Certain plant materials require enzymatic maceration prior to lipid release as their volatile components are glycosidically bound. Enzymes can be either endogenous or exogenous to the biomass. For example, methyl salicylate (wintergreen oil) is an organic ester that is naturally produced by many species of plants. The plant leaves contain the precursor gaultherin and the enzyme primeverosidase; when the leaves are macerated in warm water, the endogenous enzyme acts on the gaultherin and liberates free methyl salicylate and primeverose (Handa, 2008). In the case of the exog­enous addition of enzymes, recent advances in the field of algal lipids have demonstrated the addition of com­plex mixtures of enzymes to selectively degrade cell walls in a cascade of hydrolytic reactions. Released lipids are isolated and collected for further processing (Liang et al., 2012).

Expression (Cold Pressing)

Expression or cold pressing is commonly used in the production of essential and food oils. The term expres­sion refers to any physical process in which the essential oil glands in the biomass are crushed or broken to release the oil. The resulting oil—water emulsion is typi­cally separated by centrifugation. Traditionally, cold pressing was conducted by hand; however, for large — scale commercialization, this is impractical. Thus, with the advancement of industrialization, a number of machines have been designed to achieve the same results on commercial scale. It is important to note that oils extracted using this method have a relatively short shelf life (Martinez et al., 2008).