WHY CATTS WORKS! LISA NEVEN USDA-ARS WAPATO, WA

Fruit on the Tree While peaches are on the tree, they experience fluctuating temperatures. In response to these fluctuating temperatures, the fruit produce a number of ‘stress response’ proteins. The fruit will produce these proteins even if the daily temperatures are not in the ‘stress’ range every day.

Fruit after Harvest After harvest, the fruit will continue to make the ‘stress response’ proteins for a number of days. These proteins will help the fruit tolerate heat treatments.

Insects in the Fruit Insects in the fruit will also produce ‘stress response’ proteins when fruit temperatures reach ‘stressful’ levels. Insects will only produce these proteins when they experience stressful temperatures. When the fruit is harvested, and the insects are no longer exposed to stressful temperatures, they do not produce stress proteins.

Stress Proteins and CA The fruit will continue to produce ‘stress proteins’ on a diurnal schedule, just as if they were on the tree. The insects do not. Insects cannot produce ‘stress response’ proteins if there is not enough oxygen to support metabolism. We are not EXACTLY sure about the fruit, but we do know they have a high capacity for anaerobic metabolism.

What CATTS Does First, the oxygen level is reduced to a level which will not support active metabolism in the insects. High carbon dioxide levels prevents the insect from ‘down regulating’ metabolism and respiration. The addition of high temperature causes a metabolic stress in the insect, and large scale systems break down occurs. The addition of CA causes mortality about 2X as fast as heat alone.

Importance of Heating Rate We know that the faster the rate of heating, the shorter the time the insects have to be held at the final treatment temperature to kill them. For example, CATTS at 12°C/h to final temperature of 46°C the core average temps have to be at 45°C for 30 min, while CATTS at 24°C/h to the same temperatures, cores only have to be at 45°C for 15 min.

Fruit and CATTS There is no evidence that the high carbon dioxide and low oxygen levels during CATTS causes any additional phytotoxicity. This may be due to the high capacity for anaerobic metabolism in the fruit. We do know that heating rate is very important for preventing damage. We also know that heat disrupts many of the enzymes involved in ripening.