Modified atmosphere (MA) prevents browning of fresh-cut romaine lettuce through multi-target effects related to phenolic metabolism

• MA controlled browning of fresh-cut lettuce through a multi-target mechanism.
• MA suppressed PAL activity and the activation process from latent to active PPO.
• MA maintained or even increased the content of vitamin C.
• MA reduced the synthesis and accumulation of caffeic acid derivatives.

Browning of fresh-cut romaine lettuce was inhibited in modified atmosphere (MA) packaging with low O2 and moderate CO2 concentrations during storage. This study explains the control mechanisms of MA causing differences in phenolic substrates and oxidative enzymes related to browning of two cultivars of romaine lettuce. Modified atmosphere decreased PAL and PPO activities and prevented cut edge browning. In MA, the process from latent to fully active PPO decreased particularly in the cultivar more susceptible to browning. The content of vitamin C was maintained or even increased in MA while decreased markedly in air. Caffeic acid derivatives increased through the storage in air whereas in MA this trend was towards a decrease in these phenolics. Chlorogenic acid was the only caffeic acid derivative that showed the same trend as PAL activity with an increase at d2 after cutting and a progressive decrease after that due to browning development and transformation to isochlorogenic acid. By the analysis of the lettuce midribs, it was possible to correlate the control of browning by MA with the suppressing action on oxidative enzymes and the slowing down of the synthesis and accumulation of caffeic acid derivatives. The browning process seems to correlate better with the biosynthesis of caffeoyl quinic derivatives, rather than with that of caffeoyl tartaric derivatives, that are always the main phenolics present in romaine lettuce midribs. A deeper study of the different behaviour of both groups of caffeic acid derivatives is guaranteed.

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