Ⅰ.UAE
Ultrasonic-assisted extraction is a process that utilises the cavitation effect and mechanical action to enhance the release of soluble components. This is achieved by disrupting cells and thereby facilitating enhanced mass transfer, thus enabling solvent molecules to effectively penetrate tissue cells and come into full contact with solute molecules.The technique offers several advantages, including ease of operation, low extraction temperature, high extraction rate and no damage to the structural integrity of the extract. A study was conducted to ascertain the most effective process conditions for ultrasound-assisted extraction of cinnamon essential oil. The study concluded that the optimised process conditions resulted in a significant reduction in extraction time and improved productivity compared with traditional methods (e.g. water vapour distillation and organic solvent extraction).
Ⅱ.SD
Steam distillation is a conventional technique for the extraction of volatile oils from herbal materials. In this method, the herbal materials, which contain volatile constituents, are soaked and moistened, and then subjected to distillation either by direct heating or by passing them through water vapour. The volatile components in the herbs are carried out with the water vapour, and the distillate is collected after condensation.It is often necessary to perform secondary distillation to enhance the purity and concentration of the distillate.
Extraction times of 12 hours or more and temperatures in excess of 100°C have been shown to cause decomposition or denaturation of the active ingredients, resulting in a loss of the extraction process.However, the addition of appropriate amounts of additives (e.g. saturated NaHSO3) can improve the extraction rate and purity. In a related study, Zhou Feng et al. purified the distillation product using saturated NaHSO3, achieving a substantial increase in the cinnamaldehyde content.
Ⅲ.SWE
The principle of subcritical water extraction of cinnamon oil is predicated on the unique physicochemical properties of water in the subcritical state. Under subcritical conditions (temperatures close to but below the critical temperature of water, usually 100-374°C, and pressures less than 4 MPa), the polarity, solubility, and mass-transfer capacity of water are significantly enhanced. The application of subcritical water extraction not only reduces the required extraction time and enhances extraction efficiency, but also ensures the effective retention of active constituents such as cinnamaldehyde, thereby preserving the quality of the final product.A further advantage of this method is that it employs water as the sole solvent, thus eliminating the need for additional organic solvents and, by extension, significantly reducing environmental pollution. This approach aligns with the principles of green chemistry, emphasising the minimisation of environmental impact. The subcritical water extraction process is notable for its low energy consumption and ease of operation, which renders it well-suited for large-scale industrial production. This process has the potential to reduce costs and enhance economic benefits for enterprises.
Ⅳ.USWE
The principle of ultrasound-enhanced subcritical water extraction of cinnamon involves the utilisation of the cavitation effect of ultrasound and the high solubility of subcritical water to destroy the plant cell wall through the micro-jet generated by ultrasound and the local high-temperature and high-pressure environment, thereby accelerating the release of the active ingredients in cinnamon. The high mass-transfer efficiency of the subcritical water further enhances the extraction efficiency. This method boasts several significant advantages, including a reduced extraction time (only 25 minutes), a high extraction rate (the content of cinnamaldehyde can reach 12.662 mg/g), strong antioxidant activity, good product quality and green energy saving. This makes it a more ideal method for extracting cinnamon oil.
Ⅴ.Conculsion
In the present study, a comprehensive investigation was conducted into the efficiency of four distinct extraction methods. The first method was ultrasound-enhanced subcritical water extraction (USWE), which exhibited the shortest extraction time of 25 minutes. The second method was ultrasound-assisted extraction (UAE), which yielded the highest yield of cinnamon essential oil, but its appearance properties were poor.The third method was USWE, which yielded the highest yield of cinnamaldehyde and the highest content of cinnamaldehyde in the essential oil. With regard to the composition of the cinnamon essential oils, the physical properties of the cinnamon essential oils from the water vapour distillation (SD), subcritical water extraction (SWE) and USWE methods were found to be similar, while they differed significantly from those of the UAE method.The types and compositions of the cinnamon essential oils obtained by the SD and UAE methods were found to be similar, whereas the composition of the cinnamon essential oils obtained by the SWE and USWE methods were found to be similar. The cinnamaldehyde component was identified as the primary constituent in all four cinnamon essential oils, though their relative concentrations differed significantly.Furthermore, all four cinnamon essential oils exhibited scavenging effects on DPPH radicals, hydroxyl radicals (OH), and superoxide anion radicals (O2-), with the scavenging efficacy enhancing with increasing essential oil concentrations. The cinnamon essential oil extracted by the USWE method exhibited superior scavenging capability against these three free radicals when compared to other extraction methods.The comprehensive study concluded that the USWE method is the optimal technique for extracting cinnamon essential oil, owing to its merits of reduced extraction time, enhanced efficiency, and the assurance of the quality of the cinnamon oil.
