Utilization of residues of ajwain, summer savory and oregano essential oils distillation

Water distillation (WD) is a traditional technique for extracting essential oils (EOs). This technique yields significant amounts of water residue (WR) and solid residue (SR) as by-products. The goal of this study was to examine the effectiveness of using WR and SR by-products as antioxidant and antimicrobial agents. The chemical profile of EOs extracted from some aromaticplants rich in phenolic compounds (ajwain, summer savory and oregano) was analyzed by Gas Chromatography-Mass Spectrometry (GC–MS). The most abundant compounds were phenolic monoterpenes, such as thymol and carvacrol. The polyphenol characteristics of the analysed WR and SR extracts were defined by High Performance Liquid Chromatography (HPLC). The HPLC analysis indicated the presence of chlorogenic acid, catechin, ρ-hydroxy benzoic acid, ferulic acid, rutin and hesperidin as major components in WR. Total phenolic and total flavonoid contents were determined using Folin-Ciocalteu and aluminum chloride assays, respectively. The antioxidant potential was evaluated by 2,2-diphenyl‑1-picrylhydrazyl (DPPH) and ferric-reducing antioxidant power (FRAP) assays. The WRO (water residue from oregano) and WRS (water residue from savory) extracts exhibited higher DPPH radical scavenging activity and reducing power than butylated hydroxytoluene (BHT). The antibacterial activity of WR and SR extracts was evaluated on the example of their efficiency against six bacterial strains. The antibacterial activity of WRO extract against Salmonella typhimurium 14028 and Serratia marcescens 37 exceeded those of the standard ampicillin. Meanwhile, WRS extract exhibited greater antibacterial activity than ampicillin against Bacillus cereus 33018.