4 Basic Food Molecules Interesting Food Systems 2013

7/28/2019 4 Basic Food Molecules Interesting Food Systems 2013

1/51

Five Interesting Food Systems


2/51

Objectives: To introduce the four basic food molecules which have a

profound effect on the way we perceive and enjoy food,namely:

1. Water

2. Carbohydrate3. Lipids

4. Protein

To demonstrate by suitable examples, how these 4 basic

molecules are manipulated and fashioned into unique andpeculiar chemical food systems which we have come toaccept in our daily lives;


3/51

1. Water An inorganic molecule essential to (organic) life. Water

acts as a: Body temperature regulator;

Solvent;

Carrier of nutrients & waste;

Reactant & reaction medium;

Lubricant & plasticizer;

Stabilizer of macromolecules & catalytic (enzymatic) properties;

Water is a major component on many foods affecting Structure, Appearance & Taste; Susceptibility to spoilage & method of preservation used;

Removal of water (as in dehydrated foods) greatly altersfoods native properties.


4/51

Water Content of various Foods

extracted from:Food Chemistry, Fennema (3rd ed.), p19.

Food Water content (%)

Meat: Raw pork (lean) 53 -60

Raw Beef (retail) 50 -70

Raw chicken (less skin) 74Fish (fillet) 65 81

Fruit: Cherries, Pears 80 -85

Apples, peaches, oranges 90

Tomatoes, strawberries 90 95Vegetables: Peas 74-80

Broccoli, carrots, potatoes 85-90

Cabbage, lettuce, beans 90-95


5/51

Physical Properties of Water & IceExtracted from: Food Chemistry, Fennema (3rd edition), p20.

Properties 20 oC O oC (water) O oC (ice) - 20 oC (ice)

Density (g/cm3) 0.99821 0.99984 0.9168 0.9193

Viscosity (pa.sec) (103) 1.002 1.793 0 0

Vapour pressure (k.Pa) 2.3388 0.6113 0.6113 0.103

Heat capacity (J/g. K) 4.1818 4.2176 2.1009 1.9544

Thermal conductivity(W/m.K)

0.5984 0.5610 2.240 2.433


6/51

Structure, Properties & Interactions

The structure of water

Association of water molecules (H-bonding)

The structure of Ice


7/51


8/51

Association of water molecules (H-bonding)

The structure of Ice


9/51

Interactions

Water solute interactions

Macroscopic:water binding, hydration & holding capacity;

Molecular: Bound water Interactions with

Ions & ionic groups;

Hydrophilic solutes;

Hydrophobic solutes; Ampiphilic molecules.


10/51

Hydrophilic solutes


11/51

Hydrophobic solutes Ampiphilic molecules


12/51

Relative Vapour Pressure & Food StabilityFood stability is affected by Vapour Pressure (p/po

(Microbial growth / Enzymic hydrolysis/ Oxidation reactions /Maillardreactions)


13/51

Interesting Food SystemCarbohydrates Confectionery

Caramelisation & Caramels Gelling agents Jelly Beans, Gummy bears & Cotton Candy

Fats & Oils

Types of Creams Ice Cream; Italian Gelato Whipped cream

Fermented Milk Yoghurt Mayonnaise

Food Proteins Cheese Sausages


14/51

Carbohydrates Basic structure & nomenclature

Types: Mono-, oligo- and polysaccharides;

Starch


15/51

Common Molecules


16/51

Confectionary


17/51

Effect of Temperature on Sucrose


18/51

Caramelization & Caramels

Caramelization: the cooking of plain sugar (syrup) until it turns brownand aromatic. It leads to the development of a brown colour(browning) but does not require the presence of amino acids andproteins. It requires higher temperatures than Maillard reactions andproduces a different mixture of aromatic compounds (and f lavour);

Caramels: the brown, sweet, aromatic syrup produced in

caramelization used as colouring & flavouring agents in many dishes.It may also refer to the combination of caramelized sugar to whichmilk products (cream) has been added to generate colour & aroma.

Sugar Work: molten sucrose with a large proportion of glucose andfructose (as corn syrup HFCS, or by adding acid citric/tartaric) tohelp prevent crystallisation of sucrose. The sugar mixture is heateduntil it reaches ca. 160 oC (no water present) but not yet caramelised(>165 oC). When cooled to 50-55oC, it is pliable like dough, and can beformed or blown into hollow spheres. It can be pulled, twisted & foldedunto itself. Colour & air can be incorporated to form an attractivefabric.


19/51

Gelling Agents Pectins:

large CHO molecule (which is found in plant cell walls) bound together into acontinuous sponge like network that traps water in many several differentpockets;

Extracted from fruits by boiling in water but are negatively charged;

Bonding is encouraged by

Reducing available water (add sugar @ 55% w/w and boil to final sugar of 60 -65%);

Add acid (at 0.5% citric) to a pH of between 2.8 3.5, thus neutralizing the vecharge & allowing the bonding of pectin molecules network;

Gelatin extracted from bone & animal skin, comingled with collagen ashelix:

Large molecules of coiled protein which uncoil when heated and recoil whencooled;

Most protein behave in an opposite way: egg solidifies, milk curdles; meatstiffens;

At 1% gelatin, a sufficiently rigid network of molecules is formed (transitiontemperature = 40 C);

Desert Jellies are at 3% gelatin;


20/51

Jelly Beans, Gummy bears & Cotton Candy

Composition: Gummy Bears: Equal wts. Of Sucrose & corn syrup, and a mixture of gelatin (5 15%) &

pectins (1%);

The gelatin provides a rubbery texture while the pectin a crumbly texture;

Because gelatin is degraded at high temperature, a concentrated solution is

added to the sugar syrup after it has been cooled; Water content is about 15%;

Cotton Candy: 1904 World Fair, St. Louis:

Hard candy, filaments of sugar glass which is very fine & with theconsistency of cotton balls, dissolving in the mouth at exposure to moisture

in the mouth; Melted sugar is forced through spinnerettes into air where it instantly

solidifies into threads;


21/51

Lipids, Fats & Oils Nomenclature & classification: # of C & unsaturation;

Physical aspects: Fats vs Oils

Chemical aspects Lipolysis:

Thermal decomposition & Frying:

Smoke points & free fatty acids;

Vegetable oils @ 230 oC & Fats @ 190 oC;

Hydrogenation:

cis to trans fats.


22/51


23/51

Linoleic & Eicosa-pentaenoic acids


24/51

1. Types of Cream:Cream is a special portion of milk (with 3.5% fat) that is greatly enriched with

fat (> 20%)

and is layer of fat which separates from fresh milk left to stand.Single Cream (20%)

Cream with a low fat-content, which does not thicken when beaten. Used inboth sweet and savory dishes. Also know as light cream.

Light Cream (20% fat - range 18-30%)Pretty much the same as half and half. Also know as coffee cream or table

cream. Will whip if it contains 30% butterfat but will not be very stable.Generally contains only 20% butterfat. Also know as single cream. Light creamis not available everywhere.

Whipping Cream (30%)Cream with enough butterfat in it to allow it to thicken when whipped. Doesnot whip as well as heavy cream but works well for toppings and fillings.Almost all whipping cream is now ultra-pasteurized, a process of heating thatconsiderably extends its shelf life by killing bacteria and enzymes.

Heavy Cream / or Heavy Whipping Cream (36 to 38%)This cream whips denser than whipping cream. Whips up well and holds itsshape. Doubles in volume when whipped.


25/51


26/51

ICE CREAM STRUCTURE


27/51

Ice cream:ice crystal, conc. cream, sugar, air: Water (60%), sugar (15%), milk fat (10 -20%)

Ice cream:1. Ice crystal form (the backbone) from water molecules as they freeze the sizedetermines its texture;

2. Concentrated cream remains as the ice crystal forms. The hydrophilic solutes(sugar) retain some water into which the milk fat & proteins are dissolved;

3. With constant stirring, this mixture coats each ice crystal and allows them to

stick together;4. Air cells are trapped in the ice cream when agitated, inflating the volume by

as much as 100%! (ie. doubling the initial liquid volume);

Achieving the right balance of ice, cream & air is critical to good ice cream.

Good ice cream should be creamy, smooth and firm.

Less water small ice xstals & smooth texture:High sugar & milk solids heavy, syrupy product;

Too much fat buttery product.

Premium quality ice creammore cream (high fat) and egg yolk.

3 Steps of making Ice Cream:

Preparing the Mix, freezing it rapidly & hardening it (in small containers).


28/51

Italian Gelato

A variation of the French /custard ice cream containing the additionalingredient of egg yolk (up to 12 yolks per litre), low in milk fat andhigher in water content;

Gelato is high in both egg yolk and butterfat, and is frozen with littleincorporation of air;

How can Liquid Nitrogen be used to make ice cream?


29/51

Whipped cream:An intimate mixture of liquid cream and air a key feature being the fatconcentration of the cream being used, which must be > 30%;


30/51

2. Fresh(ly) Fermented Milk: YoghurtLactic acid bacteria (Genus: Lactococcus & Lactobacillus): responsible for

transforming (fermenting) milk sugar (lactose) to sour lactic acid, which inturn retards the growth of other microbes self preserving. Theaccumulation of acid causes the milk protein (casein) to form curds andthicken milk in 2 -3 hrs!

Yoghurt turkish for milk that has been fermented into a tart, semi-solid

mass. For commercial applications, symbiotic species Lactobacillusdelbrueckii sbsp. bulgaricusandStreptococous salivarius sbsp.thermophilus are used to develop acidity at 1% lactic acid and acetaldehydeto give the characteristic fresh flavour & aroma.

Ingredients: milk (cow, goat, sheep), bacteria, flavour;

Milk is first heated (90 C/10 min) to sterilise batch & denature whey protein lactoglobulin, and disperse casein molecules. It is then cooled to 40 45 Cand fermented by adding bacteria and held until it sets in about 2-3 hrs;

Rapid gel formation coarse casein network structure & weeping of whey;

Slow gel formation fine casein network structure & retention of wheyproteins.


31/51

3. Cold Egg Sauce: Mayonnaise:An emulsion of oil droplets (80%) suspended in water based ingredients (egg yolk,

lemon juice or vinegar, water and mustard (for flavour / CHO);

Dense and cannot be poured.

Egg Yolk as protein thickeners: 16% protein/50% water/

Salt causes the yolk to separate into its component granules (salting out) increasing surface area;

Making Mayonnaise (room temperature):1. Mix egg yolk, lemon juice, salt, mustard

2. Whisk in oil slowly at first, and then more rapidly as emulsion thickens.

Notes:

3. What is critical is the ratio of (oil: water) there must be enough (water) for

the population of oil droplets to fit into;4. The Volume of (Oil to water based) ingredient = 3: 1 ie- egg yolk & salt,

lemon juice, vinegar, and other water soluble ingredient.

5. Sensitivity: extremes of cold, heat and agitation will damage the emulsion.Adding stabilisers (CHO or proteins) can fill spaces between oil droplets.

PROBLEM: Mayonnaise becomes hard: how would you restore structure? Explain.


32/51

Food Proteins

Structure & Units Functional Properties

Denaturation

Emulsification

Enzymes Foaming

Gelation

Water Holding capacity

Hydrolysis

Protein Solubility

APPLICATIONS: Milk Protein & Cheese

Whey Protein

Caseins

Iso-electric point Micelle structure

Cheese making

Plain Cheese

Mozzarella


33/51

Structure & Units Proteins are:

Polymers of amino acid (polypeptides);

All amino acids have a commonstructure;

Proteins are composed of chains ofamino acids joined by peptide bonds;

Most proteins (polypeptides) are

made of several dozen to hundreds ofamino acids units;

Most proteins exist as non-conjugated(not bound) molecules while some areconjugated (bound) to other non

protein molecules to form complexmolecules;

1o, 2o, 3o & Quaternary Structures formincreasingly complex molecules andare stabilised by hydrogen anddisulfide bonds between amino acids.

Amino acid unit

1. Amine group2. Acid group

3. Central carbon

4. Side chain

The side chain allows for 5 classes i.e.

- acidic, basic, neutral, aromatic &sulfur-containing;

Example of conjugated protein are:

Egg white proteins are glycoproteins i.e. conjugated with sugarmolecules called ovomucoid andovalbumin;

In egg yolk, the protein is conjugatedwith lipids to form a low densitylipoprotein;

The milk protein, casein, contains

phosphate in its structure.


34/51

Peptide Bond


35/51

1o, 2o, 3o & Quaternary Structures
http://localhost/var/www/apps/Pictures/CITK/Protein%20Structure.mp4http://localhost/var/www/apps/Pictures/CITK/Protein%20Structure.mp4http://localhost/var/www/apps/Pictures/CITK/Protein%20Structure.mp4http://localhost/var/www/apps/Pictures/CITK/Protein%20Structure.mp4http://localhost/var/www/apps/Pictures/CITK/Protein%20Structure.mp4http://localhost/var/www/apps/Pictures/CITK/Protein%20Structure.mp4http://localhost/var/www/apps/Pictures/CITK/Protein%20Structure.mp4http://localhost/var/www/apps/Pictures/CITK/Protein%20Structure.mp4http://localhost/var/www/apps/Pictures/CITK/Protein%20Structure.mp4http://localhost/var/www/apps/Pictures/CITK/Protein%20Structure.mp4http://localhost/var/www/apps/Pictures/CITK/Protein%20Structure.mp4http://localhost/var/www/apps/Pictures/CITK/Protein%20Structure.mp4http://localhost/var/www/apps/Pictures/CITK/Protein%20Structure.mp4http://localhost/var/www/apps/Pictures/CITK/Protein%20Structure.mp4http://localhost/var/www/apps/Pictures/CITK/Protein%20Structure.mp4


36/51

Food Protein shapeFood Protein Protein Structure Protein Shape

Egg Albumin Globular SphericalMeat & legume globulins Globular Spherical

Collagen & Elastin Fibrous Elongated

Glycoprotein & Lipoprotein(ovomucoid & ovalbumin)

Conjugated Protein bound to sugars &lipids

Phospho-protein & metallo-proteins (myoglobin)

Conjugated Protein bound to P &metals (Fe)


37/51

Functional Properties Denaturation

Unfolding of protein structurechanging original properties &occurs when roasting meat (actin,myosin & myoglobin) or cookingeggs (ovalbumin), or even whippingegg white to form a foam;

Unique to proteins & is therelaxation of protein 3o structurewith decreased functionalproperties & solubility;

Coagulation is distinct from

denaturation and is theprecipitation of protein asindividual molecule aggregates.

Emulsification

Proteins stabilise emulsions byacting at the oil-water interface;

This gives stability to oil-wateremulsions (mixtures) as seenin common food products suchas salad dressing, sauces &frankfurters/sausages;

Proteins are isolated from foods(meat, milk, eggs, soy) for use asemulsifiers;


38/51

Proteins as Enzymes

Enzymes are

proteins used to speed up chemical

reactions;

They are used to produce variousproducts in the food industry;

Applications

Production of HFCS a major

sweetener in the food industry via

AMYLASE Corn starch to Dextrins;

FUNGAL ENZYMES Dextrins to

Glucoe, &

GLUCOSE ISOMERASE Glucose to

42% Fructose.


39/51

Other Functional Properties

Foaming Foams are colloidal

dispersions of gas in liquids;

Foods that are good foamingagents are

Egg, Milk, Soy Protein; Examples of foam foods are

Ice cream;

Whipped toppings

Beer froth

Gelation Protein can form a well

ordered gel matrix which canhold together water, fat andother ingredients;

Examples are Bread Dough

Gelatin desserts;

Tofu

Yoghurt


40/51

Food Protein interaction with H2O Water holding Capacity

The presence of hydrophilic groupsand charged groups is responsible forthis characteristic, & Influenced bypH, salt content & temperature;

Protein: protein interactions

Strong interactions when the protein

molecule is electrically neutral;

Protein: water association

Strong interactions when the proteinmolecule is polar;

Increasing salt content, protein

polarisation is increasedfacilitating increased binding withwater;

Increasing temperature to 80 oCcauses gelation of proteins whichtraps water inside the 3D gel network.

Hydrolysis

By protease enzymes (papain) Protein + H2O amino acid;

Non-enzymic hydrolysis (heat/pH)

Protein + H2O amino acid

Occurs during cooking andfood processing.

Protein Solubility

Affected by pH & temperature

Function in foods related tohydrated proteins;

Soluble proteins used to producewhipped creams products, proteinfilms and emulsions.


41/51

Milk Protein & Cheese


42/51

Milk Protein & Cheese

Excellent source of high qualityprotein;

Important proteins are

Casein 80% of all milk proteins andare comprised of 2 alpha caseins

(1 & 2), -casein, -casein & -casein.

Whey 20% of milk proteins;

Functional Properties

Whey proteins

have an ordered globular structure with

disulfide (S-S) linkages; remain colloidally dispersed in

solution;

Denatured by heat to form gels;

Caseins Exists in a disordered 3o state as

randomly coiled molecules;

Caseins are resistant to heatdenaturation due to their structure;

Addition of rennin (enzyme)causes the formation of gels;

When milk is acidified to pH 4.6,the caseins become insoluble;

Precipitate on addition of acids;


43/51

Casein Iso-electric Point (pH = pI)

A critical pH for proteins whenthe H+ & OH- are equal;

Net charge of protein is zero;

At pI, protein is unstable &insoluble;

This instability causes proteinbond to each other by H- bonds(protein: protein interactions) clumping proteins and casuingthem to precipitate (fall out ofsolutions);

Phenomenon used is cheesemaking by forming a solidprotein cheese curd due to theclumping of casein;


44/51

Micelle Structure Casein Micelles

In milk, case exists within micelles each with thousands of caseinpolypeptide molecules;

Ca-phosphate are complexed tocasein forming colloidal particles;

Sub-micelles are composed of

alpha, beta & kappa caseins,

Alpha & beta reacts with Ca &precipitates while kappa remainsfree to stabilise the colloidalsuspension by binding to H2O;

The P group of alpha & kappareact with Ca to form crosslinksbetween submicelles;

The kappa form dominates themicelle structure by aggregating toform a hydrophilic cap where nocross-linking occurs;


45/51

Cheese Making Casein micelles are stable in milk

as colloids; To make cheese, the casein

micelles must be destabilised bydisrupting the stabilising effect ofkappa casein;

Rennin, catalyses the splitting of

kappa-casein into a micelle remnant called

para -casein, and

- casein macropeptide, which islost in the whey liquid;

In the presence of Ca, para--casein is insoluble;

The casein micelles remnantsaggregate to form the cheese curd(gel);


46/51

Plain cheese vs Mozzarella
http://localhost/var/www/apps/Pictures/Thermal%20Processes/CITK/Making%20cheese%20with%20Mike%20Rowe.mp4http://localhost/var/www/apps/Pictures/Thermal%20Processes/CITK/How%20to%20make%20Mozzarella%20cheese.mp4http://localhost/var/www/apps/Pictures/Thermal%20Processes/CITK/How%20to%20make%20Mozzarella%20cheese.mp4http://localhost/var/www/apps/Pictures/Thermal%20Processes/CITK/Making%20cheese%20with%20Mike%20Rowe.mp4


47/51

Comparison of proteins


48/51

5. SausageSausage: from Latin salt & names a mixture of chopped meat and salt stuffedin an edible casing. The salt i) controls growth of microbes, and ii)dissolves the protein fiber (myosin) out of the meat and makes it availableto act as a glue, binding the pieces together.

Emulsified sausages: Frankfurters/wieners /bologna- very fine textured,homogenous, tender interior with relatively mild flavour.

They contain pork/beef/chicken meat, fat, salt, sodium nitrite, f lavouring &water homogenised together to form a smooth meat batter similar to anemulsified sauce (like mayonaise).

The fat is evenly dispersed in very small droplets, surrounded by muscle cell &

dissolved muscle protein (myosin) network. Emulsion stability is highlydependent on temperature (16 21 C) & after batter is prepared, it is stuffedinto casings & cooked (smoked) at 70 C. Heat coagulates the meat proteinsand turns the batter into a solid mass from which the casings can beremoved. The high water content (55%) makes sausages perishable and theymust be refrigerated.


49/51

Breakfast Meats:


50/51


51/51

Yoghurt & Cheese:Alpha - casein

4 Basic Food Molecules Interesting Food Systems 2013

Documents

Transcript of 4 Basic Food Molecules Interesting Food Systems 2013