The complex world of polysaccharides edited by Desiree Nedra Karunaratne

Yeast (Saccharomyces cerevisiae) Glucan Polysaccharides –  

Occurrence, Separation and Application in Food, Feed and Health Industries  57 

Only some of these effects can be promoted by regular yeast cell wall preparations. 

However separating the bioactivities caused by the selenomethionine-containing yeast 

proteins from the activity caused by the polysaccharide parts of selenized yeast cell walls is 

difficult. Comparison of genomic activity in tissues taken from animals fed with SelPlex® to 

those fed with Bio-Mos® spiked with selenomethionine indicates very large differences in 

the regulation of multiple groups of genes for both treatments (Kwiatkowski et al., 2011), 

which may indicate that the bioactivity of Sel-Plex® involves cooperation between the 

selenoprotein and the polysaccharide components of selenized yeast cell walls.  

Indeed, selected extracts from selenized yeast/yeast cell walls (Kwiatkowski et al., 2011) 

show potential as future, possible treatments of diseases such as type 2 diabetes, cancer and 

Alzheimer’s. 

5. β-(1→3)(1→6)-D-glucan as valuable by product from yeast 

fermentation 

The commercial source from which the bulk yeast cell wall polysaccharides (including β-

glucan) are produced uses the same strains of yeast as are used in fuel alcohol production. 

Le Saffre/ADM, Lallemand, Enzyme Development (New York) and DSM Life Sciences 

(Delft) are the largest suppliers of yeast for fuel ethanol producers in the United States and 

the European Union. Major factors that affect yeast cell wall composition include yeast 

strain (Hahn-Hagerdal et al., 2005), growth conditions (growth medium, temperature, 

osmotic pressure, toxic metabolites) and the time of harvesting (Aguilar-Uscanaga & 

Francois, 2003; Klis et al., 2002; Klis et al., 2006). Fuel alcohol fermentation is a high stress 

process (Devantier et al., 2005) and the cell walls of the yeast collected as its byproduct 

contain a high amount of β-glucans (Basso et al., 2008; Knauf & Kraus, 2006; Jones & 

Ingledew, 1994). In general, yeast strains of Saccharomyces cerevisiae that are used in baking 

(baker’s yeast) have a higher β-glucan-to-α-mannan ratio than those that are used for 

alcohol fermentation (brewer’s yeast), therefore it is advantageous to use pure baker’s yeast 

for producing high quality (1→3)(1→6)-β-D-glucan for medicinal applications (Kim et al., 

2007). The process of separating various yeast components has been heavily patented. 

However, the differences in the technologies are minor and in principle do not differ from 

the methodology described by Manners and Fleet (1976). The process starts from autolysing 

yeast cells at a temperature between 45

o

C and 65

o

C at slightly acidic pH, to release yeast cell 

walls that are insoluble and denser than the cytoplasmic contents and can be separated by 

centrifugation (Wheatcroft et al., 2002). These steps can be followed by incubating the yeast 

cell walls with alkaline protease at a pH of 9 to 10 to solubilize mannans and leave behind 

insoluble  β-glucan (Zapata et al, 2008), which can then be physically separated from the 

liquid fraction by centrifugation and subsequent washing (Sedmak, 2006). Additional 

enzymes, like glucoamylase and lipase, can be used to hydrolyze α-glucan from α β-glucan, 

which is still present in the cell wall material and to solubilize the residue lipids from cell 

membranes. The final step of β-glucan production is a spray-drying that produces a white-

to-maroon colored powder that does not carry any taste or aroma and is useful for feed and 

food applications. Further alkaline and acidic treatments of the food-grade β-glucan (Kelly, 

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The Complex World of Polysaccharides 

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2001) yields high purity (98.5% β-glucan, <0.1% mannan, 0.4% α-glucan, 0.3% protein, 0.2% 

chitin) microparticulate β-glucan with reduced molecular weight (from ~1-3 MDa to ~150 

kDa) that is much more easily absorbed by the digestive tract and shows improved activity 

compared with food-grade products containing only ~65% β-glucan. Even further 

hydrolysis produces soluble yeast β-glucan (Jamas et al., 1998; Lee et al., 2001) that still 

retains most of the particular β-glucan bioactivities (Janusz et al., 1986; Wakshull et al., 

1999).  

Yeast  Saccharomyces cerevisiae, its cell wall and products of its fractionation are generally 

recognized as safe (GRAS) by the US Food and Drug Administration (FDA, 1997), and they 

can be legally used as food ingredients but not as food additives. The European Food Safety 

Authority (EFSA) issued an opinion that yeast β-glucans are a “safe food ingredient” (EFSA, 

2011) that can be used as a “food supplement” up to 375 mg/day and in foods for “particular 

nutritional uses” at dose levels up to 600 mg/day. (The uses of yeast cell wall as an animal 

feed ingredient were discussed in section 4 of this chapter).  

Food-grade yeast β-glucans such as BetaRight® and WGP® (Biothera, Inc.) are used as 

ingredients in baked foods, beverages, ceral, yogurt, fruit juices, chocolate and as food 

thickeners in salad dressings, ice cream, mayonnaise, sauces and cheese. The majority of 

these applications have been patented (Zechner-Krpan et al., 2009; Thammakiti et al., 2004) 

and a critical review of 300 patented applications is available (Laroche & Michaud, 2007). 

Yeast  β-glucans improve food rheological properties, gelling, water and oil-holding 

properties, without impacting its taste or odor (Petravic-Tominac et al., 2011). Beta-glucans 

also add health benefits (Laroche & Michaud, 2007) like antioxidative, bacteriostatic and 

immunostimmulating activities. Cosmetic products used in skin treatment contain yeast β-

glucans as moisturizing and moisture-retaining components that also provide a proper 

moistening feeling. Because of its emulsion-stabilizing effects, pleasant texture and 

antioxidant activity yeast β-glucans can prevent skin injuries caused by solar radiation and 

therefore are used in sun-screens, oils and gels (Michiko & Yutaka, 2007). Deodorants 

containing yeast β-glucans have proved to be useful in oral preparations, mouthwashes and 

diapers (Michiko et al., 2005). Acid-treated cell walls (AYC) can be used as new binders in 

pharmaceutical formulations and, when mixed with traditional fillers like 

hydroxypropylcellulose or polyvinylpyrrolidone, yield harder pills with very short (~2 min) 

dissolution times (Yusa et al., 2002). Its adhesive and biological properties can be also 

utilized in producing coating for surgical instruments (Klein, 2003) and in the manufacture 

of packaging for the food industry (Cope, 1987). Its antibacterial and antiviral properties 

have found application in the control of plant pests (Kitagawa, 2007) and viral invasions 

(Slovakova et al., 1997).  

6. Medicinal application of native and chemically modified forms of  

β-(1→ 6)(1→3)-D-glucan 

Approximately 2000 research and review papers covering β-(1→6)(1→3)-D-glucan 

bioactivity and its medicinal applications have been published since the 1960’s, and the 

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