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LECTURE 6
CHEMICAL PRESERVATION OF
FOODS
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.
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
• 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.
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.
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.
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.
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
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.
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.
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
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
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.
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
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.
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.
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.
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.
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
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
Lets agree on the date for the
first test

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Lecture 5 chemical preservation of food

  • 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