Evaluation of Predrying Steps, Cadmium, and Pesticide Residues on Dried Powders from Romaine Lettuce Outer and Heart Leaves

Abstract

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.