Influence of aeration of the nutrient solution on quality changes of two baby leaf lettuce cultivars grown in a floating system at harvest and during shelf-life as fresh-cut product

The aim of this work was to assess the influence of different levels of aeration of the nutrient solution on the initial quality and throughout the shelf life of baby leaf lettuce. Two cultivars of baby leaf lettuce, the red leaf 'Diveria' and the green batavia 'Ganeria', were grown in a floating system in an autumn cycle. Three levels of aeration of the nutrient solution (high, low and no aeration) were tested. After four weeks, the lettuce leaves were harvested and the aerial part and root growth were measured. After the fresh-cut operations, the leaves were packaged in 1 L polypropylene (PP) baskets sealed with a 35 µm thickness film (20 µm polyethylene terephthalate + 15 µm PP) and stored at 5°C. The nitrate content, total phenols and microbial growth were determined in lettuce leaves on the processing day and after 7 days at 5°C. During the shelf-life, gas changes within baskets were monitored. Regarding the aerial part and root growth, no significant differences among aeration levels were found. After chilling storage nitrate content lowered and total phenols increased, particularly in plants grown in high aeration level. O₂ and CO₂ partial pressures within packages at the steady-state ranged from 16-18 kPa O₂ and 1-4 kPa CO₂ without significant differences among treatments. In general, microbial population increased during storage; particularly, after storage, the growth of psychrophilic bacteria in 'Diveria' leaves from each aeration treatment was significantly higher. In any case, high microbial quality was maintained during the entire process. Finally, no clear effect of cultivars and aeration levels were observed during shelf-life on the overall quality of fresh-cut baby lettuces leaves.