Carbohydrates

Question 1

Carbohydrates

Answer 1

Carbohydrates are among the “macronutrients” that provide substantial metabolic energy.

Question 2

Phytate

Answer 2

Phosphate-containing saccharide found primarily in cereal brans (1% in oat and 3.7% in wheat brans). They substantially bind cations (ex. Zn2+)

Question 3

Give three examples of disaccharides

Answer 3

1. Lactose 2. Sucrose 3. Lactulose

Question 4

Examples of polysaccharides

Answer 4

1. Starches: amylose, amylopectin, glycogen 2. Hemicellulose, cellulose, pectins, and gums

Question 5

Lactose

Answer 5

ß- 1,4 linked galactose + glucose

Question 6

Lactose is unique to what?

Answer 6

• Milk, the primary carbohydrate in milk
  
  • A significant portion of the energy in milk
  • Contributes substantially to osmolarity of milk
  • A poor substrate for pathogenic microbes

Question 7

What is unique about birds regarding lactose?

Answer 7

Birds do not digest lactose; they will develop diarrhea when given liquid milk or milk powder containing lactose.

Question 8

Is lactose readily digestable in adults?

Answer 8

• No, lactose is not readily digested in adults
  
  • The beta-1,4 linkage in lactose is resistance to hydrolysis by disaccharidases present in adults. Saccharides digested in animals have alpha-1,4 linkages
  • Lactose is cleaved in young animals by transient expression of “lactase”, a disaccharidase specific for lactose

Question 9

Lactulose

Answer 9

1. beta-1,4 linked galactose + fructose
2. Not hydrolyzed by mammalian enzymes
3. Hydrolyzed by some gastrointestinal microbial enzymes

Question 10

Sucrose

Answer 10

1. alpha 1,4-linked glucose + fructose
2. Digested by animals, even cats

Question 11

Sucrose - Dogs

Answer 11

1. A positive effect on the acceptability of food
2. A “humectant” in the manufacture of semi-moist foods (humectant –> keeps food moist)

Question 12

Sucrose - Cats

Answer 12

1. Indifferent to sucrose and other sweet substances
2. Causes fructosuria in high dietary concentrations, >15% of diet

Question 13

Starch

Answer 13

1. alpha 1,4 and 1,6 linkages of glucose
2. Straight chains (amylose) or in chains with branches (amylopectin in plants, and glycogen in animals)

Question 14

• Plant starches occur in….

Answer 14

• Plant starches occur in semicrystalline granules
  
  • Granules are variably resistant to digestion

Question 15

What does high moisture and heat do to the semicrystalline granules of plant starches?

Answer 15

• High moisture and heat (as with cooking of starches in commercial canned and dry expanded diets) “gelatinize” granules
  
  • Melts and hydrates starch crystals
  • Transforms starch structurally
  • Increases digestibility of starches

Question 16

Starch - Glutens

Answer 16

• Proteins that are associated with plant starches include glutens
  
  • Glutens of low water solubility, amino acids and structure vary
  • Wheat gluten causing food hypersensitivity in rare cases

Question 17

Why are plant starches not well tolerated in neonates?

Answer 17

Because neonates lack sufficient amylase activity to readily utilize starch.

Question 18

Cellulose

Answer 18

Beta-1,4 linkages of glucose

Straight chains that lie flat, forming layers held together with hydrogen

Structure forms densely packed, water-insoluble material in plant cell wall fibrils

Structure prevents digestion by animals

Question 19

What to gastointestinal microbes do with cellulose?

Answer 19

• They slowly produce organic acids from cellulose
  
  • Microbes produce beta 1,4 glucosidases which animals lack
  • Organic acids are metabolized by the host
  • Organic acids are a substantial energy source for ruminant and post-gastric fermenters

Question 20

Hemicellulose

Answer 20

• Chemically and structurally different from cellulose
  
  • A variety of saccharides in polymers that are 50 to 200 units in length with branching (unlike cellulose)
  • Insoluble in water (like cellulose)
  • Structure prevents digestion by animals (like cellulose)

Question 21

Hemicellulose and cellulose - contribution to crude fiber

Answer 21

1. Cellulose contributes greatly to crude fiber in proximate analysis
2. Hemicellulose only partially contributes to “crude fiber” in proximate analysis because some hemicellulose is soluble in dilute alkaline solution

Question 22

Polysaccharides - Pectins and Gums

Answer 22

1. Structure prevents digestion by animals
2. Good water solubility
3. Gastrointestinal microbes produce organic acids from them
4. Used in commercial pet foods
   
   • Gelling agents, making gravy, forming “meat-chunks”

Question 23

Dietary Fiber

Answer 23

DIetary fiber is structurally diverse, considered to be remnants of edible plant cells

Include polysaccharides, lignin, and other associated substances resistant to digestion by the animal host.

Question 24

Dietary Fiber - Examples of Polysaccharides

Answer 24

Cellulose, hemicellulose, pectins and gums

Question 25

Dietary Fiber - Example of non-polysaccharide

Answer 25

* Lignin * Polyfunctional phenol polymers infiltrated through the cellulose of plant cells * Imparts "woody" quality to plants, greatest in mature plants * Water insoluble * **_Cannot be digested by gastrointestinal microbes_**

Question 26

Properties of dietary fiber

Answer 26

1. Not digestible by the animal host 2. Variably water soluble 3. Variably fermentable by gastrointestinal microbes

Question 27

Dietary fiber uses in dogs and cats

Answer 27

1. Lower dietary energy density for weight reduction 2. Empirical treatment of chronic diarrhea (fermentable fibers) 3. Increase fecal bulk and moisture content depending on type of fiber * Fibers that bind little water increase fecal bulk and tend to harden the feces * Fibers that absorb large amounts of water increase fecal bulk and tend to soften the feces and increase fecal water loss 4. Manage diabetes mellitus - slows gastric emptying and absorption of alimentary carbohydrate

Question 28

Dietary carbohydrates in herbivores - what is nutritionally essential for GI function?

Answer 28

Dietary carbohydrate in the form of dietary fiber is nutritionally essential for normal GI function.

Question 29

Dietary carbohydrates in dogs and cats

Answer 29

* Dietary carbohydrate is NOT nutritionally essential, EXCEPT: * During pregnancy and lactation when dietary carbohydrate is very low or absent AND dietary protein is marginal

Question 30

Dogs and cats: "low" carbohydrate diets

Answer 30

1. **High energy diets**, more energy from fat (performance, critical care) 2. **High protein diets**, protein exhcanged for carbohydrate (feline diabetes)

Question 31

Dogs and Cats - "high" carbohydrate diets

Answer 31

1. Provide energy in place of fat and/or protein 2. **Useful clinically for weight loss treatment, canine pancreatitis**

Question 32

Carbohydrate use in commercial foods for dogs and cats - **Dry-type, extruded diets**

Answer 32

* Typically contain \>30% carbohydrate from starch in grain or potato ingredients * Extrusion requires that the dietary ingredients contain sufficient starch to form a gelatinized-dough * Carbohydrate is a less expensive source of dietary energy than protein and fat

Question 33

Carbohydrate use in commercial foods for dogs and cats - **Semi-moist diets**

Answer 33

* Carbohydrates are used as preservatives and humectants in semi-moist foods

Question 34

Carbohydrate use in commercial foods for dogs and cats - **Canned Diets**

Answer 34

* Carbohydrate content varies markedly, especially dog foods * "Meat-type" canned foods may contain very little carbohydrate