Carbohydrates (Food Sci & Nutrition Sci aspects) Flashcards
Classify carbohydrates as monosaccharide, disacchararide and polysaccharide
> Monosaccharides and disaccharides are simple carbohydrates
- Monosaccharides are single-sugars
- C6H12O6
- Most are hexoses
1. Glucose
- Occurs widely in foods, serves as the essential energy
source in the body
2. Fructose
- Occurs naturally in honey and fruits and is added to
many foods in the form of high-fructose corn syrup to
enhance sweetness and flavour
3. Mannose
- Occurs in small amount in some fruits
4. Galactose
- Rarely occurs naturally as a single sugar
> Disaccharides are pairs of monosaccharides
1. Sucrose
- Fructose and glucose
- Table sugar
- One unit of alpha-D-glucose and one unit of beta-D-
fructose joined by an alpha (1,2)-beta-glycosidic
bond
- Digested by intestinal sucrase to yield one glucose
and one fructose for absorption
- Sources: sugar cane
- Lactose
- Galactose and glucose
- Milk sugar
- Found in milk and milk products
- Milk sugar
- One unit of D-galactose and one unit of D-glucose
joined by a beta-(1,4)-glycosidic bond
- Digested by intestinal lactase to give one galactose
and one glucose unit for absorption
- Sources: human milk (5-8%), cow’s milk (4-5%) - Maltose
- Two glucose units
- Malt sugar
- Produced during germination of seeds and
fermentation of starch
- One unit of D-glucose and one unit of D-glucose
joined by an alpha-(1,4)-glycosidic bond
- In digestion maltose formed by pancreatic alpha-
amylase digesting starch
o Further digestion of maltose by intestinal maltase
yields 2 glucose units for absorption
- Example food:
o Horlicks, fermented barley with added wheat flour
o Milo, fermented barley with added cacao
Polysaccharides (The complex Carbohydrates)
- Multiple glucose units linked together in straight chain
or branched chain
- Oligosaccharides: up to 20 units
- Polysaccharides: > 20 units
- Starch
- Contained both straight chain (amylose) and
branched chain (amylopectin) - Storage form of glucose in plants
- Found in grains, tubers and legumes
- Major source of energy for body
- Contained both straight chain (amylose) and
- Glycogen
- Highly branch chain
- Storage form of glucose in plants
- Provides a rapid source of glucose (energy) when
needed
Identify some carbohydrates from food sources
- Cereals
- Root crops
- Pulses
- Vegetables
- Fruit
- Milk
Wholegrain foods are major carbohydrate source in the form of starch
Wholegrain foods, vegetables, legumes and fruits are major carbohydrate source in the form of dietary fibre
Milk products provide lactose, an important energy source for infants
Know the following terms describing carbohydrate structure:
-Fisher projection, Haworth projection, aldehyde, ketone, aldose, ketose, triose, tetrose, pentose, hexose, hemicetal, hemiketal, pyranose, furanose, glycosidic linkage, anomeric carbon, α-linkage, β-linkage, D-sugar, L-sugar
- Fischer projection
> Fisher projection presents the sugar atomic entities
in a flat 2-D open-chain form
- It doesn’t tell us how atomic entities relate to each
other spatially - Haworth projection
> Haworth projection is a way of presenting sugar
structure in a ring configuration to better
understand and explain the chemistry and property
of sugars based on the spatial relationship of the.
atomic entities, especially the OH groups - Aldehyde
> attached to an oxygen and one alkyl group and one
hydrogen - Ketone
> attached to an oxygen and two alkyl groups - Aldose
> contain aldehyde group - Ketose
> contain ketone group - Triose
> 3C sugars - Tetrose
> 4C sugars - Pentose
> 5C sugars - Hexose
> 6C sugars - Hemiacetal
> When an alcohol adds to an aldehyde, the result is
called a hemiacetal (in acidic conditions and
alcohol treatment) - Hemiketal
> when an alcohol adds to a ketone the resulting
product is a hemiketal - Pyranose
> Pyranose ring form is hexagonal with 5 carbon
atoms and 1 oxygen atom. - Furanose
> Furanose ring form is pentagonal with 4 carbon
atoms and 1 oxygen atom - Glycosidic linkage
> the linkage formed between two monosaccharide
units through an oxygen atom by the loss of a
water molecule. - Anomeric carbon
> Anomeric carbon refers to the carbon atom in a
Haworth projection that was originally part of the
carbonyl group in the Fischer projection and
became a new chiral centre - alpha-linkage
> Hydroxyl of anomeric carbon is facing down - B-linkage
> Hydroxyl of anomeric carbon is facing up - D-sugar & L-sugar
> Assigned based on the alignment of the terminal
carbon with the stereospecific structure of
glyceraldehyde
Know the structural differences between glucose, mannose, galactose & fructose
Glucose
- Is a hexose/pyranose because it’s a 6-carbon
structure
- Aldose (has aldehyde group)
- carbon 3 is different, rest same
Fructose
- Hexose/furanose commonly
- Ketose (ketone group)
- Recap: Furanose refers to the cyclic form of a
pentose that contains 4 carbon atoms and one
oxygen atom
- differs at C-2 (is a ketone)
Galactose
- Hexose/pyranose
- C4 differs to glucose (additionally to the original
glucose structure)
Mannose
- Hexose/pyranose
- Carbon 2 differs
Know the Fisher projection and Haworth projection structure of sucrose, maltose & lactose
Revise
Know some food properties of maltose, lactose and sucrose
sucrose - very sweet
maltose - less sweet that sucrose
lactose - the sweetness of milk, boiled tastes sweeter (less than maltose)
Know the sources and some food properties of these sugars: cane, palm, beet, molasses, golden syrup, corn syrup, high fructose corn syrup, inverted
- cane
- From sugarcane, almost exclusively sucrose
- Table sugar, boring sweet
- Granulated (400-600µm), castor (200-450µm), icing
(10-15µm) - Highly soluble over a wide temperature range
suitable for cooking and food preservation
- palm
- Sugar from sugary saps of various palm trees
(palmyra, date, coconut), high in Fructose
- Sugar from sugary saps of various palm trees
- beet
- From the bulb of the beetroot plant, sucrose rich
with traces of raffinose and stachyose
- From the bulb of the beetroot plant, sucrose rich
- mollasses
- All from the same family
- Treacle is defined as any syrup made in the refining
of cane sugar - Molasses is a treacle, as a by-product from the
refining of sugar (sucrose) from sugarcane juice. It
still contains some left-over sugar (sucrose) that
gives it a mild sweetness but is high in phenolic acids
and polyphenols that give it the dark brown colour
- golden syrup
- Golden syrup is also made as a by-product from the
refining of sugar (sucrose) from sugarcane juice.
However, the juice has been caramelised (heated)
to a medium flavour (lost of sucrose) that has acid
(often citric acid from lemons) In it to prevent
further crystallization. It is a milder version of
molasses.
- Golden syrup is also made as a by-product from the
- corn syrup
- Produced by enzymatic degradation of corn starch
Glucose rich
- Produced by enzymatic degradation of corn starch
- high fructose corn syrup
- Produced from corn syrup by enzymatic
isomerization of glucose to fructose - Fructose rich
- Produced from corn syrup by enzymatic
- inverted
- Produced by enzymatic degradation of sucrose
- Equal ratio of glucose and fructose
Know what are condensation and hydrolysis reactions in relation of sugars
Know the structural differences between amylose, amylopectin, glycogen & cellulose
Know the actions of carbohydrate digestive enzymes on starch and sucrose
Describe lactose and fructose intolerance, their symptoms and simple preventative measures
Know what are glycaemic response, glycemic index and glycemic load
Know how are glycaemic index are determined in foods
Know what are artificial sweeteners and sugar replacers and be able to cite some example
Know the regulatory roles of FSANZ, AOAC & AACC in relation to fibres
Define dietary, total dietary and functional fibres
Describe fibres according to their properties (solubility, viscosity, fermentability)
Know the general composition of plant cell wall
Know the descriptive structure and general property of fibres
Discuss some health benefits of fibres
Know what are cellulose, hemicellulose, pectin, Beta-glucan, gum, carrageenan, alginate, galacto-oligosaccharide, fructo-oligosaccharide, and some of their structural and physical properties
Identify three types of monosaccharides, disaccharides and polysaccharides that are important in nutrition
Summarise where starch digestion occurs and how different types of starches are digested at different rates
Describe the processes by which carbohydrates are absorbed in the gastrointestinal tract
