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Questions and Answers
Which type of carbohydrate consists of more than 20 monosaccharides and often exceeds 200 units?
What is the primary functional group of aldoses such as glucose?
Which of the following monosaccharides is considered a ketose and is relevant to food chemistry?
How many carbon atoms are present in the relevant monosaccharides for food processing such as glucose and fructose?
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Which component is NOT categorized as a carbohydrate type?
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Which type of bond is primarily found in commonly occurring fructans such as inulin?
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What is the minimum degree of polymerization (DP) for polysaccharides?
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What classification do polysaccharides fall under when they consist of the same monosaccharide unit?
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Which of the following is NOT considered a source of polysaccharides?
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Which of the following polysaccharides is derived from shellfish industry by-products?
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Fructans are primarily known for which of the following properties?
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What type of polysaccharide consists of two or more different monosaccharides?
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Which of these foods is rich in fructans?
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What is the backbone structure of galactomannans?
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What is the M/G ratio for guar gum?
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In which product is galactomannans commonly used to prevent ice recrystallization?
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What types of acids primarily make up the backbone of alginates?
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What is the main characteristic that distinguishes the different types of galactomannans?
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What is a common use of gum arabic?
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How are the M-blocks in alginates linked?
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Which sequence represents the order of rigidity for alginate blocks?
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What percentage of gum arabic is composed of the polysaccharide chains with little or no protein?
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Which of the following statements is true regarding the properties of galactomannans?
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What model is used to explain the gelation of alginates?
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Which species of acacia trees give the best gum for producing gum arabic?
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Which of the following describes pectin?
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Which segments primarily constitute pectin?
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What characteristic of underripe fruit relates to its pectin content?
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Which position of the galacturonic acid can be methyl-esterified in pectin?
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What is the primary effect of soluble dietary fiber on food formulations?
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What happens to dietary fibers during human digestion?
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Which type of starch can reach the colon undigested and act as a prebiotic?
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Which monosaccharides can be directly absorbed into the bloodstream?
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What is the primary role of human digestive enzymes regarding carbohydrates?
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Study Notes
Carbohydrates
- Divided into three groups: Monosaccharides, Oligosaccharides, and Polysaccharides
- Polysaccharides are polymers of monosaccharides, with over 20 units, forming large chains
- They are composed of chiral carbon atoms, each with four different chemically distinct atoms or groups attached
Monosaccharides
- Two types: aldoses (e.g., glucose) with an aldehyde functional group and ketoses (e.g., fructose) with a ketone functional group
- Fructose is the only ketose relevant to food chemistry
- They have at least 4 carbon atoms (4C)
- Key monosaccharides in food processing include glucose, fructose, arabinose, and xylose
- Six most essential monosaccharides for food applications: Glucose, Mannose, Galactose, Arabinose, Xylose, and Fructose
- Fructans, like inulin and levan, are chains of fructose units linked by β-(2→ 1) or β-(2 → 6) bonds
- Found naturally in asparagus, banana, garlic, leek, onion, Jerusalem artichoke and are important prebiotics, fat replacers, and texture modifiers
Polysaccharides
- Polymers of monosaccharides linked by glycosidic bonds
- Degree of Polymerization (DP) indicates the number of monosaccharides in the chain. DP is usually over 200, often over 3000.
Polysaccharide Sources
- Plants with minimal processing: e.g., rice, potato starch
- Agricultural wastes: e.g., pectin
- Other sources: Algae (alginate, carrageenan), shellfish industry by-products (chitin), Microbial fermentation (xanthan, gellan)
Polysaccharide Composition
- Categorized based on composition: Homopolysaccharides (same monosaccharide unit) and Heteropolysaccharides (two or more different monosaccharides)
Alginates
- Linear polysaccharides composed of β-D-mannuronic acid (M) and α-L-guluronic acid (G) linked via (1 → 4) glycosidic linkages
- Consists of blocks of mannuronic acid (M-blocks) or guluronic acid (G-blocks) and regions of alternating sequences (e.g., MG, MMG, GGM)
- M-blocks are flexible due to the 4C1 conformation and linked via β-(1 → 4) linkages
- G-blocks are rigid due to the 1C4 conformation of guluronate residues linked via α-(1 → 4)
- Stiffness of the blocks on the backbone is in the order: GG (most rigid) > MM > MG (least rigid)
- Selectively bind divalent and multivalent cations
- Gelation occurs through the egg-box model
Pectin
- Family of complex polysaccharides containing 1,4-linked α-D-galactosyluronic residues
- Isolated from plant cell walls, particularly in citrus peel and apple pomace
- Underripe fruit contains more pectin than fully ripe fruit
- Primarily consists of homogalacturonan (HG) and rhamnogalacturonan-I (RG-I) segments
- Interactions between HG and RG-I segments influence functional properties
- HG is the most abundant component, composed of long chains of linear 1 → 4 linked α-D-galacturonic acid residues (around 200 units)
- Some carboxyl groups are methyl-esterified at the C-6 position and acetyl-esterified at the O-2 and O-3 positions of the galacturonic acid
Galactomannans
- Seed polysaccharides commercially obtained from guar and carob (locust bean)
- Backbone of β-(1 → 4)-linked mannose with galactose branches linked with α-(1 → 6) glycosidic bonds
- Distinctive feature is the mannose-to-galactose ratio (M/G), which varies based on the source
- M/G ratio for guar is 2:1 and 4:1 for carob gum
- Form viscous solutions at low concentrations
- Can be used with xanthan and carrageenan to enhance stabilizing and gelling properties
- Used in ice cream, salad dressings, and soft cheese to prevent ice recrystallization, improve viscosity, and water holding capacity
Gum Arabic
- Exudate gum of acacia trees (A. senegal or A. seyal)
- Best gum comes from Sudan and Nigeria
- A heterogeneous material composed of two primary fractions:
- Polysaccharide chains with minimal protein (around 70% of the gum)
- Higher molecular weight molecules with protein as an integral part of their structures
Dietary Fiber (DF)
- Categorized based on solubility:
- Soluble Dietary Fiber (SDF) increases viscosity of formulations
- Insoluble Dietary Fiber (IDF) has limited capacity to enhance viscosity
Summary
- Only monosaccharides can pass through the small intestinal wall into the bloodstream
- Human digestive enzymes can only hydrolyze sucrose, lactose, starch, and starch-based oligosaccharides to monosaccharides (d-glucose, d-fructose, and d-galactose)
- DFs are indigestible, influencing fecal bulk, stool transit time, and serum cholesterol levels
- Resistant starch is a form of starch that reaches the colon undigested and serves as a prebiotic substrate for beneficial microflora
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Description
This quiz explores the classification and structure of carbohydrates, focusing on monosaccharides like glucose and fructose, as well as polysaccharides. Understand the properties and significance of these sugars in food chemistry and processing. Test your knowledge on key concepts and applications related to carbohydrates.
