Production of dihomo‐γ‐linolenic acid by<i>Mortierella alpina</i> 1S‐4

Abstract

Abstract The mycelial dihomo‐γ‐linolenic acid content of an arachidonic acid‐producing fungus, Mortierella alpina 1S‐4, was found to increase, with an accompanying marked decrease in its arachidonic acid content, on cultivation with sesame oil. The resultant mycelia were found to be a rich source of dihomo‐γ‐linolenic acid. This unique phenomenon was suggested to be due to specific repression of the conversion of dihomo‐γ‐linolenic acid to arachidonic acid by the oil. After fractionation of the oil with acetone into oil and non‐oil fractions, it was found that the effective factor(s) was present in the non‐oil fraction. In a study on optimization of the culture conditions for the production of dihomo‐γ‐linolenic acid by M. alpina 1S‐4, a medium containing glucose, yeast extract and the non‐oil fraction was found to be suitable for the production. Under the optimal conditions in a 50‐1 fermentor, the fungus produced 107 mg of dihomo‐γ‐linolenic acid/g dry mycelia (2.17 g/l of culture broth). This value accounted for 23.1% of the total fatty acids in the lipids extracted from the mycelia. The mycelia were also rich in arachidonic acid (53.5 mg/g dry mycelia, 11.2%). Other major fatty acids in the lipids were palmitic acid (24.1%), stearic acid (7.0), oleic acid (20.1), linoleic acid (6.6) and γ‐linolenic acid (4.1).