![]() |
Saccharomyces cerevisiae |
Fermentation can be defined as a process in which chemical changes are brought about is an organic substrate through the action of biochemical catalysts called enzymes elaborated by specific types of living micro-organisms.
Fermentation is a metabolic process characterized by : (i) incomplete oxidation, (ii) the transformation of large amounts of substances by comparatively small amounts of organisms. The amount of energy liberated on fermentation is rather small and approximately 25 times less than in the respiration process.
The micro-organisms of fermetation include yeasts, mould, and bacteria. These organisms lacking chlorophyll, cannot produce their own food by photosynthesis, and feed upon organic material ; they are classified as thallophyta. They differ widely in morfology, size, method of reproduction, etc., but they are similarin that they all produce enzymes by which they catalyse the reactions ascribed to them. Yeasts and bacteria are unicellular. Yeast are irregularly oval and about 0.005 mm in diameter ; they generally multiply by budding. Bacteria are smaller, often rod - shape ; they multiply by binary fission. Moulds are multicellular filaments and increase by vegetative growth of the filament and by sporulation. Classification of these micro-organisms is best left to the specialist.
The effect of enzymes is greatly influenced by two factor : the temperature and the pH of the substrate. Generally between 0˚ - 50˚ C the effect of enzymes is doubled by each 10˚ increase in temperature. In the range between 70˚ and 100˚ C the effect of enzymes being irreversibly inactivated. It should be noted, however, that some enzymes are more thermoresistant than others. The hydrogen ion concentration influences the enzymic effect but the optimum pH varies with each type of enzyme, 1.2 - 9
Certain substances, such us ether and phenylurethane, so long as they are present in the system can inhibit the enzymic effect without destroying the enzyme. Other substances like hydrocyanic acid, hydrogen sulphide, fluorides, etc., exert an irreversible poisonous effect, but a universal of enzymes does not exist.
Numerous enzymic effects demand, in addition to the true enzyme, the presence of what may be loosely termed activators or co-factors. These co-factors range from the simple and generally unspecific metallic ions of magnesium, zinc, manganese or iron to the more spesific and complex prosthetic group concerned with the transfer of protons and electrons from the substrate. They include :
- Nicotinamide Adenine Dinucleotide (NAD) and Nicotinamide Adenine Dinucleotide Phosphate (NADP)
- Flavin Mononucleuotide (FMN) and Flavin Adenine Dinucleotide (FAD)
to be continued ...................