GLA-containing oils are used in products covering a wide rage of uses, from licensed prescription medicines (hyperlidaemia, eczema, mastalgia) through functional foods (nutriceuticals), infant nutrition, bulk nutrition and cosmetics to animal health.
The largest source of GLA (gamma-linolenic acid) is the seed oil of the evening primroses (Oenothera spp.) of the subsection Euoenotherae. These species were originally natives of North America but are now widely distributed in the flora of temperate regions around the world. The crop has only recently been domesticated, with the first recorded commercial crop for oil extraction being grown in 1970. Since then, research in several countries has produced improved varieties and production techniques which have substantially improved yield, quality and reliability. Production of seed originally started in Western countries, but seed production for export as a GLA source began in China in 1980, with seed harvested from wild plants. Cultivation as a crop started in earnest in 1986 and by 1993 China had become the world's dominant supplier, helped by very favourable climatic conditions and low-cost labour. China now probably accounts for around 90% of world evening primrose seed production. Extraction of evening primrose oil in China is mostly through cold pressing followed by refining, whilst in the West solvent extraction is more common and some unrefined oils are sold which have improved stability.
Other sources of GLA exist. The most commercially important of these is borage (Borago officinalis) seed oil. Borage is also a recently domesticated plant, although rather easier to grow than evening primrose. The main production is in England, although some is grown in New Zealand and China. Another GLA source, blackcurrant (Ribes nigrum) seed, is a by-product of juice manufacture, whilst oils are also produced from a number of fungi (eg Mortierella spp.) grown in fermentation tanks. There is some evidence that these oils may have different physiological effects which cannot simply be related to their GLA content. It is therefore necessary to test each oil in each situation; it is not justified to extrapolate from one GLA-containing oil to another. In the future it is likely that the supply of GLA will be dominated by low-cost production in transgenic crops and, partly as a result, a number of new uses for GLA will arise.
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