Evaluate the postharvest quality of romaine lettuce grown in a UV-treated hydroponic system

Abstract

Romaine lettuce, a highly nutritious leafy vegetable widely consumed due to increasing consumer interest in healthy eating. To meet this demand, hydroponic systems, especially deep-water culture (DWC), offer sustainable and efficient alternatives to conventional agriculture because of their rapid growth, high planting density, and energy efficiency. Hydroponically grown lettuce provides superior food safety benefits due to the lower concentration of microorganisms than soil-grown lettuce; however, human-borne pathogen contamination is still possible. Once the hydroponic nutrient solution is contaminated, it spreads rapidly throughout the system and cross-contaminates in the edible parts of the leaves. Ultraviolet (UV) light treatment at the wavelength of 254 nm can provide alternative means for pathogen sterilization in water; however, its effect on produce quality remains unclear. The objective of this study was to investigate the impact of high and low-dose UV-C treated nutrient solutions in a DWC hydroponic system on the harvest and storage quality of romaine lettuce. The quality was evaluated based on the parameters below: leaf length, fresh weight, dry root weight, water loss, SPAD, color, texture, visual quality, respiration rate, macro and micro-nutrients, and Vitamin C. Results suggested that lettuce grown in the nutrient solution that was treated with low-dose UV-C treatment had a significantly longer leaf compared to the non-treated lettuce and significantly higher fresh shoot weight compered to both the high-dose UV-C treated and non-treated lettuce. There were no significant effects on the dry root weight between the treatments. Moreover, lettuce treated with UV-C did not impact water loss, SPAD value, texture, color, and during storage. On the other hand, lettuce gown in a nutrient solution that was treated with UV-C, especially with the high-doses, highlighted significantly better visual quality than non-treated lettuce. Furthermore, lettuce that was grown in the nutrient solution that was treated with low-dose UV-C appeared to have significantly higher Vitamin C levels than lettuce treated with the high-dose of UV-C. This study suggests that application of low-dose UV-C in the nutrient solution of hydropic grown lettuce could enhance the harvest and storage quality of the crop.