1. Classes of Enzymes According to chemical reaction
Oxidoreductases: oxidation/reduction reactions
Transferases: group transfer reactions
Hydrolases: hydrolytic reactions
Lyases: addition of groups to double bonds or vice-versa
Isomerases: group rearrangements
Ligases: combination of two molecules with involvement of adenosine 5’-triphosphate (ATP)
Grouped by substrate affected
Proteases: proteins
Lipases: lipids (fats)
Carbohydrases: carbohydrates (sugars, starches)

2. Changes produced by enzymes
Desirable changes
Formation of cheese curd by rennin
Contact lens cleaning by microbial protease
Protein digestion by pepsin, trypsin
Development of flavour in cheese by lipase, esterase
Prevention of staling in bread by amylase
Production of beer by amylase, glucoamylase, protease (in yeast)
Production of low- and no-lactose dairy products (for people with lactose intolerance) by lactase

3. Undesirable changes Rotting of foods by protease
Development of rancidity in fats by microbial lipase
Over-ripening of fruits by polygalacturonase
Softening of unblanched vegetables by peroxidase
Development of off-flavours in unblanched vegetables by catalase, lipoxygenase
Browning of certain fruit and vegetable slices by polyphenolase

4. Enzyme action Substrate + Enzyme Substrate-Enzyme Complex
Product + Enzyme

5. Two models of enzyme action

6. Effect of temperature on enzyme activity
Heat inactivation
Optimum Temperature

7. Effect of pH on enzyme activity
Optimal pH

8. Effect of substrate concentration on enzyme activity
Maximum Enzyme Activity