Is fermentation the future of steviol glycosides?

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.

Cheaper

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.

Fermentation

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.

Natural?

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.

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.