Influence of Postharvest Temperature on Brown Stain of Lettuce1,2

The incidence of brown stain on crisphead type lettuce ( Lactuca sativa L. cv. Calmar) was highly dependent on postharvest temperature. Following exposure to 2% O 2 + 5% CO 2 for 5 days at constant temperatures from 0° to 20°C, brown stain decreased as simulated transit temperature increased and was negligible at 10°C and above. Simulated market temperatures following exposure to 2% O 2 + 5% CO 2 at 0°C markedly influenced brown stain expression with near maximum expression present after a 3-day period in air at 10°C. Low O 2 (2%) was more effective in reducing respiration (CO 2 production) of lettuce at temperatures above 5°C than at 5°C, or lower.