Food Chemistry

Question 1

What is water activity

Answer 1

Aw is the water activity is a term that relates to the ability of a microbe to grow in a particular environment

Question 2

Moisture sorption isotherm

Answer 2

Moisture sorption isotherm is used to determine relationship between water content & water activity

Question 3

Water-holding capacity

Answer 3

Water-holding capacity (WHC) results from the physical entrapment of water within a food matrix that restrict flow but no other physical properties of water

Question 4

How are carbohydrates bonded

Answer 4

Glycosylic bonds

Question 5

Retrogradation

Answer 5

Retrogradation is the crystallization of starch molecules such that they begin to separate from other molecules present in the product

Question 6

How are digestible and non-digestible carbohydrates differentiated

Answer 6

Recognition

Question 7

Is glucose an aldehyde or ketone

Answer 7

aldehyde

Question 8

What are reducing sugars

Answer 8

Carbohydrates that are aldehydes are reducing sugars and can react with amino group of protein / amino acids i.e. Maillard reaction

Question 9

Why are carbohydrates soluble

Answer 9

Prescence of oh group

Question 10

What is tollens reagent used for

Answer 10

to identify reducing sugars/ aldehydes

Question 11

What are lipids

Answer 11

Soluble in organic solvents but not water

Question 12

3 main groups of lipids

Answer 12

triglycerides, sterols, phospholipids

Question 13

Triglycerides

Answer 13

3 fatty acids side chain

Question 14

Phospholipids

Answer 14

1 polar head with 2 fatty acid chains

Question 15

Sterols

Answer 15

ring structure but does not contain fatty acids

Question 16

What are Saturated fatty acids

Answer 16

They contain no c-c double bonds

Question 17

What can lipids act as

Answer 17

antioxidants & pro-vitamins

Question 18

What are trans fatty acids at room temperature

Answer 18

Solid

Question 19

Saturated fatty acids are _ are room temperature

Answer 19

solid

Question 20

Lipid hydrolysis

Answer 20

Lipid hydrolysis involves separation of a fatty acid from the glycerol backbone or phospholipid
I produces a free fatty acid & glycerol
If the free fatty acid is short-chained, it will be volatile and contribute to the odor of the food (Hydrolytic rancidity)

Question 21

Lipid oxidation

Answer 21

Lipid oxidation is a reaction of lipids with oxygen that proceeds through a free radical mechanism
Free radical consist of carbon atom with an extra electron resulting from removal of hydrogen atom allowing oxygen to attach to the free electron resulting in lipid hydroperoxide
It can generate volatile compounds that have an off-flavor
Saturated fatty acids are unable to undergo lipid peroxidation due to lack of double bonds and they tend to be more stable

Question 22

What do antioxidants do

Answer 22

Antioxidants inhibit or retard oxidation through one or more mechanisms

Question 23

Why does trans fatty acids have better van der Waals interactions

Answer 23

Saturated fatty acids tend to have stronger van der Waals interactions with other saturated fatty acids because they can stack together and form a repeating structure, very similar to a crystalline structure

Question 24

Why dies cis fatty acids have weaker van der waals interactions

Answer 24

Cis double bonds form a kink in fatty acids which interfere with stacking & interactions causing weaker Van Der Walls interactions causing it to be liquid at room temperature

Question 25

What can phospholipids be used as

Answer 25

emulsifiers in food and water

Question 26

What are proteins

Answer 26

sequence of amino acids linked by peptide bonds

Question 27

Where does the hydrophilic side chain fold to

Answer 27

Hydrophilic side chain tend to be on the surface exposed to aqueous environment

Question 28

Where does the hydrophobic side chain fold to

Answer 28

Hydrophobic side chain fold towards the core of the protein

Question 29

What are enzymes

Answer 29

Proteins which catalyze chemical reactions

Question 30

What does blanching do to enzymes

Answer 30

Blanching can denature enzymes to prevent enzymatic reactions in fruits & vegetables

Question 31

What does heating do to enzymes

Answer 31

Heating will cause the enzyme to unfold and disrupt its structure (denaturation)

Question 32

Cellular compartmentation

Answer 32

Cellular compartmentation is to control enzyme reaction in plant & animal tissue

Question 33

What are enzymes affected by

Answer 33

It is affected by pH, moisture content of food, storage temperature, presence of oxygen & carbon dioxide & light

Question 34

What are alkaloids

Answer 34

Alkaloids are naturally occurring alkaline organic compounds which contain nitrogen atom(s) in their structures

Question 35

What do sequestrants or chelating agent do

Answer 35

Sequestrants or chelating agents bind metal ions preventing them from oxidizing fats

Question 36

To participate in crosslinking what is needed

Answer 36

Multivalent cations

Question 37

What are the properties of whey protein

Answer 37

Whey proteins are sensitive to heat and will unfold to expose their hydrophobic surfaces which will interact with each other to form a gel

Question 38

What are Cassin proteins

Answer 38

Cassin proteins are heat stable but will coagulate in acidic pH as casein proteins are negatively charged. In acidic pH, the proteins will become neutral & coagulate due to hydrophobic interaction

Question 39

How is a gel formed

Answer 39

A gel is formed when polymers interact and form cross link

Question 40

What is a sol

Answer 40

a sol is when a solid is dispersed in liquid

Question 41

what is a gel

Answer 41

a gel is when a solid is dispersed in liquid

Question 42

What is a emulsion

Answer 42

an emulsion is when liquid is dispersed in liquid

Question 43

What is a foam

Answer 43

a foam is when air is dispersed in liquid

Question 44

What is a colloidal system

Answer 44

Particles dispersed in a medium that are suspended that is large enough to scatter light.

Question 45

What do carbohydrates do in a colloidal system

Answer 45

They are hydrolysed and interact with water. When cooled it will form a gel or a vicious paste

Question 46

What does high HLB indicate

Answer 46

The emulsifier is more soluble in water in oil emulsion

Question 47

What does cartorenoid do

Answer 47

It will bound to protein to give food its pigment

Question 48

What happens in the Maillard reaction

Answer 48

pyrazine compounds is formed, It contributes to the roasted flavor & aroma of foods

Question 49

what is enzymatic browning catalysed by the enzyme polyphenol oxidase

Answer 49

This enzyme catalyses the oxidation and polymerisation of polyphenols present in fruits and vegetables

Question 50

Are naturally occurring pigments more or less shelf stable

Answer 50

Less shelf stable

Question 51

How is spoilage prevented

Answer 51

Antioxidants are added to oil to prevent spoilage Oxidation is catalyzed by transition metals, adding sequestrants can retard oxidation Additives that slow down or prevent growth of microorganisms are preservative

Question 52

What are natural additives

Answer 52

Additives derived from natural food sources