The building blocks of healthy sweetness

Most effort in sweetness characterization has focused on a few trending terms when describing an alternative sweeetener, such as “just like sugar”, or “a thousand time sweeter than sugar” or “no aftertaste”. These are all valid terms, but not precise or meaningful enough. We all agree that sweetness is a hedonic experience and should stay like that. As similar to sugar as possible. But, what is the meaning of being similar to sugar, defined as sucrose.  It may mean many different things. Let’s focus on those related to the volume, structural role of sugar in foods, and what happens when we aim to replace them by alternative compounds:

 

Typical sugar replacements, in terms of bulking are:

 

  • Other sugars: Here we are excluding confusion induction synonymous expressions of sucrose, like coconut sugar, dates, apple juice or honey, as ultimately these are slightly unpurified versions of sucrose. Let’s think of Fructose, which is 20% to 40% sweeter than sugar (depending on temperature and pH). While sweeter than sugar, fructose loses its crystallinity even at room temperature in humid conditions, as a result of what is called the glass transition temperature, which is characteristic of each compound (Correia et al, 2009). It actually becomes amorphous at much lower temperatures and moistures than sucrose, or glucose, which makes it difficult to manage it industrially. Therefore, it becomes chewy, sticky and is quite difficult to use and preserve, both as an ingredient, but also in final products.

 

  • Polyols: Most of them are synthetic, enzymatically produced or fermented. A couple of notable exemptions are naturally occurring or spontaneously fermented (in NON GMO microorganisms). This is the case of Erythritol and Xylitol. While these compounds have an ugly name, they have several interesting properties from a functional, metabolic and health point of view (Wölnerhanssen et al, 2020), including solubility, hygroscopicity, anti-diabetic, intestine absorption and a lack of Maillard reaction occurrence.

 

  • Fibers: Fibers are non-digestible carbohydrates fermented in our large intestine, as a definition. They can rather be soluble or insoluble. However, just as our digestive system is not able to digest them, they are digested by our microflora, which has turned to be far more relevant that what we imagined in our immunology, behavior and homeostasis, just to name a few aspects. They are so relevant, that even breast milk includes fibers and prebiotic compounds (Human Milk Oligosaccharides) (Plaza et al, 2018), which are not digested by us, but by the microorganisms in our guts. How something can be so important that even the first food we have as human beings includes it?. Our mothers feed their first meal to us and our microorganisms at the same time. Let`s get back to fibers, some of them are soluble, others insoluble. Industrially, most soluble fibers are obtained from Chicory, Agave or synthesized from Fructose and Dextrose. Insoluble fibers are diverse as nature, and can be byproducts from lemon zest and many other crops, providing outstanding rheological (texture related) properties to drinks and foods.

 

So, which physical and functional properties should we look at when replacing sugar or sucrose?

 

 

  • Sugar is a crystalline compound: At room temperature and moisture, sugar behaves as a crystalline compound. This means that it gets sticky only when it gets humid and it provides the perfect structure giving gloss to cakes, tarts, sweets and famous desserts such as creme brûlée, or the shining crystals above a donut. This crystalline condition is enormously relevant also to allow a good chocolate to have what we call “ a good snap”. So, when we replace sugar, we need to think of those compounds that can provide a good crystalline condition under storage and consumption conditions. Inulin fiber will never provide that crystalline condition, so characteristic of sugar replacements should take into consideration this aspect. Polyols, for example, are crystalline compounds under similar conditions to sugar so they perform very well when replacing solid structures of sugar.

 

  • Dancing with solubility is an art: Ice creams stay soft depending on the temperature at which a saturated system of sugars and milk solids crystallize. Gummy bears are transparent because at the concentration where these compounds become perfectly chewy, sucrose is in a concentration where it does not become a crystal. Erythritol will crystallize in that same condition (as a result of a much lower solubility than sugar), Xylitol will perform quite effectively as sugar, and inulin or fibers, while soluble, will not provide the right combination of viscosity and chewiness needed.

 

  • The power of heat: Whenever we think of pound cakes, cupcakes or baked doughs, the browning of the dough in the oven is a key element in terms of flavor development of the dough, as well as in the aspect of it. Technically, this is what we call Maillard browning reaction, and is the results of a reaction between sugars and amino acids. This reaction provides color, taste but also is relevant because of the formation of non -desired compounds, such as acrylamides. Some sucrose replacements, like erythritol, have a neglect able Maillard browning reactions with amino acids. Others, such as Tagatose, Allulose or Isomalt have huge Maillard reaction rates. This may be desirable in specific deserts, like Creme Brûlée, but may turn baking into a difficult operation, as dough development and cooking may happen long after the product looks, tastes and feels totally burnt. Combined systems may be a good solution for this, as well as understanding the specific content of amino-acids and reducing sugars in foods.

 

And what about the health impact of these bulking, structuring sucrose replacement compounds?

Every voluminous food, i.e, that is not digested, needs eventually to be excreted. Here is where all of these compounds differ substantially.

 

Partially metabolized: Compounds like Tagatose and Maltitol are partially digested. During this process, while Maltitol is partially metabolized into Glucose and Sorbitol (and absorbed up to 80%), Tagatose is metabolized through a very similar pathway to the metabolism of fructose in the liver (EFSA 2016), providing 3 kcal/g and de-novo lipogenesis.

 

Non Metabolized: Non metabolized compounds, like Alullose, Erythritol or fibers, have different metabolic fates. While Allulose and Erythritol are absorbed in the early small intestine, and excreted principally through urine, fibers are partially digested by our microflora in our colon. This is extremely relevant, as when it comes to Polyols, those which are not excreted through urine or metabolized, create an osmotic shock in our intestines and produce diarrhea, when in excess consumption usually above 10 g to 20 g per portion, depending on the Polyol. On the other hand, fibers like inulin or fructo-oligosaccharides, feed specifically beneficial bacteria in our intestines as Bifidobacteria, which has numerous positive effects into our health. However, fiber fermentation by bacteria, while healthy, can provoke bloating and other uncomfortable symptoms when in excess. Depending on the length of the fibers (and therefore their solubility), tolerance limits (that maximum dose where a person does not have any unpleasant effect) can range as well from 10 to 20 g of fiber per portion.

 

Building sugar replacement comes down to the building blocks that replace it’s sweetness and structure. We should look carefully into sound assembles which make from sugar replacement a wonderful opportunity to improve our health.

 

References

 

  1. Natália T. Correia, Hermínio P. Diogo, Joaquim J. Moura Ramos, Slow Molecular Mobility in the Amorphous Solid State of Fructose: Fragility and Aging, Journal of Food Science, 10.1111/j.1750-3841.2009.01363.x, 74, 9, (E526-E533), (2009).

 

  1. EFSA NDA Panel (EFSA Panel on Dietetic Products, Nutrition and Allergies), 2016. Draft Scientific Opinion on the energy conversion factor of D-tagatose for labelling purposes. EFSA Journal 2016;volume(issue):NNNN, 14 pp. doi:10.2903/j.efsa.2016.NNNN

 

  1. Plaza-Díaz J, Fontana L, Gil A. Human Milk Oligosaccharides and Immune System Development. Nutrients. 2018 Aug 8;10(8):1038. doi: 10.3390/nu10081038. PMID: 30096792; PMCID: PMC6116142.

 

  1. Wölnerhanssen BK, Meyer-Gerspach AC, Beglinger C, Islam MS. Metabolic effects of the natural sweeteners xylitol and erythritol: A comprehensive review. Crit Rev Food Sci Nutr. 2020;60(12):1986-1998. doi: 10.1080/10408398.2019.1623757. Epub 2019 Jun 16. PMID: 31204494.