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What are carbohydrates

  • Group of nutirents important in our diets
  • source of energy
  • lowere energy content than fats
  • contain the elements carbon hydrogen and oxygen
  • is produce in plants during photsythesis
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What are the three main groups of carbohydrates




Monsacchrides and Disscarhides are sugars

Polysacchirdes are non sugars - (starch)

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What are monosacchirdes

  • found in food containing 6 carbon atoms
  • have the genereal formula of C6H12O6. 
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What are three important memebers of monsacchirdes

Glucose (Dextrose):

  • Found in fruits and vegetables
  • Large amounts in fruits such as grapes
  • smaller quanties such as young peas and carrots
  • it is a reducing sugar 
  • helps assist in browning (millard reaction) of baked goods


  • Chemically simmilar to Glucose however the arrangemnets of the atoms are slightly different
  • Found in many fruits and in honey


  • Chemically simliar to Glocuse
  • doesnt exist in foods but found in breast milk
  • it is produce when lactose breaks dow n during digestion
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What are reducing sugars?

  • Fructose and Glucose are reducing sugars
  • Suctrose is a non - reducing sugar
  • Have the ability to breakdown fehlings soloution to from brick red coloured preciprate.
  • allows sugar to act as a reducing agent, for ecample milard reaction
  • used widely in the confectinery buisness as glucose sugar
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What are invert sugars?

  • Equal amonuts of sucrose and fructose
  • naturally occurs in honey and is produced in jam when sugar and fruit are boiled
  • is always produced with the splitting of sucrose into equal parts of glucose and fructose

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What are dissachrides

  • The general forumla is C12H22011
  • Formed when two monsacchirde molecules combine and water is elminated
  • it is an examole of condesation reaction
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What are the three types of dissachrides


  • Ordinary householed sugar
  • prodced by the condesation of glucose and fructose
  • found in many fruits and vegetables e.g sugar cane and sugar beet


  • Formed by condesation of glucose and galactose
  • It is only found in milk where it is the sole carbohydrate.
  • Found only in milk, cow’s milk (4-5%), human milk (6-8%).
  • It is a reducing sugar.


  •  formed by the two condensation of two glucose molecules.
  • It is a reducing sugar and is produced when starch is broken down by the action of enzymes (amylases), particularly in the malting process of barley
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What are polysacchrides

  • They are condensation polymers of monosaccharide
  • made up of many monosaccharides molecules joined together, with the elimination of one water molecule at each link.
  • The General formula is C6H10O5.
  • This type of carbohydrates can be separated into two groups: Simple and Complex polysaccharides
  • 1.       Simple polysaccharides consist of long chains of one type of monosaccharide.
  • 2.       Complex polysaccharides are long chains which contain a combination of different monosaccharides.
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What are the simple polysacchirdes?


  •  major food reserve of plants. mixture of two different polysaccharides:


  • The amylose molecule consist of between 50 and 500 glucose units joined in a straight chain. Flour naturally contains amylose.
  • It is broken down by the enzyme amylase, which is naturally found in our saliva.
  • It has Excellent gelling qualities and tends to break down easily (causing syneresis)


  • This molecule consists of up to 100,000 glucose units joined in a branched – chain structure. Poor gelling qualities. Excellent ‘non-break down’ qualities.
  • No syneresis or retrogradation
  • The starch in many plants, including wheat, rice, corn and potato, consists of                 approx.80% amylopectin and 20% amylose.
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What are the simple polysacchirdes?


  • It’s a carbohydrate only found in animals.
  • It is thought to be a carbohydrate reserve in animals just as starch is the carbohydrate reserve in plants.
  • Animals store glycogen in the muscles and liver and when it is required it is converted into glucose which is then broken down to provide energy.
  • It can be readily broken down to maltose and glucose when it is required for energy.
  • When animals are being slaughter it is important that there are high levels in order to produce tender meat


  • It supplies roughage, which is sometimes known as fibre, in the diet.
  • It has the ability to hold large amounts of water, it helps form the structural part of the plants e.g. stems.
  • Amorphous cellouse can absorb large amounts of water so it is used in slimming foods, as the cellouse swells in the stomach
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What are the complex polysacchrides


  •  It is found in many fruits and some root vegetables.
  • Apples and the peel of citrus fruits is rich in pectin.
  • It is can be used as a gelling agent, especially in jam making.
  • Sugar is needed in gel formation about 65% giving best results. This is about the amount normally present in jam.
  • pH also affects gel strength, the optimum pH levels are between 3.0 – 3.5 (acidic).
  • Fruit that have high pectin content are apples, blackcurrants, damsons, plums, redcurrants, gooseberries, oranges and guavas.
  • Fruits with Medium pectin content are apricots and early blackberries.
  • Whilst fruits with Low pectin content are cherries, late blackberries, pears, rhubarb, raspberries, tomatoes and strawberries.
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What are complex polysacchirdes


  •  They have the ability to absorb large amounts of water.
  • They can form firm gels under the right conditions.
  • They are used to act as thickeners, stabilisers and emulsifiers,
  • they can be sourced from plants and seaweeds (Carrageen, Alginates).
  • They are used extensively in the food industry (e.g. ice cream.)
  • These polysaccharides can act as thickeners, stabilisers (which absorb water) and emulsifiers (which makes oil and water soluble in each other).
  •  Guar gum - acts as a stabiliser which can gel with Xanthan gum.
  •  Xanthan gum - has a thixotropic effect, meaning when agitated, it becomes thinner and thickens upon standing.
  • Alginates - this polysaccharide needs calcium to help form bonds. Alginates can thicken, gel and form thin films.
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Fibre (Non Starch Polysaccharide or NSP) in food:

  •  Fibre is present in whole grains, fruits and vegetables, especially the skin covering of seeds. 
  • It is a mixture of substances (mainly complex carbos) which cannot be digested in the small intestine.
  • The indigestible parts of food, generally consisting of cellulose, hemicellulose and pectin.
  • It is important in maintaining the proper functioning of the digestive system.
  • Fibre, also known in the UK as non-starch polysaccharides (NSP), e.g. cellulose and pectin and guar gum is found in fruits, vegetables, beans and cereals.
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Benefits of high fibre diet

  • Reduced risk of bowel disorders
  •  Provide feeling of fullness – eat less – useful in calorie-control diets
  • Fibre-rich foods tend to be low in fat
  • Reduces blood cholesterol, reduces risk of heart disease
  • High-fibre foods tend to be relatively cheap
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Recommendations on carbohydrates

  • Base your meals on starchy foods: these foods are good sources of starchy carbohydrate which is an important source of energy.
  • Around 50% of dietary energy should come from carbohydrate (starch and sugars combined).
  • No more than 11% of dietary energy should come from non-milk extrinsic sugars (loosely referred to as ‘added’ sugars).
  • Frequent consumption of sugar-containing foods particularly between meals can increase the chance of tooth decay, especially in those with poor dental hygiene.
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Functional Properties of Carbohydrates:

  • They help cause the colour change of bread, toast and bakery products;
  • Contribute to the chewiness, colour and sweet flavour of caramel;
  • Thicken products such as sauces and custards.
  • Sugar – Add sweetness & flavour, colour, aerate and caramelize
  • Texture, coating, decoration. Instant energy. Starch – thickener, gel, add bulk, slow releasing energy.
  • Fibre (NSP) – adds bulk, feel full for longer, low fat, helps the elimination of waste products
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Properties of sugars

  •   Appearance and solubility: All sugars are white, crystalline compounds which are soluble in water.
  • Sweetness: All sugars are sweet but do not have the same degree of sweetness. The sweetness of sugars can be compared as follows;
  • Sugar

    Relative Sweetness



    Invert Sugar












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intrinsic sugars and extrinsic sugars

  • Sugars can be divided into intrinsic sugars and extrinsic sugars.

  Intrinsic sugars:

  • These are within the cellular structure of the food, e.g. in whole fruit or vegetables.

 Extrinsic sugars:

  • These sugars are not bound within the cellular structure of the food, e.g. the lactose in dairy products.
  • Honey and table sugar are also examples.
  • These are referred to as non-milk extrinsic sugars (NMES). 
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  • Foods which are baked, grilled or roasted undergo colour, odour and flavour changes.
  • This is due to a reaction involving protein and a reducing sugar. 
  • These polymerise to form complex brown coloured compounds called dextrins. 
  • These compounds contribute to the colour and flavour of many foods such as toast, bread and cakes. 
  • This is known as non-enzymic browning (Maillard reaction).
  • Parts of amino acid and sugar molecules in food combine, when heated, to form brown compounds which change its colour, odour and flavour.
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Millard Reaction

  • Many foods containing carbohydrate and protein when heated (with a dry heat, e.g. a grill) a reaction occurs between the two to form a brown colour.
  • This is the result of a simple sugar reacting with an amino acid (in a protein chain). E.g. bread when toasted – from dry heat in a toaster or grill.
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  • When sucrose (sugar) is heated above its melting point it undergoes a physical change to produce caramel.  
  • This happens more readily without water, however syrups will caramelise with rapid heating.  
  • This process is used extensively in the production of confectionary.  
  • Overheating will cause the substance to become bitter and dark.
  • It is a non-enzymic browning reaction.
  • Sugar is heated to a very high temperature.
  • It is a browning reaction in the absence of proteins or amino acids.
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  •  When starch is mixed with water and heated, the starch granules swell and eventually rupture, absorbing liquid which thickens the mixture.  
  • On cooling, if enough starch is used, a gel forms.  
  • This process is used in the production of blancmange.

 Gelatinisation of Starch:

  • Ability to form a gel (thicken).
  • Does not dissolve in cold liquid, but forms a dispersion (colloidal suspension).
  • Thickens at a range of temperatures 85°C+.
  • Hydrogen bonding allows a gel network to form, trapping the water and forming a gel on cooling.
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Breakdown of Gels

  • When a starch based gel is allowed to stand or is thawed, after freezing, the bound up water ‘weeps’ out from the frozen gel structure. 
  •  E.g. white sauce left for a few days.
  • The breakdown of the network structure is known as ‘Retrogradation’.
  • The leaking out of the liquid is known as Syneresis. 
  • Retrogradation can expel water from the polymer network. 
  •  A small amount of water can be seen on top of the gel. 
  • Visual example – ready meals that contain sauces that have been thickened with starch (flour) when frozen and then defrosted – sometimes a layer of water lies on top of the sauce and the sauce can split or separate.
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