Lettuces are popularly enjoyed in sandwiches and salads but what would you do if you bit into a sandwich only to notice a slight reddening along the ribs of the lettuce. It is understandable to be mortified because this is indeed an unusual change. However, scientists say it only happened because of certain conditions the lettuce may have been stored in and that it poses no harm to human health.

THE SCIENCE EXPLAINED 

Just like many other vegetables and fruits, lettuces can undergo stress due to:

  • Aging
  • Poor handling
  • Inappropriate temperatures
  • Insufficient water intake
  • Close proximity to other food items like apples, avocados, bananas, that can emit gases that disturb the lettuce’s delicate constitution.

The lettuce's response to such stressors is developing a “pink rib,” which is the brownish pinkish area you may find on that crunchy rib of the lettuce.

Catherine Belisle, a University of Florida PhD candidate studying pink rib, explains that the lettuce's stress-fighting compounds are deployed in response to the stress. This starts a reaction that involves oxygen and causes portions of the lettuce to turn pink or brown.

In reference to a study in which she stored lettuce with pink rib at 5 degrees Celsius (41 degrees Fahrenheit) for 28 days, Belisle says:

“I didn’t see any symptoms of decay from microorganisms or from fungi. The phenolic compounds are typically defense compounds. 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, however, warns that any sight of wetness or softness on such lettuce would signal bacterial activity, indicating that it should be discarded.

BOTTOM LINE  

If the lettuce looks crisp and is only slightly pink or brown, it is probably still safe for consumption. Any part that looks slimy or wet should be trimmed  and discarded appropriately.