Lipids lecture 1 Flashcards
What is olestra?
“fat free fat”
a FA attached to a sugar
can’t be metabolized
chemical characterization of lipids?
insolubility of in water
soluble in non polar organic solvents
3 classes of lipids?
- simple
2 compound
3 derived
categories of simple lipids?
fats and waxes
types of compound lipids?
phospholipids
glycolipids
lipoproteins
what are simple lipids?
esters of FA connected to an alcohol
types of derived lipids?
fatty acids
fatty alcohols
hydrocarbons
what are fats (simple lipids)?
another name?
esters of FA connected to glycerol
R1 R2 R3 are FA (short to long chain aliphatic hydrocarbons with a COOH group at one end)
aka triacylglycerols/triglycerides
oil vs fat?
oil: low mp and liquid at room temp
fat: solid at room temp
percent of triglycerides in extractable lipid material in biological systems and in lipid that we consume?
> 90%
melting profile of pure triglyceride vs edible fat?
triacylglycerol has a very sharp melting point
edible fat melts over a wider range of temp because it is a mixture of different triacylglycerol molecules
chemical structure of waxes?
FA esterified with a simple fatty alcohol (other than glycerol)
aliphatic alcohol + FA = wax
what is a true wax
FA esterified to a SIMPLE fatty alcohol
uses of waxes?
sources of wax?
sealing agents (cheese) polishing agents (apples)
sources: injojoba oil, beesewax
jojoba oil structure and use?
structure: linear esters of mono unsat long chain FA esterified to fatty alcohols
use: cosmetics. low cal ingredient (not digested readily)
structure of cholesterol?
FA esterified to a complex alcohol
what are compound lipids? types?
simple lipid conjugated to a non lipid
structure of phospholipids?
what is the base structure?
what are the different phosphatidic acid molecule examples?
triglycerides with one FA replaced with a nonlipid moiety - phosphoric acid
base structure = phosphatidic acid (when X=OH)
other phospholipids: X=nitrogenous base
classes of phospholipids
- lecithins (phosphatidyl cholines)
- Cephalins (phosphatidyl ethanolamines): phosphatidic acid conjugated to ethanolamine (x=OH-CH2-CH2-NH2)
- Phosphatidyl inositols: non nitrogenous group + phosphatidic acid
hydrophilicity of phospholipids?
how much is found in food systems?
contains both hydrophobic and hydrophillic groups
thus, good emulsifier (ie soybean oil )
in food systems: comprises <5% of lipid material
what are glycolipids and sphingo lipids?
structure?
examples of glycolipids in cell membranes?
in cell membrane lipids in plants and animals
complex structure: combination of glycerol backbone, FA, carb, nitrogenous group
ex in cell membranes: glycoproteins, glycolipid, glycocalix
role and structure of lipoproteins?
circulates in blood to carry lipids to tissues for metabolism or storage
HDL and LDL (different sizes and levels of protein, fat and cholesterol)
structure:
inside: triglyceride + cholesterol esters
outside: phospholipid + cholesterol + apolipoprotin
LDL vs HDL?
HDL: good. accounts for 1/3 of blood circulating cholesterol. protective to heart disease
LDL: excess = plaque in blood vessels = artery blockages
what are derived lipids?
derived from simple of compound lipid categories. Still retains hydrophobic character
types of derived lipids (3)
Role in food systems?
- fatty acids
- fatty alcohols
- hydrocarbons and oxygenated derivatives
role in food systems: major role in functionality
structure of fatty acids (as type of derived lipids)?
short to long chain aliphatic hydrocarbons w/ COOH group at one end
what are short chain FA important for?
ex?
flavour compounds
can be released by lipolysis
ex: butyric acid (C3) Caproic acid (c6) caprylic acid (c8) --> rancid cheese flavor
what can presence of FFA do?
lower the smoke point of edible oils when used for frying
do long chain free fatty acids have flavour?
no
but can give soapy flavour in presence of mineral salts
short chain alcohols are…
more complex derived alcohols are….
- major contributors to flavour
2. often biologically active (ie cholesterol)
what are terpenes? what are they commonly known for?
built from isoprene units (isoprene = 5 carbons)
known for components of fragrant oils from leaves, flowers, fruits (ie. essential oils)
terpene classes?
monoterpenes = 2 isoprene units = 10C
sesquiterpenes = 3 isoprene = 15 C
diterpenes = 4
sesterterpenes = 5
triterpenes = 6
how are lipids surface active?
they are amphiphillic
2 main lipid components in food systems?
fats from simple lipids
phospholipids from compound lipids
95% of lipid from biological systems is Fat (triglycerides) with mostly phospholipids
what are key determinants of triglyceride properties?
the physical and chemical properties of the fatty acids attached to the glycerol
what are the 2 types of triglycerides?
sat FA:
- simple and least reactive
- linear series of methyl groups terminating in a COOH group
- CH3-(CH2)n-COOH
unsat FA: has one or more double bonds. most common are oleic, linoleic and linolenic
are FA in nature even or odd numbered?
even
odd numbered can’t be packed into a crystalline lattice
are short or long chain FA liquid or solid at room temp?
short chain (4-8 C): liquid at room temp
long chain (more than 10C): solids
when chain length is increased in FA, how does water solubility change?
longer chain = increased hydrophobicity = decreased water solubility
as aresult, C4-C8 FA are slightly miscible with water (b/c of small chain = low hydrophobicity)
describe surface tension properties of soap
soap = salt form of FA
water soluble but strong surface tension reducing properties
structure: has long FA chain and charged NA+ end
2 systems of nomenclature?
- trivial names
2. systematic names (IUPAC)
from where is the position of the double bond counted in the IUPAC system?
from the carboxyl end of the FA chain
what is a side reaction of hydrogenation?
natural cis form to trans
affects properties of the molecule
what are two forms to how DBs are situated relative to each other?
stability of both?
- unconjugated DB: separated by methylene group (CH2). The natural state of most FA
- conjugated DB: DB are right next to each other. not interrupted by CH2 group. Not usually found naturally, but commonly formed during oil processing.
stability: conj form is more stable but more susceptible to autoxidation
what are mixed bonding systems?
has both conjugated and unconj elements
thermodynamically preferred but very susceptible to autoxidation
responsible for reversion associated with soybean and fish oils
leads to formation of an active methylene group (CH2 positioned between a conj and unconj DB)
what is an active methylene group?
it is positioned between conjugated and unconj double bonds
what are assumptions made with the omega nomenclature?
- all natural FA are cis
2. all DB are unconjugated
what end does the “omega carbon” count carbons from?
from the CH3 end
(review omega nomenclature on slides)
DB are always 3 carbons apart
what is linoleic acid
omega 6 family
essential FA
needed for biologically active membranes
what family is linolenic in?
omega 3 family
synthesized only by plants
essential FA
what is CLA?
conjugated linoleic acids
found in meat and milk
has an anticarcinogenic effect
molecular crumpling?
caused by increase in number if cis DB
how is the crystalline lattice stabilized?
- hydrophobic interactions along acyl residues
2. more carbons in chain = energy and temp needed to melt crystal increases
what type of DB influences arrangement of crystalline lattice the most?
influenced by cis DB, but trans DB
what are branched chain FA? example?
has a hydrocarbon branch in the chain
ex: malvalic acid: in cottonseed oil. causes egg color problems in eggs
what are hydroxy acids? ex?
contains a OH group in the FA chain. found in castor bean tree
ex: ricinoleic acid
what are cyclic FA?
has a cyclic group in chain
what are actylenic FA?
has a triple bond in chain
useful as antifungal
what are 4 less common FA?
branched chain FA
hydroxy acids
cyclic FA
actylenic FA
IUPAC of C18? C10? C16? (fatty acids)
C18: octadecanoic acid
C10: decanoic acid
C16: hexadecanoic acid
IUPAC of C18:1? C18:2?
presence of a DB
C18:1 = octadecENOIC acid
C18:2 = octadecaDIENOIC acid
IUPAC name for C18:1(9)? C18:2(9,12)? c18:3(9,12,15)?
C18:1(9) = octadeca-9-enoic acid
C18:2(9,12) = Octadeca-9,12-dienoic acid
c18:3(9,12,15) = Octadeca 9,12,15-trienoic acid
why is there naturally some trans FA in butteR?
due to hydrogenation of cis FA by rumen microorganisms.
around 6% of total fat is trans
what is positional isomerism?
many combinations based on position of DB on parent chain or whether it is cis or trans
