Yeast, oat and mushroom beta-glucan: how do they differ?

All beta-glucans are long chains of glucose, but they differ in how the glucose units are linked, and that depends on where they come from. In oats and barley, beta-glucan is a straight, unbranched chain with a mix of β-(1→3) and β-(1→4) links, found in the cell walls of the grain. In yeast and in most mushrooms, beta-glucan has a backbone of β-(1→3) links with β-(1→6) side branches, found in the cell wall of the yeast or mushroom. By amount, a 2021 review gives 2 to 20 g per 100 g of dry barley and 3 to 8 g per 100 g of dry oats, while rice has 0.13 g. Beta-glucan has no Thai Reference Daily Intake (Thai RDI) of its own.

In short:

• Same building block: glucose, joined by beta links
• Oats and barley: straight chains of β-(1→3) and β-(1→4) links, no branches
• Yeast and mushrooms: a β-(1→3) backbone with β-(1→6) branches
• Where it sits: grain endosperm cell walls; yeast and mushroom cell walls
• Cereals: barley 2 to 20 g, oats 3 to 8 g, rice 0.13 g per 100 g dry weight
• Mushrooms: oyster 40.34 g, shiitake 26.26 g, button 11.36 g per 100 g dry mass in one study
• Daily amount: no Thai RDI for beta-glucan; dietary fibre as a whole is 25 g

This article compares beta-glucans by structure, source and the amounts measured in food. For the daily reference amounts of fibre and other nutrients, see What are the Thai daily reference amounts for each nutrient?

What is beta-glucan?

Beta-glucan is a polysaccharide, a large carbohydrate made of many sugar units. A 2019 review in the International Journal of Molecular Sciences, by researchers in China, describes beta-glucans as polysaccharides of D-glucose units linked through beta-glycosidic bonds, found in yeast, fungi including mushrooms, some bacteria, seaweeds and cereals such as oats and barley. The review stresses that the large-scale structure of beta-glucan differs a great deal by source.

What the numbers in the links mean

Each glucose unit has six numbered carbon atoms. A β-(1→3) link joins carbon 1 of one glucose to carbon 3 of the next; a β-(1→4) link joins carbon 1 to carbon 4; a β-(1→6) link joins carbon 1 to carbon 6. The "beta" refers to the orientation of the bond. Starch, by contrast, is made of glucose joined by alpha links. Studies of mushrooms therefore measure "total glucan", "alpha-glucan" and "beta-glucan" separately.

Two main families

Source: 2019 review in the International Journal of Molecular Sciences (structure table).

How does the structure differ by source?

Oats and barley

The 2019 review describes oat beta-glucan as an unbranched polymer of (1→3)- and (1→4)-linked β-D-glucose units, with the (1→4) links predominating, and barley beta-glucan as linear chains with (1→3) and (1→4) links. A 2021 review from the N.I. Vavilov All-Russian Institute of Plant Genetic Resources in St Petersburg explains that cereal cell walls contain little cellulose and are made mainly of arabinoxylans and (1,3;1,4)-β-D-glucans. Arabinoxylans dominate in rye and wheat, while beta-glucans dominate in barley and oats. The chains are long, with a degree of polymerisation of about 1,000 or more.

Yeast

The 2019 review lists beta-glucan from Saccharomyces cerevisiae, the yeast used for bread and beer, as β-D-glucose units with (1→3) and (1→6) links.

Mushrooms

Mushroom beta-glucans vary between species. In the 2019 review, beta-glucan from shiitake (Lentinula edodes) is a β-(1→3) chain with β-(1→6) branches that forms a triple helix in water. Beta-glucan from Pleurotus tuber-regium has a (1→3) main chain in which, on average, every third unit carries a (1→6) branch. The beta-glucan described for wood ear mushroom (Auricularia auricula-judae) is different again: a (1→4)-linked main chain with branches at carbon 6. Researchers at Kasetsart University describe the mushroom cell wall as containing beta-glucan with a β-1,3 backbone and β-1,6 branches.

Chain length

Source: 2019 review in the International Journal of Molecular Sciences. The wide ranges reflect different varieties, extraction methods and measurement methods.

How much beta-glucan is in cereals?

Beta-glucan per 100 g of dry grain

Source: 2021 review from the N.I. Vavilov All-Russian Institute of Plant Genetic Resources, which collects figures from earlier studies.

What changes the amount in grain

The same review says the beta-glucan content of barley depends on both the genotype and the growing conditions, and that it varies more with genotype and variety than most other grain components. Naked (hull-less) forms of oats and barley appear to have more beta-glucan than hulled varieties, and two-row barley varieties have more than six-row ones. It also reports a study in which sprouting barley grain lowered its beta-glucan content.

How much beta-glucan is in mushrooms?

Beta-glucan in cultivated mushrooms (dry mass)

A 2020 study from the Medical University of Bialystok in Poland measured glucans in 18 wild and 3 cultivated mushroom species, using a laboratory test kit that measures total glucan and alpha-glucan and calculates beta-glucan as the difference.

These figures are per 100 g of dried mushroom. Fresh mushrooms in the study were mostly water, with a moisture content between 90.76 and 92.54% for the three cultivated species. The authors also used a second method (Congo red), which gave different results, so the figure for a mushroom depends on how it is measured.

A Thai bamboo mushroom

Phallus atrovolvatus is a bamboo mushroom found in the forests of southern Thailand. A 2024 study led by Kasetsart University, with Prince of Songkla and Mahidol Universities, analysed mushrooms cultivated by the Department of Agriculture at two stages: the immature "egg" stage and the mature fruiting body, which is the form commonly eaten in Thailand.

The study found that almost all of the mushroom's carbohydrate was dietary fibre, at about 47% of dry matter in both stages, and that beta-glucan made up most of its glucan. Only one species, grown under controlled conditions, was tested.

Straw mushroom

Straw mushroom (Volvariella volvacea, het fang) is a mushroom eaten in Thailand. A 2023 study from Thammasat University extracted its polysaccharides with hot water, with or without high pressure first, and found protein-bound polysaccharides linked by beta-glycosidic bonds. Adding high pressure before hot water extraction gave 15 to 20% more beta-glucan in the extract than hot water alone, so the amount in an extract depends on the extraction method.

Where does yeast beta-glucan come from?

The yeast cell wall

Yeast beta-glucan comes from the cell wall of yeast, most often Saccharomyces cerevisiae. A 2002 review from the University of Amsterdam describes the wall as having an inner layer, which gives most of its mechanical strength and anchors the proteins that form an outer layer. The review notes that the make-up of the wall can vary considerably with conditions. A 2003 study from Toulouse in France measured beta-1,3-glucan, beta-1,6-glucan, mannan and chitin in the wall and found that the dry mass and polysaccharide content of the cell wall could vary by more than 50% with the carbon source, nitrogen supply, pH, temperature, aeration and way of growing the yeast.

Brewer's spent yeast and cultured yeast

A 2024 study from Korea's National Institute of Agricultural Sciences compared brewer's spent yeast, the yeast left over from making beer, with cultured S. cerevisiae. The yeast cells were first broken down (autolysed), and the insoluble residue was analysed.

Mannan is another polysaccharide of the yeast cell wall, which releases the sugar mannose when it is broken down, and chitin is a third. The two kinds of yeast differ because of where they came from and how they were grown; as the Toulouse study above found, growing conditions alone can change the cell wall by more than 50%.

Is there a recommended daily amount?

Beta-glucan itself does not have a Thai Reference Daily Intake (Thai RDI), so there is no recommended daily amount for it in Thailand. Beta-glucans are counted among dietary fibres, high-molecular-weight carbohydrates of plant origin, according to the 2021 review of oats and barley, and the Kasetsart study describes mushroom beta-glucan as a type of dietary fibre. The Thai RDI for dietary fibre as a whole is 25 g a day.

Comparing figures from different studies

The figures in this article come from different units: grams per 100 g of dry grain, grams per 100 g of dried mushroom, percent of dry matter and micrograms per milligram of yeast residue. They also come from different measuring methods. They describe how much each source contains, not how much anyone needs, and they cannot be compared directly with one another.

Who should talk to a doctor or pharmacist?

If you are pregnant or breastfeeding, or take medication regularly, check with a doctor or pharmacist before taking supplements.

Dietary supplements are not intended to prevent, treat or cure any disease.