notes

Question 1

What are Lipids?

Answer 1

They include all biological compounds that are not soluble in water but can be soluble in organic solvents such as chloroform, methane, ether or benzene.

Question 2

What do lipids include?

Answer 2

Fats, Oils, some vitamins, hormones and most nonprotein components of cell membranes

Question 3

What do lipids include?

Answer 3

They include all biological compounds that are not soluble in water but can be soluble in organic solvents such as chloroform, methane, ether or benzene.

Include: Fats, Oils, some vitamins, hormones and most nonprotein components of cell membranes

Question 4

What are lipids?

Answer 4

Lipids can be defined as fatty acids and their derivatives as well as substances related to biosythetically or functionally to said compounds

Question 5

Classification?

Answer 5

Lipids fall into two groups and the subgroups.

Saponifiable:

• Simple lipids (Fats, oils & waxes)
• Compound lipids (Phospholipids, Glycolipids)

Nonsaponifiable
- Steroids (sterols, hormones)

Question 6

Fats?

Answer 6

Lipids which are solid at room temp

Question 7

Oils?

Answer 7

Lipids which are fluid/liquid are room temp

Question 8

Function of fat in the body?

Answer 8

• • Energy source especially for muscles
• • Energy reserve
• • Major component of cell membranes
• • Nourishes hair and skin
• • Insulates the body from temperature extremes
• • Cushins vital organs to protect them

Question 9

Functions fats and oils in food?

Answer 9

• Integral part of the human diet
• Calorie rich food: 9kcal/g
• Carry fat-soluble citations and essential fatty acids
• Provide satiety
• Contribute to flavour either good or bad (Eg. unique olive oil flavour and rancid bean off flavours)
• Contribute to texture (Crispy, creamy ect)

Question 10

What is satiety?

Answer 10

Gives you the feeling of fullness

Question 11

Structure of fats and oils?

Answer 11

(see other notes for more detail)

• They are triacylglycerols or triglycerides
• Comprise about 95% of lipids in food and the human body
• Glycerol + 3 fatty acids = Triglycerides + H2O

Question 12

Classification of fatty acids

Answer 12

They are classified into Saturated and unsaturated

Unsaturated fats include Mono and polyunsaturated fats

Question 13

Structure of fatty acids

Answer 13

• Fatty acids are usually liner comprising of even no. of carbon rings ranging from 4-24 carbons
  (see other notes)

Question 14

Saturated vs. Unsaturated fatty acids

Answer 14

• In general, saturated fatty acid is a straight molecule
• The double bond in an unsaturated fatty acid produced the kink in the molecule -> this happen due to the double bond been unable to rotate
• Saturated triglycerides pack closely together
• Attractive forces in saturated fatty acids give them a high melting point
• unsaturated fatty acid molecules cannot pack closely together because of cis double bonds (causes kinks)
• Intermolecular forces are weaker and less energy is required to operate molecules so lower melting point

Question 15

Omega 3 vs. 6 fatty acids

Answer 15

• Based on the location of double bonds. “omega number”
• Omega no. is the number of c atoms between the double bond and the terminal methyl group.
• Omega 3 fatty acid
• Omega 6 fatty acid

Question 16

Cis and trans Fatty Acids?

Answer 16

Unsaturated fatty acids can exist in either the cis or trans form depending on the configuration of the hydrogen atoms attached to the carbon atoms joined by the double bonds.
cis Fatty Acids
– If the hydrogen atoms are on the same side of the carbon chain, the arrangement is called cis.
trans Fatty Acids
– If the hydrogen atoms are on opposite sides of the carbon chain, the arrangement is called trans

• The Kink in the carbon chain is much more pronounced in the cis isomer then the trans. For this reason the cis fatty acids do not solidify as easily as trans
  and cannot line up as easy

Question 17

Trans fats health concern?

Answer 17

Fatty acids with trans double bonds usually occur as a result of processing (ie hydrogenation) but can occur naturally in ruminant fats.

trans Fatty acids are thought to play a part in lowering high density lipoprotein ie HDL (also referred to as good cholesterol) and increasing low density lipoprotein (LDL).

LDL is known to contribute plaque formation in arteries leading to the potential for a myocardial infarction.

Question 18

Position of double bonds in fatty acids?

Answer 18

• Methylene interrupted
  Polyunsaturated fatty acids where the double bonds are operated by a CH2 unit
  -CH=CH-CH2-CH=CH=
• Conjugated
  Polysaturated fatty acids where the double bonds are operated by a singe bond
  -CH2-CH2=CH-CH2=CH-

Question 19

Melting point of fatty acids?

Answer 19

• Melting point is a measure of the heat necessary to break the van der waals bonds tying the fatty acid chains of neighbouring glycerides together in bringing about a transorfmation from the solid crystalline phase to the liquid phase
• Variation in melting point is a function of the extent to which fatty acids chains of neighbouring glycerides pack together to form crystals

Question 20

Melting point increase?

Answer 20

Melting point of fatty acids and the glycerides comprising the same increase with:

• Increasing chain length of fatty acids
• Increasing saturation of fatty acids
• Transformation of double bond type from cis to trans configuration

Question 21

Melting point cis vs. trans?

Answer 21

• A cis souble bond in the fatty acid structure causes a band in the chain whereas trans just causes a kink
• The degree of operation between the cis chains is greater compares to trans
• melting point of trans is greater than cis

Question 22

Crystallisation

Answer 22

• Cooling of melted fat results in the formation of crystalline fat as the randomly moving glyceride molecules lose kinetic energy and pack together
• As fats are polymorphic they are capable of solidifying into more than one crystal.
  Polymorphic= the occurrence of different forms

Question 23

Soild fat index/content

Answer 23

• The firmness of fat is affected by the extent and type of the fat crystals formed.
• The solid fat index (SFI) and solid fat content (SFC) relates to the percent of fat that is cold at various temp.
• SFI 75-80 approximated an SFC of 100 but is affected by fat toe, temp and level of SFI
• Plasticity (creaminess, spreadability) of fat is an important property

Question 24

Solid fat index ranges

Answer 24

• Within the rage of SFI 10-25, the fate is pliable and soft while able to retain shape (referred to as creamy)
• An SFI >35 means the fat is hard life refrigerated butter and SFI

Question 25

Emulsion?

Answer 25

- An emulsion is a mixture of two or more liquids that are normally immiscible - The work emulsion comes form the latin word milk - Emulsion = a collodial dispersion comprising a disperse phase and continuous phase

Question 26

W/O and O/W?

Answer 26

- W/O means water in oil emulsion (water phase dispersed throughout a continuous oil phase- e.g. butter) O/W - Oil in water emulsion (is oil phase dispersed throughout a continuous water phase e.g.. Milk)

Question 27

What is an emulsifier?

Answer 27

- It lowers the interfacial tension between the immiscible disperse phase and continuous phase - Promotes the formation of emulsion which is the distribution of the disperse phase throughout the continuous phase - Emulsifier is attracted to both phases - Is it amphilic in nature - The lipophilic (or hydrophobic) part of the molecule prefers to be in a lipid non-polar environment - The Hydrophilic part prefers to be in a polar aqueous environment.

Question 28

Emulsifier and HBL?

Answer 28

- The emulsifier is characterised by the HBL (hydrophilic, lipophilic balance) value - The continuous phase of the emulsion is usually the phase in which an emulsifier is soluble. - The original HLB scale ranges from 0-20 - An emulsifier with a high HLB value at the upper end of the scale is more soluble in water than oil - Conversely an emulsifier at the lower end of the sale has greater solubility in oil than water - An emulsifier with HLB value in the rage 3-6 is used to stabilise a w/o emulsion - o/w emulsions require emulsifier with a HLB in rage 11-15

Question 29

Examples of emulsifiers?

Answer 29

Glycerylmonostearate(GMS) – Is this an amphiphilic molecule? Yes /No? – Yes , as GMS comprises both a polar head and non-polar tail. Polyglycerylmonostearate(PGMS) – Although PGMS has little effect on interfacial tension it gives long term stability to the emulsion. Promotion of emulsion ≠ emulsion stabilization.

Question 30

Stabilisation of emulsion

Answer 30

Hydration repulsion Electrostatic Steric (see extra notes)

Question 31

Aeration/Foaming?

Answer 31

- A form of colloidal dispersion of gas and liquis - The gas phase dispersed throughout the continuous liquid phase - Aerated cake batter = foam - Cake batter in an emulsion of O/W

Question 32

Foam Vs. Gel?

Answer 32

- Foam is stabilised using a surfactant (Foaming agent) - Common foaming agent is protein: The hydrophidib part which become associated with the gaseous phase and the hydrophilic part of which enters the aqueous phase - Certain emulsifiers such as apha tending emulsifiers also have a part to play in preventing stabilisation of protein foams

Question 33

Purpose of creaming?

Answer 33

Is used in cake making | - the batter combined with the water releases co2 gas which gives volume and height to cake

Question 34

What is Wetting?

Answer 34

- Wetting agents include surfactants such as emulfisiers - Emulsifiers with a hydrophilic lipophobic balance of 8-10 promote the spreading to a liquid over a solid surface by displacing air.

Question 35

what is Plasticisation/tempering used for?

Answer 35

- Tempering step of fluid chocolate in the production of chocolate gives rise to the following desirable characteristics. - Hardness - Met in mouth property - Glossiness - Ease it can be removed from mould - freedom of chocolate from the storage defect of fat bloom

Question 36

What is hydrogenation?

Answer 36

- Process that involves the addition of hydrogen across double bonds in unsaturated fat acids in the presence of a catalyst - Increase in the melting point of glyceride comprising the fatty acids - Increase oxidation in stability of the glyceride

Question 37

Heat and mass transfer?

Answer 37

- Fats fulfil functions on heat and mass transfer | - Frying fats allow the crisp texture on fried foods

Question 38

What is Hydrolysis?

Answer 38

- Water in the food reacts with the frying oils hydrolysing the ester bonds between the glycerol and fatty acids in the glyceride molecules - This results in the formation of diglycerides and monoglycerides - This reaction causes the small and fumes hen oil is heated

Question 39

What is saponification?

Answer 39

- A glyceride in the presence of a strong base (NaOH) undergoes saponification into the Na salts on the fatty acids - Produces soap

Question 40

What is Reversion?

Answer 40

- Slight oxidation of fats and oils through exposure to air can lead to the formation of reversion flavours which differ from one oil to another - Eg the bean flavour in soy oil and the metallic flavour in palm oil

Question 41

What is oxidation?

Answer 41

- Occurs with unsaturated fatty acid chains - initiated by heat and light - The unsaturated fatty acids constituents of the glycerides are prone to form free radicals (loss of electron). Can rect with O2 to form pertly radical

Question 42

What is polymerisation?

Answer 42

- Through frying oil, unsaturated fatty acids combine o form polymers, - Oxidation products such as epoxides which from dimers - The net effect in an increase in oil viscosity and a formation of a varnish on the metal surfaces on the frying impairing heat and mass transfer.

Question 43

What is smoke point?

Answer 43

- The smoke point on an oil or fat in the temp at which, under defined conditions, wisps of smoke are observed - At this temp, volatile compounds such as free fatty acids, and shirt chain degradation products for oxidation, including glycerol come up from the oil.

Question 44

Flash point and ignition point?

Answer 44

- On further heating past smoke point, a small open flam that is passed other the hot oil causes flashes, - More heating then leads to a fire that can be ignited at the fat/oil surface

Question 45

Smoking and ignition?

Answer 45

- Each oil is classified by a specific smoke point, flash point and fire point. - Are lowered by the build up of fatty acids in the oil with frying