The document discusses various chemical preservatives that are added to foods to prevent spoilage from microorganisms and undesirable chemical changes, including traditional preservatives like salt and sugar, acids like benzoic and sorbic acid, gaseous preservatives like sulfur dioxide and carbon dioxide, and antioxidants. It provides details on the mechanisms of various preservatives and guidelines for their safe use to extend the shelf life of foods while maintaining quality and safety for consumption. Chemical preservatives are carefully regulated and tested to ensure they are used at appropriate levels and for intended purposes in specific foods.

1. LECTURE 6
CHEMICAL PRESERVATION OF
FOODS

2. PRESERVATIVES
• are substances which, under certain conditions,
either delay the growth of microorganisms
without necessarily destroying them or prevent
deterioration of quality during manufacture and
distribution.
• Can be naturally occurring or synthetic
substance that is added to products such as
foods, pharmaceuticals, paints, biological
samples, wood, etc. to prevent decomposition
by microbial growth or by undesirable chemical
changes.

3. Preservatives…………
• these substances are added in very low
quantities (up to 0.2%) which do not
alter the organoleptic and physicochemical properties of the foods at or
only very little.
• This method is usually based on the
combined or synergistic activity of
several additives, intrinsic product
parameters and extrinsic factors

4. • Food preservatives, spices, and flavouring
agents have been added to foods for
thousands of years. These compounds which
are added to foods are termed as food
additives
• Chemical food preservatives are applied to
foods as direct additives during processing, or
develop by themselves during processes such
as fermentation.

5. FOOD ADDITIVES
• Substance or mixture of substance, other
than a basic foodstuff which is present in
food as result of any aspect of production,
processing, storage or packaging.
• This definition does not include any
chemicals that are contaminants pesticides,
colour additives or new animal drugs.

6. Guidelines for use of food additives
1. Additives should be used only
to maintain the nutritional quality of food,
 to improve appearance of food
2. An additive is not justified
if it reduces the nutritive value of a food,
 if it disguise faulty quality or processing and
handling that is not allowed,
 if it deceive the customer or if the desired effect
can be obtained by other manufacturing practices
that are economically and technologically
satisfactory.

7. 3. The smallest amount of additive should be used
that will produce the desired effect under good
manufacturing practices.
4. The additive used must conform to a standard
purity.
5. Additives should be subjected to adequate
toxicological evaluation and should be kept
under observation for possible deleterious effects
6. The approval of an additive should be limited to
specific foods for specific purposes under
specific conditions. Sorbet acid for example is an
approved food additive, but its use in meat was
denied because its presence could mask spoilage
produced by microorganisms.

8. Chemical Preservatives
• The purpose of using a chemical agent as a
preservative is to retard food spoilage caused
by microorganisms the WHO has estimated that
20% of the world’s food is lost by this type of
spoilage.
• Partial prevention of this spoilage can be
achieved through the use of refrigeration,
drying, freezing and fermentation.
• The use of chemical additives or preservatives
will prolong the shelf life of the food even
further

9. Chemical Preservatives
• Chemical preservatives
Interfere with the cell membranes of microorganisms,
their enzyme activity or then genetic mechanisms.
• Preservatives may also serve
 as antioxidants,
as stabilizers,
firming agents
 as moisture retainers.
• Chemicals that function to preserve the food are
generally added after the food has been processed
and before it is packaged.

10. Chemical Preservatives
• Certain preservatives have been used either
accidentally or intentionally for centuries, and
include sodium chloride (common salt), sugar,
acids, alcohols and components of smoke.
• In addition to preservation, these compounds
contribute to the quality and identity of the
products, and are applied through processing
procedures such as salting, curing,
fermentation and smoking.

11. Chemical Preservatives
• Different chemical preservatives are used, which
involves
1. Traditional chemical food preservatives
 Sugar
 Salt
2. Acidulants
 Benzoic acid
 Sorbic acid
 Lactic acid
3. Gaseous chemical food preservatives/
leavening agents
 Sulphur dioxide and sulphites
 Carbondioxide

12. Chemical Preservatives
4. Antioxidants
 Butylated Hydroxy Anisole (BHA)
 Butylated Hydroxy Toluence (BHT)
 Propyl Gallate
 Natural/Synthetic Tocophelos (Vitamin E)
 Ascorbic Acid (vitamin C) and
 Lecithin.
5. Colour additives
6. Flavour additives
7. Sweeteners
8. Emulsifiers

13. Table Sugar and salt
• Sugar is used in making jellies and cured hams.
• Salt is used in brines or is directly applied to the food.
• Their effect is to increase osmotic pressure at a level
which will prevent microorganism development.
• The cell growth of the micro organisms is inhibited or
the organism itself may be completely destroyed.
• Salt also cause dehydration by drawing out and tying
up water from the tissue of the food.
• Salt added to food also ionizes, yielding the chlorine
ion, which is harmful to micro organisms and
interferes with the action of proteolytic enzymes. The
more salt used the greater the protection afforded by
the food.

14. Table Sugar and salt
• Sugar preserving action is determined by the
ration between the total sugar quantity in the
finished product and the total sugar
concentration in the liquid phase. The
concentrations of 60% in the finished product
assures food preservation
• The food preserved with sugar, the water
activity cannot reduced below 0.845; this value
is sufficient for bacteria and neosmophile yeast
inhibition, other technique should be employed
to prevent mould growth

15. Benzoic acid
• Benzoic acid in the form of its sodium salt,
constitutes one of the most common chemical
food preservative.
• Sodium benzoate is a common preservative in
acid or acidified foods such as fruit juices,
syrups, jams and jellies, sauerkraut, pickles,
preserves, fruit cocktails, etc.
• Yeasts are inhibited by benzoate to a greater
extent than are moulds and bacteria.

16. Sorbic acid
• Sorbic acid and its salts are practically tasteless
and odourless in foods, when used at reasonable
levels (< 0.3 %) and their antimicrobial activity is
generally adequate.
• It is considered non toxic and is metabolised;
among other common food preservatives the
WHO has set the highest acceptable daily intake
(25 mg/kg body weight) for sorbic acid.
• Sorbates are used for mould and yeast inhibition
in a variety of foods including fruits and
vegetables, fruit juices, pickles, sauerkraut,
syrups, jellies, jams, preserves, high moisture
dehydrated fruits, etc.

17. Sorbic acid
• Potassium sorbate, a white, fluffy powder, is
very soluble in water (over 50%) and when
added to acid foods it is hydrolysed to the acid
form.
• Sodium and calcium sorbates also have
preservative activities but their application is
limited compared to that for the potassium
salt, which is employed because of its stability,
general ease of preparation and water
solubility.

18. Lactic acid
• This acid is the main product of many food
fermentations; it is formed by microbial
degradation of sugars in products such as
sauerkraut and pickles.
• The acid produced in such fermentations
decreases the pH to levels unfavourable for growth
of spoilage organisms such as putrefactive
anaerobes and butyric-acid-producing bacteria.
• Yeasts and moulds that can grow at such pH levels
can be controlled by the inclusion of other
preservatives such as sorbate and benzoate.

19. Sulphur dioxide and sulphites
• SO2 and sulphites may be added to such foods as
dived fruits, fruit pulp and juices, and molasses.
• They conserve colour, act as antioxidants and
control microbial growth.
• Sulphur dioxide and its various sulphites dissolve
in water, and at low pH levels yield sulphurous
acid, bisulphite and sulphite ions.
• The various sulphite salts contain 50-68% active
sulphur dioxide. A pH dependent equilibrium is
formed in water and the proportion of SO2 ions
increases with decreasing pH values. At pH values
less than 4.0 the antimicrobial activity reaches its
maximum

20. Sulphur dioxide and sulphites
• In the past cut fruits and vegetables in salads bars
were sprayed or dipped in a solution of sulphites.
• Sulphur inhibits enzymatic browning and keeps
plant tissue fresh longer. But this practice has been
banned by the FDA because there were over 100
reported cases of adverse reactions including
death.
• Approximately 5-11% of asthmatics are sensitive to
sulphates and experience symptoms such as
headaches, nausea, abdominal pains and dizziness.

21. Carbon dioxide
• Carbon dioxide is used as a solid (dry ice) in
many countries as a means of lowtemperature storage and transportation of
food products.
• Beside keeping the temperature low, as it
sublimes, the gaseous CO2 inhibits growth of
psychrotrophic micro-organisms and prevents
spoilage of the food (fruits and vegetables,
etc.)
• Carbon dioxide is used as a direct additive in
the storage of fruits and vegetables

22. Carbon dioxide
• In the controlled/ modified environment
storage of fruit and vegetables, the correct
combination of O2 and CO2 delays respiration
and ripening as well as retarding mould and
yeast growth.
• The final result is an extended storage of the
products for transportation and for
consumption during the off-season.
• The amount of CO2 (5-10%) is determined by
factors such as nature of product, variety,
climate and extent of storage.

23. Nitrates and Nitrites
• Have been used as preservatives for meats for
centuries especially in hams, bacon, bologna hotdogs
and sausages.
• Their use produces a cured meat flavour and helps
stabilize the pink colour.
• Nitrites prevent the growth Clostridium botulinum,
micro organisms that secrete a deadly toxin these
micro organisms grow in anaerobic condition readily
found in the interior of ham or in meat that has been
vacuum package.
• However, it has been found that nitrite has the ability
to react with amino acids (found in proteins of meat)
to form nitrosamines. These compounds have been
reported to include livers cancers in animals.

24. Antioxidants
• Antioxidants are beneficial in preventing rancidity in
fats and foods containing fats.
• Fats exposed to light, moisture, heat or heavy metal
ions become activated and oxidize (reach with
available oxygen) to peroxides.
• The most used antioxidants are Butylated Hydroxy
Anisole (BHA), Butylated Hydroxy Toluence (BHT),
Propyl Gallate, Natural/Synthetic Tocophelos
(Vitamin E) Ascorbic Acid (vitamin C) and Lecithin.
• BHA + BHT are frequency used in variety of products
because they are relatively stable to heat and
maintain their effect in cooked products.

25. Colour Additives
• The acceptance of food products is determined
largely by its appearance, consumers become
accustomed to standardized colours in familiar
foods and base their purchasing habits/decisions
or past experiences.
• In order to improve the colour of foods colorants
are added to carbonated beverages, frozen
desserts some dairy and baked products.

26. Flavour additives
• Natural food flavours are rarely used because the
methods required to obtain the necessary amounts
are expensive. In addition may are not uniform in
flavour quality or chemical composition and main
availability is dependent on the season.
• Suppose that a manufactures wanted to produce
bananas ice-cream, it will take 5 tons of bananas to
extract ½ litre of banana oil.
• Hence if the demand for flavourings agents in our
food supply is to be met, artificial flavourings become
a necessity.
• The flavouring agents commonly used are Esters C
pentylacetate responsible for banana flavour,
aldehyde like benzylaldehyde with cherry flavour.

27. Sweeteners
• Are added to many foods to enhance taste they
can be classified as nutritive or non nutritive.
• Nutritive sweeteners contain calories because
they are metabolized by the body to produce
energy
• Examples of nutritive sweetener include sucrose,
glucose (dextrose, fructose and invert sugar. High
fructose corn syrup)
• High fructose corn syrup are produced from corn
syrups, that have been treated with an enzyme,
glucose isomerase’s. This enzyme converts the
corn syrup to a product containing 42% fructose
50% glucose.

28. Sweeteners
• Further fractionation of the 42% HFCS result into
second generation that contains 90% fructose.
Because fructose is sweeter either sucrose or glucose,
the use of HFCS in food products permits a smaller
amount of sugar to be added especially in the
manufacture of soft drinkers
• Non nutritive sweeteners, such as saccharin do not
provide calories because they are not metabolized.
Aspartame is classified as a non nutritive sweeter
even though it is metabolized to two amino acids
(phenylalamine and aspartic acid) because the level of
aspartame used is extremely small only of aspartame
is weeded to produce a sweetness that is equivalent to
sucrose.

29. Emulsifiers
• Emulsifiers allows molecule that are mutually
antagonistic (water and oil) to mix together.
They also improve the texture, volume and
body of baked goods by maintaining an even
distribution of ingredients.
• One of the most used emulsifiers is lecithin
found naturally in milk, eggs and soybeans.

30. Lets agree on the date for the
first test