Aromatic Plant Residues from Essential Oil Steam Distillation as a Potential Source of Antioxidants

Steam distillation residues (SDRs) of aromatic plants were utilized to produce antioxidant extracts using hydroalcoholic solvents with increasing percentages of ethanol (0, 50, 75 and 100% v/v). The phenolic composition and antioxidant power were measured and compared to the corresponding fresh aromatic plants (FAPs). The largest amount of polyphenols, ranging from 14.15 (lemon balm FAP) and 19.61 (lavender SDR) mg gallic acid equivalents/g dry matter (DM), was found in 0% ethanol (pure water) extracts. The phenolic content of lavender and spearmint SDR extracts was higher than that of the corresponding FAP extracts, while the opposite was observed with lemon balm. Rosmarinic acid was the most abundant hydroxycinnamic acid detected, ranging from 608.65 µg/g DM in lemon balm 50% ethanol FAP extract to 697.47 µg/g DM in spearmint 50% ethanol SDR extract. The lavender and spearmint SDR extracts exhibited higher antioxidant power than the FAP extracts, while the extracts from fresh lemon balm were more antioxidant than the SDR. The lavender 50% ethanol SDR extract showed the highest scavenging activity (67.16%) and ferric reducing power (16.60 mg ascorbic acid equivalents/g DM). These results prove that spent aromatic residues can be utilized to produce antioxidant blends for various industrial applications.