Lipids III Flashcards
Differentiate simple and mixed triglycerides.
Simple: one type of fatty acid
Mixed: more than one type of fatty acid
What does the triglyceride “stearodilinolein”?
There are two types of fatty acids: mixed
What is a simple analytical method to separate, isolate and identify individual triglycerides?
There are none
What allows the separation of cis from trans isomers?
Silver ion chromatography
What are triglycerides used as in plant seeds?
Used as a source of energy for germination
What are some non-edible oils obtained from plant sources? What are they used for?
- Castor oil, linseed (flax) oil
- Used for industrial (paint/chemical plasticizer) purposes
What can linseed (flax) oil can be transformed into using plant biotechnology?
To edible Linola
What kind of lipid is biodiesel?
Methyl esters
What is sesame oil high in according to GC?
High in palmitic acid, oleic acid and linoleic acid
How do you get the percentage of fatty acids from GC?
Add all of the contributions (except the internal standard - IS) and then divide each by the total to get a percentage
Which fatty acid group is useful in cosmetics?
Lauric acid group
What is the fatty acid breakdown of olive oil?
- Oleic (75%) - M
- Palmitic (10%) - S
- Linoleic (10%) - U
Why does canola oil have 60% oleic fatty acids?
It is trying to imitate olive oil
Which oil is the most reactive? Why?
- Soybean
- High linoleic, high linolenic
Why should the animal fat depot group be an oil rather than a solid?
Because they have 50-60% oleic and linoleic acid
What is the fatty acid profile of lard?
- Saturated fatty acids (62.2%)
- MUFA (34.7%)
What is the first step of the processing of oilseeds?
- Crush the oilseed
- Give the crush a heat treatment
What does the heat treatment of a crush do?
Aids in knocking out the enzymes lipase and lipoxygenase, which can cause a deteriorative reaction
What deteriorative reactions do lipases cause? How? What are they present in?
- Lipolysis
- Hydrolysis of the ester linkage between glycerol and a fatty acid in the TG
- Enzyme present in every living system
What deteriorative reactions do lipoxygenase cause? How?
- Autoxidation
- Oxidation of polyunsaturated fatty acid chains that have a cis,cis-1,4-pentadiene group (e.g. linoleic and linolenic)
Which fatty acids have a cis,cis-1,4-pentadiene group?
Linoleic and linolenic
What is the best way to inactivate an enzyme? What happens when you treat it?
- By heat
- Treatment: oil is no longer virgin
What are the three ways in which oils are obtained from plant sources?
1) Hydraulic Pressing
2) Expelling
3) Solvent Extraction
How does hydraulic pressing form an oil from a crush?
Screw press applies pressure and crushes the seed to force the oil out of the crush
What are the downsides to hydraulic pressing? (3)
- Slow process
- Not efficient: significant levels of residual oil are left in the meal
- Oil quality is poor
Why is the oil quality poor in hydraulic pressing?
Due to the time factor, which allows enzymes (lipases and lipoxygenases) to act, leading to deteriorative reactions and development of flavours
Which oil has hydraulic pressing as its preferred method? Why?
- Virgin olive oil
- Want the flavours to develop
What is expelling? How does it compare to hydraulic pressing?
- Mechanical version of hydraulic pressing; continuous process
An expeller is a simplified version of an ________. How does it work?
- Extruder
- Archimedes screw in a barrel which tapers toward the end; pressure is increased and the oil is squeezed out
What are the downsides of expelling?
Meal/press cake still contains significant levels of oil
What is expelling usually followed by?
Solvent extraction
How does solvent extraction extract oil? Which solvent is usually used?
Organic solvent (usually hexane) is used to extract the residual oil from the oilseed cake produced by the expelling operation
What are the advantages and disadvantages of solvent extraction?
Advantage: very efficient
Disadvantage: only economically advantageous when economies of scale are involved
In the case of fats and oils from animal and fish sources, what is the most common method of processing?
Rendering
Why is solvent extraction inefficient with animal/fish tissue?
- Tissue contains high levels of moisture
- Extraction with HYDROPHOBIC solvents is inefficient
How does rendering work?
- Ground meat/fish is placed into a large pressurized vessel and heated with steam under pressure
- Lipids melt and are released from the tissue
- The fat is skimmed off and then further processed
Following extraction of the oil by expelling/solvent extraction, what happens to the residual “press cake”? (2)
- Desolventized (remove residual organic solvent) and is usually sold as animal feed (bulk)
- Press cake may be further processed to obtain soybean protein for human consumption (minor amounts)
What is the dark brown colour of the extracted oil following expelling/solvent extraction due to? What does it smell like?
- Lipid-soluble pigments (carotenoids and chlorophyll and pheophytin)
- Smelly (paintlike to fishy)
What components are contained in the extracted oil following expelling/solvent extraction?
- Cellular debris (protein and carbohydrates)
- Free fatty acids (released from TG by lipases)
- Oxidative breakdown products
- Phospholipids (lecithins)
- Free and complexed metal ions
- Flavour components
What are the four steps most oils go through following extraction?
1) Settling/degumming
2) Refining
3) Bleaching
4) Deodorizing
What happens in settling/degumming?
Vigorously mixing the oil with water and allowing it to stand in a conical tank for some time
What is the use of settling/degumming? What does it get rid of?
- Carbs, proteins and phospholipids hydrate and associate themselves with the aqueous phase
- Over time, aqueous phase separates from the oil, carrying with it the cellular debris, carbs and phospholipids
Why is settling and degumming used rarely?
Because of the time factor involved and the capability of the oil to continue deteriorating during this time
What is used instead of settling/degumming today?
- Steam injection into the oil tank is used to accelerate the hydration process (higher temperature)
- Oil is then continuously centrifuged to rapidly separate the aqueous phase from the oil
In the settling/degumming phase of soybean oil, what is recovered from the aqueous layer? Why?
- The phospholipids since soybeans contain 5-8% phospholipids (mainly lecithin)
- They have commercial value as emulsifiers
What does refining remove?
Removes the free fatty acids from the oil
How does refining work?
- Treatment of the oil with dilute alkali
- Convert the fatty acids into soap
- Soap formed is removed with the aqueous phase
Why does the alkali have to be carefully measured in refining? It requires accurate measurement of the ___________ content of the oil
- To avoid saponification of the oil
- Free fatty acid content
How does modern processing systems combine settling, degumming and refining into one operation?
Using steam injection of dilute base combined with centrifugation
What removes 99.9% of the moisture and particulates from the oil?
Centrifugation and filtration
What does bleaching remove?
Designed to remove the coloured material from the oil (carotenoids, chlorophyll, and pheophytin)
Why are colour compounds slightly more polar than triglycerides?
- Hydrophobic in character
- But, they tend to contain many double bonds (are oxygenated to some extent)
After centrifugation in the refining step, the oils are essentially _______-free
water-free
What compound is capable of absorbing slightly polar compounds in the ABSENCE OF MOISTURE?
Dry bentonite (bleaching clay) or charcoal
How does bleaching work?
Passing the dry centrifuged oil through a bed of bentonite or activated charcoal to absorb the colored compounds
Bleaching is also often used as a secondary filtration process to remove what? What colour oil does it produce?
- Residual colloidal material or hydrogenation catalyst from oils
- Produce a clear pale yellow oil
What does deodorization remove?
Removes the volatile compounds that give the oil off-flavours
How does deodorization work?
- By steam stripping, which involves spraying the oil into an evacuated chamber containing steam flowing counter-current to the oil droplets
- Volatiles are carried away with the steam
In olive oil, what compounds are not removed for the best quality? Which steps are not used?
- Flavour and colour compounds
- Only pressed; bleaching and deodorization are not used
What does virgin mean?
Means the oil was produced by the use of physical means and no chemical treatment
Are refined oils or virgin oils of higher quality?
Virgin oils are of higher quality (paying more for less processing)
What does a refined oil mean?
Means that the oil has been chemically treated to neutralize strong tastes (characterized as defects) and neutralize the acid content (free fatty acids).
What is olive pomace oil?
Means oil extracted from the pomace using solvents, mostly hexane, and by heat.
What is the most sought-after olive oil?
Cold-press
What is winterization used for?
Used to produce salad oils from oils not suitable for this purpose
What is the problem with winterization?
Clouding of an oil under refrigeration conditions
What can crystallization break? In what process?
- Breaks emulsions
- Winterization
In what conditions does oil cloud in winterization?
Clouding of an oil under refrigeration conditions may occur due to fractional crystallization of the more saturated triglycerides at refrigerator temperatures (~4oC)
Which oil helped develop winterization? Why?
- Cottonseed oil
- Stored in the winter, the more saturated triglycerides precipitated out
How is winterization carried out nowadays?
- Heat exchanger
- Same result, more efficient manner
What does winterization separate?
One fraction highly saturated, the other is unsaturated
What is large-scale fractional crystallization carried out with? What does it produce?
Carried out with palm oil to produce palm stearin or palm fat, a useful source of natural hard vegetable fat for food applications.
What is hydrogenation used for?
- Hydrogenation is a process used to change the physical and chemical properties
of fats and oils by reducing their overall degree of unsaturation. - Used to convert an oil into a fat or to reduce the susceptibility of an oil to oxidative rancidity.
How is hydrogenation achieved?
Achieved by treating oil with H2 at high temperatures/pressures in the presence of a nickel catalyst
What is the hydrogenation a function of? (3)
(a) Form and concentration of the catalyst
(Ni catalyst must be in a finely divided state)
(b) Temperature and H2(g) pressure
(c) Amount of agitation of the oil
What is the significant reaction in hydrogenation?
Isomerization of the natural cis form to the trans form
The solidification achieved by catalytic hydrogenation processes is caused by a combination of what?
combination of hydrogenation and formation of trans isomers.
What are the double bonds in hydrogenated oils capable of?
“wandering” (positional isomerism)
What does positional isomerism result in?
Conversion of unconjugated double bonds to CONJUGATED double bonds or MIXED bonding systems.
Define selectivity. It is a property of what?
- Preferentially hydrogenating more highly unsaturated fatty acids
- Property of the catalyst
What does the selectivity ratio to produce C18:0 imply?
sr = C18:2/C18:1 = 12.2
Implies that stearic acid is produced 12x faster from linoleic acid than from oleic acid (presumably because the catalyst has a higher affinity for highly unsaturated fatty acids)
What is the effect of selectivity? What accumulates?
Accumulation of more monounsaturates
How can selectivity vary?
By selecting specific reaction conditions (varying catalysts/operating conditions)
What is proprietary?
Knowledge of conditions and selectivity characteristics provides control
What is the method that compensates for hydrogenation?
Interesterification
The properties of a fat are a function of what? (2)
- Fatty acid composition
- Fatty acid distribution
What fat explains the process behind interesterification?
Lard has a similar fatty acid composition to vegetable oils but is a solid due to the high levels of fatty acids present in a specific configuration - GS3 (3%) and GS2U (27%).
What causes lard to be “grainy”?
In lard, the GS2U component is largely made up of oleopalmitostearin, which has a propensity to form large crystals.
What can overcome the grainy texture of lard?
By randomizing the fatty acid distribution by interesterification.
Define interesterification.
Exchange of fatty acids on the glycerol backbone, using heat and a catalyst such as tin, lead, zinc or alkali earth metals
If interesterification is carried to completion, there will be complete _________”
randomization of the fatty acid on the glyceride; changes the physical properties of the fat/oil
What catalyst can be used for interesterification?
Carbonyl anion of diacylglycerol
What happens when interesterification is carried out at lower temperatures?
- The more saturated long-chain glycerides will FRACTIONALLY crystallize out
- The oil portion becomes more unsaturated, while the fat portion becomes more saturated.
What are the two uses of interesterification?
- Used extensively to remove the graininess from lard
- Change the characteristics of other fats and oils to give properties other than those naturally present.
Which technique produces randomization?
Chemical interesterification produces fats which have a random distribution of fatty acids in TAGs molecules
How can the structure of lipids in human milk be reproduced artificially?
Enzymatic interesterification reaction using sn-1,3 specific lipase as a catalyst.
Which method is better suited when the aim is to produce lipids with highly specific compositions for functional and medical applications?
Enzymatic interesterification
Why is cocoa fat/butter expensive?
Has the property of having a sharp melting point at body temperature; unique melting point
How can cocoa fat/butter be imitated?
proper modification of other fats and oils, so that they can be used as extenders – reduce the amount of more expensive cocoa butter needed
What is used for the manufactore of mono and di-glycerides for emulsification? (2)
- Interesterification
- Enzymatic reaction employing lipase
Do fats have a sharp melting point? Why or why not?
- No
- A fat is a complex mixture of triglycerides, each of which has its own melting point; leads to a broad melting range
Fat appears to be “solid” at room temperature, what does it consist of really?
Consist of oil trapped in a crystalline matrix.
There can be as little as ___% solids in a fat that still retain a solid character
10
Why can fat have plasticity or spreadability?
Because a fat is made up of a liquid in a crystalline matrix
The crystalline matrix of fat forms a 3-D network that holds the system together by what force? How does it explain plasticity?
- Van der Waals forces
- Because they are weak forces, they can be broken and readily re-formed again
The plasticity of a fat is a function of the __________ ratio, which in turn is a function of _________.
Solid-to-liquid, temperature
When a fat can be deformed readily, it is said to be in what range?
Plastic range
What is the plastic range a function of?
Function of the fatty acid composition of the triglycerides and the distribution of the fatty acids on their glycerol backbones.
Which ingredient has a wide plastic range? Why?
- Soft margarine
- To be plastic at refrigerator temperatures but not melt at room temperature.
How is butter the opposite of margarine?
Solid at refrigerator temperatures, but melts at body temperature
