WOUND-INDUCED RESPIRATION AND ETHYLENE PRODUCTION IN FRESH CUT ROMAINE LETTUCE

Understanding of the physiological and biochemical processes induced by cutting can help in devising strategies to improve fresh-cut lettuce quality. We evaluated the response of Romaine lettuce to cutting temperature by cooling overnight and processing five, freshly harvested heads at 5 or 15°C. Undamaged, expanded leaves were immersed for 1 min in 5 or 15°C chlorinated water (1.34 mM NaOCl; pH 7), cut in half longitudinally then cut transversely into 2-cm wide pieces, the cut pieces were re-immersed in chlorine solution, and the excess liquid removed with a salad spinner. Cut pieces from each head (100 g) were measured in flow-through systems every 2 h for 24 h for O2, CO2, and C2H2 by gas chromatography. The CO2 evolution immediately after cutting was approximately 3.5-fold higher at 15°C than at 5°C, and O2 consumption was approximately 2.2-fold higher at 15°C. The CO2 evolution at 15°C increased during the first 4 h after cutting and thereafter remained steady; at 5°C, a small increase occurred during the first 8 h with a slight decline thereafter. The O2 consumption at 15°C increased during the first 3 h after cutting, decreased until hour 10, then remained steady or declined slowly. The O2 consumption at 5°C decreased by half during the first 12 h after cutting and changed little thereafter. The respiratory quotient (RQ) was <1.0 during the first 8-12 h after cutting, rose and remained steady at approximately 1 for 8-10 hours at 5°C and for about 8 h at 15°C, then finally increased to about 1.1 at 5°C and 1.7 at 15°C. Ethylene production was 6-fold higher at 15°C than at 5°C and did not change over time. These relative changes in CO2 production and O2 consumption suggest that non-respiratory oxidative reactions play a significant role in the post-cutting wound response of fresh-cut lettuce.