Effect of olive oil on the production of mycelial biomass and polysaccharides of Grifola frondosa under high oxygen concentration aeration

In this research, the factors of oxygen concentration (21%, 30%, and 40%) and olive oil addition were studied on the production of mycelial biomass and polysaccharides of Grifola frondosa in a 5-L jar fermentor. The 40% oxygen was found to inhibit both cell growth and polysaccharide production with a higher rate of glucose consumption. The highest cell concentration was found at 9.29 g/L at day 9 with 1 vvm at 21% O2. With 30% O2 the inter-cellular polysaccharide (IPS) level increased earlier than 21% O2 and reached the maximum concentration at day 8 with 21.9 mg/g. On the other hand, 21% O2 reached the maximum concentration at day 11 with 19.5 mg/g. With 1% olive oil addition in 21% O2 and 40% O2, the production of mycelial biomass was enhanced and increased to 10.1 and 14.9 g/L, respectively, after 9 days’ cultivation. And the extra-cellular polysaccharide (EPS) production increased from 0.7–0.9 g/L to 2.24 g/L and 3.00 g/L at day 13 with 21% O2 and 40% O2 aeration, respectively. In addition, the IPS increased rapidly and reached the maximum level of 28.2 mg/g at day 7 and this level remained till day 13 through the whole fermentation. The scanning electron microscopy (SEM) of the mycelia and cell activity were studied to investigate the role of olive oil under high concentration of oxygen aeration. The vegetative cell was observed from both the 7-day-old culture and the 9-day-old culture from both 21% O2 and 40% O2 with olive oil addition. With 40% O2 aeration, low growth activity and significant wrinkles appeared on the surface of mycelia on both 7-day-old culture and 9-day-old culture. The olive oil addition in media was observed to reduce the wrinkles appeared on the surface of mycelia under high concentration oxygen and made the cell be aging more slowly.