The extraction method of onion essential oil
The traditional extraction methods of onion essential oil include steam distillation, organic solvent extraction, and supercritical CO2 extraction.
Steam distillation method
The steam distillation method is to use the target components that are volatile, insoluble, or insoluble in water and steamed out with water vapor to achieve the purpose of separation. Due to the long time and high extraction temperature of steam distillation, some heat-sensitive components in the essential oil are lost due to pyrolysis and hydrolysis, resulting in a significant decrease in the yield and quality of onion essential oil.
Organic solvent extraction method
The organic solvent extraction method has the advantages of low cost and easy operation, but the existing solvent residues will not only affect the quality of essential oils but also affect people’s health.
CO2 extraction process
The supercritical CO2 extraction process has no residue, high yield, no pollution, and mild extraction conditions, which determines that the supercritical fluid extraction technology is the best green extraction method.
Onion essential oil steam distillation process
Reagent
Distilled water, dichloromethane, and anhydrous sodium sulfate.
Equipment
Pulverizer, constant temperature water bath, steam distillation device, vacuum concentration device, extraction device, etc.
The extraction method of onion essential oil
Raw material → pretreatment → leaching → distillation → extraction → dehydration → concentration → onion oil.
The extraction process of onion essential oil
- Raw materials. Made with fresh onions.
- Pretreatment. Peel the onion and put it in a grinder to make a smooth paste.
- Leaching. Distilled water was added to the homogenate at a ratio of 1 g: 1 mL of material to water, stirred and mixed, and immersed in water at a constant temperature of 30 °C for 3 h. Remove water-soluble impurities. The leaching solution was filtered to discard the filtrate, and the filter residue was retained.
- Distillation. The filter residues are put into steam distillation equipment, and the distilled liquid is collected by vacuum distillation for 3-3.5h under the condition of vacuum degree of 5~8kPa.
- Extraction. The collected distillate was extracted with dichloromethane as an extractant. Extract 3 times and combine the extracts.
- Dehydration. 8 g of anhydrous sodium sulfate was added to the extract for dehydration treatment.
- Concentrated. The dehydrated extract is concentrated in vacuo, and the dichloromethane solvent is recovered to obtain onion oil.
The CO2 extraction process of onion essential oil
The extraction rate of supercritical CO2 to extract onion oil is high, the process is simple, the oil quality is good, and it has a good application prospect.
Reagent
CO2
Equipment
Grinders, supercritical CO2 extraction machines, etc.
Method of extraction
Raw material → pretreatment-supercritical CO2 extraction → onion oil.
The CO2 extraction process of onion essential oil
- Raw material. Made with onions.
- Preprocessing. Remove the dry skin of the onion, rinse with water, and grind the onion into a paste with a grater.
- Supercritical CO2 extraction. The optimal conditions for extracting onion oil are extraction pressure 14-16Mpa, extraction temperature 32-35℃, CO2 flow rate 2L/min, and extraction time within 6h.
Physicochemical properties of onion oil
Onion oil is a clear volatile essential oil of amber yellow to amber orange, with a strong spicy aroma and aroma unique to the onion.
The main components are diallyl disulfide, dipropyl disulfide, dimethyl disulfide, methallyl sulfide, and other sulfur-containing compounds, of which the sulfur content of dipropyl disulfide is equivalent to the total sulfur content of onions. 80%~90%. Although the sulfur content of diallyl disulfide is less than 1%, it is the main flavor source of onion. The mixture of these volatile sulfides produces a unique strong spicy taste, antibacterial power, and significant physiological effect of onion. In addition, onion also contains a small amount of citrate, carboxyl, cinnamic acid, ferulic acid, and other aroma substances.
Application
Onion oil is not only a flavoring agent in the food industry but also a raw material for many medicines and functional foods. The health benefits of onion oil are of increasing interest.