Romaine lettuce (Lactuca sativa var. longifolia) outer leaves are discarded in fields during
harvest and present
a prime upcycling opportunity. Although Romaine lettuce is abundant
in healthy nutrients, it may contain trace amounts of heavy metals,
mainly cadmium (Cd), and pesticides that could lead to acute poisoning.
Physical attributes, total soluble phenolics, antioxidant capacity,
Cd, and pesticides in powders with different predrying treatments
for hearts and outer leaves of two varieties of Romaine lettuce from
farms with different Cd content in soils were quantified. Lettuce
powders from the Valencia variety had a higher greenish color and
true density than the Duquesne variety. Heart leaves from Valencia
variety presented higher total soluble phenolics. However, outer leaves
from Valencia and Duquesne varieties presented similar levels of total
soluble phenolics. Valencia outer and heart leaves presented higher
antioxidant capacity. Infrared dry blanching resulted in lower color
parameters, total soluble phenolics, and antioxidant capacity, evidencing
thermal degradation during this predrying step. Cd concentrations
were 10 times higher in the soil where Duquesne Romaine lettuce variety
was grown. Accordingly, Duquesne had significantly higher levels of
Cd in outer or heart leaves. Outer leaves had higher levels of Cd
compared to heart leaves. No differences in pesticides were found
in lettuce from both harvesting fields. It is possible to obtain edible
powders from Romaine lettuce outer leaves from low-Cd soils and controlled
pesticide management, and it may be an alternative way to reduce nitrogen
leaching in agricultural soils.
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