One hundred spearmint (Mentha spicata) plantlets were regenerated from apical shoot segments of ten fieldgrown
donor plants. Although the accumulation of rosmarinic acid and total phenolics in vitro was almost half than in
vivo, regenerants demonstrated a tenfold-higher hydrogen peroxide compared to the donor plants. This finding may have
been associated with the increased activity of hydroxyphenylpyruvate reductase, a key enzyme of the phenolic biosynthetic
pathway and the increased production of yet unidentified phenolic compounds in vitro. This process of in vitro culture
associated with a reduction of rosmarinic acid and total phenolics and with an increase of the antioxidant capacity indicated
the possible promotion of in vitro-specific biosynthetic pathways.