Shiitake Mushrooms May Improve Human Immune Function, Especially If Grown On Old Oak Logs

These mushrooms contain high-molecular-weight polysaccharides (HMWP), which some studies suggest may improve human immune function. Other research indicates that the shiitake compound eritadenine may help lower cholesterol levels.

Agricultural Research Service (ARS) agronomist David Brauer has been studying shiitake production at the agency's Dale Bumpers Small Farm Research Center, Booneville, Ark. Working in collaboration with producers at the Shiitake Mushroom Center in Shirley, Ark., Brauer evaluated whether shiitakes grown on logs have higher levels of HMWP than shiitakes grown on commercial substrates.

The group inoculated logs with spores from three different shiitake varieties and compared the yield with shiitake yields grown on commercial substrates. They found that the log-grown shiitakes had HMWP levels as much as 70 percent higher than the substrate-grown shiitakes. The team also observed that shiitakes grown on red and white oak logs had higher levels of HMWP than shiitakes grown on sweet gum logs.

Logs used in shiitake production generally provide good yields for around two to three years. Larger shiitake farms may have 3,000 or more logs on the premises, and retire around 1,000 of them every year.

Not to let those used logs go to waste, Brauer’s team chipped a selection of spent logs, added urea and green grass cuttings to the chips and then composted the mixture. They found that the nitrogen levels in the resulting compost were comparable to nitrogen levels in other purchased soil amendment materials.

The researchers used the log compost to amend soil in a greenhouse spinach production system and found that the seedlings exhibited greater growth rates than seedlings cultivated in soil that had not been amended. Using recycled log compost provides another way for shiitake mushroom growers to increase their profits.

In 2004-2005, producers harvested approximately 9 million pounds of shiitake mushrooms, which sold for an average price of $3.21 per pound. Brauer’s findings lend a range of support to farmers interested in starting--or boosting profits from--log-grown shiitake production.