Week 3 & Week 4: Carbohydrates
Introduction & Monosaccharides: simple sugars, building blocks of carbohydrates ✅
Oligosaccharides & Polysaccharides ✅
Starches ✅
Starch Applications ✅
Other Polysaccharides Application
3 Chemical functional groups
(R-OH) Hydroxyl group
Ketone group 
Aldehyde group 
in Ketose
in Aldose
are Reducing sugars
contains chiral carbon atoms: One that can exist in two different spatial arrangement that can not be superimposable on each other.
D-sugars vs L-sugars: L-sugars are less numerous and less abundant in nature ✅
D-glucose is the most abundant carbohydrate
When it is written in an open or vertical straight-chain fashion, the aldehyde group (position 1) at the top and the primary hydroxyl group (position 6) at the bottom
The mirror image is known as a L-glucose
It contains a polyalcohol and an aldehyde
D-fructose is a prime example of this type of sugar
Isomerisation catalysed by either a base or an enzyme can converted the ketose into aldoses
Ring formation
✅
Carbonyl groups of aldehydes are reactive and easily undergo nucleophilic attach by the oxygen atom of a hydroxyl group to produce a hemiacetal
D-Glucose ring formation
It is the hemiactel that is involved in most reactions of glucose
Hemiacetal can react with alcohol to produce a condensation effect to form glycosidic links
Carbon 1 and carbon 5 react to form the ring structure
fructose, the ring structure is formed by ketone group on C2 and hydroxyl at carbon 5
Sugar with free aldehyde in open chain configuration can reduce cupric ions (Cu2+ )to cuprous ions (Cu+)
Only open chains are able to produce a reducing effect
cause non-enzymic browning in food
Open chain has the active aldehyde and monosaccharides can only act as reducing sugar in this form
Formation of red precipitate in Fehling solution is dependent on open chain because equilibrium exist
produce brown colour that are desirable and important in some foods
Common browning of foods on heating or on storage is usually due to a chemical reaction between reducing sugars, mainly D-glucose and a free amino acid or a free amino group – Maillard reaction
Maillard reaction may be produced by frying, roasting, baking or storage
Oligosaccharides: contains 2 to 20 sugar units joined by glycosidic bonds ✅
Glycosidic bonds: Joins 2 monosaccharides.
formed by condensation reactions: one molecule of water is released during the joining of two monosaccharides
Hydrolysis
3 examples
Maltose: Obtained by hydrolysis of starch using enzyme β-amylase
Lactose: Primary carbohydrate source for developing mammals, Occurs mainly in milk
Sucrose: not crystallised, has got great hydrophilicity and solubility, can form highly concentrated solutions of high osmolality
during malting of grains especially barley
Can be used as a mild sweetener for foods
to utilise lactose for energy, hydrolysis must occur first.
Ingested lactose that is only partially hydrolysed, it results in lactose intolerance
Lactose that passes into the large intestine can undergo anaerobic bacterial fermentation to lactic acid and gases. This can result in diarrhea, bloating and cramping
Lactose that is left present in the lumen results in fluid retention within the gut producing abdominal distention and cramps
Fermentation process to produce yogurt, buttermilk etc. reduces/ removes lactose in milk, decreasing the effect of lactase deficiency
Can be used as sweeteners, preservatives and humectants
Polysaccharides: polymers of monosaccharides
High molecular weight
Either linear or branched units
✅
Two classification
Homoglycans – made up of same sugar units e.g. starch or cellulose
Heteroglycans – made up of two or more different monosaccharide units e.g. guar gum, locust bean gum
Functionality in Food
Modify and control mobility of water in food systems
Used as thickener
Acts as a gelling agent
Modify and control rheological properties
Produce high viscosity at low concentration
Acts as cryostabilisers – produces freeze-concentrated matrix that limits molecular mobility or restricts ice crystal growth
Properties
Occurs naturally as discrete particles (granules)
Relatively dense
Insoluble
Hydrate only slightly in cold water
Can be dispersed in water to produce low viscosity slurries
Viscosity building (thickening) only occurs when a slurry of granules is cooked
Consists of a mixture of two polymers ✅
Amylose: linear
with 1 4 linked -D-glucopyranosyl units
✅
Amylopectin: highly branched
Consist of linear - 1,4 linked D-glucose units with (16) branch points every 15 to 20 glucose units
✅
Double helix structure
Hydroxyl groups are positioned on the exterior of the coil
Interior of helix contains only hydrogen atoms and is lipophilic
Most starch contain about 25% amylose
High amylose corn can contain about 52% or 70-75% amylose
2 Properties
Able to form light polymer network after gelatinisation
Able to form complexes with lipids and proteins
Presence of these complexes also inhibit starch swelling, prevents excessive water absorption of amylopectin to better maintain starch integrity
helps strengthen the formation of protein network
Constitute about 75% of most common starches
Waxy starch – consist entirely of amylopectin
2 properties
Chain branching also retards gel formation
Better solubility
Amylose and amylopectin molecules are arranged radially: Forms crystalline and non-crystalline regions
Crystalline areas (dense area) are formed by clustered branches of amylopectin
Dense layers of starch granules alternate with less denser amorphous layers
In Starch Granule ✅
2 types
B granules – small (1-10μm), spherical in shape
A granules – large (10-35μm), lenticular in shape
account for 3-5% of total granules present but constitute more than 70% of total starch weight
account for 90% of total starch, less than 30% of total starch weight
Starch Gelatinisation: disruption of molecular order within granules
and Pasting 
Undamaged starch granules are insoluble in cold water but can absorb water reversibly
Heated in water, starch granules undergo gelatinisation
Further granule swelling with continuous heating in excess water
The application of shear leads to total disruption of granules
Evidence of the loss of order includes irreversible granule swelling and loss of regular structure
Leaching of amylose also occurs during gelatinisation
Additional leaching of soluble components (primarily amylose)
Granule swelling and disruption produce a viscous mass
Retrogradation: On cooling, some starch molecules partially reassociate to form a particule or gel
The firmness of the gel depends on the extent of junction zone formation
Junction zone formation is influenced by:
Amount of water present
Presence of other ingredients such as fats, proteins, sugars and acids
consists of a continuous phase of solubilised amylose and/ or amylopectin and a discontinuous phase of granule remnants
8 Types of Starches – Unmodified Starches ✅
Common Starches: 25% amylose and 75% amylopectin
Waxy Starch: Contains only amylopectin no amylose
Forms thickened viscous pastes that do not gel on cooling
High Amylose Starch: Amylose content of about 52% or 70-75%
High gelling properties
Main sources: corn (maize), rice etc.
Waxy maize starch: Clear cohesive pastes used in extended cereal and snack food products, in dry mixes for soups and cakes
Rice Starch: Produces opaque gels useful for baby food
Waxy Rice Starch: Clear and cohesive
Wheat Starch Gels: Weak, slight flavour due to residual flour components
Tuber (potato) and root (tapioca) starches: Weak intermolecular bonding and swell greatly to give high viscosity pastes
Viscosity decreases with moderate shear because the highly swollen granules break easily
Modification of Starch: so that resultant pastes can endure the conditions of heat, shear and acid associated with particular processing conditions and to introduce specific functionalities : ✅
Types
Cold Water Soluble (Pregelatinised) Starch: Uses 20-40% starch slurry & atomized with steam (70C). Directly into spray dryer Suspended granules gelatinised (60% moisture content)
Can be applied to both chemically modified and unmodified starches
Typically used in dry mixes such as instant pudding mixes, instant soups
Cold water Swelling Starch
: 20% starch slurry in 75% ethanol solution
Pressure (4MPa), High temperature (75C)
Can be used in sugar solutions in the production of gum candies - produce rigid gels that can be easily sliced
Useful in making desserts and also to keep particles such as blueberry in muffin batters “suspended
Hydrolysis
Enzyme treatment of starch
: Results in the production of maltodextrins
Acid treatment of starch: Acid is sprayed onto starch,, neutralised, product is recovered washed and dried
Crosslinking: Hydroxyl functional group (-OH groups) present in starch are used for cross linking with di- or poly reagents
E.g. of reagents used are phophoryl chloride or sodium tripmetaphosphate
Maltodextrins properties are linked with the degree of polymerisation (DE)
Those with low DE are non-hygroscopic while those of highest DE tend to absorb moisture
Acid modified starches form gels with improved clarity and increased strength even though they provide less solution viscosity
Uses
Can be used as film formers and adhesives in products such as pan-coated nuts and candies
Can also be used to form strong gels such as in gum candies
Linking starch chains with phosphate diester reinforces the granules and reduces both the rate and degree of swelling and subsequent disintegration
As crosslinking is increases,
the granule becomes more and more tolerant to physical conditions
The starch becomes more acid-stable
The starch becomes less and less dispersible by cooking
Crosslinked starches are used in canned soups, gravies, puddings and in batter mixes
Cellulose: A high- molecular weight, linear, insoluble homopolymer of repeating β-D-glucopyranosyl units joined by (1→4) glycosidic linkages
✅
Occurs as a basic structural polysaccharide in cell walls of higher plants
Insoluble and hence serve as dietary fibre
Derivatives : ✅
Microcrystalline cellulose (MCC): A purified insoluble cellulose.
used primarily as a flavour carrier and as an anticaking agent
Colloidal MCC is water dispensible and has similar properties to those of water-soluble gums
used to stabilize foams and emulsions especially during high-temperature processing
Carboxymethylcellulose (CMC): Consists of long, fairly rigid molecules that bear a negative charge due to numerous ionized carboxyl groups,
stabilises protein dispersions especially near their isoelectric pH value
tend to be both highly viscous and stable
Can be used as
Thickener for cottage cheese and cheese spread
Emulsion stabiliser in sauces, soups and dressings
Protein stabilisers and retarder of crystal formation in ice cream
Methylcelluloses: cellulose treated with methyl ester groups
& Hydroxypropylmethylcellulose: cellulose treated with both propylene oxide and methyl chloride
Both are cold water soluble
Used as fat replacers in food
provide fat-like properties so that fat content of a product can be reduced
They reduce adsorption of fat in products being fried
Guar and Locust Bean Gum: Both gums are the ground endosperm of seeds with main component, Galactomannans
Guar gum – guar bean seeds
Locust Bean Gum – carob tree
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Guar – evenly spaced galactosyl units
Locust bean gum – long naked chain sections
Soluble in water giving highly viscous solutions
Stable in pH range 4-10
Typically used as a thickener, viscosity modifier, and stabiliser of dispersion in food and beverages
in cold water only swells and form a viscous dispersion
Does not gel on its own
Increases agar and carrageenan gel elasticity and strength
Typically used as
Emulsion stabiliser
Thickening agent for dairy products and filling for frozen foods and bakery products
Xanthan Gum: Produced by bacterium (xanthomonas campestris)
✅
Interacts with guar gum, gives synergistic increase in solution viscosity
Interacts with LBG produces a heat reversible gel
Unique characteristics:
Used as a thickener for sauces, to prevent ice crystal formation in ice cream and as a low calorie substitute for fat
Soluble in hot or cold water
High solution viscosity at low concentration
Soluble and stable in acidic systems
Excellent compatibility with salt
Good solution stability when exposed to freezing and thawing
Carrageenans: Extracted from seaweed
Stable over a wide range of pH
3 different types: kappa (), iota (), and lamba ()
Dissolved in water to form high viscous solutions
Key uses
Typically used to gel, thicken, or suspend, so they are used in emulsion stabilisation for syneresis control, and for bodying, binding and dispersion
Iota carrageenan – used in dessert gel formulations
Kappa carrageenan – used to ice cream to control meltdown, used in infant formulation to create fat and protein stabilisation
Lambda carrageenan – used in aerosol whipped cream/ shakes to stabilise overrun
Pectin: from citrus peel and apple pomace ✅
Two types depending on degree of esterification (DE)
High-methoxy pectin - over 50% DE, gels in medium with more than 55% soluble solid content
Low-methoxy pectin – DE less than 50%, gelation is controlled by introducing calcium ions and occurs in a medium with 20% soluble solids at pH between 2.5 and 6.5
Uses/ Applications of Pectin
Leading agent used to impart a gelled texture to foods, mainly fruit based foods
Used in jams and jellies as a gelling agent
Used in fruit preparation for yogurt
Used in confectionary products
stabilised by hydrophobic binding of methyl ester groups as well as intermolecular hydrogen bonding
stabilised by inter chain binding by Ca2+
Made by hydrolysis of purified wood pulp, followed by separation of constituent microcrystals of cellulose
electrostatic repulsion causes its molecules in solution to be extended