Comprehensive Guide to Food Enzyme Classification and Applications

Fundamentals and Catalytic Properties of Enzymes

• Definition and Specificity:
  • Enzymes are characterized as highly specific biological catalysts.
  • They function by significantly lowering the activation energy ($E_a$) required for a chemical reaction to occur, especially when compared to non-enzyme catalyzed reactions.
  • The primary role of an enzyme is to accelerate the rate of chemical reactions.

Historical Timeline of Food Enzyme Development

• Ancient Civilization:

  • China and Japan: Early use of fermentation processes involved amylases and proteases for the production of soy-derived essential foods.
  • 400 BC (Homer's Iliad): The text mentions the early production of cheese facilitated by the use of a kid's stomach (rennet source).

• The 19th Century Foundations:

  • Berzelius (1835): The Swedish chemist introduced the term "catalysis" specifically to describe the breakdown or hydrolysis of starch.
  • Louis Pasteur (1858): Studied the fermentation of sugar into alcohol by yeast. He concluded that this process was driven by a "vital force" called "ferments," which were originally believed to function exclusively within living cells.
  • Chr. Hansen (1874): Established the first company based on applied biocatalysis. The company focused on producing rennet (chymosin) extracted from calf stomachs for commercial cheese making.
  • William Kuhne (1878): Introduced the word "enzyme" (derived from the Greek for "in yeast").
    • The term "enzyme" was designated for non-living catalytic substances derived from organisms.
    • The term "ferment" continued to refer to chemical activity produced by living organisms.
  • The Buchner Brothers (1897): Demonstrated that cell-free extracts from yeast could successfully break down glucose into ethanol and carbon dioxide ($CO_2$). This proved that fermentation is driven by chemical substances (enzymes) rather than needing whole, living cells.

• The 20th Century Advancements:

  • 1926: Scientific consensus established that enzymes are proteins.
  • Warburg & Christian (1935): Partially purified an enzyme that appeared yellow due to the presence of riboflavin (a co-factor). This was termed "the yellow enzyme" and was foundational for understanding cellular respiration and the relationships between enzymes and co-factors.
  • 1955: Over $600$ enzymes were known and had been partially characterized by this date.

Nomenclature and the IUBMB Classification System

• Historical Naming Conventions:

  • Standard naming often involved adding the suffix "-ase" (e.g., amylase).
  • Some enzymes retained the suffix "-in" (e.g., trypsin, pepsin, papain).
  • Historically, naming was largely left to the discoverer.

• The International Union of Biochemistry and Molecular Biology (IUBMB):

  • Created in $1956$ to standardize enzyme nomenclature.
  • Classification Structure: Recommended dividing enzymes into major classes (originally 6, now 7) with sub-classes and sub-sub-classes.
  • Naming Requirements:
    1. Common Name: A trivial name normally used (e.g., peroxidase, cellulase).
    2. Systematic Name: Follows specific rules to allow anyone to determine the exact reaction catalyzed based on the name alone.
    3. EC (Enzyme Code) Number: Assigned exclusively by the IUBMB based on the enzymatic reaction.

• General Principles of Classification:

  • The suffix "-ase" is reserved only for preparations containing single enzymes.
  • Enzymes are classified primarily according to the chemical reaction they catalyze.
  • Subdivisions are determined based on the specific substrates involved.

• Systematic Naming Rules:

  • Components: Names of the substrate(s) followed by the reaction type ending in "-ase."
  • When multiple substrates are involved, they are separated by a colon (:). Example: Sarcosine:oxygen oxidoreductase (demethylating).
  • If two reaction types are involved (e.g., oxidative demethylation), the primary class is named first, followed by the second type in parentheses ($$.

The Seven Enzyme Commission (EC) Classes

• 1. Oxidoreductases:

  • Function: Catalyze redox processes (transfer of electrons between molecules).
  • Mechanism: Couple an exothermal oxidation with an endothermal reduction. Protons ($H^+$) are often transferred with electrons via coenzymes like $NAD^+$ or $NADP^+$.
  • Sub-classes: Include dehydrogenases, reductases, or oxidases.
  • Example: EC $1.1.1.1$ (Alcohol:$NAD^+$ oxidoreductase).

• 2. Transferases:

  • Function: Catalyze the transfer of a functional group (e.g., methyl, acyl, phosphate) from one molecule to another.
  • Significance: Crucial for the synthesis of molecules within the cell.
  • Example: Glycogen phosphorylase (EC $2.4.1.1$).

• 3. Hydrolases:

  • Function: Cleave molecules through the addition of water ($H_2O$), adding a hydroxyl group ($-OH$) and a proton ($H^+$) to the broken bond.
  • Properties: The reaction is normally exothermal and unidirectional in physiological conditions.
  • Examples: Amylase (starch), Proteases (peptide bonds), Lipases (ester bonds), Chymosin, Pepsin.

• 4. Lyases:

  • Function: Cleave molecules through reactions other than oxidation or hydrolysis. This often involves removing a group to form a double bond or adding a group to a double bond.
  • Synonym: Frequently referred to as "synthases."
  • Properties: These reactions are reversible.
  • Example: Aspartate amino-lyase (EC $4.3.1.1$).

• 5. Isomerases:

  • Function: Catalyze isomerization reactions (rearrangement of functional groups within the same molecule).
  • Properties: The molecular formula remains identical (brutto-formula); only the structure changes. Reversibility depends on product concentration.
  • Examples: D-xylose isomerase (used in starch syrup/cola production to convert glucose to fructose).

• 6. Ligases:

  • Function: Catalyze the connection of two molecules.
  • Energetics: Requires energy, typically derived from the hydrolysis of $ATP$.
  • Synonym: Historically called "synthetases," though the IUBMB discourages this term to avoid confusion with synthases.
  • Examples: DNA-ligase, carboxylases ($CO_2$ addition).

• 7. Translocases (Formed August 2018):

  • Function: Catalyze the movement of molecules or ions across membranes.

Enzyme Numbering (The EC System Code)

• Format: EC $X.X.X.X$ (Class.Sub-class.Sub-sub-class.Serial Number).
• Case Study: Alcohol:$NAD^+$ Oxidoreductase (EC $1.1.1.1$):
  • EC 1: Oxidoreductase class.
  • EC 1.1: Sub-class indicating the donor of $H^+$ is an alcohol.
  • EC 1.1.1: Sub-sub-class indicating $NAD^+$ is the acceptor of $H^+$.
  • EC 1.1.1.1: Serial number indicates the specific donor is ethanol.
  • Reaction: $Ethanol + NAD^+ = Acetaldehyde + NADH + H^+$

Sources of Food Enzymes

• Endogenous (Indigenous): Produced naturally within the organism itself.
• Exogenous: Sourced externally.
• Microbial Origin:
  • Fungal, bacterial, or yeast sources.
  • Can be categorized as GMO (Genetically Modified Organisms) or Non-GMO.
• Non-microbial Origin:
  • Animal sources (e.g., Chymosin from calf stomach).
  • Plant sources (e.g., Papain from papaya, Bromelain from pineapple, barley malt).
  • Other animal sources (e.g., Lysozyme from egg whites).

Industrial Applications in the Food Industry

General Biotechnology-Derived Enzymes

• Acetolactate decarboxylase (EC 4.1.1.5): Diacetyl reduction and aging in beer.
• $\alpha$-amylase (EC 3.2.1.1): High fructose corn syrup (HFCS) production.
• Amylo-1,6-glucosidase (EC 3.2.1.33): HFCS production.
• Chymosin (EC 3.4.23.4): Milk clotting for cheese manufacturing.
• Lactase (EC 3.2.1.108): Hydrolysis of lactose.
• Glucan 1,4-$\alpha$-maltohydrolase (EC 3.2.1.133): Anti-staling in bread.

Bakery Applications

• Amylase: Maximizes fermentation; produces even crumb structure and high loaf volume.
• Maltogenic Alpha-amylases: Increases shelf-life for bread and cakes.
• Glucose oxidase: Strengthens weak dough by reacting with gluten; makes dough drier and more elastic.
• Lipase: Modifies natural flour lipids to strengthen dough.
• Lipoxygenase: Bleaching agent; dough strengthening.
• Xylanase: Conditioning; improves dough handling and crumb structure.
• Protease: Weakens gluten for plastic properties in biscuit dough.
• Asparginase: Reducts acrylamide formation during the baking process.

Proteolytic Enzyme Applications

• Baked goods: Softens dough, reduces mixing time, increases extensibility.
• Brewing: Aids in nutrient development, filtration, clarification, and chill-proofing.
• Cereals: Improves drying rates and product handling (e.g., tofu/miso production).
• Chocolate/Cocoa: Action on beans during fermentation.
• Meat: Tenderization and protein recovery from bones.
• Fish: Solubilization of fish protein concentrate; oil and protein recovery from inedible parts.

Enzymes in Cheese Manufacturing

• Coagulation:

  • Chymosin (EC 3.4.23.4): Acts on $\kappa$-casein to produce para-$\kappa$-casein and glycopeptide.

• Proteolysis (Ripening):

  • Proteases/Endopeptidases: Break high molecular weight proteins into peptides and amino acids.
  • Peptidases (Amino, di-, tri-): Breakdown of peptides into individual amino acids for flavor development.

• Amino Acid Decomposition (Flavor Chemistry):

  • Aspartate transaminase (EC 2.6.1.1): L-Aspartate + 2-oxoglutarate $\rightarrow$ oxaloacetate + L-glutamate.
  • Methionine $\gamma$-lyase (EC 4.4.1.11): Produces methanethiol (sulfur flavor).
  • Tryptophanase (EC 4.1.99.1): Produces indole, pyruvate, and $NH_3$.

• Decarboxylation (Amine Formation):

  • Lysine $\rightarrow$ cadaverine.
  • Glutamate $\rightarrow$ aminobutyric acid.
  • Tyrosine $\rightarrow$ tyramine.
  • Arginine $\rightarrow$ putrescine.
  • Histidine $\rightarrow$ histamine.