C₁₂H₂₂O₁₁ — Sucrose

Sucrose, commonly known as table sugar, is a naturally occurring carbohydrate with the chemical formula \(C_{12}H_{22}O_{11}\). It is a disaccharide composed of one molecule of glucose and one molecule of fructose joined together by a glycosidic bond. Sucrose is one of the most abundant sugars in nature, found in sugarcane, sugar beet, maple syrup, and various fruits and vegetables.

Sucrose serves as a primary sweetener in the human diet and an important source of energy. It plays a central role in the food, beverage, and pharmaceutical industries. Biologically, sucrose acts as a transport form of carbohydrate in many plants, moving energy from photosynthetic tissues (leaves) to storage tissues (roots, stems, fruits).

Sucrose is a disaccharide consisting of α-D-glucose and β-D-fructose linked via a 1,2-glycosidic bond. The linkage forms between the anomeric carbon (C1) of glucose and the anomeric carbon (C2) of fructose, creating an acetal connection that prevents the molecule from acting as a reducing sugar.

Due to this bonding pattern, sucrose does not have a free aldehyde or ketone group, and thus it does not react with Fehling’s or Tollen’s reagents. Structurally, sucrose can exist in crystalline or amorphous forms, with strong hydrogen bonding contributing to its stability and solubility.

Sucrose occurs widely in nature as a natural carbohydrate synthesized by green plants during photosynthesis. It serves as a major product of photosynthesis and an essential energy transport molecule. Major natural sources of sucrose include:

• Sugarcane (Saccharum officinarum): The primary commercial source of sucrose globally.
• Sugar beet (Beta vulgaris): A key source in temperate regions, especially Europe.
• Maple trees: Sucrose is present in maple sap, which is used to produce maple syrup.
• Fruits and Vegetables: Bananas, pineapples, carrots, and sweet potatoes contain natural sucrose.

In plants, sucrose is transported from photosynthetic leaves to other parts of the plant for storage or energy use, a process vital for plant growth and development.

1. Extraction from Sugarcane:

Sucrose is extracted from sugarcane through the following process:

• Crushing: Sugarcane stalks are crushed to extract juice.
• Clarification: Lime (Ca(OH)₂) is added to remove impurities.
• Evaporation: The clarified juice is concentrated by evaporation to form thick syrup.
• Crystallization: On cooling, sugar crystals separate out and are centrifuged to obtain raw sugar.

2. Extraction from Sugar Beet:

In the beet sugar industry, sliced beets are soaked in hot water for diffusion, followed by purification, evaporation, and crystallization processes similar to cane sugar extraction.

The obtained raw sugar is then refined by washing, dissolving, filtering, and recrystallizing to produce pure white sucrose crystals suitable for consumption.

Physical Properties:

• Appearance: White crystalline solid with a sweet taste.
• Solubility: Readily soluble in water due to strong hydrogen bonding.
• Optical Activity: Sucrose is dextrorotatory with a specific rotation of +66.5°.
• Hygroscopic Nature: Absorbs moisture from air and can form sticky syrup under humid conditions.

Chemical Properties:

• Hydrolysis: Sucrose hydrolyzes in the presence of acid or the enzyme invertase to form an equimolar mixture of glucose and fructose, known as invert sugar.

\(C_{12}H_{22}O_{11} + H_2O \xrightarrow{H^+ / invertase} C_6H_{12}O_6 (glucose) + C_6H_{12}O_6 (fructose)\)

• Caramelization: When heated above its melting point, sucrose decomposes to form caramel, a brown-colored compound used in food flavoring and coloring.
• Oxidation: Sucrose is a non-reducing sugar and does not react with oxidizing agents like Fehling’s or Benedict’s solution due to the absence of a free carbonyl group.
• Esterification: It reacts with acetic anhydride to form sucrose octaacetate, confirming the presence of multiple hydroxyl groups.

Sucrose serves as a key dietary carbohydrate and energy source for humans and animals. Upon ingestion, sucrose is hydrolyzed by the enzyme sucrase in the small intestine into glucose and fructose, which are then absorbed into the bloodstream to provide immediate energy.

In plants, sucrose functions as the primary transport molecule for carbohydrates, moving from leaves (sites of photosynthesis) to other plant parts for storage or metabolic use. This process supports plant growth, seed development, and fruit ripening.

In humans, moderate consumption of sucrose contributes to energy metabolism, but excessive intake may lead to obesity, diabetes, and dental caries. Thus, dietary balance is essential.

• Food Industry: The most common use of sucrose is as a sweetener in food, beverages, baked goods, and confectionery. It enhances flavor, texture, and shelf life.
• Pharmaceuticals: Used as a stabilizer, bulking agent, and coating in syrups and tablets.
• Preservative: High concentrations of sucrose inhibit microbial growth in jams and jellies by lowering water activity.
• Fermentation: Acts as a substrate for yeast fermentation to produce ethanol, CO₂, and other industrial chemicals.
• Biotechnology: Used as a carbon source in microbial culture media and biochemical assays.
• Caramel and Invert Sugar Production: Used to prepare caramel coloring and invert sugar syrup for confectionery and beverage industries.

Sucrose is safe for human consumption when consumed in moderate quantities. It provides 4 kcal of energy per gram and supports brain and muscle function. However, overconsumption can lead to metabolic health issues, such as type 2 diabetes, tooth decay, and obesity.

Environmentally, the sugar industry has both positive and negative aspects. While sugarcane cultivation supports livelihoods and economies, excessive use of fertilizers and water resources can harm ecosystems. Sustainable agricultural practices and improved processing methods are essential for minimizing its environmental footprint.