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Five Interesting Food Systems
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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;
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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.
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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
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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
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Structure, Properties & Interactions
The structure of water
Association of water molecules (H-bonding)
The structure of Ice
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Association of water molecules (H-bonding)
The structure of Ice
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Interactions
Water solute interactions
Macroscopic:water binding, hydration & holding capacity;
Molecular: Bound water Interactions with
Ions & ionic groups;
Hydrophilic solutes;
Hydrophobic solutes; Ampiphilic molecules.
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Hydrophilic solutes
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Hydrophobic solutes Ampiphilic molecules
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Relative Vapour Pressure & Food StabilityFood stability is affected by Vapour Pressure (p/po
(Microbial growth / Enzymic hydrolysis/ Oxidation reactions /Maillardreactions)
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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
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Carbohydrates Basic structure & nomenclature
Types: Mono-, oligo- and polysaccharides;
Starch
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Common Molecules
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Confectionary
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Effect of Temperature on Sucrose
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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.
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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;
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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;
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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.
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Linoleic & Eicosa-pentaenoic acids
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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.
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ICE CREAM STRUCTURE
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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).
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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?
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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%;
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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.
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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.
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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
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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.
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Peptide Bond
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1o, 2o, 3o & Quaternary Structures
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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)
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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;
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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.
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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
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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.
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Milk Protein & Cheese
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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;
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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;
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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;
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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);
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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 -
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Comparison of proteins
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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.
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Breakfast Meats:
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Yoghurt & Cheese:Alpha - casein