Lipids lecture 2 + 3 Flashcards
1
Q
what are the 3 forms of nomenclature of triglycerides?
A
1 simplest: TGC that has only one type of FA attached to the 3 positions on the glycerol (simple glycerides)
2 mixed glycerides: more than one type of FA
3 position of each FA is numbered
2
Q
what is sapoinification
A
hydrolyzing the fat
3
Q
what is FAME?
A
FA methyl esters
4
Q
how to determine overall FA composition of a fat?
A
- saponify: hydrolyze the fat and react it with NaOH to release FA
- methylate the FA to convert them to volatile FAMEs (FA methyl esters)
- separate FAMEs using gas chromatography
5
Q
what has GC analysis demonstrated?
A
that each natural fat source has a relatively consistent FA composition
6
Q
fats from plants and fish tend to be…
A
oils (ie liquid at room temp)
7
Q
what are TGC used as in plant seeds?
A
source of energy for germination
8
Q
what are common primary plant sources of edible oils?
A
north america:
soybean
rapeseed (canola)
peanut
other locations:
olive
coconut
cocao and palm
9
Q
are seeds and fruits of plants good or bad sources of lipid?
A
very good sources
10
Q
what are the 3 most common sources of fats?
A
plants
animals
fish
11
Q
fat in animal sources?
A
fat rendered as a by product of meat production (from trimmings and carcasses of cattle, hogs, sheep)
12
Q
fat in fish sources?
A
fatty fishes such as sardines, herrings, menhaden
13
Q
what are fats and oils classified by?
A
their fatty acid composition and distribution determined by gas chromatography
14
Q
what are the 7 groups of fat classifications?
A
1 milkfat 2 lauric acid 3 oleic linoleic 4 linolenic 5 animal fat depot 6 marine oil 7 erucic
15
Q
describe the milkfat group classification?
A
includes fat from milk of lactating ruminants (cow, goat, yak ,sheep, water buffalo)
major use: butter production
features: high levels of long chain sat FA
substantial portion of short chain (
16
Q
why are some of the unsat FA in the milkfat group trans?
A
because of the biohydrogenation in the rumen by microorganisms
17
Q
what is the short chain FA responsible for in the milkfat group?
A
- rancid like odor
- undesirable flavor in milk (due to enzymatic lipolysis)
- desirable flavor of aged cheese (enhanced by microbial lipases)
18
Q
what is the major use of milkfat group?
A
production of butter (water in oil emulsion)
19
Q
sources of lauric acid C12 group? their distinguishing properties?
A
from species of palms (oil palm, coconut and babasu)
commonly known as tropical oils
distinguished by: high content of lauric acid. accounts for 40-50% of total FA content
20
Q
saturation in lauric acid?
are they resistant to oxidative rancidity?
crystallization?
A
most FA are saturated = oils at room temp = resistant to oxidative rancidity
can be fractionally crystallized (fractionated) to produce distinct fat and oil fractions
21
Q
why are palm and palm kernal oils (lauric acids) highly valued?
A
resistant to oxidative rancidity = their major use is as an oil or fat in baked goods = long oxidative shelf life
22
Q
cottonseed, sunflower,safflower, olive, peanut and corn oil are what type of group?
A
oleic linoleic acid
23
Q
compoisition of oleic linoleic acid group?
A
sat FA make up less than 20% of FA composition
predominant FA are long chain: oleic (C18:1) and linoleic (C18:2)
very little C18:3 = thus oils don’t undergo reversion = relatively stable = can be turned into plastic edible fats by partial hydrogenation (shortenings)
24
Q
describe the linolenic acid (C18:3) group
why are they categorized as industrial “drying oils”?
examples?
A
high quantities of linolenic acid (in conjuction with oleic and linoleic acid)
high in polyunsat FA
linolenic is very reactive and readily oxidized
categorized as industrial drying oils because they can polymerize into a hard film if applied as a thin layer on surfaces
ex: soybean, linseed, castor, hempseed, perilla oils
25
what is C18:1?
oleic acid
26
what is C18:2
linoleic
27
what is C18:3
linolenic (omega 3)
28
what is reversion?
how is this overcome by processing?
rapid transition from a bland, tasteless oil to a grassy, hay like fish flavour (common in unmodified processed soybean oil)
can reduce reversion by hydrogenation. Converts linolenic to oleic and linoleic acids
29
source of animal fat depot group?
lard from pigs, tallow from sheep and cattle
30
how does the fatty acid distribution on the glycerol affect physical properties of the animal fat depot group?
FA distribution animal fat depot group has higher ratio of di-saturated (gs2u) and tri-saturated (gs3 glycerides than oleic-linoleic acid group = causes melting point to be much higher than oleic-linoleic acid group, even though they have similar unsat FA levels
also influences plasticity and crystal formation in the fat (affects functionality)
31
marine oil group?
properties?
reversion?
what are they commonly used for?
fish oils
properties:
- low levels of sat FA.
- high in long chain unsat FA (C16-C22)
- high in omega 3 FA
high unsat FA = tends to undergo reversion = very susceptible to autoxidation
common uses: margarine and shortening production in europe
32
Erucic acid group?
ie rapeseed and mustard oil
rapseed: originally sued as marine motor oil (good lubricating properties)
- has 40-50% erucic acid = health hazard = infuses into heart muscle in rats
33
what is canola oil?
rapeseed oil converted by plant breeding to a type that has low erucic acid. has similar properties to oleic-linoleic acid oils
34
omega 3 and 6 are...
omega 9 is...
3 and 6: polyunsat
9: monounsat
35
how are oilseeds processed for fats and oils?
1. crush oilseed
2. give crush a heat treatment. This knocks out enzymes lipase and lipoxygenase which causes deteriorative reactions (lipolysis and autoxidation). Crushing causes tissue disruption = lipids are exposed to enzymes, oxygen and other reactive agents
36
what is lipase
catalyzes lipolysis (ie hydrolysis of ester linkage between glycerol and FA in TGC
37
what is lipoxygenase
catalyzes direct oxidation of polyunsat FA that have cis,cis-1,4-pentadiene group (ie linoleic and linolenic)
38
why is heat applied to oilseed crush?
to denature enzymes (lipase and lipoxygenase) to reduced their effects on the oil
39
what are the 3 ways that oil is obtained from plant sources?
1 hydraulic pressing
2 expelling
3 solvent extraction
40
what is hydraulic pressing?
using a screw press to apply pressure and crush the seed = forces oil out
pros/cons:
- slow and not efficient (lots of residual oil left in the meal).
- low oil quality because requires too much time (more time = allows enzymes lipase and lipoxygenases acts = deterioration = off flavors are formed)
41
what is the preferred method of producing virgin olive oil?
hydraulic pressing
b/c takes more time = allows lipases and lipoxygenases to act = flavors to develop
42
what is expelling?
mechanical and continuous version of hydraulic pressing. usually followed by solvent extraction
prons/cons
-high output, but oil will still remain
43
what is solvent extraction?
an organic solvent (usually hexane) is used to extract residual oil from oilseed cake from the expelling operation
pros
-very efficient
cons
-very few solvent extraction plants in canada
44
what is rendering (from animal sources)
why can animal and fish tissue not be extracted by hydrophobic solvents?
most common method of processing animal and fish sources
1. ground meat/fish is placed into a large pressurized vessel and heated with steam under pressure
2. lipids melt + released from tissue
3. fat is skimmed off and further processed
(cannot be extracted with hydrophobic solvents because animal tissue is high in moisture)
45
how are oils processed further after extraction?
what happens to the press cake?
what does extracted oil look like?
ie soybean oil
residual "press cake" is desolventized and sold as animal feed. Or press cake can be further processed for soybean protein (human consumption)
extracted oil would be dark brown, smelly liquid with cellular debris (mostly protein and CHO). dark color is due to o lipid-soluble pigments such as carotenoids and chlorophyll and pheophytin(produced by loss of Mg2+ ion from chlorophyll)
46
what are components present in extracted oil?
what do components affect?
- free FA (Released from TGB)
- oxidative breakdown productsts formed by enzymatic action and attack by oxygen during the crushing operation
- Phospholipids (lecithins) naturally present in the oil
- Free and complexed metal ions e.g., Mg2+in chlorophyll)
- Flavor components
all this affects functionality, palatability and stability = affects quality and value of oil
47
describe settling and degumming.
pros/cons?
original process:
1. vigorously mixing the oil with water and allowing it to stand in a conical tank for some time
2. During mixing, the carbohydrates, proteinaceous extraneous matter and phospholipids hydrate and associate themselves with the aqueous phase
3. Over time, the aqueous layer separates from the oil, carrying with it the cellular debris, carbohydrates and phospholipid
modern process:
1. steam injection into the oil tank accelerates hydration process
2. oil is centrifuged to separate aqueous phase from oil
48
describe the refining oil process
refining = removal of free FA from oil
1. treats oil with dilue alkali = converts FA into soap (salt of FA)
2. soap forms and is removed with the aqueous phase
modern process: combines settling, degumming and refining in one operation n using steam injection of dilute base combined with centrifugation. Centrifugation and filtration removes 99.9% of the moisture and particulates from the oil.
49
describe the bleaching process
designed to removed colored material (ie carotenoids, chlorophyll, etc...)
- most oil soluble pigments are hydrophobic with many DB
- Some are oxygenated
- Most are more polar than TGC (use dry bentonite or charcoal to absorb color compounds)
bleaching can also be used as a secondary filtration (removes reidual colloidal material or hydrogenation catalyst = produces clear pale yellow oil)
50
use of dry bentonite or charcoal in oil processing?
aka "beaching clay"
can absorb slightly polar compounds (ie colored compounds) in the absence of moisture
51
describe deodorization in oil processing
the last compounds left in the oil are contaminants that give off-flavors
compounds can be removed by steam stripping = spraying oil in an evacuated chamber with superheated steam = volatiles are carried away w/ the steam = result is a bland clear oil
52
what are the 4 steps after extractions before being sold?
1 settling/degumming
2 regining
3 bleaching
4 deodorization
53
why is virgin olive oil only pressed and not processed further?
flavor and compounds are desirable and valuable
bleaching and deodorization are not used
54
virgin vs refined olive oil?
olive pomace oil?
virgin = oil produced by physical means. no chemical treatment
refined = oil has been chemically treated to neutralize strong tastes (defects) and acid content (free FA)
-lower quality than virgin
olive pomace oil = oil extracted from the pomace using solvents and heat
55
what are 3 additional/supplementary processes for oil?
1. winterization
2. hydrogenation
3. interesterification
56
what is winterization
to prevent the TB from crystallizing and becoming cloudy
57
what happens when oil is refrigerated under 4 deg c?
how is this process done now?
- fractional crystallization of sat TG (ie winterization). Can cause clouding
- problem: crystallization breaks emulsions
- process developed with cottonseed oil (couldn't be used as a salad oil until it had been stored over the winter when sat TG have been precipitated out)
process done now:
- by heat exchanger
- large scale fractional crystallization w/ palm oil = produces palm stearin or palm fat = good source of natural hard veg fat
58
what is hydrogenation?
what is it used for?
used to change the physical and chemical properties of fats and oils by reducing deg of unsaturation (adding H2 across the DB of an unsat FA of a glyceride)
used to convert oil to fat or reduce susceptibility of an oil to oxidative rancidity
59
what are variables in the rate of hydrogenation?
1. form and concentration of catalyst
2. temp and H2 pressure
3. amount of agitation of the oil
60
what are side reactions in hydrogenation?
effects of this?
isomerization of the natural cis form to trans form
effect: trans has a much higher mp than cis
61
what is the natural form of FA?
cis form
62
causes of solidification from hydrogenation?
formation of trans isomers
63
what is positional isomerism? geometric isomerism?
after DB is broken (half hydrogenated) and there is not enough H finish hydrogenation, the DB will be reformed again (reverse reaction).
The DB can be formed in cis or trans (geometric isomerism) or in at a adjacent carbon (positional)
64
what is selectivity?
preferentially hydrogenating more highly unsat FA
65
how can selectivity be controlled?
by varying catalysts and operating conditions
66
what is the main use of hydrogenation?
convert oils to fats (usually for margarine and shortening)
67
what is interesterification?
exchange of FA on glycerol backbone using heat and a catalyst (ie tin, lead, zinc, alkali earth metal)
- used to overcome randomized FA distribution by changing physical properties of the fat/oil
- allows change or physical properties without forming trans FA (ie trans free margarines)
- used to remove graininess from lard
68
how can interesterification be controlled?
if reaction happens at a lower temp = more sat long chain glycerides will fractionally crystallize out = Oil becomes more unsat while fat becomes more saturated
69
what is randomization (in interesterifcation)
when interesterification produces fats which have a random distribution of FA in TAGs molecules
70
best use of enzymatic interesterification?
functional and medical applications (b/c it is highly specific)
ie: can reproduce structure of lipids in human milk
71
interesterification in cocoa butter?
cocoa fat/butter naturally has very sharp mp at body temp, but also very expensive
can be imitated by modifications of other fats/oils to be used as *Extenders*
72
do fats have a sharp mp?
no
b/c fats are a mixture of TG, each has its own mp = each fat has a unique mp
73
why can fat have plasticity or spreadability properties?
it is oil trapped in a crystalline matrix held together by
74
describe a fat that is in the plastic range
fat that can be deformed readily
plasticity of a fat: function of the solid to liquid ratio = function of temperature
75
what kind of plastic range do soft margarines have?
range of butter?
wide plastic range (plastic at fridge temp but not melt at room temp)
butter: solid at fridge temp but melts at body temp
76
what is polymorphism?
changing from one crystal form to another
77
what are the 3 most common polymorphic forms?
which is least and most stable?
alpha (least stable)
beta prime
beta (most stable)
78
how to form alpha crystals?
melt fat and cool quickly. most of the TG will crystallize into alpha
79
properties of alpha crystals?
- thin, leaf-like crystals
- random packing arrangement
- relatively unstable
80
what causes crystal form to change?
if holding temperature rises above temperature of stability
81
how to form beta prime crystal?
re-melting and cooling more slowly (gives more time for molecular arrangement)
82
properties of beta prime?
- small and uniform crystals
| - smooth
83
how to form beta crystal form?
re-melting and cooling very slowly
84
properties of beta crystals?
- very dense, large form of glyceride crystal
| - large and grainy = undesirable
85
ways to determine solid fat content or index?
index: dilatometry
content: nuclear magnetic resonance (NMR)
86
what is dilatometry?
technique based on the measurement of the change in specific volume (inverse of density) per unit temp
expansion of fat (change in volume) is measured as the temp is changed in specific increments
87
what does the graph of specific volume vs temp represent?
A. thermal expansion of solid fat
B. expansion due to change in state
C. thermal expansion of liquid only
refer to slide 92 (lect 3)
88
what is the solid fat index equation?
X(25)/Y x 100
89
why is it important to know solid fat content?
for blending and obtaining consistent textural characteristic for a fat
