Step 1: Understanding the Concept:
Fresh horticultural crops (fruits and vegetables) continue to respire after harvest, consuming oxygen and releasing carbon dioxide, which leads to senescence and decay.
Modifying the storage atmosphere can slow down this respiration rate and extend shelf life.
Detailed Explanation:
- Controlled Atmosphere Storage (CAS) (4): A preservation technique where the concentrations of oxygen ($\text{O}_2$), carbon dioxide ($\text{CO}_2$), and nitrogen ($\text{N}_2$), as well as temperature and relative humidity, are constantly monitored and adjusted within an enclosed storage chamber.
- Typically, the oxygen concentration is reduced (from the normal atmospheric level of $21\%$ down to $1\text{--}5\%$) and the carbon dioxide concentration is increased (from the normal level of $0.03\%$ up to $1\text{--}10\%$).
- This low-$\text{O}_2$ and high-$\text{CO}_2$ environment slows down respiration, inhibits ethylene production (delaying ripening), and limits the growth of decay-causing microorganisms.
- It is widely used for the long-term storage of apples, pears, and kiwifruit.
- Cold storage (1) and Frozen storage (2) only regulate temperature, while Lyophilization (3) is freeze-drying.
Step 2: Final Answer:
The storage method that utilizes high $\text{CO}_2$ and low $\text{O}_2$ concentrations is Controlled Atmospheric Storage.