Recent research reveals that some varieties of mushrooms, when pressure-cooked, unleash an exponential increase of flavonoids and vitamin C compared to raw. How is this even possible given that most foods lose their nutrients when cooked?!? Let’s delve into the scientific literature to uncover the facts and understand the mechanism behind these results.
Before we get into the sensational-sounding results, I want to emphasize that all the research I consulted noted that different cooking methods might be better for different varieties, kind, and texture of mushroom. So, pressure cooking is not going to coax multiple-fold increase in nutrients from all mushrooms – in some cases, it might not be any better than boiling.
The most recent study  compared the nutritional properties of five mushroom varieties in-the-raw compared to steamed, boiled, microwaved and pressure cooked.
The lead researcher, doctor Zhi Xiang Ng of Nottingham University in Malaysia, sent photos of the samples they used for testing (illustrated in this article) and shared that his lab used a Premiere 5L aluminum pressure cooker to carry out the tests. The team’s goal, according to Dr. Ng, was to mimic the domestic pressure cooking time adopted by Asians (around 10 minutes) to pressure cook the mushrooms – while the study actually pressures cooked them for 15 minutes this is much less time than used in other studies I reviewed.
Interestingly, microwaving the mushrooms proved detrimental to all the nutrients measured for every single mushroom, save one nutrient measured in one variety. While non-pressure steaming was favorable for the tender Button mushrooms and Golden Needle, for the tough and woody Shiitake and King Oyster mushrooms it was pressure cooking that offered the most eye-opening results.
Specifically, pressure cooked Oyster mushrooms increased their Vitamin C content by 200%, Shiitake by 375% and increased the flavonoids of King Oyster mushrooms by 811% – compared to raw. The researchers theorize that the pressure cooking broke down the mushroom to reveal antioxidants that were not easily released when measured the raw.
The improvement of antioxidant activity in pressure cooked mushrooms may be due to the release of active antioxidants from the fibrous complexes during pressure cooking (low moisture level and high temperature). This is further supported by our observation that the increased of FRAP values in the pressure cooked P. ostreatus [Oyster mushroom] and P. eryngii [King oyseter mushroom] were accompanied by the significant (p\0.05) increased of L-AA by 200% and flavonoid content by 811% in respective mushroom. 
This study did not find increased benefits to Shiitake mushrooms compared to other cooking methods, but another study  which measured the antioxidants of Shiitake mushrooms raw, boiled and pressure cooked at high pressure for 15 and 30 minutes found that a long, high-temperature cook increased Shiitake’s antioxidant scavenging activity.
A separate study that checked six types of oyster mushrooms  also threw its support towards pressure cooking for three of them.
Pressure cooking increased the antioxidant activity of Pleurotus flabellatus [Pink Oyster mushroom], P. floridanus [White Oyster] and P. pulmonarius [Gray Oyster]. This suggested that customized cooking
method including pressure cooking might increase the health beneficial effects associated with increase of antioxidant activities.
While there were nutrient losses, compared to raw, from abalone mushrooms, they were actually less than those provoked from microwaved and boiled. The King Oyster mushroom, which had recorded exponential increases in the first study, only faired a little better in the pressure cooker than boiled. That’s probably because even though it was cooked at the same temperature and time as the first study. Here, the sample was steamed in a covered bowl using an autoclave which likely slowed-down the actual heat-up of the mushroom (technically cooking it at a lower temperature).
Unfortunately, pressure cooking was the worst cooking method for Yellow Oyster mushrooms – ranking as the cooking method the bottom of nutrient retention – maintaining only half of the measured antioxidants compared to the second-worst method, boiling. The big winner was the White Oyster, with the suspicion that the rougher textured benefitted from pressure cooking by teasing out the antioxidants.
For the mushrooms subjected to pressure cooking, P. floridanus [White Oyster] again showed the highest scavenging ability(>200 %) when compared to all the mushrooms processed and uncooked. The improvement in antioxidant activity could be due to the release of active antioxidants from the fibrous complexes during pressure cooking (low moisture level and high temperature).
It’s worth mentioning that while a study on four varieties of Porcini Mushrooms  did not have any compelling evidence for pressure cooking this variety over other cooking methods, it did show that pressure cooking Porcini was not any worse than steaming, boiling or frying and at a slight advantage over microwaving them.
Shiitake, Oyster, King Oyster mushrooms have their nutritional profiles enhanced by pressure cooking and Porcini mushrooms don’t do any worse than other cooking methods in the pressure cooker and show a slight nutritional advantage over microwaved.
Each mushroom variety will be affected differently by pressure cooking and evidence supports that the toughest, most fibrous mushrooms can have their nutritional potential un-locked with pressure cooking.
See Also: Pressure Cooker Nutritional Information
pressure cook them ‘shrooms!
Here are some hip ideas on how to get the best out of your mushrooms, with pressure! You can easily exchange the kind of mushroom called-for in the recipe for Shiitake or Oyster as a delicious, and nutritious, alternative.
1. Ng, Zhi Xiang, and Wan Chein Tan. “Impact of optimised cooking on the antioxidant activity in edible mushrooms.” Journal of food science and technology 54.12 (2017): 4100-4111.
2. Choi, Y., et al. “Influence of heat treatment on the antioxidant activities and polyphenolic compounds of Shiitake (Lentinus edodes) mushroom.” Food Chemistry 99.2 (2006): 381-387.
3. Tan, Yee-Shin, et al. “Influence of customized cooking methods on the phenolic contents and antioxidant activities of selected species of oyster mushrooms (Pleurotus spp.).” Journal of food science and technology 52.5 (2015): 3058-3064.
4. Sun, Li Ping, et al. “Effects of different cooking methods on nutritional characteristics of Boletus aereus.” Advanced Materials Research. Vol. 634. Trans Tech Publications, 2013.