Lipids Flashcards
Triglycerides: known as triacylglycerol
3 FA joined to glycerol by ester bond
3 FA might be a combination of SFA, MUFA,
Nonpolar, hydrophobic and contain no electrically charged or highly polar functional groups
Many different types depending on position of 3-FA’s esterified to glycerol
• Symmetrical: similar in chain length FA; align easily
• Asymmetrical: different in chain length & kinks (double bonds); align less easily
Characteristics of Lipid
o Organic substances that are relatively non-polar, slightly soluble in water
o Soluble in organic solvents due to hydrocarbon chain structure.
o Composed of triglycerides, phospholipids and sterols
o Hydrophobic or lipophilic: having a strong attraction to lipids; promoting dissolvability or absorbability of lipids
FA
o Short: 4-10 o Medium: 12-14 o Long: 16 + o Fats & Oils Mixture of FA differing in chain length and degree of saturation o Saturated: C-C bonds Hard fat o Unsaturated: C=C bond(s) Oil Mono (1 double bonds) Poly (2+ double bonds)
Melting Point
Temperature at which a solid is converted to a liquid
o Fats have high MP
Solid at room temp
o Oils have a low MP
Liquid at room temp
o Fat molecules exist in crystalline form
MP: an index of the force of attraction b/t molecules
• The greater the attraction b/t molecules the easier they will form a solid
• High MP indicates a strong attraction force
o The mixture of FA determines whether fat will be a liquid, solid, plastic at ambient temp
o FA chain length
Short: Low MP, less potential for attraction
Long: High MP, more potential for attraction
o Degree of unsaturation (# of double bonds)
# of double bonds increases then the MP decreases
saturated high MP
o Cis and Trans
Stearic: saturated; 18:0; MP 70
Oleic: Cis-usaturated; 18:1; MP 19
Elaidic: trans-unsaturated; 18:1; MP 43
Crystallization
o Both solid and oil contain small fat crystals
Composed of triglycerides
o Polymorphism: Fat molecules pack into different crystalline forms
o Turning fork: the packing of triglycerides/FA’s into a three dimensional array
o A fat may crystallize in different forms
FA composition
Conditions
Alpha: lowest MP, extremely fine
Beta prime: medium MP, very fine
Beta: highest MP, coarse
Oxidation
Rancidity (predominant type- lipoxidation)
o UFA’s are subject to oxidative rancidity
The more double bonds the greater the opportunity for addition of O
• Chemical reactivity
o Triggered by heat, light, metals (iron copper) and lipoxygenases
o 3 stages
Initiation: Formation of “free radicals”, catalyzed by heat, light, metals (copper iron). H on a C atom adjacent to one carrying a double bond is displaced and transformed into a free radical.
Propagation: Oxidation of free radical results into activated peroxide.
• This displaces another H from UFA
• The displaced H forms hydroperoxide + free radical
• This reaction repeats or propagates itself
Termination: Ends when all of the fat molecules have reacted or antioxidants reacts with a radical
Hydrolysis
Reaction requiring heat and water.
o Separates FA’s from glycerol
o Hydrolytic rancidity: fats become rancid when they react with water and heat and FA’s are liberated (short-chain FA C4)
Short-chain FA’s cause off flavors & odors
o The reaction is catalyzed by heat and lipases
Prevention
o Store in cool dark environment
o Closed container to minimize O2 availability
o Cooking utensils free of copper or iron
o Antioxidants donate e- to free radical
BHA, BHT, ascorbic acid and tocopherols
Chemical Reactivity
deterioration of fats
• Chemical reactivity with H or O.
• Chemical reactivity of UFA determined by position and # of double bonds.
o The higher degree of UFA the greater the reactivity
o Provided that the double bonds occur in a series with a single bond in-between conjugated double bonds.
Conjugated: C=C-C=C-C
Non-conjugated: C=C-C-C=C
o When double bonds are separated by a methylene (CH2) unit greater reactivity results.
C=C-C-C=C
Such as omega FA’s
Omega FA
• Polyunsaturated • Methylene interrupted pattern • Essential Fatty Acids: o Omega 6 Linoleic Acid: First double bond is located on the 6th C from the omega end (CH3).
Hydrogenation
The forced addition of H to the unsaturated bonds
• Convert liquid oils to semisolid fats (plastic fats)
• Increases the thermal stability (increase MP)
• Increase oxidative stability (shelf life)
• Converts Cis to Trans configuration
o Unsaturated FA’s come in two configurations. Defined by their structure at the double bond.
Trans isomers
Cis and Trans
• Affect melting point
• Cis: H located on same side C=C
• Trans: H located adjacent sides C=C
Most UFA in foods are mostly Cis
Interesterification
Removal of FA’s from glycerol and their following rearrangement.
• Differ from the original fat molecule
• From simple to mixed FA profile
• Improved fat properties
• Applied to hard fats: lard, beef tallow
• Does not change: degree of unsaturation, isomeric state (cis or trans)
• Can be followed by hydrogenation
Plasticity
Its softness at a given temperature.
• Responds to an external force by deforming.
o Will squeeze or spread
o Hold shape on a flat surface
• A two-phase system: contains solid fat crystals surrounded by liquid oil
What happens chemically during lipoxidation?
• The UFA reacts with O and forms hydroperoxide
o A chain reaction results
o Hydroperoxide decomposes to yield aldehydes, ketones, acids and alcohols, which cause “rancidity”- off flavors and odors.
• Initiation: formation of free radicals
o Catalyzed by heat, light, metals (copper iron)
o H on a C atom adjacent to one carrying a double bond is displaced into a free radical
• Propagation: oxidation of free radicals into activated peroxide
Protein Structure
• Primary: linear AA sequence joined by peptide bonds
o Polypeptide backbone: determines the final structure of the protein
o 2-50 AA polypeptide code for genes
• Secondary: a-helix and b-sheet
o Polypeptide folded in a particular way
• Tertiary: 3-D disulfide and hydrophobic bonds
o Achieved by folding of the entire protein molecule
o 50-2000 AA; average protein is 100 AA
o Myoglobin
• Quaternary: 3-D disulfide and hydrophobic bonds
o Two or more polypeptide complexes
o Hemoglobin
Sustainable protein
- Environment
- Production
- Quality
- Communication
Protein properties
• Amphoteric: act as acid or base depending on the pH solution (buffers)
• Amphipathic: expose hydrophobic and hydrophilic groups (emulsifiers)
• Denaturation:
o Heat, pH, physical agitation, hydrolysis
Quinoa
- Superfood, ancient grain, pseudocereal
- Complete protein
- Gluten free
- No known allergic reactions
- Non-GMO
- Grows in marginal soils
Functions of food proteins
- Nutritional
- Texture: gels, coagulation, stabilizing foams and emulsions
- Water holding capacity: important in meat proteins, restructured meats, meat analogs, foams, emulsions
- Flavor, aroma and color: flavoring binding, maillard reaction/non-enzymatic browning, myoglobin
- Bioprocessing: malting, fermentation, modified starches, syrup, protein hydrolysates, and enzymatic browning.
Protein classification
• Divided into four types of solubility:
o Glutelins: soluble in weak acids or bases
o Prolamines: soluble in 70% ethyl alcohol
o Albumins: soluble in water
o Globulins: soluble in dilute salt solutions
• Glutelins & Prolamines are typically found in the endosperm
o Gluten is high in glutamine and proline
• Albumins & globulins are typically found in the embryo, bran and germ
o Metabolically active enzymes
Protein structure
• Polypeptides: polymers of amino acids
o Polypeptides can be a few dozen to several hundred AA long
o Amino acids contain: amine group (NH2), acid group (COOH), central C to H and side chain R
Side chains (R) categories:
• Polar but uncharged
• Hydrophobic (nonpolar)
• Positively charged
• Negatively charged
• Peptide bond: Usually occur b/t two amino acids. Chemical bond formed b/t two molecules when the carboxyl group of one molecule reacts with the amino group of the other molecule, releasing a H2O molecule. Dehydration synthesis reaction.
Conjugated protein
combined with nonprotein substances such as:
• Insoluble products formed by heat or alchole
• CHO; glycoproteins contain sugar molecules (egg whites)
• Lipid; lipoproteins (LDL, chylomicron, egg yolk)
• Metals; metalloproteins (myoglobin, hemoglobin)
Denaturation
Unfolding of the protein structure.
• Usually due to acid or heat
• Causes a change or loss in functional property
• A major change in the native structure that does not involve alteration of the AA sequence.
Coagulation
The grouping together of small particles in a solution into larger particles. Such a solution eventually coagulates with the particles forming either a precipitate or a gel.
Essential AA
• Cannot be made by the body. They must come from food. 9 essential AA.
Limiting AA
• The AA in shortest supply in relation to need
Complementary proteins
• The low quality proteins combined
o Legumes + grains
o Corn + legumes
Digestibility
- Proportion of food nitrogen that is absorbed after ingestion
- Quality depends on the extent to which AA are utilized in the body
- Protein from animals sources are better digested
Factors that affect protein digestibility
- Conformation: structural state of a protein influences its hydrolysis by enzymes
- Antinutirional factors: contain inhibitors that impair complete hydrolysis
- Binding with other food components: reduces the rate and completeness of hydrolysis
- Processing: undergo chemical alterations
Evaluation of protein nutrient value
• Chemical score/AA score method
o Determining AA content and comparing with AA pattern of an ideal ref protein
• Calculate
o Chemical score (CS) = mg AA/g test protein/mg same AA/g reference protein * 100
Who needs greater mg AA/g protein? Infant vs adult
• Infant (26) vs adult (16)
Biological methods of protein assessment
• Based on weight gain in animals when fed a protein diet
• Expensive and time consuming
• Evaluation of protein quality
• Classical method
o Ingested N – (fecal N + urine N)/ ingested N
• PER know how to calculate
o Wt gained when fed test protein/wt gained when fed reference protein
o Measure of protein quality
o Measures how well a protein promotes growth in animals
o The old method used by FDA for food labels intended for infants
• NPU: Net protein utilization
o Measure of protein quality
o Compares the amount of N retained in the body with amount eaten
o Takes into account endogenous protein
• BV: Biological Valve method
o Measure of protein quality
o Compares the amount of N retained in the body with amount absorbed from the diet
o Percent ABSORBED N
o Takes into account endogenous protein
• Protein digestibility corrected for AA score (PDCAAS)
o Replaces PER, accepted by FDA for children over 1 yrs old
o Measure of protein quality that is calculated by adjusting the AA score for digestibility
Functional Properties
• Denaturation/coagulation
o Denaturation: unfolding of the protein structure usually due to acid or heat. Causes a change or loss in functional property. UNIQUE TO PROTEINS.
• Protein hydrolysis for flavoring
o Protein + water + protease (or heat or pH)
o Enzymatic to produce HVP’s
o Nonenzymatic to product Maillard browning reactions & flavors
• Buffering
o Preventing a pH change by undergoing an ionization reaction
• Isoelectric point
o The pH at which the total number of positive and negative charges on the surface of the protein molecule are equal; thus, the net charge on protein is zero
o At a low pH the protein is positively charged
o At a high pH the protein is negatively charged
o At the isoelectric point the protein has no net charge and therefore no longer migrates in the electric field.
• Emulsification
o Stabilizes emulsions by acting at the oil-water interface
Protein molecules contain both hydrophilic and hydrophobic
• Water holding capacity
o Proteins bind water (hydrophilic R group)
Milk proteins
• Casein micelle structure
o 80% of total protein (conjugated)
alpha, deta, kappa
o Structure is based on the concept of submicelles
• Whey protein
o 20% of total protein
lactalbumin
lactoglublin
immunoglobulins
whey ordered globular structures containing disulfide linages
