In the blog, we’ve already published a more general entry dedicated to fibres. As you may remember, we discussed aspects such as nutritional advantages, legislative issues, and their influence on the final product. However, we also mentioned that this influence greatly depends on the type of fibre and promised that there would be specific entries about some of these fibres. So, in this entry, we’re going to talk about soluble fibres that have little capacity for water absorption, and therefore do not significantly increase the consistency or viscosity of doughs or pastes, at least when compared to other fibres.

Fibres like celluloses or gums have a high-water absorption capacity, and if we include them in a formula, we need to increase the amount of water or liquids. In the case of celluloses, it’s most common to substitute flour for these fibres, slightly increasing hydration. With gums, it’s very difficult to incorporate a large quantity, and if we do, we must significantly increase dough hydration, resulting in final products that are very different from the originals. But in the case of the fibres we’re discussing in this entry, we can introduce them with little change to the original formulation, with minor adjustments. Among the fibres with these characteristics, fructooligosaccharides stand out, such as inulin and oligofructose, as well as polydextrose and Nutriose®.

Fructooligosaccharides are fructose polymers (fructans), just as starch or cellulose are glucose polymers. In this case, similar to cellulose, the fructose units are linked in such a way that these bonds are not easily broken down in the intestinal tract, so they are not assimilated by the body and are considered as fibres. These compounds are present in some natural products, such as chicory or Jerusalem artichoke (Helianthus tuberosus). There are also significant amounts in garlic, and to a lesser extent in onion or rye. The commercial products I know are obtained from chicory.

In the case of fructooligosaccharides, the degree of polymerization, or in other words, the number of fructose units forming the chains, is very important, ranging from 2 to 60. Generally, when the degree of polymerization is low, less than 10, they are usually called oligofructoses, and if it is higher, we use the name inulin. However, commercial inulins usually do not exceed a degree of polymerization of 20 since they are obtained from chicory, where fructooligosaccharides do not exceed this degree. Among commercial inulins, we can find them with different degrees of polymerization, and therefore with different properties, something to consider.

In general, the higher the degree of polymerization, the greater the thickening power, and this is something to consider. The degree of polymerization also modifies the melting point, gelation properties, and others, and therefore must be considered when incorporating these types of fibres into a formulation. It’s also important to consider that these products may undergo some depolymerization at high temperatures, generating sugars and enhancing Maillard reactions and caramelization on the outer part of baked products, enhancing their colour. Lastly, it’s worth noting that if we incorporate these products without modifying the formulation, in some cases, the dough may become stickier, which can make handling difficult on industrial lines. In these cases, this effect can usually be offset with minor formulation adjustments.

Inulin has been proposed as a substitute for fat, and oligofructose as a substitute for sugars, but my experience in this regard is not very good. Both products can perform certain functions similar to those of these compounds, but never all of them. For example, in the case of sugar substitution, oligofructose can serve part of the structural function of sugars in some formulations, but they do not provide sweetness, or do so to a much lesser extent. And inulin does not provide the typical juiciness that products with fat have. Perhaps it can be a good substitute in some creams or dairy products, where fat provides creaminess, although I have no experience in such applications. But in baked products, such as cakes or cookies, my experience with these products as substitutes for fat or oil is not good. Or at least, it should be considered along with other products that compensate for their shortcomings.

It’s more common to incorporate these products to increase the fibre level in the final product, and for their specific health benefits. The most positive and proven effect of inulin is its prebiotic nature. Inulin passes through the intestinal tract undigested, but upon reaching the colon, it is fermented by bacteria, improving gastrointestinal microflora, known as the prebiotic effect. This fermentation produces short-chain fatty acids, increases faecal mass, and lowers the pH of the colon. These changes in microflora, especially in lactobacilli and bifidobacteria, reduce the presence of pathogens, improve the immune system, reduce the risks of constipation and colon cancer. Although the effects on constipation are better demonstrated in other types of fibres. The incorporation of these fibres also allows better absorption of certain nutrients such as calcium. This is due to the greater solubility of calcium as pH decreases. And this improved calcium absorption has been linked to the reduction or prevention of osteoporosis problems.

There are also some studies on the ability of these fibres to reduce cholesterol levels or lower the glycaemic index, typical positive effects of other soluble fibres. In my opinion, these studies are still very scarce and do not guarantee these effects, which have been widely demonstrated in other fibres with much greater water absorption capacity, such as beta-glucans or arabinoxylans.

As a possible negative effect, precisely because they enhance fermentations in the colon, some people may experience flatulence problems due to the gases generated. These problems depend a lot on individual sensitivity, and while some individuals tolerate doses of 5-10 grams without any problems, others experience issues with just one gram. However, unlike with polyols in some countries, it is not necessary to declare these effects on the labelling.

In summary, inulin and oligofructose are fibres that can be incorporated into the formulation of various products to increase the fibre level of the final product, with a clear prebiotic effect, but without providing other health benefits typical of other types of fibres. Although they are soluble fibres and have less thickening power than other fibres, these characteristics will depend on the degree of polymerization, a factor that must be taken into account when studying their inclusion.

Other Soluble Fibres with Low Thickening Power

Although oligofructose and inulin are much more well-known, there are other fibres, developed by some companies, with properties similar to inulin or oligofructose. Among these fibres, polidextrose stands out, which as its name indicates, is a polymer of dextrose or glucose, and therefore with a composition very similar to that of starches or dextrins, but with bonds that are not easily broken down in the intestinal tract. This fibre is a synthetic product, and therefore may have less of a natural connotation than inulin or oligofructose, which are extracted from natural compounds. Its properties are similar, but since it is commercialised by a company, there are fewer studies. The company that marketed polidextrose was Danisco, but this company was acquired by the Dupont group and subsequently by IFF. To this day, I am not sure who markets it.

Another similar fibre is Nutriose®, a fibre obtained by the starch company Roquette Laisa. This fibre is obtained from wheat or maize and is basically a resistant dextrin. Like the previous ones, it is a soluble fibre with little thickening capacity, so it can function similarly in formulations. And like inulin, it passes through the intestinal tract until it reaches the colon, where 75% is fermented (15% is hydrolysed in the small intestine and 10% is excreted). Studies on Nutriose® show that it has health benefits like those of inulin, such as the prebiotic effect or improvement in the absorption of certain nutrients, but the studies conducted are much less abundant.

One final note. Some of these fibres (at least inulin) are not detected in some dietary fibre analyses. The topic of fibre analysis is quite complex and continues to evolve, and although some analyses already detect this type of fibre, others do not. Therefore, we must take this into account if we want to analyse the fibre content of a product enriched with this type of fibre.