Analysis And Adsorptive Isolation Of Chemical Components From Hydrolates Of Fresh Flowersfrom Several Species

Hydrolates are important by-products generated during industrial distillation for essential oils and generally contain certain amounts of water-soluble essential oil components. Up to now, effective isolation of water-soluble oil components from hydrolates is still the key technical problem to be solved in industrial essential oil production. In this work, aromatic plants from Zhejiang and Jiangsu provinces were selected as case studies. Isolation was performed using hydro-distillation, liquid-liquid extraction, adsorption and supercritical fluid extraction, while analysis was achieved by gas chromatography, gas chromatography-mass spectrometry and high performance liquid chromatography. Studies focused on analysis and adsorptive isolation of chemical components from hydrolates of fresh flowers. The main results are as follows:(1) Chemical components from hydrolates of fresh flowers of Osmanthus fragrans, Cerasus subhirtella and C. serrulata were investigated. The main components of O. fragrans hydrolate were linalool oxides, whereas the main volatiles from O. fragrans cold infusion were phenylethyl alcohol derivatives and linalool oxides. The key components of hydrolates of C. subhirtella and C. serrulata were benzaldehyde and mandelonitrile. Components of hydrolates from three species were mainly oxygenated compounds which contribute greatly to the organoleptic quality of hydrolates.(2) Methods were developed for fast analysis of essential oils and hydrolates. Towards fast identification of essential oil components, a new method was established based on comprehensive matching index MMS+RI, which fully utilized the matrix characteristics of data of gas chromatography-mass spectrometry. It improved identification efficiency of terpenes in Yulania liliiflora oil and oxygenated terpenes in O. fragrans water-soluble oil. Based on this method, a database of essential oil components of fresh flowers from 8 aromatic plant species characteristic of China was established; Fast analysis of hydrolates was established based on high performance liquid chromatography-diode array detection. Rosa damascena and R. rugosa were selected as case studies. Fast quantification of the major component phenylethyl alcohol (PEA) and identification of the minor component benzyl alcohol was achieved. The recovery for PEA determination ranged from 99.3% to 101.0%. The limit of quantitation and limit of detection were 0.3318 and 0.09953 μg cm-3, respectively.(3) Fundamental characteristics of adsorption-supercritical desorption towards PEA and rose hydrolate were studied. Kinetics, equilibrium and thermodynamics of adsorption were investigated towards PEA using different types of granular activated carbons (GAC). The effective diffusion coefficients were of the order of 10"12 m2 s-1 under experimental conditions. Adsorption equilibrium fitted well to Freundlich equation. Taking into account physical properties of GAC, adsorption rate, adsorption capacity and desorption ratio, the activated carbon CAL proved superior to F400D and 207CX; Dynamic adsorption of PEA onto GAC fixed bed was investigated. The bed saturation capacity was up to 301.9 mg g-1 under experimental conditions. Yoon-Nelson model described well the breakthrough behavior of PEA. Dynamic adsorption towards rose hydrolate indicated that competitive adsorption was the main factor influencing the chemical composition of water-soluble oil loaded on GAC; Supercritical desorption was investigated towards PEA-loaded GAC. Pressure and temperature were found to be the main factors influencing desorption ratios. Desorption ratio of PEA was 95.1% as achieved by supercritical carbon dioxide (SC-CO2) under optimized conditions. Supercritical desorption towards GAC loaded with water-soluble rose oil indicated that the main components of oil (PEA, citronellol and geraniol, etc.) can be desorbed effectively with SC-CO2. Desorption ratio of eugenol, however, was rather low (38.6%) probably due to oxidative coupling reactions it had undergone.(4) Application characteristics of adsorption-desorption process were evaluated towards isolation of water-soluble essential oils from hydrolates. The water-soluble oil of Michelia figo was isolated through adsorption onto GAC-desorption with ethyl acetate. The oil obtained herein possessed higher yield and better chemical profile (higher level of esters and lower level of short-chain fatty acids) compared to that isolated by ethyl acetate extraction. The oil was mainly composed of linalool, isoeugenol methyl ether and r-muurolol; The water-soluble oil of Y. denudata was recovered through adsorption onto GAC-desorption with diethyl ether. The yield was comparable to that achieved by diethyl ether extraction but the solvent consumption was less. The water-soluble oil of Y. denudata was mainly composed of eucalyptol and a-terpineol; The water-soluble oil of Y. liliiflora was isolated by adsorption onto GAC-desorption with SC-CO2. The yield was higher than that achieved by methylene chloride extraction. The oil was mainly composed of eucalyptol, a-terpineol and terpinen-4-ol. As it turned out, water-soluble essential oils can be recovered effectively from hydrolates through adsorption onto GAC desorption with organic solvents or SC-CO2. The latter was more suitable for industrial production.The outcome of this work provides experimental and theoretical basis for recycling valuable essential oil resources and environmentally-friendly essential oil production.