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
What are the three main groups of carbohydrates
Monsacchrides and Disscarhides are sugars
Polysacchirdes are non sugars - (starch)
What are monosacchirdes
- found in food containing 6 carbon atoms
- have the genereal formula of C6H12O6.
What are three important memebers of monsacchirdes
- 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
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
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
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
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
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.
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.
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
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.
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.
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.
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
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.
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
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;
intrinsic sugars and extrinsic sugars
- Sugars can be divided into intrinsic sugars and extrinsic sugars.
- These are within the cellular structure of the food, e.g. in whole fruit or vegetables.
- 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).
- 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.
- 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.
- 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.
- 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.
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.