BMS1064 - Wk3 - Lipids intro Flashcards
What are lipids?
- solubility
- structure
Compounds that are soluble in non-polar solvents and are in-soluble in water.
Structure:
- fatty acid chains
- bound to glycerol via ester bond
What are the 3 classifications of lipids? Give Examples.
- Simple lipids (MGs, DGs, TGs, waxes, FAs)
- Compound lipids - structural lipids, polar (phosphoglycerates, glycolipids)
- Derived lipids (sterols, cholesterol, fat-sol vitamins)
What is the Carboxyl group (structure) in fatty acids?
Why are lipids important? (3 categories)
Nutrition - Lipid bilayer, supply calories, essential FAs, vitamin carriers (help with absorption of fat-sol vitamins)
Palatability - flavour, texture, influencing appetite etc
Processing - Heat transfer (frying) and lubrication
What is the structure of glycerol, FAs and TGs?
What is the difference between simple and mixed TGs?
Simple - all FAs are the same
Mixed - different FAs
What is the structure of phosphoglyceride?
Glycerol - 2 FAs, 1 phosphate group
Similar to TGs but polar
What are waxes?
What does the suffix -enoic mean? -dienoic?
-enoic molecule contains a double bond - monounsaturated.
-dienoic = 2 double bonds - polyunsaturated
Give examples of trivial names of TGs
Olive oil, palm oil etc
Describe IUPAC names of TGs
-anoic = saturation
-enoic = unsaturation
names derived from Greek numbering
Describe the Carboxyl-reference system
Indicated number of Cs and positions of double bonds using numbers.
Carboxyl C = n.o. 1
e.g. below = 18:2Δ9,12
18 = number of Cs
2 = number of double bonds
9,12 = position of double bonds
Describe the Omega Labelling system
Greek letters used to note positions relative to the carboxyl carbon..
1st carbon (carboxyl C) = the alpha C
Last carbon = the omega C
Double bonds noted in relation to OMEGA carbon.
e.g. below = 18:2(ω-6)
18 = number of Cs
2 = number of double bonds
6 = position from omega-carbon
note: only notes 1st double bond from omega carbon - others ignored.
What is the difference between trans and cis fatty acids?
Cis - alkyl groups on same side
trans - alkyl groups on opposite side
cis FAs have a greater ‘kink’ so lower m.p.
TGs with high m.p.s form ______ at room temperature.
Solids (e.g. lard)
What is TG m.p. dependent on?
it’s constituent FAs and crystal structure
How do different FAs affect m.p. of TGs?
FAs:
- the shorter the chain - less intermolecular bonds - lower m.p.
- the more more unsaturated - more kinks (especially cis-fats) - less intermolecular bonds - lower m.p.
How does crystal structure affect m.p. of TGs?
Crystal structure
ALPHA:
- least ordered
- melts easily
- limited application
[low melting range]
[least stable]
Formed by rapid cooling.
BETA ‘:
- forms small-like crystals
- soft plastic fats
BETA:
- most ordered
- large crystals, hard (cocoa butter, lard)
[high melting range]
[most stable]
Formed by slow cooling.
What kind of FAs are in Ruminant Milk Fat TGs?
Short chain, trans FAs
Branches and odd numbered FAs
–> generally soild
What kind of FAs are in vegetable fat and oil TGs?
Low content of saturated fats - seed oils
High sat/unsat ratio - veg fats
no fully saturated TGs
What kind of FAs are in animal fats?
Fully saturated TGs
Some unsaturated FAs
What kind of FAs are in marine oils?
Low in saturated FAs - liquid at room temp
high in long chain polyunsaturated FA (PUFAs)
What are the most common TGs in chocolate?
What is ‘tampering’ in reference to chocolate?
Controlled crystalisation that is necessary to induce the desired form of cocoa butter in finished product (e.g. right m.p., texture etc)
Last stage in process.
Ensures choc is correct crystalline structure.
What is the chocolate-making process for lipids?
Liquid cooled to initiate crystallisation
Reheated at 32 degrees C to melt out unwanted crystals.
Stir - allow formation of very small Beta-3 crystals.
Solidify
What are plastic fats?
A mixture of TGs with short chain and long chain FAs.
2 phase system - solid and liquid
e.g. spreads, margarine etc.
What are the natural comodoties that lipids are obtained from?
PLANTS - oil seeds and fruit pulp (olive, palm etc)
ANIMALS AND FISH - Lard (from pigs), Tallow (from sheep and cattle) and Marine oils (from fish and whales)
How is butter produced?
By churning whole milk or cream - allows separation of butter fat and butter milk.
What are the two categoric ways or refining oils?
Chemical/caustic refining
Physical Refining
How are fats and oils extracted from lipid-rich fruits?
- Fruit pulp ground to a paste.
- Pressed
- Sepated (via decantation or vertical centrifuge).
- Heated (Solvent Extraction)
How is (extra) virgin olive oil produced?
Produced solely by physical means.
Pressed from the fruit pulp without further refinement.
Keeps superior flavour.
Other types of olive oil go through refining process. (tend to be lighter in colour)
How are fats/oils extracted from lipid-rich seeds? (Milling)
Seeds cleaned
Seeds crushed (breaking)
Seeds cooked at 70-100 degrees C
Expelling
Solvent extracted (hexane/heptane)
Solvent distilled off and reused.
What is Wet Rendering? Describe the process.
A method of oil/fat extraction from animals
- Tissue heated with steam (high temp)
- Lipid melts
- Lipid separated by decanting or centrifugation
Produces white lipid with neutral flavour (e.g. Lard)
Process more gentle than dry rendering.
How is dry rendering different from wet rendering?
- Uses high heat alone (no steam)
- A harsher process than wet wendering
- Browner lipid with stronger flavour
- Non-food uses -e.g. soap
What are the benefits of refining oils/fats?Overview.
Improves flavour, colour and stability (+ therefore shelf-life).
Removes free FAs, phospholipids, proteins, water and pigments.
Removes toxicants.
What is Degumming?
The removal of phospholipids + some protein from Crude lipids.
What is the neutralisation phase when refining crude lipids?
Removing free fatty acids
What happens in the bleaching phase when chemically refining crude lipids?
Colours and pro-oxidants are removed.
What is deodorisation?
The removal of volatile compounds and flavours from a substance.
Name the steps involved with the chemical refining of crude lipids.
Degumming
Neutralisation
Bleaching
Deodorisation
Name the steps involved with physically refining crude lipids.
Degumming
Steam distillation under high vacuum (neutralisation and deodorisation in one step)
Bleaching
How long should boiled oil last?
A year.
