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143 Cards in this Set
- Front
- Back
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Emulsion |
Two non miscible Components Non-homogenous Usually Turbid (thick, cloudy mixtures) |
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Typical Emulsion |
Oil and Water |
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Two Phases of emulsions |
Disperse- Internal Continuous- external |
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Homogenization |
Process of dispersing one into the other with mechanical energy |
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Emulsion examples |
Oil in Water: Milk, Cream, Mayo, Sauces Water in oil: Butter, margarine |
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Are emulsions stable? |
Non-stable Internal phase droplets coalesce due to high surface tension |
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Phase Separation depends on: |
Droplet size Temperature Emulsifiers Viscosity of continuous phase |
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coalescence |
Process of coming together as one whole internal phase starts to come together from many separated droplets to bigger ones in phase separation |
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Breaking |
Emulsion separates back into two distinct components |
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Creaming |
Droplets of internal phase form "cream" or layer at top of external phase of many droplets. |
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Flocculation |
A breakdown of a good emulsion where the particles of a dispersion form larger-size clusters Small to medium droplets of internal phase cluster together |
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Emulsion internal phase ratio |
Volume of Internal Phase/ (Volume of Internal phase + Volume of external phase) |
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low internal phase ratio |
< 0.3 Whole milk: o/w; 3.5% fat Butter: w/o; >80% fat |
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High internal phase ratio |
>0.7 Salad dressings; usually o/w |
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Emulsifiers/ Surfactants |
Reduce Interfacial surface tension (amount of work required to homogenize two non miscible phases) |
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Emulsifiers mechanism |
Orient on interface and form a chargedbarrier Droplets repel rather than coalesce |
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What do emulsifiers help with |
form and stabilize emulsions at very lowconcentrations |
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Amphiphilic |
Lipophilic: Hydrocarbons in fatty acids– + Hydrophilic: Polar groups (COOH, OH, NH2,OPO3) |
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Emulsifier alignment |
Encircle internal phase with appropriate end facing internal phase and the other facing external. Hydrophobic faces oil phase, hydrophilic faces water phase |
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Effect of emulsifer concentration onsurface tension of water |
Interfacial ST high at 0% Emulsifier conc. but is decreased as conc. increases. Levels out around 30% concentration and doesn't change |
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Common Emulsifiers in foods |
Monoglycerides Diglycerides Phospholipids Spans Tweens Selected proteins Emulsion stabilizers: – Selected gums (viscosifier) – Spices |
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Spans |
sorbitol based fatty acid esters |
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Tweens |
polysorbate fatty acids esters |
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Natural Emulsifiers |
Egg Yolk Soy Lecithin |
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Synthetic Emulsifiers |
Sorbitan monolaurate (Span) Sorbitan monosterate (Span) |
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HLB Values |
Hydro-lipophilic balance of emulsifiers Range from 1-20 Bulk of emulsifier orients on outside ofdroplet |
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~3-7 HLB Value |
w/o emulsion: more lipophilic |
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~10-17 HLB Value |
o/w emulsion: more Hydrophilic |
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Lipid Oxidation |
AKA: autoxidation and/or peroxidation a free radical reaction |
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Effects of Lipid Oxidation in foods |
Off flavor Off Odor < storage stability < nutritional value (essential fatty acids, lipid soluble vitamins) |
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Three steps of lipid oxidation |
Initiation Propagation Termination |
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Initiation |
• Free radical formation – electron (H) removed from fatty acid – H is removed from carbon next to double bond(usually α-methylene group) – results in unpaired electrons • Caused by– irradiation, superoxide, singlet oxygen, freeradicals, light, metals .… (initiator) • RH R* + H* |
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Propagation |
Lipid radical (R*) is highly reactive – now removes a hydrogen from another fattyacid, turning it into a free radical • Oxygen addition usually occurs – R* changed to peroxy radical (ROO*)• ROO* removes hydrogen from anothermethylene group (RH) – hydroperoxide (ROOH) and a new R* formed • Chain reaction– repeats over and over |
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Change which occurs during propagation |
fatty acid changes from a nonconjugated diene to a conjugateddiene hydroperoxide |
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Termination |
Free radical is stabilized (quenched) – addition of an electron – chain reaction stopped • Combination of a radical plus anantioxidant, or • Combination of two radical products to forma non-radical – R* + R* – R* + ROO* – ROO* + ROO* • Hydroperoxides are typically formed |
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Autoxidation Cycle |
a |
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Oxidation Initial Products |
Hydroperoxides – No off-flavors/odors – Unstable: many decomposition products |
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Oxidation Secondary Products |
Aldehydes - hexanal, propanal, … - dienals - malonaldehyde (MDA) |
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Oxidation Tertiary Products |
-Carboxylic acids -Alcohols |
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Lipid Oxidation Rate is Influenced by: |
– Fatty acid composition – Temperature – Oxygen concentration – Water activity – Light – Surface area – Free fatty acid level |
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Oxidation Rates |
> unsaturation = > lipid oxidation |
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Pro-oxidants |
Transition metals (Copper, manganese, nickel, iron) Decrease Induction period Natural |
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Antioxidants |
Delay onset of oxidation Slow rate of oxidation Synthetic and natural Must be approved |
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Two types of Antioxidants |
Hydrogen donators Chelators (pick up/attach to metals) |
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Tracking Oxidation |
Peroxide Value TBARS Fatty Acid Analyses Headspace analysis of aldehydes Iodine value |
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Peroxide Value |
Measure peroxide (Primary Product) -Transient product -Measure over time |
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TBARS |
- Measures malonaldehyde (secondary product) – Transient, measure over time |
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Fatty Acid Analyses |
Decrease PUFAs with oxidation |
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Iodine Value |
< with oxidation |
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Hydrogen Donors |
– Inhibit chain reaction by accepting free radicalswithout becoming radicals themselves – Exhibit resonance stabilization – AH + R* RH + A– AH + ROO* ROOH + A |
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Examples of Hydrogen Donors |
Phenols BHA, BHT, Propyl Gallate, TBHQ (synthetic) Tocopherol, chlorogenic acid, caffeic acid (naturally occurring phenolic compounds) |
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Chelators |
– Function by binding to pro-oxidant metals |
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Some approved food grade chelators: |
• EDTA • Citric acid • Ascorbic acid (can also donate hydrogen) • Phosphoric acid |
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Antioxidant synergism |
Mixing different types of antioxidants Function better in a mixture |
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Examples of Antioxidant Synergism |
Examples: – Tocopherol (hydrogen donor) and citricacid (chelator) – Propyl gallate (hydrogen donor) andphosphoric acid (chelator) |
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Antioxidant Selection |
Solubility – BHA/BHT (oil) – Propyl gallate (water) • Carry through characteristics – BHA (heat resistant) – BHT (non-heat resistant) • FDA approval • Cost • Availability • Interaction with other components • Marketability – “natural”: spices, citrus peel, oilseeds, tea – Application: mixed, sprayed, dipped, packaging |
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Effects of fat in foods |
• texture • flavor • appearance • mouthfeel • nutrition • processing • stability |
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Replacing fats in food |
No single fat replacer can replace all the functions of fat in foods Combinations typically used |
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Types of Fat Replacers |
CHO Based Protein Based Fat mimetics |
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CHO Based Fat Replacers |
• 4 kcal (or less) vs 9 kcal per gram • Used in high moisture products |
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Functions of CHO based Fat Replacers |
- bind water (hydrocolloids) – provide texture – act as thickening agents (swell up) |
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Gums/ Hydrocolloids |
– xanthan gum, guar, carrageenan … – thickening, viscosity – common in low-fat salad dressings |
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Starches |
– corn, potato, rice – native or modified – salad dressings, low fat spreads – not good in cookies, crackers |
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Polydextrose |
– water soluble – branched polymer(10 – 12 units) – polymerized glucosedigestion resistant – 1 kcal/g – prebiotic fiber – Ex: Litesse (Danisco) Randomly cross-linked polymer of Glucose |
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Oatrim |
– hydrolyzed oat bran – developed by USDA labs – heat stable – used in baked goods, dairy products |
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Pectin |
– from fruits/vegetables, citrus peel, beet pulp – used for gel formation – frozen desserts, sauces, spreads, gravies – “Slendid” (Kelco) |
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Cellulose |
– fiber-based fat replacer – stabilizes foams, emulsions – increases viscosity, acts as thickener – used in sauces, fillings, drinks |
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Fruit Blends |
– pureed prunes, plums .. – “lighter bake” |
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Protein Based Fat Replacers |
• 4 kcal vs 9 kcal/g • High moisture products |
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Soy, Whey, and Egg Proteins |
– emulsification – gelling, texture modification – frozen desserts, lunchmeats |
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Microparticulated Proteins |
– small round particles, provide creaminess – used in dairy, ice cream, sauces …. – no high temperature frying (spheres collapse) – “Simplesse” |
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Fat based Replacers |
Fat mimetics Salatrim, caprenin, olestra, |
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Salatrim |
- Short and long acyltriglyeride molecule – acetic, propionic, butyric, and stearic (or palmitic) – 4.5 - 6 kcal/g – Physical properties of fat – FA composition and position effect properties – Used in low moisture foods – Chocolate, confections, dairy, baked goods – Not for frying – Benefat® (Danisco) |
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Caprenin (P&G) |
– Capric (8:0), caprylic (10:0), behenic (22:0) acid– 5 kcal/gram – substitute for cocoa butter – in chocolate, confectionery coatings, soft candies |
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Olestra (P&G) |
– “Olean” – sucrose polyester w/6, 7, or 8 FAs – react FAs with OH groups of sucrose w/catalyst – C:12 – C:20 (tailored) – 0 kcal/g (not absorbed) – Lipase sterically inhibited – same taste and cooking properties of fats/oils – high temperature frying – $200 million/ 25 years for approval • Gastric distress • “leakage” • Stripping of fat soluble vitamins |
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Amino Acids |
Basic unit of proteins 20 common AA in foods Properties of proteins depends oncumulative properties of amino acids |
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AA's Contain |
Amino group = NH2 or NH3+ Carboxyl group = COO- or COOH Side chain = R |
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AA Side chain Influences |
the physiochemical properties ofthe amino acid and the protein |
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AA Classification |
Non-Polar or hydrophobic side chains Polar, Uncharged S.C. Polar, + Charged S.C. Polar, - Charged S.C. Sulfur Group Aromatics Branched Chain Hydroxyl |
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Non-Polar AA |
less soluble in water than polar amino acids > hydrophobicity with > chain length Glycine, Valine |
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Polar, No Charge AA |
– more hydrophilic – neutral, polar, functional groups • hydrogen bond with water • hydroxy groups –OH • amine group -CO-NH2 • thiol group –SH Theronine, Asparagine, Tyrosine |
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Polar, + AA at PH 7 |
basic amino acids (lysine, arginine, histidine) |
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Polar, - AA at PH 7 |
acidic amino acids (glutamic acid, aspartic acid) |
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Sulfur AA's |
Methionine and Cysteine |
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Aromatic AA's |
Tryptophan, Tyrosine, Phenylalanine |
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Branched Chain AA's |
Valine, Leucine, Isoleucine |
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Hydroxyl AA's |
Serine, Threonine, Tyrosine |
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Amino Acids in aqueous solution |
equilibrium exists between dipolar ion and the anionic and cationic forms of the AA. |
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Isoelectric Point |
pI pH at which the net charge of theamino acid (or protein) in solution iszero Predominantly in Zwitterion form |
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AA solubility at pI |
Poor |
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Zwitterion |
AA with neutral charge, + from amino group and - from COOH group cancel each other out. |
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Primary Protein Structure |
– amino acids bound together throughcovalent peptide bonds – reaction of amino and carboxyl group – an amide is formed and water is released – amino acid selection determined by DNA – amino acid chain determines thestructure/function of protein |
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Secondary Protein Structure |
Beta-Pleated sheet Alpha Helix Random Coil |
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Beta Pleated Sheet |
stable, provides rigidity • hydrogen bonding between C=O and NH • parallel or antiparallel orientation |
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Alpha Helix |
• coiling of the polypeptide chain • hydrogen bonding between C=O and NH • provides rigidity |
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Random Coil |
• no stability • interfering side chain chains (large, similar charges, orproline) |
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Tertiary Protein Structure |
– determine the overall shape and functionof proteins – interactions among amino acid residuesthat are far from each other on chain – binding, looping of proteins • clustering of hydrophobic residues • electrostatic attraction of oppositely chargedresidues • disulfide bridges |
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Quartenary Protein Structure |
– Association of two or more polypeptidesubunits in some proteins – Held together by non-covalent bonds |
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Examples of Quartenary Structure |
• Actomyosin structure of muscle • Hemoglobin • Some enzymes • Collagen |
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Categories of proteins |
Simple Proteins and Compound Proteins |
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Simple Proteins |
Globulins Albumins Prolamines Glutelins Scleroprotein |
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Globulins |
– Most common simple proteins – reserve proteins in plants – animal products: milk, meat, eggs – slightly acidic: pI 5-6 because of highdicarboxylic amino acid content – insoluble in water |
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Albumins |
– Second main group ofproteins – Usually occur withglobulins in food – Water soluble – Sulfur rich – Serum = serum-albumin – Milk = lactalbumin – Egg white = ovalbumin |
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Prolamines |
– Endosperm of grain – No lysine – Celiac disease (gliadin in wheat and rye) |
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Glutelins |
– Occur with prolamines in grain seeds – Combination = gluten – Contain lysine |
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Scleroprotein |
– Fibrous: structural proteins – Collagen: connective tissues • Hydrolyze to form gelatin • No tryptophan - Keratin: hair, nails, horns - High sulphur content |
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Compound Proteins |
• Amino acid + prosthetic group – phosphoproteins, glycoproteins, lipoproteins • Occur more widely in nature than simpleproteins Phosphoproteins Lipoproteins Glycoproteins |
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Phosphoproteins |
– protein covalently bound to phosphate group– H3PO4 bound as ester to serine & threonine – Why? presence of hydroxyl groups – Example: casein in milk |
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Lipoproteins |
– Proteins covalently bound to lipid group – Natural emulsifiers – Present in milk, egg yolks, |
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Glycoproteins |
– Proteins covalently bound tocarbohydrate – AKA mucoproteins – Physiologically important |
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Celiac Disease |
Autoimmune disease • Most common genetic disorder in US?? • Gliadin fraction of gluten (wheat, barley, rye)causes inflammation of microvilli in mucosaof small intestine • Malabsorption of food • Only treatment is a gluten-free diet |
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Essential Amino Acids |
Phenylalanine, Valine, Tryptophan, Threonine, Methionine, Histidine, isoleucine, leucine, lysine |
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Limiting amino acids for wheat and rice |
1st: Lysine 2nd: Threonine |
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Limiting AA Corn |
1st: Lysine 2nd: Tryptophan |
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Limiting AA soybean |
Methionine |
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Limiting AA cottonseed |
Lysine |
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Limiting AA Peanuts |
Lysine and threonine |
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Limiting AA Beans |
Tryptohan and sulfur contain AA |
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Whole Egg and Breast milk Limiting AA |
None, Complete protein |
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Animal vs. plant protein digestibility |
Animal protein typically more bioavailable |
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Processing effects on protein digestibility |
Maillard browning reduces lysine digestibility |
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Antinutritional factors in protein digestibility |
Trypsin and Chymotrypsin inhibitors in plant protein. Lectins (glycoproteins) bind to mucosa and interfere with AA absorption |
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Protein Efficiency ratio |
Measures Protein quality in foods wt gained / per g protein consumed |
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Biological value |
Measures protein quality
• Protein retained in body/proteinabsorbed)*100 • Takes urinary and fecal nitrogen losses intoaccount |
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Net protein digestibility |
Biological value * digestibility |
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Chemical score |
Based on essential amino acid contentcompared to requirements – Cheaper than animal studies mg primary limiting aa/g protein x 100 / mg same aa per g reference protein |
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Enzymatic method |
– Measure amino acids released afterprotease action in vitro |
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Biological Methods |
Dietary and fecal matters |
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Nitrogen determination |
– Kjeldahl analysis • acid/heat digestion – Combustion analysis – Protein ~ 16% nitrogen – Crude protein =nitrogen content x 6.25 |
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Protein denaturation |
• Modification of native proteinconformation • Changes in 2°, 3°, and 4° structure |
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Are peptide bonds ruptured in denaturation? |
no |
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End result of denaturation |
New conformation often intermediary • May result in partially or totallyunfolded polypeptide structure |
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Bonds involved in protein structure |
Covalent C-C: 83 kcal/mol bond energy Covalent S-S: 50 Hydrogen: 3-6 Ionic electrostatic: 3-7 Hydrophobic: 3-5 van der waals: 1-2 |
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Is denaturation reversible? |
Sometimes reversible, sometimes irreversible |
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When is denaturation often reversible? |
If S-S bridges contribute to native structure |
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Effects of denaturation |
• Decreased solubility – unmasking of hydrophobic groups • Altered water binding capacity • Loss of biological activity (enzymatic orimmunological) • Increased susceptibility to attack byproteases– unmasking of peptide bonds |
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Physical Agent Causes of denaturation |
Heat Interfaces Mechanical treatments |
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Chemical causes of denaturation |
pH (acids and alkilis) Organic solvents |
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Heat |
– rate depends on temperature – rate increases about 600 x per 10 C– due to low energy involved in stabilizinginteractions – Decreased solubility – water facilitates heat denaturation |
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Interfaces |
– many proteins migrate to interfaces – hydrophilic groups remain in aqueousphase – proteins partly or completely lose nativestructure |
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Mechanical treatments |
– Kneading: disruption of alpha helices anddisulfide bridges – Whipping: egg whites – Irradiation: rupture of s-s bridges by UV |
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Acids and alkilis (pH) |
– High or low pH – Sometimes reversible |
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Organic Solvents |
– Alter electrostatic interactions – Apolar solvents: • penetrate into hydrophobic regions • disrupt interactions between amino acid residues – Some increase prevalence of alpha helices • Ovalbumin: 31% alpha-helices in water and 85% in chloro-2-ethano |
