FOOD TECHNOLOGY CARBOHYDRATES

Transcription

1 FOOD TECHNOLOGY CARBOHYDRATES

2 FORMULA FOR CARBOHYDRATES CxH2Oy Carbohydrates can be split up into: Sugars Non Sugars Monosaccharides Disaccharides Simple Polysaccharides Complex Polysaccharides Glucose Fructose Maltose Sucrose Lactose Starch Cellulose Glycogen Pectin Gums

3 MONOSACCHARIDES These contain 2-7 carbon atoms. Most common Monosaccharide in food contain 6 carbon atoms (called hexoses) therefore their formula is C 6 H 12 O 6.

4 GLUCOSE Found in large amounts of grapes and smaller amounts in carrots and peas. Glucose syrup which is used in commercial manufacture is not pure glucose, but a mixture of other carbohydrates, glucose and water. Formula for Glucose Alpha Glucose Beta Glucose

5 GLUCOSE CONT. There are two forms of glucose alpha and beta. It s important to remember that the only difference in the two is that in alpha glucose, the hydroxyl group (OH), is at the bottom of the structure and in Beta glucose, the OH is at the top. Glucose is a reducing sugar, this means it has the ability to break down Fehling s solutions to form a brick red coloured precipitate. Fehling s solution is a mixture of 2 solutions which have to be mixed at the time of carrying out the test for reducing sugar.

6 FRUCTOSE Fructose is one and a half times sweeter than glucose. An equal mixture of fructose and sucrose is called invert sugar found in honey, made when making jam. The structure of Fructose changes depending on if it is found in its own or whether it is joined with other sugars.

7 FRUCTOSE STRUCTURE Fructose in the free state: Fructose when it is joined with other sugars:

8 GALACTOSE This doesn t occur in foods but it is formed when lactose if broken down during digestion.

9 DISACCHARIDES Disaccharides have the formula C12H22O11. These sugars are formed when two Monosaccharides join together during a condensation reaction (when water is eliminated).

10 LACTOSE This sugar is found only in milk. Cow s milk 4 to 5% Human milk 6 to 8% This reducing sugar is formed by joining together Glucose and Galactose.

11 MALTOSE Is formed when two Glucose units join together. When the two units join, water is eliminated and the remaining O2 atom forms a bridge between the two glucoses. This bridge is called a Glycosidic Link. Maltose is a reducing sugar. During digestion starch is broken down by the enzyme amylase (this enzyme is present in our saliva).

12 SUCROSE Sucrose is not a reducing sugar. Sucrose is formed by 1 glucose unit joined with 1 fructose unit. Ordinary sugar is almost pure sucrose (caster sugar/ sugar in tea etc). RECAP Glucose + Glucose = Maltose Glucose + Fructose = Sucrose Glucose + Galactose = Lactose

13 HYDROLYSIS It s the chemical breakdown of a molecule when it combine with water and produces two smaller molecules. C12 H22 O11 + H2O = 2C6 H12 O6 Hydrolysis of different disaccharides: Glucose Maltose + Water -> Glucose + Glucose Fructose Sucrose + Water -> Glucose + Fructose Galactose Lactose + Water -> Glucose + Galactose

14 SIMPLE POLYSACCHARIDES Long chains of 1 type of monosaccharide joined together. Usually insoluble in water. Most polysaccharides usually have a 1-4 Glycosidic link, but sometimes 1-6 link, a 1-2 link or a 1-3 link. The general formula for simple polysaccharides is (C6H10O5)n. n here represents many thousands of monosaccharide units.

15 STARCH Types of starch Amylase: Consists of between glucose units joined in a straight chain. Amylopectin: This molecule consists up to 100,000 glucose units joined in a branched-chain structure.

16 PROPERTIES OF STARCH Appearance and Solubility: Starch is a white powder which is insoluble in cold water. Hydrolysis breaks down starch: Starch -> Dextrins -> Maltose -> Glucose

17 PROPERTIES OF STARCH CONT. Effect of Heat Gelatinization (with water): Water penetrates the outer layers of granules and the granules begin to swell when the temperature rises from 60 C to 80 C. Granules swell up to 5x the original size mixture becomes viscous (thick). At 80 C the starch granules break up and disperse throughout the water. Long chain molecules unfold and the starch/water mixture becomes more viscous forms a sol. On cooling, starch molecules form a network with the water and produce a gel.

18 CELLULOSE Insoluble Long chain of glucose units are the building blocks of plants being found in cell walls. Cellulose is important for providing fibre (NSP) in the diet. Non-starch polysaccharides (NSP) is necessary for efficient passage of food through the alimentary canal and regular emptying of the bowel.

19 GLYCOGEN Carbohydrate only found in animals Animals store glycogen in muscles and liver and when required, it converts it to glucose which is broken down to provide energy. Glycogen, like Amylopectin, is composed of branched chains of glucose units.

20 COMPLEX POLYSACCHARIDES These are long chains of different monosaccharide's joined together and often with branches.

21 PECTIN Complex mixture of polysaccharides found in many fruits and some root vegetables. Apples and the peel of citrus fruits are particularly rich in pectin. Main importance: Gelling Agent (e.g. jam making) Pectin is broken down in fruit as fruit ripens Jam will not gel well if made from over ripe fruit. For pectin to form a really good gel, 65% of it needs to be sugar. ph affects gel strengths (ph ). Lemon juice lowers this setting.

22 GUMS Tragacanth, arabic and guar Produced by plants and are used in food manufacturing as thickeners, stabilizers and gelling agents in foods. E.g. Ice cream, salad dressing and fruit pie fillings. Certain seaweed extracts are used in a similar manner. These include carrageenan (Irish Moss), alginates e.g. sodium alginate and agar (agar-agar). Agar is also used in the preparation of microbiological media.

23 THE PROPERTIES OF CARBOHYDRATES Sugar The effect of heat: Melting point of sucrose is 160 C to 161 C. After sugar is melted and cooled slowly, it forms an amorphous (shapeless) sugar sometimes called barley sugar. If sucrose is heated above melting point, brownishcoloured substances called caramel is formed. Maltose melts at about 100 C, therefore it decomposes more easily by heat than sucrose.

24 THE PROPERTIES OF CARBOHYDRATES CONT.. Aeration: A soufflé will rise because of the trapped air in the egg whites adding sugar will make the egg whites more stable. The sugar interacts with the whipped foam structure to make the foam more elastic so that the air cells can expand and take up more air and therefore rise.

25 MODIFIED STARCH Also a novel food It is classified as a smart food and is used by manufacturers in a variety of products. Pizza Toppings topping thickens when heated in the oven and will not run off the pizza. Sauce/ Gravy granules boiling water can be added to thicken without the sauce going lumpy.

26 MODIFIED STARCH CONT.. Modified starch is used as a fat replacer in low-fat meals. The noodles in pot snacks are pre-gelatinised; so boiled water will reheat and cook them. Modified starch is used in cup-a-soups to improve mouth-feel, thicken then drink/soup when the boiled water is added, and blend uniformly without lumps. Modified starches allow sauces to be reheated by syneresis*. This is useful in dishes that are cooked from frozen e.g. Lasagne. *When a sauce that has cooled and solidified is reheated, often goes lumpy and a watery liquid may separate from it.

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