Carbohydrates Flashcards
3 main energy substrates
-carbohydrates
-lipids
-proteins
Types of carbohydrates
- glycemic carbohydrates
- Fibre
Glycemic carbohydrates
-glucose, sucrose, fructose, lactose
-starch
Fibre
Cannot be digested by the host organism
-cellulose
-hemicellulose
Simple sugars
-glucose
-galactose
-fructose
Diasaccharides
Bonds must be cleaved for any absorption
-sucrose
-lactose
-maltose
Starch
Major storage carbohydrate in higher plants
-polymers of glucose
Two types of starch
-Amylose
-Amylopectin
Amylose
-linear polymer of glucose in a helical structure
-glucose residues attached by alpha 1-4 linkages
Why is amylose slowly digested?
Because helix is resistant to enzyme degradation
**partial digestibility
**heat and water (cooking) can get space in between and allow for better access for enzymes
Amylopectin
-branched polymer of glucose with alpha 1-4 and alpha 1-6 linkages
which allows for an open structure and enzyme degradation access
**if amylopectin high, will be rapidly digestible (in general whether uncooked or cooked)
Starch in feeds
Includes cereals (wheat, rice, corn) and some pulse crops (beans, peas, lentils)
Why do feeds contain high amounts of starch?
Because it is cheap, can maximize use
Levels of amylose in cereals
20-30% amylose
-means more rapidly digestible because lower amounts and therefore large spikes in glucose and good anabolic effects/growth and weight gain
Levels of amylose in pulse crops
Ranges but generally higher and therefore more slowly digestible
-Peas: 60-88%
-Lentils: 32-63%
-Faba bean: 17-42%
Glycemic indices of common ingredients
Ingredients with high starch (lower amylose) and therefore rapidly digestible therefore glucose spikes are occurring and causing higher glycemic indices
What is the result of low glycemic starch sources?
Reduce the protein deposition
-means slowly digestible and less growth
Where is fibre?
The structural carbohydrates in plants
-in stem, husk (chaff) of seeds
Soluble fibre
-some hemicelluloses
-pectin
-gums
-beta-glucans
**microbiome friendly (increase diversity and quantity)
**but can form jello like substance that can tie up some nutrients and prevent absorption
Insoluble fibre
-lignin
-cellulose
-some hemicelluloses
*enzymes cannot access and digest, therefore called bulk forming fibre because stays in feces and bulks it up
Cellulose
-long linear polymer of repeating glucose units in beta 1-4 linkage
-insoluble in water
-indigestible by vertebrate enzymes and therefore rely on microbes for digestion
Hemicellulose
Heterogeneous group of polysaccharide substances
-sugars in backbone and side chains
-includes beta 1-4 and alpha 1-2 linkages making it hard to digest
What sugars form the backbone of hemicellulose?
-xylose
-mannose
-galactose
What sugars form the side chains of hemicellulose?
-Arabinose
-glucuronic acid
-galactose
Lignin
Highly branched poly-phenolic polymer composed of phenol units with strong bonding
-plant lignin content increases with age
-indigestible by mammal enzymes and microbial enzymes
-Termites digest
Pectin
Complex group of polysaccharides called galacturonoglycans
-alpha 1-4 linked galacturonic acid units with sugar side chains
**microbial fermentation
Beta-glucans
*Present in barley and oats
Homo-polymers of glucopyranose units with beta 1-4 and beta 1-3 links
-water soluble, highly fermentable
Beta-glucans presence in poultry diets
Poultry viscous intestinal fluid interferes with its digestion SO add beta-glucanase to diets with barley and oats
Why add beta-glucans to diets?
Used as functional fibre to reduce cholesterol and postprandial glucose levels
**occurs because forms a gel in intestines and results in trapping of certain nutrients (cholesterol) and elimination in feces
eg. reason for promotion of cheerios being heart healthy
Soluble Xylans
beta-linked xylose backbone with arabinose side chains
-Found in Rye and wheat and form gel (poor nutrient digestibility in poultry)
**need to add Xylanase to poultry diets
Structure of fibre
Cell walls in plants with cellulose, hemicellulose, and lignin forming microfibrils (lignocellulose)
Digestion of fibre
Vertebrates do not have the digestive enzymes required to break down fibre
BUT microbes can digest fiber via fermentation
