FOOD

CHEMISTRY
THE CHEMISTRY AND FUNCTIONALITY
OF WATER, CARBOHYDRATES, LIPIDS
AND PROTEINS IN THE FOOD SYSTEMS
WATER

Learning outcomes: After completing this subunit, you will be able to

1. Describe the physical and chemical properties of water such as
polarity, solubility, boiling point, freezing point, water activity,
specific heat.
2. Explain how these properties impact food quality.
3. Identify the role of water in food spoilage.
  Water, H2O, is the most abundant molecule in
food.
 It is colorless, odorless and tasteless at room
temperature.
 Water is essential for life and thus all living

WATER IS organisms contain water.

 Almost all foods contain water. The amount of
water can vary a lot between foods.

ESSENTIAL  Raw ripe tomatoes 94% water

 Milk approximately 88% water

FOR LIFE  Cooked chicken about 65% water

 Cooked salami 45% water
 butter approximately 15% etc.
 Typically, vegetables and fruits contain more
water than meats, and grains.
 PROPERTIES OF WATER
 Polarity: Water is a polar molecule. Due to this polarity, water can form hydrogen bonds
with other molecules.
 Solubility: water dissolves a variety of molecules and is thus nearly a universal solvent.
 Water dissolves molecules by two phenomenon, ionization and hydrogen bonding. Common salt, NaCl
ionizes in water and thus dissolves in water and forms a true solution. Sugar (chemistry is discussed
later) is a much larger organic molecule (macromolecule) which forms hydrogen bonds with water and
thus dissolves in water to form a true solution.
 Not everything forms a solution with water. The substances that readily dissolve in water are called
hydrophilic, while those that do not dissolve in water are called hydrophobic.
 Suspension: Such as starch in water
 Emulsions: Oil-in-water (ex. Milk), Water-in-oil (ex. butter)

What’s an emulsifier?
Image: https://seos-project.eu/marinepollution/marinepollution-c02-s14-p01.html
 PROPERTIES OF WATER CONTINUED
Boiling point is the
 Boiling point VAPOR
temperature at PRESSURE
VAPOR
PRESSURE
 What is boiling point? which VP = AP
 What is water’s normal boiling point?
 Why does the water boil at lower temperature at higher altitudes?
 What happens to the boiling point of water, when salt or sugar are added to it?

 Freezing point: What’s thawing?

 Pure water at sea level freezes at 0 °C.
 Water is the only known molecule that is less dense at frozen state than at liquid state. The density of water is the highest at 4 °C.
 The addition of solutes such as sugar lower the freezing point of water.
 The higher the rate of freezing (that is the lower the temperature of the freezing medium), the smaller would be the ice
crystals.
 The larger the ice crystals formed in frozen food the more would be the damage to the texture of the food upon thawing.
Thawing: Bringing a frozen product to unfrozen state
 PROPERTIES OF WATER CONTINUED…

 Water activity (aw)

“Water activity (aw) is the partial vapor pressure of water in
a substance divided by the partial vapor pressure of water
at the same temperature” (Principles of Food Chemistry by DeMan
et al. (2018).

 Essentially, it is an expression of relative humidity

surrounding the food system.
 Water activity does not correlate with the amount of Image: http://toidumikrobioloogiaalgkursus.weebly.com/vee-aktiivsus.html

water, rather with the amount of solute in the

mixture.
 Low water activity inhibits microbial growth, provides textural characteristics such
as crispness and crunchiness in products like snack foods and ready to eat
breakfast cereals.
 Most pathogenic bacteria growth is inhibited below about aw = 0.90 (equivalent to about 57%
w/w sucrose)
 similarly, most yeasts cease growing below aw = 0.87 (equivalent to about 65% w/w sucrose) and
most molds cease growing below aw = 0.80 (equivalent to about 73% w/w sucrose)
 Products with higher aw tend to support more microbial growth. Bacteria usually require at least
0.91, and fungi at least 0.7
 Water activity below 0.6 will cease growth of all microorganisms.

 Water will migrate from areas of high aw to areas of low aw.

PROPERTIES OF WATER CONTINUED

 Specific heat of water

 Other than Ammonia, water has higher specific heat than all known liquids because of its
hydrogen bonding. Highest specific heat means it can absorb and lose the most heat when
temperature increases or decreases by 1 °C. This is why water has a very important role in
temperature regulation.
 In foods, the high specific heat of water contributes to faster cooking.
 Food cooks much faster in boiling water (100 °C) than in oven at 100 °C. In oven, it is
the dry heat that is cooking the food. Dry heat has much lower specific heat than water.
 The higher the moisture in the air the hotter it feels. Steam (air + water) from food
causes more sever burns than dry heat coming out of the oven.
 PROPERTIES OF WATER CONTINUED

 Role of water in the osmotic pressure of the cells: A living cell is filled with fluid that is
surrounded by a semipermeable membrane. If the fluid volume in the cell increases,
the cell will burst. If there is too little fluid in the cell, the cell will shrink and too much
shrinkage will lead to cell death. In a living cell, the fluid inside is maintained by a
phenomenon known as osmosis.
 What is osmosis? (5 min)
`

 The crispiness of vegetables and fruits is dependent on the osmotic pressure of their
cells.
 The water loss from both extra and intracellular spaces lead to loss or crispiness of
the vegetables and fruits.
 To minimize this water loss, many fruits are coated with paraffin wax which seals the
pores on the fruit skin preventing evaporation. Osmosis has an application in food
dehydration discussed later in the course.
CARBOHYDRATES (CHO)

Learning outcomes:
After completing this subunit, you will be able to
1. Classify carbohydrates based on the number of saccharide molecules
2. Enumerate the sources of different types of carbohydrates.
3. Defend the recommendation of Canada Food Guide to eat more whole fruits and vegetables than
drinking their juices.
4. Differentiate between lactose intolerance and milk allergy.
5. List the properties of a variety of carbohydrates including sugars, starch, soluble and insoluble fibres.
6. Explain how these properties impact food quality traits such as color, texture and flavors.
WHAT ARE CHO? HOW ARE THEY CLASSIFIED?

 Carbohydrates are hydrates of carbon and are thus made up of carbon,

hydrogen and oxygen. Formed in green plants through photosynthesis
whereby the sun’s energy converts carbon dioxide from the atmosphere and
water from the soil into glucose (C6H12O6). Watch the video below: (2.5min)
Photosynthesis
As you learned from the video, the process
of photosynthesis produces glucose. From
this glucose, a variety of other
carbohydrates are formed in the plants.

The carbohydrates are classified as

• Sugars: Monosaccharides, Disaccharides
• Oligosaccharides
• Polysaccharides

A Saccharide is a sugar molecule.

CHO: SUGARS, MONOSACCHARIDES

 Monosaccharides- are simple sugars

 are sweet in taste

 one sugar molecule (mono means one).

 Some examples of monosaccharides are glucose, fructose, and galactose.

 Do not require Digestion.

 Monosaccharides rarely occur in freeform.

 CHO: SUGARS, DISACCHARIDES

Disaccharides
 are also called simple sugars but contain two sugar molecules connected. (Di means two).
 Disaccharides are also sweet like monosaccharides
 Require digestion.
 Some examples of disaccharides are
 sucrose (Table sugar, glucose + fructose), digested with the help of sucrase
 Maltose (malt sugar, glucose + glucose), digested with the help of maltase
 Lactose (Milk sugar, glucose + galactose), digested with the help of lactase

What happens if the enzyme needed to digest a disaccharide is not produced in sufficient amount?
Sources:
 Sugars are naturally present in plant tissues and milk. In free form sugars are mainly
present in fruits and honey. Sugar cane and sugar beets contain sucrose and are used for
making the table sugar.
 Milk is the only non-plant source of sugar.
FUNCTIONALITY OF SUGARS

 Sweetener
 Are all sugars equally sweet? The table sugar is considered a reference for sweetness; so, if it has
sweetness of 1, then lactose has a much lower sweetness level of 0.16. Maltose- 0.33-0.45, Glucose-
0.74-0.8, and Fructose is much sweeter at sweetness level between 1.17-1.75.
 How sweet a sugar tastes to us is also dependent upon our genetics.
 Sugars taste sweeter at high temperature.

 Hygroscopicity:
 Sugars are hygroscopic, that is, they attract water and adsorb or absorb water (in other words they bind
water).
 sugars can be used as humectants. Humectant is a substance that holds moisture in food. (This is
opposite to the sugars’ ability to act as a desiccant where sugar absorbs the water from the surroundings
so as to keep the material free of water).
 FUNCTIONALITY OF SUGARS

 Contributes colors and flavors through browning phenomena:

 Sugars impart brown color and many flavors to foods such as baked goods, gravy, etc. in two
prominent ways:
1. Caramelization: When dry heated at high temperatures, sugars melt and turn brown. This is called
caramelization. This leads to the development of not only the brown color but also the caramel
flavors. Think Crème brûlée.
2. Maillard reaction: This is a non-enzymatic reaction between a reducing sugar (all
monosaccharides and most disaccharides except sucrose are reducing sugars), and an amino acid
(amino acids are the smallest subunits of proteins). When heated, these sugars and amino acids
undergo a series of reactions which lead to the production of a complex mixture of brown
compounds called melanoidins, which also impart distinct aroma.
Maillard reaction
FUNCTIONALITY OF SUGARS
• Reducing the freezing point
• Sugars affect the freezing point of foods. The higher the concentration of sugar, the lower
the freezing point.
• It reduces the risk of large crystals of ice formation in frozen desserts.
• Crystallization
• When the supersaturated sugar solution is cooled, the sugar starts to separate from the
water and starts to recrystallize. This is the principle of candy making.
• If you wish to make a hard candy, you should let this solution cool slowly without disturbing
it. This would result in large sugar crystals desirable in such candies.
Rock candy (6 min)
• If you are making a fudge, the sugar crystals must be very fine. To make such candies, the
supersaturated solution should be cooled rapidly with agitation.
What’s a super-
saturated solution?
CHO: OLIGOSACCHARIDES
 Oligosaccharides contain 3-10 sugar molecules connected (Oligo means a few).
 Oligosaccharides are water soluble
 Common examples: raffinose, stachyose, and verbascose are made up of three, four, and five sugar
molecules, respectively.
 Humans do not have the enzymes to digest oligosaccharides and therefore they pass unchanged to the
colon (large intestine), where the normal intestinal bacteria ferment them to gases (methane carbon
dioxide and hydrogen). Present in significant amounts in dried beans light kidney beans, black beans,
lima beans etc.
 Consumption of beans can cause flatulence or gas because of the fermentation of the oligosaccharides
in colon.
 Because oligosaccharides are water soluble soaking the beans in tap-water for a few hours is a good
way to get rid of these oligosaccharides before cooking the beans. This can reduce the flatulence
caused by the beans.
CHO: POLYSACCHARIDES

 Polysaccharides- are complex

carbohydrates that contain more
than 10 but typically hundreds of
sugar molecules connected (poly
means many). Polysaccharides
are classified as starches, fibres
and glycogen.
 CHO: POLYSACCHARIDES, STARCH
 Polysaccharides- are complex carbohydrates that contain more than 10 but typically hundreds of sugar molecules
connected (poly means many). Polysaccharides are classified as starches, fibres and glycogen.

 Starch
 is a storage form of carbohydrates in plant cells.
 Pure starch is a white, tasteless and odorless powder that is insoluble in cold water.
 It is made up of hundreds and thousands of glucose molecules only.
 There are two types of starch molecules, amylose and amylopectin. Amylose is linear chain of glucose molecules
while amylopectin is highly branched.
 The proportion of amylose and amylopectin varies in different species and varieties of plants. Normal starch
consists of approximately 25% amylose and 75% amylopectin. The starches that contain no amylose are called
zero-amylose or waxy starches. Low amylose starch contains approximately 5% amylose while high amylose starch
contains more than 40% amylose.
 In nature, starch polymers are packed in granules called starch granules. The size of granules also varies.
 Human digestive system produces the enzymes required for the digestion of starch. When completely digested
starch is broken down into monomers of glucose.
FUNCTIONALITY OF STARCH

Sources: Plant foods such as potatoes, yam, cassava, cereal grains, beans and lentils
are good sources of starch. Typically, starchy foods are staple for humans, and thus
starch is the major carbohydrate in human diet. Starch is often extracted from corn,
rice, potatoes and other plant sources and is used in a variety of food products
discussed below.
FUNCTIONALITY OF STARCH

Starch gelatinization, pasting, gelation, retrogradation and syneresis. Gelatinization,

gelation, retrogradation and syneresis
Please watch the videos above and below to understand the phenomena.
Gelatinization under light microscope
Due to the property of gelatinization of starch, it is used as a thickener in food industry
and in our kitchens, for example in technique soups and gravies. The ability of the
starch to form a paste makes it an excellent binder, for example binding proteins in
meat or plant patties. The ability of the starch to form a three-dimensional gel is very
important for the gel like soft texture of baked goods, puddings etc.
FUNCTIONALITY OF STARCH

▪ Due to the property of gelatinization of starch, it is used as a thickener in food

industry and in our kitchens, for example in technique soups and gravies.
▪ The ability of the starch to form a paste makes it an excellent binder, for example
binding proteins in meat or plant patties.
▪ The ability of the starch to form a three-dimensional gel is very important for the
gel like soft texture of baked goods, puddings etc.
 FUNCTIONALITY OF STARCH

• Dextrinization: When starch is heated in the absence of water, it turns brown and starts
to breakdown a little, such that smaller chains of starch are formed. These chains are
sweeter than the raw starch. This is called dextrinization. Dextrin is a mixture of partially
broken-down fragments of starch. The fragments can be as small as two glucose molecules
(maltose) but are of various lengths depending on the extent of breakdown. This
dextrinized starch tastes sweet, has flavor, color and aroma. This is reason why the turkey
gravy tastes so good! Dextrinization also reduces the starch’s ability to form a gel.
 FUNCTIONALITY OF STARCH

• Starch as a sweetener: Native starch is tasteless even though it is made up of glucose molecules. Bound
glucose molecules are unable to bind to our taste receptors and thus we cannot taste them. But if the starch
is hydrolyzed, the glucose molecules start to become free which can bind to our taste receptors, and thus
taste sweet. Thus, starches are being used to make sweeteners.
• Corn syrup is one such example. Corn starch and water mixture is treated with alpha and beta-amylases
which are the enzymes that help hydrolyze starch. As these enzymes breakdown the starch, the mixture
starts becoming sweeter.
• How sweet is the corn syrup? Corn syrup is not as sweet as sucrose solution because it only contains
glucose, while sucrose contains glucose and fructose.

What’s hydrolysis?
FUNCTIONALITY OF STARCH

 High fructose corn syrup (HFCS)

 As the name suggests this is also made from corn starch but it contains fructose in addition
to glucose. The more fructose you have, the sweeter the syrup would be. To make high
fructose corn syrup glucose isomerase enzyme is used to convert some of the glucose into
fructose. HFCS 42 means that this syrup contains 42% fructose and 58% glucose in water.
CHO: POLYSACCHARIDES: GLYCOGEN

 Glycogen is also made up of hundreds and thousands of glucose molecules but is

more branched than starch.
 This is the storage form of carbohydrate in human beings and other animals, mainly stored in their
liver and muscles.
 Human body produces enzymes to break down glycogen as well.
 The meat we consume is mainly animal flesh which is mostly muscle mass.
 Even though muscles store glycogen, the meat has little glycogen.
 When an animal is slaughtered, its glycogen is used up and this leads to the formation of lactic
acid. Thus meat, other than liver, is not a significant source of carbohydrates.
CHO: POLYSACCHARIDES: DIETARY FIBRES

 Dietary fibre is another type of polysaccharides that is part of plant material.

 It is resistant to enzymatic digestion in human digestive system. Our digestive system
doesn’t produce the enzymes required for the breakdown of fibres.
 Cattle can digest fibre. Their digestive system includes a four-chambered stomach. The
microbes in their rumen produce the enzymes to break down fibre.
 Fibre includes cellulose, noncellulosic polysaccharides such as hemicellulose, pectic
substances, gums, mucilages and a non-carbohydrate component lignin.
 One way to classify fibres is by its solubility. Some fibres are water soluble while others
are water insoluble.
 DIETARY FIBRES: SOLUBLE VS. INSOLUBLE
 Water soluble fibres
 Dissolve in water and increase the viscosity of the water. Therefore, these fibres are also
What’s chyme?
known as viscous fibres.
 Examples: Certain hemicelluloses, pectic substances, gums and mucilages
 These fibres when consumed increase the viscosity of the chyme in our digestive system.
This leads to slow movement of the chyme through our digestive system. - peristalsis
 This slowed movement results in keeping our stomach full for a longer period and slows
down the absorption of nutrients through the intestinal wall.
 The slow absorption of glucose prevents sharp increase in blood glucose levels.
 Water soluble fibres also lower the blood cholesterol levels and thus may reduce the risk
of heart diseases. (This is why oats are often advertised as heart-healthy) beta-glucan
 Sources: beans (kidney beans, black beans, lima beans, chickpeas etc.), vegetables (esp.
Brussel sprouts, broccoli etc.), fruits (esp. oranges, grapefruit, pear, apple etc.), and some
cereal grains (oats, barley and rye). Images:
https://gfycat.com/farawaywickedgoosefish
 DIETARY FIBRES: SOLUBLE VS. INSOLUBLE

 Water-insoluble fibres
 do not dissolve in water and thus have no impact on the viscosity of water. These fibres are also
known as non-viscous fibres.
 Examples: Celluloses, some hemicelluloses and lignin are insoluble fibres. These fibres are present
in the outer layers of all plant foods such as fruit peels, vegetables, whole grains, beans etc. The
removal of outer layers of fruits, grains and beans results in significant loss of insoluble fibres.
 Insoluble fibres also bind minerals, phytochemicals and some vitamins. With the loss of insoluble
fibres, much of these nutrients and non-nutrient compounds are also lost.
 Thus, the Canada Food Guide recommends consuming whole grains rather than refined grains.
APPLICATIONS OF FIBRES IN FOOD INDUSTRY

 For improving texture: Soluble fibres increase the viscosity and bind water. Thus soluble fibres are
often added to baked goods to retain water in the baked goods and to slow down starch retrogradation
and syneresis.
 As a bulking agent in reduced-sugar applications: Soluble fibres can replace some of the sugar in
food because sugar and soluble fibres both hold on to water.
 To manage moisture in the replacement of fat: They can give creamy smooth texture to low fat
frozen desserts.
 to add colour: Fibres, especially insoluble fibres are bound to many color compounds especially in
vegetables and fruits. Adding fruit and vegetable fibre to grain products can add colors to such
products. These color compounds and other phytochemicals may act as natural antioxidants.

What’s a gel?
 APPLICATIONS OF FIBRES IN FOOD INDUSTRY

 Special type of soluble fibres called Pectic substances are present in both cell walls and in space between plant
cells and aid in cementing plant cells together. These fibres form a transparent gel under special circumstances
and have a wide application in fruit jam and jelly industry. Pectins are made up of D-galacturonic acid (a
modified galactose monomer). Some of these monomers are esterified with a methyl group. CH3=methyl
 There are two main types of pectins present in plant material, high methoxy and low methoxy pectins (HM
and LM pectins).
1. HM pectin forms a gel at pH below 3.5, and at least
55% sugar.
2. LM pectin can form gel between pH 2-7, without any
sugar, but requires the presence of calcium ions to
form a three-dimensional gel. Thus LM can be used
to make low sugar jams and jellies.

Image: http://www.journalijar.com/uploads/774_IJAR-14400.pdf
LIPIDS
Learning outcomes: After completing this subunit, you will be able to
1. Differentiate between fats and oils and identify their sources in human diet.
2. Identify the general structures of triglycerides, phospholipids, sterols, saturated, unsaturated (mono
and poly) fatty acids, trans fats.
3. Explain the chemical changes taking place during hydrogenation.
4. Defend the recommendation of Canada Food Guide to replace some of the animal source protein with
plant source protein, and to include fish in our diet.
5. Discuss the health impact of different types of lipids in our food.
6. List the properties of lipids in foods.
7. Explain how these properties impact food quality traits such as color, texture and flavors.
LIPIDS, FATS AND OILS
 Mainly made up of C, H and O
 Lipids are organic macromolecules that are generally insoluble in water but are soluble in non-
polar solvents such as alcohol and ether.
 Based on their physical properties, lipids are broadly classified as fats and oils. Fats are solid at
room-temperature (22 degree Celsius), while oils are liquid at room-temperature.
 Sources of fats: most animal foods such as beef, chicken, turkey, pork, and mutton contain lipids
that are solid at room temperature. The lipid in fish however is not a fat. Amongst plant foods,
solid lipids are present in coconut (coconut oil is not an oil), palm oil (a fat).
 These plant lipids are wrongly called oils. This misnomer exists probably because most plant
lipids are liquid at room temperature (oils) except for palm and coconut oils.
 Sources of oils: Most plant lipids such as the lipids from canola, rapeseed, grapeseed, olives,
sunflower seed are liquid at room temperature and are thus called oils. As noted above, fish lipids
are called oils, and these days duck oil is gaining popularity as well.
CLASSIFICATION OF LIPIDS, TRIGLYCERIDES

Based on the chemical structure, lipids are broadly classified as triglycerides, phospholipids, and sterols.
(Other classes such as sphingolipids, waxes etc. also exist)
 Triglycerides: Also called triacylglycerols, is the major form of dietary lipid in fats and oils, whether
derived from plants or animals.
 Approximately 95% of all lipids in nature are triglycerides. A triglyceride is composed of three fatty
acids esterified to a glycerol molecule.
 Please watch the following clip to learn about the chemical structure of a triglyceride. The video clip
also talks about the different types of fatty acids (short, medium, and long chain; saturated vs unsaturated
(mono and polyunsaturated); cis vs trans fatty acids) and their physical and chemical properties.
Fatty acids, triglycerides and hydrogenation

Saturated, Monounsaturated, polyunsaturated

 CLASSIFICATION OF LIPIDS, TRIGLYCERIDES

 The more solid a lipid at room temperature the more saturated fatty acids it contains. Butter,
pork fat (lard), Beef fat (Tallow), chicken fat, turkey fat, and most animal fats other than fish oil are
all solid at room temperature and contain high amounts of saturated fat. Hydrogenated oils are also
high in saturated and trans fatty acids and are solid at room temperature.
 Oils are low in saturated fatty acid and high in mono and polyunsaturated fatty acids
 High intake of saturated and trans fat intake is linked with an increased risk of heart diseases. The
more animal-source foods, and processed foods we consume, the higher our intake of saturated
and/or trans fats.
 Unsaturated fatty acids provide some protection against heart diseases if not consumed in
excess.
 This is one of the reasons the Canada Food Guide recommends replacing some animal-based
protein foods with plant-based proteins in our diet and including fish in our diet.
 CLASSIFICATION OF LIPIDS: PHOSPHOLIPIDS

 Phospholipids: Phospholipids have two fatty acids and phosphorous containing

molecule attached to glycerol molecule. The fatty acid chains are hydrophobic while
phosphorous is hydrophilic, this gives phospholipids a unique property to bind fats and
water which otherwise are immiscible. Thus, phospholipids act as emulsifiers. An
emulsifier is a substance that can keep two immiscible states mixed.

 Please watch the following video clip to understand the structure of a phospholipid:

Phospholipids (6-7 min)

CLASSIFICATION OF LIPIDS: STEROLS
 Sterols: Sterols are a class of lipids containing a common steroid core of a fused four-ring structure with a
hydrocarbon side chain and an alcohol group.

 The most common form of a steroid in animal cells is cholesterol. Cholesterol is part of all animal cells and
plays important functions in our body.
 Health concern about cholesterol: For about 1/3rd of human population, high intake of dietary cholesterol may
increase the risk of their heart diseases. Saturated and trans fatty acids pose more risk than dietary cholesterol.

Sterols: cholesterol

 Though cholesterol is present in animal tissues only (meat, eggs, milk etc), cholesterol like compounds are often
found in some plant foods and are called phytosterols. They are present in significant amounts in beans (soybeans),
nuts and oil seeds. Research is ongoing to learn about their effects on human health. Early studies show that they may
reduce the risk of certain types of cancers. More evidence is needed to confirm such findings.
SPECIAL TOPIC: LIPIDS AND HUMAN HEALTH

Read: Trans fats and health

 Discuss: Is margarine better for health than butter?
 Discuss: Which oil is ideal for cooking?
 Discuss: Is olive oil better than canola oil?
PROPERTIES AND APPLICATIONS OF LIPIDS IN FOODS
 Frying: Lipids are used for frying. Most oils and fats can be heated to
temperatures higher than 160°C, many can be heated to well above 200°C.
Flax seed oil however has a smoke point of 107°C. The smoke point, also
known as the burning point, is the temperature at which an oil or a fat starts
producing a steady stream of smoke and can’t be heated beyond that
temperature. Since oils and fats can be heated to a much higher temperature
than water (boiling point, 100°C), thus food cooks much faster when fried
in hot oil or fat than in boiling water.
 How are potato chips made (4 min)
PROPERTIES AND APPLICATIONS OF LIPIDS IN FOODS

 Plasticity: Plasticity is the ability of a solid material to undergo

permanent deformation, a non-reversible change of shape in response to
applied forces. Solid fats exhibit this property thus such fats spread easily
and are used in a variety of spreads. Due to the property of plasticity, fats
are also widely used in baking, and are a major contributors in the baked
goods’ texture
PROPERTIES AND APPLICATIONS OF LIPIDS IN FOODS

 Flavouring property:
 Fats and oils provide distinctive flavours. Butter has a different flavour profile than
olive oil, for example. Fats and oils are important flavour enhancers in salad
dressings, baked goods, cheeses etc.
 Fats mask undesirable flavors such as bitterness. Compare regular cream cheese
with low fat cream cheese. You will notice more bitterness in low fat cream
cheese.
 This is why food processors often add other ingredients such as sugars, salts,
herbs, fat replacers etc in low fat products to compensate for the fat.
 Oils are used to retain flavours in dried herbs.
 Chemicals that contribute aroma (flavour = taste +aroma) in herbs and spices are volatile and thus
escape easily. For example, dried basil leaves like most herbs, eventually lose their flavour over
time. Oils can trap these aromas. This is why we see products like garlic infused olive oil.

▪ Please do not store home made herb infused oils, use them promptly. If not prepared properly,
and if any moisture enters the herbs, such oil can be an ideal breeding ground for anaerobic
bacteria ( ex. Clostridium botulinum about which we will learn more later).
 PROPERTIES AND APPLICATIONS OF LIPIDS IN FOODS

Tenderness: Plastic fat provides tenderness to the food product. This why the baked goods like cakes,
muffins, croissants, biscuits are tender.
 Farmers would add extra fat to animals’ diet a few days before slaughter to increase the fat content and
distribution in the meat.
 As we are rightly mindful of our saturated fat intake, lean meats (meats that contain less than 10%
fat) and extra lean meat (less than 5% fat) are preferred
 Meat contains two main types of fats based on the location of fat, cover fat and marbled fat.
 The higher the marbled fat, the more tender the meat is upon cooking.
 The cover fat though contributes to the flavour; it has little impact on meat tenderness.

Watch the following video to see the impact of marbling on

consumers’ preference for steak:
Steak marbling and tenderness (5 min)
PROTEINS: CHEMISTRY AND FUNCTIONALITY IN FOOD

Learning outcomes: After completing this unit, you will be able to

1. Identify the basic structure of an amino acid.
2. Explain the primary secondary, tertiary and quaternary structure of proteins.
3. Define denaturation and identify the role of a variety of denaturing agents in food
quality.
4. Identify desirable and undesirable effects of protein denaturation in food processing
5. List the properties of proteins in foods.
6. Explain how these properties impact food quality traits such as color, texture and
flavors.
 PROTEIN CHEMISTRY
 Proteins are chain(s) of amino acids linked with peptide bonds. (amide bonds)
 Twenty amino acids form the building blocks of most proteins in our body and our
food.
 Amino acids are linked by peptide (amide) bonds formed between amine and
carboxylic acid groups of neighbouring amino acids in the polypeptide sequence.
 Over 300 naturally occurring proteins have been reported. These can confer distinctive
and interesting properties to some food systems.

Watch the following

Amino acids and polypeptide bond
PROTEIN STRUCTURE

Each protein has a unique

sequence of amino acids, and
thus a unique structure. There
are four levels of protein
structures:
 PROTEIN STRUCTURE
 Primary: Primary structure is a linear structure and indicates the sequence of amino acids in the
chain(s).
 Secondary structure: The backbones of amino acids in a polypeptide chain form hydrogen
bondings with one another, leading to the folding of the chain. This leads to a two-dimensional
structure of the protein. The two most common folding patterns are alpha helix and beta sheets.
 Tertiary: The side chains of the amino acids in a polypeptide chain interact with one another and
lead to the folding of the beta sheets or alpha helices (secondary two-dimensional structure). This
folding results in a three-dimensional protein structure. The specific sequence of amino acids
determines the type of interactions and thus the three-dimensional shape. Since each protein has a
unique amino acid sequence thus each protein has a unique three-dimensional shape. This shape is
critical to the protein functionality.
 Quaternary: Many proteins are formed from multiple (2 or more) polypeptide chains. These are
called subunits of the protein. The interactions between the subunits results in a unique shape of the
protein. This is called quaternary structure of proteins that are made from multiple polypeptide chains
 PROPERTIES AND APPLICATIONS OF
PROTEINS IN FOODS

1. Denaturation of proteins: Reversible or irreversible change

in the protein shape is called denaturation. Some of the
denaturing agents are listed below:

 pH change (Acid): Hydrochloric acid is produced in our

stomach primarily to denature the food proteins.

What’s pH? Image:https://library.sweetmarias.com/glossary/acidity/

 PROPERTIES AND APPLICATIONS OF
PROTEINS IN FOODS

 Heat: Heating an egg denatures its proteins, leading to solidification of the egg.
If our body temperature rises above 108°F (42.2°C), the enough cell proteins
would denature, to cause death. We cook meat to a certain minimum internal
temperature, not just to denature meat proteins but also to kill bacterial cells by
denaturing their proteins by heat. This makes the meat safe for consumption.
 Alcohol: When we consume alcohol (ethanol), it penetrates our cells and denatures
cell proteins. Thus, alcohol is considered a toxin, not a nutrient even if it provides
energy. Alcohol is used as a disinfectant to denature the proteins of the microbial cell.
 UV radiations: Exposure to strong UV radiations causes denaturation of some of the
proteins in our skin cells. This damage to our skin cells is commonly called “sun burn”.
In rare cases, repeated, prolonged exposure can cause skin cancer.
 Heavy metals (ex. Mercury): Mercury can denature our cell proteins and thus
ingesting mercury by accident leads to mercury poisoning.
 PROPERTIES AND APPLICATIONS OF PROTEINS IN FOODS

2. Water holding capacity and solubility

 Depends on the pH of the medium and the type of amino acids.
 The pH at which a protein has a net zero charge, such that the number of positive and negative
charges is equal, that pH is called the protein’s Isoelectric point (IP).
 Different proteins have different isoelectric points.
 At its IP, a protein is least soluble and has the lowest water holding capacity because at this pH,
proteins shrink and start losing their water.
 Meat structure (Please watch)

• Actin (thin filaments) and myosin (thick filaments) are major proteins in myofibrils
• In connective tissues, you have collagen and elastin as the proteins
• Myoglobin (pink)– the protein that carries oxygen to muscles (some hemoglobin is also there)
 When an animal is slaughtered, its glycogen stored in the muscles is converted into lactic
acid. This acid lowers the meat pH to 5.2-5.4 which is the isoelectric point of major muscle
proteins (actin and myosin). As the pH drops to the IP, the muscle cells start losing their
water. This water seeps into extra-cellular (outside the cell) spaces making the meat soft,
pale and exudative (dripping fluid).
 Collagen (IP = 8.26) at pH 5.2-5.4 is highly soluble and thus imparts softness to the meat.
Thus, lactic acid production is important for the juiciness of the meat.
 Tough meats are sometimes marinated before they are cooked. This marinate often
contains an acidic ingredient (vinegar, lemon juice, yogurt etc). This lowers meat pH and
thus make the meat soft.
PROPERTIES AND APPLICATIONS OF PROTEINS IN FOODS

Water holding capacity and solubility continued….

 In dairy industry, acid (such as vinegar, citric acid etc) is added to hot milk. Fresh milk pH is
between 6.5-6.7. When an acid is added the pH drops. At pH 4.6, casein proteins of milk
coagulate as they are no longer soluble in the milk. This coagulum of the milk is called curd
which can be used for making some types of cheeses such as Ricotta and Paneer. Most
cheeses are however formed by coagulating casein proteins by enzymes (the enzyme
mixture is called rennet).

How is cheese made?

(10 min)
PROPERTIES AND APPLICATIONS OF PROTEINS IN FOODS

Texture
 Proteins are important for the fibrous texture of the meat. Those who consume meat relish it
partly because of the fibrous texture that is very hard to achieve from a plant protein.
 The muscle fibres, their length and thickness, are the determinants of the fibrous texture of meat.
Impossible burger (6 min)

Gelation
 Some proteins solubilize when heated with water. Upon cooling they form a three-dimensional soft
structure called a gel. One such protein commonly used in food industry is collagen. When solubilized
upon heating with water, it is termed as gelatin. Gelatin is used in many products such as marshmallows,
Jell-O, many frozen desserts, etc.
PROPERTIES AND APPLICATIONS OF PROTEINS IN FOODS

Color: Some proteins impart color to the food.

 For example, most meats have a degree of pink/red color which is due mainly to a
protein called myoglobin, and to a lesser extent due to hemoglobin.
 While hemoglobin supplies oxygen to all the cells in the body, myoglobin supplies
oxygen to muscles only
 When an animal is slaughtered the myoglobin (pink) gets exposed to the oxygen in
the air.
 Oxymyoglobin which is bright red in color. How can you prevent the
 Metmyoglobin is brown in color (undesirable to the consumers) formation of metmyoglobin
in raw meat?
 Oxidized form
 Nitrates and nitrites in processed meat
 PROPERTIES AND APPLICATIONS OF PROTEINS IN FOODS
Emulsification and fat holding capacity
 Proteins are made up of amino acids, which may have hydrophobic or hydrophilic side chains. If on the
surface of a protein there are both hydrophobic and hydrophilic side chains, such a protein acts as an
emulsifier.
 Milk protein casein is an excellent emulsifier and is often added to processed meat products such that
the fat doesn’t separate from the food and the surface doesn’t feel greasy. Hot dogs
Enzymes
 Most of the known enzymes except ribozyme are proteins.
 In all living cells, all chemical reactions are catalyzed by enzymes. What’s an
emulsifier?
 Enzymes are specific in their action
 As you saw earlier, cheeses are generally made by the action of enzymes (enzyme mixture is called
Rennet) Renin is the enzyme.
 Another common use of enzyme in food industry is in meat tenderization. Eg: Papain enzyme.
PROPERTIES AND APPLICATIONS OF PROTEINS IN FOODS
Foaming properties of proteins
 Foam is a mixture air and a liquid. The air is trapped in the fluid to form a solid three-dimensional structure.
 Eggs contain a variety of proteins. The main protein in the albumen (egg white) is ovalbumin. Ovalbumin
has the highest foaming capacity amongst all food proteins. This is why eggs are added in cakes, meringue and
several other baked goods when a spongy product is desirable.
 Foaming capacity is the maximum foam volume achieved from a certain amount of a protein dissolve in a
specific conditions.
Foaming capacity and foam stability (3min)

 Food scientists have created egg white substitutes but continue to look for better alternatives. Some students
at our university made an egg white substitute from chickpea proteins.
PROPERTIES AND APPLICATIONS OF PROTEINS IN FOODS
Three-dimensional network formed by wheat proteins
 Wheat proteins called gliadins and glutenins which together form a viscoelastic
structure called gluten. The strength of gluten determines the loaf volume of wheat
bread.
 Rye has significant amounts as well. Barley has trace amounts of gluten-forming
proteins. Triticale (Wheat x Rye)
 Wheat breads are the most common types of breads.
Gluten structure (10 min)
 Pasta is typically made from a special type of wheat called durum wheat. This
gluten of durum wheat has very high strength, which is not suitable for breads, but
durum can be mixed with another wheat flour to improve its gluten strength. The main
use of durum is in pasta though because pasta dough passes through extruders at very
high pressure.
 SPECIAL TOPIC: CELIAC DISEASE AND GLUTEN INTOLERANCE

Discuss
 What is this disease? It is an autoimmune disease
 Which grain products are considered safe for people with this condition?
 Rice, amaranth, buckwheat, millets, corn, quinoa
 Which grains are considered unsafe for people with this condition?
Image source: https://www.beyondceliac.org/celiac-disease/