Intrinsic factors

Question 1

How to measure water activity

Answer 1

• put sample in sealed container and wait until the vapour pressure of the water in the sample and the water in the air equilibrates
  the relative humidity of the air is equal to the water activity

Question 2

Inhibitors in food examples

Answer 2

• lysozyme in egg whites: cleaves the bonds in peptidoglycan
• eugenol in cloves - essential oil in the spice that damages membranes
• agglutinins in milk - clumps microbes
  menthol in mint - disrupts biofilm production

Question 3

Modified atmosphere packaging

Answer 3

CO2 has an inhibitory effect on many microbes
N2 creates an inert atmosphere, retards microbial growth and slows rancidity
O2 maintains oxy-myoglobin in packed meat Problem:
Product and microbial respiration (removal of O2 by microbes)
Dissolution of CO2 into aqueous phase
Differing rates of gaseous exchange across various types of packaging film

Question 4

Controlled atmosphere packaging

Answer 4

• constant gas comp.
• e.g. apples stored in 10% CO2 to reduce ethylene ~ causes post-harvest ripening in fruits

Question 5

Active packaging

Answer 5

• components that control moisture, generate O2, control CO2 and remove odours by oxygen scavengers

Question 6

Temperature groups in bacteria

Answer 6

Thermophiles: optimum at 55
Mesophiles: optimum at 35
Psychrophiles: “ “ 15
Psychrotrophs: grow at refrigerator temps (0-5)
Thermoduric: survive pasteurisation