Foodchem Lecture 20

You make D-fructose

Had about 1.3x the sweetening power of glucose and is considered somewhat sweeter than sucrose

Advances in enzyme technology have made this ultimate conversion economical and it is now used extensively

about 45% D-fructose

Not really, except in special applications such as pharmaceuticals and fine chemicals

invert sugar

An equimolar mixture of glucose and fructose commonly produced by the acid hydrolysis of sucrose

• Sucrose - especially in the soft drink sector
• (The reason for this direct comparison is that sucrose is commonly ''inverted'' to stabilize its sweetness, especially if incorporated into acidic products, a classic acidic application being the sweetening of soft drinks)

Assist in prevention of crystallization of sucrose when used at high concentrations in food systems

• The alpha-1 and beta-2 glycosidic linkage in sucrose is acid labile and readily hydrolyzed by heat and/or acid (over time)
• For acidic beverages (mostly soft drinks) the resukt is a change in sweetness over time
• This can be avoided by inverting sucrose prior to its addition to the beverage so its sweetness is stable, which avoids sweetness changes in the product over time

Yes - high fructose corn syrup effectively has this property built into the base product and does not require the inversion step needed for glucose

• 1. Intrinsically sweeter than glucose
• 2. More soluble than glucose
• 3. Does not crystallize readily (so good for frozen products) as it is a sugar mixture already
• 4. The syrup also becomes sweeter as temperature decreases

Lowered demand on sucrose, so affected the supply side (Cuba, Philippines, Hawaii)

• 12 million tons
• Canada produces about 2% of the total

USA

Bio-ethanol

• Texture modification
• Gel formation
• Raw material as a syrup and sweetener
• Stabilizer for emulsions

To minimize hydrolysis as a result of heat treatment

To preven sticking

In the confectionary industry

• Made up of D-glucose like starch, but has beta-1,4 glycosidic linkages making it indigestible for humans but not ruminants
• (vs alpha-1,4 glycosidic linkages)

Linear, no branched counterpart

Exists as fiber-like bundles which have extensive crystalline regions - highly organized by hydrogen bonding

• Cellulose
• Hemicellulose
• Pectin
• Lignin

• Yes, think about stability of paper and how long it takes wood to rot
• Used in textile industry as a fiber (rayon or viscose)

Yes, but no one has successfully applied them on a large scale to commercially produce glucose

• Largely useless in food, functionally and nutritionally
• But modified celluloses are useful and have important functional roles

• Can be used as a bulking agent without contributing calories
• Also used extensivle to convert liquid products into free flowing powders by adsorption
• (Honey, cheese, syrups, etc. can be converted into free flowing powders by mixing with microcrystalline cellulose and then dispersing the coated powder into food products)

• A methylated derivative of pure cellulose formed by hydrating cellulose in a strongly basic solution and reacting cellulose with sodium chloroacetate
• The net reaction is the replacement of an OH group with a carboxymethyl on the polymer

A more soluble charged polymer that is dispersible and capable of contributing viscosity to a solution as well as forming weak gels

Based on the average molecular weight of the polymer and the extent of derivatization

Makes it susceptible to pH changes and may precipitate out of solution around its isoelectric point

The carboxyl groups repel the other polymers

Use divalent ions to crosslink the polymers to form a gel

CMC has found a wide application in the food industry as a viscosity enhancing agen hich contributes no calories

Provides a smooth texture and inhibits ice crystal growth during storage (which causes graininess)

Hydroxypropyl and methyl cellulose

No, because they are non-ionic

Heat setting gels which associate by hydrogen bonding

Are polysaccharides associated with the middle lamella found between plant cell walls

Act as binders to hold the plant cells together

Used extensively as a gelling agent for the preparation of jams and jellies

Complex and non-homogeneous and their properties depend on the plant source

Typically citrus peel or apple pomace extracts

Polygalacturonic acid, a complex polysaccharide, which can be extracted from plant material

Galacturoic acid, an acid analog of galactose, with its carboxyl group being either the free acid (or its salt) or esterified to a methyl group

Based on their relative degree of methylation (DM)

• 1. pectic acids
• 2. pectinic acids
• 3. pectin

Polymers of predominantly polygalacturonic acid, free of methyl ester groups

Polymers of polygalacturonic acid with some degree of methylation (low methoxy pectin)

Polymers of polygalacturonic acid with >50% of the carboxyl groups methylated (regular --> high methoxy pectins)

• The source
• The method of extraction

On the functional properties of the polysaccharide

In combination with sugar and acid, these form a gel, which in combination reduces water activity and pH to inhibit microbial growth after a mild thermal process

about 50%

pH 2.8-3.2

Sugar, acid, and water

The repulsive charge of the residual carboxyl groups is reduced, while the sugar competes for water of hydration allowing the polymers to associate in a 3D manner to form a gel

Yes, but it is uneconomical as large amount are required

As a by-product of the citrus and apple juice processing (orange/grapefruit peels or apple pomace) being extracted using dilute acid

Because the methyl groups are labile and are readily lost at neutral or basic pH

Both quality and price of pectin

Serve well for jellies (no suspended material) where the rate of gel setting is of no major consequence

For jams, which contain particulate matter, a rapid setting or high methoxy pectin is usually required

• Requires special extraction procedures and will set at higher temperatures
• Useful in preventing particulate material from settling out (more expensive)

Diet jams and jellies

By controlled hydrolysis of the methyl group using either alkaline conditions or using the enzyme pectin methyl esterase

Much like in CMC, a gel can be produced using divalent ions to crosslink the polymers at the carboxyl groups

• No sugar needed
• pH range is much broader

Antimicrobial agents (like benzoic acid or proprionic acids) are generally required to compensate for the missing osmotic (water activity) reduction hurdle when sugar is not used in the product

Seeds of some plants contain unique polysaccharides called gums rather than starch as their germination energy source

Guar gum and locust bean gum

• Galactomannans (polymers of galactose and mannose)
• Important ancillary hydrocolloids used in foods

From a leguminous plant which is widely grown in India and Pakistan

roughly 2:1

Been produced on a commercial scle for the food industry for >30 years and used locally for millennia

A linear chain of mannose (beta-1,4) with D-galactose branches interspersed roughly every other mannos unit (alpha-1,6 linkage)

• Is its ability to hydrate very rapidly in cold water and form a very viscous solution
• This is particularly useful property in assisting in the rehydration of dry powders used in ''instant products'' - ex. instant soup (rehydrating agent) by including it in the formulation

• Another galactomannan polysaccharide which also has beta-1,4 glycosidic linkages for the mannose main chain, with galactose branches present approximately every fourth or fifth mannose unit (~4-5:1)
• Somewhat similar to guar, except that it requires more heating to go into solution

• Used in ice cream to impart a smooth meltdown and freeze/thaw resistance
• Also used to produce a softer dough in the baking industry
• Guar gum and locust bean gum are largely inerchangeable from a functional standpoint and used accordingly depending on price and availability

• 1. Viscosity does not alter much with pH
• 2. Stability and rheology are not affected much by processing
• 3. These gums are compatible with starches, cellulose and other gums
• Often used to subtly modify the texture of other gums or starches

• By wounding specific tropical trees and shrubs and collecting the exudate
• Excluded from USA embargo of sudanese products

• Gum arabic, ghatti, karaya, and tragacanth
• All these gums are all charged heteropolysaccharides

C1-C3 linkage with branches at C6

• Due to the presence of glucuronic acid (COO-)
• The distinguishing feature of gum arabic that is extremely soluble in water - can make up to 50% solutions (W/W)

• As a flavor carrier/dispersant
• Commonly used to encapsulate citrus essential oil flavor emulsions into a water-dispersible powder by spray drying
• Also extensively used to inhibit sugar crystallization and as a thickener in candies, jellies, and chewing gums
• Is also used as a foam stabilizer in beer

• 1. Irish moss - Carrageenan
• 2. Red algae - Agar
• 3. Giant kelp (brown algae) - Alginates

• Same function as pectin in plants - hold cells into place
• These polysaccharides are the ''pectins of the sea''

Composed of D and L-galactose and along with 3,6 anhydro-D-galactose units with some of the galactose moieties being sulfonated

Depends on the source and the method of extraction (again much like pectin)

Linear and branched

To complex with milk proteins to form a very light gel

• Used extensively to suspend insoluble chocolate solids in chocolate milk
• Also used in ice cream to minimize drip
• In research often used to separate proteins by size exclusion column chromatography

Red algae

Unique ability to form a thermo-reversible gel around 40°C

Its use in making bacteriological media due to the hysteresis between its gel setting and melting temperatures

• Dissolves 95-100°C
• Sets at 40°C

Avoids thermal shock to the bacteria, but entraps them

As a gelling agent and binding agent for bakery products, confections, meat and fish products

Brown algae (giant kelp)

Made up of largely linear polymers of D-mannuronic and L-glucuronic acids

To pH and ionic strength of a food system

Using base to convert them into their sodium salts so that they will be readily soluble

Using divalent ions such as calcium

• A bacteriological medium
• No heat required, just crosslink with CaCl₂

• Extracellular polysaccharides
• Many microorganisms produce them
• A wide variety have been isolated and investigated - some very useful ones have been discovered

• Type of microbial gum
• Extra-cellular polysaccharide produced by leuconostoc mesenteroides made up of glucose

The fermentation of sucrose

• Because the glucose units are linked together by alpha-1,6 rather than alpha-1,4 linkages and uses alpha-1,3 linkages for branching
• Also, not an organized crystalline granule, but is excreted as an amorphous polymer

Largely non-nutritive - difficult to digest

Can be controlled genetically

Dough conditioner, ice cream stabilizer, and providing protective films on meat and fish products

Complex heteropolysaccharide produced by xanthomonas campestris made up of D-glucose, D-mannose and D-galacturonic acid present in a ~3:3:2 ratio

• 1. Excellent heat stability - almost no change in viscosity with temperature
• 2. Viscosity is highly affected by shear, but returns immediately after shear is removed (pseudoplastic)
• 3. Viscosity is practically independent of pH - very useful in highly acidic foods
• 4. Will form a gel with locust bean gum in very low concentrations

In production of instant puddings or gels without the need for heat

It can produce xanthan gum from a variety of cheap carbohydrate substrates

Starch

One generally just has to try a number of different ones