A. CARBOHYDRATES
1. Major components of food
Carbohydrates, proteins, and lipids are the three major classes of organic constituents present in food systems. They contribute to the nutritional, structural, and functional properties of foods.
2. Occurrence of carbohydrates
Carbohydrates are widely distributed in plants, animals, and microorganisms. Their chemical forms and concentrations vary according to the biological source.
3. Glucose
Glucose is an important monosaccharide occurring in animal tissues and serves as a major carbohydrate substrate in metabolism.
4. Glycogen
Glycogen is the principal storage polysaccharide in animals. It is a highly branched polymer of glucose.
5. Classification of carbohydrates
Carbohydrates are classified into three major groups:
- Monosaccharides
- Oligosaccharides
- Polysaccharides
6. Monosaccharides
Monosaccharides are single sugar units that cannot be hydrolyzed into simpler carbohydrates. Examples include glucose, fructose, galactose, xylose, and ribose.
7. Oligosaccharides
Oligosaccharides contain a small number of monosaccharide units linked by glycosidic bonds. Important examples include sucrose, lactose, maltose, raffinose, stachyose, and verbascose.
8. Cellulose
Cellulose is a major structural polysaccharide of plant cell walls and is one of the most abundant polysaccharides in nature.
9. Important polysaccharides
Important polysaccharides and carbohydrate polymers associated with foods include starch, glycogen, cellulose, hemicelluloses, lignin, pectin, modified starches, carboxymethyl cellulose, chitin, and arabinoxylans.
10. Dietary fiber
Several non-digestible carbohydrate polymers and associated plant components contribute to dietary fiber. These materials influence intestinal function and the physical properties of foods.
11. Types of dietary fiber
Dietary fiber is commonly classified into:
- Soluble fiber
- Insoluble fiber
12. Soluble fiber
Pectin and gums are examples of soluble fiber. They can interact with water and may contribute to increased viscosity and gel formation.
13. Insoluble fiber
Cellulose, hemicelluloses, and lignin are examples of insoluble fiber. They contribute mainly to the structural fraction of plant materials.
14. Important properties of carbohydrates
Important physicochemical properties of carbohydrates in food systems include mutarotation, caramelization, and crystallization.
15. Mutarotation
Mutarotation is the change in optical rotation observed when a reducing sugar undergoes interconversion between its α- and β-anomeric forms through the open-chain form in aqueous solution.
16. Caramelization
Caramelization is a non-enzymatic browning process produced by the thermal degradation and subsequent reactions of sugars during heating.
17. Caramel formation
When sugars are subjected to sufficiently high temperatures, particularly under low-moisture or concentrated conditions, they undergo dehydration, fragmentation, and condensation reactions that produce caramelized compounds.
18. Sucrose caramelization
The supplied notes associate sucrose caramelization with heating at approximately 200°C. This should be regarded as a study-note value rather than a universal processing condition, because caramelization depends on factors such as moisture, pH, sugar concentration, and heating conditions.
19. Crystallization of sugars
Crystallization is the process by which dissolved sugar molecules arrange into an ordered solid crystalline phase. It is an important property in products such as confectionery and concentrated sugar foods.
B. PROTEINS
20. Protein composition
Proteins are macromolecules composed of amino-acid residues arranged in specific sequences. The source notes describe approximately twenty amino acids as the basic units of proteins.
21. Peptide bonds
Amino acids are linked by peptide bonds formed between the amino group of one amino acid and the carboxyl group of another, producing peptide chains.
22. Polar and non-polar amino acids
Amino acids may be classified according to the polarity of their side chains. Polar side chains interact more readily with water, whereas non-polar side chains are generally less hydrophilic.
23. Wheat proteins
Gliadins and glutenins are major storage proteins of wheat. Their molecular characteristics contribute to the formation and properties of gluten.
24. Occurrence of proteins in foods
Proteins occur in both animal-derived and plant-derived foods and provide important nutritional and functional properties.
25. Animal protein sources
Meat, milk, and eggs are important sources of dietary protein in animal-based foods.
26. Plant protein sources
Legumes, pulses, beans, and nuts are important sources of plant proteins and are particularly significant in vegetarian diets.
27. Essential amino acids
Essential amino acids are amino acids that the human body cannot synthesize in adequate amounts and therefore must be supplied through the diet. The supplied notes identify nine essential amino acids.
28. Classification of proteins
Proteins are traditionally classified into:
- Simple proteins
- Conjugated proteins
- Derived proteins
29. Simple proteins
Simple proteins yield predominantly amino acids on hydrolysis. Examples given in the notes include albumins, globulins, glutelins, prolamins, scleroproteins, histones, and protamines.
30. Conjugated proteins
Conjugated proteins consist of a protein component combined with a non-protein component known as a prosthetic group.
31. Examples of conjugated proteins
Examples include:
- Phosphoproteins — contain phosphate groups
- Lipoproteins — associated with lipids
- Nucleoproteins — associated with nucleic acids
- Glycoproteins — associated with carbohydrate components
- Chromoproteins — associated with colored prosthetic groups
32. Derived proteins
Derived proteins are products formed when native proteins undergo chemical, physical, or enzymatic modification.
33. Examples of derived proteins
Proteoses, peptones, and peptides are examples of protein-derived products.
34. Sources of proteins
Important food sources include meat, milk, eggs, pulses, beans, and nuts.
35. Levels of protein structure
Protein structure is described at four levels:
- Primary structure: amino-acid sequence
- Secondary structure: local structural arrangements such as α-helices and β-sheets
- Tertiary structure: three-dimensional folding of a polypeptide chain
- Quaternary structure: association of multiple polypeptide subunits
36. Protein denaturation
Denaturation is the alteration of the native higher-order structure of a protein without necessarily breaking its primary peptide-bond sequence. It may be caused by heat, pH changes, chemicals, or other environmental conditions.
37. Proteins and Maillard reaction
Proteins participate in the Maillard reaction, a non-enzymatic browning reaction involving reducing sugars and amino groups. The reaction contributes to the color, aroma, and flavor of many heated foods.
38. Functional properties of proteins
Food proteins provide important functional properties, including:
- Emulsification
- Foaming
- Water absorption or retention
- Binding
- Texture modification
C. LIPIDS AND FATTY ACIDS
39. Lipids
Many food lipids are composed predominantly of fatty acids esterified with glycerol. Triacylglycerols are the major storage lipids in many foods.
40. Classification by fatty-acid chain length
Fatty acids may be classified according to carbon-chain length as short-chain, medium-chain, and long-chain fatty acids.
41. Classification according to saturation
Based on the presence or absence of carbon-carbon double bonds, fatty acids are classified as:
- Saturated fatty acids
- Unsaturated fatty acids
42. Saturated fatty acids
Saturated fatty acids contain no carbon-carbon double bonds; the carbon chain contains only C–C single bonds.
43. Unsaturated fatty acids
Unsaturated fatty acids contain one or more carbon-carbon double bonds. They may be further classified as monounsaturated or polyunsaturated fatty acids.
44. Examples of saturated fatty acids
Examples listed in the supplied notes include butyric, caproic, caprylic, capric, lauric, myristic, palmitic, stearic, arachidic, and valeric acids.
45. Examples of unsaturated fatty acids
Examples include myristoleic acid, palmitoleic acid, oleic acid, linoleic acid, linolenic acid, arachidonic acid, EPA, and DHA.
46. Hydrogenation of fats
Hydrogenation is a chemical process in which hydrogen is added to carbon-carbon double bonds of unsaturated fatty-acid residues. The process reduces the degree of unsaturation.
47. Importance of hydrogenation
Hydrogenation can modify the melting behavior, consistency, and plasticity of oils and fats. Historically, this process has been used in the manufacture of products such as margarine.
48. Oxidative rancidity
Oxidative rancidity is the deterioration of fats and oils caused by oxidation of susceptible fatty acids. It can generate secondary oxidation products responsible for undesirable odors and flavors.
49. Hydrolytic rancidity
Hydrolytic rancidity results from the hydrolysis of ester bonds in lipids, releasing free fatty acids. Lipases and other factors can promote this reaction, and some released fatty acids produce undesirable flavors or odors.
D. WATER IN FOOD
50. Free and bound water
Water is a major constituent of foods and occurs in different physical states and associations. Free water is relatively mobile and available for many physical and chemical processes, whereas bound water is associated with food components and is less mobile and less readily available.
Quick Revision Sequence
Carbohydrates:
Classification → examples → dietary fiber → mutarotation → caramelization → crystallization
Proteins:
Amino acids → peptide bonds → classification → protein structure → denaturation → Maillard reaction → functional properties
Lipids:
Fatty acids → saturation → examples → hydrogenation → oxidative rancidity → hydrolytic rancidity
Water:
Free water → bound water