Lesson 2.2 Flashcards
rest of major components (fats and oils, protein, water) and minor components
Fats and oils in our diets
major component
- produce 9 Cal/g
- should contribute no more than 30% of our caloric intake
- dietary fats/oils, essential fatty acids are needed by the body to maintain proper health and functioning
Chemical composition of fats
triglycerides (TG), which are triesters of glycerol and fatty acids
* glycerol: 3-carbon molecule containing 3 alcohol groups (OH)
* fatty acids: hydrocarbon chains (R1, R2, R3) with carboxylic acid (COOH) at one end and a methyl group (CH₃) at the other end
- FAs have more than 3 carbons (e.g. butyric acid with 4 carbons is the simplest) and R refers to the rest of the molecule, which is quite large
- broken down in the body by digestive enzymes (lipases)
What holds fatty acids to glycerol in triglycerides?
or fats
esther bonds join OH groups of glycerol to COOH groups of fatty acids
Most common fatty acids in food triglycerides
C-16, C-18
* some foods have shorter-chain fatty acids (e.g. coconut oil C-12)
* others also contain longer-chain fatty acids (e.g. salmon C-20, C-22)
What are saturated and unsaturated fats?
saturated and unsaturated fatty acid constituents
* saturated have no double bonds C-C
* unsaturated have double bonds C=C (e.g. monounsaturated, polyunsaturated)
Common formula of fatty acids
Y: X (n-Z)
* Y= number of carbons
* X= number of double bonds
* n= numbering of double bonds from methyl group (CH₃)
* Z= location number of first double bond
3 examples of 18-carbon fatty acids
- Stearic (saturated): CH₃(CH₂)₁₆COOH
- Oleic (monounsaturated): CH₃(CH₂)₇CH=CH(CH₂)₇COOH
- Linoleic (polyunsaturated): CH₃(CH₂)₄CH=CH-CH₂-CH=CH(CH₂)₇COOH
- 18:0
- 18: 1(n-9), an omega 9 fatty acid because its first double bond from the methyl end starts on carbon 9
- 18: 2(n-6), an omega 6 fatty acid
Animal fats
- usually solid at room temperature
- high in saturated fatty acids
- consist of linear chains that pack together tightly = higher melting point
2 kinds of configurations in unsaturated fatty acids
- cis configuration: carbon chains on the same side of the double bond that bend toward each other, creating a kink in the chain; less tightly packed = lower MP
- trans configuration: carbon chains on either side of the double bond (or across); more tightly packed = more semi-solid texture and higher MP
trans FAs taste buttery!
Vegetable oils
- usually liquid at room temperature
- high in unsaturated fatty acids (MUFA, PUFA)
- cis configuration so pack less tightly together = lower melting point
Properties of unsaturated fatty acids
e.g. vegetable oils
- less stable and easily oxidized (oxidative rancidity) due to double bonds
- PUFAs more reactive than MUFAs
i.e. require less energy to be broken down
Rancidity
and 2 types
process of breaking down fats and oils through improper storage, repeated exposure to high temp
1. oxidative
2. hydrolytic or lipolytic
Oxidative rancidity
oxidation (double bonds + oxygen) results in products like off-flavors, carcinogenic compounds
e.g. UFA (or PUFA) + oxygen, heat, light (promote oxidation) > hydroperoxides > OHs
Hydrolytic or lipolytic rancidity
unrelated to saturation/unsaturation!
hydrolysis (triglyceride + lipase enzyme) causes the bond between glycerol and FAs to break, releasing short-chain (free) FAs and glycerol (odorous)
How can you reduce the rate of oxydative rancidity?
- proper storage and packaging (away from light, oxygen, warm temp)
- limiting repeated exposure to high temp
- adding antioxidants (natural and synthetic)
- hydrogenation
Hydrogenation (partial)
to reduce the rate of oxydative rancidity
- hydrogen atoms are forced into the double bonds of the UFA, raising the MP and making it less prone to oxidize
- also used in food industry to harden liquid oils into semi-solid fats and can generate trans FAs (e.g. margarine)
newer margarines use blending to achieve the desired solid-liquid ratio and melting properties
Trans fat
- behaves like saturated fat
- raises LDL (“bad”) cholesterol, which causes Coronary Heart Disease
- labelling required (amount of trans-fat)
Functional properties of fats and oils
- mouthfeel (lubricant in food)
- shortening/tenderizing power (e.g. helps with entrapment of air in baked goods)
- carrier of aroma and flavor
- high-temperature medium (e.g. deep fat frying)
- gradual softening
- emulsifier
lubricant makes food softer and stay longer in palate (gradual swallowing)
Lecithin
fats and oils as emulsifiers
- a phospholipid from egg yolk, soybean oil that consists of 2 FAs + phosphoric acid linked to glycerol (amphiphilic molecules)
- helps reduce interfacial tension to form an emulsion
Amphiphilic/amphipathic molecules
fats and oils as emulsifiers
-
hydrophilic: water-loving (i.e. glycerol linked to an organic acid)
hydrophobic/lipophilic: water-hating or lipid-loving groups (i.e. fatty acid)
molecules stay connected and in uniform shape
Stabilizers
not the same as emulsifiers!
increases the viscosity of the continuous phase by keeping the droplets suspended or dispersed (i.e. not precipitate toward the bottom)
e.g. polysaccharides
Proteins in our diet
major component
- contribute 4 Cal/g
- require 0.8g protein per kg body weight in adults
- excess is converted into energy or stored as fat
Chemical composition of proteins
polymers or long chains of amino acids linked by peptide bonds
* amino group (NH₂) and acidic group (carboxylic COOH) on the same carbon atom
* R, the side chain, is hydrophobic, charged, polar, aromatic
Amino acids
building blocks of proteins
- 20 different amino acids naturally occurring in the human body and in foods
- 9 of which are essential (cannot be synthesized by humans) and must be obtained from food
e.g. Leucine, Phenylalanine (used in aspartame), Tryptophan, etc.
What do the amino acid sequence and 3D structure of proteins determine?
- functional properties in food
- nutritive value of proteins
more essential amino acid = higher-quality protein
Plant vs animal proteins
plant proteins…
* are less digestible than animal proteins
* have less favorable ratio and quantity of 1 or more essential amino acids
* usually have lower quality
How can you improve protein quality in foods?
mixing (complementation, supplementation)
e.g. 30g of breakfast cereal when consumed with 125ml of milk represents a good source of protein
Functional properties of proteins
- emulsifiers (e.g. egg yolk proteins in mayonaise)
- foams (e.g. meringue, bread, ice cream)
- gels (e.g. gelatin, yogurt, cheese, frankfurters)
- enzymes
- allergies (due to inability to digest)
Enzymes
functional property of proteins
function as biological catalysts
* promote a chemical reaction that cannot occur spontaneously
* inherent in food or added in processing
* desireable or undesireable reactions in food
Allergies
functional property of proteins
inability to digest certain proteins may lead one to exhibit symptoms of allergic reactions
12 most common food allergens/sensitivity promoters: peanuts and tree nuts (most common), crustaceans and molluscs, eggs, fish, gluten, milk, mustard, sesame, soybeans, wheat and triticale, sulphites (not a protein but produces same reaction)
Water
major component
- plays key role in the quality of foods
- comes in 2 forms: free and bound
Free water
- properties typical of water
- found in tissue food systems and dispersions
- available for all chemical, enzymatic reactions and microbial growth
Bound water
- absorbed on macromolecules (e.g. proteins, polysaccharides)
- bound to smaller molecules (e.g. sugar, salt)
- not readily available for chemical, enzymatic, or microbial activity
Water activity (aw)
indication, not estimation, of water available for chemical reactions (primarily free water), microorganisms, etc.
vs water content = total amount measured by weighing (e.g. an apple) before and after dehydration
Are water activity and water content related?
not always
* salami: 0.90 aw; 61% water content
* bread: 0.96 aw; 35% water content
How can water activity in foods be controlled?
- addition of solutes (sugars, salts), which bind to free water, reducing its availability
- physically removing free water from foods through processing (e.g. freezing), concentration, dehydration
Functions of organic acids in food
minor component
- impart flavor and tartness
- some used as antimicrobial agents
- adjust pH or acidity of food (i.e. used as acidulants)
Examples of organic acids
- malic acid (apples)
- citric acid (citrus fruits, tomatoes, strawberries)
- tartaric acid (grapes)
- lactic acid (yogurt, cheese, olives, sauerkraut)
2 ways to determine acidity
organic acids
- taste: sour or acidic taste is a positive indicator though highly subjective (individual differences in sensitivity)
- pH meter: measure H+ concentration then convert to pH value
pH meters are used by inserting a probe inside food and measuring the concentration of hydrogen ions
What is pH?
range and critical value
the measure of acidity
* ranges from 0 (very acidic) to 7 (neutral) to 14 (very alkaline)
* 4.6 is the critical pH value in the food industry, the borderline between acid and low-acid foods
anything below 4.6 inhibits microbial growth and foods with this pH are less susceptible to bacterial contamination
What is the importance of pH in foods?
- determines the rate of chemical and enzymatic reactions
- microbial growth/survival in foods
Examples of acidic foods vs low-acid foods
- acidic foods (pH < 4.6): fruits and fermented products (e.g. citrus juices, apple juice, strawberries, apples, pickles)
- low-acid foods (pH > 4.6): meat, fish, poultry, vegetables
- acidic foods won’t support growth of most disease-causing microorganisms
- low-acid foods require a more intense process for preservation
Total acidity vs pH
- total acidity (i.e. titratable acidity) measures the total acid concentration
- pH (i.e. active acidity) quantifies H+ concentration
Colors and pigments
minor component
- naturally occur in foods
- or extracted from natural or synthetic sources then added to foods
3 classes of pigments
- carotenoids: carotenes confer red in tomatoes (lycopene) and orange in carrots (beta carotene)
- anthocyanins in blueberries, cherries, cranberries, plums, and red cabbage
- chlorophyll
Aroma and taste compounds
- aroma compounds are volatile while taste compounds are non-volatile
- aroma and taste profiles of foods = flavor
- complex flavors comprise 100s or 100s of compounds (e.g. aldehydes, ketones, acids, alcohols, fatty acids)
- present as part of the food matrix (e.g. strawberries) or modified (e.g. cooked strawberries)
non-volatile = do not readily evaporate at room temperature
Vitamins and minerals
minor component
- no effect on flavor, color, texture of food
- low (or adequate) amounts in diet to maintain health
examples of minerals: Ca, Mg, Na, K, Fe, Zn
2 sets of vitamins
- water soluble: vitamin C, B complex, folic acid
- fat soluble vitamins: vitamins A, D, E, K
some used as food additives like preservatives (antioxidants)
