4.2 Functional properties of carbohydrates in foods

Carbohydrates are crucial in shaping food's taste, texture, and appearance. From the sweetness of simple sugars to the thickening power of starches, they play diverse roles in our favorite dishes. These versatile molecules can bind water, form gels, and even help create stable emulsions.

Beyond their structural functions, carbohydrates undergo fascinating transformations during cooking. They crystallize in candies, participate in browning reactions that give bread its crust, and caramelize to create rich flavors. Understanding these properties helps us appreciate the science behind our meals.

Sensory Properties

Sweetness and Flavor Enhancement

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• Carbohydrates contribute sweetness to foods with simple sugars (monosaccharides and disaccharides) being the sweetest
• Sweetness decreases with increasing molecular weight of the carbohydrate
• Sucrose (table sugar) is often used as a reference for sweetness intensity
• Fructose is perceived as sweeter than sucrose at the same concentration
• Carbohydrates can enhance or modify flavors in foods by interacting with other components (proteins, fats, and flavor compounds)

Bulk, Texture, and Mouthfeel

• Carbohydrates provide bulk and texture to foods by influencing their physical structure
• Starch granules swell and gelatinize when heated in the presence of water, contributing to the texture of foods (bread, pasta, and sauces)
• Cellulose and other insoluble fibers provide a fibrous texture to foods (fruits, vegetables, and whole grains)
• Soluble fibers (pectin and gums) can create a smooth or slimy mouthfeel in foods (jams, jellies, and some beverages)
• The crystalline structure of sugars affects the texture of foods (granulated sugar vs. powdered sugar)

Functional Properties

Water Binding and Solubility

• Carbohydrates can bind water through hydrogen bonding, influencing the water activity and stability of foods
• Soluble fibers (pectin, gums, and mucilages) have a high water-binding capacity and can form viscous solutions or gels
• Insoluble fibers (cellulose and lignin) have a lower water-binding capacity but can still retain water within their matrix
• The solubility of carbohydrates depends on their molecular structure and interactions with water
• Monosaccharides and disaccharides are highly soluble in water, while polysaccharides have varying solubilities depending on their structure and degree of branching

Gelation and Thickening

• Some carbohydrates can form gels or thicken solutions when heated and cooled
• Starch gelatinization occurs when starch granules are heated in the presence of water, causing them to swell, rupture, and release amylose and amylopectin
• The released amylose and amylopectin form a network that traps water, creating a gel or thickened texture (puddings, sauces, and pie fillings)
• Pectin forms gels in the presence of sugar and acid, which is the basis for making jams and jellies
• Gums and mucilages (xanthan gum, guar gum, and carrageenan) can thicken solutions and stabilize emulsions (salad dressings and ice cream)

Emulsification and Stabilization

• Certain carbohydrates can act as emulsifiers or stabilizers in food systems
• Gums and mucilages (gum arabic, modified starches, and pectin) can stabilize oil-in-water emulsions by forming a protective layer around oil droplets
• This protective layer prevents the coalescence of oil droplets and improves the stability of the emulsion (mayonnaise and salad dressings)
• Carbohydrates can also stabilize foams by increasing the viscosity of the continuous phase and reducing the surface tension (meringues and whipped cream)
• Modified starches can stabilize frozen foods by inhibiting ice crystal growth and reducing syneresis (ice cream and frozen desserts)

Physical Transformations

Crystallization and Recrystallization

• Carbohydrates can undergo crystallization, which influences the texture and stability of foods
• Sugars (sucrose, glucose, and fructose) can form crystals when a supersaturated solution is cooled or evaporated
• The size, shape, and number of crystals depend on the cooling rate, agitation, and presence of impurities
• Crystallization is important in the production of confectionery products (rock candy and fondant)
• Recrystallization can occur in foods with high sugar content, leading to a grainy or sandy texture (honey and ice cream)
• Controlling the crystallization process is crucial for achieving the desired texture and stability in food products

Browning Reactions

• Carbohydrates participate in browning reactions, which contribute to the color, flavor, and aroma of foods
• Maillard browning occurs when reducing sugars react with amino acids (proteins) in the presence of heat, producing brown pigments (melanoidins) and complex flavors
• Maillard browning is responsible for the appealing color and flavor of many foods (bread crust, roasted coffee, and grilled meats)
• Caramelization is a non-enzymatic browning reaction that occurs when sugars are heated to high temperatures, resulting in the formation of brown pigments and characteristic flavors
• Caramelization is important in the production of caramel sauces, candies, and some baked goods
• Enzymatic browning occurs when enzymes (polyphenol oxidases) catalyze the oxidation of phenolic compounds in the presence of oxygen, leading to the formation of brown pigments
• Enzymatic browning is a concern in fresh-cut fruits and vegetables (apples, potatoes, and avocados) and can be prevented by acidification, heating, or the use of antioxidants