Lecture 11: MAP

Question 1

what is MAP?

Answer 1

enclosure of food pdts in gas barrier materials (or films of selective permeability) in which the gas environment has been changed to slow RR to reduce microbial growth and to retard enzymatic spoilage to extend shelf life

Question 2

how is CA/MA inside the package achieved?

Answer 2

by selective diffusion of O2 (into package) and CO2 (out of packae)

Question 3

what does equilibrium of MAP represent?

Answer 3

balance between produce resp and package permeation

Question 4

why is temp management critical for MAP?

Answer 4

b/c resp and permeability both depend on T

Question 5

what is the aim of MAP?

Answer 5

• reduce O2
• elevate CO2

maintain gases at required level

Question 6

what are 2 active components in MAP?

Answer 6

O2 and CO2

rest is N which is more a filler

Question 7

how does increasing O2 conc affect RR?

Answer 7

RR decreases at first to EP (extinction point), then increases after

Question 8

how does increasing CO2 conc affect RR?

Answer 8

RR decreases as CO2 increases

Question 9

what are examples of commodity generated MA (not controlled)

Answer 9

• air tight cold storage rooms
• packaging in films, wraps, bags
• polyethylene liners
• pallet shrouds

Question 10

what are 2 stage operations of MAP?

Answer 10

MA generation

• active process (gas flush) for a quick control of resp, quick control of ethylene and vacuum to remove toxic gases
• passive process (produce resp) is slow and results in some loss of quality

MA maintenance
- through selective permeability
0 film type depends on needs

Question 11

what are types of barriers for the commodity?

Answer 11

1. commodity’s dermal system (epidermis, cuticle, stomata, lenticels) and added barriers (wax coatings or film wraps)
2. package
3. storage room or transit vehicle wall
4. other barriers: consumer packages inside master container and plastic pallet over containers

Question 12

describe film permeability when gas conc is the same inside and outside package

Answer 12

• no exchange of gases until resp starts to deplete O2 and release CO2
• RQ = 1; equal conc gradients are initiated until permeability starts influencing movement of gases

Question 13

describe film permeability when O2 > CO2 gradients

Answer 13

with equal permeability, O2 inward flow rate = CO2 outward flow rate (unless moderated by film permeability)

Question 14

describe 2 equilibrium conditions inside the package

Answer 14

1. film w/ no permeability: high CO2

2. film w/ equal permeability to match respiration

Question 15

describe the permeability of gases for polyethylene

Answer 15

very high permeability to CO2

lower permeability to O2

Question 16

what are factors that affect the atmospheric modifications with polymeric films?

Answer 16

1. commodity factors: RR and RQ; type, maturity, quantity inside package (initial free volume)
2. film/package related factors: type; structure; permeability; thickness; surface area
3. environmental factors: temp, atmospheric composition in package

Question 17

gas flux is proportional to what?

what does this relationship depend on?

Answer 17

change in conc x permeability

J(O2) = K (deltaC x P) O2 = RO2 x Q

J(CO2) = K(deltaC x P) CO2 = RCO2 x Q

depends on K (surface area and thickness of film)

Question 18

resp flux = ?

Answer 18

RR x mass

Question 19

if RQ = 1 and J(CO2) = J(O2), deltaC ratio will determine what?

Answer 19

ratio of P

(deltaC x P)O2 = (deltaC x P) CO2

Question 20

describe complex situations of MAP. What two situations will occur?

Answer 20

when RR does not equal permeation rate due to altered resp/permeation rates during storage

• when resp is greater than permeation
• when permeation is greater than respiration

Question 21

what happens if resp is greater than permeation?

Answer 21

• faster depletion of O2 inside
• greater accumulation of CO2
• damaging of F&V

Question 22

what happens if permeation is greater than resp?

Answer 22

• O2 flows inward (higher levels)
• CO2 flows out (lower levels)
• less effective MA or no MA at all

Question 23

describe the gas flow in and out of a fruit

Answer 23

• H2O out
• O2 in
• CO2 out

Question 24

describe the role of edible films/coatings vs active packaging

Answer 24

edible films: provides MAP within; moisture barrier; biodegradable

active: MAP; moisture barrier; other functions (fungicides, bio-active materials)