Canadian Sugar Institute - Functional Properties of Sugar

It is common for individuals to associate sugar (sucrose) with its inherent taste properties. Aside from providing a sweet taste and flavour, sugar imparts numerous functional properties that make it an important ingredient in many foods. Specific functional properties of sugar can be classified into four broad categories: sensory, physical, microbial and chemical. These properties also make sugar an exceptional functional substance for non-food applications.

Taste - Sweetness is generally the most recognized functional property of sugar. The preference for sweetness, regarded as being innate, is apparent soon after birth and prior to postnatal learning. Perception of the relative sweetness of sugar depends on factors such as temperature, pH, concentration, presence of other ingredients, and the difference in individuals' ability to taste (e.g. detection threshold).

Caramelization - is a browning reaction that results from the action of heat on sugars. At high temperatures, the chemical changes associated with melting sugars result in a deep brown colour and new flavours.

Flavour - Flavours result when tastes (sweet, sour, bitter, salty) are combined with sense of smell when food is consumed. Through interaction with other ingredients, sugar is an important contributor to flavour. Depending on the food application, sugar has the unique ability to heighten flavour or depress the perception of other flavours. For example, sugar is added to tomato-based products (e.g. barbeque, spaghetti and chilli sauces) to reduce the acidity of the tomatoes. Sugar itself also provides flavour when it is heated due to caramelization (see Appearance).

Texture - Sugar makes an important contribution to the way we perceive the texture of food. For example, adding sugar to ice-cream provides body and texture which is perceived as smoothness. This addition helps prevent lactose crystallization and thus reduce sugar crystal formation that otherwise causes a sandy, grainy texture that is sometimes associated with frozen dairy products.

In candy-making, controlling the rate and extent of sugar crystallization provides a vast array of textures. These range from the soft textures of fudges where crystallization is minimized, to hard candies where crystallization results in a desired grainy structure.

Tenderizer - Sugar acts as an important tenderizing agent in foods such as baked products. During the mixing process, sugar competes with other ingredients for water. In bread making for example, the affinity of sugar to bind to available water will delay the development of gluten, which is essential for maintaining a soft or tender product. Gluten strands, in general, are highly elastic, and this property allows the batter to stretch under the expansion of gases. Too much gluten formation, however, will cause the dough or batter to become rigid and tough. When the correct proportion of sugar is added in the recipe, an appropriate amount of gluten develops and optimum elasticity results.

Maillard Reaction - results from chemical interactions between sugars and proteins at high heat. An amino group from a protein combines with a reducing sugar to produce a brown colour in a variety of foods (e.g. brewed coffee, fried foods & breads).

Appearance - Sugar is responsible for the yellow-brown colours that develop in baked foods. Sucrose itself develops colour through caramelization. However, the monosaccharide components of its hydrolysis (glucose and fructose) can also undergo browning reactions (Maillard reaction). For example, the reactivity of glucose upon heating contributes to the subtle orange-red colour in bread crust that is a result of this browning.

Sugar also contributes to product colour of preserves and jellies through its capacity to attract and hold water. By absorbing water more readily than other components, such as fruit, sugar prevents the fruit from absorbing water which would otherwise cause colour to fade through dilution.

Solubility - Sugar is very soluble in water. The ability to produce solutions of varying sugar concentrations is important in many food applications. A high level of solubility, for example, is essential in beverages to provide sweetness and to increase viscosity to create a desirable 'mouthfeel'. Its solubility is also important in the preparation of canned fruits, jams, jellies, preserves and syrups to impart the desired level of sweetness and to aid in preservation (see Preservation).

Freezing Point - Sugar is effective in lowering freezing points. Freezing point depression is an important property in ice-creams, frozen desserts and freeze-dried foods to ensure the development of fine crystal structure and product smoothness.

Boiling Point - The concentration of sugar in a solution affects the boiling point by raising it. This characteristic is important in candy manufacture as boiling point elevation allows for more sugar to be dissolved in solution, creating a 'super saturated' and more concentrated solution. It is this specific concentration of the supersaturated sugar syrup, which is achieved at specific boiling points, which inevitably determine the candy's final consistency.

Preservation - Sugar plays a role in the preservation of many food products. The addition of sugar to jams and jellies, for example, inhibits microbial growth and subsequent spoilage. Having the ability to absorb water, sugar withdraws moisture from micro-organisms. As a result, micro-organisms become dehydrated, and cannot multiply and cause food spoilage.

The interaction between sugar and water controls the level of moisture in baked products. Sugar's high affinity for water helps to slow moisture loss in cakes and biscuits, for example, to prevent drying out and staleness, thereby extending their shelf life.

Fermentation - Sugar is extremely important in the baking and brewing industries. Yeasts use sugars as food to produce ethanol, carbon dioxide and water through the process of fermentation. In baking, sugar increases the effectiveness of yeast by providing an immediate and more utilizable source of nourishment for its growth. This hastens the leavening process, by producing more carbon dioxide which allows the dough to rise at a quicker and more consistent rate.

Fermentation of sugar by yeast also occurs in the production of wine and beer. Sugar or other carbohydrates are the raw materials for the production of ethanol (alcohol). The extent to which the fermentation reaction is allowed to proceed (degree to which sugar is fermented), contributes to the alcohol content and sweetness of wine, and the flavour of beer.

Antioxidant Activity - Sucrose has been reported to exhibit antioxidant properties which help to prevent the deterioration of textures and flavours in canned fruits and vegetables. These effects may be partially attributed to sucrose's ability to lower water activity.

In addition, the products of the hydrolysis of sucrose (glucose and fructose) appear to have the ability to block the reactive sites of ions such as copper and iron and, to a lesser extent, cobalt. This characteristic of monosaccharides aids in food preservation by impeding catalytic oxidation reactions.

Furthermore, Maillard reaction products are known to have antioxidant properties in food systems. For this reason, some mixtures of Maillard reaction products have been employed in the food industry as food additives for biscuits, cookies and sausages.

Sugar is valued in cough syrups for its solubility and bodying effects. Sugar also functions as a diluent, to control the concentration of active ingredients in tablets and as a binder to hold ingredients together. In addition, tablets are often covered with sugar coatings in order to protect the exterior from chipping.

Sugar also functions in the "time-release" capability of preparations that are made up of layers of active and inactive ingredients. Sugar crystals are used as a base for depositing active ingredients. In this type of preparation, inter-layers of active and inactive ingredients alternate, allowing the use of more than one active ingredient and providing the ability to control the sequence and time for release of the medication.

Scientists have reported success with the use of sugar to treat serious wounds and burns that are unresponsive to conventional therapy. By dissolving in the tissues of an open wound, sugar produces an environment in which bacteria cannot grow. It has also been suggested that sugar supplies nourishment to damaged tissues needed for re-growth.

Researchers are continuously investigating functional properties of sucrose in attempts to develop products with promising uses. Specific sucrose-derived products that have generated interest from researchers and industry representatives include sucrose esters, sucrose epoxies and bioplastics.

Sucrose esters - Sucrose esters are obtained by linking sucrose with fatty acids derived from animal fats or vegetable oil. They have been used as emulsifiers and texturizing agents in the food industry but have wide application in terms of non-food uses, such detergents and cosmetics. Sucrose esters can be made into mild, biodegradable detergents with inherent anti-bacterial properties. They are non-toxic and their level of detergency makes them effective components of powder and liquid detergents for many types of materials (e.g. cotton, silk, wool). Sucrose esters are also widely used in the cosmetic industry. In addition to being biodegradable, non-toxic and mild to the skin, sucrose esters contribute to skin moisturization and protection while reducing irritant properties of other substances present in cosmetic formulations.

Sucrose epoxy - Sucrose is the main ingredient in new liquid epoxies that can bind wood, metal, glass, concrete and other materials. Large markets for these sucrose-based adhesives are foreseen in non-woven textiles, wallboard, home insulation, and marine construction materials. Sucrose epoxies lack ingredients normally contained in chemical epoxies that have been controversial due to their potential to disrupt the reproductive system of mice and possibly humans. Other benefits of such sucrose epoxies include an ability to harden in conditions over a great range of temperatures and bonding strengths comparable to those of chemical products.

Bioplastics - Bioplastics refer to the production of natural biodegradable plastics produced by microorganisms. Sucrose has been noted as a preferred carbon source for various bacterial species that produce biodegradable plastics as storage material synthesized and accumulated within their cells. Bioplastics can be used to manufacture a variety of containers and packaging materials which otherwise are produced using non-degradable plastics.

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