Polysaccharides B

Why are native starches rarely used in commercial food processing?

Because they lack specific functional properties required in industrial applications, so food processors prefer modified starches tailored for certain behaviors.

Why is most modified starch in North America derived from corn?

Corn is abundant, inexpensive, and easily processed, making it the primary starch source for industrial modification.

What is the purpose of modifying starch for food processors?

To provide specific properties such as thickening, stability, texture control, freeze‑thaw stability, and reduced retrogradation.

What happens to starch granules during pre‑gelatinization?

They are heated below their gelatinization temperature (50–80°C), causing partial swelling and structural disruption before drying.

Why does pre‑gelatinization make starch dispersible in cold water?

Because heating disrupts granule organization, allowing water to penetrate easily without requiring heat during use.

Why do pre‑gelatinized starches require higher usage levels compared to native starch?

Because partial disorganization reduces their thickening power, so more is needed to achieve similar viscosity.

Why are pre‑gelatinized starches popular in the food industry?

They hydrate instantly in cold water, save processing time, and simplify preparation steps.

What is the basic principle of drum drying in pre‑gelatinized starch production?

A starch slurry is spread onto a heated drum surface, rapidly dried into a film, scraped off, and ground into granules.

Why does drum‑dried pre‑gelatinized starch form brittle flakes before grinding?

Rapid water evaporation forms a hardened starch film that shatters upon scraping.

Why can spray‑dried pre‑gelatinized starch improve the fluidity of dry solids?

Its spherical, hollow, uniformly shaped particles reduce friction between particles, improving flow

What structural characteristic distinguishes spray‑dried pre-gelatinized starch from native starch?

It exhibits hollow, shriveled, spherical particles smaller than natural granules

How does spray drying affect the particle size of pre‑gelatinized starch?

It reduces particle size, making the powder finer and more functional for instant foods.

What is the major structural change produced by extrusion‑based pre‑gelatinization?

Extrusion destroys all granule integrity, producing fully amorphous, molten starch material.

Why does extrusion produce more amorphous starch than drum or spray drying?

High pressure, shear, and heat completely disrupt granule organization.

Why are pre‑gelatinized starches commonly used in instant foods?

They thicken without heating, making them ideal for instant puddings, gravies, and sauces.

What defines acid‑modified starches, commonly called thin‑boiling starches?

Starch is held just below gelatinization temperature in an acidic medium, partially hydrolyzing glycosidic bonds.

Why does acid modification maintain granule integrity despite hydrolysis?

Acid selectively cleaves glycosidic bonds without destroying the granule structure itself.

Why are acid‑modified starches called “thin‑boiling”?

Because they form low‑viscosity hot solutions that become firm gels upon cooling.

Why are thin‑boiling starches useful in candy manufacturing?

They pour easily when hot but set into firm, stable gels such as in jujube candies.

What is the main purpose of cross‑linking starch?

To strengthen swollen granules so they resist breakdown from heat, shear, and acidity.

Why do normal starch granules break down under high shear?

When swollen extensively, their granule walls weaken and rupture easily.

How does cross‑linking chemically reinforce starch granules?

Cross‑linkers create covalent bridges between hydroxyl groups of adjacent polymer chains.

What common chemicals are used as starch cross‑linking agents?

Acetic, citric, or adipic anhydrides, which form covalent linkages between starch chains.

Why is C‑6 of glucose frequently targeted during starch cross‑linking?

It is the least sterically hindered hydroxyl group, making it the most reactive site.

What structural effect does citric acid anhydride have when cross‑linking starch?

It forms diester bridges between starch chains, creating starch citrate.

What is Distarch Phosphate and what functional group links the chains?

A cross‑linked starch where two chains are joined by a phosphate diester group.

What cross‑linking chemical forms Distarch Phosphate?

Phosphorus oxychloride, sodium tripolyphosphate (STPP), or sodium trimetaphosphate (STMP).

What type of linkage is formed in epichlorohydrin‑crosslinked starch?

An ether linkage between two starch chains.

What structural feature results from epichlorohydrin cross‑linking?

Chains are linked by –O–CH₂–CHOH–CH₂–O– bridges.

What type of bonds does citric acid form when used as a cross‑linking agent?

Diester bonds between starch chains

What linkage does malic acid create during starch cross‑linking?

Diester bonds between starch chains, forming malate cross‑linked starch.

What is Distarch Adipate and which agent forms it?

A starch cross‑linked by adipic acid, forming adipate diester bridges.

How do STMP and STPP cross‑link starch molecules?

By forming phosphodiester bridges between chains.

What is a key functional result of starch cross‑linking?

Granules swell less but maintain their structural integrity under shear and heat.

Why do cross‑linked starches have lower maximum viscosity than native starches?

Because restricted swelling reduces peak thickening potential.

Why are cross‑linked starches more resistant to acid hydrolysis?

Cross‑links compensate for bonds broken during acid exposure, preventing excessive degradation.

What is a starch derivative?

A starch chemically modified through esterification, etherification, oxidation, or cationic treatment.

What general goal does starch derivatization achieve?

Reducing polymer‑polymer hydrogen bonding through steric hindrance or charged group introduction.

Why are starch derivatives used to control retrogradation?

They hinder molecular reassociation, preventing gels from firming or syneresis.

What chemical change occurs in oxidized starches?

Hydroxyl groups are converted to carboxyl groups (and sometimes aldehydes or ketones) by oxidizing agents like NaOCl or H₂O₂.

What functional properties do oxidized starches gain due to the introduction of carboxyl, aldehyde, and ketone groups?

They gain improved stabilization, adhesion, gelling properties, and enhanced clarity in food systems.

Why does oxidation reduce starch retrogradation?

Carboxyl groups disrupt polymer‑polymer interactions, making it harder for chains to realign and crystallize.

Why are acid-converted (thin‑boiling) starches important in liquid food formulations?

They lower viscosity while hot, allowing easy pumping and mixing, but form gels upon cooling.

What is the main application for acid‑converted starches in the food industry?

Gum candies and liquid foods requiring controlled viscosity.

What functional benefit does oxidation provide during starch use in batters and coatings?

It improves adhesion and produces smoother, more stable films.

Why are dextrins highly soluble in water?

Pyroconversion reduces molecular size and disrupts crystallinity, enhancing solubility.

What functional roles do dextrins serve in the food industry?

Binding, coating, encapsulation, and gloss enhancement.

Why are dextrins used in flavorings, spices, and oils?

They provide high solubility and effective binding, helping anchor flavors to particles.

How does cross‑linking improve the performance of starch in pie fillings and sauces?

It prevents granule rupture under heat, acid, and shear, maintaining consistent thickness.

Why are cross‑linked starches used in infant foods and baby formulas?

They offer stable viscosity that withstands heat processing and storage.

Why does esterification modify starch behavior in candies and emulsions?

Ester groups reduce intermolecular bonding, improving stability and lowering the temperature needed for gelatinization.

What advantage does combining esterification with cross‑linking give starch?

It improves stability but also produces starches sensitive to alkaline conditions.

Why is etherification used in soups and frozen foods?

It produces starches stable at low temperatures with reduced retrogradation.

What is the purpose of dual‑modified starches?

To combine multiple benefits—such as stability, clarity, and reduced retrogradation—into one starch.

Why are dual‑modified starches preferred in complex products like salad dressings?

Their combined modifications resist separation, temperature changes, and acidity.

What are the two basic types of starch conversion and what are they used for?

Dry pyroconversion for cold‑water‑soluble starches, and acid hydrolysis for dextrins and sugars.

What conditions are required for pyroconversion to occur?

Starch is sprayed with dilute HCl and subjected to high temperatures.

How does pyroconversion hydrolyze starch?

By breaking α‑1,4 and α‑1,6 linkages under heat and acidity.

What is transglucosidation during starch pyroconversion?

The breaking of α‑1,4 bonds and formation of new, random linkages such as 1,3 and 1,5.

Why does repolymerization occur during pyroconversion?

Free sugars produced by hydrolysis can recombine into new polymers.

Why does caramelization occur during pyroconversion?

Free sugars exposed to high heat undergo browning reactions.

Under what conditions are white dextrins produced?

High moisture, high acid, and relatively low temperature favor hydrolysis over browning.

Why are white dextrins soluble in cold water?

Their lower molecular weight and loss of granule structure increase solubility.

How is viscosity controlled in white dextrin production?

By adjusting moisture, acid concentration, and heating time.

Under what conditions are yellow dextrins produced?

Low moisture, moderate acid, and higher temperatures.

Why do yellow dextrins develop a yellow color?

Due to non‑enzymatic browning (caramelization) during heating.

How are viscosity and DP controlled in yellow dextrins?

By adjusting processing temperature, acid level, and exposure time.

What distinguishes British gums from white and yellow dextrins?

They are produced with little or no acid and high heat, leading to extensive transglucosidation and minimal hydrolysis.

Why are British gums dark in color?

High temperatures cause significant caramelization and browning reactions.

Why do British gums form stiff gels?

They retain higher molecular weight and have unique transglucosidation‑derived structures.

Why are British gums widely used in candy manufacture?

They form strong, stiff gels ideal for confectionery textures.

Why is acid hydrolysis considered the older method of converting starch to sugars and syrups?

It was historically used before enzymatic technology provided more control.

What happens when starch is heated with hydrochloric acid and pressurized steam?

It gelatinizes and is simultaneously hydrolyzed, producing sugars and dextrins.

Why is acid hydrolysis described as extensive and random?

The acid attacks glycosidic bonds without specificity, breaking chains unpredictably.

How is the degree of starch hydrolysis monitored?

By measuring the reducing sugar content of the hydrolysate.

Why does reducing sugar content increase during hydrolysis?

More mono-, di-, and oligosaccharides are produced, all of which have reducing ends.

What is the definition of dextrose equivalent (DE)?

The ratio of reducing power of a syrup compared to pure dextrose, expressed as a percentage.

What does a DE value of 100 represent?

Complete hydrolysis of starch to pure glucose.

Why can acid hydrolysis rarely produce DE values above 50?

Repolymerization and equilibrium reactions prevent full conversion to glucose.

Why is acid hydrolysis not used for high‑DE syrups?

It cannot produce high sweetness levels efficiently, making enzymatic methods preferable.

Why is enzymatic hydrolysis preferred over acid hydrolysis for producing high‑DE syrups?

Because enzymes offer specificity, control, and can produce very high sweetness levels that acid hydrolysis cannot achieve.

What general class of enzymes hydrolyzes starch into sugars?

Amylases, which break down starch through cleavage of glycosidic bonds.

Why are microorganisms used commercially to produce amylases?

Microbes can be genetically manipulated to overproduce specific enzymes, and the enzymes are easy to isolate in large quantities.

How does enzyme selection allow precise control of starch conversion?

Each enzyme targets specific bonds and positions, allowing control over molecular weight, sweetness, and viscosity of the final syrup.

Why is enzymatic conversion useful for producing different types of sweeteners?

By adjusting enzymes and process conditions, industries can produce syrups of varying viscosities and sweetness for beverages, syrups, baked goods, and more.

How does an α‑amylase enzyme act on starch molecules?

It randomly cleaves internal α‑1,4 glycosidic bonds, reducing viscosity rapidly.

Why is α‑amylase known as a liquefying enzyme?

Because it quickly reduces viscosity by breaking long chains into smaller fragments.

What products result from α‑amylase activity?

Oligosaccharides, glucose, maltose, and pannose (a trisaccharide containing an α‑1,6 link).

Why does α‑amylase not hydrolyze α‑1,6 branch points?

Its active site is specific to α‑1,4 linkages, so branching points remain intact.

How does β‑amylase act on starch molecules?

It is an exoenzyme that cleaves maltose units from the non‑reducing ends of starch chains.

Why is β‑amylase called a saccharifying enzyme?

Because it produces maltose rapidly, increasing sweetness without greatly reducing viscosity.

Why does β‑amylase not significantly change solution viscosity?

It works only at chain ends, leaving most of the polymer intact, so thickening remains largely unchanged.

What capability distinguishes glucoamylase from other amylases?

It removes single glucose units from non‑reducing ends and can hydrolyze both α‑1,4 and α‑1,6 bonds.

Why is glucoamylase important for producing high‑glucose syrups?

It can completely convert starch fragments into glucose.

What are “limit dextrins” and how are they formed?

They are branched oligosaccharides left after α- and β‑amylase action because enzymes cannot easily access α‑1,6 branch points.

How does pullulanase assist in complete starch breakdown?

It hydrolyzes α‑1,6 branch points, enabling the breakdown of limit dextrins.

Why is pullulanase essential for full conversion to glucose when used with glucoamylase?

It removes branch points so glucoamylase can access and hydrolyze all remaining linkages

How does combining multiple enzymes affect starch hydrolysis outcomes?

It allows complete debranching and conversion, producing syrups with desired sweetness and viscosity profiles.

Why is enzymatic control critical for producing specific sweetener formulations?

Different enzymes generate specific sugar profiles needed for products such as beverages, candies, pancake syrups, and baby foods.

What enzymatic reaction transforms D‑glucose into D‑fructose?

Isomerization by glucose isomerase.