FORMULA FOR CARBOHYDRATES CxH2OyCarbohydrates can be split up into:Sugars MonosaccharidesDisaccharidesGlucoseFructoseMaltoseSucroseLactoseNon Sugars SimplePolysaccharidesComplexPolysaccharidesStarchCelluloseGlycogenPectinGums
MONOSACCHARIDES These contain 2-7 carbon atoms. Most common Monosaccharide in food contain 6carbon atoms (called hexoses) therefore theirformula is C6H12O6 .
GLUCOSE Found in large amounts of grapes and smalleramounts in carrots and peas. Glucose syrup which is used in commercialmanufacture is not pure glucose, but a mixture ofother carbohydrates, glucose and water.Formula for GlucoseAlphaGlucoseBetaGlucose
GLUCOSE CONT. There are two forms of glucose alpha and beta. It‟s important to remember that the only differencein the two is that in alpha glucose, the hydroxylgroup (OH), is at the bottom of the structure and inBeta glucose, the OH is at the top. Glucose is a reducing sugar, this means it has theability to break down Fehling‟s solutions to form abrick red coloured precipitate. Fehling‟s solution is a mixture of 2 solutions whichhave to be mixed at the time of carrying out the testfor reducing sugar.
FRUCTOSE Fructose is one and a half times sweeter thanglucose. An equal mixture of fructose and sucrose is calledinvert sugar – found in honey, made when makingjam. The structure of Fructose changes depending on ifit is found in its own or whether it is joined withother sugars.
FRUCTOSE STRUCTURE Fructose in the free state: Fructose when it is joined with other sugars:
GALACTOSE This doesn‟t occur in foods but it is formed whenlactose if broken down during digestion.
DISACCHARIDES Disaccharides have the formula C12H22O11. These sugars are formed when twoMonosaccharides join together during acondensation reaction (when water is eliminated).
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 togetherGlucose and Galactose.
MALTOSE Is formed when two Glucose units join together. When the two units join, water is eliminated and theremaining O2 atom forms a bridge between the twoglucoses. This bridge is called a Glycosidic Link. Maltose is a reducing sugar. During digestion starchis broken down by the enzyme amylase (thisenzyme is present in our saliva).
SUCROSE Sucrose is not a reducing sugar. Sucrose is formed by 1 glucose unit joined with 1fructose unit. Ordinary sugar is almost pure sucrose (castersugar/ sugar in tea etc).RECAPGlucose + Glucose = MaltoseGlucose + Fructose = SucroseGlucose + Galactose = Lactose
HYDROLYSIS It s the chemical breakdown of a molecule when itcombine with water and produces two smallermolecules.C12 H22 O11 + H2O = 2C6 H12 O6Hydrolysis of different disaccharides:GlucoseMaltose + Water -> Glucose + GlucoseFructoseSucrose + Water -> Glucose + FructoseGalactoseLactose + Water -> Glucose + Galactose
SIMPLE POLYSACCHARIDES Long chains of 1 type of monosaccharide joinedtogether. Usually insoluble in water. Most polysaccharides usually have a 1-4 Glycosidiclink, 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 ofmonosaccharide units.
STARCHTypes of starch Amylase: Consists of between 50 – 500 glucoseunits joined in a straight chain. Amylopectin: This molecule consists up to 100,000glucose units joined in a branched-chain structure.
PROPERTIES OF STARCH Appearance and Solubility:Starch is a white powder which is insoluble in coldwater.Hydrolysis breaks down starch:Starch -> Dextrins -> Maltose -> Glucose
PROPERTIES OF STARCH CONT. Effect of HeatGelatinization (with water): Water penetrates the outer layers of granules andthe granules begin to swell when the temperaturerises from 60 C to 80 C. Granules swell up to 5x the original size – mixturebecomes viscous (thick). At 80 C the starch granules break up and dispersethroughout the water. Long chain molecules unfold and the starch/watermixture becomes more viscous – forms a sol. On cooling, starch molecules form a network withthe water and produce a gel.
CELLULOSE Insoluble Long chain of glucose units – are the buildingblocks of plants being found in cell walls. Cellulose is important for providing fibre (NSP) inthe diet. Non-starch polysaccharides (NSP) is necessary forefficient passage of food through the alimentarycanal and regular emptying of the bowel.
GLYCOGEN Carbohydrate only found in animals Animals store glycogen in muscles and liver andwhen required, it converts it to glucose which isbroken down to provide energy. Glycogen, like Amylopectin, is composed ofbranched chains of glucose units.
COMPLEX POLYSACCHARIDES These are long chains of differentmonosaccharides joined together and often withbranches.
PECTIN Complex mixture of polysaccharides found in manyfruits and some root vegetables. Apples and the peel of citrus fruits are particularlyrich in pectin. Main importance: Gelling Agent (e.g. jam making) Pectin is broken down in fruit as fruit ripens – Jamwill not gel well if made from over ripe fruit. For pectin to form a really good gel, 65% of it needsto be sugar. pH affects gel strengths (pH 3.0-3.5). Lemon juicelowers this setting.
GUMS Tragacanth, arabic and guar – Produced by plantsand 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 similarmanner. These include carrageenan (Irish Moss), alginatese.g. sodium alginate and agar (agar-agar). Agar is also used in the preparation ofmicrobiological media.
THE PROPERTIES OF CARBOHYDRATES SugarThe effect of heat:Melting point of sucrose is 160 C to 161 C.After sugar is melted and cooled slowly, it forms anamorphous (shapeless) sugar sometimes called“barley sugar”.If sucrose is heated above melting point, brownish-coloured substances called caramel is formed.Maltose melts at about 100 C, therefore itdecomposes more easily by heat than sucrose.
THE PROPERTIES OF CARBOHYDRATES CONT..Aeration:A soufflé will rise because of the trapped air in theegg whites – adding sugar will make the egg whitesmore stable.The sugar interacts with the whipped foam structureto make the foam more elastic so that the air cellscan expand and take up more air and thereforerise.
MODIFIED STARCH Also a „novel food‟ It is classified as a smart food and is used bymanufacturers in a variety of products. Pizza Toppings – topping thickens when heated inthe oven and will not run off the pizza. Sauce/ Gravy granules – boiling water can beadded to thicken without the sauce going lumpy.
MODIFIED STARCH CONT.. Modified starch is used as a fat replacer in low-fatmeals. The noodles in „pot snacks‟ are pre-gelatinised; soboiled water will reheat and „cook‟ them. Modified starch is used in „cup-a-soups‟ to improvemouth-feel, thicken then drink/soup when the boiledwater is added, and blend uniformly without lumps. Modified starches allow sauces to be reheated bysyneresis*. This is useful in dishes that are cookedfrom frozen e.g. Lasagne.*When a sauce that has cooled and solidified is reheated, oftengoes lumpy and a watery liquid may separate from it.