
Lap-mei, despite its nitrate/nitrite level and potential
risk of nitrosamine, its relatively high fat content is
sufficient to call for a moderation in its intake for individuals
especially for those with diabetes, heart disease and high
cholesterol. They should choose sausages with low
fat content. Nevertheless, the public is highly recommended
to maintain a balanced diet in order to safeguard their
health.
37.
Besides, infants are highly susceptible to the nitrite toxicity
and should be avoided consuming Lap-mei. As for young
children, their intake should also be restricted.
38.
Practical advice to consumers in purchasing, cooking and
storing are as follows.
Purchase
(a)
Surface should be firm and dry
(b)
Colour should be naturally pinkish (not bright red)
(c)
Surface of cross section should be firm and shiny.
(d)
Fat should be whitish without red specks.
Cooking
(a)
Remove the part of meat connected to coloured threads; and
(b)
Ensure thorough cooking (for at least 10 mins in boiling
water).
Storage
Refrigerate
unused and leftover Lap-mei.
Chart 1
Product of Preserved
Pork, Sausage and Duck
References
[1]
Binkerd EF and Kolari OE. The history and use of nitrate
and nitrite in the curing of meat. Food Cosmet.
Toxicol. 13:655(1975)
[2]
Eichholzer M and Gutzwiller F. Dietary nitrates, nitrites,
and N-nitroso- compounds and cancer risk: A Review of the
Epidemiological Evidence. Nutrition Review 1998 Apr;
56(4 Pt 1): 95-105
[3] N-Niyrosodiethylamine International
Agency for Research on Cancer (IARC) Vol.17, 1978; IARC
Suppl. 4, 1982; IARC Suppl. 7, 1987
[4]
N-Nitrosodi-n-propylamine International agency for
Research on Cancer (IARC) Vol.17, 1978; IARC Suppl. 4, 1982
[5]
N-Nitrosodimethylamine International agency for Research
on Cancer (IARC) Vol.17, 1978; IARC Suppl. 7,1987
[6]
Sodium Nitrate Summary of Evaluations Performed by the Joint
FAO/WHO Expert Committee on food Additives (JECFA) Report:
TRS 857-JECFA44/29,32
[7]
Sodium Nitrite Summary of Evaluations Performed by the Joint
FAO/WHO Expert Committee on food Additives (JECFA) Report:
TRS 859-JECFA44/29,31
Last
review date: 19-01-2005