Lecture 9: Special MA systems

Question 1

membrane CA is based on what?

Answer 1

gas diffusion through special films to achieve and maintain CA

idea is from use of plastic films as pre-packaging material

uses membranes with differencial permiability with respect to CO2 and O2

Question 2

with membrane storage systems, the resulting CA condition depends on what?

Answer 2

• permeability, A of membrane, conc gradient
• resp rate, quality of produce
• both permeability and resp rate depend on many factors (temp, gas conc…)

Question 3

what does Fick’s law state?

Answer 3

gas flux is propertional to chance in conc x permeability

J = K * conc * P * A

Question 4

describe the O2 and CO2 flow rate with a membrane that allows 19% O2 in and 5% CO2 out

Answer 4

O2 inward flow rate = Co2 outward flow rate * (19/5)

Question 5

what is the assumption about equal permeability to O2 and CO2?

Answer 5

O2 absorbed = CO2 released

Question 6

is it better for the membrane to be more permeable to CO2 or to O2?

Answer 6

more permeable to CO2

• can do this by inversely matching permeability ratio with conc ratio

ex. if O2 in rate = CO2 out rate * 19/5
- then make O2 permeablility to be equal to CO2 permeability * 5/19

Question 7

describe membrane storage systems from 1960’s to now

Answer 7

60: Atmolysair and Marcelin
70s: impermeable membrane and silicon elastomer window to control atm inside
80s: MA packaging using polymers
90’s to now: active packaging

Question 8

what is hypobaric storage?

Answer 8

form of CA storage where produce is stored at very low pressures under continuous flow of saturated air

Question 9

what are components in hypobaric storage?

Answer 9

• gas/air tight chamber
• vacuum pump
• pressure regulator
• flow regulator
• humidifier
• refrigeration and temp control

Question 10

what are advantages of outward diffusivity?

Answer 10

• better quality
• better removal of ethylene, CO2 and toxic volatiles
• very small conc diff
• efficient flushing due to continuous flow

Question 11

LPS yields ___ (lower/higher) heat of respiration

Answer 11

lower

Question 12

what kind of heat removal does LPS have?

Answer 12

indirect (jacketed)

Question 13

what does LPS stand for?

Answer 13

low pressure systems

Question 14

what are other names of hypobaric storage systems?

Answer 14

vacuum or LPS

Question 15

what are advantages of LPS?

Answer 15

• low heat of resp
• indirect heat removal (jacketed)
• reduced atm comp at reduced pressures
• increased gas diffusivity
• reduced conc gradients
• good control of O2 levels

Question 16

what are disadvantages of LPS?

Answer 16

• expensive
• involves special structures
• some stored produce lacks flavour
• inward implosion