Carbohydrates: Properties, Classification, and Reactions
1. What are Carbohydrates?
Carbohydrates are the primary organic compounds produced from CO2 and water through photosynthesis in plants. Starch and sucrose are key examples.
Most Used Carbohydrates by Humans
Starch and sucrose are among the most commonly used carbohydrates.
2. Classification of Carbohydrates
- Monosaccharides: Aldose, Ketoses
- Oligosaccharides
- Polysaccharides
3. Homoglycans vs. Heteroglycans
Homoglycans: Polysaccharides composed of the same type of monosaccharide.
Heteroglycans: Polysaccharides made up of different types of monosaccharides.
4. Hygroscopicity
Definition: Hygroscopicity is the ability of a substance to absorb moisture from the air.
Types of Hygroscopicity
- Favorable: Helps retain moisture in foods.
- Unfavorable: Can cause clumping in granulated or powdered products, limiting solubility.
5. The Glassy State
Definition: The glassy state is an amorphous state with high viscosity, preventing sugar crystallization.
Achieving the Glassy State
- Freezing
- Rapid dehydration or concentration of a solution
- Melting crystalline sugars followed by rapid cooling
6. Achieving Crystallization
Crystallization is achieved by slowly cooling saturated sugar solutions, allowing molecules to reorganize and form crystals.
7. Sugar Inversion
Sugar inversion is the hydrolysis of sucrose using an enzyme (invertase), acid (HCl), or sulfonic resins, resulting in invert sugar.
8. Functional Properties of Polysaccharides
- Hydrolysis
- Solubility
- Viscosity
- Gel formation
9. Dietary Fibers
Dietary fibers are insoluble polysaccharides that contribute to food texture and promote intestinal motility.
Polysaccharides and Water Mobility
Polysaccharides control water mobility due to their hydroxyl groups, which form hydrogen bonds with water molecules.
Polysaccharides and Food Texture
Polysaccharides influence food texture when interacting with water.
Polysaccharides in Solution
In solution, polysaccharides rotate freely and occupy an “effective volume.”
Effective Volume of Polysaccharides
Linear polysaccharides occupy more space than branched polysaccharides with the same molecular mass.
Viscosity of Polysaccharide Solutions
Linear polysaccharides form more viscous solutions than branched polysaccharides at the same concentration due to increased friction.
Gel Firmness
Gel firmness depends on the forces binding the crystalline regions.
Caramelization Reactions
Caramelization involves complex reactions upon heating carbohydrates, especially sucrose and reducing sugars, leading to dehydration, double bond formation, and unsaturated ring formation.
Effects of Double Bonds and Rings in Caramelization
Double bonds absorb light, creating color. Condensed rings contribute to color and flavor development.
Maillard Reaction
The Maillard reaction is a complex series of reactions between reducing sugars and amino groups in proteins, producing brown pigments and flavor changes.
Non-Enzymatic Browning
Non-enzymatic browning occurs during food processing or storage, accelerated by heat.
Effects of Heating Foods with Proteins and Sugars
Heating foods with proteins and sugars can lead to the loss of essential amino acids, reducing nutritional value.
Effects of Acid Treatment on Starches
Acid treatment hydrolyzes starch granules, primarily in amorphous areas, resulting in lower viscosity and gel firmness.
Preparation of Pregelatinized Starch
Pregelatinized starch is prepared by dehydrating a preheated starch solution, used in foods requiring quick thickening.
Viscosity of Crosslinked Starch Solutions
Crosslinking starch with ester and ether bonds prevents granules from bursting, maintaining viscosity.
Similarities Between Starch and Glycogen
Both starch and glycogen contain amylopectin.
Cellulose Association
Cellulose is found in plant cell walls, associated with lignin and hemicelluloses.
CMC and Its Uses
Carboxymethylcellulose (CMC) is a cellulose derivative used to increase food viscosity, providing stable solutions between pH 5 and 10.
Hemicelluloses in Baking
Hemicelluloses improve water retention, reduce mixing energy, aid protein incorporation, and increase volume in baked goods.
Dietary Fiber
Dietary fiber consists of soluble non-starch polysaccharides resistant to digestion, including cellulose and lignin.