Understanding Carbohydrates: Types and Functions

• Carbohydrates are organic compounds containing carbon, hydrogen, and oxygen, and can be simple or complex molecules.
• Key food carbohydrates are monosaccharides, dextrins, starches, celluloses, hemicelluloses, pectins, and gums.
• Carbohydrates are significant as a source of energy and fiber in diets and for their functional roles as sweeteners, thickeners, stabilizers, gelling agents, and fat replacers.
• Plants store solar energy by converting sunlight into glucose through photosynthesis, which uses carbon dioxide, water, and chlorophyll; the general equation is 6CO2 + 6H2O + sunlight → C6H12O6 + 6O2.
• Plants produce glucose and convert it into sugars, starches, or fiber and as plants mature, glucose becomes fiber for structure, while seeds convert carbohydrates from sugars to starches.
• Categories of carbohydrates include sugars, starches, and fibers.

Sugars and Classes of Sugars

• Sugars, known as saccharides in organic chemistry, are organic compounds composed of carbon that are classified by structure, all containing hydroxyl groups (-OH).
• Sugars are divided into monosaccharides and disaccharides.

Classes of Sugars

• Monosaccharides are simple carbohydrates with three to eight carbon atoms; with glucose and fructose (C6H12O6) being the most important in foods and examples include glucose, fructose, and galactose
• Disaccharides contain two sugar units per molecule, examples are sucrose, lactose, and maltose.

Sources of Sugars

• Sugars provide 4 kilocalories per gram and include granulated, brown, and confectioners sugars, as well as honey, corn syrup, molasses, and maple syrup.
• Common sugar sources include sugar cane, sugar beets, maple trees, corn, and sorghum.
• Brown sugar, made from unrefined cane sugar or with added molasses, has a moist texture and unique flavor.
• Confectioners sugar is finely ground granulated sugar with corn starch and designations like 4X, 6X, and 10X indicating fineness.

Sweetness

• Sugars like glucose, fructose, and sucrose are known for sweetness, with fructose being the sweetest while lactose is the least sweet.
• Sugars function as sweetening agents in candies, baked goods, and beverages and contribute to texture, preservation, and caramelization, enhancing food appeal and shelf life.

Formation of Solutions and Syrups

• Sugars are water-soluble and form syrups due to water molecules forming hydrogen bonds with sugar, disrupting sugar's crystalline structure.
• Sugar solubility increases with temperature; hot solutions dissolve more sugar than cold ones, and evaporation leads to crystal formation, important in candy making.

Body and Mouthfeel

• Sugars increase the viscosity of food, thickening it and creating desirable textures in syrups, sauces, and desserts.
• Non-nutritive sweeteners lack the bulk of sugar, which can result in a watery consistency, which can be counteracted by adding modified starches or gums to mimic sugar’s textural properties.

Fermentation

• Sugars are digested and metabolized by the human body, with 4 cal/g, and also by microorganisms, where yeast ferments sugar to produce carbon dioxide, which leavens bread.

Preservatives

• Sugars, at high concentrations, function as natural preservatives by reducing water activity (aw), which inhibits microbial growth.
• High sugar concentration in jams, jellies, and syrups preserves flavor and limits spoilage.
• Jams and Jellies: Sugar interacts with pectin, lowering water activity to prevent bacteria growth.
• Candied Fruits and Syrups: Sugar creates a hypertonic environment that dehydrates microbes.
• Water activity below 0.85 prevents most microbial growth, but osmotolerant yeasts and molds require additional sterilization methods.
• This method enhances shelf life, taste, and texture in traditional and commercial food production.

Reducing Sugars in Millard reaction

• Reducing sugars have a free carbonyl group (-C=O) and participate in chemical reactions like reducing compounds.
• Monosaccharides: All monosaccharides (e.g., glucose, fructose, galactose) are reducing sugars, where carbonyl groups are free to react.
• Disaccharides: Disaccharides (e.g., maltose and lactose) are reducing sugars if at least one monosaccharide unit has a free carbonyl group; sucrose is a non-reducing sugar since both carbonyl groups are involved in a glycosidic bond.
• Reducing sugars contribute to browning and flavor through the Maillard reaction, where the carbonyl group reacts with amino acids.
• Bread Baking: Glucose and amino acids react during baking for a golden-brown crust and aromatic flavor.

Non-Reducing Sugar Exception

• Sucrose must first break down into glucose and fructose to participate in the Maillard reaction.

Caramelization

• Upon heating, sugars undergo caramelization, which leads to browning.
• The process occurs at high temperatures and involves sugar decomposition, producing organic acids, aldehydes, and ketones.
• Caramelization doesn't require proteins and is purely sugar-driven, unlike the Maillard reaction.

Sugar Alcohols

• Sugar alcohols like xylitol, sorbitol, and mannitol are produced by reducing the carbonyl group in sugars making them sweet but less so than sucrose.
• They are non-cariogenic and less likely to cause tooth decay as a result of not being easily fermented by oral bacteria.
• Sugar alcohols provide 1-3 kcal/g and are metabolized less efficiently than sugars; they are mostly converted into fructose, not glucose, making them suitable for diabetics.

Oligosaccharides

• Oligosaccharides are carbohydrates composed of 3-10 monosaccharide units linked by glycosidic bonds.
• Common oligosaccharides include raffinose and stachyose, found in legumes like dry beans and peas.
• Humans cannot digest these oligosaccharides due to a lack of enzymes, leading to fermentation by bacteria in the large intestine and gas production.
• Oligosaccharides act as prebiotics, promoting gut health but can also cause digestive distress.

Practical applications of oligosaccharides

• Oligosaccharides are Prebiotics, like fructooligosaccharides (FOS) and galactooligosaccharides (GOS), and promote beneficial bacteria in the gut.
• Beneficial bacteria such as bifidobacteria help to improve digestive health, enhance immune function, and reduce the risk of certain diseases.
• They are often added to functional foods like yogurt, infant formulas, and dietary supplements.
• Oligosaccharides functions as Sugar Substitutes: Inulin, provides a sweet taste with fewer calories and does not significantly affect blood sugar levels, useful in products such as sugar-free candies, baked goods, and beverages.
• Functioning as Food Texturizers and Fat Replacers: They improve texture and mouthfeel and serve as stabilizers in products like dressings, sauces, and ice cream
• They Improve Gut Health: They resist digestion in the small intestine, ferment in the large intestine, and enhance gut barrier function, benefiting those with conditions such as IBS.
• Medical Uses: They modify immune responses and act as immune modulators in the treatment of infections or inflammation

Animal Feed

• Oligosaccharides promote gut health and improve the growth rate of livestock and poultry.

Polysaccharides

• Polysaccharides, including starches, pectins, and gums, are complex carbohydrate polymers with distinct properties based on their sugar units, glycosidic linkages, and branching.
• Starches: Polymers of glucose composed of amylose (linear) and amylopectin (branched); the ratio of amylose to amylopectin determines digestibility, gelling, and thickening properties; found in foods like potatoes, corn, and wheat.
• Pectins: Composed of galacturonic acid and used as gelling agents, with the degree of methylation and branching affecting gelling and solubility; pectins are key for texture in jams and jellies.
• Gums: Complex polysaccharides from plants or microorganisms, like guar gum and xanthan gum, function as thickeners, stabilizers, or emulsifiers, typically soluble in water, which makes them useful for viscosity or suspension.
• Structural differences dictate function; branching impacts thickening, while glycosidic linkages influence gelling and stabilizing for food industry applications.

Seaweed polysaccharides

• Seaweed polysaccharides include agars, alginates, and carrageenans from marine algae, and are gums noted for gelling.
• Agar: Derived from red algae, is used as a gelling agent in microbiological media and foods such as jellies and desserts; it is non-digestible and low-calorie.
• Alginates: Derived from brown algae, function as thickeners and stabilizers, forming viscous solutions and stabilizing emulsions, used to produce gummy candies.
• Carrageenans: Obtained from red seaweed, used for gelling and thickening in dairy and meat products, with different types determining gel strength and functionality.
• These are critical ingredients that provide texture, stability, and consistency in products ranging from desserts to processed meats.

Cellulose and hemicellulose

• Cellulose and hemicellulose are structural polysaccharides in plant cell walls that are indigestible to humans and contribute to insoluble dietary fiber.
• These are important for gut health, increasing stool bulk and aiding waste passage, thus promoting regularity, reducing colorectal cancer risks, improving gut microbiota health, and helping blood sugar control.

Starch

• Starch, stored in roots, seeds, and grain kernels, is a vital polysaccharide in plants and provides 4 calories per gram of energy.
• Upon consumption, starch is broken down into glucose, which is essential for physiological functions and brain energy.

Starch Structure and Composition

• Starch has two main components: Amylose, a linear chain, and amylopectin, a highly branched polymer.
• These form granules that are insoluble in cold water but absorb water and swell with heating, releasing starch molecules and thickening the mixture.
• Amylose consists of long chains linked by a-1,4 glycosidic bonds and forms a three-dimensional network when cooled, promoting gelation in cooked starch pastes; high amylose starches can form and maintain gels, while low amylose starches only thicken

Amylopectin

• Amylopectin constitutes about 75% of starch polymers with a highly branched structure linked by a-1,4 and a-1,6 glycosidic bonds.
• Amylopectin-rich starches thicken but do not form gels, creating viscous pastes without gelling ability.

Gelatinization Process in Cooking

• Starch is insoluble in water when uncooked forming a temporary suspension that will settle, it cannot be described as being "in solution".
• Starch is significant as a thickening agent; when starch is heated in water, the granules begin to absorb liquid and swell, leading to a key change in consistency in cooking starch-based products.
• Gelatinization involves multiple steps that transform starch from solid to gel-like.
• Gelatinization Temperature is reached when Starch-water mixtures increase from about 140-160°F (60–71°C), leading to hydrogen bond exchanges with starch molecules.
• Starch Granules Swell as they absorb sufficient water.
• Amylose chains begin to diffuse out of the granules.
• An ordered crystalline structure is lost and Birefringence disappears; the starch mixture becomes translucent.
• Granule Swelling and Viscosity Increase: As the granules continue to swell, they occupy more space, and the mixture thickens; the starch paste is more viscous.
• Continued Gelatinization and Development of Texture: The paste reaches its final consistency and becomes more viscous; over stirring at this stage causes swollen granules to rupture.
• Final Step Flavor Development: Cooked starch pastes should cook for an additional 5 minutes or more.
• Gelatinization of starches is typically completed at temperatures of around 190–194°F (88–90°C) or higher

Gelation or Setting of Gelatinized Starch Pastes During Cooling

• During cooling, amylose undergoes gelation and transitions.
• This gel is a two-phase colloidal system of a solid phase (3D network of amylose polymers) and a dispersed liquid phase (trapped water).
• The Reduction in kinetic energy allows amylose molecules to form hydrogen cross-bonds, which stabilize the network, creating the elastic structure characteristic, contrasting with the previous fluid sol state.
• Unlike amylose, amylopectin's branched structure prevents gel formation, maintaining a sol state that results in a thick, viscous consistency.

Retrogradation

• Starch retrogradation is the process where gelatinized starch molecules revert to a more ordered and crystalline structure during cooling.
• While involving both amylose and amylopectin, amylose retrogrades rapidly to prompt the initial firming of texture soon after the product cools.
• Amylopectin retrogrades more slowly, contributing to long-term staling for baked goods.
• As retrogradation progresses, the textural qualities of food change and products become firmer resulting in moisture loss, dryness.
• The process is influenced by time and temperature; amylose retrogrades quickly, while amylopectin requires longer and is accelerated by refrigeration.
• Understanding retrogradation is crucial to enhancing shelf life and texture.
• Techniques used are: adding anti-staling agents, incorporating modified starches, and adjusting storage conditions to mitigate its effects.

Syneresis

• Syneresis, releases water from a cooked and cooled starch gel, often caused by gelation and retrogradation.
• Amylose molecules reassociate over time causing a contraction of the gel leading to water loss in the food product.
• Cooling conditions are a factor in the gel's strength. Rapid cooling may prevent amylose micelles formation. Slow cooling can cause excessive alignment of amylose molecules, trapping less water.
• To minimize syneresis, modified starches or non-gelling amylopectin-based starches are used to increase stability

Modified Starch

• Modifying starches improves functionality, texture, clarity, stability, and performance to benefit producers and consumers.
• Pregelatinized Starch: After gelatinization, this type is dried, enabling it to swell in liquid without heat, as in instant pudding mixes.
• Cold Water-Swelling (CWS) Starch: Remains as intact granules and does not require cooking and is ideal for cold-process applications such as creamy salad dressings.
• Cross-Linked Starch: Chemically bonded to withstand low pH, high shear, and high temperatures, suitable for acidic foods but less tolerant of cold.
• Stabilized (Substituted) Starch: Prevents gelling and syneresis during freeze-thaw cycles, which helps in frozen and cold-stored products.

Acid-Modified Starch

• Are treated with dilute acid below gelatinization, forming less viscous mixtures that create a stable gel upon cooling.
• This is useful for foods needing texture at cooler temperatures and modifications allow starches to meet processing and storage conditions, which broadens uses.

Starches in food systems

• Starches are a versatile thickening, water-binding, and gelling agent, thickening products like soups, sauces, and dressings.
• Starches as fat replacers mimic the texture and mouthfeel of fats; amylose chains hold water, and maltodextrins simulate the viscosity and bulk of fats to reduce fat content.