Carbohydrates

Uses in foods

• sweeteners

• influences body and mouth feel

• fat replacers

• manupulation of flow characteristics

  • ensure texture for ketchup

• Crystallization agents in candy

• used to lower Aw and elongate shelf life of products

• fermentation of substrates in yogurt, wine etc

• used in colour and flavouring

Monosaccharides

• glucose and fructose

• simple sugars that cannot be hydrolized further

• can join together to form larger molecules through glycosidic linkages

Disaccharides

• sucrose and lactose

• 2 monosaccharides

• glycosidic linkages connect the monosaccharides to one another to create them

Oligosaccharides <20 sugar units

• stachyose

• only a few of them are natural and most come from polysaccharide hydrolysis

Polysaccharides >20 sugar units

• cellulose

Maillard reaction

• colour, taste and aroma of cooked foods

• involves reducing sugars

Reducing sugars

• sugars with C=O group of aldehyde joins with -OH group on C-5 to form a hemiacetal (OH and OR attached to the same C)

• sugars with hemiacetal is in equilibriam wiht its acyclic form

  • contains CHO in acyclic form

• Can be an open or closed circle

• all monosaccharides and some disaccharides, oligosaccharides and polysaccharides

• involved in the maillard reaction

Non reducing sugars

• sugars with acetal have 2 OR groups attached to the same C

• acetals lock the sugar in place so it does not open into acyclic form

  • no reducing

3 stages of the maillard reaction

• early maillard:

  • carbonyl group of the reducing sugar condenses with an amino group on a free amino acid or free amino group on a protein

    • produces glycosylamine and water

  • Glucosamine undergoes Amadori rearrangement to yield a 1-amino-2-keto sugar

• Advanced maillard reaction

  • Amadori compound is split apart

  • in acid reaction is slow, in basic it is fast

  • forms hydroxymethylfurfural (HMF)

• Final Maillard reaction

  • melanoidin formation (brown nitrogen containing polymers

  • Amino compounds + sugar fragments

  • HMF + amino compounds

  • intermediates (reductones and aldehydes) + amino compounds

Early maillard reaction

• carboxyl group of the reducing sugar condenses with an amino group on a free AA or free amino group on a protein

  • produces glycosylamine and water

• glucosamine undergoes Amadori rearrangement to yield a 1-amino-2-keto sugar

  • amadori compound is colourless

Glycosylamine and water

• produced in the early maillard reaction

advanced maillard reaction in acid

• amadori compound is split apart → amino group removed

  • produces deoxyketose

• deoxyketose undergoes dehydration and produces hudromethylfurfural (HMF)

• Reaction is slow

Advanced maillard reaction (basic conditions)

• amadori compound breaks apart → amino group removed

  • produces deoxyosone

• goes through dehydration producing

  • maltol and isomaltol

• these are the flavour and aroma compounds

HMF

• yellow product of acidic advanced maillard step

Maltol and isomaltol

• flavour and aroma compounds produced from neutral an basic pH advanced maillard reaction

final maillard reaction

• melanoidin formation

  • the brown nitrogen containing polymers

• amino compounds + sugar fragments

• HMF + amino compounds

• intermediates (reductones and aldehydes) + amino compounds

Pros of maillard reaction

• contributes to flavour, aroma and colour compounds

Cons of maillard reaction

• reduced nutritional value,

• decreased protein quality

  • AA + reducing sugar ruins the AA

  • this is especially relevant for essential amino acids like lysine

• heterocyclic amine production

  • these are mutogenic

factors that influence the maillard reaction

• temperature

• pH

• Aw

• metal ions

• sugar structures

Temperature effect on maillard

• reaction occurs in the presence of heat and during storage

• the higher temperature, creates a more brown pigment

  • shown through spray drying palm sap

    • the sap was more brown when it was dried at a higher temperature

pH effects on maillard reaction

• Amadori products undergo dehydration fo form HMF at 4-7pH but prefer <5

• pH >7 the amadori products form deoxysones whch react and polymerize to form melanoidins

• in real food there is a variety of intermediates

• production of melanoidins will be faster at more alkaline pH

• very little browning occurs at <6pH

water activity impact on maillard

• high rates of maillard at 0.6-0.7 Aw

  • intermediate Aw

• at high Aw amino groups and reducing sugars are diluted by too much free water

• at lower Aw less free water so reagents are more concentrated and have limited movement

• at interemediate Aw, the reactant mobility is highest and reaction occurs quickly

Metal ions and maillard reaction

• Copper 2 & 3 and iron 2 &3 ions form unstable complexes with amadori products

• Copper 2 ions oxidize glucosamine in early maillard reaction

  • regenerate free primary amino groups speeds up breakdown of protein complexes that can form melanoidins

Copper 2 ions

• oxidize glucosamine in the early maillard reaction

• acts to regenerate free primary amino groups

• speeds up breakdown of protein complexes that can form melanoidins

sugar stuctures influence on maillard

• maillard requires reducing sugars in the open chain form

  • sugars carbonyl in the aldehyde group reacts with amino groups of amino acids

  • some sugars spend more time in the open chain form

  • sugars in open chain form undergo maillard reaction more rapidly

sulphites

• act to inhibit maillard reaction by blocking hydroxymethylfurfural and therefore preventing the melanoidins

order of sugars in open chain going through maillard fastest to slowest

• D-xylose → L-arabinose → hexoses → disaccharides

Caramelization

• carbohydrates (sucrose, reducing sugars) are heated without nitrogen containing compounds

• facilitated by using small amounts of acids or alkali and certain salts

• thermolysis causes dehydration of the sugar

  • introduction of double bonds or formation of anhydro rings

• furans like HMF are formed (unsaturated rings)

• conjugated double bonds absorb light and produce colour

• unsaturated rings condense and polymerize → colours, aroma, taste

• catalysts are added to increase reaction rate and to direct the reaction

What facilitates the formation of caramelization

• small amounts of acids or alkali and certain salts

Thermolysis in caramelization

• introduces of double bonds or formation of anhydro rings

• causes dehydration of the sugar

how are caramel flavours and colours industrially produced

• heating a sucrose solution with ammonium salts or ammonium bisulphite

• rate of caramel colour formation increases with increasing temperature and pH

• reaction is optimal at pH 8

• heat decomposes sugar to unsaturated rings to produce flavours

• maltol and isomaltol imitate odor and flavour of freshly baked bread

• used in ice cream, cookies and other baked goods

maltol and isomaltol flavours

• imitate the odor and flavour of freshly baked bread

Cellulose

• primary cell wall components of plants

• D-glucose bound by B-(1,4)-glycosidic bonds

  • has crystaline and amorphous regions with higher degree of crystalinity

• crystaline regions are ordered, and parallel

• OH on the glucose from one polysaccharide chain H-bonds with O on the neighbouring chain to give it high strength and insolubility

  • dietary fibre

• can be modified to bind water and increase viscosity

Starch

• main polysaccharide in plants made of amylose and amylopectin in granules

• 20-30% amylose and 70-80% amylopectin

  • the composition depends on the source and type of starch

• granuoles have an organized layered structure

• crystaline and amorphous regions

• water soluble and digestible with the addition of heat

  • without temperature it is insoluble

crystaline layers in starch

• less dense and ordered with amylopectin in a double helixal pattern

amorphous layers in starch

• less dense and unordered with both amylose and amylopectin

maltese cross pattern in starch

• birefringence in raw starch under polarized light

• caused by the organized structure of amylopectin

water solubility of starch

• water insoluble and digestible with the addition of heat

amylose structure

• low molecular weight

• linear chains of a-D-glucose

• units joined by a-1,4 glycosidic linkages

amylopectin

• high molecular weight

• high branded chains (long or short)

• a-D-glucose linked by a-1,4 and a-1,6 glycosidic bonds

  • creates the branched pattern

Gelatinization

• starch granuoles are heated in water

• causes the molecule to vibrate and breaks the intermolecular H-bonds

• water enters the granuole in the amorphous regions first (less ordered)

• linkages in the crystaline region are broken in crystalline region

• water enters and H-bonds with amylopectin

• granuoles swell and birefringence is lost

gelatinization in starch with hgih amylopectin

• higher granule swelling power and higher viscocity at low temperature

  • amylopectin H-bonds with water, swells and reaches a large granule size causing highest viscocity in short time

starches with higher amylose (and lower amylopectin)

• low swelling power and low viscosity even at a hgih temperature

Granule size increase causes…

• amylose leaches out and amylopectin stays in the swollen granule

  • when heat is removed the starch solution cools and viscosity increases

birefringence over temperature in native and high amylose

• decrease birefringence at increasing temperature

• native maize lost birefringence at lower temperature compared to high amylose maize

stirring gelatinization

• breaks the granules

peak viscosity

• point where the paste swells to a max size

• should remove the semi-solid gel at this time

• further cooking and or continuous agitation results in ruptured granules and lower viscosity

what happens to paste upon cooling

• retrogradation

• syneresis

retrogradation

• starch molecules H-bond with neighbouring molecules to form junction zones to achieve a more ordered state

• junction zones form when 2 or more polymer chains interact and bind eachother along part of its chain length to form a 3D gel network

• increase in viscosity and gel-like ocnsistency

• amylose is primarily involved but over time, amylopectin is also involved but at a slower rate

Junction zones

• determine gel firmness

• if they grow after the gel forms the network becomes more compact

example of retrogradation

• film on top of gravy

syneresis

• junction zones growing after gel formation causing the network to become more compact

• the structure contracts and water is pushed out from between the starch molecule

sugar effect on paste viscocity

• sugar binds water leaving less available to hydrate the starch

• causes a delay in gelatinization until a higher temperature

• less water enters the granule and causes more thermal energy to be needed before the start can swell and gelatinize

• lower peak viscosity and weaker gel strength

fat effect on viscosity

• fat coated granules can prevent water from reachign the granule and prevents absorption

• lipids form complexes with amylose where the hydrophobic part of the lipid is inside the helixal starch structure and lipid head is outside the helix

• delays gelatinization and requires a higher temperature

salt effect on viscosity

• salt competes with the starch granules for water

• reduction in granule swelling

• delays gelatinization

  • starts at higher temperature

• decreased viscosity

pH effect on viscosity

• acids hydrolyze glycosidic bonds leading to shorter starch polymers

• pH <4

  • cookign and water entry to granule can prematurely rupture the granule and cecrease viscosity

• pH >10

  • improves solubility of the starch so there is more interaction with water

  • more swelling

  • increased viscosity

protein effect on viscosity

• gelatinization of starch and the denaturation of gluten in doughs and batters increase structure, body and viscosity

3 types of protein interactions

• swollen granules break open and amylose and amylopectin leach out and starch binds the protein

  • proteins with hydrophillic groups, amide, hydroxyl, carboxyl form bonds wiht hydroxyl groups

• adsorption of proteins at the surface of the starch granule

• proteins aggregate around the surface of the starch granule

  • gelatinizaition of starch and denaturation of gluten in dough structure

retrogradation on bread

• causes hardening upon cooling

• staling depends on ingredients, how it was baked and how its stored

• amorphous state of starch in the bread starts to be more ordered and crystalline state

  • amount of water is just enough to gelatinize the starch

• amylose is leached out and may finish intermolecular h-bonding to achieve a more ordered state by the time the bread cools to room temperature

  • firm and slicable

• amylopectin takes a longer time to retrograde and continues even after its fully cooled

• involves interactions between its outer branches

  • outer branches come together, align and form intra-molecular bonds

  • structure is rigid

  • crumb firmness

control of bread staling

• heat can temporarily shift the amylose and amylopectin from semi-crystalline state to amorphous state

• reheating bread with small amounts of water can temporarily reverse the retrogradation

• emulsifiers like mono and di-glycerides can reduce staling by interacting with starch

• emulsifiers form complexes with amylose and linear branch chains of amylopectin

  • slows down the recrystalization of amylopectin and retrogradation to give softer crumb

emulsifiers effect on retrogradation

• mono and diglycerides may reduce staling by interacting with starch

• form complexes with amylose and linear branch chains of amylopectin

• slows recrystalization of amylopectin and retrogradation to give softer crumb