Enzymes
Introduction
Enzymes used in different products
Juices: pectinase, cellulase
Cheese: protease, lipase, lipoxygenase
Sweets: alpha-amylase, glucoamylase, pullanase, glucose isomerase
Cereal processing: amylase, protease
What are enzymes
Enzymes = proteins
Enzymes can be present IN the raw material ENDOgenous
Enzymes ADDED during processing EXOgenous
Enzymes in food
- can be suppressed if they cause undesired reactions (enzymatic browning)
- can be steered in the right direction in order to obtain desired properties in food
Enzyme classification
Each enzyme should have 3 names;
1. systematic name based on the substrate and enzyme class (-ase)
o example: pectin lyase
2. A trivial name
o Example: pectinase, amylase
3. An enzyme commission (EC) number
o Directly derived from the enzyme classes
o EC + 4 digits (e.g. EC1.1.1.1)
Enzymes: EC numbers
Example: EC1.1.1.1
First digit: refers to the enzyme class (1 to 6)
Second to fourth digit: refers to type of reaction the enzyme catalyzes and specificity of the reaction
, Enzyme classes (first digit of EC numbers)
Enzyme class Type of reaction catalyzed
1 Oxidoreductases Oxidation-reduction reactions
2 Transferases Remove and transfer of functional groups
3 Hydrolases Cleavage of bonds with introduction of water
4 Lyases Cleavage of bonds (H2O); introduce double bonds
5 Isomerase Rearrangements (glucose fructose example)
6 Ligases Formation of a linkage, using ATP/UTP or CTP
Classification into main groups
Main group Examples of enzymes
Oxidoreductases PPO, catalase, peroxidase, lipoxygenase, glucose oxidase
Transferases Cyclodextrin glycosyltransferase
Hydrolases Peptide hydrolases: proteolytic enzymes
Glycoside hydrolases: amylolytic enzymes, (hemi)cellulases, endo-
polygalacturonase
Ester-hydrolases: Pectin-esterase, lipase, chlorophyllase,
ribonuclease
Enzyme specificity
Substrate specificity: Enzyme is specific for a structural characteristic of the substrate
Reaction specificity: Several enzymes catalyze on the conversion of the same substrate; however
only type of reaction takes place for a certain enzyme
**Specificity arises from the 3D structure of the enzymes active site
Enzyme activity: effect of pH
Wrong pH can result in an irreversible inactivation of the enzyme.
At too high/low pH the enzyme can become damaged or denatured resulting in irreversible
inactivation.
Enzyme activity: effect of temperature
Reaction rate vs temperature:
- Increased reaction rate at elevated temperature up until a certain point
- Desired reaction at optimum temperature
Rate of inactivation vs temperature:
- Irreversible inactivation caused by denaturation at elevated temperatures above optima
- Undesired reactions can be eliminated above the inactivation temperature
Introduction
Enzymes used in different products
Juices: pectinase, cellulase
Cheese: protease, lipase, lipoxygenase
Sweets: alpha-amylase, glucoamylase, pullanase, glucose isomerase
Cereal processing: amylase, protease
What are enzymes
Enzymes = proteins
Enzymes can be present IN the raw material ENDOgenous
Enzymes ADDED during processing EXOgenous
Enzymes in food
- can be suppressed if they cause undesired reactions (enzymatic browning)
- can be steered in the right direction in order to obtain desired properties in food
Enzyme classification
Each enzyme should have 3 names;
1. systematic name based on the substrate and enzyme class (-ase)
o example: pectin lyase
2. A trivial name
o Example: pectinase, amylase
3. An enzyme commission (EC) number
o Directly derived from the enzyme classes
o EC + 4 digits (e.g. EC1.1.1.1)
Enzymes: EC numbers
Example: EC1.1.1.1
First digit: refers to the enzyme class (1 to 6)
Second to fourth digit: refers to type of reaction the enzyme catalyzes and specificity of the reaction
, Enzyme classes (first digit of EC numbers)
Enzyme class Type of reaction catalyzed
1 Oxidoreductases Oxidation-reduction reactions
2 Transferases Remove and transfer of functional groups
3 Hydrolases Cleavage of bonds with introduction of water
4 Lyases Cleavage of bonds (H2O); introduce double bonds
5 Isomerase Rearrangements (glucose fructose example)
6 Ligases Formation of a linkage, using ATP/UTP or CTP
Classification into main groups
Main group Examples of enzymes
Oxidoreductases PPO, catalase, peroxidase, lipoxygenase, glucose oxidase
Transferases Cyclodextrin glycosyltransferase
Hydrolases Peptide hydrolases: proteolytic enzymes
Glycoside hydrolases: amylolytic enzymes, (hemi)cellulases, endo-
polygalacturonase
Ester-hydrolases: Pectin-esterase, lipase, chlorophyllase,
ribonuclease
Enzyme specificity
Substrate specificity: Enzyme is specific for a structural characteristic of the substrate
Reaction specificity: Several enzymes catalyze on the conversion of the same substrate; however
only type of reaction takes place for a certain enzyme
**Specificity arises from the 3D structure of the enzymes active site
Enzyme activity: effect of pH
Wrong pH can result in an irreversible inactivation of the enzyme.
At too high/low pH the enzyme can become damaged or denatured resulting in irreversible
inactivation.
Enzyme activity: effect of temperature
Reaction rate vs temperature:
- Increased reaction rate at elevated temperature up until a certain point
- Desired reaction at optimum temperature
Rate of inactivation vs temperature:
- Irreversible inactivation caused by denaturation at elevated temperatures above optima
- Undesired reactions can be eliminated above the inactivation temperature
