food chemistry 1 (m.s.m)

FOOD CHEMISTRY

DEFINITION

Is the study of the composition and properties of food, the chemical changes it undergoes

during handling, processing and storage, and the principles underlying the improvement of food

F.1.1: DISTINGUISH BETWEEN FOOD AND NUTRIENT

FOOD

• A food may be considered as any substance that we deliberately take into our mouth and swallow it. That is any natural or artificial material intended for human consumption.

• Logically, a food must contain one or more nutrients which some foods are rich in nutrients, whereas others have very little nutrient value.

NUTRIENT

• A nutrient is a component of food that is used by body to provide energy, or for the growth and repair of tissue.

• Examples of nutrients: carbohydrates, lipids, proteins, vitamins, minerals

• Water which is essential for biochemical processes to occur, is also considered a nutrient

• Malnutrition can occur when either too little or too much of the essential nutrients are eaten

F.1.2: DESCRIBE THE CHEMICAL COMPOSITION OF LIPID (fats and oils), CARBOHYDRATES AND PROTEIN

LIPID

• Fats and oils belong to a group of compounds called lipid which are esters of a glycerol and three fatty acids

• An average diet should contain about 10-20% fats

• Lipids are insoluble in water but soluble in non-polar solvent

• As we can see R1, R2, and R3 represent long hydrocarbon chains, which may be same or different. The hydrocarbon chains may also:

- Saturated (containing carbon-carbon single bond) - Unsaturated (containing carbon-carbon double bond) - Polyunsaturated (containing a number of carbon- carbon double bonds)

• The nature of R group determines the physical and chemical properties of the lipid:

- Saturated fats tend to be solid at room temperature - Unsaturated fats (e.g as in vegetable oils) tend to be liquid

• Lipid is a source of energy and vital for the construction of cell membranes

• It provide more concentrated energy source than carbohydrates

• The carbon atoms are less oxidized as the molecules have fewer oxygen atoms in their molecules. So, more energy is released when the molecules are completely oxidized to CO2 and H2O

• The fat stored in adipose tissue provides insulation, which regulates the temperature of the body, and protective covering for some part of the body

CARBOHYDRATES

• Carbohydrates have empirical formula of CH2O and the simplest carbohydrates are monosaccharides with the general formula (CH2O)n (n>2)

• Plants are the main source of dietary carbohydrate, which are produced from CO2 and H2O by photosynthesis

• Sugars are crystalline solids and dissolve in water to give sweet solution

• The main function of carbohydrate is as a source of energy. They also use for construction of cell.

• One of the simplest sugars is glucose:

MONOSACCHARIDES

• Each monosaccharide contains one carbonyl group (C=O) and at least two hydroxyl group (-OH).

• They are either aldehyde (aldose) or ketones (ketose)

• Examples of monosaccharides include glucose, fructose and ribose. They are soluble in water as the hydroxyl (OH) functional groups are able to form hydrogen bonds with the water molecules

• There are two types of monosaccharides:

DISACCHARIDES

• Condensation of two monosaccharides forms a dissacharide by elimination of one water molecule.

• There are many disaccharides found, but those important to the food industry are maltose, sucrose and lactose:

• Maltose, for example, is formed from the condensation between two molecules of a-D-glucose which are thereby joined by a, 1,4-glycosidic bond; the C1 forms the linkage with the hydroxyl group on the C4 of the second a-D-glucose molecule

POLYSACCHARIDES

• Polysaccharides are condensation polymers formed from monosaccharides with the elimination of water molecules

• Carbohydrates comprise sugars and polymers such as starch and cellulose derived from monosaccharide.

• Starch is a polymer of a-D-glucose.

PROTEIN

• Proteins are polymers of amino acids• All proteins contain C, H, O, and N and some also

have S and P• Based on figure below, R1, R2 and R3 represent the

side chain of amino acids involved and they may be same or different

• As amino acids have both carboxylic acid group and an amino group, they are able to undergo condensation reaction:

• The product, a dipeptide, is an amide made up of two amino acids joined by a peptide bond or peptide linkage.

• One example of alanine and glycine, for example, can form two dipeptides:

• The two dipeptides above can be represented as Ala-Gly and Gly-Ala

• The primary structure of a protein is the sequence of amino acids which form the protein.

• The secondary structure of a protein describes the way in which protein chains fold or align themselves by intramolecular hydrogen bonding between different groups at different position.

• The tertiary structure describes the overall three-dimensional shape of the protein and is determined by a range of interactions such as:

- Hydrogen bonding between polar groups on the side chain - Salt bridges (ionic bonds) formed between -NH2 and

–COOH groups - Dipole-dipole interactions - Van Der Waals forces between non-polar groups - Disulphide bridges formed between two cysteine molecules from different positions along the chain