Enzyme Functions and Properties

Ligases

• Catalyze the synthesis of various bonds, primarily C-X bonds, using energy from substrates like ATP.

Properties of Enzymes

• Exhibit high specificity for their substrates, catalyzing only one particular reaction.
• Remain unchanged during reactions and can be reused.
• Form enzyme-substrate (ES) complexes when they react with substrates.
• Require only small amounts to catalyze large quantities of substrates.
• Operate quickly, having high turnover numbers, converting many substrate molecules per unit time.
• Affected by changes in temperature and pH.
• Many require cofactors to function.
• Can be slowed down or stopped by inhibitors.

Functions of Enzymes

• Degradation reactions (catabolic).
• Synthesis (anabolic).
• Digestion.
• Protection.

Enzyme Kinetics and Reactions

• Studying enzyme kinetics reveals catalytic mechanisms, metabolic roles, activity control, and potential drug or agonist inhibition.

Activation Energy (Ea)

• Minimum energy needed for a chemical reaction to occur.
• Enzymes act as catalysts, lowering activation energy by changing the reaction pathway.
• Reduced activation energy increases the number of reactant molecules reaching sufficient energy to form products.

Factors Affecting Enzyme Activity

Temperature

• Increased temperature increases kinetic energy, leading to more collisions between molecules.
• Initially, this enhances reaction rate due to increased collisions between enzymes and substrates.
• However, excessive heat strains bonds within enzymes, causing active site shape changes and reduced substrate complementarity.
• This leads to a decrease in reaction rate as temperature rises further.

pH

• H+ and OH- ions interfere with hydrogen and ionic bonds maintaining enzyme structure.
• Enzymes have optimal pH values where their active site conformation best complements their substrate.
• Deviation from the optimal pH reduces reaction rate.
• Extreme pH changes can denature enzymes, permanently disrupting their function.

Concentration

• Changing enzyme and substrate concentrations influences reaction rates.
• Increasing concentration of a limiting factor boosts the reaction rate until saturation is reached.
• As reactions proceed, substrate depletion lowers reaction rates.
• Initial Reaction Rate represents the maximum rate achievable in experimental conditions.
• Increasing substrate concentration increases the rate until a plateau is reached where it becomes nonlimiting.

Maillard Reaction

• Reaction between reducing sugars and free amino acids, common during heating and storage of foods.
• Produces both desirable and undesirable products:
  • Desirable: Caramel aromas, golden brown colors.
  • Undesirable: Food darkness, off-flavor development, loss of lysine.
• Significantly reduces the nutritional value of food.
• Toasting can halve the protein efficiency ratio of bread.

Browning Measurement

• Measured by increased absorbance at 420 and 560 nm using reflectance colorimetry, indicating colored substance formation.

Kinetics of Nonenzymatic Browning

• First-order and zero-order models are employed to evaluate browning development.
• Complex kinetics involving browning and pigment degradation require multifaceted models.
• First-order kinetics is suggested for pigment destruction during thermal treatment.
• A two-stage model is proposed:
  • Zero-order color formation.
  • First-order pigment destruction.
• Increased temperature accelerates browning, increasing kinetic constants associated with color formation.

Factors Controlling Maillard Reaction Products

• Temperature, pH, moisture level (Aw), oxygen, metals, phosphates, sulfur dioxide, and inhibitors influence browning.
• Higher temperature and pH accelerate the Maillard reaction.

Food Color

• Reflects or emits different quantities of energy at wavelengths stimulating the retina, creating color perception.
• Visible light encompasses wavelengths between 380-770 nm.
• Color perception plays a significant role in influencing consumer purchasing decisions.
• Color is associated with quality and maturity in foods (e.g., redness of meat signifies freshness).
• Color influences flavor perception:
  • Red drinks are expected to have strawberry or cherry flavors.
  • Yellow drinks are associated with lemon.
  • Green drinks are associated with lime.
• Color can affect perceived sweetness.
• Many food pigments are unstable during processing and storage.

Natural Colors

• Pigments derived from seeds, fruits, vegetables, algae, insects, and flowers.
• Examples and uses of natural colors are extensively listed in the provided text.

Permitted Natural Colors in India

• The Prevention of Food Adulteration Act, 1954 and associated rules permit the use of several natural colorants.

Limitations of Natural Food Colors

• Some natural colors have their flavors that can alter final product taste.
• Color retention can be affected by high temperatures.
• Some may cause allergic reactions.
• Natural colors are generally more expensive than artificial ones.
• Natural ingredient scarcity can occur.