If we describe here the extraction on a laboratory scale of lipids from various biological materials to run analytical procedures, different processes may lead also to the extraction of oil from many seeds, nuts, and kernels for use as nutritional supplement, as well as raw material for industrial applications.
The type of instrument that is appropriate depends on the size of the operation. Oil processing operations range from “cottage industries” processing some kg per day, to factories processing several thousand tons of seed per day. In all cases, the sequence of operations includes cleaning, dehulling, grinding, and pressing. Furthermore, oils generally need refining to remove cloudiness, excess color and unpleasant flavors. As many crude oils contain variable amounts of mucilaginous compounds (gums) combined with phospholipids, a degumming process has to be run (Dijkstra AJ, OCL 1998, 5, 367). In several instances, and especially when seeds have low oil content (like soybeans) more complex methods including solvent extraction are processed. If hexane is the most commonly used solvent, isohexane appears to be the most likely candidate to replace n-hexane as the preferred oilseed extraction solvent, mainly in USA to avoid federal environmental regulations applying to the use of n-hexane. Several studies have shown that the extraction performances of the two isomers are quite similar (Inform 2002, 13, 282).
Those who are interested in oilseed processing will find a comprehensive description of basic processes with sources for additional information and a list of suitable raw material in the ATTRA (National Sustainable Agriculture Information Service) publication :
Aqueous enzymatic oil extraction is an emerging technology since it offers many advantages such as elimination of solvent consumption, degumming operations and removal of some toxins. A review of aqueous and enzyme-based processes may be consulted (Rosenthal A et al., Enzyme Microb Technol 1996, 19, 402). Applications of that methodology to the oil extraction of Irvangia seed kernels (Women HM et al., Eur J Lipid Sci technol 2008, 110, 232) and canola seeds (Latif S et al., Eur J Lipid Sci Technol 2008, 110, 887) have been reported.
Comparative experiments on tobacco seeds have demonstrated that the best oil recovery was obtained by cold pressing (Stanisavljevic IT et al., Eur J Lipid Sci Technol 2009, 111, 513). Shortly, seeds were pressed by a hydraulic press (Komet, Germany) through three nozzles (diameter of 15, 10 and 6 mm). The press does not involve mixing and tearing of the seeds. The seed cake was ground by an electrical mill and the residual oil was extracted by using n-hexane at a seeds-to-solvent ratio of 1 : 3 g/mL and 25°C for 60 min. This recovery technique is said to be more acceptable than the other methods, not only for economic but also for environmental, health and safety reasons.
As hexane presents numerous drawbacks like high flammability, dangerousness for health and environment, it has ben variously replaced by agro-solvents. An overview of these techniques are presented in the work of Fine F et al. (Fine F et al., OCL 2013, 20, A502).