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Questions and Answers
What causes the discoloration in fruits and vegetables during enzymatic browning?
Which fruit is known to turn brown but never black due to enzymatic browning?
What determines the final color of discoloration in fruits and vegetables?
Which factor is NOT mentioned as influencing the amount of browning in fruits and vegetables?
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What is the primary process that leads to the formation of caramel aroma and brown-colored products?
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How does the browning behavior of bananas differ from that of apples?
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What is the role of polyphenol oxidase (PPO) in the process of enzymatic browning?
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As fruits ripen, how does the amount of enzymatic browning change for certain fruits?
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Which method can effectively deactivate enzymes to prevent enzymatic browning?
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Which compound is the immediate result of the oxidation of ascorbic acid?
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What is the effect of refrigeration on enzymatic activity during storage?
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What is the main reason that maturity affects browning in fruits like apples and bananas?
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How can a change in pH help in inhibiting enzymatic browning?
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What is the primary cause of lipid peroxidation?
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What is one way dehydration helps to prevent enzymatic browning?
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Which of these is a potential product formed from the decomposition of diketogulonic acid?
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What is the main function of proteases in laundry detergents?
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What role do digestive supplements play for individuals with digestive issues?
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How does glucose oxidase help in food preservation?
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What is the role of amylase in food production?
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Pectinase and cellulase improve the quality of which type of food product?
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Which enzyme is NOT typically involved in digestion?
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Which enzyme aids in the production of dairy products like yogurt and cheese?
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How do natural enzymes benefit the body's nutrient absorption?
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What does the Lock and Key model suggest about enzyme specificity?
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What is the primary function of enzymes in bioconversion?
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How does the induced fit model differ from the Lock and Key model?
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Which of the following statements best describes cofactors?
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What is the term for the protein part of an enzyme?
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What role does enzyme immobilization serve?
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What is a characteristic of coenzymes compared to prosthetic groups?
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What is the role of regulatory enzymes in metabolic reactions?
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Which of the following is NOT a method of enzyme immobilization?
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Which of the following describes the classification of enzymes?
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Which of the following enzymes catalyzes the polymerization of nucleotides?
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What is the role of ribozymes in enzymatic reactions?
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What is the main function of the active site of an enzyme?
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Which of the following best describes how enzymes affect activation energy?
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Who was the first to isolate and crystallize the enzyme urease?
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Which process uses enzymes like cellulase to break down waste products?
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Study Notes
Discoloration in Fruits & Vegetables
- Discoloration results from the oxidation of colorless phenolic compounds by enzymes called polyphenol oxidase (PPO), a type of mixed-function oxidase.
- The amount of browning depends on the concentration and nature of phenolic compounds present.
- Enzymatic activity determines the initial browning.
- Substrates also determine the discoloration color.
- Apples, apricots, peaches, and pears turn brown but never black.
- Bananas and potatoes initially turn pink, then brown, and eventually, black.
- Maturity affects browning. Persimmons, apples, potatoes, and bananas increase in browning as they ripen but decrease as the amount of substrate decreases with maturity.
Methods To Prevent Enzymatic Browning
- Blanching: Heat treatment that can deactivate enzymes (30 seconds dip in water, 70-100°C).
- Refrigeration/Freezing Treatment: Cold temperatures can inhibit enzymes. Enzyme activity resumes after thawing (0-10°C for refrigeration, below 0°C or -17°C for freezing).
- Change in pH: An acidic environment (above pH 4.0) inhibits enzymes.
- Dehydration: Inhibits, but does not destroy enzymatic browning by removing water.
- Caramelization: Thermal degradation of sugars leading to the formation of volatiles (caramel aroma) and brown-colored products. It involves isomerization, dehydration, degradation, condensation, and polymerization reactions.
- Ascorbic Acid Browning: Ascorbic acid is first oxidized to dehydroascorbic acid, then transformed into diketogulonic acid. This eventually decomposes to furfural or related compounds, which polymerize or react with nitrogen (as in the Maillard reaction) to form brown pigments. Observed during vegetable drying.
- Lipid Peroxidation: Occurs by the action of oxygen and reactive oxygen species on fatty acids, especially unsaturated fatty acids. This leads to aldehydes and ketones, which react with amino acids to form brown pigments similar to the Maillard reaction. Peroxidation products may also induce the browning reaction of Amadori products.
Importance of Enzymes
Role in Food Science
- Food Production: Enzymes like amylase and protease play crucial roles in fermentation processes used in brewing beer, making bread, and producing dairy products like yogurt and cheese. They convert raw ingredients into desired products with specific textures and flavors.
- Food Preservation: Glucose oxidase reduces oxygen levels in food packaging, inhibiting spoilage and extending shelf life of products.
- Bioconversion: Converts food waste into valuable products (e.g., using proteases to turn protein-rich waste into animal feed or cellulase to break down plant waste into biofuels).
Role in Daily Lives
- Digestion: Natural enzymes like amylase, lipase, and protease, found in saliva, stomach, and intestines, are essential for breaking down food into absorbable nutrients. Without them, nutrient absorption is inefficient, leading to malnutrition and digestive disorders. Digestive supplements help break down foods more effectively in individuals with digestive issues.
- Food Processing: Enzymes like pectinase and cellulase improve the yield and clarity of fruit juices and wines. They break down complex plant cell walls, releasing more juice and enhancing product quality.
- Household Products: Enzymes like proteases and lipases are found in laundry detergents to break down protein-based stains (blood, sweat) and fat-based stains (grease), making laundry more effective at lower temperatures and reducing energy consumption.
- Biodegradation: Enzymes are used in bioremediation to break down pollutants in the environment (e.g., oil spills or waste treatment), contributing to cleaner ecosystems.
Classification of Enzymes
- Enzymes often end with the suffix “-ase” added to the name of their substrate or a word describing their activity.
- Examples:
- Urease catalyzes the hydrolysis of urea.
- DNA polymerase catalyzes the polymerization of nucleotides to form DNA.
Substrate Binding
- Enzyme-catalyzed reactions involve the formation of an enzyme-substrate (ES) complex.
- Substrate binding occurs in a pocket on the enzyme called the active site.
- Enzymes lower the activation energy for a reaction, enhancing the reaction rate.
- Enzymes are specific in terms of the substrates they bind and the chemical reactions they catalyze.
Lock and Key Model
- Proposed by Emil Fischer in 1894.
- Suggests that the substrate and enzyme have specific complementary shapes that fit exactly into one another.
Induced Fit Model
- Introduced by Daniel Koshland in 1958.
- Enzymes undergo conformational change during catalysis.
Composition of Enzymes
- Most enzymes are proteins, although some are catalytic RNA molecules called ribozymes.
- Some enzymes require non-protein molecules called cofactors for activity.
- Cofactors can be inorganic or organic.
- Organic cofactors can be Coenzymes, which act as transient carriers of specific functional groups, or prosthetic groups, which are tightly or covalently bound to the enzyme.
- The protein part of an enzyme is called the apoenzyme, while the enzyme with its required cofactors is called a holoenzyme.
Enzyme Immobilization
- A technology that aims to produce reusable, stable, and active enzymes.
- Methods include physical absorption, ionic and covalent bonds, and techniques like binding, entrapment, encapsulation, and cross-linking.
- Enzymes can be immobilized on various organic and inorganic materials or carriers.
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Description
This quiz explores the enzymatic browning process in fruits and vegetables, focusing on the role of polyphenol oxidase and phenolic compounds. Learn about how different methods, such as blanching and refrigeration, can prevent discoloration and maintain the quality of produce. Test your knowledge on the factors affecting browning and the specific discoloration patterns of various fruits and vegetables.
