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Nutrition Semester 1 > BMS1064: Wk4 - Lipid Modification + Rancidity > Flashcards

BMS1064: Wk4 - Lipid Modification + Rancidity Flashcards

1
Q

What is lipid modification?

A

The alteration of one or more fatty acids in a lipid, resulting in a change in the properties of the lipid.

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2
Q

Why modify lipids?

A

Most edible oil in the world is vegetable oil.

Vegetable oil:
- m.p not suitable for processing
- crystal structure not fit for purpose
- cloudy when cooled
- unstable (easily oxidises)

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3
Q

What are the 3 methods of lipid modification?

A

Hydrogenation
Interesterification
Fractionation

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4
Q

Describe Hydrogenation - what are the positives? Negatives?

A

Removal of C=C bonds (makes FAs more saturated)

  • Increases m.p.
  • Improves stability (prevents oxidation-> longer shelf-life)
  • can convert cheap oils into plastic fats -> (high smoke point - good for frying)
  • Cheaper than other lipid modification methods

However, generates trans fats if reaction is incomplete (converts cis-> trans bonds)
And more saturated fats -> coronary heat disease.

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5
Q

What is selectivity in relation to hydrogenation?

A

The first C=C bonds to get saturated are:
- bonds furthest from the glycerol backbone or…
- bonds in the most unsaturated fats

Allows greater formation of less saturated FAs with less chance of producing fully saturated FAs.

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6
Q

Why is selective hydrogenation better than non-selective hydrogenation.

A

Greater production of mono-unstaturated FAs with a smaller chance of producing fully saturated FAs.

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7
Q

Describe Inesterification

A

Rearranging FAs on the triglyceride molecule. Occurs under certian conditions (catalyst, temp etc)

  • Changes m.p. , crystal structure and properties (more plastic)

2 types: Chemical and Enzymatic

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8
Q

What is the effect of interestification on Lard.

A

Lard has Beta crystal structure. Physical Esterification changes this structure to Beta prime crystal structure.

So m.p. not changed, but crystal structure is, so properties changed - less solid.

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9
Q

What are the differences between Interestification and Hydrogenation?

A

Interestification
- more commonly used
- more EXPENSIVE
- little/no trans FAs
- produces MORE PUFAs
- SPREADABLE

Hydrogenation
- less commonly used
- CHEAPER
- contains TRANS FAs :(
- Produces more saturated and less PUFAs
- HARD fats produced

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10
Q

Describe Enzymatic Interestification

A

Lipases catalyse the hydrolysis of lipids.

Carried out under low temp.
Enzymes need the presence of water.
Can be CONTROLLED and TARGETED (specific FAs to specific positions on molecules).

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11
Q

Compare chemical vs Enzymatic interesterification.

A

Chemical
- cheaper
- high processing loss
- high temp process
- more processing steps

Enzymatic
- more expensive
- minimum processing loss
- low temp process
- better quality finished product

  • Lipases provide specificity, so products which cannot be obstained by chemical interesterification can be produced.
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12
Q

Describe Fractionation

A

The selective removal of triglycerides from lipids based on melting points.
(oils cooled - allow high m.p. TGs to crystalize out and be removed by filtration)

  • Produces lipids with specific m.p.
  • Stops clouding (crystalising) at room temp
  • produces clear, clean and cheaper oil
  • Physical process - not chemicals used.
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13
Q

What is palm oil usually fractionated to?

A
  • Olein/Super Olein for frying
  • Hard PMF (Palm mid-fractionation) for confectionary
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14
Q

Frying oils function as ______ _______ mediums and contribute _______ and ___________ to the food.
They must be _______ under abusive conditions (high temperatures).

A

Heat Transfer
Flavour and lubrication
Stable

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15
Q

Which oils are particuarly susceptible to oxidation?

A

Oils rich in linolenic acid (unsaturated) - e.g. soybean and rapeseed oils.

Soybean oil is partially hydrogenated to reduce lionlenic acid content.

The more unsaturated, the less stable, so greater chance of oxidative breakdown.

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16
Q

How is margarine made?

A

Fat phase (oils + addatives) combined with Milk Phase (ripened milk, NaCl, preseratives) via emulsification.

Cooled in a controlled way to get desired crystalisation. (repeated)

Kneading.

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17
Q

How does normal margarine and High PUFA, low zero trans Margarine compare?

A

Normal:
- 85% interestified mixed veg oils
- 15% hydrogenated soybean oil.

High PUFA:
Fully hydrogenated veg oil –> solid fat (high sat)
Solid fat + Liquid veg oil (high PUFAs) – interestification —> Margarine

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18
Q

How are lipid substitues classified?

A

By their chemistry:
- Carbohydrate based
- Protein based
- Fat based (most acceptable)

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19
Q

What are 2 example of carbohydrate based fat substitutes? Where are they derived from?

What are they both unsuitable for?

A

Avicel
- derived from natural fruit and veg
- contains cellulose - cannot break down
- no calories

Stella
- starch-based product derived from corn
- reduces calories and fat while increasing complex carb intake.

Both unsuitable for frying.

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20
Q

Name and describe 1 protein based fat substitute.

A

Simplesse
- Comes from whey protein
- Good for lubrication
- Fat is dispensed in a similar way to milk -> texture

Also not suitable for frying.

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21
Q

Name and describe 3 lipid-based fat substitutes. Are they recognised by the body?

A

Have the most acceptable tastes and applications of all fat substitutes:

Olestra
- sucrose polyester (like TGs but with sucrose instead of glycerol).
- no calories

Salatrim
- TG with very short and very long FAs
- Stands for ‘short-and long-chain acyl triglyceride molecules’
- Made by interestification
- Lower calorie

Caprenin
- TG with long chain FAs (saturated)
- Lower calories

None of these are recognised by the body - so are not absorbed - no nutritional benefit.

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22
Q

What is the structure, advantages and disadvantages of Olestra as a fat substitute?

A

Structure: centre unit of sucrose with 6,7 or 8 FAs attached.

Advantages:
- no calories
- best palatability
- can be used for frying

Disadvantages:
- not absorbed
- unabsorbed fat lubricates bowel contents (laxative)

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23
Q

Food must contain _______ to go rancid.

A

Fat

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24
Q

What examples of desriable aspects of fat deteriation?

A

Sour cream, fermented milk, blue vein cheeses, greek cheese -> important in flavour

25
Q

Name 3 causes of rancidity.

A

Endogenous enzymes.
Enzymes produced by invading microbes.
Chemical transformations

26
Q

What are 3 ways to control rancidity

A

Reduce activity of endogenous enzymes
- reduce temp
- heat treat food

Minimise microbial growth
- reduce temp
- heat treat food

Control oxidation
- omit air
- add antioxidants

27
Q

What endogenous enzymes cause rancidity?

A

Lipases and phospholipases - break down TGs

Lipoprotein lipase (LPL) - found in milk - can be destroyed through heating.
- also breaks down TGs into FAs and glycerol

28
Q

How do microbes cause rancidity? What is the biggest issue with them?

A

Their lipases hydrolyse TGs.
Their lipases are HEAT STABLE. Major issue in processed milk products.

29
Q

Endogenous enzymes and microbes cause ________ rancidity.

A

Hydrolytic

  • changes characteristics of dairy products, palm oil and crude fish oil.
  • changes odour, colour etc.
30
Q

What does lipoxygenase do? What does it affect?
Where is is found? What can it cause?
How can it be treated?

A

Enzyme that catalyses oxygenation (by O2) of FAs.
- polyunsaturated FAs only

Soya bean is particuarly rich in lipoxygenase. Also found in carrot, maize, cereal grains, peas.

Produces derivates with characteristic tates - issue in soy milk.

Difficult to inhibit. Treat by heat and antioxidants.

31
Q

What is ketonic rancidity?
- What does it affect?

A

TGs –> FFAs
Subsequent INCOMPLETE Beta-oxidation (breaking down FAs) produces ketones and secondary alcohols (e.g. 2-heptanone and 2-heptanol -> randcid almonds)

Affects both UFAs and SFAs.

Associated with the growth of xerophilic moulds (dry conditions).

32
Q

Describe how chemical hydrolysis can lead to a safety hazard when frying food.

A

Occurs when oils are heated.
WATER must be present.

Frying oils - water derrived from the food.
TG + H2O + heat –> glycerol + FFAs

Glycerol is flamable (reducing flash point)

33
Q

In De Saussure’s experiment on auto-oxidation, what did he find?

A

Measured O2 uptake Daily. Observed 3 distinct phases:
- first 8 months, very little uptake
- next 10 days, large and rapid O2 uptake
- sebsequent 3 months, little uptake
Initiation, Propogation, Termination

Oil became thick and evil smelling.

34
Q

Why was the initiation stage so long in de Saussure’s experiment?

A

Reaction between UFAs and O2 is thermodynamically difficult -> slow

Production of first few radicals occurs via PHOTOSENSITIZATION.

35
Q

What is photo-oxidation? (initiation phase)

A

Interaction between a fatty acid double bond and an excited oxygen molecule to form hydroperoxides (–> radicals)

The more unsaturated a molecule, the more susceptable to initiation.

36
Q

Oxygen is normally in the _____ ground state. It is activated by ____ in the presence of a _______ to form singlet/excited oxygen, which has 1500 times the reactivity of ‘normal’ oxygen.

A

Triplet
light
sensitizer

37
Q

Give example of Sensitizers

A

Cholophyll - plant pigment
Myoglobin - muscle pigment
Riboflavin - vitamin
Erthrosine - food colorant

38
Q

How can we protect food from photo-oxidation?

A

Carotenoids - present in many crude oils, have capacity to quench singlet/excited O2.
BUT considered unacceptable to consumer.

Oils refined and bleached - removes carotenoids but also natural photosensitizers - reducing action of O2*.

Store in dark / use light-absorbent packaging.

39
Q

Initiation forms Hydroperoxides. What radicals do these form?

A

Alkoxyl (RO.) radicals + Peroxyl (ROO.) radIcals

40
Q

When are hydroperoxides most unstable?

A

Temps above 150 degree C
In the presence of transition metal ions (Fe2+, Cu2+) - could be affected by cooking utensils etc.

41
Q

How do alkoxyl and peroxyl radicals react with fatty acids in the propogation phase?

A

They abstract H from vulnerable sites in monoenoic and polyenoic FAs (unsaturated).

(vulnerable site - CH2 group next to a double bond. The more c=c bonds near, the more vulnerable.)

42
Q

What can alkoxyl radicals react to form?

A

Either:
- Ketones
- Secondary alcohols
- or Aldehydes

43
Q

How does the auto-oxidation of PUFAs compare to UFAs?

A

PUFAs:
- react faster
- produce smaller, more volatile fragments
- increased likelihood of di-radicals (frying oils)

44
Q

What is the main source of lipid peroxidation?

How does a diet rich in oxidised lipids affect health?

A

main source = fried food

Decreases vitamin E levels
Potential link with arterial disease?

45
Q

Test for rancidity: how do you test for hydroperoxides (ROOH)? (primary product)

A

TITRATION with thiosulphate and starch.
ROOH + KI –> I2

Typical values:
Fresh oils: <10 mEq/kg
Extra Virgin olive oil: up to 20 mEq/kg
Rancid oils: 20-40 mEq/kg

46
Q

Test for rancidity: How do you test for secondary products?

A

Thiobarbituric acid (TBA) reacts with aldehyde at 100 degrees C to produce PINK colour.

However, heat can decompose ROOH (more secondary products) - amplification. Addition of antioxidant can help control excess being fromed.

Test takes 2-3 hours.

47
Q

Test for rancidity: p-anisidine reacts with non-volatile ________- to form a ____ colour. How do you measure this?

A

aldehydes
RED

measure by spectrometry

Test takes <2mins

48
Q

Test for rancidity: how do you test for tertiary products?
(e.g. ethane and pentane - end products of lipid peroxidation)

A

Gas chromatography

49
Q

Which is the best method to test for rancidity?

A

Each test measures something different (primary vs secondary vs teriary products)

Best not to rely on one measurement.

TOTOX VALUE - takes into account >1 type of product.

50
Q

How do you measure hydrolytic rancidity?

A

Acid-based titration using KOH.
KOH neutralizes FFAs.

Test involves determining the n.o. of mg of KOH required to neutralise the acidity in a sample.

Note: FFA may not be only acid present!

51
Q

PUFAs are more susceptable to rancidity than MUFAs. Therefore, helpful to find out the degree of unsaturation of an oil.

How can you do this?

A
  1. Determine the IODINE VALUE of the oil by adding I2. (reacts with C=C bonds). - The more unsaturated, the more I2 taken up.
    - Free iodine is titrated with sodium thiosulphate to give iodine value.
  2. REFRACTIVE INDEX - very rapid, indicates proportion of unsaturated FAs present.
  3. Response to abuse - heat oil, bubble through oxygen. The more UFA and PUFA the more oxidation.
    - Also able to assess effects of different anitoxidants using this method.
52
Q

What are a pro and con of abuse tests to measure unsaturation?

What a con of Iodine Value and Refractive Index methods?

A

PRO - Useful to assess effectiveness of antioxidants.

CONS - Results difficult to relate to product (e.g. biscuits on supermarket shelf).

IV and IR Methods: do not take into account content of antioxidants - high PUFA foods contain high levels of vitamin E.

53
Q
A
54
Q

What is an antioxidant?

A

A compound that prevents or delays rancidity or other deteriations due to oxidation.

  • Includes both natural and synthetic antioxidants.
  • Important in foods with large SA.
55
Q

Addition of antioxidants to food is regulated. What are the permitted synthetic antioxidants?

What is the typical intake of synthetic antioxidants?

A

E300-E321
(E300 - L-ascorbic acid (vit c))

Typical intake - 60mg/d

56
Q

Give 3 examples of Radical Scavengers (antioxidants)

A

Vitamin E
- good scavenger of peroxyl radicals.
- Inhibits radical chain reaction.
- Scavenges radicals 1000x faster than radicals attack RH.

Vitamin C
- important water-soluble scavenger
- donates Hydrogen
- resulting ascorbyl radical is unreactive

Ascorbyl Palmitate (E304) - mix of ascorbic acid and lipids -> makes vitamin C lipid soluble

57
Q

Phenolic antioxidants: (safer than synthetic antioxidants)

_____ is used in dried potato and chewing gum. BUT discolours in presence of ____ ______.

BHT is also an effective antioxidant, but is _______ _______.

A

Gallates
metal ions

steam volatile (evaporised easily)

58
Q

Chelating agents (e.g. citrate) slow rancidity because…

A

They bind to metal ions (e.g. Cu2+) which promote ROOH decomposition.

59
Q

How else can food randicity be reduced? (Other than adding chelating agents and antioxidants)

A

Oxygen scavengers and displacers.
- Ascorbic acid reacts with oxygen
- Flush packaging with nitrogen

Protective packaging - from light and O2.

Avoid unsaturated fats in food production
Hydrogenate fats

Nutrition Semester 1 (10 decks)

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