Technical Talk – April 2009

Continuing our series about the basic ingredients of baking, what are the types of alternative sweeteners used in baked goods, what is their functionality, and what is new in this area?

Concerns about the amount of sugar in our diets are increasing among health professionals, consumers and the food industry. Obesity, diabetes, heart disease and other ailments are becoming more prevalent as sugar consumption increases, leading to attempts to develop foods using low-calorie sweeteners.

To properly replace sugar, its role must be understood. Sugar provides sweetness, bulk, moisture binding and colour development. In yeast-fermented breads and baked goods, sugar fuels the growth of yeast and carbon dioxide production.

The role of traditional sugars in baking was discussed in last month’s Technical Talk. Sugar replacement will affect the flavour, colour, texture and volume of a product. Removing sugar also affects shelf life.

It’s difficult to find a sugar substitute that provides all these functional properties, so using more than one kind is common. I’ll discuss two main kinds of sugar substitutes: those that provide bulk and those that provide high-intensity sweetness.

The first kind usually supplies fewer calories and has a lower glycemic index. The second kind tends to be hundreds or thousands of times sweeter than sugar, so they are used in extremely small quantities. In the April 2005 Bakers Journal we discussed the different types of alternative sweeteners available and now we’ll build on that previous information.

Bulking Agents
Bulking agents can be digestible (sugar alcohol, maltodextrins), partially digestible (polydextrose, fructooligosaccharides) or non-digestible (cellulose). The most common non-sugar bulking agents are sugar alcohols (polyols). Sugar alcohols (sorbitol, lactitol, isomalt and maltitol) contain only hydroxyl groups as functional groups, so they provide water-binding properties, control viscosity and texture, add bulk, reduce water activity, control crystallization and improve softness. Sugar alcohols are sweet, but less so than sucrose. They also have lower energy values than sucrose, ranging from 1.6 to 3.0 kcal per g, whereas sucrose is 4.0 kcal per g. They can be added in liquid or dry form. When used in dry form, they produce a cooling sensation. Sugar alcohols cannot participate in Maillard browning reactions, so they do not contribute to colour development.

Various types of polyols are available. For example, xylitol has the same sweetness intensity as sucrose. It produces a cooling sensation, provides moisture to baked goods, and promotes the glossiness of frostings. Maltitol is 90 per cent as sweet as sucrose. It has a similar solubility and melting point to sucrose, and has low hygroscopicity. Maltisorb is a 99 per cent pure maltitol made by Roquette, the world’s largest producer of polyols. Erythritol is 70 per cent as sweet as sucrose and non-caloric (0.2 kcal per g). It improves baking stability and shelf life. Mannitol and sorbitol are 60 per cent as sweet as sucrose, but mannitol has low hygroscopicity, whereas sorbitol has high hygroscopicity and helps control water activity. Isomalt is 50 per cent as sweet as sucrose, has low hygroscopicity, inhibits moisture absorption, and helps to achieve a crisp texture in baked goods. Lactitol is 30-40 per cent as sweet and has similar properties to sugar.

Maltodextrins (MD) are partial hydrolysates of starch made with acids and enzymes. They can be derived from corn, potato, tapioca and wheat. MDs form weak gels and thus can help stabilize emulsions. Maltodextrin is used as a bulking agent, which is important for maintaining yield and texture. For example, maltodextrin added to no-sugar biscuit dough helps to maintain the dough’s molding characteristics.

Polydextrose is another common bulking and texturizing agent, as well as being a soluble fibre ingredient. It promotes browning reactions due to thermal degradation. Unfortunately sensory analyses have shown it has a bitter and metallic aftertaste. Tate & Lyle offers Sta-Lite, a polydextrose that can replace sugars and fats while delivering fibre and fewer calories.

Polydextrose, fructooligosaccharides and tagatose are bulking agents that are also prebiotics that promote the growth of desirable bacteria in the colon. They are poorly metabolized, so they are fermented in the large intestine. Polydextrose provides only 1 kcal per g.

High Intensity Sweeteners
Intensive sweeteners are many times sweeter than sugar, so even if they have the same caloric value as sugar, they are used in such small quantities that they provide zero calories. Unfortunately, a bitter, metallic aftertaste is noted with some intensive sweeteners. Many of them are slower than sucrose to trigger the sensation of sweetness, and the flavour lingers longer after swallowing.

Some intensive sweeteners (e.g., aspartame) are broken down by heat, so they cannot be used in baked goods. Saccharin is 300-400 times as sweet as sucrose, heat stable, readily soluble and stable, but has a bitter, metallic aftertaste. Acesulfame-K is 200 times sweeter than sucrose, heat and pH stable, and soluble. Sucralose is 400-800 times sweeter than sucrose, heat and pH stable, and has a similar sensory profile to sucrose.

Splenda is a brand of sucralose that is recommended for use in baked goods. It is available in various forms and as a blend with white or brown sugar and fibre.

Sugar plays important roles in the production of baked goods. During mixing, it competes with gluten to bind water, so there is less gluten development and the final product has a tender crumb and good volume. Its water-binding properties also increase batter viscosity. Sugar promotes air incorporation and production of a more viscous and stable foam. During baking, it increases dough fluidity because it melts with heat.

Sugar also delays starch gelatinization so air bubbles have time to expand properly before the product sets. Air bubbles are produced by carbon dioxide and water vapour. Cakes, for example, contain a sugar concentration of 55-60 per cent, which delays starch gelatinization from occurring at 57 C to 92 C. Sugar also delays protein coagulation by dispersing the proteins and interfering with bond formation. As a result, the proteins coagulate at a higher temperature.

Polyols and other bulking agents affect dough and baking properties differently than sugar. A decrease in batter stability occurs during the heating stage of baking, which is related to a decrease in batter viscosity and an increase in foam bubble size. There are changes in the thermosetting mechanism, caused by different interactions between the bulking agent, starch, and protein. The bulking agent affects starch gelatinization and protein denaturation temperatures. For example, a decrease in these temperatures results in premature setting of the protein or starch matrix. Setting starts at the crust, the part of the product that has direct contact with heat. This prevents vapour pressure from escaping and causes inadequate expansion of air bubbles, resulting in decreased product volume. Crack-like connections may form in the crumb as the vapour tries to escape.

These changes result in variations to product quality. In cookies, completely replacing sucrose with polyols usually results in a softer product, whereas polydextrose produces harder but more fragile cookies. Combining polydextrose with a polyol such as sorbitol could provide the desired texture. The differences in firmness are affected by the bulking agents’ different water-binding capacities, which affect water loss during storage, and by their interactions with starch, which affect starch retrogradation. Sugar-free cookies have higher values of moisture content and water activity, which can shorten shelf life.

The lesson here is that using one replacement is not enough to produce a product comparable to the sugar-containing original. For instance, xylitol has the same relative intensity as sucrose and provides moisture to baked goods, but produces a very soft texture. Polydextrose and oligofructose provide colour, but they result in a bitter aftertaste. Such small amounts of intensive sweeteners are used, so bulking agents must be added to the formula as well, so collectively these ingredients provide all the functional properties of sugar. Determining the correct mixture of replacements is where the challenge lies, but with experimentation and advice from suppliers and experts acceptable products can be obtained. / BJ

John Michaelides is Guelph Food Technology Centre’s director of research and technology. Adrienne Shum is his assistant. Contact GFTC at 519-821-1246 or gftc@gftc.ca.