4. Lipids Flashcards
What is the role of lipids in diet and food industry?
- Provide energy, essential fatty acids, fat soluble vitamins, phytosterols and antioxidants
- Sensory attributes for food texture and flavour - either as carrier of aroma or as aromatic precursors
- In food industry, as heat transfer liquid (frying) or as surface treatment agent (facilitate food processing)
Which lipids are able to undergo saponification?
Neutral lipids, phospholipids, waxes and cutins
Which lipids are NOT able to undergo saponification?
Hydrocarbons, pigments, sterols and fat soluble vitamins
What are cutins?
COndensation polymers of long chain hydroxy acids found on the surface of plant leaves
What is the common feature about the length of the carbon chain in fatty acids?
• Length of carbon chain – even number of carbon, 4-30 carbon atoms, most common 18 carbon (usually 12-24 carbon atoms)
What size fatty acid chain is classified as short medium or long?
Short is up to 6, medium is 6-10 and long is 12-24
What are the two naming systems of the fatty acids?
Which one is the omega carbon and which is the alpha carbon in fatty acids?
- From the carboxylic acid group the C1 is the carboxylic acid group carbon but alpha carbon is the second carbon.
- From the omega side carbon 1 is the methyl group carbon
How are lipids classfied as either fats or oils?
Fats: lipids that are solid at room temperature (25°C)
Oils: lipids that are liquid at room temperature (25°C)
Which fatty acids have higher melting points considering saturation and isomers?
trans fatty acids > cis isomers
but saturated faty acid > trans > cis
How does unsaturation affect stability for fatty acids?
HIgher degrees of unsaturation leads to more susceptible to oxygen and less stability.
What methods are there to protect the stability of fatty acids in food?
- Packaging: air-tight package, protect from light and refrigerated;
- Add antioxidant, Vit E, butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT)
- Hydrogenation
What is hydrogenation of fatty acids?
What is tranesterification?
It is a modification of the triglyceride structure by the intra or intermolecular rearrangement of fatty acid chains on the glycerol molecules
Why is transesterification a good alternative to partial hydrogenation?
It does not generate trans fatty acids. It is just exchanging the fatty acids between the different types of triglycerides - not generating new ones
What are eicosanoids?
- 100 compounds, produced from arachidonic acid / EPE (hormone like substance)
- Eicosanoids from O3 fatty acids are generally less potent than those from the O6 series in promoting the formation of blood clots involved in CHD
Which fatty acid are other long chain fatty acids synthesised from?
Can omega 3 fatty acids change to O3 or O9?
- They cannot be changed from one family type to another
- Humans are very poor at doing this particularly with omega-3 PUFA
What is the pathway to synthesise arachidonic acid?
How is the composition of triglycerides in food determined?
- For short chain fatty acid – analysed directly by Gas chromatograph ionized flame detector (GC-FID)
- For media and long chain fatty acid– need to go through the transmethylation process to transfer fatty acid into FA methyl esters
What is the structure of phospholipids?
What are some side groups that a phospholipid may have?
all phospholipid need to have phosphate but not necessarily have nitrogen
What are four important functions of phospholipids in food?
- In Food: as emulsifier
- In Cell: constitute of cell membrane; help fat soluble substance pass cell membrane;
- Fat transportation in blood;
- Food source: egg, liver, soybeans, wheat germ and peanuts.
How do phospholipids act as emulsifiers in food systems?
- Phospholipid molecules orientate themselves at the oil water interface to allow their polar groups to interact with the aqueous continuous phase.
- In most foods the pH is low and ionisable groups of the phospholipid will carry a net positive charge.
- therefore they attract negatively charged ions present in the aqueous phase
- mutual repulsion of layers of negative charge keeps droplets apart and prevents them from coalescing
What is HLB?
- in 1965 griffin introduce HLB , hydrophile lipophile balance system, a scale of 1 to 20 for quantifying the emulsifying capability of surfactants.
- Surfactants with low HLB values, those between 4 and 6 most lipophilic and best for water in oil
- Oil in water HLB in 8-18 range
What is the most common emulsifier?
Best known source of emulsifying properties in food preparation is egg yolk. Approx 33% of yolk of hen’s egg is lipid (protein amounts to further 16%) of which about 67% is trigylcerides, 28% phospholipid and remainder mostly cholesterol
Name these sterols
What is the origin of cholesterol in the body?
Origin of Cholesterol: endogenous (body produce 800-1500 milligram per day)/exogenous (food, ~ 300 milligram per day)
What is the role of sterol in the body?
- Role of sterol: bile acids, sex hormones (testosterone, androgen and oestrogen), adrenal hormones (cortisol, cortisone and aldosterone), Vit D, and cholesterol. Cholesterol are used to biosynthesis these compounds.
In cell membranes what sterols are present?
What types of compounds are these?
What happens when lipids in food oxidise?
- Causes spoilage of foods, usually caused by oxygen and polyunsaturated lipids
- May form different chemicals such as aldehydes, ketones, alcohols, hydrocardons and polymers
- Mostly emit unpleasant taste or odors - rancidity
- Sometimes cooking of meat or ripening of certain cheese produce desirable flavour
Which lipids tend to get oxidised more?
- Free fatty acids more likely to be oxidised than triglycerides which have a more closed structure
- Polyunsaturated fatty acids more likely
What factors is oxidation facilitated by?
What are the two main challenges for food manufacturers when it comes to managing oxidisation?
- Reduce the degree of unsaturation (not desirable for nutritional value)
- Modulate natural antioxidant and pro-oxidant activity
How is antioxidant activity modulated when managing the oxidation of fatty acids?
- Avoid exposing foods to oxidation catalysts;
- Reducing the content of pro-oxidant agents in food processing
- Genetically select plaints low in lipoxygenase activity;
What are some anti oxidants?
How is the melting temperature influenced by fat properties?
Since natural fats are mixtures each component has its own melting point, a fat does not have a discrete melting point but a melting range
What are the three main crystal arrangements for fats?
- When a TAG melts it is cooled quickly and solidified in the lowest melting form, alpha
- When heated slowly it melts and resolidifes in the beta form
- A more stable beta is obtained from the beta’
What is polymorphism?
• Ability of compound to exist in more than one crystalline state is referred to as polymorphism
