Brownish pink color on your lettuce's edges and ribs?
What you see: Lettuce that’s brownish, pinkish along the ribs
What it is: Pink rib!
Eat or toss: If the lettuce looks slimy, trim that portion away. If the rib is simply pink or a little brown, it’s probably fine.
As we’ve talked about in other posts, humans aren’t the only living things to contend with stress. Consider lettuce, which is stressed by aging; rough handling; imperfect water intake; uncomfortable temperatures; and even the wrong kinds of neighbors (apples, avocados, bananas and the like emit gases that trouble lettuce’s delicate constitution). Not to mention boring salad dressing.
A common way for lettuce to respond to such stressors is something called “pink rib,” which you can see in the brownish pinkish area on the crunchy rib of the lettuce in the image above.
“It’s a prolific disorder,” said Catherine Belisle, a University of Florida PhD candidate studying pink rib. Once you’ve determined there are no signs of decay (think slimy, squishy bits), she said the lettuce should still be good for your salads and sandwiches.
Stress-fighting compounds cause pink and brown color
When the lettuce experiences stress, it deploys defensive compounds. This starts a reaction that involves oxygen and causes portions of the lettuce to turn pink or brown. Belisle has examined such lettuce in experiments.
“I didn’t see any symptoms of decay from microorganisms or from fungi,” she said, referencing a study in which she stored lettuce with pink rib at 5 degrees Celsius (41 degrees Fahrenheit) for 28 days. “The phenolic compounds are typically defense compounds,” she said. “With pink rib what you'll find is that the sections that have that discoloration are typically dry because it's part of its defense mechanism.”
Belisle said she's never found pink ribs to taste any different, though "in theory lettuce with pink rib may be more bitter."
The thing to look out for, however, is anything that looks wet and soft.
“Any type of wet-looking tissue, that is more associated with bacterial decay,” Belisle said. “In that situation I would not consume the lettuce.”
Catherine Belisle. PhD Candidate. Postharvest Horticulture Sciences, University of Florida.