Different agronomic and fertilization systems affect polyphenolic profile, antioxidant capacity and mineral composition of lettuce

• Green lettuce was cultivated both organically and conventionally.
• Changes in the levels of plant phenols and mineral content were examined.
• Higher plant phenols and antioxidant capacity were found in the conventional system.
• Higher yield and plant mineral content were found in the organic farming system.
• The results were discussed in relation to the agronomic and fertilization systems.

The present paper aims to investigate phenolic profiles, antioxidant capacity and mineral composition of lettuce (Lactuca sativa L., var. ‘Maravilla de Verano’) grown under conventional (CON) and an organic (ORG) systems with four different fertilization treatments. The polyphenolic profiles of leaf extracts were determined by ultra-high-performance liquid chromatography (UHPLC), the levels of mineral elements by means of inductively coupled plasma mass spectrometry, whereas total phenolic content and antioxidant capacity were determined spectrophotometrically. Yield, soil and meteorological parameters were measured. In all the fertilization treatments, total phenolic acids and flavonols in CON were significantly higher compared to ORG. A trend parallel to that of single phenols was observed for total phenolic content and total antioxidant capacity. Plant mineral distribution revealed significant changes between CON and ORG systems in some plant macronutrients (N, Mg, S, Na, Fe) and micronutrients (Se, Mn, Mo). The differences among fertilization treatments for all the parameters considered were also discussed. From the overall analysis of the results, the higher content of phenolics observed in CON system could be associated to the presence of more stressful conditions, in terms of plant and/or soil mineral deficits. On the other hand, the adoption of an organic management determined higher yields and a better plant mineral balance.

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