Evaluation of predrying steps, cadmium, and pesticide residues on dried powders from romaine lettuce outer and heart leaves

Authors: Avena-Bustillos, Roberto; Klausner, Noah; MILCZAREK, REBECCA - Former ARS Employee; TERÁN-CABANILLAS, ELI - Autonomous University Of Sinaloa; ALEMÁN-HIDALGO, DAVID - Autonomous University Of Sinaloa; McHugh, Tara

Submitted to: ACS Food Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2022
Publication Date: 12/12/2022
Citation: Avena Bustillos, R.D., Klausner, N.M., Milczarek, R., Terán-Cabanillas, E., Alemán-Hidalgo, D.M., McHugh, T.H. 2022. Evaluation of predrying steps, cadmium, and pesticide residues on dried powders from romaine lettuce outer and heart leaves. ACS Food Science and Technology. 3(1). Article 41-49. https://doi.org/10.1021/acsfoodscitech.2c00234.
DOI: https://doi.org/10.1021/acsfoodscitech.2c00234

Interpretive Summary: Romaine lettuce has the double of phenolic compounds than Iceberg lettuce, three times more vitamin C, four times more carotenoids, and four times more chlorophyll while content of carbohydrates is equal. Moreover, depending on the part of lettuce, these nutritional components may vary substantially; for example, full size outer leaves of Romaine lettuce have twelve times more chlorophyll and three times more carotenoids than heart leaves. Nowadays, the outer leaves of Romaine lettuce are discarded in the field during the harvest of Romaine hearts. The magnitude of this loss is considerable since above 100% of the product found in the market is wasted during harvesting. In addition, the presence of discarded outer leaves can be a liability in terms of nitrogen management. Thus, the outer leaves of Romaine lettuce present a prime opportunity for simultaneous food waste reduction and valorization (upcycling) for the leafy greens industry. Food drying of high moisture content foods such as lettuce, requires methods that utilize large amounts of energy, so energy-efficient alternatives need to be pursued. An energy efficient form of drying involves infrared dried blanching patented by our group. While Romaine lettuce is abundant in nutrients that are beneficial to the human body, it may contain trace amounts of Cd and pesticide residues. In this study we evaluated the concentrations of these harmful chemicals in dried outer and heart lettuce leaves powders. Comparison of physical parameters of dried lettuce powders from different varieties indicates that significant differences in color and composition can be expected. Using thinner outer leaves for dried lettuce powders can be done in shorter drying time than using thicker lettuce hearts. Upcycled outer leaves lettuce powders with bright green color are possible to be obtained without shredding, acid-dipping and infrared blanching, reducing equipment needed to obtain hot-air dried powders for this potential food product. From our findings, it is advisable to use lettuce from low cadmium soils to reduce this heavy metal in the final powders. Safe to eat Romaine lettuce outer leaves powders with low cadmium content and pesticide residues can be obtained following good agricultural practices. Using upcycled outer leaves from Organic certified Romaine lettuce harvesting will also significantly reduce the presence of residual pesticides to allow this dried product to be used as a food additive. Outer leaves lettuce powder has a bright and attractive green color, pleasant odor, and a taste reminiscent to Nori dried seaweed. Sensory evaluation of this powder could demonstrate its potential for specific food applications.

Technical Abstract: Compared to Iceberg lettuce, Romaine lettuce has equal carbohydrate content, double the phenolic compounds, three times the vitamin C, and four times the carotenoids and chlorophyll. Depending on the part of lettuce, these nutritional components may vary substantially. For example, full size outer leaves of Romaine lettuce have twelve times more chlorophyll and three times more carotenoids than heart leaves. Currently, the outer leaves of Romaine lettuce are discarded in the field during the harvest of Romaine hearts. The magnitude of this loss is considerable, with the amount of harvested product is roughly equal to the amount discarded during harvesting. In addition, the discarded outer leaves are a liability in terms of nitrogen management. Thus, the outer leaves of Romaine lettuce present an opportunity for food waste reduction and valorization (upcycling). Current methods for drying of high moisture foods such as lettuce utilize large amounts of energy and alternatives are needed. An energy efficient form of drying involves infrared dried blanching. While Romaine lettuce is abundant in beneficial nutrients, it may contain trace amounts of Cd and pesticide residues. In this study we evaluated the concentrations of these harmful chemicals in dried outer and heart lettuce leaves powders. Comparison of physical parameters of dried lettuce powders from different varieties indicates that significant differences in color and composition can be expected. Using thinner outer leaves for dried lettuce powders can be done in shorter drying time than using thicker lettuce hearts. Results indicate that it is advisable to use lettuce from low cadmium soils to reduce this heavy metal in the final powders. Safe to eat Romaine lettuce outer leaves powders with low cadmium content and pesticide residues can be obtained following good agricultural practices. Using upcycled outer leaves from Organic certified Romaine lettuce harvesting will also significantly reduce the presence of residual pesticides to allow this dried product to be used as a food additive.