Download 10 Food Preservation Technology

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Family and LifeStyle
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Contents
Page
10 Food Preservation Technology
10.1 Food Preservation
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10.1.1 Why is Food Preservation Important?
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10.1.2 Principles of Food Preservation
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10.1.3 Methods of Food Preservation
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10.1.4 Are Preservatives Safe?
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10.2 Food Packaging
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10.3 Nutrition Labelling
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10.3.1 Why is the Nutrition Labelling Scheme
needed?
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10.3.2 What is in the Scheme?
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10.3.3 Are nutrition labels on all prepackaged food? 13
10.4 How to read a Nutrition Label?
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10 Food Preservation Technology
10.1 Food Preservation
Food is a perishable commodity. The primary objective of food preservation is to prevent
or slow down the growth of micro-organisms including moulds, yeasts and bacteria as
the growth of these micro-organisms causes spoilage of food.
10.1.1 Why is Food Preservation Important?
(A) To increase the shelf life of food as well as its supply. Although the freshness,
palatability and nutritive value may be altered with time delay, perishable foods
can be preserved to prevent spoilage and made to be available throughout the
year. In this way, preservation helps to increase variety in our diet and makes it
better balanced.
(B) To save food for future use at the time of scarcity or drought etc. after suitable
preservation and proper storage. Preservation of food also minimises the
preparation time and energy at home.
(C) To stabilise the price of food throughout the year since seasonal food can be
preserved and made available for consumption throughout the year.
10.1.2 Principles of Food Preservation
(A) Prevention or delay of the growth of micro-organisms
(i) Avoiding invasion of micro-organisms e.g. by aseptic techniques
(ii) Removing micro-organisms e.g. filtration
(iii) Inhibiting the growth and activity of micro-organisms e.g. freezing, refrigeration,
drying, anaerobic conditions, chemicals or antibiotics
(iv) Killing the micro-organisms e.g. heat or irradiation
(B) Prevention or delay of self-decomposition
(i)
Destruction or inactivation of inherent enzymes naturally existing in food e.g. by
blanching
(ii) Prevention or delay of chemical reactions e.g. prevention of oxidation by using
antioxidants
(C) Prevention of damage from insects or animals
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(i) By using suitable chemicals to kill insects or animals from destroying the foods.
(ii) By storing foods in dry, air tight containers to prevent the insects or animals from
destroying them.
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Figure 10.1
Major Food Preservation Techniques
Food preservation methods
Inhibition
Inactivation
Avoid recontamination
Low-temperature storage
Reduction of water activity
Decrease of oxygen
Increase of carbon dioxide
Acidification
Fermentation
Adding preservatives
Adding antioxidants
Control pH
Freezing
Drying
Concentration
Surface coating
Structural modifications
Chemical modifications
Gas removal
Changes in phase
transition
Hurdle technology
Sterilisation
Pasteurisation
Irradiation
Electrifying
Pressure treatment
Blanching
Cooking
Frying
Extrusion
Light
Sound
Magnetic field
Packaging
Hygienic processing
Hygienic storage
Aseptic processing
HACCP
GMP
ISO 9000
TQM
Risk analysis and
management
10.1.3 Methods of Food Preservation
(A) Asepsis
Asepsis is the absence of micro-organisms. Packaging prevents the entry of microorganisms into food.
(B) Filtration
Filtration can successfully remove micro-organisms from water, fruit juice, beer, soft
drinks, wines, etc. This method is used for liquid only. The liquid is filtered through a
sterilised filter by applying pressure. Micro-organisms in the liquid cannot pass through
the filter and may stay on one side while the liquid without micro-organisms will pass
to another side of the filter.
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(C) Anaerobic condition
Anaerobic condition means a condition lack of or containing only minimum amount of
air or oxygen. It can prevent the surviving bacteria in food from growing in the container.
The container is completely filled with food and air in unfilled space is removed or
replaced by nitrogen or carbon dioxide.
(D) Heat treatment
Heat is the most commonly used media for preservation by killing micro-organisms.
The heat treatment required depends on the kind of the target micro-organisms to be
killed and the composition of the food. Basically, heat treatment can be classified into
three categories:
(i)
Pasteurisation (temperature below 100℃)
Pasteurisation is a heat treatment that kills part of the micro-organisms present
in food using a temperature under 100℃. The temperature used ranges from 6575℃. There are two ways of pasteurisation:
❖ HTST (High temperature-short time)
Food product is heated at high temperature for a short time. For example,
milk is heated to 72℃ and held for 15 seconds.
❖ LTLH (Low temperature-long time)
Food product is heated at a lower temperature for longer period of time.
For example, milk is heated to 62.8℃ and held for 30 minutes.
(ii) Boiling or heating at about 100℃
Most fruits and vegetables can be preserved for a longer time by applying heat at
about 100℃. Inherent enzymes which initiate self-decomposition can be destroyed
after boiling at 100℃. This process is called blanching.
(iii) Sterilisation (temperature 100℃ or above)
It is a process that all micro-organisms are being killed at high temperature or
radiation. The time and temperature necessary for sterilisation vary with the type
of food. For example,
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Type of food
Temperature
Duration
Fruit and tomato
100℃
30 minutes
Vegetables
116℃
30-70 minutes
Milk
(ultra
Heat
Treatment
(UHT))
135℃
not less
then 1 second
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Table 10.2 Major differences between pasteurisation and sterilisation
Pasteurisation
Sterilisation
Function
Partial destruction of microorganisms
Complete destruction of microorganisms
Temperature
Temperature below 100℃
Temperature 100℃ and above
Advantage
Minimal damage to flavor,
texture, and nutritional quality
Long shelf life.
No other preservation method is
necessary
Disadvantage
Short shelf life.
Another preservation method
must be used, such as
refrigeration or freezing
Food is overcooked.
Major changes in texture, flavor,
and nutritional quality
(iv) Canning
Canning is a process in which over 100℃ is used for killing all spoilage organisms
and their spores as well as inactivating enzymes and sealing in sterile airtight
containers. The packaging materials for canning can be tin or glass.
(E) Use of low temperature and cold preservation
Low temperature can lower the rate of chemical reactions and the action of enzymes.
Generally, freezing can prevent the growth of most food-borne micro-organisms and
the usual temperature for cold storage is 4.5-7℃. Refrigeration temperature lowers
the growth rate of micro-organisms and chilling can slow down the enzymatic and
microbial changes in food. For frozen food, it should be stored at or below -18℃ where
the enzymatic and microbial changes may be stopped or extremely slow.
(F) Drying or dehydration
Foods are preserved by drying for a long history, especially in Chinese foods.
Mushrooms, dried shrimps and salted fish are some typical examples. Both the terms
“drying” and “dehydration” mean the removal of water. “Drying” usually describes the
process of drying under sunshine or open air. The other term, dehydration, usually
describes the removal of moisture by applying artificial heat current under controlled
conditions.
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Table 10.3 Comparison of dehydration and sun-drying
Dehydration
Sun-drying
A faster process
A slower process
Under controlled hygienic conditions U n d e r o p e n - a i r c o n d i t i o n s w i t h l i t t l e
hygienic control
Not dependent on the weather
Not possible in cloudy weather or rainy days
I n v e s t m e n t o n m a c h i n e r y a n d No machinery and processing cost is
processing cost is needed
needed
(G) Use of preservatives
Preservatives serve as antimicrobials which prevent or slow down the growth of
moulds, yeasts and bacteria. By preventing the growth of moulds, yeasts and bacteria,
preservatives can improve the safety of food as well as prevent the wastage of seasonal
surplus by making it last longer on the shelf or in the fridge. An ideal preservative
should meet the following criteria:
(i)
can inhibit the growth of a wide range of micro-organisms
(ii) should be non-toxic to humans
(iii) should not be expensive
(iv) should not affect the flavour, taste or aroma of the food product
(v) should not be inactivated by the food itself
(vi) should not promote the development of resistant micro-organisms
(vii) should kill rather than inhibit the micro-organisms
Table 10.4 Some common preservatives
Preservatives
Target
Organism(s)
Sulfites
Yeasts and
bacteria
Action
Examples of Application(s)
in Food
Antioxidant
Dehydrated fruits and vegetables,
wine, juice, sausages
Sodium nitrate Bacteria
Antimicrobial
Cured meats
Propionic acid Moulds
Antimicrobial
Bread, cakes, cheese
Sorbic acid
Moulds
Antimicrobial
Cheeses, cakes, salad dressing,
wines
Benzoic acid
Yeasts and
moulds
Antimicrobial
Soft drinks, ketchup,
salad dressings
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Table 10.5 Maximum limits of the commonly used preservatives listed in Hong
Kong Food law
Chemicals
Specific food
Maximum parts per million (ppm)
Sulfites
Cabbage, dehydrated
Cider
Coffee extract, solid
Fruit juices
Wine
2500
200
150
350
450
Sodium nitrate
Bacon
Ham
Meat, pickled
Pork, preserved
500
200
200
200
Propionic acid
Bread
3000
Sorbic acid
Cheese
Salad dressing
1000
1000
Benzoic acid
Soft drinks
Salad dressing
Ketchup
160
250
300
(Adapted from Part V (Food and Drugs) of the Public Health and Municipal Services Ordinance (Cap. 132))
(H) Use of salt and sugar
Sugar binds moisture and thus can preserve food by preventing the growth of microorganisms if a high concentration (65% or above) is used. Products such as jams and
jellies are preserved by using sugar.
Salt in high concentration (15-20%) can prevent the water from being available for
bacterial growth. It can slow down the growth rate of bacteria and thus the food is
preserved. Salt can be used in brine (salt water) or applied to food directly.
(I) Use of acids (vinegar or citric acid)
Acids lower the pH and thus inhibit the growth of many micro-organisms. It is more
effective against yeast and bacteria than moulds. About 20% vinegar (acetic acid)
prevents the spoilage of most products. It is used in the preservation of pickles, sauces
and chutney. Another acid, citric acid, is also used in the preservation of certain fruits
and vegetables. Products of jams, jellies and squashes may contain citric acid. It lowers
the pH of the food products and can prevent the growth of moulds.
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Table 10.6 Examples of acidulants used in the food processing industry
Acid
Comment
Acetic
Provides flavour, decreases pH
Sodium acetate is salt form present in vinegar
Benzoic
As sodium benzoate, effective antimicrobial agent
Occurs naturally in cranberries
Citric
Provides flavour, decreases pH, acts as chelating
and sequestering agent
Occurs naturally in citrus fruits
Lactic
Provides tartness
Malic
Provides flavour
Occurs naturally in apples
Phosphoric
Provides flavour and tartness in beverages
Enhances juiciness in meats (as phosphate)
Propionic
As calcium propionate, effective antimicrobial agent
Produced in some cheeses
Tartaric
Present in baking powder as potassium tartrate salt
Occurs naturally in grapes
(J) Irradiation
Food absorbs and is heated up by radiant energies. Radiant energies can kill microorganisms without marked increase of temperature as well as marked changes in the
nature of food. Gamma rays, x-rays and electromagnetic, ultra-violet radiations are
commonly used for food preservation. Irradiation can be used in a wide range of area
in food preservation:
(i)
Poultry products and seafood
(ii) Fruits
(iii) Prevention of sprouting in potatoes and onions
(iv) Delaying ripening in fruits
(v) Preservation of seafood
(vi) Prevention of insect infestation in dry foods and food products
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Table 10.7 Applications of food irradiation
Application
Sterilisation
Dose range
(kGy)
7-10
Up to 50
Examples of foods
Countries with
commercial processing
Herbs, spices
Belgium, Canada, Croatia,
Czech Republic, Denmark,
Finland, Israel, Korea(Rep.),
Mexico, South Africa, USA,
Vietnam
Long term ambient
storage of meat
(outside permitted
dose)
None
Sterilisation
of packaging
materials
10-25
Wine corks
Hungary
Destruction of
pathogens
2.5-10
Spices, frozen poultry,
meat, shrimps
Belgium, Canada, Croatia,
Czech Republic, Denmark,
Finland, France, Iran,
Netherlands, South Africa,
Thailand, Vietnam
China, South Africa, USA
Control of
moulds
2-5
Extended storage of
fresh fruit
Extension of
chill life from 5
days to 1 month
2-5
Soft fruit, fresh fish and China, France, Netherlands,
South Africa, USA
meat at 0-4℃
Inactivation/
control of
parasites
0.1-6
Pork
--
Disinfestation
0.1-2
Fruit, grain, flour, cocoa
beans, dry foods
Argentina, Brazil, Chile,
China
0.1-0.2
Potatoes, garlic, onions
Algeria, Bangladesh,
China, Cuba
Inhibition of
sprouting
10.1.4 Are Preservatives Safe?
All preservatives must go through rigorous safety assessment and approval procedures.
They are permitted for food use only when they are proved to present no hazard to the
health at the level of use proposed.
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Although many allergic reactions to foods are caused by natural food ingredients such
as milk, fish and peanuts, some are caused by food additives such as sulphur dioxide.
Sulphur dioxide is used as preservative in a wide range of foods, in particular soft
drinks, sausages, dried fruits and vegetables. Sulphur dioxide, benzoic acid and sorbic
acid all have long history of safe use. They are generally of low acute and chronic
toxic effects, and should not pose significant health effect to consumers upon normal
consumption of the preserved fruits and vegetables concerned.
Nitrite is mainly used in sausages, ham, bacon and pickled meat to inhibit the growth
of Clostridium botulinum. Accidental intake of large amount of nitrite can cause a kind
of blood disorder called methaemoglobinaemia. Ingested nitrite, in the presence of
protein substances in the stomach, may form N-nitroso compounds, which have been
shown to be probable human carcinogen and may increase the risk of stomach cancer.
Nitrite also occurs naturally in food like cereals and vegetables.
If consumers have balanced diets, exposure to a specific chemical will be lowered and
so is the risk.
10.2 Food Packaging
Commercially sterile foods are processed and packaged in a manner that leaves the
food free of micro-organisms of public health significance, and prevents the growth of
any microorganism under normal non-refrigerated storage condition and distribution.
This may be accomplished by aseptic processing and packaging.
Aseptic processing and packaging refers to a technique in which food is commercially
sterilised outside the package, cooled and aseptically filled in a previously sterilised
package, followed by hermetical sealing with a sterilised closure in an atmosphere
free from micro-organisms. The end product is a hermetically sealed container holding
sterile food, which can be stored for prolonged periods of time at ambient conditions.
According to the acidity, foods may be divided into low-acid foods and acid foods.
Low-acid food means any food, other than alcoholic beverages, where any component
has a pH value greater than 4.6 after heat processing. These foods are considered
perishable as pH above 4.6 may support growth of food spoilage or poisoning microorganisms such as Clostridium botulinum. A good manufacturing practice is essential
to ensure the safety and quality of these food products.
Aseptic processing and packaging of low-acid foods is a complex food manufacturing
operation. It requires careful control at all stages of production to produce and maintain
the asepsis of the food processing, filling and packaging systems. The control system
embraces a large number of operations which are inter-related.
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10.3 Nutrition Labelling
Nutrition information on food labels is an important public health tool to promote a
balanced diet, hence enhancing public health. This information assists consumers to
better understand the nutritional value of food. It enables consumers to compare the
nutritional values of similar food products and then make healthy food choices based
on the relevant nutrition information. For those who are on special diets (e.g. people
suffering from diabetes or high blood lipid), nutrition information on food labels enables
them to select suitable food and help manage their conditions.
The Food and Drugs (Composition and Labelling) (Amendment: Requirements for
Nutrition Labelling and Nutrition Claim) Regulation 2008 (the “Amendment Regulation”),
enacted by the Legislative Council on 28 May 2008, came into force on 1 July 2010.
The Amendment Regulation introduces a Nutrition Labelling Scheme which covers two
types of nutrition information on food labels, namely nutrition labelling and nutrition
claims. The Scheme requires that nutrition labels setting out the content levels of energy
and seven nutrients specified for labelling (namely protein, carbohydrates, total fat,
saturated fat, trans fat, sodium and sugars) will become mandatory for all applicable
prepackaged food products. In addition, nutrition claims made on food labels or in
advertisements of prepackaged food products will also be regulated. Manufacturers
can only use nutrition claims if their products meet specified conditions.
10.3.1 Why is the Nutrition Labelling Scheme needed?
(A) A Nutrition Labelling Scheme (the Scheme) aims to
assist consumers:
(i) to make informed food choices
(ii) to encourage food manufacturers to apply sound nutrition principles in the
formulation of foods
(iii) to regulate misleading or deceptive labels and claims.
(B) Consumers can use the information on the nutrition
label in many ways:
(i)
to compare nutritional content among different foods for a healthier choice, e.g.
to choose food lower in fat, sodium (or salt) and sugars.
(ii) to understand the nutritional content of food and estimate their contribution to the
overall diet.
(iii) to meet individual’s dietary needs.
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10.3.2 What is in the Scheme?
Both nutrition labels and nutrition claims are included in the Scheme; these two elements
serve two different purposes. Nutrition labels provide consumers with information on
energy and nutrient values of the food so that they can make use of the information
to choose foods that are good for their health. Setting conditions for nutrition claims
standardise the meaning of various claims so that consumers can know the real
meaning behind each claim. For example, when they see a claim of “low sugars”, they
can know that the product should contain not more than 5 g of sugars per 100 g/mL of
the food.
(A) Nutrition Labels
(i)
Nutrition label is a systematic way of presenting nutrition information of food
products. It is usually in a tabular format with a heading like “Nutrition
Information”, “Nutrition Facts” or “Nutrition Label”.
(ii) Once the Scheme is enforced, consumers can find “1+7” items (i.e. the values
of energy plus seven specified nutrients-protein, total fat, saturated fat, trans
fat, carbohydrates, sugars and sodium) on the nutrition labels.
(B) Nutrition Claims
(i)
Generally, claims are eye-catching descriptors found on food packages. They
can serve as a quick reference for selected nutrition information. They may
highlight the content of certain nutrients (e.g. low fat, high fibre, etc.), or tell you
how the nutritional content of a particular food product differs from another
similar food (e.g lower cholesterol), or describe the physiological function of a
nutrient which is present in the food (e.g. calcium builds strong bones). These
nutrition claims will be regulated from 1st July 2010 and they must meet certain
specified conditions before making the claims.
(ii) There are 3 main types of nutrition claims:
❖ Nutrient content claim is related to the contents of nutrients found in food. It
describes the level of a nutrient contained in a food, such as, “High calcium”,
“Low fat” and “Sugars free”. Overall speaking, there are five categories of
nutrient content claims namely “Free” claim, “Very low” claim, “Low” claim,
“Source” claim and “High” claim. Words with similar meaning may be used as
well.
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❖ Nutrient comparative claim is also related to the contents of nutrients found
in the food. Rather than describing the nutrient level, nutrient comparative
claim compares the nutrient levels of two or more similar food products, such
as “Reduced fat-25% less than the regular product of the same brand”.
Similar to nutrient content claims, wordings with similar meaning may be
used.
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For detailed conditions, please refer to the Amendment Regulation and
Technical Guidance Notes on Nutrition Labelling and Nutrition Claims:
http://www.cfs.gov.hk/english/food_leg/food_leg_nl_guidance. h t m l
❖ Nutrient function claim describes the physiological role of a nutrient in growth,
development and normal functions of the body (e.g. “Calcium builds strong
bones.”). It must fulfil several general principles, such as the claim must be
supported by science and the information about the physiological role of the
claimed nutrient must be included in the claim. Nutrient function claims that
are commonly used, such as “Protein helps build and repair body tissues” and
“Iron is a factor in red blood cell formation”, can be found on the webpage of
the Centre for Food Safety:
http://www.cfs.gov.hk/english/food_leg/files/Acceptable_Nutrient_Function_
Claims_bilingual.pdf
(iii) Nutrition claims should be used as a quick reference only. The content value of
the claimed nutrient can be found on the nutrition label. At any time, consumers
should not focus only on the claimed nutrients. Consumers are advised to refer
to the nutrition label for detailed information on the overall nutritional property of
the food product for making healthy food choices.
(iv) For instance, although a product with a “low sugars” claim should have a low
enough sugars content in order to bear such claim, consumers should refer to
the nutrition label to ascertain that the product does not have high contents of
fat or energy, particularly if he/she is interested in weight maintenance. In
addition, a product with a “sugars free” claim does not necessarily mean that
it is free of carbohydrates. Consumers, particularly diabetic patients, should
refer to the nutrition label to verify the carbohydrates content of the product.
10.3.3 Are nutrition labels on all prepackaged food?
Majority of the prepackaged food will have nutrition labels after 1st July 2010. However,
some products are exempted from the requirements due to various reasons. For
example, there may be practical difficulties for providing nutrition labels in very small
packages (e.g. a container with a total surface area of less than 100 cm2). Food,
such as tea leaves, spices and distilled water, which contain insignificant amount
(nearly zero) of energy and specified nutrients, as well as raw meat, fresh fruits and
vegetables without any addition of ingredients are also exempted from the nutrition
labelling requirements.
Furthermore, prepackaged food products with annual sales volume of 30,000 units
or below may also apply for exemption from the requirements of nutrition labelling.
Products exempted due to low volume of sales will have stickers on the packages to
indicate their exemption status. Such stickers may be in circular, square or rectangular
shapes. Sometimes, an exemption number may be found on the stickers as well.
For imported foods, they are also required to follow the labelling scheme. On the other
hand, the format of the original label is as the Nutrition Facts Panel which is under
the Federal Food Drug and Cosmetic, the USA. Food labelling is required for most
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prepared foods, nutritional labelling for raw produce (fruits and vegetables) and fish
is on a voluntary basis. The nutritional information should be labelled as the Nutrition
Facts Panel format.
Under the proposal, nutritional labels must conform to a particular way for expressing
the nutrient content, the basic format is to express the energy or nutrient content in
absolute amount in kilocalories/metric unit per 100g of food but not as Nutrition Facts
Panel format. In addition, nutritional labels should be displayed conspicuously on the
package. At present, there is no plan to regulate the format of the labels other than
those expressing the nutrient contents.
Figure 10.8 Example of a nutritional label proposed to be used in Hong Kong in 2010.
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10.4 How to read a Nutrition Label?
Sample label for Macaroni & Cheese
① Start Here
② Check Calories
③ Limit these Nutrients
⑥ Quick Guide to % DV
．5% or less is Low
．20% or more is High
④ Get Enough of
these Nutrients
⑤ Footnote
① Serving Size
To read a nutritional label, first we should identify the serving size and the number
of servings appeared on the package. Serving sizes are standardised to make it
easier to compare similar foods with familiar units, such as cups or pieces, and
followed by the metric amount like the number of grams.
② Calories (and Calories from Fat)
Calories provide a measure of how much energy is obtained from a serving of food.
The unit should be in Kcal or C.
③ Limit these nutrients
Nutrients including fat, cholesterol and sodium should be limited in their intake and
eaten in adequate amounts.
④ Get Enough of these Nutrients
Get enough dietary fibre, Vitamin A, Vitamin C, calcium, and iron in every diet.
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⑤ Footnote
The footnote in the lower part of the nutritional label indicates the statement: “% DVs
is based on a 2,000 calorie diet” on all food labels. But the remaining information in
the full footnote can be exempted if the size of the label is too small. The footnote
should be the same and should not be different from product to product.
⑥ The Percent Daily Value (%DV):
The % Daily Values (%DVs) is based on the Daily Value recommendations for key
nutrients but only for a 2,000 calories daily diet. The %DV indicates whether a serving
of food is high or low in a particular nutrient. This allows consumers to compare
different brands and also to distinguish nutrition claim of particular nutrients such as
reduced fat, or low fat by using this %DV.
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Not for Sale
The copyright of the materials in this booklet belongs to the Education Bureau. The
materials can be used by schools only for educational purpose. Written prior permission
of the Education Bureau must be sought for other commercial uses.
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