Foto Sebastian Pichler

Polydextrose – from seed to Eureba

With an ability to provide the same volume and consistency as sugar – with 75 per cent fewer calories and almost no effect on blood sugar levels – polydextrose is like a miracle ingredient that makes the bun light and juicy. The tasteless dietary fibre has barely noticeable sweetness, but many other properties in common with sugar (and fat). Polydextrose is produced from the naturally occurring substances glucose, sorbitol and citric acid. In practice, production starts with wheat or other starch-rich crops. But how is it done? We will tell.

27 January 2020 • and

Consumers demand less sug­ar to keep calo­ries in check and reduce the effect on blood sug­ar lev­els. But it is rarely as sim­ple as adding less if any sug­ar at all. We can eas­i­ly com­pen­sate the sweet­ness with a high-inten­si­ty sweet­en­er, for exam­ple, ste­vi­ol gly­co­sides. The big chal­lenge is to main­tain the per­fect mouth­feel. No one wants an ice cream that doesn’t melt the right way in the mouth or an ener­gy bar that crunch between teeth in a wrong way between. Then poly­dex­trose can be the solu­tion. It is an ingre­di­ent that pro­vides soft­ness and juici­ness in the same way as fat and pro­vides vol­ume, tex­ture and mouth­feel like sugar.

A successful recipe

In the 1960s, Hans Rennhard and his research team at Pfizer exper­i­ment­ed with nat­ur­al ingre­di­ents to pro­duce low-calo­rie sub­sti­tutes for sug­ar, fat, flour and starch. The exper­i­men­ta­tion gave results in 1965. They mixed 89 per cent glu­cose, 10 per cent sor­bitol and 1 per cent cit­ric acid, heat­ed the mix­ture and got polydextrose.

Although poly­dex­trose is pro­duced from nat­ur­al ingre­di­ents, the sub­stance itself is not found in nature, and could, there­fore, be patent­ed. Pfizer did so in 1973. Then, years of stud­ies fol­lowed on the food’s tech­ni­cal prop­er­ties and how safe it is for humans. It turned out to have suit­able tech­ni­cal prop­er­ties and not only be harm­less but even great for peo­ple. It was approved as dietary fibre in the United States in 1982. The EU fol­lowed 1995.

Glucose

The main ingre­di­ent in the pro­duc­tion of poly­dex­trose is glu­cose. The mono­sac­cha­ride is abun­dant in fruits and berries, but for food pro­duc­tion, glu­cose is made from starch from nat­ur­al sources such as corn, wheat, pota­toes and cassava.

Manufacturing starts with dis­solv­ing starch in water and adding acid or enzymes (or both) and heat­ing every­thing up. This makes the starch, which con­sists of long chains of glu­cose mol­e­cules, to break up into increas­ing­ly short­er and short­er chains. A chain reac­tion if you wish. The treat­ment is called hydrol­y­sis and the result is glu­cose syrup – a caloric bomb with sky-high gly­caemic index (GI).

Potatis

Sorbitol

The oth­er ingre­di­ent in the pro­duc­tion of poly­dex­trose is sor­bitol. It is a sug­ar alco­hol found nat­u­ral­ly in plums, pears, peach­es, apples and a host of dif­fer­ent fruits and berries. The sub­stance is also found in rowan berries, and this is where it was first dis­cov­ered. However, indus­tri­al­ly, sor­bitol is pro­duced from glu­cose. You can read how it’s done in a sep­a­rate arti­cle on sor­bitol.

Fågel på en gren
Photo Gustav Melin

Citric acid

The third and last ingre­di­ent in the pro­duc­tion of poly­dex­trose is cit­ric acid. As the name sug­gests, it is found in cit­rus fruits, but also in a vari­ety of oth­er fruits and berries.

Citric acid can be extract­ed from, among oth­er things, unripe lemons and oth­er cit­rus fruits. That is how it usu­al­ly was pro­duced from the end of the 19th cen­tu­ry and well into the 20th cen­tu­ry. But as ear­ly as 1917, the American food chemist James Currie dis­cov­ered that the fun­gus Aspergillus niger – com­mon­ly known as black mould – is a capa­ble pro­duc­er of cit­ric acid. Practically all cit­ric acid sold today is pro­duced by black mould.

The fact that black mould is used to pro­duce food is a hot top­ic in some cir­cles on the inter­net. But there is no cause for con­cern. There are non-tox­ic strains of black mould used in the pro­duc­tion of cit­ric acid. Thus, it is not the same strains that cre­ate harm­ful mould in damp houses.

Citric acid pro­duc­tion begins with the hydrol­y­sis of starch to pro­duce glu­cose syrups with which the fun­gus than are fed. In return, they pro­duce cit­ric acid, which is extract­ed in sev­er­al steps which includes purifi­ca­tion, evap­o­ra­tion, crys­tal­liza­tion and drying.

Citroner
Photo Ernest Porzi

Preparation of polydextrose

We now have all the ingre­di­ents nec­es­sary to make poly­dex­trose: glu­cose, sor­bitol and cit­ric acid. Note that in prac­tice, all three are made from starch, which comes from wheat, corn, pota­toes, cas­sa­va or anoth­er starch-rich crop.

Polydextrose is pre­pared by mix­ing 89 parts of glu­cose, 10 parts of sor­bitol and 1 part of cit­ric acid and heat­ing the mix­ture till it becomes liq­uid. Then the cit­ric acid acts as a cat­a­lyst and makes glu­cose and sor­bitol to react with each oth­er to form short­er, and longer glu­cose chains, which in turn are attached to each oth­er and form branched mol­e­cules of glu­cose parts.

It is these branched mol­e­cules of glu­cose that are poly­dex­trose. On aver­age, they have twelve glu­cose mol­e­cules, but the num­ber can vary from three to over one hun­dred. That is why they are called poly­dex­trose; poly means many in clas­si­cal Greek, and dex­trose is anoth­er name for glucose.

But all glu­cose and sor­bitol are not con­vert­ed. And the cit­ric acid, which was just a cat­a­lyst, remains. Also, some lev­oglu­cose, which is a nat­u­ral­ly occur­ring organ­ic sub­stance, has been formed.

Polydextrose is dietary fibre

So what makes poly­dex­trose a fibre? The answer lies in how the glu­cose mol­e­cules are attached to each other.

When a car­bon atom in one glu­cose mol­e­cule and a car­bon atom in anoth­er glu­cose mol­e­cule hold the same oxy­gen atom in their hands, they become linked. The two car­bon atoms and the oxy­gen atom is called a gly­co­side bond. These are denot­ed by α or β fol­lowed by two num­bers, for exam­ple, α-(1→4) and β-(1→6). The num­bers tell which car­bon atoms hold the oxy­gen atom in their hands, and the Greek let­ter says whether the car­bon atoms are turned in dif­fer­ent or the same direc­tion. (You will find a more detailed descrip­tion with illus­tra­tions in the arti­cle on dex­trin.)

A poly­dex­trose mol­e­cule has a jum­ble of gly­co­side bonds: α- and β-(1→2), (1→3), (1,→4) and (1→6). There are most of α-(1→6) and β-(1→6).

Although they are called almost the same thing, our bod­ies han­dle them very dif­fer­ent­ly. Our diges­tive sys­tem quick­ly breaks down α-(1→4) bonds, which are the gly­co­side link­age in starch and com­mon sug­ars, but strug­gle with α- and β-(1→6) bonds. If a glu­cose chain has more than one α- or β-(1→6) bind­ing, the body does not have time to break it down before it reach­es the large intes­tine. Such car­bo­hy­drates are called dietary fibres.

Since α- and β-(1→6) are com­mon in poly­dex­trose, most of it will pass the stom­ach and small intes­tine before with­out being touched. This, togeth­er with the fact that poly­dex­trose has a favourable phys­i­o­log­i­cal effect as sci­en­tif­ic demon­strat­ed, makes poly­dex­trose approved as dietary fibre.

Kemi schema
Polydextrose con­sists of branch­es of glu­cose chains. A poly­dex­trose mol­e­cule is, on aver­age, com­posed of twelve glu­cose mol­e­cules, but the num­ber varies from three to over one hun­dred. The glu­cose mol­e­cules are linked by var­i­ous α- and β‑linked 1→2, 1→3, 1→4 and 1→6 gly­co­side bonds.

Better on the stomach

Polydextrose is bet­ter on the stom­ach than sug­ar alco­hols. Studies show that you can eat up to 50 grams of poly­dex­trose at one time, and up to 90 grams dur­ing a day with­out stom­ach prob­lems. The lim­it val­ues are well above the 25 to 35 grams of fibre that an adult should eat per day (and few­er than half come up to). Therefore, poly­dex­trose may be used with­out restric­tion in most foods, but not more than necessary.

Several features in the same ingredient

Glass med kolasås
Photo Kobby Mendez

Polydextrose has many use­ful prop­er­ties that make it a pop­u­lar ingre­di­ent in every­thing from drinks, ice cream and pas­tries to dress­ings and jams. With neu­tral taste, it’s a chameleon that fits in many contexts.

The gas­tric-friend­ly dietary fibre, made from nat­ur­al ingre­di­ents, is a good start­ing point for cre­at­ing a sweet­ened fibre. Since poly­dex­trose is not sweet in itself, it must be sup­ple­ment­ed with a sweet­en­er such as ste­vi­ol gly­co­sides and/​or sug­ar alco­hols. Precisely what to com­ple­ment poly­dex­trose and in what pro­por­tions vary from appli­ca­tion to application.

We can help you

Don’t hes­i­tate to con­tact us if you want help find­ing the right ingre­di­ents and pro­por­tions to replace sug­ar with sweet­ened fibre. Chances are that we already have a ready-made solu­tion for you. If not, we can help you devel­op one.


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