Mushrooms Part II: Why they taste amazing, why they're healthy, and why we need more choices in our grocery stores

If you haven't read Part I: Mushroom Materials Mania!

HEY! I thought this blog was about materials and chemicals?

Well you’re right, I’ve swerved from the path I was on and took a detour, I like driving on the scenic route instead of the highway so if I take an exit here and there, do stay along for the ride. I’ve tried to put informative headings so you can jump to whatever you’re interested in reading. If you wish to take the long road with me then get comfy.

After my mom was diagnosed with onset diabetes, I became interested in learning about nutrition. Turns out genetics play a crucial role, but also my conception of what is a “sugary” food was flawed. Starchy foods like potatoes, bananas, rice, and bread can release substantial amounts of glucose into the blood stream just like foods containing refined sugar. Hopefully at a future date I’ll talk more about this, but for now I’d just like to talk a little bit about the nutritional features of mushrooms. As a person of South Asian descent diabetes and heart diseases are our death knell. Although not part of typical South Asian cuisine, maybe a food like mushrooms with their high protein and high fibre content might be something worth learning about.

Why plant-based proteins are becoming more popular?

Much work has been done on the energy intensity and carbon dioxide emissions associated with meat-based diets. This is mainly due to the amount of food and water required over the life time of the animal to produce a small amount of meat, but also on the changes in land-use as forested areas are cleared for pasture land. This is why plant-based proteins are becoming more popular, especially for those who would like to avoid or lower their meat consumption for social / ethical reasons.

Edible mushrooms: cultivated vs. wild

If you're lucky enough to live near a large grocery store you may have at your disposal maybe 10 or so different types of mushrooms. These are edible mushrooms produced on an industrial scale, but there are over 100 types of mushrooms that are cultivated, and a staggering amount of edible wild species estimated at 3000. [1] China is the largest producer at over 1.5 million metric tonnes of mushrooms and although you can't get fresh mushrooms from China perhaps dried mushrooms may be a route towards expanding your mushroom palate.

Why mushrooms are tasty - Umami!

We are all familiar with the taste sensations of sweet, bitter, salty, and sour. Taste receptors respond to sugars to produce a sweet taste, salt for salty, acids for sour, and a variety of compounds for bitter. The amino acid glutamic acid (and to a slight degree aspartic acid) and nucleic acids (inosine/ guanosine monophosphate) trigger taste receptors for what is known as umami.[2] Glutamic acid is found in beef, poultry, eggs, and fish but it is often locked within tough protein. This means that if you don't stew or slow cook your meat that umami taste never gets unlocked. Only when the meat is cooked extensively is the glutamic acid released. It can also be found in cheese, yogourt, soybean products, and of course mushrooms! In these cases the proteins are far more accessible and so it is easier to produce a umami taste. Mushrooms contain aspartic acid and glutamic acid and together they help produce that unique taste. If you look at Figure 1 you can see what fraction of the amino acids (protein) contribute towards an umami flavour. This data is based on a set of wild-edible mushrooms, some of which are depicted in Figure 2. It would appear that protein content can vary greatly and as a result the umami content also increases.  

Figure 1: Amino acid (AA) content in mushrooms varies between species. a) shows the Non-Umami AA and the Umami-AA ( Glutamic acid and Aspartic acid) content and b) shows the essential amino acids (EAA) and the non-essential amino acids (NEAA) content of 13 wild-edible species of mushrooms, some of which are depicted in Figure 2. The plotted values are mg of amino acid / kg of dry matter. This is important to state since mushrooms contain a high amount of water content when fresh. Data was taken from Wang et al.[3] and analyzed and plotted by Jason D'Souza.

Figure 2: A few of the mushrooms discussed in Figure 1. Various Sources[b]

Nutritional profile of mushrooms

Mushrooms are considered to be highly nutritious because of their high protein, high fibre, and low fat content as shown in Figure 3. These macronutrients are complemented by the presence of micronutrients like phenolic compounds (may possess anti-oxidant behaviour), tocopherols (a vitamin E compound), ascorbic acid (vitamin C), and carotenoids (may possess anti-oxidant behaviour).[1] These will be discussed more below.

Figure 3: Protein content of a variety of wild mushrooms. Data was taken from Wang et al.[3] and analyzed and plotted by Jason D'Souza.

Protein:
Mushrooms can play an important role in nutrition due to their protein content. When evaluating the protein content of a food the main considerations are the concentration, the type of protein (the chemical structure of the amino acid is also important as some are more preferable than others), and their digestibility (how much is actually taken from the food and retained in the body). Just like any other protein, how the food is processed and cooked will also dictate how much protein actually makes it into your stomach.

Essential amino acids cannot be made by your body, and so a higher EAA index represents a greater nutritional value. Oyster mushrooms have been given an amino acid index rating of 85. [4] In Figure 1 you can also see a graph showing the breakdown of EAA vs. non-essential amino acids (NEAA). Although there is some minor variation in the ratio of EAA/NEAA, the amount of variation between the overall protein content between species seems to have a more dominant role.

We rarely achieve that complete intake and this is because of digestibility. Mushroom proteins were shown to be digested up to 79 %, which is comparable to legumes that ranged from 70-90%, and rice from 84-100%. [4] Protein digestibility corrected amino acid score (PDCAAS) for some edible mushrooms from Thailand (Pleurotus sajorcaju, Pleurotus ostreatus, Lentinus edodes, Lentinus lepidus) had a score ranging from 0.38 - 0.45, while casein (the protein in milk) had a score of 0.86.[5] Wikipedia's list of PDCAAS states that mycoprotein (protein from fungases like mushroom) at 0.99. Wikipedia's table cites mycoprotein.com who in turn cites Marlow Foods. This large discrepancy between a scientific paper and the results of industry-based tests makes it difficult to assess in general where mushrooms actually fall within the spectrum of high protein food digestibility. Unfortunately, with limited access to scientific papers a more thorough analysis into this could not be done.

You've probably heard enough about protein, so let's briefly touch on some of those other macro- and micronutrients.

A quick discussion of carbohydrates and nutrition
The world of carbohydrates (also referred to as polysaccharides, polymers of sugar structures) is complex and varied. Digestible carbohydrates like starch are rich in energy (glucose is the most common digestible carbohydrates.

Polysaccharides that cannot be digested are referred to in the world of nutrition as fibre. The benefits of high fibre diets are well known, helping with regularity and health of your digestive system. Although most typically this indigestible fibre is cellulose-based there are a variety of indigestible carboyhydrates as shown by Chart 1- List of Polysaccharides and Food Examples by nutrientsreview.com. It is believed that some of these non-typical sources of indigestible fibre like beta glucans may have additional health benefits like boosting the immune system, being anti-cancer, help control of blood lipids, and glucose levels,[6]. although this appears to be an area of research that is still under much investigation and so claims touting these benefits should be taken with some skepticism. The work by Cheug et al. [6] cites many papers that discuss these health benefits with regard to mushrooms. As someone quite removed from this field of (biopharmalogical effects of foods) I will leave it for others to discuss the validity of these claims.

           

Carboyhydrates in mushrooms:
Mushrooms have been reported to contain indigestible carbohydrates like beta-glucans, chitin, and mannans. [3] It can be seen from Figure 3 that upwards of 50% of a mushroom is carbohydrates, and of that a substantial portion are non-digestible carbohydrates that could pose health benefits as discussed above.

Anti-oxidants:
These class of compounds are quite controversial at the moment. They are varied in structure and believed to protect the body from harmful radicals (energized species) that cause damage in the body. As I don't feel capable to provide an in depth discussion of this, nor is this the place, I will simply provide some information to fuel a healthy skepticism: 1) anti-oxidant behaviour in-vitro (done in glass with cells) is different than in-vivo behaviour (done in the body), and 2) that digestion of foods with anti-oxidants does not guarantee those compounds make it to cells or areas of the body where those anti-oxidant compounds are needed. Nonetheless, if a consensus is reached, mushrooms have been found to contain the following anti-oxidants: quercitin, catachin, p-coumaric acid, caffeic acid, and gallic acid at concentrations of less than 100 mg/kg.[3]

Minerals:
Mushrooms are good at accumulating minerals with potassium concentrations greater than 16000 mg/kg of dry matter, phosphorus ranging from 4000-19000, calcium from 70-2000, magnesium from 500-1500, and sodium from 100-1600, and less than 1000 for Fe, Zn, Cu, and Mn.[3]

Let's make these numbers a little less abstract!
A typical portion is let's say about a handful of mushrooms that is about 40 g, button (oyster) mushrooms are about 89% water [thanks whole foods], and for possibly anemic out there the average Fe content for those mushrooms studied above was 493 mg/kg dry matter[3], so that works out to 2.2 mg of iron per serving (40 g). This article by the greatist.com  has daily recommended amounts for a variety of minerals and vitamins (and lots of citations, hooray for citing material!), and lists 8 mg as the requirement for iron. Therefore a 80 gram serving of mushrooms would have 4.4 mg of iron compared to a 3 oz (85 g) serving of beef that has 2.3 mg! Not too shabby for our fungal friend!    

Toxic elements
Although mushrooms are also good at accumulating toxic elements like like As, Hg, Cd, Pb. Concentrations ranging from 0.5-2 mg/kg (dry material) of As, Cd, Hg, Pb were found in some wild mushroom in China. [3] The fact that mushrooms are good at removing toxic compounds is why they are also being researched for their potential in bio-remediation, referred to as myco-remediation and myco-filtration.

Where do these toxic compounds come from?
Well they can come from industrial waste, leached from mining operations or garbage dumps, or via pesticides, but some may just be naturally occurring in the soil. Rachel Carson's book Silent Spring eloquently describes how toxic organic compounds can bio-accumulate as they progress up the food chain (plants - insects - birds/rodents- carnivorous mammals including us). Thus small concentrations can build-up in higher species. It should be noted that there is a big difference between a pure element and an element within a compound, as demonstrated by the toxicity of Mercury (Hg) and an inorganic/organic compound of mercury such as ethyl-mercury which is not toxic, as discussed by the world health organization. Therefore, the takeaway is that although mushrooms appear to show an ability to concentrate toxic elements, consumption of regular food crops and pasture land that feed livestock can lead to exposure as well. We should be more cognizant of where our foods are coming from, demand better farming practices, and fight for laws that protect our health and environment from pollution.

Summary
Hopefully this foray into nutrition and mushrooms has shown that mushrooms have a lot to offer, from their umami taste and their macro- and micronutrients. For most people the selection of mushrooms are quite limited, but there remains a great variety of edible mushrooms available for cultivation. As we begin to appreciate the nutrition and health benefits of eating mushrooms, in addition to the possible environmental benefits, perhaps we can start to see a greater variety in the mushrooms being cultivated!

Now if all this talk about the yumminess of mushrooms has you salivating then get cooking! Check out the Mushrooms Canada Blog for great recipes or check out this Pinterest board full of mushroom recipes

What's coming up next...
Well I'd like to get into a few of the actual applications of mushrooms, their use as colourants, myco-remidiation and mycofiltration, as faux-leather, and as a binder for making bio-based building material or insulation. Stay tuned!

References

[1] F. S. Reis, L. Barros, A. Martins, and I. C. F. R. Ferreira, “Chemical composition and nutritional value of the most widely appreciated cultivated mushrooms: An inter-species comparative study,” Food Chem. Toxicol., vol. 50, no. 2, pp. 191–197, 2012.

[2] N. Choi and J. H. Han, How Flavour Works: The Science and Taste of Aroma. WILEY-BLACKWELL, 2015.

[3] X. M. Wang et al., “A mini-review of chemical composition and nutritional value of edible wild-grown mushroom from China,” Food Chem., vol. 151, pp. 279–285, 2014.

[4] M. Friedman, “Nutritional Value of Proteins from Different Food Sources. A Review,” J. Agric. Food Chem., vol. 44, no. 1, pp. 6–29, 1996.

[5] Y. Cuptapun, D. Hengsawadi, W. Mesomya, and S. Yaieiam, “Quality and quantity of protein in certain kinds of edible mushroom in Thailand,” J. Agric. Food Chem., vol. 44, no. 4, pp. 664–670, 2010.

[6] P. C. K. Cheung, “Mini-review on edible mushrooms as source of dietary fiber: Preparation and health benefits,” Food Sci. Hum. Wellness, vol. 2, no. 3–4, pp. 162–166, 2013.

Images
Soup , Burger , Saute , Pizza

[a] - Images not sourced from Wikipedia are Collybiaalbuminosa , Lactariushatsudake , Macrolepiotaalbuminosa