the power of goo

January. Time of New Year’s Resolutions, time for many people to consider living a more healthy life, including more exercise and eating less and better food.

Looking further into this matter one finds references to so called “dietary fibers”, which are non-digestable non-starch polysaccharides, as well as cellulose, lignin, chitins, pectins, beta-glucans, inulin and oligosaccharides.

Although any of the mentioned molecules are worthy of a detailed look, I will focus on inulin at this point, as it is often used in prebiotic foods.

So, first of all: what IS inulin, or better: what are inulins?

Inulins are a group of natural oligosaccharides containing between 2 and 140 fructose units; this is not exactly the range of molecular weights some would expect when talking about polymers. (But then this is a completely different and philosophical question which we might dwell on in a later post). Let’s just assume we all agree that we are, especially when talking about biopolymers, in the lower regions of (bio)polymers.

Oligosaccharides, as you may know, are composed of different simple sugar molecules, which are linked together by ether bonds. There are many different sugars as well as different modes of linking these sugars together, so that in nature there are many different oligosaccharides with various structures and of course functions.

Inulin itself is a mixture of many different fructose polymers; it can be found in many plants where it is used as a storage molecule (just like some plants store sugars as starch). High concentrations on inulins can be found in plants like

• Dandelion (Taraxacum officinale)
• Jerusalem artichokes (Helianthus tuberosus)
• Chicory (Cichorium intybus)
• Onion (Allium cepa)
• Garlic (Allium sativum)
• Agave (Agave spp.)

Oligofructose is a small subfraction of inulin consisting of chains with less than 10 fructose units. It is used as a mild sweetening agent (its is much less sweet than sugar or starch).

The molecules themselves are based on fructose repeating units, mostly containing a terminal glucose as well. The fructose units are joined via a beta-(2-1)-glycosidic link. The simples type of inulin is 1-kestose, which has two fructoses and one glucose unit. (see image above, n = 0)

Because of this structure inulin cannot be digested by the human enzymes ptyalin and amylase, which are used when digesting starch. Inulin can be digested by certain bacteria which live in the colon, resulting in the prebiotic effect. It is then digested by lactobacteria to produce carbon dioxide and/or methane. In addition to this inulin can feed and thus stimulate the growth of prebiotic bacteria in the gut (see figure) — in contrast to prebiotic yoghurt, which tries to implant new bacteria into the gut. This implantation process is difficult as these bacteria need to survive extreme conditions on their way, killing most of them and making the whole process quite inefficient, if it is possible at all.

The manufacturing of inulin is quite similar to the extraction of sugar from sugar beets. Roots are harvested, sliced and washed. Using a hot water diffusion process inulin is then extracted, yielding a polymer with an average DP of 10 to 12, and a chain length distribution between 2 and 60 repeating units.

Further links

• A good overview of chemical structures and uses of oligosaccharides
• Inulin and Oligofructose: What are they? Journal of Nurtrition. 1999; 129; 1402-1406. link
• Update (see first comment below): www.polysaccharidecenter.com