Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 29, 2008
Publication Date: January 1, 2009
Citation: Evangelista, R.L. 2009. Oil extraction from lesquerella seeds by dry extrusion and expelling. Industrial Crops and Products. 29(1):189-196. Interpretive Summary: Lesquerella is an oilseed crop belonging to the mustard family. Lesquerella oil has similar properties as castor oil which is used in a variety of industrial applications such as lubricants, corrosion inhibitors, engineering plastics, plasticizers, emulsifiers, and coatings. Like the other mustard seeds, the objective in preparing Lesquerella seeds for oil extraction is to minimize the formation of anti-nutritional compounds in the coproduct meal while maintaining good oil quality. The process of seed preparation depends on the method of oil extraction. This study evaluated the use of an extruder for simultaneous grinding and cooking of Lesquerella seed before full press oil extraction. The seed is cooked by the heat generated by friction between the seed and the internal surface of the extruder. The conventional method of seed cooking uses heated cookers. The results showed that extrusion cooking produced lesquerella oil with better quality than the oil obtained by conventional seed cooking. This study provided the first guidelines on conditions for extrusion cooking and full press oil extraction of Lesquerella.
Technical Abstract: Whole Lesquerella seeds with 6% (as is) and 12% moisture were extruded at different residence times by varying screw speeds and feed rates. The temperature of the extrudate was recorded and its moisture content was determined. The extent of seed cooking was evaluated by measuring the protein solubility and thioglucosidase (TGSase) activity in the extrudate. Uncooked whole seeds (UWS), whole seeds cooked in a seed cooker (CWS), and extrusion-cooked seeds (ECS) were screw pressed and the crude oils were analyzed for foots, free fatty acid (FFA), phosphorus, calcium, magnesium, and sulfur. The screw speed and feed rates employed resulted in residence times ranging from 22 to 110 sec. The corresponding exit temperatures of the extrudates ranged from 88 to 143 deg C. Seeds with 6% initial MC dried to 4.3% at extrudate temperatures less than or equal to 125 deg C regardless of residence time, while seeds with 12% initial MC came out at 7-9% MC. Extruding seeds with 6 and 12% starting MC for 34 and 41 sec, respectively, provided the same degree of cooking as that of 12% MC CWS. All CWS and ECS tested negative for TGSase activity. ECS with 6% initial MC generated much higher foots (6.4-9.4%) in the oil compared with that of the 12% MC ECS (1-1.7%). The crude oils from CWS had the lowest FFA content at 1.25%. Crude oils from UWS and ECS had FFA ranging from 1.4-2.8%. The crude oil from 12% MC CWS had 374 ppm sulfur which was 3 to 8x higher than what were found in crude oils from 6% MC CWS and ECS. The highest P (23 ppm), Ca (14 ppm), and Mg (6 ppm) levels in the crude oil were from 12% MC CWS, which were comparable to totally degummed oils. An 81% oil recovery from 6% MC ECS (22 sec residence time) was obtained at 19 rpm expeller screw speed. Increasing the expeller's screw speed from 19 to 37 rpm decreased the oil recovery 0.2%/ rpm, increased the throughput by 3.3 kg/rpm, from 70 to 130 kg/h, and reduced the press load from 91 to 67%.