Study On The Extraction Of Onion (Allium Cepa L.) Oil

Onion (Allium cepa L.) is one of the most large-production vegetables in China, and it is also a traditional drug-food herb in Asia, because of its therapeutic effects. These effects are attributed to biologically active sulfur compounds in onion oil. However, the amount of oil in fresh onion is so little that people's daily intake cannot have the ideal therapeutic effects. So methods of effectively extracting onion oil were studied with the aim of gaining the maximum sulfur compounds.In this dissertation onion oil was extracted by steam distillation (SD), simultaneous distillation and solvent extraction (SDE) and supercritical carbon dioxide extraction (SFE) respectively, the effects of different processing conditions and the optimal parameters were studied. The results were summarized as follows:1.Methods for qualitative and quantitative analysis of onion oil by GC-MS and GC were established respectively. Compounds in onion oil were successfully separated. And 27 compounds were identified, of which 24 compounds were sulfur compounds.2.The parameters of steam distillation for extracting onion oil were optimized. Effects of cultivar, time, temperature and pH of the action of alliinase, saturated sodium chloride solution and the ratio of the onion homogenate and water on the extraction of onion oil were studied. The results of orthogonal experiment showed that the optimal parameters were enzymatic temperature, 30℃; enzymatic time,120 min; extracting time, 60 min. Under the above condition the concentration of sulfur compounds reached 25. 07ul/kgFW.3.The optimal parameters of simultaneous distillation and solvent extraction (SDE) for onion oil were obtained for the first time. Effects of extracting time, the volume of solvent, the ratio of the onion homogenate and water and the concentration of the sodium chloride solution on the extraction of onion oil were studied. The results of orthogonal experiment showed that the optimal parameters were enzymatic temperature, 35℃; enzymatic time, 150 min; extracting time, 150 min. Under the above condition the concentration of sulfur compounds reached 45. 37 ul/kg FW.4.The parameters of supercritical carbon dioxide extraction (SFE) were optimized. Effects of particle size, coefficient of water contents, extracting pressure, extracting time, extracting temperature and the volume of co-solvent on the yield of onion oil were studied. The results of orthogonal experiment showed that the optimal parameters were extracting pressure, 27.98 MPa; extracting temperature, 42.18 ℃; extracting time, 216.6 min. Under the above condition the yield of onion oil reached 0.483%. The products had pleasant aroma characteristics of fresh onions.