Extraction Of Onion Essential Oil And Onion Flavone

According to the calculation of relative solubility parameter between the main active ingredients in onion and the supercritical CO₂ fluid, supercritical CO₂ fluid extraction (SCFE) combined with solvent exhaustion method was applied to extract essential oil and flavone from onion. The contrasts between SCFE and other extract methods were researched, and effect and influence factors of these different extract methods were confirmed. Especially, the flavone was extracted from the remainder of essential oil extracted by SCFE. The different preliminary treatments were used to onion, the analysis methods were selected and established applied to the ingredient of the extractive.When the onion essential oil was the aim extractive, the four operational paths have be investigated as follows: water vapor distillation was used to extract essential oil from the fresh onion; solvent was used to extract essential oil from the fresh onion; solvent was used to extract essential oil from onion dried routinely; SCFE method was used to extract essential oil from onion freeze-dried., the SCFE was the optimality method to obtain the highest yield of the essential oil. in the four methods.When the flavone was the aim extractive, three operational paths were investigated as follows: using water to extract flavone from the fresh onion; used ethanol to extract flavone from the fresh onion; using water to extract flavone from the SCFE remainder. By contrasting these three methods, we found that the third one was the optimality method to obtain the flavone.Above all, the optimality operational path was: using SCFE to extract essential oil from onion being freeze dried; using water to extract flavone from the SCFE remainder.Connected with the above-mentioned operational path, Uniform Design was adopted to arrange the experiments and the experimental results were processed by the software. Two correlation equations had been gained as follows.The correlation equation between SCFE rate of the essential oil and extraction conditions: In which: 7 represents the weight-loss ratio of the freeze-dried onion; X₁～X₃ represents SCFE pressure, temperature and extraction time respectively.The correlation equation between flavone yield and SFE extraction conditions:In which: Y represents the flavone yield; X₁～X₃, represents SCFE temperature, extraction time and the water amount per 15 kilogram onion respectively.By optimizing the experimental data, we arrived at a conclusion that: the highest weight-loss ratio of the freeze dried onion was 2.92%, corresponding technological conditions were as follows: extraction pressure was 32MPa, extraction temperature was 37℃and extraction time was 3.6h. The weight-loss ratios of two repeat experiments were 2.86% and 2.78% respectively.The highest flavone yield was 0.0081 %, corresponding technological conditions were as follows: Extraction temperature was 85℃, extraction time was 5h, 360ml water per 15 kilogram onion. The experiment result confirmed that the flavone yields of two repeat experiments were 0.0084% and 0.0086% respectively.In this paper, systemic evaluation method was established. Measuring sulfur method was applied to measure the content of sulfur compounds in onion essential oil; GC/MS method was applied to detect the ingredient of the onion essential oil; spectrophotometry was applied to measure the content of the flavone in the onion extractiveThe comparison of the detection result of measuring sulfur method and GC/MS method applied in onion essential oil and the extraction rate was as follows: there was no great difference in the extraction rate of steam distillation essential oil and solvent extraction, but the sulfur containing compounds in the essential oil in the former were lower than the latter. The sulfur containing compounds obtained by SCFE from cold-dried onion essential oil was 3.65%, and the extraction rate obtained by the solvent was 3.76%. Obviously there was no significant difference between the two methods. But the color, luster and flavor of essential oil obtained by SCFE were better than that obtained by solvent extraction technique. Besides the process of SCFE was less-pollution and the essential oil could be purified easily. The flavone content of onion extract determinated by spectrophotometric method was as follows: the extraction rate of fresh onion from water and ethanol was 0.0079% and 0.0088 % respectively, and the impurity content of flavone extracted from ethanol was lower. The extraction rate of flavone in the SCFE remaining from water was 0.0085 %, and its color and flavor were better than that obtained from water and ethanol directly.The innovative point was establishing a system method of freezing dried onions, extracting onion essential oil first and then extracting flavone from the extraction residue, and obtained high-quality onion essential oil and flavone.