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235 Cards in this Set
- Front
- Back
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Why were the preservation processes developed? |
to handle surplus supplies of vegetables and fruits that do not store well |
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Why are some commodities cooled after initial sorting? |
to remove field heat so as to improve quality, shipability and ultimate shelf-life |
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What is Metabolism? |
the sum of constructive (anabolism) and destructive (catabolism) biochemical reactions that continually occur inside living tissue |
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Anabolism |
"constructive" metabolic processes within tissues
Synthesis of proteins, starch, cellulose, and chlorophyll |
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Catabolism |
"destructive" metabolic processes within tissues
degredation of starch into sugars; chlorophyll breakdown, fat breakdown |
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What does knowledge of metabolism allow us to do? |
manipulate commodities for increased storage life |
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An aspect of catabolism is the process known as _______. |
Respiration |
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Five aspects of (catabolism) Respiration |
1. Degradative process
2. Net result => produces energy for biochemical reactions
3. It is a carefully controlled enzymatic process
4. When starch is converted to sugars CO2, water, ATP (useful energy), and waste heat are produced
5. When fats are converted into glycerol and fatty acids, CO2, water, ATP and waste heat are formed |
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What represents a loss in dry matter |
Respiration |
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T/F: Respiration rate is related to the amount of food reserves. |
False; respiration rate is NOT related to the amount of food reserves. |
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Formula to convert Centigrade to Fahrenheit |
°C= (°F-32°)(5)/9 |
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Formula to convert fahrenheit to centigrade |
°F = [(°C)(9)/5] + 32 |
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Q10 definition |
the relationship between a commodity and its respiratory response to an increase (or decrease) in temperature
for the range of 32°F to ~90°F
Quotient; therefore a "pure" number without terms |
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Relationship between temperature and tissue respiration |
Increasing temperature increases tissue respiration |
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At what rate does respiration of a commodity increase in relation to temperature? |
respiration rate of a commodity may increase 2 to 3 times for every 18°F (10°C) increase in temperature |
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Flower Q10 |
much higher: 5-6 |
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How are the units for respiration rate written? |
ml or mgCO2 [produced]/kg[commodity] hr
or
ml or mg O2 [consumed]/kg[commodity] hr |
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0°C to °F |
30°F
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5°C to °F` |
41°F |
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10°C to °F |
50°F |
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20°C to °F |
68°F |
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30°C to °F |
86°F |
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Two processes with respect to respiration |
glycolysis and krebs cycle |
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A sequence of many reactions, each catalyzed by a separate enzyme |
Glycolysis |
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During gylcolysis, Glucose is metabolized to what? |
Pyruvic Acid |
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During what process is glucose metabolized to pyruvic acid? |
Glycolysis |
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Chemical equation of Glycolysis |
1 Glucose --> 2 pyruvic
2 pyruvic --> Acetyl CoA |
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What does the end product of glycolysis depend on? |
the concentration of oxygen present |
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What can come from too high of a stack of potatoes? |
formation of anaerobic conditions resulting in the production of ethanol through fermentation |
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Where does glycolysis occur? |
In the cytoplasm of cells |
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What happens during the Krebs cycle? |
pyruvic acid is converted to acetyl-CoA and fed into a enzymatic system which produce reductants which eventually lead to the formation of ATP molecules |
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What is the ultimate receiver of electrons in the Electron transport chain (ETC)? |
Oxygen |
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What happens when there is an absence of oxygen during the krebs cycle? |
Krebs cycle cannot function without oxygen
the system backs up and ATP production stops
Glycolysis is sped up to keep the plant alive |
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Between glycolysis, krebs, and ETC, how much ATP could you theoretically expect to gain? |
36 (2 from glycolysis and 34 from krebs) |
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Factors affecting respiration rate |
1. Respiratory Substrate
2. Age of tissue
3. Type of tissue
4. Temperature
5. Oxygen level
6. Carbon Dioxide levels
7. Wounding or mechanical damage
8. Plant Disease
9. Lesser extent: cultivar, area of production, growing conditions (irriagtion and fertigation too), growing season |
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Respiratory substrate |
RQ indicates what substrate is being utilized by plant tissues
Carbohydrates, fats, or organic acids |
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RQ |
Respiratory quotient
Ratio of CO2 produced to O2 consumed
indicates what substrate is being utilized by plant tissues (Carbs, fats, organic acids) |
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Respiratory Quotient (RQ) values |
>1 burning organic acids
<1 Burning off fats
~1 Burning carbohydrates |
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T/F: Respiration rates increase as tissues mature |
False: Respiration rate is highest when tissues are young |
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Where does respiration rate begin and stop to increase? |
the respiration rate increases from just above teh freezing point of a commodity to the thermal death point of the commodity |
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Thermal death point |
temperature at which enzymes begin to denature (lose their tertiary and quartenary structures) |
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Thermal death point of tomatoes |
between 130-140°F (relatively high) |
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High levels of oxygen in storage |
harmful due to the oxidation of free radicles |
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How does super ambient levels of CO2 affect respiration? |
retards respiration by inhibiting enzyme function
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what affects on respiration does too high of CO2 levels cause? |
tissue damage (CO2 is toxic in high concentration) |
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What does wounding or mechanical damage do to respiration rate? |
increases respiration |
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T/F: Gas rates depend greatly on temperature |
True |
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plant disease and respiration |
plant disease increases rate of respiration
dying tissues = decrease in O2 and increase of CO2 |
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Methods of slowing down respiration |
1. Lower temperatures
2. Controlled Atmospheres
3. Modified Atmospheres
4. Low pressure (hypobaric) storage
5. Ventilation |
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optimum rates of CO2 and O2 in Controlled atmosphere storage |
CO2: 1-10%
O2: 1-5% |
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What is modified atmosphere storage? |
similar to controlled atmosphere but the gas levels are not precisely controlled
primarily used with packaging; specific plastic packs have been developed for commodities. |
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Low pressure or hypobaric storage |
low pressure reduces oxygen levels and increases the rate of gas release from fruits and vegetables, slowing respiration and reducing storage problems
expensive, potential for implosion, pressure is so low you will die. |
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Ventilation in storage with regards to respiration |
removes heat especially the heat of respiration which increases the respiration rate (only works when the outside air is colder than storage room)
removes undesirable gasses in storage atmosphere, such as ethylene |
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Measuring CO2 |
Gas Chromatograph
Infrared Gas analyzer |
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Measuring O2 |
Gas chromatograph
paramagnetic, polarographic, or electrochemical oxygen analyzers |
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Chemical methods to measuring gasses |
Orsatz analyzer
Much less accurate due to the subjectivity |
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Gas chromatograph |
CO2 and O2 are separated from other components of a gas mixture based on affinity for various absorbents or liquid phases within a column |
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Infrared Gas Analyzer |
detects CO2 in a flowing gas stream through absorption of infrared light rays
Allows for continuous accurate measurements of low levels of CO2
(infrared is good for detecting double bonds between Oxygen such as found in CO2, NO2, etc.)
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Respiratory Drift |
1. Change in rate with time
2. Not a quantitative expression
3. Depicted graphically (upward, downward, unchanging) |
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High pressure vs boiling point |
high pressure = high boiling point (more energy to get to heat of vaporization) |
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Low pressure vs boiling point |
Low pressure = low boiling point (less energy to get to heat of vaporization) |
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Different types of preservation |
Drying
pickling (pickles, sauerkraut, olives)
fermentation (wine, cheese, beer)
sugar preservation (jellies/jams, citron)
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What began with the development of roads? |
commerce |
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How did the development of railroads in the 1800s affect food transportation? |
1. Allowed the transport of perishable goods over long distances relatively quick
2. beginning of non-local marketing of vegetables
3. Became viable with advent of refrigerated cars
4. By 1890, california shipping produce across country |
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What is the single most important means of preserving harvested produce
(what has the greatest effect on the postharvest life of produce?) |
Refrigeration |
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Definition of refrigeratio |
the process of removing heat from or maintaining the temperature of a pre-cooled commodity |
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How does refrigeration work? |
1. Heat moves from an area of greater conentration to an area of lesser concentration
2. heat is moved by conduction, radiation, and convection
3. Source of cooling is a liquid refrigerant that absorbs and releases heat as it is changed from a liquid to a vapor |
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British Thermal Unit (BTU) |
the amount of heat required to raise one pound of water 1°F |
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Parts of a refrigerator |
1. Refrigerant gas (freon) - Ammonia
2. Compressor
3. Condenser
4. Expansion Valve
5. Evaporator |
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Commonly used freon |
Ammonia (NH3) |
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Function of a Compressor |
Raises the pressure of the system, which raises the boiling point of the coolant. |
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Function of a Condenser |
Holds a high pressure from the compressor and accepts the freon gas (ammonia gas) into its tubes where it is then cooled (by air passing through fins) as it passes through converting the gas back into liquid state once the coolant hits its heat of vaporization |
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Function of the Expansion Valve |
once the freon is in liquid form, it flows to the expansion valve which allows more or less refrigerant into the evaporator, depending on the desired temperature. It also regulates the pressure of the evaporator by opening and closing. |
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Function of the evaporator |
The evaporator remains at a low pressure. When it accepts the liquid freon from the expansion valve, the freon travels through the evaporator coils and once again reaches its heat of vaporization, where the liquid then boils. As the freon boils, heat is absorbed from the room to the cooling medium through evaporation. The gas then carries the heat back down, through the compressor and into the condenser, where the heat is then released as it once again reaches the point of vaporization and converts back into liquid. |
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What is the benefit of a small temperature split in a cooler? |
small temperature splits minimize the dehydration of the air in the cooler |
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What happens to the heat exchange as the temperature between the coolant and the room begin to decrease? |
The larger the temperature difference, the faster the heat exchange. So as the temperature difference begins to decrease, the exchange of heat slows |
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How much BTU is absorbed during refrigeration, and where is it absorbed? |
600 BTU is absorbed in the evaporator |
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How much BTU is released during refrigeration, and where is it released from? |
600 BTU is released from the condenser |
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R values |
Higher R value = slower transfer of heat
Lower R Value = faster transfer of heat |
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Why can't a refrigerator be used to cool a home? |
Because the heat released from the coolant (radiating off of the condenser) is put back into the home equally as fast as the evaporator absorbs the heat causing a short circuit |
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What is the function of insulation in a cooler? |
Insulation slows the transfer of heat from high concentration to low concentration
it maintains the balance of heat in a refrigerator system |
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Brine Evaporator |
Keeps ice off of evaporator
Brine solution is washed over evaporator coils to keep ice from forming on coils (increasing efficiency and humidifying the air)
Brine leaks may occur
The salt solution will corrode the metals in the system causing damage. |
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How much water loss will cause damage to produce? |
3-5% water loss will show signs of damage |
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Dry Evaporation |
Air blows directly over the coils
Fins are added to coils to increase surface area and improve efficiency
Frost accumulation on coils reduce efficiency; it is necessary to have a method of frost removal |
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what is the optimal temperature split between the commodity room temperature and the temperature of the evaporator? |
2-3°F
small difference = less dehydration and frost problems
for large differences in cooling, it is necessary to have a lot of cooling surface |
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Most common type of refrigerant for large installations? |
Ammonia |
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Benefits of using ammonia as a refrigerant |
1. Cheap
2. Vapor to liquid at nominal pressures
3. absorbs a great amount of heat upon vaporizing (600 BTU) |
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Disadvantages of using ammonia as refrigerant |
Highly toxic to plant tissue and human health
When ammonia vapor combines with water it forms a highly corrosive solution
Ammonia can be explosive in certain concentrations |
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Halide Refrigerants |
Flurocarbons and hydroflurocarbons
(Freon 22, R134, R134a) |
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Benefit of halide refrigerants |
non-toxic and non-flammable |
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disadvantage of halide refigerants |
causes ozone reduction in upper stratosphere |
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Low ozone depleting refrigerants |
CO2 - promising but potentially toxic above 5% in air due to displacement
Propane |
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What is refrigeration load calculated as? |
tons of refrigeration |
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What is 1 ton of refrigeration equal to? |
1 ton of refrigeration is equal to the amount of heat absorbed by 1 ton of ice melting at 32°F within 24 hours (the ice must melt completely within 24 hours)
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How much BTU is required to melt 1 lb of ice at 32°F? |
144 BTU to melt 1lb of ice at 32°F |
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How much BTU to melt 1 ton of ice at 32°F? |
288,000 BTU is required to melt 1 ton of ice at 32°F |
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How much heat is absorbed by 1 ton of refrigeration in one hour? |
12,000 BTU/hr |
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What must the refrigeration requirement of any storage facility be based on? |
Peak refrigeration load |
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What does the peak refrigeration load depend on? |
1. The amount of commodity received each day.
2. The temperature of the commodity at the time it is placed under refrigeration
3. The final temperature of the commodity (how much cooling does it require to reach that temp)
4. Specific heat of the commodity
5. The speed of cooling required. |
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Sources of heat that determine refrigeration requirements |
1. Sensible or field heat
2. Vital heat or heat of respiration
3. Heat leakage (opening doors, cracks, or poor insulation)
4. Utility heat (forklifts, equipment, workers)
5. Containers (number, size, material)
6. Size of storage and relative humidity (cooling water in air requires more refrigeration) |
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What is precooling |
Rapid removal of field heat before shipment or cold storage
(5 min to 3-4 hours) |
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What is the purpose of precooling |
reduces refrigeration needs in storage and during transport of produce which cuts down on cost of storage facility |
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How do most precooling methods work |
transfer heat from the commodity to a cooling medium such as air or water |
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What is the relationship between the time to remove field heat and the storage life of that product? |
the quicker field heat is removed, the greater the storage or shelf life of the commodity |
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What determines the amount or length of time for precooling? |
the commodity temperature |
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Half cooling time |
the time required to reduce temperature difference between commodity and coolant by 1/2.
independent of initial temperature and remains constant throughout cooling period
constant dependent on commodity |
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What does half cooling time depend on? |
1. accessibility of product to cooling medium
2. temperature difference between product and coolant
3. Velocity of the coolant
4. type of cooling medium
5. commodity being cooled |
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What does the accessibility of the commodity to the cooling medium depend on? |
1. how produce is packed in the container (tight or lose; bagged or naked, etc.)
2. Type of container being used (number of vents, size of vents)
3. Placement of vents (allowing for pass of media) |
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Types of precooling |
1. Contact Ice, top ice
2. Forced Air or Pressure cooling
3. Hydrocooling
4. Vacuum Cooling |
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What types of produce should be precooled using top icing? |
Broccoli, leafy vegetables - mustard, bok choy, kale, endive, green onions, sometimes carrots and radishes |
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why don't buyers like top icing? |
half of the weight is water and ice |
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Explain how pressuring cooling works |
by lowering the atomspheric pressure of the room, the water reaches a boiling point and cools the product through evaporation. |
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Explain how forced air cooling works |
pressure systems force cool air rapidly through the boxes and around the product, thus cooling it
an atomizer may be put into the room to minimize water loss |
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T/F: Increasing air velocity during forced air cooling not only decreases cooling time but actually reduces the amount of water lost from the product |
True |
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T/F: Plastic film wrapped around produce reduces the amount of water loss. |
True |
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Benefits of Forced-air cooling |
Gentle - adaptable to many products
Relatively easy to set up
Not much energy to run it; you're paying for the fan |
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Problems with pressure cooling |
moisture loss unless humidity is 100%
Takes 2-3 times longer than hydrocooling (2.5 - 3 hours) makes a big difference in shelf life. |
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How could moisture loss be minimized in a pressure cooling system |
maintain temperature of coolant close to 32°F so that minimize condensation on coils
maintain the optimal air velocity
use humidifiers and/or plastic wrap |
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Which hydrocooling method cools the quickest? |
immersion is probably the quickest method due to the most contact with produce |
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Advantages of hydrocooling |
1. Water is an excellent coolant
2. Relatively quick method
3. Washes produce
4. Rehydrates produce; moisture loss is no longer a problem (this is why it is preferred for celery)
5. Water prevents moisture loss from produce |
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Disadvantages of hydrocooling |
Need flow through vents if in boxes; boxes must be waterproof
Aqueous disinfectant must be used (typically chlorine, chlorine dioxide, or ozone)
Increased decay from recycled contaminated water |
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Chlorine pH |
pH sensitive (6-7)
99% active chlorine at pH6; turns into hypochloronic acid (HOCL)
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Health risks associated with Chlorine |
can form trihalomethanes which is formaldehyde |
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Forms of Chlorine |
gas (Cl2)
sodium hypochlorite (NaOCL) or calcium hypochlorite (Ca(OCL)2)
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Factors affecting chlorine effectiveness |
1. pH of solution (active form, hypochlorous acid, HOCL)
2. Concentration of available chlorine
3. Contact time
4. Temperature
5. Organic Matter
6. Type of microorganism |
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Chlorine level depends upon _____ and _____ |
commodity and its tolerance
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recommended ppm for chlorine |
100-150ppm
often much less (50-100 ppm or less) |
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high pH chlorine solution |
very poor control |
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low pH chlorine solution |
if pH is too low, you have out-gassing of chlorine causing health concerns |
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Problems with chlorine |
1. Health Risk
2. Combines with organic matter to produce trihalomethanes (formaldehyde) or at a high pH, with ammonia to produce chloramines |
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Chlorine alternatives |
chlorine dioxide
ozone
UV
vacuum cooling |
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Chlorine Dioxide benefits |
effective over pH range of 6-10
2.5x more oxidizing potential
used at concentrations of 3 to 5 ppm
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Disadvantages of Chlorine Dioxide |
Cannot be transported; must be produced on site; expensive
Toxic to humans and it commonly off-gasses from wash water; closed systems are necessary if workers are present
Doesn't produce trihalomethanes but can produce chlorite and chlorate
explosive at concentrations >10%
simple assays to determine levels are not currently available |
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Benefits of ozone |
one of the strongest oxidizing agents available
half-life of about 15 minutes at STP |
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Disadvantages of Ozone |
generated on site; generation is expensive
difficult to maintain levels above 1ppm
works best at pH of 6-8
Toxic above 4ppm
highly corrosive and requires stainless steel
water filtration required so organic matter doesn't destroy the ozone |
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UV Sanitation |
not practical at this time but may be used for water disinfecting
water requires filtration to remove particulates for best efficacy |
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How could chlorine efficacy be improved? |
1. Surfactants
2. Ultrasonics
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T/F: Hydrocooling can be done with room temperature water |
False; water should be kept cool (at about 33°F) |
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Commonly hydrocooled commodities |
asparagus, celery, cantaloupes, green peas, radishes, sweet corn (snap beans for processing) |
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Commodities that are sometimes hydrocooled |
cucumbers, peppers, other melons, and early-crop potatoes |
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Flash point |
point at which the boiling point is equal to the temperature of the commodity |
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T/F: forced air cooling has the best water loss uniformity |
false; vacuum cooling has the most uniform water loss |
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Ammonia coils in Vacuum cooling |
contains ammonia coils but it does not cool the product; it only freezes water vapor to reduce the relative humidity so that less energy is needed for the vacuum pump; thus increasing the potential efficiency of the system |
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At what temperature does water boil? |
212°F (100°C) |
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What is boiling? |
rapid change of a liquid to a gas resulting in gas rapidly escaping from many points within the liquid --> turbulent loss of gas from the liquid (gas forms on particles within the liquid as well as on contact points on surface of containing vessel)
only a process by definition |
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Heat of fusion of water |
144 BTU/lb |
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Heat of vaporization |
972 BTU |
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To raise or lower the temperature of water between freezing and boiling requires _____ energy than heat of vaporization and heat of fusion. |
less energy; 1 BTU
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At what pressure does water boil at 32°F? |
4.6 mm mercury |
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How many BTUs are removed from produce in vacuum rooms |
972 BTU/lb |
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T/F: Boiling is a process which removes heat but which itself is not dependent on sensible heat |
True |
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Which precooling process is most efficient with a high surface area/mass product? On which products does this work the best on? |
Vacuum cooling
leafy vegetables, celery, cauliflower, sweet corn, lettuce |
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When using vacuum cooling, what variables are good to consider? |
time to cool varies with density of the commodity
The denser the product the longer it takes to cool |
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What is the percent water loss to temperature ratio for produce? |
For every 11°F drop in temperature there is a ~1% loss of water |
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What percent of water do commodities lose during vacuum cooling? |
1.5 to 5%; however, since the waterloss is equal throughout the entire product, damage is not noticeable until after 5% loss |
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Explain the function of a hydrovac |
a vacuum cooling system with an atomizer that mists the produce during cooling. The water on the surface of the products evaporates, taking the heat from the product, thus cooling the product |
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T/F: Benefits of precooling will be lost if products are not promptly refrigerated afterwars |
True |
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Ethylene is known as what kind of hormone? |
the ripening or senescent hormone |
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What has ethylene historically been used as? |
ripening agent for fruit |
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What were kerosene stoves used for in 1912? |
producing ethylene in order to degreen citrus |
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Who isolated ethylene as the active ingredient in incomplete combustion of kerosene in 1924? |
Denny; he then identified ethylene as the active component in the combustion fumes from the kerosene stoves and described the use of ethylene as a ripening hormone |
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Endogenous |
internal cause or origin |
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What did crocker, Hitchcock, and Zimmerman propose in 1935? |
they proposed that ethylene is an endogenous fruit hormone |
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what did Yang and Adams determine in 1979? |
determined that methionine goes to SAM to ACC to ethylene in apples |
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Chemical symbol for ethylene |
C2H4 |
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what are the products of ACC oxidase in the presence of O2? |
CO2 and cyanide |
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What promotes ACC? |
fruit ripening, flower senescence, wounding, chilling, drought stress, flooding stress |
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Ethylene imitators |
Propylene (tricarbon compound)
acetylene (triple bond)
many of same effects as ethylene, however the concentration necessary for action is 100 to 1000 times greater than for ethylene |
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Where is ethylene produced? |
endogenous plant hormone and it is produced within all tissues of higher plants
does not fit the "classical" definition of a hormone |
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T/F: Plants are the only things able to produce ethylene |
False; ethylene is produced by basically all living creatures including warm-blooded animals, though in very small amounts
fungi, bacteria, decomposing wood, burning rubber, and decaying rubber gaskets |
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What is methionine? |
an amino acid building block of protein that is a precursor for ethylene |
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What machine is used to measure ethylene? |
Gas chromatograph |
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at what concentration is ethylene easily measured? |
2-3 ppm |
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What does increased ethylene production trigger in fruit? |
increased ethylene production triggers the climacteric in fruit which undergoes this type of ripening |
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What does ethylene action depend on? |
1. Physiological age of the tissue
2. Temperature (cool = more ethylene)
3. Concentration
4. Duration of exposure |
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What can override physiological age factor for ethylene action? |
concentration and duration
for climacteric fruits (tomato, banana) ethylene induces the climacteric in immature fruits and accelerates the ripening of physiologically mature fruits |
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What products are commonly ripened with ethylene? |
Tomatoes, bananas, honeydew melons |
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Shatter |
Flower falling off stem |
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Physiological roles of ethylene |
1. respiration in fruits, flowers, vegetables
2. Chlorophyll degradation
3. Abscission
4. Softening - a change in texture. Can also promote toughening as with asparagus
5. Many other senescent and growth effects
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How might auxin affect ethylene production? |
Auxin at high enough concentrations induces ethylene production |
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Vertilization |
induction of a flower structure (too cold for tissue to respond, it will not respond) |
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How might one promote uniformity of tomato ripening for once-over mechanical harvesting? |
spray with ethephon (ethrel, Florel)
spray about 1-2 weeks before harvest when about 10% of tomatoes are red, and 90% are green
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Ethephon |
(2-chloroethyl)phosphonic acid
Cl-CH2-CH2-PO3H2 + 2OH- CL- + [CH2 = CH2] + H2PO4- + H20 |
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At what pH do you get ethylene release after applying ethephon? |
pH 7-8
very little ethylene released at pH 4.1 |
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How is ethylene used in pineapple production? |
used to induce flower formation in pineapples for greater and more uniform harvests |
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at what temperature is ethylene most effective? |
68°F |
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how can the action of ethylene be inhibited? |
high CO2 or lack of oxygen |
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Temperature and ethylene efficacy. |
The lower the temperature above freezing, the less ethylene activity and production there is
at temperatures higher than 85-86°F, ethylene response is present, but there is less production, therefore you see less effect |
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Ethylene concentration and duration for fresh market tomatoes |
100 ppm for 1-2 days |
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Ethylene concentration and duration for bananas |
0.1% (1000ppm) for 24 hours
fruit is gassed before or after it is shipped, but definitely before distribution |
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How does CO2 affect ethylene efficacy? |
CO2 directly competes for the sites of action of ethylene (at levels greater than or equal to 1%) |
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how does oxygen affect ethylene efficacy? |
oxygen is absolutely needed to produce ethylene (at levels less than 8%, start getting reduction in ethylene production) |
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Cabbage exposed to ethylene |
not extremely sensitive:
10 ppm at 1°C for 5 weeks will bring pronounced loss of color
1ppm at 32°F for 6 months will also bring loss of color |
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Cucumber exposed to ethylene |
Very sensitive
.01 to 10ppm ethylene can cause yellowing
Between 5-10 ppm, get tremendous amounts of tissue softening in cucumber |
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In what commodities does ethylene commonly cause abscission? |
cabbage, cauliflower, Chinese cabbage, eggplant
.8ppm for 2 days and get stem and calyx abscission
get big promotion in decay
with 2 day exposure, have reduced storage life of about 100% |
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Asparagus and ethylene |
100 ppm for 1 hour accelerates lignin biosynthesis
toughness is increased, particularly at the bottom of the spear |
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carrots and ethylene |
ethylene promotes isocoumerin formation which imparts a strongly bitter flavor to the tissues |
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Ethylene and irish potatoes |
thought to promote sprouting |
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lettuce and ethylene |
very sensitive - russet spotting of midribs and lower leaf blades |
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Broccoli and ethylene |
sensitive; yellowing of buds and buds abort, falling from the head |
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Kiwi fruit and ethylene |
50 ppm enhances softening at 0°C |
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Ethylene and floriculture problems |
Dried sepal of orchids
floret drop of snapdragons
sleepiness of carnation buds
malformation of rose buds
epinasty of ornamental leaves |
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Epinasty |
leaves twist and turn under |
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What causes ethylene production in rotting tissues? |
from the dying tissues themselves and in some cases the microbes destroying the tissues |
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T/F: Internal combustion engines can produce enough ethylene to become a problem |
True; specifically diesel and propane engines |
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How can ethylene concentration be increased in a room? |
gas tanks bled into rooms, mixed with fans, to achieve desired level
ethylene generators - ethanol with catalyst- ethanol is "cracked" to produce ethylene
ripe fruits may be used to stimulate unripe fruits (old school method)
Chemicals such as ethrel, Florel, etc. |
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Potassium permanganate (KMnO4) |
used for ethylene removal in storage
safe method
usually spray K-permanganate solution onto solid carrier to produce a granule with a large surface area (aluminum oxide, vermiculite, perlite, pumice, brick)
large areas; use air blowing through layers of reactant
small areas: add sachet of purafil (like in boxes of kiwi being shipped)
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Purafil |
well known commercial name for a ethylene destroying granule
small and pink; but when ethylene is destroyed, the permanganate is reduced, turning brown
only about 5% KMnO4
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Activated Charcoal |
adsorbs ethylene and can be reused |
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Brominated charcoal |
Destroys ethylene |
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UV scrubbers |
produce ozone which destroys ethylene while being destroyed itself |
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catalytic oxidizers |
platinized surfaces in contact with heated air containing ethylene; ethylene destroyed |
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Ventilation |
at night to reduce refrigeration requirement to cool incoming air |
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Ethylene action inhibitors |
silver (Ag+)
Aminooxyacetic acid (AOA) and aminoethoxyvinylglycine (AVG)
1-MCP: 1-methylcyclopropene |
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At what concentration is ethylene explosive? |
3.1 to 32% in air |
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Silver as ethylene inhibitor |
irreversibly binds to ethylene receptor preventing ethylene action
very effective, easy to apply
costly
heavy metal with serious health effects, use requires special considerations to trap and dispose of used solution
industry rapidly abandoning use of this chemical |
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1-methycyclopropene (1-MCP) as ethylene inhibitor |
irreversibly binds to ethylene receptor
easily applied fumigant
since plants continuously produce receptors, commodity can slowly become sensitive to ethylene during storage
economical
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Ethyl-bloc |
trade name for 1-MCP
sold by floralife, a subsidiary of Rohm and Haas.
for flowers only |
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Smartfresh |
Trade name for 1-MCP
sold by agrofresh, a subsidiary of Rohm and Haas.
Registered for use with apples, pears, cantaloupes, avocados, tomatoes, and bananas |
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How does aminooxyacetic acid (AOA) and aminoethoxyvinylglycine (AVG) act as an ethylene inhibitor? |
they inhibit the action of ACC oxidase, an enzyme which converts 1-aminocyclopropane-1-carboxylic acid (ACC) into ethylene, thus reducing endogenous levels of ethylene |
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T/F: avoiding temperature fluctuations in storage is a method of minimizing water loss from stored produce |
True
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T/F: It is often a good strategy to precool a commodity before packing it |
True |
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T/F: mature (fully grown) tissues usually respire more rapidly than young tissues |
False |
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T/F: REspiration represents a loss in dry matter (food reserves) for the plant |
True |
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T/F: sucrose and cellulose are major storage forms of carbohydrates in plants |
False |
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T/F: the heat of vaporization of a commodity is the amount of heat 1 lb of the substance must release to change from a gas to a liquid |
True |
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T/F: The Krebs cycle does not function in the absence of oxygen |
True |
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T/F: The ultimate receptor of electrons during aerobic respiration is oxygen |
True |
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At a given concentration, cooling your wash water will make chlorine (more/less) effective |
less effective |
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Definition of field heat |
The amount of heat, due to the sun, that must be removed from a commodity to achieve its storage temperature |
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For any cooling commodity or cooling method combination, the factors that will determine the value for the half-cooling time includes |
the cooling medium
access of the medium to the commodity
the velocity of the cooling medium |
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When adding chlorine to water, the active ingredient is |
HOCl |
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When determining the refrigeration capacity needed for a precooler, some of the things that must be considered are: |
the expected respiratory heat of the commodity under the "worst case" conditions
Heat of commodity container under worst case conditions
sensible heat of commodity under "worst case" conditions |
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T/F: the act of boiling is dependent on sensible heat |
False; water can boil just as easily at 32°F as 212°F |
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When inspecting a refrigerator, the expansion valve |
regulates the flow of refrigerant into the evaporator coils
allows a pressure drop on the surface of the refrigerant |
