Carbohydrate Analysis Methods Quiz

Carbohydrate Analysis

• Carbohydrates are the most abundant food component in nature (55-60%) of the caloric intake in the human diet.
• Carbohydrate structures are composed of C, H, and O in the ratio 1:2:1.
• The general formula is (CH₂O)ₙ where n represents the number of times the ratio is repeated.
• Digestible carbohydrates provide an energy source.
• Indigestible carbohydrates are known as dietary fiber.
• Glycoproteins are carbohydrate molecules covalently linked to proteins.
• Glycolipids are carbohydrate molecules covalently linked to lipids.
• Carbohydrates are classified based on the number of monomers:
  • Monosaccharides (e.g., glucose, fructose, galactose)
  • Disaccharides (e.g., maltose, sucrose, lactose)
  • Oligosaccharides (e.g., raffinose, stachyose)
  • Polysaccharides (e.g., starch, glycogen, cellulose)

Carbohydrate Analysis (continued)

• Simple sugars are water-soluble crystalline compounds.
• Aliphatic aldehydes or ketones containing one carbonyl group and one or more hydroxyl groups are reactive centers in simple sugars.
• Natural monosaccharides have either 5 (pentose) or 6 (hexose) carbon atoms.
• Monosaccharides have reactive carbonyl and hydroxyl groups.

Classification

• Monosaccharides: Simple sugars.
• Disaccharides: Two monosaccharides bonded together.
• Oligosaccharides: Short chains of 3-10 monosaccharides.
• Polysaccharides: Long chains of monosaccharides.

Oligosaccharides

• Low molecular weight polymers of monosaccharides (<20).
• Covalently bonded through glycosidic linkages.
• Yield monosaccharides after hydrolysis.
• Disaccharides consist of two monomers (e.g., maltose, sucrose, and lactose).

Polysaccharides

• High molecular weight polymers (>20).
• At least 20% of carbohydrates in nature are in the form of polysaccharides.
• Homopolysaccharides contain all the same monomer (e.g., starch, glycogen, cellulose, and dextrins).
• Heteropolysaccharides can contain more than one type of monomer (e.g., D-galacturonic acid, methylester, hemicellulose, and gums).
• Starch is the only polysaccharide humans can digest and use as an energy source.
• Other polysaccharides are indigestible.

Hydrolysis

• Hydrolysis breaks down disaccharides/oligosaccharides into monosaccharides.
• Water is used in the hydrolysis process.

Importance of analysis

• Nutritional labelling informs consumers about nutritional content
• Standards of identity ensure composition conforms to government regulations.
• Food processing efficiency relies on carbohydrate type and concentration.
• Food quality (sweetness, appearance, texture, and stability) depends on carbohydrate type and concentration.

Food Carbohydrate Content

• Provide examples of food and their carbohydrate content in percentages.

Sample Preparation

• Accurate and consistent results are crucial due to the complex nature of food.
• Sample purification to remove possible interferences is required.
• Techniques depend on the product and carbohydrate being analyzed.
• Aqueous solutions (e.g., fruit juice, syrup, honey) generally require little preparation.
• Solid samples (e.g., nuts, cereals, bread, fruit, and vegetables) often need isolation techniques.
• Isolation helps to separate the desired component from other components.
• Boiling defatted samples with 80% alcohol extracts low MW carbohydrates.
• Mono- and oligosaccharides are soluble in alcohol; polysaccahrides are not.
• Soluble components are separated using filtration, and the filtrate is then collected.

Analysis of Components in Solution

• Soluble components contain additional small molecules (enzymes, amino acids, metals, organic acids, pigments, vitamins), causing interference in subsequent analysis.
• Compounds can appear as colored or cloudy, affecting analysis methods.
• Removing these components is critical prior to carbohydrate analysis.
• Clarifying agents (e.g., lead acetate) form insoluble complexes to remove interference.
• Ion exchange separates nonpolar charged molecules from polar charged molecules.

Carbohydrate Analysis Methods Overview

• Monosaccharide and Oligosaccharide Analysis Methods:
  • Chemical methods: Titration, gravimetric, colorimetric (Somogyi-Nelson, Anthrone, Phenol-sulfuric, DNS)
  • Biochemical methods: Enzymatic methods
  • Optical/Physical methods: Refractive index, polarimetry
  • Chromatographic method
• Polysaccharide Analysis Methods
  • Determination of nutrient polysaccharides (e.g., Blue-Value for amylose content)
  • Determination of structural polysaccharides (e.g., Crude/Dietary Fiber)
  • Total carbohydrate calculation by difference
• Specific Carbohydrate Types Analysis Methods
  • Analyzing reducing sugars (Lane-Eynon method)
  • Using self-reading automated methods (Munson-Walker, Somogyi-Nelson, Anthrone) -Using self-reading automated methods (Phenol-Sulfuric acid, Dinitrosalicylic)

Carbohydrate Analysis Techniques

• Refractive index, polarimetry, IR, and density are physical methods for determining carbohydrate concentration in foods.

• Enzymatic analysis for starch in natural form, including total change and kinetic method.

Analysis of Starch

• Starch exists as water-insoluble granules in its natural form.
• Composed of two glucose homopolysaccharides (amylose and amylopectin).
• Varying physicochemical properties of each component.
• Determining the concentration of each individual component, along with the overall starch concentration, is important to food characterization.

Analysis of Starch (continued)

• Processed foods can have altered starch structure due to treatments (like heating).
• Isolation from other components is essential in the analysis of starch.
• Granules are separated using drying, grinding, steeping in water, filtration, or centrifugation.
• Water-insolubility and relatively high-density (1500 kg/m³) help with separation in natural foods, like legumes, cereals, or tubers.

Sample Preparation for Starch Analysis

• For processed foods, samples are normally dried, ground, and dispersed in hot 80% ethanol solutions.
• Monosaccharides and oligosaccharides are soluble in ethanol, while starch is not.
• For semi-crystalline starch samples, dispersion in water and heating until gelatinization occurs is necessary.
• Introducing perchloric acid or calcium chloride can aid the solubilization process.

Calculation By Difference

• Calculating carbohydrate content by difference involves subtracting the sum of other measured components from 100%.

• Measuring other components (moisture, protein, lipids, and minerals) before calculating carbohydrate content is crucial for accuracy. It may lead to errors if there are errors in other measurement.

• Summary of chemical techniques to analyze carbs:

• Most chemical techniques rely on reducing sugars reacting with chemical agents to form precipitates or colored complexes, which can be quantified through solubilization, titration, or spectrophotometry.

• Methods are often non-stoichiometric and need a standard curve.

• Accuracy issues may arise when analyzing multiple sugars at once.

• No universal procedure exists for analyzing polysaccharides, so isolation methods need to precede the measurement.

Crude/Dietary Fiber Determination

• Crude fiber is a measure of indigestible substances in food.

• Sequential extraction or selective precipitation follows enzymatic solubilization.

• Gravimetric measurement of the insoluble content is necessary.

• Indigestible components are collected following the solubilization of digestible carbohydrates, proteins, and lipids.

• Analytical Methods for Crude Fiber:

• Liquid removal (solvent extraction) to remove lipids from the food sample.

• Protein removal (enzymes, strong acids/alkalies) to break down and solubilize proteins.

• Starch removal (gelatinization, enzymes, strong acids/alkalies) to break down and solubilize starch.

• AOAC method digests protein and starch to determine fiber content.

• Crude fiber is primarily cellulose and lignin.

• Pectin and hemicellulose can't be separated or detected.

Methods for Crude Fiber Analysis and Dietary Fiber (Overview)

• Methods for crude fiber are chosen based on their accuracy and the results.
• Often involves gravimetric and chemical approaches.
• Methods give comparable estimates of fiber content for most foods.
• Gravimetric measurement has an issue with overestimating foods high in simple sugars (e.g., glucose, fructose, and sucrose) in dry fruits, as sugars are trapped in the precipitate.
• EC methods don't measure lignin and resistant starch.
• Issues with proteolytic enzymes in gravimetric and EC methods, which might increase the measurement of soluble fiber.
• Factors like time, equipment, chemicals, and technical skill are important to consider when choosing an analysis method.
• Analysis with automated instruments: use automated systems like fiber test, Fibertec, fiber analyzer, or Fibretherm FT1 2.

Browning and Non-Browning Reactions (Overview)

• Browning is a common color change in food during pre-preparation, processing, or storage.
• It varies in intensity, ranging from cream and pale yellow to dark brown and red.
• Enzymatic browning (e.g., apples, potatoes): Related to phenolase (polyphenoloxidase), an enzyme dependent on oxygen. Phenols are converted to o-quinones. O-quinones undergo further reactions producing brown pigments. Prevented with cold water immersion or acidity or antioxidants
• Non-enzymatic browning (Maillard reaction): Reactions between amino acids and reducing sugars, typically require heat. The Maillard reaction produces a variety of compounds that contribute to flavor, aroma, and the dark color in many foods.
• Caramelization: Reaction of sugars (e.g., sucrose) under heat. It produces brown pigments that are not related to proteins.
• Prevention of browning reactions is important in food processing to maintain food quality and safety.

Maillard Reaction

• Chemical reaction between amino acids and reducing sugars, usually requiring heat.
• Leads to flavor, aroma, and brown color changes.
• Can be a source of potentially toxic and mutagenic compounds.

Caramelisation

• A browning reaction that occurs from heating carbohydrates, often sucrose with the presence of acids, bases, or salts.
• Produces complex mixtures of polymeric compounds, flavors, and aromas.
• Results from dehydration reactions, forming double bonds and anhydro rings.
• Catalysts increase reaction rate and help to specify caramel color types, solubility, and acidity.
• Different classes of caramel exist based on their preparation processes.

Other Notes

• Include details about the objectives, duration, and the date of the presentation for the Food Analysis 1 course.
• All methods names, principals, measured aspects, troubleshooting processes, precautions, advantages, and disadvantages for each analysis need to be included in the notes.
• All chemical equations that were in the slides also need to be included.
• Key steps in sample preparation for each type of analysis.
• Specific examples of applications/uses of each analysis. This is especially important regarding food, its nutritional value, and preservation/storage.