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Principles of Food Science
Table of Contents
Unit 4 Overview: Carbohydrates: Structure and Function
4.1 Classification and structure of carbohydrates
4.2 Functional properties of carbohydrates in foods
4.3 Sweeteners and sugar alternatives
4.4 Starch and modified starches in food applications

Carbohydrates come in simple and complex forms. Simple carbs include single-sugar monosaccharides like glucose and fructose, and two-sugar disaccharides like sucrose and lactose. These provide quick energy and sweetness in foods.

Complex carbs have more sugar units. Oligosaccharides have 3-10 units and can act as prebiotics. Polysaccharides like starch and cellulose have many units, providing energy storage in foods and fiber for digestion.

Simple Carbohydrates

Monosaccharides

  • Simplest form of carbohydrates consisting of a single sugar molecule
  • Glucose is the most common monosaccharide and primary source of energy for cells
    • Found in fruits, vegetables, and honey
    • Blood sugar refers to the concentration of glucose in the bloodstream
  • Fructose is another common monosaccharide known as fruit sugar
    • Naturally occurs in fruits, vegetables, and honey
    • Sweeter than glucose and often used as a sweetener in processed foods (high fructose corn syrup)

Disaccharides

  • Carbohydrates composed of two monosaccharide units joined by a glycosidic bond
  • Sucrose, commonly known as table sugar, is a disaccharide made up of glucose and fructose
    • Produced by plants and extracted from sugar cane or sugar beets
    • Widely used as a sweetener in food products and beverages
  • Lactose is a disaccharide found in milk and dairy products
    • Composed of glucose and galactose
    • Some individuals may be lactose intolerant due to a lack of the enzyme lactase needed to break down lactose

Complex Carbohydrates

Oligosaccharides

  • Carbohydrates containing 3-10 monosaccharide units linked by glycosidic bonds
  • Examples include raffinose (found in beans) and stachyose (found in soybeans)
  • Some oligosaccharides, such as fructooligosaccharides, act as prebiotics promoting the growth of beneficial gut bacteria

Polysaccharides

  • Carbohydrates composed of many monosaccharide units joined by glycosidic bonds forming long chains or branched structures
  • Starch is a storage polysaccharide in plants consisting of amylose (linear) and amylopectin (branched)
    • Major source of energy in the human diet found in foods like potatoes, rice, and wheat
    • Amylose has a linear structure of glucose units linked by α-1,4 glycosidic bonds
    • Amylopectin has a branched structure with glucose units linked by α-1,4 and α-1,6 glycosidic bonds
  • Cellulose is a structural polysaccharide in plant cell walls made up of glucose units linked by β-1,4 glycosidic bonds
    • Most abundant organic compound on Earth providing structure and support to plants
    • Humans lack the enzymes to break down cellulose, making it an important source of dietary fiber

Key Terms to Review (19)

Carbohydrate Classification: Carbohydrate classification is the systematic categorization of carbohydrates based on their structure and function. This classification encompasses simple sugars, complex carbohydrates, and their derivatives, highlighting the differences in their molecular composition and biological roles. Understanding these classifications is crucial for comprehending how carbohydrates interact within food systems and their implications for nutrition and health.
Energy Source: An energy source refers to any material or process that can produce energy for use by living organisms or machines. In the context of carbohydrates, energy sources are vital because carbohydrates are one of the primary macronutrients that provide the body with glucose, which is crucial for metabolism and overall energy production.
Fiber: Fiber is a type of carbohydrate that the body cannot digest, which is essential for maintaining a healthy digestive system. It comes in two main forms: soluble and insoluble fiber, each playing unique roles in health. Soluble fiber dissolves in water and can help lower blood cholesterol and glucose levels, while insoluble fiber adds bulk to the stool and aids in digestion.
Cellulose: Cellulose is a complex carbohydrate and a key structural component of plant cell walls, made up of long chains of glucose molecules linked by β(1→4) glycosidic bonds. This polysaccharide is essential for maintaining the rigidity and strength of plant cells, enabling them to withstand external pressures. Cellulose is classified as a dietary fiber in human nutrition and plays a significant role in digestive health and the functioning of the ecosystem.
Amylopectin: Amylopectin is a highly branched polysaccharide and one of the two components of starch, the other being amylose. It plays a crucial role in the structure and function of starch in food products, providing the gel-like properties that are important in cooking and processing. Understanding amylopectin is essential for grasping how carbohydrates function in food science, particularly in applications involving thickening agents and texture modification.
Starch: Starch is a complex carbohydrate made up of numerous glucose units linked together, serving as a primary energy storage molecule in plants. It is formed through photosynthesis and can be found in various forms, primarily as amylose and amylopectin, which influence its digestibility and functionality in food science.
Fructooligosaccharides: Fructooligosaccharides (FOS) are a type of carbohydrate made up of short chains of fructose molecules. They belong to a group called oligosaccharides and are commonly found in many plants, such as onions, garlic, and bananas. FOS are considered prebiotics, meaning they promote the growth of beneficial gut bacteria, thus playing a key role in digestive health and overall well-being.
Amylose: Amylose is a linear polysaccharide made up of glucose units connected by α(1→4) glycosidic bonds, forming a helical structure. It is one of the two main components of starch, the other being amylopectin, and plays a crucial role in determining the functional properties of starches in food science.
Stachyose: Stachyose is a tetrasaccharide composed of two galactose units, one glucose unit, and one fructose unit, making it part of the oligosaccharides group. This carbohydrate is commonly found in various legumes and some vegetables, and it plays a significant role in human nutrition as it is not fully digestible, often leading to fermentation in the large intestine. Understanding stachyose contributes to our knowledge of carbohydrate classification and structure, particularly in the context of non-digestible carbohydrates and their effects on gut health.
Raffinose: Raffinose is a complex carbohydrate, specifically a trisaccharide, made up of three simple sugars: galactose, glucose, and fructose. It is part of the oligosaccharide family and is commonly found in various plants, particularly in beans, cabbage, Brussels sprouts, broccoli, and whole grains. Understanding raffinose is important for recognizing how certain carbohydrates are classified and structured, as well as their implications for human digestion and nutrition.
Oligosaccharides: Oligosaccharides are carbohydrates composed of a small number of monosaccharide units, typically ranging from 2 to 10. These carbohydrate chains can be linear or branched and play significant roles in biological processes, such as cell recognition and signaling. Oligosaccharides are important in the context of food science due to their impact on digestion, nutritional value, and their functional properties in food products.
Glycosidic bond: A glycosidic bond is a type of covalent bond that connects two monosaccharides, or simple sugars, forming a disaccharide or polysaccharide. This bond is formed through a dehydration reaction where a water molecule is released as the hydroxyl group of one sugar reacts with the anomeric carbon of another sugar, linking them together. Glycosidic bonds are crucial for the structure and function of carbohydrates, influencing their properties and how they are utilized in biological systems.
Fructose: Fructose is a simple sugar, or monosaccharide, found naturally in many fruits, honey, and root vegetables. Known for its sweet taste, fructose is classified under carbohydrates and plays a crucial role as a primary energy source for many organisms. Its unique structure distinguishes it from other sugars, particularly in how it interacts with sweetness receptors, making it a popular ingredient in food products as both a sweetener and sugar alternative.
Glucose: Glucose is a simple sugar and one of the primary energy sources for living organisms. It is a monosaccharide that plays a crucial role in cellular respiration, where it is broken down to produce ATP, the energy currency of the cell. Being a fundamental carbohydrate, glucose serves as a building block for more complex carbohydrates and is often found in various food sources, directly influencing sweetness and energy content.
Lactose: Lactose is a disaccharide sugar composed of two monosaccharides, glucose and galactose, commonly found in milk and dairy products. It serves as an important source of energy for many organisms, especially in early development, and is classified within the larger category of carbohydrates, specifically as a non-reducing sugar due to its unique structure.
Polysaccharides: Polysaccharides are complex carbohydrates formed by long chains of monosaccharide units linked together by glycosidic bonds. They play vital roles in energy storage and structural support within living organisms, highlighting their importance in the classification and structure of carbohydrates as well as in the functions of macronutrients.
Disaccharides: Disaccharides are carbohydrates composed of two monosaccharide units linked together by a glycosidic bond. They are important energy sources and play crucial roles in various biological processes. Common examples include sucrose, lactose, and maltose, each contributing to our daily nutrition and metabolic functions.
Monosaccharides: Monosaccharides are the simplest form of carbohydrates, consisting of single sugar molecules that cannot be hydrolyzed into smaller carbohydrates. These basic units serve as the building blocks for more complex carbohydrates and play essential roles in energy metabolism and cellular functions.
Sucrose: Sucrose is a disaccharide composed of glucose and fructose, commonly known as table sugar, and it plays a crucial role in food science due to its sweetness and functional properties. It is widely used in food processing to enhance flavor, act as a preservative, and influence the texture and moisture of various products. Understanding sucrose is essential for managing water activity in foods, classifying carbohydrates, and exploring sweeteners and sugar alternatives.