Carbohydrates Flashcards
Formation of Carbohydrates
Carbohydrates are formed in plants by a process known as photosynthesis
Carbon dioxide is absorbed from the air through the leaves
Water is absorbed from soil through the roots
Energy is absorbed from sunlight by chlorophyll (green pigment)
This energy is used to create glucose from carbon dioxide (CO2) and water (H2O)
Oxygen is released into the air
Elemental composition of carbohydrates
Carbon
Hydrogen
Oxygen
Classification of carbohydrates
Monosaccharides
Disaccharides
Polysaccharides
Monosaccharides
Monosaccharides are simple sugar units. They are the basic units of all carbohydrates
Monosaccharide Formula
C6H12O6
Examples of monosaccharides
Glucose - fruit
Fructose - fruit, honey
Galactose - cheese
Disaccharides
Disaccharides are formed when two monosaccharides join together with the elimination of water (condensation reaction)
Disaccharides formula
C12 H22 O11
Examples of disaccharides
Sucrose (glucose, fructose) - sugar
Lactose (glucose, galactose) - milk
Maltose (glucose, glucose) - barley
Polysaccharides
Polysaccharides are formed when many monosaccharides join together with the loss of a water molecule each time (condensation reaction).
They may be in straight or branched chains.
Examples include starch, pectin, cellulose and glycogen.
Pectin, cellulose and glycogen are referred to as non-starch polysaccharides
Polysaccharide formula
(C6 H10 O5 )N
N - number of monosaccharides present
Examples of polysaccharides
Starch - potatoes, cereals
Cellulose - fruit, vegetables, whole grain
cereals
Glycogen - meat (stored animal starch)
Pectin - fruit
Sources of SUGAR Carbohydrates
Sugar
Biscuit
Cake
Honey
Sweets
Fruit
Sources of STARCH Carbohydrates
Breakfast cereals (Eg:) fruit and fibre
Potatoes
Rice
Pasta
Flour: bread and cakes
Sources of CELLULOSE Carbohydrates
Fruit and vegetables (skin on)
Whole grain breakfast cereal (Eg:) fruit and fibre
Whole meal bread and pasta
Brown rice
Nuts
Properties of SUGAR Carbohydrates
List
Solubility
Flavour
Maillard Reaction
Foam formation
Caramelisation
Crystallisation
Hydrolysis
Inversion
MIFFCCHS
Sugar - solubility
Sugars are white crystalline compounds that are soluble in water.
Solubility is increased when you heat the water.
Culinary Application
Combining sugar and water to form a syrup served with pancakes
Used as a preservative in canned foods (eg:) peaches
Sugar - flavour
Sugars vary in sweetness. For example sucrose is much sweeter than lactose. Sucrose has a relative sweetness of 170, lactose is 15
Culinary Application
Adding sugar to sweeten desserts and cakes
Sugar - Maillard reaction
Non-enzymic browning that occurs when sugars and amino acids react in dry heat, giving the food an attractive appearance and flavour.
Culinary Application
Crust forming on bread as it bakes in the oven
Roast potatoes
Shortbread biscuits
Sugar - assists aeration/foam formation
Sugar helps to denature egg protein. When eggs are whisked the heat produced by the friction coagulates the protein around the air bubbles, allowing aeration to occur.
Cooking further coagulates the protein forming a permanent foam.
Culinary Application
Aeration of meringues and sponge cakes
Sugar - caramelisation
When sugar is heated on its own, it melts and then caramelises - in other words, it changes to a brown syrup (caramel).
If caramel is overheated, it will carbonise its burn.
There are ten gradual changes in the sugar between melting and caramelisation.
These changes occur between 104°C - 177°C.
Caramelisation usually occurs at 160°C.
Resulting in an attractive amber brown colour and sweet taste.
Culinary Application
Caramel used in chocolate caramel slices
Sugar - crystallisation
This occurs if more sugar is added than can be absorbed by a liquid.
Crystal particles are deposited from the solution
Culinary Application
Used in the confectionary, fudge and sweet industry
Sugar - hydrolysis
Sugars (disaccharides) react with water and enzymes and break down into monosaccharides.
Culinary Application
Hydrolysis occurs during digestion
Sugar - inversion
Sugars are capable of being inverted (changed back to monosaccharides).
Invert sugars are monosaccharides that result from the hydrolysis of disaccharides — for example, sucrose is hydrolysed, it is inverted to glucose and fructose.
Invert sugars are very sweet and do not crystallise.
Culinary Application
Used in jam making to produced a smoother texture
Properties of STARCH Carbohydrates
Solubility
Flavour
Gelatinisation
Hygroscopic
Dextrinisation
Hydrolysis
HHDFGS
Starch - solubility
Starch is a white powder that is insoluble in cold water
Culinary Application
Must be blended well before being used as a thickening agent
Starch - flavour
Starch is not sweet in flavour
Culinary Application
Flour is used as a base ingredient in both savoury and sweet dishes
Starch - gelatinisation
When starch grains are headed in liquid, they swell and burst and absorb the liquid, forming a thickens solution.
Upon cooling, this becomes a gel
(55°C - 70°C)
Culinary Application
Using flour or corn flour to thicken soups and sauces
Moist heat - roux sauce/ lemon curd
Dry heat - popcorn/pastry
Starch - hygroscopic
Starch absorbs moisture - for example, biscuits soften and loose crunch if not stored in a sealed container
Culinary Application
Helps to retain moisture in cakes
Starch - dextrinisation
When carbohydrate foods are heated short chains of polysaccharides called dextrins change to long chained polysaccharides called pydrodextrins, causing the surface of the food to brown, resulting in an attractive brown appearance
Culinary Application
Toasting bread
Starch - hydrolysis
Starch may undergo hydrolysis
Culinary Application
Hydrolysis of starch occurs during digestion
Pectin
Pectin is a non starch polysaccharides that occurs naturally between plant cells and in the cell walls of some fruit and vegetables.
Pectin - property
Gel formation
Pectin is a gelling or setting agent found in varying quantities in ripe fruit.
(Only present in ripe fruits).
When heated it combines with sugar to form a gel.
Heat and acid, such as lemon juice, help to extract pectin from the fruit
Culinary Application
Used to set jam, jellies and marmalades
Pectin extraction
Use a fruit rich in pectin, such as apples
Heat must be applied to extract the pectin
Acid, such as lemon juice, assists in pectin extraction from the fruit
Dietary fibre/ Cellulose
Dietary fibre is found in the cell walls of plants.
It is indigestible but can absorb large amounts of water, which adds bulk to the diet without adding kilocalories.
It stimulates peristalsis, helping food to move quickly through the digestive system and thereby reducing the incidence of bowel disorders.
The recommended dietary allowance (RDA) is 25-35g
To increase fibre intake
Choose whole grain bread, pasta breakfast cereals and rice
Reduce the intake of sugar and refined foods such as white bread
Increase the intake of fruit and vegetables (skin where possible)
Add nuts, seeds and bran to breakfast cereals and homemade breads
Sugar consumption
High sugar consumption is associated with an increased risk of obesity and type 2 diabetes, as many sweet foods are high in kilocalories , leading to weight gain
Refined carbohydrates cause an increase in insulin production, which raises low-density lipoprotein (LDL) levels, which in turn increases the risk of heart disease.
Sugar has also been identified as a major cause of tooth decay
Consuming too much sugar may lead to a diet lacking in more nutritious foods such as vegetables, causing deficiencies of some nutrients, such as minerals and vitamins
To reduce the intake of high sugar foods
Replace sugar-rich snack foods with fruit,
vegetables and nuts.
Be aware of other terms used on food labels that indicate sugar content, such as sucrose, glucose and maltose.
Drink water instead of soft drinks and be
aware of the sugar content of fruit juices.
Choose wholegrain, less refined breakfast cereals instead of more processed varieties which have sugar added (eg:) porridge over Frosties
Use artificial sweeteners instead of sugar
Culinary applications of Carbohydrates
Sugar
Sweetens desserts, cakes and beverages
Adds colour, (e.g:) when brown sugar is
used
Acts as a preservative
in jams
Stabilises egg white foam
Main ingredient in icings and syrups
Necessary in yeast fermentation
Culinary applications of Carbohydrates
Starch
Thickens soups and sauces
Main ingredient in bread and cakes
Absorbs water - used in baking powder to prevent chemicals reacting before use
Browning of foods caused by dextrins eg: toast
Culinary applications of Carbohydrates
Adds texture Eg: whole grain breakfast cereals and bread
Culinary applications of Carbohydrates
Pectin
Setting agent in jams and jellies
The effects of heat on carbohydrates
Moist heat
Sugar dissolves easily in warm liquids (Eg:) it is used to sweeten custard sauces or in syrups
Moist heat causes starch grains to swell and burst and absorb liquids (Eg:) four is used to thicken gravy
Heating fruit in a small amount of water assists the extraction of pectin (Eg:) jam-making
Moist heat causes cellulose to soften (Eg:) cooked vegetables
The effects of heat on carbohydrates
Dry heat
Dry heat results in carbohydrate food browning because if the presence of dextrins (Eg:) toast
Dry heat causes sugar to caramelise (Eg:) toffee-making
Dry heat results in the Maillard reaction due to a reaction between carbohydrates and amino acids
(Eg:) roast potatoes
Biological functions of carbohydrates
Carbohydrates are used to produce head and energy in the body
Sufficient carbohydrate in the diet allows protein to be used for its primary function: growth and repair
Excess carbohydrate is converted into glycogen and stored in the liver and muscles as an energy reserve or converted into fat and stored as adipose tissue, which acts as an insulator
Cellulose helps food to move through the digestive system, preventing constipation and other bowel disorders
Digestion of Carbohydrates
Mouth: food is chewed. Amylase changes some starch to maltose
Stomach: no carbohydrate digestion
Small intestine: amylase into dudodeum, changes starch to maltose
Intestinal juice contains three enzymes:
Maltase
Lactase
Sucrase
Mouth/Salivary glands
Secretion: Saliva
Enzyme: Salivary amylase
Substrate: Starch
Product: Maltose
Pancreas
Secretion: Pancreatic juice
Enzyme: Amylase
Substrate: Starch
Product: Maltose
Small intestine
Secretion: Intestinal juice
Enzyme: maltase, lactase, sucrase
Substrate: maltose, lactose, sucrose
Product: glucose, glucose and galactose, glucose and fructose
Absorption and utilisation of carbohydrates
Monosaccharides are absorbed through the villi of the small intestine into the bloodstream. The portal vein carries them to the liver.
In the liver:
Fructose and galactose are changed to glucose
The glucose goes into the bloodstream, where it is oxidised to produce heat and energy
Some glucose is converted into glycogen and is retained in the liver as an energy store
The excess glucose is converted to fat and stored as adipose tissue
Equation for photosynthesis
6CO2 + 6H2O + sunlight —> C6H12O6 +
6O2
Carbon dioxide + water + energy —> glucose + oxygen
