Is fermentation the future of steviol glycosides?

Steviol glycosides are extracted from stevia leaves, refined and turned into stevia extracts. This is how all steviol glycosides are produced in the European market. But in the United States and elsewhere in the world, there are also steviol glycosides made from glucose syrup with genetically modified yeast fungi. What does that mean? What are the advantages and drawbacks? We take a closer look at the matter in this article.

29 June 2020 •

The demand for ste­vi­ol gly­co­sides is ris­ing. Within a few years, demand is expect­ed to be greater than the sup­ply. In addi­tion, we want the rare but tasty ste­vi­ol gly­co­sides – like Reb M. This has dri­ven the big American com­pa­nies to devel­op meth­ods for pro­duc­ing ste­vi­ol gly­co­sides through the fer­men­ta­tion of glu­cose syrup. In this arti­cle, we will find out more about how it works and what ben­e­fits and dis­ad­van­tages there are.

Stevia and steviol glycosides

Stevia’s leaves con­tain sweet sub­stances called ste­vi­ol gly­co­sides. They all con­sist of a ste­vi­ol por­tion on which one or more glu­cose moi­eties hang. The only thing that chem­i­cal­ly sep­a­rates them is the num­ber of glu­cose moi­eties and their gly­co­side binding.

The small vari­a­tions make a big dif­fer­ence in taste. Most ste­vi­ol gly­co­sides are ste­vio­side. The dried leaves of ste­via con­tain between five and ten per cent of ste­vio­side. Unfortunately, it has a bit­ter taste and long and liquorice-like off-taste.

The best tast­ing ste­vi­ol gly­co­side is Rebaudioside M (Reb M). It tastes almost like sug­ar (except it is up to 350 times sweet­er). Unfortunately, there is very lit­tle Reb M in the dried leaves. Less than 0.1 per cent.

Other ste­vi­ol gly­co­sides fall between these extremes in terms of both taste and quantity.


In the EU, 11 ste­vi­ol gly­co­sides are approved as sweet­en­ers. Of these, Reb M is per­haps the eas­i­est to use. Its sug­ary taste makes it unprob­lem­at­ic. No taste or after­taste that needs to be masked.

But the low quan­ti­ties make Reb M expen­sive. Therefore, researchers have looked at alter­na­tive ways to pro­duce Reb M and oth­er exclu­sive ste­vi­ol glycosides.

The environment

Environmental con­cerns are anoth­er rea­son for devel­op­ing alter­na­tive ways of pro­duc­ing ste­vi­ol glycosides.

Cultivation of ste­via and extrac­tion of ste­vi­ol gly­co­sides are already much more envi­ron­men­tal­ly friend­ly today than cul­ti­va­tion of sug­ar beet and extrac­tion of sucrose. According to one study, water con­sump­tion is 92 per cent low­er and car­bon diox­ide foot­print 82 per cent low­er for the pro­duc­tion of ste­via extracts com­pared to the pro­duc­tion of beet sug­ar with the same sweetness.

But soon, the demand for ste­vi­ol gly­co­sides is expect­ed to exceed sup­ply. And then there is a risk that arable land, which can be used bet­ter, will be occu­pied by ste­via cul­ti­va­tion if there is no alternative.

The alternative

Since ste­vi­ol gly­co­sides are only nat­u­ral­ly found in the plant ste­via, the search for alter­na­tive ways of pro­duc­ing them means a search for a process that can con­vert anoth­er raw mate­r­i­al into ste­vi­ol glycosides.

Today, the food indus­try uses a wide range of ingre­di­ents pro­duced in this way. For exam­ple, starch from wheat, pota­toes, corn, cas­sa­va, rice with sev­er­al starchy crops is con­vert­ed into a wide vari­ety of prod­ucts, includ­ing glu­cose syrup, malti­tol and erythritol.

Some of these con­ver­sions are pure­ly chem­i­cal, such as hydro­gena­tion which con­verts mal­tose syrup into malti­tol, while oth­ers are bio­chem­i­cal, such as fer­men­ta­tion of glu­cose syrup to erythritol.

Similarly, Reb M and oth­er exclu­sive ste­vi­ol gly­co­sides can be pre­pared by adding yeast fun­gi that con­vert glu­cose syrup to Reb M.

Steviol gly­co­sides pro­duced in this way are not allowed in the EU but are used in the US and else­where in the world. It may per­haps be allowed in the EU one day too. Nevertheless, it’s an excit­ing technique.


Of course, there is no ordi­nary yeast fun­gus that con­verts glu­cose syrup into Reb M. But it’s also not a mag­ic mush­room. It fol­lows a clas­sic arrange­ment that has been used for decades.

First, researchers iden­ti­fy what enzymes ste­via uses to cre­ate Reb M. Then researchers find out what genes make ste­via pro­duce these enzymes. Finally, these genes are copied into yeast, which then begins to pro­duce the same enzymes as stevia.

This yeast is then fed with glu­cose syrup, which in turn is made from corn starch. The result is a super sweet syrup with, among oth­er things, Reb M.

Reb M is then extract­ed from the super sweet syrup and refined in the same way as ste­vi­ol gly­co­sides extract­ed from dried ste­via leaves. The result is a ste­via extract of high and con­sis­tent quality.

Scalable and environmentally friendly

Preparation of Reb M by fer­men­ta­tion of glu­cose syrup is done in large steel tanks. It is easy to scale up with increased demand. In addi­tion, no arable land is need­ed that needs plen­ty of water result­ing in large car­bon foot­prints. Thus, it is envi­ron­men­tal­ly friend­ly, accord­ing to the advocates.

But wait a minute, the crit­ics may say. The glu­cose syrup is made from starch that comes from corn, and corn is grown. So plen­ty of arable lands must be occu­pied, albeit indirectly.

Totally cor­rect. But with fer­men­ta­tion you get between five and ten times as much ste­vi­ol gly­co­side per hectare of land grown with maize as per hectare cul­ti­vat­ed with stevia.


Within the EU, con­ven­tion­al­ly pro­duced ste­via extract can­not be mar­ket­ed as a nat­ur­al sweet­en­er. In order to be called nat­ur­al, it must at most have under­gone ‘min­i­mal treat­ment’ (eg peeled, sliced or torn). The process of extract­ing ste­vi­ol gly­co­sides is not con­sid­ered minimal.

(Given that reg­u­lar sug­ar is extract­ed from sug­ar beet and sug­ar cane in a sim­i­lar way, it shouldn’t be con­sid­ered nat­ur­al either. But which E-num­ber has sug­ar?)

Now those who pro­duce ste­vi­ol gly­co­sides through fer­men­ta­tion hope that these will be con­sid­ered nat­ur­al. It is prob­a­bly a pious hope. And even if it were to be con­sid­ered nat­ur­al, con­sumers might not like it, because there is a thing called GMO.


The yeast that con­verts glu­cose syrup into Reb M con­tains genet­i­cal­ly mod­i­fied organ­isms (GMOs). Many con­sumers are averse to GMO and regard it as some­thing that has noth­ing to do in food.

But this is not real­ly the case, say the advo­cates of fer­men­ta­tion. GMO is present in the yeast, but not in the raw mate­r­i­al (assum­ing GMO-free maize is used). And the yeast is killed by heat­ing and then fil­tered off.

They have a point; many oth­er ingre­di­ents in the food indus­try are also made from genet­i­cal­ly mod­i­fied yeast fun­gi, and nobody seems to care.

Flip or flop?

Are ste­vi­ol gly­co­sides pro­duced by fer­men­ta­tion a flip or flop? It remains to be seen.

If they are to be approved in the EU, one of the major pro­duc­ers must first pay for the exten­sive stud­ies required by the European Food Safety Authority (EFSA). Then con­sumers have to accept it in food.

It may not even be a flip in the US. Plant refine­ment, as well as the devel­op­ment of more effi­cient extrac­tion meth­ods, have simul­ta­ne­ous­ly been under­way, which has made it pos­si­ble to buy Reb M from ste­via leaves at a rea­son­able price. In addi­tion, knowl­edge has pro­gressed regard­ing how to mask unwant­ed side and off-taste, using thau­matin for example.

In any case, it will be excit­ing to fol­low the development.

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