Dietary Fiber, Resistant Starch & Prebiotics

Comprehensive review flashcards covering dietary fiber definitions, analytical methods, physicochemical properties, resistant starch classifications, and prebiotics in pet nutrition.

How did the FDA (2016) define dietary fiber?

Non-digestible carbohydrates ($3$ or more sugar units) plus lignin that are intrinsic and intact in plants, as well as isolated or synthetic non-digestible carbohydrates recognized by the FDA to have health benefits (such as lowering blood glucose, lipids, or blood pressure, or promoting laxation or satiety).

What is the structural characteristic and fermentability of cellulose in dogs and cats?

It consists of a long, straight chain composed exclusively of glucose connected by $\beta\text{-1,4}$ linkages (crystalline or amorphous) and exhibits very low to no fermentation by dogs and cats.

What is the structure of hemicelluloses and how do they differ from cellulose in fermentation?

Hemicelluloses are branched chains of many different sugars featuring a straight backbone with $\beta\text{-1,4}$ linkages and side chains linked by $\beta\text{-1,4}$, $\beta\text{-1,2}$, or $\beta\text{-1,3}$; they are often bound to lignin and ferment more than cellulose.

Why is lignin not classified as a carbohydrate, and what role does it play in plant cell walls?

Lignin is composed of phenylpropanoid units rather than sugars; it functions as the "glue" that physically prevents cellulose and hemicellulose from being broken down and is highly resistant to fermentation.

What is pectin primarily composed of, and what are its physical and fermentation characteristics?

Pectin is made mostly of D-galacturonic acid connected by $\alpha\text{-1,4}$ linkages; it is readily fermented, forms gels, and is abundant in apples and citrus products.

How do the chemical linkages of $\beta\text{-glucans}$ differ between cereal grains and yeast/fungi?

In cereal grains (oats, barley), $\beta\text{-glucans}$ consist of glucose chains with $\beta\text{-1,3}$ and $\beta\text{-1,4}$ linkages in endosperm cell walls; in yeast and fungi, they feature $\beta\text{-1,3}$ links with $\beta\text{-1,6}$ branches.

What is the soluble-to-insoluble fiber proportion found in beet pulp?

Approximately $20\%$ soluble fiber and $80\%$ insoluble fiber.

How does the Crude Fiber (CF) analytical method mimic digestion, and what reagents does it use?

It boils the food in dilute sulfuric acid ($H_2SO_4\ 0.255\,N$) followed by dilute alkali ($NaOH\ 0.312\,N$).

What components does the Crude Fiber method fail to detect, and by how much does it typically underestimate pet food fiber?

It misses approximately $80\%$ of hemicellulose, $60\%$ of lignin, and $50\%$ of cellulose, commonly underestimating total fiber in pet foods by $30\text{--}50\%$.

What are the advantages of Total Dietary Fiber (TDF) over Crude Fiber, and what is its main limitation?

TDF measures total, soluble, and insoluble fiber with better control of starch, protein, and lipid interference; its main limitation is that some soluble oligosaccharides are not detected.

Which short-chain fatty acid (SCFA) produced by fiber fermentation is primarily utilized by the colon lining cells?

Butyrate.

How do viscous fibers and highly insoluble fibers differ in their effects on gastrointestinal transit time?

Viscous fibers slow food down (increase transit time, decrease rate), whereas highly insoluble fibers speed food up (decrease transit time by up to $50\%$, increase rate).

How can inclusion of $10\text{--}15\%$ fibrous ingredients impact nutrient digestibility in pet diets?

It can lower protein digestibility by $5\%$ or more, lipid digestibility by up to $10\%$, or reduce mineral digestibility by trapping nutrients or supplying phytates, oxalates, tannins, or enzyme inhibitors.

What fiber concentration is typical for premium pet foods versus weight loss diets?

Premium pet foods typically contain $4\text{--}6\%$ fiber, while weight loss diets may contain up to $20\text{--}25\%$ fiber.

Up to what inclusion level can beet pulp be fed as a single fiber source without lowering nutrient digestibility?

Up to $7.5\%$ of the diet.

What are the four types of resistant starch (RS1 to RS4) and where are they found?

RS1 is physically inaccessible starch in whole/partially milled grains, seeds, and legumes; RS2 is uncooked B-type granules in raw potatoes and unripe bananas; RS3 is retrograded starch in processed/cooked and cooled foods; RS4 is chemically modified starch (ester or ether groups).

Which type of resistant starch is the most common form found in pet foods?

RS3 (retrograded starch).

What is the energy value of non-digestible oligosaccharides and why is it low?

$1.5\text{--}2.0\,\text{kcal/g}$, because bacterial fermentation in the colon is less efficient at yielding energy than enzymatic digestion in the small intestine.

What are the distinct definitions of a prebiotic, a probiotic, and a postbiotic?

A prebiotic is a substrate selectively utilized by host microorganisms conferring a health benefit; a probiotic consists of living microorganisms conferring a health benefit; a postbiotic is a preparation of inanimate (dead) microorganisms and/or their components conferring a health benefit.

Which beneficial bacteria are targeted by prebiotics, and which harmful bacteria do they help suppress?

They target beneficial bacteria such as Bifidobacterium, Lactobacillus, and Faecalibacterium, while suppressing harmful bacteria like Salmonella, Campylobacter, and Listeria.

What is the typical dietary inclusion rate for prebiotics in pet food, and which species is more responsive to fermentation?

Prebiotics are usually included at less than $1\%$ of the diet; cats are more responsive to fermentation than dogs.

How long does it take for gut microbiota to revert to baseline once prebiotic feeding is stopped?

Within $4\text{--}7$ days.

Give examples of fibers that have high viscosity and high fermentability versus fibers that have low viscosity and low fermentation.

High viscosity and fermentable: guar gum and pectin. Low viscosity and low fermentation: cellulose, soybean hulls, and hemicellulose.