Types of Sugars

Sugar is one of the ingredients in many baking products, but it can also occur naturally in some of the used ingredients. The term “sugar” encompasses many chemical compounds. The sugar commonly used in households is sucrose, a combination of glucose and fructose. If we break the bond that connects both compounds in sucrose, we obtain what is called inverted sugar, which is nothing more than a combination of glucose and fructose. Another sugar typically present in products made with cereal flours is maltose. Maltose is a combination of two glucose molecules. Starch is composed of glucose molecules, so, after the action of enzymes, it can generate both glucose and maltose, or more complex sugars. In wheat, we find alpha and beta amylases, and the latter naturally generates. There are enzymes that can produce glucose, but these are present in smaller quantities in flours and are usually added if needed. Lastly, in some doughs, lactose, the sugar present in milk, can be found. Lactose is composed of two sugars, glucose, and galactose. In the human body, enzymes capable of hydrolysing this sugar exist, but lactose-intolerant individuals lack this enzyme.

Where are the Sugars?

Sugars are present in numerous ingredients, but they can also be added to doughs in more or less pure forms. Sucrose, glucose, or fructose can be purchased in crystallized form or as syrup. It is also possible to buy purified lactose and inverted sugar. Sucrose is usually obtained from sugar beets in Europe and sugarcane in other countries. On the other hand, glucose and fructose are typically obtained from cornstarch through enzymatic hydrolysis. Besides their purified form, these sugars are also concentrated in some natural products, such as honey or maple syrup. Therefore, these products can also be used as a source of sugars. Other products with a high sugar concentration, such as agave syrups, molasses, or fruit syrups, also exist. Fruits usually contain fructose, and concentrated fruit juices have a high concentration of this component.

Maltose usually comes from the hydrolysis of damaged starch by amylases. In wheat flour, we have both damaged starch and amylases, although in some cases, it is advisable to incorporate an extra dose of exogenous amylases. In batters for cakes and cookies, where the time from flour hydration to baking is short, there is usually not enough time for a significant amount of maltose to be generated. In some gluten-free doughs made with starches, the absence of damaged starch and amylases reduces the maltose generated in the process.

Lactose is usually present in milk and dairy products. The inclusion of these products has been common in baking. However, the increasing number of people allergic to milk proteins or lactose intolerant has reduced this practice in some cases.

Function of Sugars

The main function of sugars in food is to sweeten, i.e., provide a sweet taste to the final product. If our goal is to sweeten, we must consider the sweetness power of sugar. For this, sucrose is taken as a reference, considered the benchmark against which others are compared. Thus, sucrose will have a sweetness power of 100. Fructose has a slightly higher sweetness power than sucrose, while glucose (or dextrose) has a slightly lower sweetness power than sucrose. Inverted sugar also has a somewhat higher sweetness power than sucrose. In the literature, you can find data on the sweetness power of these sugars compared to sucrose, but these can vary depending on the sugar concentration used for comparison. Maltose and lactose hardly have any sweetness power. Sweetness power is one of the parameters used to choose possible sugar substitutes, which will be discussed in later entries.

In baking, one of the main functions of sugar is to provide food for yeast, so that they are transformed into alcohol and CO₂, which increases the volume of the dough and provides fluffiness to the final products. Lactose is not a fermentable sugar, so it cannot assist in this function and will remain in the final product. In doughs that do not incorporate added sugars, the main fermentable sugar is maltose, which is generated after the hydrolysis of damaged starch. To enhance the presence of maltose, it may be advisable to incorporate amylases. In some baking formulas, it is common to add a small percentage of sugar. In these cases, it can be helpful at the beginning of fermentation, as yeast quickly transform glucose and fructose. They then transform sucrose, as yeast has an enzyme called invertase, capable of separating sucrose into glucose and fructose. Maltose is more complex to transform as it must be “ingested” by the yeast cell before its transformation. In gluten-free bread formulas, it is also common to incorporate sugars because, if they are based on starches, the percentage of damaged starch and amylases is too low to generate maltose naturally. An alternative would be to add some flour with a high content of damaged starch and external amylases, but it is usually simpler to incorporate external sugars.

The third function of sugars is to give colour to products. The colour of the outer part of bread, cakes, or cookies is partly due to Maillard reactions and partly to the caramelization of sugars. Sugars caramelize at temperatures above 100ºC, but this temperature varies depending on the sugar. Thus, fructose caramelizes at temperatures close to 110ºC, while sucrose and glucose do so at temperatures close to 160ºC. Therefore, this reaction only occurs on the outer part of the pieces, as the interior of bread and cakes does not exceed 100ºC throughout the process. Maillard reactions occur between amino acids and reducing sugars, influencing both the colour of the crust and the aroma of the bread. The temperature at which Maillard reactions occur will depend on the pH and other factors, but in baking, they occur at temperatures above 100ºC, so they will not occur in the inner part of the pieces. The colour of the products will vary slightly depending on the sugars and amino acids present. It is often said that doughs with lactose (milk or its derivatives) tend to have a more reddish colour than pieces that do not incorporate this sugar. It should be remembered that lactose is not a fermentable sugar, so it remains in the dough until baking, and, in fact, the main contribution of lactose in these products is based on the colour, taste, and aroma it helps provide.

Issues with Sugar

Although sugar, in small concentrations, aids fermentation, when it is highly concentrated, it is a potent antimicrobial. Therefore, products with a high sugar concentration usually have a long shelf life. Therefore, as we increase the sugar concentration in the doughs, we may have problems with fermentation. To solve this problem, we often resort to using a higher percentage of yeast or using osmotolerant yeasts, which can function with higher sugar concentrations. This drawback for fermentation can also be an advantage in other products where yeast action is not necessary, as it can help reduce the development of molds or other microorganisms.

Sugars also modify the rheology of doughs, something that must be taken into account. They will do so differently depending on the added sugar and the form in which it is added (solid or liquid). In doughs where gluten network development is necessary, it is usually necessary to reinforce it, as sugars can weaken it. In these cases, stronger flours or reinforcing additives can be used. In doughs like those of cookies, these changes will influence how these doughs can be handled, as more liquid doughs are difficult to laminate, and more solid doughs cannot be extruded. In these cases, other ingredients can also be modified. Lastly, sugars also influence the gelatinization of starch, delaying it. This delay will depend on the type of sugar and can be an advantage by delaying the moment of completion of dough expansion in the oven. But in cake batters, this moment must be coordinated with the action of the leavening agents.

The last problem with sugar is nutritional. We all know that sugar is not a very healthy product. Excessive sugar intake has been linked to many diseases. Therefore, even though it is necessary for life, its intake should be limited. Some brands are opting to limit the sugar content of products as much as possible. Others are trying to improve the image of their products by eliminating the word “sugar” from their labels. Thus, they use honey, molasses, or various syrups, such as agave or some fruits. Although these products may provide some other nutrients, they still significantly increase the sugar content and, therefore, do not greatly improve the nutritional quality of the final product if used in proportions similar to sugars. It should also be noted that there is a significant group that should not consume sugars, such as diabetics. In later entries, we will discuss what options we have to eliminate sugar from our formulations.