Exam 1 Flashcards
What a dollar spent for food pays:
$0.23 - Farm Value
$0.77 - Food Processing
Food processing has 2 primary functions:
-convert inedible agricultural products into edible food
-preserve oversupply of agricultural products for later use
What 5 functions does the food industry perform today?
- provide quality foods
- preserve food
- provide safe food
- provide nutritious food
- process food
Food quality factors:
- Visual Perception
- Flavor
- Lots of other factors
Food Quality: Perception
-color
-size
-transparency
-shape
Food Quality: Flavor
-Taste
-Mouthfeel
-odor
Miscellaneous factors that influence food choices
-media pressure
-culture, tradition, ethnicity
-individual experience (lactose intolerance)
-religion
-geographic location
-convenience
What factors must processors take into consideration to preserve food?
-physical
-chemical
-biological
Control of Insects/Rodents
FDA established a maximum level of “filth”
ex: 5 fly eggs per 250 mL juice and 1 maggot per 50mL juice – anything above maximum can be seized
What are foods composed of?
composed of either pure chemical compounds or mixtures of chemical compounds
Chemistry
the study of properties, composition and structure of matter
Matter
anything that has weight and takes up space: solid, liquid, gas (water can be all 3)
What are atoms composed of?
protons, neutrons and electrons
Neutral atom
of protons = # of electrons
Atomic Mass (weight)
of protons + # of neutrons
Atomic Number
of protons
How many electrons does the outer orbital “want” to be complete?
8 valence electrons
Element
-a simple substance that consists of a single type
-element cannot be reduced to simpler forms by any routine chemical process
-111 elements have been discovered, but only 92 occur naturally
Most common elements in food:
H, C, N, and O
Compounds
-substances that contain 2 or more elements
-some atoms of certain elements are incapable of existing by themselves and are found in combination with elements of the same type: H2, O2
-this process forms a molecule
Molecule
-a molecule is the smallest particle of the compound that can exist and still retain the properties of the compound
-compounds are also made of unlike elements
Chemical reaction
-a process where substances are changed into different substances
-this a chemical change, not physical
- chemical bonds are broken and reformed to make new chemical bonds, to make new products
Mixture
not a chemical combination of elements, but a physical one
Formation of compounds
-can be fairly easy, or they can require a tremendous amount of energy
-common methods include: heating, dissolving in water and then heating
-some elements are very reactive, while other are unreactive or very stable
How are compounds formed?
Ionic Compound Formation: electrons are transferred from one compound to another
Covalent Compound: atoms share electrons instead of transferring ownership
-the atoms “share” the valence, so they are covalent ex: methane (CH4)
Organic Chemistry
-the study of covalent carbon compounds
-named “organic” because they were first discovered in living organisms
-all forms of life on earth are based on organic carbon compounds
-there are more carbon compounds than all other chemical compounds put together
Carbon
-can form covalent bonds with many elements
-has a valence of 4, can bond at most with 4 atoms
-organic compounds synthesized in a lab are identical of those isolated from lifeforms
-not limited to single covalent bonds, can form double or even triple bonds
-the sharing of 2 electrons between atoms is double, 3 is triple
What are the types of simple organic compounds?
Alkanes, Alcohols, Carboxylic Acids, Aldehydes, Amino Acids
Alkanes
Common feature: saturated hydrocarbons
(all bonds are single bonds, so considered saturated with hydrogen)
Ex:
-methane
-ethane
propane
-butane
Alcohols
common feature: -OH functional group
Ex:
-methanol
-ethanol
-glycerol
Carboxylic Acid
common feature: -COOH functional group
Ex:
-acetic acid
-butyric acid
-lactic acid
Aldehydes
common feature: -COH
Ex:
-formaldehyde
-acetaldehyde
Carbohydrates
-organic compounds composed of carbon, hydrogen, and oxygen (CHO) used as the primary source for derivation of energy in human metabolism
-classified into sugars, starches, dextrins and glycogen
-other types like cellulose are not digestible by humans (fiber)
Monosaccharides
ex: sucrose (table sugar), lactose (sugar in milk), maltose (malt sugar), and glucose (sugar found in blood)
-sugars are the simplest of carbohydrates
-the simplest sugars are monosaccharides
-the most common saccharides are 6 carbon sugars called hexoses
What are the 5 monosaccharides/hexoses that occur freely in nature?
glucose, mannose, galactose, fructose and sorbose
Glucose
sweet and is key in browning reactions; converts (polymerizes) to starches
Fructose
the higher the levels of glucose and fructose in potatoes, the more susceptible to non-enzymatic browning
-storage at low temp <40 degrees 5-6mo) inhibits sprouting but induce CHO –> sugar conversion
-if the potato is conditioned by holding 2 wks @ 70 degrees, the sugars will reconvert to CHO
Where to carbohydrates come from in the human diet?
Plants; through photosynthesis
6CO2 + 6H2O + Sunlight = C6H12O6 + 6O2
Disaccarides
-when 2 monosaccharide molecules chemically combine
Maltose = 2 glucose molecules
Lactose = galactose + glucose
Oligosaccharides
raffinose = galactose/glucose/fructose
stachyose = galactose/glucose/fructose found in soybeans and not readily digestible
Polysaccharides
-starch
-long chains of simple sugar like starch
-composed of 2 polysaccharides: 20% Amylose and 80% Amylopectin
Amylose
50-500 glucose molecules connected in a straight chain
Amylopectin
up to 100000 glucose in branched chains
-both chains are held together by hydrogen bonding
Conversion
-reverse photosynthesis
-converting glucose to glycogen
Indigestible polysaccharides
insoluble dietary fiber
Properties of carbs
-enolization
-heating glucose
-caramelization
-maillard browning reaction
Enolization
-heating process in the presence of alkaline solution
-get a lot of isomerization (change in structure)
Heating glucose
-under acidic conditions result in brown pigment
-sulfites can be used to prevent browning
Caramelization
reaction controlled by pH
acidic = color only
basic = color and flavor
Maillard Browning Reaction
-reducing sugar and some compound with a primary amine (donated by a protein(
1. condensation - sugar + amine = schiff’s base (glycosylamine)
2. amadon rearrangement
3. stecker degradation - loss/destruction of amino acids
How to control maillard reaction:
- temperature
- remove/reducing sugar
- add sulfites
- pH
Properties of Starch
A high amylose starch:
-difficult to gelatinize
-requires more heat
-forms tighter crystalline structure
A high amylopectin starch:
-easier to gelatinize
-easier to hydrate (branches)
-gelatinizes at lower temp
Gelatinize
-starch is granular, but in the presence of heat and water the chains hydrate and soften then swell
-as starch swells the mixture thickens
-the more amylose, the stronger the gel
Flavor
Taste and Olfactory perception
-operate differently but not separately
What are the 5 modalities of flavor?
sweet (sucrose), salt (sodium chloride), umami (msg), sour (acetic acid), and bitter (quinine)
Olfactory receptors
-at top of nasal cavity
-can distinguish 1000’s of different stimuli (not just 5)
-olfactory nerve can also attenuate (get used to smell)
Sweetness
-structural basis of sweet modality
-not everything that gives sweet perception is a sugar: chloroform fits sweet receptor
-fructose fit better so perceived as sweeter (threshold is lower)
Bitterness
-similar structure to sweet (can get flavors mixed up)
-a compound can fit into different taste buds
-Quinine, Creatine, Caffeine and theobromine, limonin
Bitterness: quinine
medicinal agent, desirable in some alcoholic drinks
Bitterness: Creatine
found in muscle (secondary energy system)
Bitterness: caffeine and theobromine (in cocoa)
very similar structures, desirable bitter compounds
Bitterness: Limonin
bitter flavor in citrus = defect develops with aging of juice
Humolone convert to isohumolone (beer)
desirable flavor, but can be easily changed to a skunky flavor by uv light (bottle in dark bottle or cans)
Sour
-commonly associated with acidity but do not correlate
Umami
-newly discovered receptor in 2000
-found that there were glutamate receptors on tongue and stomach tissue
-the umami taste is often described as meaty, broth-like or savory and is independent from the other 4 modalities
Flavor enhancers
-maltol, isomaltol
-L-Glutamine, salt (msg)
-NaCL
Astringency
-tannins
Pungency
-capsaicin (red peppers)
-gingerol (ginger)
-piperine (B&W pepper)
Sulfur volatiles
-horseradish
-radish
-shitake mushrooms
Flavor volatiles in muscle foods
-species specific, enzymatic
-mutton like
-cooked fish smell
-fishy odor
-formaldehyde
Fat soluble vitamins
Vitamin A, E, D, K, B1, B2, B6, B12, C
Vitamin A
-found only in animals
-required for vision and resistance to infection
Vitamin E
-alpha, beta, gamma and delta - tocopherols
-found in seed germ
-serves as an antioxidant
-deficiency affect not clear
Vitamin D
-normal tooth and bone development
-fish oils
-body can synthesize sterols like cholesterol
-D and A are added to milk
-deficiency may result in rickets
Vitamin K
-needed for synthesis of prothrombin for clotting of blood
-good sources are spinach and cabbage
Vitamin B1: Thiamin
-high in legumes
-B1 is destroyed by SO2, so SO2 should not be used as a preservative
Vitamin B2: Riboflavin
-sensitive to high pH and light but heat stable
-milk, liver, eggs are good sources of
Vitamin B12: Folacin
red blood cell formation
Vitamin C: Abscorbic Acid
-readily oxidized by Cu ++ and Fe ++ in contact with metals during processing
-deficiency causes scurvy
Iron
-trace mineral (because it is needed in small amounts)
-iron from animal sources thought to be absorbed better
-Vitamin E and C help with Iron absorption
Calcium
-humans require this mineral in the greatest amount
-needed for bone and tooth structure, as well as for nerve and muscle function
-also needed for blood clotting
-deficiencies lead to osteoporosis
-Vitamin D and lactose essential for absorption of calcium
Other major minerals
sodium, chlorine, potassium, phosphorus, magnesium, sulfur, iodine, fluorine, copper, cobalt, zinc
Organic acids
-contribute to flavors, aroma, tartness
Pigments
Anthocyanins (flavonoids):
-low pH triggers red color
-high pH triggers blue/violet color
Metals:
-flavonoids will leak from fruit during processing and interact with metals, which will change colors due to changed pH
High Temperature:
-can result in brown pigment
Oxygen
-added to reduce rapid degeneration
Blanching
preserves anthocyanins by deactivating the enzymes that cause degradation. However, too much heat/time will degrade the pigment too
Carotenoids
-fat soluble b-carotene = vitamin A (orange)
-fat soluble lycopene = no vitamin A (red)
-fat soluble chlorophyll = Mg ++ present (green)
Myoglobins
-CO2 carriers (respiration of muscle cells)
Proteins
-most abundant macromolecule in animal cells
-constitute over half the dry weight of most organisms
-made up of amino acids
Functions of proteins
enzymes (catalysts to chemical reactions), transporters (hemoglobin, lipoproteins), contractile proteins (muscle contraction), structural proteins (collagen, keratin)
Structure of proteins
-amino acids joined together by peptide bonds
-2 amino acids form a peptide bond
- di-, tri-, polypeptides
-polypeptide = protein
Isoelectric Point (pI) of a protein
the pH at which the molecule is neutral (zero net charge; positives = negatives)
Layers of protein structure
Primary, secondary, tertiary, quatenary
Primary protein structure
-the number and sequential order of amino acids
-typical proteins contain 100-500 aa’s
Secondary protein structure
refers to the shape that the polypeptide chain assumes along it’s axis (coiled helix)
Tertiary protein structure
refers to 3-D shape from folding of protein
Quatenary structure
-2 or more chains join together
-very sensitive to heat
-ex: pleated sheet
Amino Acids composed of chains of:
H00C-CH-NH2
Denaturation of Proteins
-the conformation of proteins is altered
-denaturation is the loss of biological activity
-denatured proteins are less soluble and less able to bind water
-caused by: heat, acids, solvents, salt, mixing
Artificial sweeteners
-synthetic carbohydrates that were found to be many times sweeter than sucrose
-most common: saccharin, cyclamate, aspartame and acesulfame
Lipids
-important constituent of food
-contain carbon, hydrogen and oxygen
-fats are also called lipids or triglycerides
-lipids are of plant or animal origin
-insoluble in water
-major members are fats and oils
Structure of lipids
3 fatty acids on a glycerol backbone
Saturated fats
have straight carbon chains with single bonds
Unsaturated fats
have one or more double bond
Monounsaturated fats
more than one double bond
Single bonds
saturated with hydrogen
Fats vs Oils
-oils are more unsaturated
-fats are more saturated
-unsaturated fats can be turned into saturated fatty acids called hydrogenation
Reaction of Fats
-hydrogenation: hydrogen chemically added to double bonds
-Saponification: adding alkali to produce glycerol and soap
-Hydrolysis: breakdown lysis of lipid from heat & water effects
-Rancidity: a type of spoilage due to instability of fat
2 kinds of rancidity
-Lipolytic rancidity: caused by action of the enzyme lipase; enzymes leave the glycerol backbone, releasing fatty acids
-Oxidative rancidity: oxygen attacks fats at the sites of unsaturation; causes bond to break
What are lipids carriers of?
flavor
Artificial lipids
Simplesse and Olestra
Water Chemistry
Most familiar chemical compound, but most
important influences are least visible:
– Moderates climate, carves landscape, and all life
exists in a water solution!
– Humans 60% water (by weight)
* raw meat = 75%
* fruits and vegetables up to 95%
The importance of hydrogen bonds
- Hydrogen bonds:
– weak but important bonds between H on one
molecule, and O or N on another. - Water has two H and one O atom
- The covalent bonds between O and H are
ASYMMETRICAL . - O has a greater affinity for electrons than hydrogen,
so the shared electrons are held closer to the O atom
importance of hydrogen bonds continued
If all three atoms were in a straight line, the
molecule would be symmetrical.
* The net positive charges on the H would balance
each other, and water would not function in all
the incredible ways that we see in nature!
* Because of the disposition of other electrons in
the O atom, the covalent bonds are not at an
180 angle, but 105.
* Therefore, the molecule forms a V-like shape.
As a result of the bonding angle and the
electrical asymmetry of each bond,
WATER MOLECULES ARE POLAR
First physical peculiarity of water
-Abnormally high melting and boiling points
Not like other hydrogen compounds of the
other elements in oxygen’s column of the
periodic table:
– sulfur, selenium, tellurium:
* Freezing point = - 150F
* Boiling point = - 110F
* If this were the case, water on earth would be gas
and life as we know it would not exist!
First physical peculiarity of water continued
Because of the asymmetrical bonds, it is
more difficult to separate one water
molecule from another.
– This results in an abnormally high melting and
boiling points.
– This also gives water an unusually high
“latent heat of vaporization”:
* The energy water absorbs without a rise in
temperature as it changes from liquid to gas
First physical peculiarity of water continued
Plants and animals have used this property for
temperature regulation.
– As we overheat, we excrete water onto outer surfaces.
– As the water evaporates, it absorbs large amounts of
energy from the body and carries it away.
* Ancient cultures used the same principle for
cooling water and wine.
– Porous clay vessels evaporate moisture continuously
from their surfaces.
Second physical peculiarity: Ice Floats
Normally, the solid phase of a given
substance is more compact and dense
than the liquid phase.
– Molecules move around less and settle into a
compact arrangement.
In solid form, the bond angle of water
changes from 105 to 109 in order to
form a crystalline ordered structure.
* As ice crystals begin to form, water
expands by about one-eleventh.
* Because ice is less dense that water,
IT FLOATS
In everyday life, this can be inconvenient!
– Water pipes burst when heat fails in the winter.
– Bottled beverages placed in the freezer for a quick
chill and left forgotten pop open.
– Containers of leftover soup will shatter if not enough
room is left for expansion.
– Plant and animal tissue may be damaged during
freezing when expanding ice crystals rupture cell
walls.
Third Physical Peculiarity:
Water is Slow to Heat
Water has a abnormally high SPECIFIC
HEAT
– the amount of energy required to raise its
temperature by a given amount
Third Physical Peculiarity:
Water is Slow to Heat Continued
The consequence of this peculiarity is
considerable:
– Living organisms (which are 50 –95% water) can
moderate the sudden environmental temperature
changes.
– We can absorb or lose considerable amount of energy
without becoming dangerously hot or cold.
– We are like miniature oceans or lakes, which even out
climatic changes by soaking up or releasing energy in
extreme conditions without reaching extreme
temperatures themselves
Third Physical Peculiarity:
Water is Slow to Heat Continued
The consequence of this peculiarity is
considerable:
– When we want to cook something delicate
(like custard) we do so in a water bath rather
than exposing it to direct heat.
– Water is involved in reactions in most foods.
– Water influences texture, stability, etc.
Free Water:
This water retains its physical properties and thus acts as the
dispersing agent for colloids and the solvent for salts.
Adsorbed Water:
This water is tightly held or is occluded in cell walls or
protoplasm and is help tightly to proteins.
Water of hydration
This water is bound chemically
Bound water
– that water which exists intimately associated
with the solute molecule.
– It has reduced molecular ability (won’t freeze
at -40C) and can’t be removed by
conventional drying techniques (only way to
remove is essentially ashing it)
– Type I water: Vicinal water
first layer of bound water molecules
– Type II water: Multilayer water
second layer of bound water molecules
Bulk phase water
– Type III water:
Entrapped water (in capillaries) and free
water
Water activity (aW)
aW = the partial pressure of water vapor
above the sample, divided by partial
pressure of pure water vapor at the same
temperature.
* aW = vp of water above sample
vp of pure water at same T
Water activity (aW) continued
aW can be used as predictor of microbial
growth
* 0.7 – 0.8 = yeast, mold, bacterial growth
* 0.2 – 0.7 = Maillard browning (non-enzymatic
browning)
* also an indicator of certain major chemical
reactions that occur in food (lipid oxidation
and enzymatic browning)
