Surface morphology and chemical composition of lamb’s lettuce (Valerianella locusta) after exposure to a low-pressure oxygen plasma

The influence of a low-pressure oxygen glow discharge plasma on secondary metabolites of lamb’s lettuce was examined. After extraction and hydrolysis the compounds were analysed by means of RP-HPLC. Whereas pure compounds showed a time-dependent degradation (flavonoids) or remained unchanged (phenolic acids), the exposure of lamb’s lettuce to the oxygen plasma led to a significant increase of protocatechuic acid, luteolin, and disometin after 120 s treatment time, independent of the applied plasma driving voltage. Contact angle (CA) measurements show an increased wettability of adaxial leaf surfaces after plasma exposure. A successive degradation of epicuticular waxes and cutin of the plant’s epidermis has been indicated by means of FTIR (ATR) and scanning electron microscopy (SEM). These findings suggest that reactive species in the plasma play a crucial role for the observed changes upon exposure to non-thermal plasma.