3. Results and discussion
3.1. Inhibition of fatty acid desaturase in M. alpina by p-anisidine Δ6 desaturase activity was defined as a desaturase index. i.e., the ratio of 18:2ω6 to 18:3ω6þ20:3ω6þ20:4ω6 in total mycelial fatty acids, since the desaturation reaction is not reversible and 20:4ω6 is not further metabolized in the fungus (Yamada et al., 1987; Sakuradani et al., 2013). Therefore, the desaturation index increases when the desaturase activity is reduced and the substrate 18:2ω6 for Δ6 desaturase is not consumed through Δ6 desaturation. Table 1 shows that p-anisidine supplementation caused increases in stearic acid (18:0), oleic acid (18:1ω9), and 18:2ω6, and decreases in 20:3ω6 and 20:4ω6. Addition of p-anisidine to the culture medium is considered to cause Δ6 desaturation inhibition through an increase in the Δ6 desaturase index. Similarly, the supplementation of methyl p-coumarate and propyl gallate caused inhibition of the Δ6 desaturase activity (Kawashima et al., 1996a, 1996b). On the other hand, the supplementation of (þ)-sesamine, which is a specific inhibitor of Δ5 desaturase, hardly influenced the fatty acid composition, except for the levels of 20:3ω6 and 20:4ω6, and caused a remarkable decrease in only the Δ5 desaturase index (Shimizu et al., 1991).
