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Lecture 21

HNSC 1200 Lecture 21: Unit 4.1

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University of Manitoba
Human Nutritional Sciences
HNSC 1200
Snehil Dua

Carbohydrates Learning Objectives:  Identify the sources of carbohydrates Describe the different types of carbohydrates  Differentiate between the different types of fibre, describe their roles in health, and identify food sources Course Notes: Carbohydrates contain carbon, hydrogen and oxygen, so they are often abbreviated CHO They are produced in green plants via photosynthesis – H2O and CO2 combine to form glucose Scientists cannot reproduce this reaction; green plants are needed Light is needed to provide the chemical energy to hold the bonds between the atoms in a glucose molecule together The plant uses some, but not all of the energy stored at glucose, meaning that animals and humans can obtain some energy when the plant is eaten Carbohydrate foods Cereal grains and flours (e.g., wheat, rye, corn, rice) Legumes (e.g., peas, beans, lentils) Starchy roots, tubers or stems (e.g., potatoes, yams, cassava, celery) Fruits (e.g., oranges, apples, bananas) Sugars, honey, jams, molasses Milk products Classification of Carbohydrates Carbohydrates are classified according to the number of basic sugar (saccharide) units: Monosaccharides – simple sugars (1 unit) Disaccharides – simple sugars (2 units) Oligosaccharides – simple sugars (3-10 units) Polysaccharides – complex sugars (many units) SEE TABLE 3: Monosaccharides, Disaccharides and Polysaccharides Commonly Found in Foods 1. Monosachharides o Includes 6 carbon hexoses and 5 carbon pentoses o Hexose sugars such as glucose, mannose and galactose are building blocks of starches Pentose sugars such as ribose, xylose and arabinose are the building blocks of fibres and gums Six sugar molecules are important in nutrition. All of their chemical names end in –ose, which means sugar. OSDP Glucose Glucose is the most abundant sugar in the world Found in fruits, plant juices and honey Often present with other sugars (e.g., in honey with fructose) Glucose is the form of sugar that circulates in the bloodstream. It is broken down in the body to give three products: Water, energy and carbon dioxide Many complex carbohydrates such as starch and cellulose have glucose as the basic unit Major component of corn syrup, which is formed by hydrolysis of starch. Corn syrup and crystalline glucose are widely used in the baking industry Fructose Found in fruits, plant juices and honey o Sweetest of all common sugars Very soluble and does not crystallize easily Galactose Not normally found in its free form in foods o Forms a bond with glucose to produce lactose (milk sugar) Some galactose is found in free form in fermented milk products (e.g., yogurt) where hydrolysis of lactose has occurred Galactose is the basic unit of some complex carbohydrates such as vegetable gums Disaccharides Disaccharides are two monosaccharide’s linked together Sucrose (glucose + fructose) o Table sugar o Extracted from sugar cane and sugar beets o Consists of glucose and fructose chemically bonded to each other o Present with other sugars in fruits, honey and vegetables Maltose (glucose + glucose) o Found in germinating grain and corn syrup. A product of starch hydrolysis o Important for production of malted beverages such as beer Consists of 2 glucose molecules chemically bonded to each other Lactose (glucose + galactose) Milk sugar o Consists of glucose and galactose chemically bonded to each other Only found naturally in milk and milk products Oligosaccharides Carbohydrate molecules that contain 10 or fewer monosaccharide’s Include raffinose and stachyose commonly found in dried beans Not digested by humans but broken down by bacteria in intestinal tract resulting in gas formation oSDP 4. Polysaccharides Complex CHO/polysaccharides are chains of sugar units linked together. Starch, glycogen and fibre are al polysaccharides Up to several hundred thousand monosaccharide’s joined together Homo-polysaccharides (homoglucans) are composed of the same type of monosaccharide Hetero-polysaccharide (heteroglucans) are composed of at least 2 types of Monosaccharides May be straight chains or highly branched chains SEE TABLE 5: Applications of Various Polysaccharides Used in Food Processing Starch (homoglucan) is a plant’s storage form of glucose. It can be branched or unbranched and is water insoluble (so cannot wash away from plant via rain). Starch provides plants with energy and humans/animals with energy when eaten, as we can digest starch Basic storage form of carbohydrates in plants – found in abundance in seeds, roots and tubers. Consist of only glucose mol
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