The document discusses ratio control in process systems where the ratio of flows between two streams is maintained at a setpoint by controlling one of the streams. A ratio controller measures disturbances in the flows and adjusts the controlled stream to keep the ratio at the desired level while the other stream remains uncontrolled. It also provides information on controlling the atmosphere during storage of fruits and vegetables using control atmosphere (CA) and modified atmosphere (CA) techniques to restrain their respiratory activity and metabolic processes to extend shelf life. Various gases like oxygen, carbon dioxide and ethylene are modified and controlled surrounding the produce.

1. Flow Ratio Control
A ratio controller is a special type of feed forward controller
where disturbances are measured and their ratio is held at a
desired set point by controlling one of the streams. The other
uncontrolled stream is called wild stream. The ratio of flow rates
of two streams are being held at a desired ratio by controlling the
flow rate of one stream. The flow rates are measured through
flow transmitters (FTs).

3. Control atmosphere (CA) and Modified
atmosphere (MA) storage
• Fruits and vegetables are still alive after harvest, it is necessary to restrain
their respiratory activity.
• Metabolic activity changes color, flavor, aroma and softening changes in
commodities. The energy needs usually obtained from respiration.
• Respiration is basically characterized by O2 consumption and CO2
emission.
• Control of respiration
• 1-Storing at low temperatures.
• 2-Usinge chemicals i.e. 1-MCP
• 3-Controlling the atmosphere surrounding the harvest produce.
• 4-Combination of them.

4. Control atmosphere (CA) and Modified
atmosphere (MA) storage
• Extended shelf life
• 1-Harvesting at optimum maturity, minimum mechanical injury, proper
sanitation procedures, and optimal temperatures and RH are maintained.
• 2-Modification and control of O2, Co2 and ethylene surrounding the
produce to level different from those in normal air.
• 3- This modification is commonly based on the effect of low O2 or
moderate Co2 to restrain respiration, because both O2 and Co2 are
biological-active molecules that play a decisive role in primary and
secondary metabolic processes in plant organs.
• Their global influence on metabolism has led to their use for modification
of plant behavior with the purpose of extending both storage duration and
shelf-life.

5. Modified of the atmosphere
• The principle of storage of fruits and vegetables under a MA consist of a
change of the quantitative relation of the normal ambient air components
by eliminating or adding gases in a refrigerated and gastight area.
• Depending on how the modification of the atmosphere is reached and
applied, this technique is known as control atmosphere (CA) or MA.
• CA storage consists of a permanent stable control of the gas composition
that surrounding produce during refrigerated storage or transport at
optimal temperature and RH in an airtight cold room or container.
• MAP When the generation and stabilization of favorable atmosphere are
obtained by packaging refrigerated produce in closed polymeric films of
reduced dimentions (bags, boxes, pallets), the technique is called MAP.

6. The beneficial effects of CA and MAP depend
on:
• Produce itself (Species).
• Cultivar.
• Growing conditions.
• Harvesting system.
• Physiological stage.
• Post-harvest handling.
• Gas composition.
• Storage temperature and
• Time

7. Beneficial effects (MAP)
• 1-O2 delays ripening at <8 kPa, lower the O2 concentration the, greater
the effect.
• 2-Higher CO2 levels (above 1 kPa) decrease or inhibit ethylene Reduced
biosynthesis. These effects are additive to those of reduced O2
atmosphere.
• 3-MAP limits softening by decreasing lignification or inhibiting
polygalacturonase activity.
• 4-Colour preservation by the inhibition of important reactions in a number
of tissues i.e. chlorophyll degardation.
• 5-MAP also seems to preserve nutritional value (Organic acid, Vitamine A
and C. No sugar changes
• 6-Reduction of chilling injury.
• 7-Very low O2 (0.5 kPa) and very high CO2 (>40 kPa) levels have the
potential to act as insect control.

8. 2-Benefical effects (MAP)
• 8-MAP can replace or reduce the dose of certain postharvest chemical e.g.
diphenylamine or daminozide against scald in pears and apples.
• 9-Prolong the pre-climacteric and climacteric periods and therefore
produce can be harvest in a physiological stage closer to full maturity to
ensure better sensory characteristics.
• 10-The use of essential oils (eucalyptol, eugenol, mentol or thymol) seems
to improve the benefical effects of MAP.
• 11- After MAP effects (respiration, softening, colour change ..).