Proteins

From the Greek “proteios” or primary.

Properties of Amino Acids:Zwitterions are electrically neutral, but carry a

“formal” positive or negative charge.Give proteins their water solubility

Shape Interactions of Proteins

Emulsoids and Suspensiods

Proteins should be thought of as solids Not all in a true solution, but bond to a lot of water

Can be described in 2 ways:

Emulsoids- have close to the same surface charge, with many “shells” of bound water

Suspensoids- colloidal particles that are suspended by charge alone

Quick Application: Food Protein Systems

Milk- Emulsoid and suspensoid system Classified as whey proteins and caseins Casein - a phosphoprotein in a micelle structure Suspensoid - coagulates at IEP (casein)

Egg (Albumen) – Emulsoid Surface denatures very easily Heating drives off the structural water and creates a

strong protein to protein interaction Cannot make foam from severely denatured egg white,

requires bound water and native conformation

Functional Properties of Proteins3 major categories Hydration properties

Protein to water interactions Dispersion, solubility, adhesion, viscosity Water holding capacity

Structure formation Protein to protein interactions Gel formation, precipitation, aggregation

Surface properties Protein to interface interactions Foaming and emulsification

1. Hydration Properties (protein to water)

Most foods are hydrated to some extent. Behavior of proteins are influenced by the presence of water and

water activity Dry proteins must be hydrated (food process or human digestion)

Solubility- as a rule of thumb, denatured proteins are less soluble than native proteins

Many proteins (particularly suspensoids) aggregate or precipitate at their isoelectric point (IEP)

Viscosity- viscosity is highly influenced by the size and shape of dispersed proteins Influenced by pH Swelling of proteins Overall solubility of a protein

2. Structure Formation (protein to protein)

Gels - formation of a protein 3-D network is from a balance between attractive and repulsive forces between adjacent polypeptides

Gelation- denatured proteins aggregate and form an ordered protein matrix Plays major role in foods and water control Water absorption and thickening Formation of solid, visco-elastic gels

In most cases, a thermal treatment is required followed by cooling Yet a protein does not have to be soluble to form a gel (emulsoid)

Texturization – Proteins are responsible for the structure and texture of many foods Meat, bread dough, gelatin Proteins can be “texturized” or modified to change their

functional properties (i.e. salts, acid/alkali, oxidants/reductants) Can also be processed to mimic other proteins (i.e. surimi)

3. Surface Properties (protein to interface)

Emulsions- Ability for a protein to unfold (tertiary denaturation) and expose hydrophobic sites that can interact with lipids. Alters viscosity Proteins must be “flexible” Overall net charge and amino acid composition

Foams- dispersion of gas bubbles in a liquid or highly viscous medium Solubility of the protein is critical; concentration Bubble size (smaller is stronger) Duration and intensity of agitation Mild heat improves foaming; excessive heat destroys Salt and lipids reduce foam stability Some metal ions and sugar increase foam stability

Factors Affecting Changes to Proteins

Denaturation

Aggregation

Salts

Gelation

Changes to Proteins Native State

The natural form of a protein from a food The unique way the polypeptide chain is oriented

There is only 1 native state; but many altered states The native state can be fragile to:

Acids Alkali Salts Heat Alcohol Pressure Mixing (shear) Oxidants (form bonds) and antioxidants (break bonds)

Changes to ProteinsDenaturation

Any modification to the structural state The structure can be re-formed If severe, the denatured state is permanent

Denatured proteins are common in processed foods Decreased water solubility (i.e. cheese, bread) Increased viscosity (fermented dairy products) Altered water-holding capacity Loss of enzyme activity Increased digestibility

Changes to Proteins Temperature is the most common way to denature a

protein Both hot and cold conditions affect proteins

Every tried to freeze milk? Eggs?

Heating affects the tertiary structure Mild heat can activate enzymes

Hydrogen and ionic bonds dissociate Hydrophobic regions are exposed Hydration increases, or entraps water Viscosity increases accordingly

Changes to ProteinsWe discussed protein solubility characteristicsSolubility depends on the nature of the solution

Water-soluble proteins generally have more polar amino acids on their surface.

Less soluble proteins have less polar amino acids and/or functional groups on their surface.

Isoelectric PrecipitationsProteins have no net charge at their IEP

- -

- -- -

- - - -

- -

+ +

+ ++ +

+ ++ +

+ ++ +

+ ++ +

+ ++ +

+ +

- -

- -+ +

+ + - -

+ +

- -

- -- -

- - - -

- -

- -

- -+ +

+ + - -

+ +

Strong Repulsion

(net negative charge)

Strong Repulsion

(net positive charge)

Aggregation

(net neutral charge)

Isoelectric PrecipitationsProteins can be “salted out”, adding charges

- -

- -- -

- - - -

- -+ +

+ ++ +

+ ++ +

+ +Aggregation

(net neutral charge)

Na+Na+ Na+ Cl-Cl- Cl-

Measuring IEP PrecipitationsEmpirical measurements for precipitationA protein is dispersed in a buffered solution

Add salt at various concentrations Add alcohols (disrupt hydrophobic regions) Change the pH Add surfactant detergents (i.e. SDS)

Centrifuge and measure quantitatively The pellet will be insoluble protein The supernatant will be soluble protein

Gel Formation Many foods owe their physical properties to a gel

formation. Influences quality and perception. Cheese, fermented dairy, hotdogs, custards, etc

As little as 1% protein may be needed to form a rigid gel for a food.

Most protein-based gels are thermally-induced Cause water to be entrapped, and a gel-matrix formation

Thermally irreversible gels are most common Gel formed during heating, maintained after cooling Will not reform when re-heated and cooled

Thermally reversible gels Gel formed after heating/cooling. Added heat will melt the gel.

What is more important in foods?Protein precipitation

orProtein solubilization

???

Effects of Food Processing

Processing and StorageDecreases spoilage of foods, increases shelf life

Loss of nutritional value in some cases Severity of processing

Loss of functionality Denatured proteins have far fewer functional aspects

Both desirable and undesirable flavor changes

Processing and StorageProteins are affected by

Heat Extremes in pH (remember the freezing example?) Oxidizing conditions

Oxidizing additives, lipid oxidation, pro-oxidants Reactions with reducing sugars in browning rxns

Processing and Storage Mild heat treatments (< 100°C)

May slightly reduce protein solubility Cause some denaturation Can inactive some enzymes Improves digestibility of some proteins

Severe heat treatments (for example: >100°C) Some sulfur amino acids are damaged

Release of hydrogen sulfide, etc (stinky)

Deamination can occur Release of ammonia (stinky)

Very high temperatures (>180°C) Some of the roasted smells that occur with peanuts or coffee

Enzymes

A quick review, since we

know the basics already

Enzyme Influencing Factors Enzymes are proteins that act as biological catalysts They are influenced in foods by:

Temperature pH Water activity Ionic strength (ie. Salt concentrations) Presence of other agents in solution

Metal chelators Reducing agents Other inhibitors

Also factors forInhibition, including:

Oxygen exclusionand

Sulfites

Enzyme Influencing Factors

Temperature-dependence of enzymes Every enzyme has an optimal temperature for maximal

activity The rate/effectiveness of an enzyme: Enzyme activity For most enzymes, it is 30-40°C Many enzymes denature >45°C Each enzyme is different, and vary by isozymes Often an enzyme is at is maximal activity just before it

denatures at its maximum temperature

pHLike temp, enzymes have an optimal pH where

they are maximally activeGenerally between pH 4 and 8

with many exceptions

Most have a very narrow pH range where they show activity.

This influences their selectivity and activity.

Water ActivityEnzymes need free water to operateLow Aw foods have very slow enzyme reactions

Ionic StrengthSome ions may be needed by active sites on the

protein Ions may be a link between the enzyme and substrate Ions change the surface charge on the protein Ions may block, inhibit, or remove an inhibitor Others, enzyme-specific

Enzymes Before a chemical reaction can occur, the activation energy (Ea)

barrier must be overcome Enzymes are biological catalysts, so they increase the rate of a

reaction by lowering Ea

Enzymes

The effect of temperature is two-fold From about 20, to 35-40°C (for enzymes) From about 5-35°C for other reactions

Q10-Principal: For every 10°C increase in temperature, the reaction rate will double

Not an absolute “law” in science, but a general “rule of thumb”

At higher temperatures, some enzymes are much more stable than other enzymes

Enzymes Enzymes are sensitive to pH – most enzymes active only within a pH range of

3-4 units (catalase has max. activity between pH 3 & 10!)

The optimum pH depends on the nature of the enzyme and reflects the environmental conditions in which enzyme is normally active: Pepsin pH 2; Trypsin pH 8; Peroxidase pH 6

pH dependence is usually due to the presence of one or more charged AA at the active site.

Nomenclature

Each enzyme can be described in 3 ways: Trivial name: -amylase Systematic name: -1,4-glucan-glucono-hydrolase

substrate reaction

Number of the Enzyme Commission: E.C. 3.2.1.1 3- hydrolases (class) 2- glucosidase (sub-class) 1- hydrolyzing O-glycosidic bond (sub-sub-class) 1- specific enzyme

Enzyme Class Characterizations

1. OxidoreductaseOxidation/reduction reactions

2. TransferaseTransfer of one molecule to another (i.e. functional groups)

3. HydrolaseCatalyze bond breaking using water (ie. protease, lipase)

4. LyaseCatalyze the formation of double bonds, often in dehydration reations

5. IsomeraseCatalyze intramolecular rearrangement of molecules

6. LigaseCatalyze covalent attachment of two substrate molecules

1. OXIDOREDUCTASES

OxidationIsLosing electrons

ReductionIsGaining electrons

Xm+ Xm2+

e-

oxidizedreduced e-

Electron acceptor

Electron donor

Redox active (Transition) metals (copper/ iron containing proteins)

1. Oxidoreductases: GLUCOSE OXIDASE -D-glucose: oxygen oxidoreductase Catalyzes oxidation of glucose to glucono- -lactone

-D-glucose Glucose oxidase D glucono--lactone

FAD FADH2 +H2O

H2O2 O2 D Gluconic acidCatalase

H2O + ½ O2

Oxidation of glucose to gluconic acid

1. Oxidoreductases: Catalase

hydrogenperoxide: hydrogenperoxide oxidoreductase Catalyzes conversion of 2 molecules of H2O2 into

water and O2:

Uses H2O2 When coupled with glucose oxidase the net result is

uptake of ½ O2 per molecule of glucose Occurs in MO, plants, animals

H2O2 ------------------- H2O +1/2 O2

1. Oxidoreductases: PEROXIDASE (POD)

donor: hydrogenperoxide oxidoreductase

Iron-containing enzyme. Has a heme prosthetic group

Thermo-resistant – denaturation at ~ 85oC

Since is thermoresistant - indicator of proper blanching (no POD activity in blanched vegetables)

N N

NN

Fe

1. Oxidoreductases: POLYPHENOLOXIDASES (PPO)

Phenolases, PPO Copper-containing enzyme Oxidizes phenolic compounds to o-quinones: Catalyze conversion of mono-phenols to o-diphenols In all plants; high level in potato, mushrooms, apples, peaches,

bananas, tea leaves, coffee beans

Tea leaf tannins

CatechinsProcyanidins PPO o-Quinone + H2OGallocatechins O2

Catechin gallates

Colored products

Action of PPO during tea fermentation; apple/banana browning

1. Oxidoreductases: LIPOXYGENASE

OOH

HH

HC

C

H

H

CC

C

cistrans

HH

H

CC

H

H

CC

C

cis cis

+ O2

……..………

……..

Oxidation of lipids with cis, cis groups to conjugated cis, trans hydroperoxides.

Enzymes !!!We have observed carbohydrate hydrolysis

Sucrose into glu + fru Starch into dextrins, maltose, and glucose

We will observe lipid hydrolysis Break-down of fats and oils Enzyme-derived changes

So….the enzyme discussion is not over yet.

Enzymes !!!We have observed carbohydrate hydrolysis

Sucrose into glu + fru Starch into dextrins, maltose, and glucose

We will observe lipid hydrolysis Break-down of fats and oils Enzyme-derived changes

So….the enzyme discussion is not over yet.

Worthington Enzyme Manual

http://www.worthington-biochem.com/index/manual.html

IUPAC-IUBMB-JCBNhttp://www.chem.qmul.ac.uk/iubmb/enzyme

Lipids

Lipids

Main functions of lipids in foodsEnergy and maintain human health Influence on food flavor

Fatty acids impart flavor Lipids carry flavors/nutrients

Influence on food texture Solids or liquids at room temperature Change with changing temperature Participation in emulsions

LipidsLipids are soluble in many organic solvents

Ethers (n-alkanes) Alcohols Benzene DMSO (dimethyl sulfoxide)

They are generally NOT soluble in waterC, H, O and sometimes P, N, S

Lipids Neutral Lipids

Triacylglycerols

Waxes Long-chain alcohols (20+ carbons in length) Cholesterol esters Vitamin A esters Vitamin D esters

Conjugated Lipids Phospholipids, glycolipids, sulfolipids

“Derived” Lipids Fatty acids, fatty alcohols/aldehydes, hydrocarbons Fat-soluble vitamins

Lipids

StructureTriglycerides or triacylglycerolsGlycerol + 3 fatty acids>20 different fatty acids

Lipids 101-What are we talking about?

Fatty acids- the building block of fatsA fat with no double bonds in it’s structure is said to

be “saturated” (with hydrogen)Fats with double bonds are referred to as mono-, di-,

or tri- Unsaturated, referring to the number of double bonds. Some fish oils may have 4 or 5 double bonds (polyunsat).

Fats are named based on carbon number and number of double bonds (16:0, 16:1, 18:2 etc)

LipidsOil- liquid triacylglycerides “Oleins”Fat- solid or semi-solid mixtures of crystalline

and liquid TAG’s “Stearins”Lipid content, physical properties, and

preservation are all highly important areas for food research, analysis, and product development.

Many preservation and packaging schemes are aimed at prevention of lipid oxidation.

NomenclatureThe first letter C represents Carbon The number after C and before the colon

indicates the Number of Carbons The letter after the colon shows the Number of

Double Bonds ·The letter n (or w) and the last number indicate

the Position of the Double Bonds

Saturated Fatty Acids

Mono-Unsaturated Fatty Acids

Poly-Unsaturated Fatty Acids

Lipids

Properties depend on structure Length of fatty acids (# of carbons)

Short chains will be liquid, even if saturated (C4 to C10) Position of fatty acids (1st, 2nd, 3rd) Degree of unsaturation:

Double bonds tend to make them a liquid oil Hydrogenation: tends to make a solid fat

Unsaturated fats oxidize faster Preventing lipid oxidation is a constant battle in the

food industry

Lipids 101-What are we talking about?

Fatty acid profile- quantitative determination of the amount and type of fatty acids present following hydrolysis.

To help orient ourselves, we start counting the number of carbons starting with “1” at the carboxylic acid end.

O

C

OH

CCCCCCCCCCCCCCCCC118

Lipids 101-What are we talking about?

For the “18-series” (18:0, 18:1, 18:2, 18:3) the double bonds are usually located between carbons 6=7 9=10 12=13 15=16.

O

C

OH

CCCCCCCCCCCCCCCCC118 91012131516

Lipids 101-What are we talking about?The biomedical field entered the picture and ruined

what food scientists have been doing for years with the OMEGA (w) system (or “n” fatty acids).

With this system, you count just the opposite.Begin counting with the methyl endNow the 15=16 double bond is a 3=4 double bond

or as the biomedical folks call it….an w-3 fatty acidC

C

OH

CCCCCCCCCCCCCCCCC181 1097643

Melting Points of Lipids

Tuning Fork Analogy-TAG’s Envision a Triacylglyceride as a loosely-jointed E Now, pick up the compound by the middle chain,

allowing the bottom chain to hang downward in a straight line.

The top chain will then curve forward and form an

h Thus the “tuning fork” shape Fats will tilt and twist to this lowest free energy

level

Lipids Lipids are categorized into two broad classes.

The first, simple lipids, upon hydrolysis, yield up to two types of primary products, i.e., a glycerol molecule and fatty acid(s).

The other, complex lipids, yields three or more primary hydrolysis products.

Most complex lipids are either glycerophospholipids, or simply phospholipids contain a polar phosphorus moiety and a glycerol backbone

or glycolipids, which contain a polar carbohydrate moiety instead of phosphorus.

Lipids

Other types of lipidsPhospholipidsStructure similar to triacylglycerolHigh in vegetable oilEgg yolksAct as emulsifiers

Fats and Oils…can also be convertedto an emulsifier…

Production of mono- and diglycerides Use as Emulsifiers Heat fat or oil to ~200°C Add glycerol and alkali Free Fatty Acids will be added to the glycerol

C

C

C

H

H

H

H

H

O

OH

OH

C

O

Fatty Acid Chain

Fats and Oils: Processing

ExtractionRenderingPressing oilseedsSolvent extraction

Peanut

Rape Seed

Safflower

SesameSoybean

Fats and OilsFurther Processing

Degumming Remove phospholipids with water

Refining/Neutralization Remove free fatty acids (alkali +

water)

Bleaching Remove pigments (charcoal filters)

Deodorization Remove off-odors (steam, vacuum)

OilRefining

Where Do We Get Fats and Oils?Neutralization Free fatty acids, phospholipids, pigments, and waxes exist in the crude oil These may promote lipid oxidation and off-flavors Removed by heating fats and adding caustic soda (sodium hydroxide) or soda

ash (sodium carbonate).  Impurities settle to the bottom and are drawn off.  The refined oils are lighter in color, less viscous, and more susceptible to

oxidation.

Bleaching The removal of color materials in the oil. Heated oil can be treated with diatomaceous earth, activated carbon, or

activated clays. Colored impurities include chlorophyll and carotenoids Bleaching can promote lipid oxidation since some natural antioxidants are

removed.

Where Do We Get Fats and Oils?Deodorization Deodorization is the final step in the refining of oils. Steam distillation under reduced pressure (vacuum).Conducted at high temperatures of 235 - 250ºC. Volatile compounds with undesirable odors and tastes can be removed. The resultant oil is referred to as "refined" and is ready to be consumed. About 0.01% citric acid may be added to inactivate pro-oxidant metals.

Where Do We Get Fats and Oils? Rendering Primarily for extracting oils from animal tissues.  Oil-bearing tissues are chopped into small pieces and

boiled in water.  The oil floats to the surface of the water and skimmed.  Water, carbohydrates, proteins, and phospholipids

remain in the aqueous phase and are removed from the oil. 

Degumming may be performed to remove excess phospholipids.

Remaining proteins are often used as animal feeds or fertilizers.

Where Do We Get Fats and Oils? Mechanical Pressing Mechanical pressing is often used to extract oil from

seeds and nuts with oil >50%.  Prior to pressing, seed kernels or meats are ground into

small sized to rupture cellular structures.  The coarse meal is then heated (optional) and pressed in

hydraulic or screw presses to extract the oil. Olive oils is commonly cold pressed to get virgin or

extra virgin olive oil. It contains the least amount of impurities and is often edible without further processing.

Some oilseeds are first pressed or placed into a screw-press to remove a large proportion of the oil before solvent extraction.

Where Do We Get Fats and Oils? Solvent Extraction Organic solvents such as petroleum ether, hexane, and 2-propanol can be added

to ground or flaked oilseeds to recover oil.  The solvent is separated from the meal, and evaporated from the oil. Neutralization Free fatty acids, phospholipids, pigments, and waxes exist in the crude oil These promote lipid oxidation and off-flavors Removed by heating fats and adding caustic soda (sodium hydroxide) or soda

ash (sodium carbonate).  Impurities settle to the bottom and are drawn off.  The refined oils are lighter in color, less viscous, and more susceptible to

oxidation. Bleaching The removal of color materials in the oil. Heated oil can be treated with diatomaceous earth, activated carbon, or activated

clays. Colored impurities include chlorophyll and carotenoids Bleaching can promote lipid oxidation since some natural antioxidants are

removed.

Hydrogenating Vegetable oils can produce trans-fats

C C

H H

C C

H

H

Cis-

Trans-http://www.foodnavigator-usa.com/Regulation/Trans-fats-Partially-hydrogenated-oils-should-be-phased-out-in-months-not-years-says-expert-as-FDA-considers-revoking-their-GRAS-status

The cis- and trans- forms of a fatty acid

Lipid Oxidation

Effects of Lipid Oxidation Flavor and Quality Loss

Rancid flavor Alteration of color and texture Decreased consumer acceptance Financial loss

Nutritional Quality Loss Oxidation of essential fatty acids Loss of fat-soluble vitamins

Health Risks Development of potentially toxic compounds Development of coronary heart disease

Simplified scheme of lipoxidation

C C

H H

CC R

H

H

H

H

R C C

H

CC R

*

H

H

H H

R C C

H

CC R

O

H

H

H H

O

R

+ Oxygen+ Catalyst

LIPID OXIDATION and Antioxidants Fats are susceptible to hydrolyis (heat, acid, or lipase enzymes)

as well as oxidation. In each case, the end result can be RANCIDITY.

For oxidative rancidity to occur, molecular oxygen from the environment must interact with UNSATURATED fatty acids in a food.

The product is called a peroxide radical, which can combine with H to produce a hydroperoxide radical.

The chemical process of oxidative rancidity involves a series of steps, typically referred to as:

Initiation Propagation Termination

Lipid Oxidation

Initiation of Lipid Oxidation There must be a catalytic event that causes the initiation of

the oxidative process Enzyme catalyzed “Auto-oxidation”

Excited oxygen states (i.e singlet oxygen): 1O2 Triplet oxygen (ground state) has 2 unpaired electrons in the same spin in

different orbitals. Singlet oxygen (excited state) has 2 unpaired electrons of opposite spin in the

same orbital. Metal ion induced (iron, copper, etc) Light Heat Free radicals Pro-oxidants Chlorophyll Water activity

Considerations for Lipid OxidationWhich hydrogen will be lost from an unsaturated

fatty acid?The longer the chain and the more double

bonds….the lower the energy needed.

Oleic acidOleic acid

Radical Damage,Radical Damage,HydrogenHydrogen

AbstractionAbstraction

Formation of aFormation of aPeroxyl RadicalPeroxyl Radical

Propagation Reactions

Initiation Ground state oxygenPeroxyl radical

Hydroperoxide New Radical

Hydroperoxide decomposition

Hydroxyl radical!!Start all over again…

Propagation of Lipid Oxidation

C C

H H

CC R

H

H

H

H

R C C

H

CC R

*

H

H

H H

R C C

H

CC R

O

H

H

H H

O

R

+ Oxygen+ Catalyst

Termination of Lipid Oxidation Although radicals can “meet” and terminate propagation

by sharing electrons…. The presence or addition of antioxidants is the best way in

a food system. Antioxidants can donate an electron without becoming a

free radical itself.

Antioxidants and Lipid Oxidation BHT – butylated hydroxytoluene BHA – butylated hydroxyanisole TBHQ – tertiary butylhydroquinone Propyl gallate Tocopherol – vitamin E NDGA – nordihydroguaiaretic acid Carotenoids

Physical Properties of Lipids

Fats and OilsMelting and Texture

Think of a fat as a crystal, that when heated will melt.

Length of fatty acid chain Short chains have low melting points

Oils vs soft fats vs hard fatsDegree of unsaturation

Unsaturation = presence of double bonds Unsaturation = low melting point

Fats and Oils in Foods SOLID FATS are made up of microscopic fat crystals. Many fats

are considered semi-solid, or “plastic”. PLASTICITY is a term to describe a fat’s softness or the

temperature range over which it remains a solid.

Even a fat that appears liquid at room temperature contains a small number of microscopic solid fat crystals suspended in the oil…..and vice versa

PLASTIC FATS are a 2 phase system: Solid phase (the fat crystals) Liquid phase (the oil surrounding the crystals).

Plasticity is a result of the ratio of solid to liquid components. Plasticity ratio = volume of crystals / volume of oil Measured by a ‘solid fat index’ or amount of solid fat or liquid oil in a

lipid

As the temperature of a plastic fat increases the fat crystals melt and the fat will soften and eventually turn to a liquid.

Shortening

Plastic range Temperature range over which it is solid

(melting point)Want a large plastic range for shorteningWant it to remain a solid at high temps.

Holding air during baking

Frying Oils

Want a short plastic rangeLiquid or low melting pointDo not want mono- or diglycerides or oil

will smoke when heatedMust be stable to oxidation, darkeningMethyl silicone may be added to help

reduce foaming

Fat and Oil: Further ProcessingWinterizing

Cooling a lipid to precipitate solid fat crystals DIFFERENT from hydrogenation

Plasticizing Modifying fats by melting (heating) and solidifying

(cooling) Tempering

Holding the fat at a low temperature for several hours to several days to alter fat crystal properties

(Fat will hold more air, emulsify better, and have a more consistent melting point)

Fat Crystals: α, ß’, ß The proportion of fat crystals to oil also depends on the melting points

of the crystals.

Most fats exhibit polymorphism, meaning they can exist in one of several crystal forms. These crystal forms are 3-D arrangements.

Three primary crystal forms exist: α-form (not very dense, lowest melting point), unstable ß’-form (moderate density, moderate melting point), not as stable ß-form (most dense, highest melting point), very stable

Rapid cooling of a heated fat will result in fine α crystals. Slow cooling favors formation of the coarse ß crystals. Fat crystals are easily observed when butter/shortening is melted and

allowed to re-solidify.

Fat Crystals in Commercial Oilsα, ß’, ß

Crystal forms are largely dependent on the fatty acid composition of the lipid Mono-acid lipids (3 of the same fatty acids) Mixed lipids or heterogeneous lipids (different FA’s)

Some fats will only solidify to the ß-form Soybean, peanut, corn, olive, coconut, cocoa butter, etc

Other fats will harden to the ß’-form Cottonseed, palm, canola, milk fat, and beef tallow

ß’ forms are good for baked goods, where a high plastic range is desired…..but...

Chocolate Bloom In chocolate (cocoa butter), the desired stable

crystal form is the ß-formProcessing involves conching (blending cocoa

and sugar to a super-fine particle) and Tempering (heating/cooling steps).Together, these give ß crystals to the final

chocolateFine chocolates control this well.

ChocolateMaking chocolate The polymorphs of chocolate affect quality and keeping quality. When making chocolate, the tempering process alters the fat crystals and

transforms to a predominance of ß-forms. This process begins with the formation of some ß crystals as “seeds” from

which additional crystals form. The chocolate is then heated to just below the temperature for ß-forms to melt

(thus melting all other forms), and allows the remaining fats to crystalize into ß-forms upon cooling.

Chocolate Bloom When chocolate has been heated and cooled, fat and sugar can rise to the

surface, and change crystalline state (fat) or crystallize (sugar). When melted fat re-cools, less stable and lower melting point α crystals can

form. The different crystals also physically look different (white, grey, etc) against

the brown background of the chocolate bar.