1. Carbohydrates

Monosaccharides

E.g. glucose & fructose

Oligosaccharides

• 2-10 monomers

• Disaccharides (glucose + fructose)

• Trisaccharides (galactose + glucose + fructose)

Polysaccharides

• >10 monomers

• Starch: 1000-2×10^6 glucose monomers

• Cellulose: 7000-15000 glucose monomers

• Pectin: 200-500 monomers

Isolation to form pure ingredients

• Sugar made from sugar cane or sugar beets

• Pectin powder made from orange peels

• Lactose powder made from milk

• Starch powder made from potatoes

Nutritional functionality of carbohydrates

• Energy supplier

• Fibers

Technical functionality of carbohydrates

• Sweetener

• Humectant/water binder

• Texture: thickener, gelling agent

• pre-cursor for color and flavor

Ring opening

• Mostly closed (>99%)

• But can open (<1%)

Aldose vs Ketose

• Aldose =O on C1 (aldehyde)

• Ketose =O on C2 (ketone)

Anomeric carbon

• C- atom next to O atom in the ring and connected to a second O atom

• In an open structure, this carbon is the C-atom connected to the =O

Pyranose vs furanose

Pyranose: 6 membered ring

Furanose: 5 membered ring

Hexose vs Pentose

• Hexose: 6 C atoms (glucose & fructose)

• Pentose: 5 C atoms (Xylose & arabinose)

Alpha or beta glucose

Alpha is in starch

Beta in cellulose

D or L

• Are mirror images of each other

• If the functional group on second last C-atom is to the right then it is D-form

• If the functional group on second last C-atom is to the left then it is L-form

Uronic acids

• Has an acid group on the sixth carbon

• Instead of a hydroxyl group, it has an acid group

Alpha or beta linkage

Alpha when the linkage is drawn down, beta when zigzagged

• If both are up or both are down = alpha

• If opposite = beta

Properties reducing sugar

• Can undergo reactions which normal sugars cannot (caramelization, maillard)

• They can open up their ring

• It can reduce other reactants

• OH group is free on the anomeric carbon (not bonded to another molecule)

• e.g. lactose = reducing

• e.g. saccharose = not reducing, has no reducing ends

  • When it hydrolyses, it can react in a reducing reaction

Calculating Dextrose equivalent

DE = 100 * number of reducing ends/glucose monomers

• The more you cut the higher the DE

N and O glycosidic bonds

• When an anomeric carbon is bonded to an oxygen or a nitrogen

Mutarotation

When alpha molecules turn into beta molecules and vice versa

Two main groups of polysaccharides

• Homoglycan (1 type of monomer)

• Heteroglycans (2 or more types of monomer)

• Both homo and heteroglycans can exist of linear and branched structures

Example of linear homoglycan polysaccharides

• Amylose (alpha 1→ 4 linkages)

  • Forms a helical structure

  • More flexible and soluble

  • Digestible for humans

• Cellulose (Beta 1→ 4 linkages)

  • Very rigid and water in-soluble complexes

  • Non digestible

  • Formation of microfibrils

Example of branched homoglycan

• Amylopectin

  • Starch molecule

  • Consists of D-glucose molecules only

  • Linkages in the linear part are alpha 1→ 4

  • Linkages in the branched part are alpha 1→ 6

Example of linear heteroglycan

• Alginate

  • Consists of guluronic acid and mannuronic acid

  • Guluronic acid are monosaccharides with a carboxylic acid group.

    • Depending on the pH guluronic acid can lose an H on it carboxyl group and become charged

Example of branched heteroglycan

• Galactomannan

• Consists of galactose and mannose

Techno functionality of polysaccharides

• Thickener

• Gelling agent

How are polysaccharides responsible for viscosity?

• High viscosity = high friction

• When there are more polysaccharide chains, friction develops between them, making the solution thick

Effect of size, charge & flexibility on thickening

• The more space it takes up = the greater the thickening effect. 

• Larger size = more thickening

• More rigid = more thickening

• More charge = more thickening

Gelling with polysaccharides

• Happens when polysaccharides from junction zones

  • exist of hydrogen bonds, hydrophobic interactions, electrostatic interactions

• They form a 3D network which can hold a liquid.

What are the two roles that polysaccharides usually have in fruits and vegetables?

• Storage polysaccharide

• Cell wall polysaccharide

Examples of storage and plant cell wall polysaccharides

• Storage: starch & glycogen

• Cell wall: agar, cellulose and pectin

Properties of sugars

• Are hydrophilic

  • Because of: polar hydroxyl groups (attracts polar water molecules)

• Means sugar dissolves well

Limitations to solubility of sugar

• If solubility is exceed, the solution becomes over-saturated and crystallization may occur

• This means that solid sugar particles are formed in the form of crystals (ordered structures)

Temperature and solubility

• Lactose is the least soluble of the common sugars and fructose has the highest solubility

• A big advantage of the use of saccharose is that its solubility hardly depends on the temperature

Why do products with a lot of sugar have a low water activity?

• There is less free water because the water molecules are bound to the sugar molecule

• As a result, water is less free or looses the possibility of free motion

Advantages and disadvantages of low Aw due to high sugar

Advantages: low microbes, slows down reactions that are catalyzed by enzymes and non-enzymatic browning

Disadvantages: The autoxidation of fat is accelerated for foods with aw values below 0.2

Humectants

• One of the measures that can be taken to lower the water activity of foods is the addition of additives with a high water binding capacity, these are called humectants

• E.g. invert sugar, starch syrups and sorbitol

• Fructose can also serve as humectant: the water binding capacity of fructose is larger than that of glucose and saccharose. Therefore, fruit powder is more hygroscopic [hygroscopy is ability to attract and hold water] when the fructose content of the processed fruit is higher (more sugar inversion)

Temperature and sweetness in sugars

• Different isomers of fructose vary in sweetness. β-D-fructopyranose is the sweetest form.

• As temperature increases, the proportion of β-D-fructopyranose decreases, while the amounts of β-D-fructofuranose and α-D-fructofuranose increase—these forms are less sweet.

• Therefore: Fructose tastes sweeter in cold beverages than in hot ones because the sweetest isomer is more abundant at lower temperatures.

NDO’s

• Non-digestible oligosaccharides

• Are not degraded by the digestive enzymes of the gastrointestinal tract

• Therefore they arrive in the large intestine undigested

• This way they can play a role as prebiotic

Prebiotic

• Prebiotics are defined as compounds that cannot be digested by the human digestive tract

• Therefore, they reach the large intestine unchanged

• They can stimulate the growth and/or activity of a specific set of health promoting bacteria

• Therefore some NDOs are used as prebiotics

Dietary fibre

Includes all soluble and insoluble polysaccharides in a food, with the exception of starch

• They are all non-digestible polymers

• They do not have a function as energy source

Health effect of dietary fibres

• Offer protection against a number of diseases of civilization such as:

  • atherosclerosis

  • Constipation

  • Diabetes

  • Gallstones

  • Crohn’s disease

  • Obesity

Gums

• Are added to foods as a fibre additive

• Used in breakfast drinks, cereal bars, cookies, cakes, breads etc 

Isomerization of monosaccharides via enolization

Known as the “Lobry de Bruyn van Ekenstein isomerization”

Dehydration of enediol

Forms dicarbonyl

Dehydration of dicarbonyl

• Formation of HMF

• Higher temp and longer treatment = more HMF

Maillard reactions

• When heating carbohydrates and free amino groups Maillard happens

Steps of Maillard reaction

• There is no general structure for melanoidins

• They are the brown pigments that you see

Formation of imine/glycosylamine

Amadori rearrangement

Heyns rearrangement

Enolization Maillard reaction

Cyclic intermediate Maillard Reaction

• The deoxyosones react further into heterocyclic intermediate products. 

Strecker degradation

Conditions influencing Maillard reactions

pH

• low pH: hydrolysis into reducing sugars

• High pH: amino group is in NH2 form

Temperature

• Low T (~60C): only initial phase

• High T: Also intermediary and final phase

Water activity (balance is optimum)

• Low aw: no diffusion of compounds

• High aw: no dehydration reactions

Advantages of Maillard reaction

• Melanoidins are formed (brown pigments)

• Volatile compounds are formed (flavor compounds)

Disadvantages of Maillard reaction

• Essential amino acids are lost (lysine, methionine)

• Mutagenic or carcinogenic compounds are formed (acrylamide, HMF)

• Cross linking of proteins (Loss of functionality/digestibility)

What does viscosity depend on?

• Degree of polymerization

• Volume

• Form

• Flexibility

• Charge

More space it takes up = larger viscosity

Branched polysaccharides take up less space if they have equal DP as a linear polysaccharide. 

Why does a drink with aspartame have less kcal than a drink with saccharose?

Because aspartame has such a high sweetness level that it doesn’t require a lot of aspartame to be added.

Steps in the formation of a gel

1. Macromolecules turn and fold

2. Polysaccharides associate

3. Loops/junction-zones/double helixes are formed

4. When there are enough knots, a 3D network will arise

5. Water is retained in this network: a gel

Follow up reactions 1,2 -enediol and 2,3 enediol

When does the Maillard reaction happen?

When:

• Sugars are acyclic

• There are a lot of NH2 instead of NH3+ groups in amino acids/peptides

Effect of pH on maillard

• Low pH = lower reaction rate, however the amount of Maillard reactions is higher as hydrolysis takes place at a low pH

• Hydrolysis produces the substrates for the Maillard reactions, such as reducing sugars and amino acids)

Effect of sulphite on browning?

Sulphite inhibits browning because it reacts with carbonyl intermediates (blocking formation of colored melanoidins).

are pentoses or hexoses more reactive when browning?

Pentoses

Structure of pectin

• 65% homogalacturonan (important for its gelling properties)

• 35% rhamnogalacturonan I and II (highly branched)

Structure of homogalacturonan part of pectin

• Consists of D-galacturonic acid

• alpha 1→ 4 linkages

• DP of 60-100

Degree of methyl esterification (DM)

• Varies between 20% - 80%

• Low DM = LM pectin, meaning that DM < 50%

• High DM = HM pectin, meaning that DM = 60-75%

How are junction zones stimulated in a sugar acid gel

Formation of junction zones is stimulated by:

• Interaction of two pectin polymer chains

• Low pH - to ensure no charge on the pectin so the chains will not repel each other

• High concentration of sugar - gives low Aw so that it draws away water from pectin molecules, which makes the pectin molecules less soluble causing them to come closer and form hydrogen bonds & hydrophobic interactions with each other

• Typically and HM pectin used for this type of gel, because there are less carboxyl groups that could carry a charge and the methyl groups make the pectin more hydrophobic

Calcium gel

• The negatively charged groups on the pectin form ionic bonds with positively charged calcium ions, forming a so-called eggbox model

• The eggs are the calcium ions that are trapped between two polymers

• Several calcium ion bonds in a row form a junction zone

• Typically an LM pectin is used or this type of gel, because charged group are needed and LM pectins have enough free carboxyl groups

• Sugar free jam usually contains a calcium gel 

Endogenous enzymes

Enzymes that are naturally present in the plant

Use of pectin enzymes in food technology

• Higher yields for fruit juices

• Clarification of fruit juices

• Production of tomato paste (done by endogenous pectin enzyms)

The four locations where pectinases act on pectin

Polygalactaronase

• A glycoside hydrolase

• The enzymes hydrolyzes the glycosidic linkage next to a galactronic acid with a free carboxyl group (uses a water molecule)

• Therefore, pectin with a low degree of methyl esterification is degraded by this enzyme

Pectate lyase

• Cleaves the glycosidic linkage next to a galactronic acid with a free carboxyl group

• Pectin with a low degree of methyl esterification is degraded by this enzyme. 

• Pectin lyase belongs to the lyase group meaning that is cleaves the glycosidic linkage by beta alumination

• In this reaction, a double bond is introduced in a newly formed non-reducing chain end. 

• No water is introduced in this cleavage since it is not a hydrolysis reaction!

• All reaction products have a double bond.

Pectin lyase

• cleaves the glycosidic linkage next to a methyl esterified galactronic acid.

• Therefore pectin with a high degree of methyl esterification is degraded by this enzyme

• Belongs to the lyase group with means that it cleaves the glycosidic linkage by beta alumination

• A double bond is introduced in a newly formed non-reducing chain end

• With this reaction alum pectin is depolymerized into smaller oligosaccharides

• All reaction products have a double bond

pectin esterase (or pectin methyl esterase)

• Is an esterhydrolase

• Very specific to the methyl ester group

• Saponifies the astro bond, introducing water and releasing a methanol group.

• What is left is the carboxyl group

• Pectin esterase turns a pectin with a high degree of methyl esterification such as DM70 pectin, into a pectin with a low degree of methyl esterification such as DM30

Cold break juice vs hot break juice

Roles of starch as additive in food

• Thickening of soups, pie filling

• Gelling: gum drops

• Encapsulation: flavors

• Crisping: fried snacks

What do starch granules look like?

Composition of starch

• Amylose

  • 25-30% of starch

  • DP between 500-6000

  • Linear, alpha 1→4 linkage

• Amylopectin

  • 70-75% of strach

  • DP between 3×10^5-3×10^6

  • Branching, alpha 1→ 4 linkage for linear part. Alpha 1→ 6 for branched part

Organization of a starch granule

Crystalline area: highly branched and ordered = amylopectin

Anamorphous: amylose (less structured)

Hilum starch granule

the central point or origin of a starch granule, where its growth begins

Heating starch granule

• Gelatinization

Gelatinization and pasting

• Process is irreversible!

How do you monitor gelatinization in starch molecules

• Measure and track viscosity

What is the increase of viscosity in starch called when cooling

• Retrogradation

• Is caused by reassociation of the starch molecules, mostly amylose molecules

• Involves the formation of chain entanglements and crystallization of double helical aggregates

• Retrogradation makes products stiff

• It is a major factor in the staling of old bread and other bakery products

• This process is reversible!

• When heating a retrogredated product, the starch molecules disassociate again forming separate molecules

Applications in processing of gelatinizing starch

Physical:

• Pregelatinized starch: dissolves without heat

Chemical:

• Thin-boiling starch: reduced hot-paste viscosity (starch has been treated with acid to partly hydrolyze polysaccharides gives a low and uniform viscosity)

• Cross-linked starch: retains viscosity when heated/stirred (has been chemically treated to form cross-links between starch molecules)

• Substituted starch: reduced gelation/retrogradation (Starch molecules are substituted with extra groups, these groups hinder interaction between starch molecules)

Amylases

• Enzymes that hydrolyze glycosidic linkages in starch molecules

• Alpha and beta amylase hydrolyze exclusively 1→ 4 linkages.

• Glucoamylase splits both 1→4 linkages and 1→6 linkages (but much slower)

• Isoamylase hydrolyzes the branched linkages (1→6)

Alpha amylase

• Endoenzyme (cleaves in the middle of the chain)

• Cleaves only 1→4 linkages. 

• A mixture of unbranched and branched malto-oligosaccharides with a DP of 2 to 6

  • This is also called dextrins

Beta amylase

• Exoenzyme - Acts on the non-reducing chain end

• Forms maltose & dextrin

• Keeps going until stopped by an alpha 1→6 linkage

• The released maltose is in the beta form 

Glucoamylase

• Exoenzyme - acts on the starch molecule from the non-reducing end.

• Forms glucose

• Can hydrolyze 1→ 4 and alpha 1→ 6 linkages but 1 to 6 is much slower

• Therefore a complete hydrolysis can be done

Isoamylases

• Exo-enzymes

• Cleaves alpha 1→ 6 linkages

• Product is relative long linear alpha 1→4 glucan chains

• In practice is usually comined with glucoamylase

Steps in gelatinization of starch

1. Sedimentation without stirring

2. Gelatinization temperature (~60C)

3. H-Bridges in amorphic areas break up

4. H-bridges in crystalline areas break up

5. Increase of viscosity due to separation of amylose

6. Maximum swelling volume of the granules

7. Highly crystalline areas break up

8. Swollen granules fall apart

9. A thick dispersion 

10. Retrogradation