Types of Carbohydrates

Today's lesson features carbohydrates!

Monosaccharides
-The sweet taste of edible sugars (fructose and sucrose) was an evolutionary advantage because sweetness guided humans to select plants with the highest energy value.
-Reducing Sugars: hydroxyl group can reduce (donate hydrogen); examples are glucose and galactose
-Glucose, Galactose, Fructose

Glucose
-Most widely distributed sugar in nature
-Glucose + Fructose = Sucrose (make up a large content of fruits and vegetables)
-Also referred to as "blood sugar"

Fructose
-Other names: levulose, fruit sugar
-The sweetest
-Fruits are generally 1-7% fructose
-Vegetables have 3% fructose
-Honey is 40% fructose
-As fruit ripens, enzymes cleave sucrose into glucose and fructose resulting in a sweeter taste.

Galactose
-Produced from lactose (milk sugar) by hydrolysis in the digestive process.

Disaccharides
-Monosaccharide units joined by glycosidic linkages.
-Sucrose= fructose + glucose
-Maltose = glucose + glucose
-Lactose = glucose + galactose

Sucrose
-When used in preparation of acidic foods it becomes inverted and sweeter

Honey
-More calorie dense because monosaccharides are packed more closely together than disaccharides
-1 tbsp honey = 64 kcal
-1 tbsp sugar = 46 kcal

HFCS
-Manufactured by changing glucose in cornstarch to fructose
-Added to canned/frozen fruits to preserve

Oligosaccharides
-Polymers containing 2-20 sugar molecules.
-Water soluble and often sweet
-Nondigestible oligosaccharides: resistant to stomach acid and action of amylase, enter intestine intact
-Raffinose: in sugar beets (galactose + glucose + fructose)
-Stachyose: in legumes and squash (2 galactose + glucose + fructose)

Polysaccharides
-Plants store carbohydrates as starch granules in plastids within cellulose walls
-Edible plants make 2 types of starch (amylose, amylopectin)
-In whole foods, starch is poorly digested. Moist cooking will improve digestibility.
-Carbohydrates that cannot be digested are classified as dietary fiber.

Resistant Starch
-Remains intact throughout cooking
-Limited glucose is produced for absorption

Waxy Starch
-Obtained from corn and rice strains bred to increase amylopectin
-When dissolved in water, forms a smooth paste
-Used as a thickener for frozen pies and sauces

Modified Food Starch
-Used for instant puddings, salad dressings, and baby food
-Adds viscosity and gel-like properties

Cellulose
-A nondigestible carbohydrate found in celery, broccoli, carrots, and many other vegetables
-Falls in the category of insoluble fiber

Pectins/Gums
-Contains sugars and sugar alcohols that make them water soluble
-Pectin is found in apples, citrus, strawberries, jams, and jellies
-Gums are galactose units combined with other sugars found in oats, legumes, and barley

Fructooligosaccharides
-Poorly digested in the upper GI tract
-Provide 1kcal/g, half as sweet as sucrose
-Used as a sugar replacement
-Naturally found in onions, garlic, bananas
-Increase colonic bacteria growth and have been added to yogurts marketed as a prebiotic

Lignin
-Woody insoluble fiber found in stems and seeds of fruits and vegetables and flaxseed
-Also found in the bran layer of grains

Carrageenan
-Extracted from macroalgae or seaweed.
-Used to stabilize food mixtures in pudding and infant formula
-Some studies have shown at high doses to increase cancer risk
http://www.webmd.com/vitamins-supplements/ingredientmono-710-carrageenan.aspx?activeIngredientId=710&activeIngredientName=carrageenan

Chitosan
-Sugar extracted from the shells of crabs, lobsters, and shrimp
-Hypocholesterolemic effect
-Positive charge on chitosan binds negatively charged lipids and blocks their absorption
http://www.webmd.com/vitamins-supplements/ingredientmono-625-chitosan.aspx?activeIngredientId=625&activeIngredientName=chitosan

See the next post on how carbohydrates impact health!

Mahan L, Escott-Stump, S. "Food, Nutrition, and Diet Therapy." Saunders. 2004.