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Food Science & Nutrition > lips/triglycerides- week 3/4 > Flashcards

lips/triglycerides- week 3/4 Flashcards

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1
Q

what is the melting point of a triglyceride based on

A

its dependent on its fatty acids & its crystal structure (polymorphism)

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2
Q

1) TG with high melting points are ………. at room temp.
2) TG with low melting points are ……. at room temp.

A

1) solid
2) liquid

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3
Q

when do fatty acids melt

A

occurs when intermolecular (van de waals) are broken
by heat energy (not intramolecular bonds)

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4
Q

what decreases the melting point of a fatty acid

A

increasing unsaturation
The more C=C bonds the lower the melting point

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5
Q

what increases the melting point of fatty acids

A

increases with chain length (number of carbons)
The longer the chain, the higher the melting point
Longer chains = more intermolecular bonds = more heat energy needed

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6
Q

how does the unsaturation of the fatty acid influence the melting point (2 points)

A

-trans C=C bonds introduce a slight kink and lower intermolecular bonds and thus less heat energy needed to melt
-cis C=C bonds introduce a larger kink (~42o
) and lower intermolecular bonds even more and thus even less
heat energy needed to melt

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7
Q

Triglycerides are polymorphic, what is it meant by polymorphic

A

means that TG can exist in more than one crystalline form

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8
Q

what are the three main polymorphic forms

A

α : alpha
β’ : Beta prime
β : Beta

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9
Q

what is the melting range of MP of fats dependent on

A

on the arrangement of TG molecules
i.e. their crystal structure

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10
Q

What are the properties of α-types (3 points)

A
  • Limited applications in foods and food processing (don’t form solids)
  • Randomly formed
  • Melts very easily
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11
Q

what are the properties of β’ -types (2 points)

A
  • Form small needle like crystals
  • Form soft plastic fats for use in margarine
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12
Q

what are the properties of β -types (3 points)

A
  • Form large crystals giving grainy texture (cocoa butter, lard)- too hard
  • Well ordered; hard texture
  • Not good for margarine
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13
Q

what is the definition of Tempering explain in terms of chocolate

A

controlled crystallization that is necessary to induce the desired form
of cocoa butter in the finished product (Used to Prepare Food with Desired
Polymorphic State of a Lipid)

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14
Q

what are the 3 states that lipids can exist depending on temperature

A

-solid (All TGs liquid)
-plastic (TGs with short chain FA liquid TGs with long chains solid)
-liquid (All TGs liquid)

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15
Q

Outline the difference between a simple and mixed triglyceride

A

In a simple triglyceride such as palmitin or stearin, all three fatty-acid groups are identical. In a mixed triglyceride, two or even three different fatty-acid groups are present; most fats and oils contain mixed triglycerides.

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16
Q

how is the process of tempering used to form chocolate

A

-Liquid cooled to initiate crystallisation
-Reheated to 32 degrees (just below the mpt of β-3 type) and
held – this melts out unwanted crystals
-Stir at 32 degrees, allow formation of very small β-3 crystals
and then finally solidify

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17
Q

what are the natural commodities lipids are obtained from (3 points and give examples of each)

A

-plants-
Oil Seeds (Rape, Sunflower, Palm Kernel, Soybean,
Cottonseed, Corn germ, Peanut, Coconut)
Fruit Pulp (Olive, Palm Fruit)
-animals & Fish-
* Lard (rendered from pig kidney fat, fatback, caul fat)
* Tallow (The rendered form of fat from sheep and cattle)
* Marine oils (Fish, Whales)
-Milk fats-
produced from churning whole milk or cream

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18
Q

Describe how lipids are purified from natural commodities from FRUIT (4 points)

A

-Grinding to a paste
-Pressing
-Separation (decantation or vertical centrifuge)
-Heating/Solvent Extraction

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19
Q

Describe how lipids are purified from natural commodities from seeds (5 points) - Milling

A

-Cleaning
-Breaking
-Cooking 70-100oC (to denature the enzymes like lipase & killing microbes)
-Expelling
-Solvent Extraction (hexane/heptane)

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20
Q

what are the 2 ways of Oil/Fat Extraction from Lipid-Rich Animals

A

wet rendering and dry rendering

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21
Q

what are the steps for wet rendering (5 steps)

A
  • Tissue heated with steam (high temp of about 100-110oC)
  • Lipid melts
  • Lipid separated by decanting or centrifugation
  • White lipid with neutral flavour, e.g., Lard
  • Process milder than dry rendering
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22
Q

what are the steps for dry rendering (4 steps)

A
  • Uses high heat alone
  • A harsher process than wet rendering
  • Browner lipid with stronger flavour
  • Non food uses e.g. soap
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23
Q

what are the 2 ways of refining oils

A
  • Caustic or chemical refining
  • Physical refining
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24
Q

what are the steps for caustic or chemical refining (6 steps + define each step)

A

-Crude Lipid (TGs, water, protein, phospholipids)
-DEGUMMING (Removal of phospholipids + some protein)
-NEUTRALISATION (Removal of free fatty acids)
-BLEACHING (Removal of colour and pro-oxidants)
-DEODORISATION (Removal of volatile compounds and flavours)
-Crude Lipid (TGs, water, protein, phospholipids)
Refined Oil (one of the purest foods known)
Refining Steps in Detail
DEGUMMING
2-3% water added + agitation at ~50 degrees
Water phase removed after phase separation

25
Q

what are the steps for physical refining (5 steps + explain each step)

A

-Crude Lipid (TGs, water, protein, phospholipids)
-DEGUMMING (Removal of phospholipids + some protein)
-STEAM DISTILLATION UNDER HIGH VACUUM (Removal of free fatty acids and deodorisation in one step)
-BLEACHING (Removal of colour and pro-oxidants)
-Refined Oil is produced

26
Q

give in DETAIL the process of DEGUMMING in Caustic or Chemical Refining

A

2-3% water added + agitation at ~50 degrees
Water phase removed after phase separation

27
Q

give in DETAIL the process of NEUTRALISATION in Caustic or Chemical Refining

A

Caustic soda added to heated fat
Aqueous solution (soap stock) removed; Washed with hot water

28
Q

give in DETAIL the process of BLEACHING in Caustic or Chemical Refining

A

Heated to 85 degrees and absorbents added
(Fullers earth or activated carbons); The bleaching earth removed by filtration

29
Q

give in DETAIL the process of DEODOURISATION in Caustic or Chemical Refining

A

Steam distillation-steam passed through oil under reduced pressure
Citric acid is often added to sequester metals

30
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

31
Q

Why are lipids modified (5 points)

A

Most of our food products is oil/ 75% of world edible oil is vegetable oil
Melting point not suitable for processing
Crystal structure not fit for production
Cloudy when cooled
Unstable (oxidation)

32
Q

What are the 3 different methods of lipid modification

A

Hydrogenation

Fractionation

Interesterification

33
Q

Explain hydrogenation
(What does it do to FAs/what does it produce/characteristics of hydrogenated FAs)

A

-removed double carbon bonds- end up with trans fatty acids(increase HDL
-means it increases the melting point
-can convert cheap vegetable oils into plastic fats
-improves stability
-Generates hydrogenated vegetable oils (HVO)/trans fats

34
Q

What is Interesterification/ what can it do to the lipid/ what’s its properties

A
  • Rearranges fatty acids on the glycerol
    backbone of TGs
  • Can change melting point
  • Can change crystal structure
  • Improves properties (more plastic)
    (Can change to what you what the product you want, and it doesn’t produce trans-fatty acids)
    *Converts cis bonds into trans double bonds
35
Q

what are the importance of lipids in food

A

-Nutrition (essential FAs, e.g linoleic acids & lipids are essential of bilayers)
-Palatability (flavour, texture, solubility)
-Processing (heat transfer)

36
Q

what are lipids

A

Compounds that are soluble in non polar solvents and are insoluble in water

37
Q

what are the major classes lipids can be classified into

A

» Simple lipids (waxes, fatty acids, mono-, di-, triglycerides)
» Compound lipids-structural lipids (phosphoglycerides, glycolipids- all are polar)
» Derived lipids (sterols, fat soluble vitamins)

38
Q

what is it meant by a lipid is polar

A

it has a hydrophobic tail and hydrophilic head

39
Q

what is the structure of glyceride and how can you tell if its a simple or mixed triglyceride

A

glycerol + FA = triglyceride

in the triglyceride has the SAME variable regions = SIMPLE
if 2 are a least DIFFERENT it means its MIXED

40
Q

what is the difference between a phosphoglyceride and a triglyceride

A

Similar to triglycerides (TGs) but are polar (eg.
emulsifying agents

41
Q

what is the structure of a phosphoglyceride

A

it has:
-choline
-glycerol
-phosphate
-Fatty Acid

42
Q

what is a Fatty Acid

A

FAs are chains of carbon and hydrogen atoms with a terminal carboxyl group

43
Q

How are saturated Fatty acids named

A

Named in accord with the number of C atoms including the COOH group
i.e: CH3CH2 CH2 CH2 CH2COOH —–>HexANOIC (Caproic acid)

CH3CH2 CH2COOH
ButANOIC (Butyric acid)

anoic -means its a saturated FA

44
Q

in unsaturated fatty acids what are the 2 types of methylated double bonds

A

-Methylene interrupted
-Conjugated (where this there is no CH2 in between the double bounds- Rare)

45
Q

what is it meant by methylene interrupted

A

FA is interrupted by a CH2 in between the double bonds

46
Q

what are the influence of TG structure in the nature/use of lipids

A

-Type of FA and arrangement responsible for the varied properties of TGs in foods
—->TG melting point is dependent on its fatty acids & its crystal structure (polymorphism)

47
Q

give examples of lipid rich foods and the content of TG in them (4)

A

-Ruminant Milk Fat TGs
* Short chain FAs (C4
-C12) + trans FAs
-Vegetable Fat and Oil TGs
* Seed oils-low in sat FAs
* Vegetable fats, High sat/unsat ratio
No fully saturated TGs
- Animal Fats
* Fully saturated TGs present; solid at room temp (20oC)- some unsat
- Marine Oils
* Low in saturated FAs; liquid at room temp
* High in long chain polyunsaturated (PU) FAs

48
Q

describe how the Fatty acid structure influence TG properties (3 points)

A

-Melting of fatty acids occurs when intermolecular (van de waals) are broken
by heat energy (not intramolecular bonds)
-Melting point increases with chain length (number of carbons)
The longer the chain, the higher the melting point
-Melting point decreases with increasing unsaturation
The more C=C bonds the lower the melting point

49
Q

what influence does the chain length have on the Melting point of FAs

A

Longer chains = more intermolecular bonds = more heat energy needed

50
Q

rank in Oder from the highest MP to the lowest MP:
TGs have C18 Saturated FAs
TGs have C4-C12 Saturated FAs
TGs have Unsaturated FAs

A

highest —>lowest MP
TGs have C18 Saturated FAs
(solid- e.g Lard)
TGs have C4-C12 Saturated FAs
(semi-solid- e.g butter)
TGs have Unsaturated FAs
(liquid- e.g oils)

51
Q

define polymorphic and give an example of one

A

Triglycerides are polymorphic meaning they can exist in more than one crystalline form

52
Q

what are the three main polymorphic forms

A

α - alpha
β’ - beta prime
β - beta

53
Q

what causes the different polymorphic forms to form

A

The forms that grow depend on HOW the liquid is cooled

54
Q

how does α-types affect the application of Lipids/ what’s its characteristics

A
  • Limited applications in foods and food processing
  • Randomly formed
  • Melts very easily
55
Q

how does β’-types affect the application of Lipids/ what’s its characteristics

A
  • Form small needle like crystals
  • Form soft plastic fats for use in margarine
56
Q

how does β-types affect the application of Lipids/ what’s its characteristics

A
  • Form large crystals giving grainy texture (cocoa butter, lard)
  • Well ordered; hard texture
  • Not good for margarine
57
Q

define Tempering

A

Used to Prepare Food with Desired
Polymorphic State of a Lipid—->controlled crystallization that is necessary to induce the desired form
of cocoa butter in the finished product
» This is the last stage in the process
» Ensures that chocolate is in the correct crystalline state

58
Q

Which polymorphic state exists in chocolates and margarine?

A

small β-3 crystals

59
Q

what are the natural commodities lipids are derived from

A

-Plants: Oil SEEDS(i.e sunflower ,rapeseed, soybean) & fruit PULP (olive, palm fruit)
- Animals & Fish: Lard (rendered from pig kidney fat), Tallow (The rendered form of fat from sheep and cattle), Marine oils
-Milk fats: butter produced from churning whole milk or cream.

*rendering =product that is melted in order to separate out the impurities.

Food Science & Nutrition (6 decks)

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