Influence of soil and soilless agricultural growing system on postharvest quality of three ready-to-use multi-leaf lettuce cultivars

In this study the influence of soil and soilless growing systems (sub-strate 3:1 v/v perlite:peat) on quality and microbial traits of three multi-leaf lettuce cultivars (two green, 'Eztoril' and 'Ezabel', and one red, 'Ezra') was evaluated at harvest and after 7 and 13 days of storage at 8°C. At harvest, 'Ezra' showed a respiration activity and a total phenol content respectively 2-fold and 25% significantly higher than the green cultivars. Soil lettuces resulted more stressed than those grown in soilless, as indicated by their initial content in antioxidants. As for nitrate content, soilless grown lettuces at harvest showed an average concentration higher than soil-grown ones, although values are generally lower than limits imposed by the EU Regulation (No. 1258/2011). During storage, soilless lettuces showed no ammonium accumulation, differently from those cultivated in soil. In addition, lettuce cultivars grown in soilless condition showed unchanged content in the antioxidant activity and total phenols, and lower microbial counts than soil lettuces. Results of the present study showed that soilless growing system can positively affect qualitative and microbiological parameter of lettuces studied, and it can be considered a good soilless growing technique in order to obtain high quality multi-leaf lettuces for ready-to-use industry.