Postharvest Sample Questions

Transcription

1 What is the physical principle that allows mechanical refrigeration systems to remove heat from the storage environment? Draw or describe the basic components of a compression refrigeration system (=the most common type). Describe three ways one might cool storage facilities. Describe what important factors you would need to consider when designing a cold storage facility? In determining size of refrigeration system for a cold storage room, what sources of heat must be accounted for? How can warm air intrusion be minimized when traffic through cold room doors is high? How does the evaporator coil area and the temperature drop across the evaporator coil affect the relative humidity of a storage room? A (larger/smaller) coil would tend to maintain higher room relative humidities. (circle one). 1

2 How does ice build up on the evaporator affect room relative humidity? How might added humidity affect the ice build up? How might one reduce the ice buildup? In a typical mechanical refrigeration system for storing produce, a temperature difference of 5-10 C is maintained between the evaporator coils and the air, which results in relative humidity of around 70-80%. A temperature difference of 0.5 C would be expected to result in about 95% relative humidity. a) Why are typical refrigerated storage systems designed to maintain a 5-10 C temperature difference between the evaporator coils and the air rather than a 0.5 C difference? b) Explain how the temperature difference between the evaporator coils and the air influences the relative humidity of the air. 2

3 Listed below are the five general categories of heat sources in a fruit or vegetable storage facility: Sensible or field heat Vital heat or heat of respiration Heat transmission across walls, floors, etc. Air change or leakage Miscellaneous heat sources (lights, motors, personnel, etc.) a. Which one is most important during cooling or initial loading of a storage room? b. Which one is more important during long-term storage (after initial cooling or loading)? What methods can be used to store fresh fruits and vegetables if mechanically-refrigerated cold storage facilities are not available? What are the major effects of lowered O 2 and increased CO 2 concentrations that make extension of the storage life of horticultural commodities possible? How might one want to modify gasses within a storage room to improve shelf life? 3

4 What is the difference between a modified and controlled atmosphere? What is meant by a passive modified atmosphere? Describe the barriers to gas diffusion between the surrounding atmosphere and the cells in the center of a perishable horticultural commodity? What are potential advantages of using Modified or Controlled atmospheres for perishable horticultural commodities? What are potential disadvantages of using Modified or Controlled atmospheres for perishable horticultural commodities? Describe some ways (other than commodity-generated) that modified or controlled atmospheres can be generated. 4

5 What are some ways in which commodity-generated modified atmospheres are created? How is excess carbon dioxide removed from modified or controlled atmosphere rooms? List five ways in which a harvested commodity can alter its immediate environment. For each environmental factor listed, indicate its possible effect (positive or negative) on the commodity or on other commodities in the same environment. High relative humidity is important during both cooling and storage of horticultural crops. List four ways to maintain high relative humidity in a storage room. Discuss briefly the benefits and hazards of using controlled atmospheres during transport and storage of fresh horticultural commodities. What methods can be used to store fresh fruits and vegetables if mechanically-refrigerated cold storage facilities are not available? 5