Lecture 9: Special MA systems Flashcards
membrane CA is based on what?
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
with membrane storage systems, the resulting CA condition depends on what?
- permeability, A of membrane, conc gradient
- resp rate, quality of produce
- both permeability and resp rate depend on many factors (temp, gas conc…)
what does Fick’s law state?
gas flux is propertional to chance in conc x permeability
J = K * conc * P * A
describe the O2 and CO2 flow rate with a membrane that allows 19% O2 in and 5% CO2 out
O2 inward flow rate = Co2 outward flow rate * (19/5)
what is the assumption about equal permeability to O2 and CO2?
O2 absorbed = CO2 released
is it better for the membrane to be more permeable to CO2 or to O2?
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
describe membrane storage systems from 1960’s to now
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
what is hypobaric storage?
form of CA storage where produce is stored at very low pressures under continuous flow of saturated air
what are components in hypobaric storage?
- gas/air tight chamber
- vacuum pump
- pressure regulator
- flow regulator
- humidifier
- refrigeration and temp control
what are advantages of outward diffusivity?
- better quality
- better removal of ethylene, CO2 and toxic volatiles
- very small conc diff
- efficient flushing due to continuous flow
LPS yields ___ (lower/higher) heat of respiration
lower
what kind of heat removal does LPS have?
indirect (jacketed)
what does LPS stand for?
low pressure systems
what are other names of hypobaric storage systems?
vacuum or LPS
what are advantages of LPS?
- 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
