Carbohydrates and Glycosidic Bonds

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Questions and Answers

What are carbohydrates understood to be today?

Polyhydroxylated compounds, which include polyhydroxylated aldehydes, polyhydroxylated ketones, and their derivatives.

How many main categories of carbohydrates are there in animal nutrition?

  • Two (correct)
  • Three
  • Four
  • One

What are non-fiber carbohydrates?

Those that can typically be degraded by an animal's endogenous enzymes.

What are fibers?

<p>Long-chain carbohydrates that cannot be degraded by an animal's endogenous enzymes.</p> Signup and view all the answers

Animal endogenous enzymes can hydrolyze a-glycosidic bonds but are generally unable to break down β-glycosidic bonds, except in specific cases where the first sugar is _____ (e.g., lactose, which consists of a β-galactose and a glucose unit).

<p>galactose</p> Signup and view all the answers

What is starch?

<p>A polysaccharide made up of long chains of glucose units.</p> Signup and view all the answers

What is amylose?

<p>A linear, unbranched chain of 200–300 glucose units linked together.</p> Signup and view all the answers

What happens during gelatinization?

<p>Water and heat cause the starch granules to swell, leading to the loss of their crystalline structure. (D)</p> Signup and view all the answers

What is retrogradation?

<p>The process where amylose and amylopectin begin to recrystallize as starch cools.</p> Signup and view all the answers

What is resistant starch?

<p>Starch that becomes resistant to amylase activity and is degraded more slowly.</p> Signup and view all the answers

In monogastrics, what is one of the primary effects of starch digestibility?

<p>Its influence on glycemic and insulinemic responses.</p> Signup and view all the answers

In ruminants, to what is the impact of starch digestibility primarily linked?

<p>To fermentation dynamics in the rumen.</p> Signup and view all the answers

What is rumen acidosis?

<p>A serious metabolic disorder that arises when the fermentation of highly digestible starch produces short-chain fatty acids (SCFAs) at a rate faster than the rumen can buffer them.</p> Signup and view all the answers

What happens as grass matures and grows?

<p>The levels of hemicellulose, cellulose, and lignin increase, leading to a gradual decline in digestibility.</p> Signup and view all the answers

Lignin is a carbohydrate

<p>False (B)</p> Signup and view all the answers

Animal enzymes can hydrolyze fiber.

<p>False (B)</p> Signup and view all the answers

What is the Weende method used for?

<p>Determining fiber content on feed labels.</p> Signup and view all the answers

What does Neutral Detergent Fiber (NDF) measure?

<p>Hemicellulose, cellulose, and lignin.</p> Signup and view all the answers

What does Acid Detergent Fiber (ADF) measure?

<p>Cellulose and lignin.</p> Signup and view all the answers

What does Acid Detergent Lignin (ADL) measure?

<p>Lignin, the completely indigestible fraction of fiber.</p> Signup and view all the answers

What is the Prosky method used for?

<p>To differentiate between soluble and insoluble fibers (NDF).</p> Signup and view all the answers

How do ruminants digest fibers?

<p>Through microbial fermentation and rumination.</p> Signup and view all the answers

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Flashcards

Polyhydroxylated Compounds

Carbohydrates containing multiple hydroxyl groups (alcohol functions), contributing to water solubility. They include aldehydes, ketones, and their derivatives, and may contain amines or carboxyl groups.

Non-Fiber Carbohydrates

These are carbohydrates that can be broken down by an animal's own enzymes, including simple sugars and starches.

Fibers

Long-chain carbohydrates that cannot be digested by animal enzymes but can be fermented by microbes. Commonly found in plant cell walls.

Alpha (α) Glycosidic Bonds

Formed from the anomeric carbon in the α-configuration of the first sugar.

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Beta (β) Glycosidic Bonds

Formed from the anomeric carbon in the β-configuration of the first sugar.

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Amylose

A polysaccharide composed of long, unbranched chains of glucose units, which is slowly degraded.

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Amylopectin

A highly branched starch molecule composed of long chains of glucose with branches, which is more easily degraded.

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Gelatinization

A process where starch granules swell with water and heat, lose their crystalline structure, and become more accessible to amylases

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Retrogradation

A process where amylose and amylopectin recrystallize as starch cools, making it less digestible.

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Rumen Acidosis

A condition in ruminants when rapid starch fermentation leads to an accumulation of short-chain fatty acids, dropping the ruminal pH.

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Study Notes

  • Carbohydrates were once thought to be carbon and water, now known as polyhydroxylated compounds including aldehydes, ketones, and derivatives.
  • The presence of multiple hydroxyl groups gives carbohydrates their water solubility.
  • Some carbs have amines (NH2) and carboxyl groups (COOH).

Carbohydrate Categories

  • Non-fiber carbohydrates can be degraded by an animal's endogenous enzymes.
  • Fibers are long-chain carbohydrates not degraded by animal enzymes but fermentable by microbes like bacteria, yeast, and fungi.
  • Fibers are found in the cell walls of plants and include cellulose, hemicelluloses, pectin, gums, mucilage, and algal polysaccharides.
  • Fiber encompasses lignin, a non-carbohydrate polyphenolic compound that is indigestible and plays a role in plant structure.

Glycosidic Bonds

  • Alpha (α) bonds form when the bond originates from the anomeric carbon in the α-configuration.
  • Beta (β) bonds form when the bond originates from the anomeric carbon in the β-configuration.
  • Animal enzymes can hydrolyze α-glycosidic bonds but generally not β-glycosidic bonds, except when the first sugar is galactose.
  • Microbial enzymes from bacteria, fungi, and yeast can efficiently degrade β-linkages.

Starch

  • Starch consists of long chains of glucose units in two forms.

Amylose

  • Amylose is a linear, unbranched chain of 200–300 glucose units.
  • Amylases can only degrade starch from the ends of the chains; amylose degrades slowly.

Amylopectin

  • Amylopectin is a highly branched starch with short chains of 24-30 glucose units attached at regular intervals.
  • Amylopectin is more easily degraded by amylases due to its branching, leading to faster breakdown than amylose.

Starch Granules

  • In grains, starch is stored in starch granules, embedded in a protein matrix, consisting of alternating layers of crystalline and amorphous starch.
  • A-type crystals are degraded faster, B-type more slowly, and C-type are intermediate.
  • The structure of starch granules influences the rate of starch degradation.
  • Smaller granules are degraded faster.
  • Granules with pores are degraded more rapidly.
  • Starch with higher amylopectin content degrades faster.
  • Denser granules are degraded more efficiently.
  • A-type crystals are more easily hydrolyzed.

Starch Digestibility

  • Starch digestibility can be improved through cooking via gelatinization, where water and heat cause granules to swell and lose their crystalline structure, becoming solubilized.
  • Retrogradation occurs as starch cools, with amylose and amylopectin recrystallizing, making the starch less digestible.
  • Resistant starch becomes resistant to amylase activity and is degraded more slowly, influenced by starch type, cooking conditions, storage time, and moisture content.

Starch and Animal Health

  • Starch digestibility and degradability regulate the glycemic, insulinemic response, and starch fermentation in the digestive tract.
  • The impact of starch digestibility varies between species.
  • In monogastrics, starch digestibility affects glycemic and insulinemic responses; highly digestible starch leads to rapid glucose and insulin increases.
  • It is essential to regulate starch intake in species like pets and horses to avoid metabolic disorders.
  • In ruminants, starch digestibility is linked to fermentation dynamics in the rumen; rapid fermentation can cause rumen acidosis.
  • In this condition the fermentation of digestible starch produces short-chain fatty acids (SCFAs) faster than the rumen can buffer them.
  • Managing starch digestion requires balancing digestible, resistant, and total starch.
  • Equids and lagomorphs rely on enzymatic digestion in the small intestine and microbial fermentation in the large intestine.

Fibers

  • As grass matures, hemicellulose, cellulose, and lignin increase, decreasing digestibility.
  • These are classified as dietary fibers, where lignin is not a carbohydrate.
  • Lignin impacts fiber digestibility by binding to hemicellulose and cellulose.
  • Animal enzymes and microbial populations cannot break down lignin, but some ruminal fungi can partially separate lignin from cellulose.
  • Fiber-rich forages become difficult to digest as fiber content rises; animal enzymes cannot hydrolyze fiber, and microbial digestion is time-consuming.
  • Higher fiber content in grass lowers overall digestibility and energy availability.

Fiber Analysis Methods

  • The Weende method is the official method of determining fiber content on feed labels; it involves treating the sample with acid and base but underestimates total fiber content.
  • The Van Soest method is a three-step procedure offering a detailed classification of fiber fractions.
  • Neutral Detergent Fiber (NDF) uses a neutral detergent and amylase to extract hemicellulose, cellulose, and lignin; it is associated with forage bulkiness and affects rumination time, feed intake, and digestibility.
  • Acid Detergent Fiber (ADF) uses an acid detergent to extract cellulose and lignin, removing hemicellulose; it correlates with diet digestibility.
  • Acid Detergent Lignin (ADL) uses sulfuric acid to isolate lignin, the indigestible fiber fraction.
  • The Prosky method differentiates between soluble and insoluble fibers (NDF); soluble fibers modulate digestion and gut health, while insoluble fibers contribute to intestinal motility and bulk.
  • Ruminants digest fibers through microbial fermentation and rumination; microbiota produces enzymes that break β-glycosidic bonds.
  • Rumination involves regurgitating and rechewing ruminal content to reduce particle size and increase surface area.
  • During fiber fermentation, microbiota produces short-chain fatty acids (SCFAs), primarily acetic, propionic, and butyric acids, serving as a major energy source.
  • Carbon dioxide and hydrogen are released as byproducts, converted to methane by methanogenic archaea.
  • Acetic and butyric acids are converted into fatty acids for milk production; propionic acid is metabolized into glucose.
  • Acetic and butyric acids are produced by fibrolytic bacteria, while propionic acid derives from amylolytic bacteria
  • The production of acids also results in methane release.

Fiber Classification

Solubility

  • Some fibers dissolve in water.
  • Soluble fibers are easier to degrade.
  • Insoluble fibers are preferred for ruminants and herbivorous monogastrics, while soluble fibers are favored in non-herbivorous monogastrics.

Viscosity

  • Viscosity is the ability to form a gel through water retention.
  • Viscous fibers normalize digestion, slowing transit and softening stools.

Water retention

  • Some fibers swell in the presence of water.
  • In animals like horses, fibers with high water retention can lead to choke unless hydrated first.

Ionic exchange capacity

  • Some fibers adsorb minerals, decreasing digestibility and bioavailability.

Filter effect

  • Some high-viscosity fibers filter between nutrients, enzymes, and gut transporters.

Fermentescibility

  • Some fibers are more quickly fermented.
  • In ruminants and herbivorous monogastrics, highly fermentable fibers limit acidosis risk, while non-herbivorous monogastrics benefit from them for butyric acid production.

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