Q.1 What is the primary product of lactic acid fermentation performed by Lactobacillus species?
Ethanol
Lactic acid
Acetic acid
Carbon dioxide
Explanation - Lactobacillus converts sugars to lactic acid, which preserves food and gives yogurt its tart flavor.
Correct answer is: Lactic acid
Q.2 Which gas is primarily released during yeast fermentation of glucose?
Oxygen
Nitrogen
Carbon dioxide
Hydrogen
Explanation - Saccharomyces cerevisiae metabolizes glucose to ethanol and CO₂; CO₂ causes dough to rise.
Correct answer is: Carbon dioxide
Q.3 In a batch fermentor, how does the dissolved oxygen level affect aerobic bacteria growth?
Higher oxygen reduces growth rate
Oxygen level has no effect
Lower oxygen increases growth rate
Higher oxygen promotes growth up to a saturation point
Explanation - Aerobic bacteria require oxygen; growth increases with dissolved O₂ until saturation limits metabolic capacity.
Correct answer is: Higher oxygen promotes growth up to a saturation point
Q.4 What parameter is most critical for maintaining the pH during yogurt production?
Temperature
Inoculum size
Buffer capacity of milk
Fermentation time
Explanation - Milk's natural buffers resist pH changes; controlling them keeps yogurt acidic enough without over-acidifying.
Correct answer is: Buffer capacity of milk
Q.5 Which of the following is NOT a typical by-product of ethanol fermentation?
Water
CO₂
Acetic acid
Ethanol itself
Explanation - Ethanol fermentation by yeast produces ethanol and CO₂; acetic acid is a by-product of acetobacter, not yeast.
Correct answer is: Acetic acid
Q.6 During a fed-batch fermentation, the substrate is added continuously. What is the main advantage of this approach?
It reduces mixing time
It keeps substrate concentration low to prevent inhibition
It eliminates the need for pH control
It allows for immediate product collection
Explanation - Adding feed gradually maintains optimal substrate levels, preventing product inhibition and improving yields.
Correct answer is: It keeps substrate concentration low to prevent inhibition
Q.7 Which of the following is a common indicator of successful lactofermentation in pickles?
High sugar content
pH > 6.5
Acidity and a sour smell
Blue discoloration
Explanation - Lactic acid bacteria produce acid, lowering pH and giving pickles their sour taste.
Correct answer is: Acidity and a sour smell
Q.8 What is the function of a pH-stat in a fermentor?
Maintain constant temperature
Control oxygen supply
Add acid/base to keep pH constant
Measure cell density
Explanation - A pH-stat automatically adds acid or base to keep pH at a set level, crucial for enzyme activity.
Correct answer is: Add acid/base to keep pH constant
Q.9 Which microorganism is primarily responsible for the fermentation of coffee beans during processing?
Bacillus subtilis
Saccharomyces cerevisiae
Pseudomonas aeruginosa
Enterococcus faecalis
Explanation - Enterococcus species participate in the natural fermentation of coffee cherries, influencing flavor.
Correct answer is: Enterococcus faecalis
Q.10 In continuous fermentation, the dilution rate (D) is defined as:
Volume added per hour
V / V0
D = F/V
Cell growth rate
Explanation - Dilution rate equals the flow rate (F) divided by the reactor volume (V) and determines substrate concentration.
Correct answer is: D = F/V
Q.11 What is the primary role of protease in cheese ripening?
Hydrolyze fats
Hydrolyze proteins into peptides and amino acids
Produce gas
Increase acidity
Explanation - Proteases break down casein, contributing to texture and flavor during ripening.
Correct answer is: Hydrolyze proteins into peptides and amino acids
Q.12 Which parameter is most critical for controlling the viscosity in a stirred tank fermentor?
Stirrer speed
Temperature
Feed rate
pH
Explanation - Stirrer speed affects mixing and shear, directly influencing fluid viscosity and mass transfer.
Correct answer is: Stirrer speed
Q.13 Which of the following is a common medium used for cultivating lactic acid bacteria?
MRS agar
MacConkey agar
Blood agar
Sabouraud agar
Explanation - MRS (de Man, Rogosa, Sharpe) medium is specifically formulated for Lactobacillus species.
Correct answer is: MRS agar
Q.14 Which gas is a sign of spoilage in dairy fermentations due to Clostridium contamination?
Oxygen
Hydrogen sulfide
Nitrous oxide
CO₂
Explanation - Clostridium produces H₂S, causing a rotten-egg odor in spoiled dairy products.
Correct answer is: Hydrogen sulfide
Q.15 During the production of kefir, which component is primarily responsible for the thickening of the beverage?
Casein
Lactose
Maltose
Polysaccharides produced by kefir grains
Explanation - Kefir grains synthesize exopolysaccharides that increase viscosity and create a creamy texture.
Correct answer is: Polysaccharides produced by kefir grains
Q.16 What is the main advantage of using a membrane bioreactor in fermentation processes?
Easy cleaning
High shear tolerance
Simultaneous product separation
Lower operating cost
Explanation - Membrane bioreactors allow in‑situ separation of product from broth, improving downstream processing.
Correct answer is: Simultaneous product separation
Q.17 Which of the following is a key factor that limits yeast growth in high‑gravity fermentations?
Temperature drop
Oxygen depletion
High sugar concentration causing osmotic stress
Low pH
Explanation - Osmotic pressure from high sugar levels stresses yeast cells, reducing viability and fermentation rate.
Correct answer is: High sugar concentration causing osmotic stress
Q.18 In a fed-batch fermentation, the feed strategy is designed to:
Maintain constant temperature
Prevent substrate inhibition
Keep the pH above 7
Increase oxygen transfer rate
Explanation - Feeding at a controlled rate avoids high substrate concentrations that inhibit microbial metabolism.
Correct answer is: Prevent substrate inhibition
Q.19 Which of the following is NOT a typical product of acetolysis by Clostridium acetobutylicum?
Acetone
Butanol
Ethanol
Acetic acid
Explanation - Clostridium acetobutylicum produces acetone, butanol, and ethanol; acetic acid is not a major product.
Correct answer is: Acetic acid
Q.20 What is the role of the N‑acetylglucosamine‑acetyltransferase enzyme during cheese fermentation?
Break down lactose
Produce CO₂
Synthesize exopolysaccharides
Regulate pH
Explanation - This enzyme contributes to exopolysaccharide formation, which improves texture and water retention.
Correct answer is: Synthesize exopolysaccharides
Q.21 In a packed bed fermentor, what is the main challenge related to mass transfer?
High shear stress
Low nutrient diffusion
High gas solubility
Excessive temperature rise
Explanation - The packed bed geometry restricts nutrient movement, limiting microbial growth at the bed bottom.
Correct answer is: Low nutrient diffusion
Q.22 Which of the following factors does NOT affect the rate of acid production in lactic acid fermentation?
Inoculum size
Temperature
Electrical conductivity of the medium
Carbon source type
Explanation - Conductivity is a physical property; acid production depends mainly on biological and environmental factors.
Correct answer is: Electrical conductivity of the medium
Q.23 What is the purpose of a sterilization step before starting a batch fermentation?
Increase nutrient concentration
Remove oxygen
Kill unwanted microorganisms
Adjust pH to neutral
Explanation - Sterilization ensures that only the desired inoculum grows, preventing contamination and product spoilage.
Correct answer is: Kill unwanted microorganisms
Q.24 Which parameter is directly influenced by the choice of fermentor type (batch vs. continuous)?
Fermentation time
Temperature profile
Cell density at the end
All of the above
Explanation - Batch fermentations have fixed time, temperature, and cell density, whereas continuous processes maintain steady states.
Correct answer is: All of the above
Q.25 Which of these is a characteristic of anaerobic fermentation?
Requires oxygen
Produces CO₂ and water
Produces methane
Produces only CO₂
Explanation - Methanogenesis is a typical anaerobic pathway that converts CO₂ and H₂ into methane.
Correct answer is: Produces methane
Q.26 Which component of the yeast cell membrane is essential for maintaining proton gradients during fermentation?
Chitin
Mannoprotein
Ergosterol
Cellulose
Explanation - Ergosterol provides fluidity to the membrane, allowing proton pumps to maintain gradients.
Correct answer is: Ergosterol
Q.27 In a pH-controlled fermentor, a sudden drop in pH indicates:
Excessive temperature
High substrate concentration
Cell death releasing acids
Insufficient oxygen
Explanation - Dead cells release intracellular acids, lowering pH; monitoring helps detect process anomalies.
Correct answer is: Cell death releasing acids
Q.28 Which of the following best describes the term 'oxygen transfer rate' (OTR) in bioreactors?
Rate of oxygen dissolution in the liquid
Rate of oxygen consumption by cells
Rate of oxygen generation by photosynthesis
Rate of oxygen release by the gas sparger
Explanation - OTR quantifies how fast oxygen from the gas phase dissolves into the aqueous phase, critical for aerobic cultures.
Correct answer is: Rate of oxygen dissolution in the liquid
Q.29 Which type of fermentation is most commonly used in the production of soy sauce?
Lactic acid fermentation
Acidic fermentation
Enzymatic fermentation
Alcoholic fermentation
Explanation - Soy sauce fermentation relies on acid-producing microorganisms to develop flavor over several months.
Correct answer is: Acidic fermentation
Q.30 During a fed-batch process, what happens if the feed rate is too high?
Cells produce more product
pH drops too quickly
Cells experience substrate inhibition
Temperature increases
Explanation - Excess substrate can inhibit enzyme activity, reducing cell growth and product formation.
Correct answer is: Cells experience substrate inhibition
Q.31 What is a key advantage of using a hollow fiber bioreactor for microbial fermentation?
Simplifies agitation
Provides a membrane for selective product removal
Increases oxygen solubility
Reduces nutrient cost
Explanation - Hollow fibers allow selective permeability, enabling continuous product extraction while retaining cells.
Correct answer is: Provides a membrane for selective product removal
Q.32 Which of the following is a typical by‑product of lactic acid bacteria during dairy fermentation?
Acetone
Butyrate
Butyric acid
Hydrogen
Explanation - Butyrate production is common in certain lactic acid bacteria, contributing to flavor profiles.
Correct answer is: Butyric acid
Q.33 Why is agitation speed important in a stirred‑tank fermentor?
It changes the temperature
It adjusts the pH
It improves mass transfer between gas and liquid phases
It controls feed addition
Explanation - Higher agitation increases surface area, enhancing oxygen or CO₂ transfer to cells.
Correct answer is: It improves mass transfer between gas and liquid phases
Q.34 Which enzyme is most crucial for the saccharification step in ethanol fermentation from corn mash?
Amylase
Protease
Lipase
Cellulase
Explanation - Amylase breaks down starch into fermentable sugars for yeast to convert into ethanol.
Correct answer is: Amylase
Q.35 In continuous fermentation, what does the term 'steady state' refer to?
Constant temperature
Constant feed composition
Constant biomass concentration and product rate
Constant pH
Explanation - Steady state means all key variables remain unchanged over time despite continuous input and output.
Correct answer is: Constant biomass concentration and product rate
Q.36 Which of the following is an advantage of using a membrane bioreactor compared to a conventional fermentor?
No need for sterile filtration
Higher shear tolerance
Simpler scale‑up
Higher product purity due to membrane separation
Explanation - Membrane bioreactors allow simultaneous cell growth and product separation, improving purity.
Correct answer is: Higher product purity due to membrane separation
Q.37 What is the typical range of the optimum temperature for most lactic acid bacteria?
4–10 °C
20–30 °C
40–50 °C
60–70 °C
Explanation - Lactobacillus species generally grow best between 20‑30 °C, which is also convenient for dairy processes.
Correct answer is: 20–30 °C
Q.38 Which gas is typically used to sparge in aerobic fermentations to provide oxygen?
Carbon dioxide
Nitrogen
Oxygen
Helium
Explanation - Sparging with pure O₂ provides the required oxygen for aerobic microorganisms.
Correct answer is: Oxygen
Q.39 In a packed bed fermentor, the term 'dead volume' refers to:
Volume where cells cannot survive
Volume of gas that does not contact cells
Volume that remains unutilized in the packed bed
Volume of liquid that passes through without reacting
Explanation - Dead volume is the part of the reactor that does not contribute to productive fermentation.
Correct answer is: Volume that remains unutilized in the packed bed
Q.40 Which of the following is NOT a typical parameter monitored during a fermentation process?
pH
Temperature
Humidity
Oxygen transfer rate
Explanation - Humidity is irrelevant in liquid fermentations; the key parameters are pH, temperature, and O₂ transfer.
Correct answer is: Humidity
Q.41 During a fed‑batch process, the feed composition is adjusted to maintain a constant:
Substrate concentration
Cell density
pH
Temperature
Explanation - Feeding ensures the substrate stays at a level that supports optimal growth and product formation.
Correct answer is: Substrate concentration
Q.42 Which of the following is a common cause of foaming in fermentation?
High agitation speed
Low dissolved oxygen
High sugar concentration
Low pH
Explanation - Rapid stirring creates bubbles that can lead to foaming, especially in viscous cultures.
Correct answer is: High agitation speed
Q.43 Which of the following is a typical product of anaerobic fermentation by Bacillus coagulans?
Acetate
Butanol
Lactic acid
Methane
Explanation - Bacillus coagulans produces lactic acid in anaerobic conditions, useful for food fermentation.
Correct answer is: Lactic acid
Q.44 The term 'bioreactor' in fermentation technology refers to:
A device used to maintain temperature
A vessel where biological reactions occur under controlled conditions
A machine that sterilizes media
An instrument that measures pH
Explanation - Bioreactors house the culture and provide control over environment for efficient fermentation.
Correct answer is: A vessel where biological reactions occur under controlled conditions
Q.45 Which of the following is an indicator of product inhibition in fermentation?
Increase in dissolved oxygen
Decrease in cell growth rate
Increase in temperature
Decrease in pH
Explanation - When product accumulates, it can inhibit enzymes, slowing cell proliferation.
Correct answer is: Decrease in cell growth rate
Q.46 Which type of fermentation is responsible for producing lactic acid in sourdough bread?
Alcoholic fermentation
Acidogenic fermentation
Methanogenic fermentation
Phototrophic fermentation
Explanation - Lactobacillus spp. in sourdough produce lactic acid, giving the bread its characteristic tang.
Correct answer is: Acidogenic fermentation
Q.47 What is the main role of a temperature probe in a fermentor?
To measure dissolved oxygen
To measure cell density
To monitor temperature accurately
To inject nutrients
Explanation - Accurate temperature monitoring is essential for maintaining optimal microbial growth conditions.
Correct answer is: To monitor temperature accurately
Q.48 Which of the following is a characteristic of an anaerobic fermentor?
Requires continuous oxygen supply
Has a high pressure setting
Excludes any form of aeration
Uses a sparger for CO₂ removal
Explanation - Anaerobic fermentors are sealed from oxygen to support anaerobic microorganisms.
Correct answer is: Excludes any form of aeration
Q.49 During a fed-batch fermentation, the feed solution typically contains:
Only water
High concentrations of nutrients
Inhibitors
Oxygen gas
Explanation - The feed provides nutrients without overwhelming the culture, maintaining growth rates.
Correct answer is: High concentrations of nutrients
Q.50 Which of the following factors most directly influences the yield of ethanol from a sugar-based substrate?
pH of the medium
Temperature
Yeast strain
Fermenter volume
Explanation - Different yeast strains have varying efficiencies for converting sugar to ethanol.
Correct answer is: Yeast strain
Q.51 Which of the following is an example of a 'process analytical technology' (PAT) in fermentation?
Visual inspection
Online pH monitoring
Manual weighing of cells
Batch sampling
Explanation - PAT includes real‑time measurements that improve control and product quality during fermentation.
Correct answer is: Online pH monitoring
Q.52 The presence of which ion in high concentration can inhibit yeast fermentation?
Calcium
Sodium
Potassium
Magnesium
Explanation - High Na⁺ can create osmotic stress and inhibit yeast growth and ethanol production.
Correct answer is: Sodium
Q.53 Which of the following is a typical by-product of the production of kefir?
Lactose
Carbon dioxide
Acetic acid
Bacterial spores
Explanation - Kefir fermentation produces CO₂, which can cause packaging to inflate slightly.
Correct answer is: Carbon dioxide
Q.54 In a stirred‑tank fermentor, what is the main function of the baffle?
Reduce turbulence
Increase shear forces
Prevent vortex formation
Control temperature
Explanation - Baffles disrupt swirling motions, ensuring uniform mixing and better mass transfer.
Correct answer is: Prevent vortex formation
Q.55 The primary advantage of using a high‑shear bioreactor for yeast fermentation is:
Better oxygen transfer
Lower operating costs
Reduced product viscosity
Longer fermentation times
Explanation - High shear improves mixing and gas transfer, which is beneficial for aerobic yeast cultures.
Correct answer is: Better oxygen transfer
Q.56 Which of the following is a typical component of a minimal growth medium for lactic acid bacteria?
Glucose, salts, and vitamins
Lactose only
No sugar
High concentrations of protein
Explanation - Minimal media provide essential nutrients for bacterial growth while limiting extraneous components.
Correct answer is: Glucose, salts, and vitamins
Q.57 During cheese ripening, what role does the enzyme chymosin play?
Breaks down lactose
Hydrolyzes casein into curd
Produces carbon dioxide
Increases acidity
Explanation - Chymosin is a protease that cleaves κ-casein, leading to coagulation and curd formation.
Correct answer is: Hydrolyzes casein into curd
Q.58 Which parameter is used to calculate the dilution rate in a continuous fermentor?
Temperature
Feed flow rate
Biomass concentration
Pressure
Explanation - Dilution rate (D) is the feed flow rate divided by reactor volume, influencing cell growth.
Correct answer is: Feed flow rate
Q.59 What is the main advantage of a membrane bioreactor for product recovery?
Lower cost
No need for downstream processing
Simultaneous cell separation and product recovery
Higher temperature operation
Explanation - Membrane separation allows continuous removal of product while retaining cells in the reactor.
Correct answer is: Simultaneous cell separation and product recovery
Q.60 Which microorganism is commonly used for the production of fermented soy sauce?
Lactobacillus casei
Streptomyces coelicolor
Aspergillus oryzae
Pseudomonas fluorescens
Explanation - A. oryzae is a mold used in the koji step of soy sauce fermentation, producing enzymes for flavor.
Correct answer is: Aspergillus oryzae
Q.61 During a batch fermentation, the term 'lag phase' refers to:
The period of rapid growth
The time when cells adjust to the new environment
The period of product formation
The period of cell death
Explanation - Lag phase is the adaptation period before exponential growth begins.
Correct answer is: The time when cells adjust to the new environment
Q.62 Which of the following is NOT a typical component of a bioprocess control system?
Temperature sensor
pH sensor
Manual stirring
Oxygen probe
Explanation - Control systems use automated agitators; manual stirring is impractical for large scale.
Correct answer is: Manual stirring
Q.63 What is the main reason for adding a buffering agent during lactic acid fermentation?
To increase sugar concentration
To maintain stable pH
To provide nutrients
To reduce temperature
Explanation - Buffers resist changes in pH, ensuring optimal enzyme activity during acid production.
Correct answer is: To maintain stable pH
Q.64 Which of the following is a typical product of the fermentation of whey?
Lactose
Casein
Ethanol
Lactic acid
Explanation - Lactose in whey is fermented by lactobacilli to produce lactic acid, useful in food industry.
Correct answer is: Lactic acid
Q.65 The term 'bioreactor volume' is directly related to which of the following?
Oxygen transfer capacity
Maximum cell density
Fermenter geometry
All of the above
Explanation - Volume influences mass transfer, cell density, and design of the fermentor.
Correct answer is: All of the above
Q.66 Which of the following is a characteristic of an aerobic fermentor?
No agitation
Closed environment
Continuous aeration
No pH control
Explanation - Aerobic fermentors provide oxygen through sparging or dissolved oxygen control.
Correct answer is: Continuous aeration
Q.67 Which of these is a typical by‑product of alcoholic fermentation in the production of vinegar?
Methanol
Acetic acid
Butanol
Lactic acid
Explanation - Acetobacter oxidizes ethanol to acetic acid, producing vinegar.
Correct answer is: Acetic acid
Q.68 What is the role of the gas sparger in a bioreactor?
Inject nutrients
Provide agitation
Introduce gas for mass transfer
Control pH
Explanation - The sparger distributes gas bubbles into the liquid for oxygen or CO₂ transfer.
Correct answer is: Introduce gas for mass transfer
Q.69 Which of the following is a typical component of a feed solution in a fed‑batch fermentor?
Only water
High sugar and nutrient concentration
Acids for pH control
Oxygen gas
Explanation - Feed solutions provide additional substrates to maintain growth without over‑inhibiting the culture.
Correct answer is: High sugar and nutrient concentration
Q.70 Which type of fermentation is used to produce yogurt?
Acidogenic fermentation
Alcoholic fermentation
Methanogenic fermentation
Phototrophic fermentation
Explanation - Lactobacillus species ferment lactose to lactic acid, creating the sourness of yogurt.
Correct answer is: Acidogenic fermentation
Q.71 What is the typical pH range for lactic acid bacteria during fermentation?
1.5–2.5
4–6
7–9
10–12
Explanation - Lactobacilli thrive in mildly acidic environments; pH 4–6 is optimal for growth and acid production.
Correct answer is: 4–6
Q.72 Which of the following is NOT a common method for measuring cell density in a fermentor?
Optical density
Coulter counter
pH measurement
Cell counting by microscopy
Explanation - Cell density is assessed by optical methods, counters, or direct counting; pH does not give cell density.
Correct answer is: pH measurement
Q.73 The term 'hydrolysate' in fermentation refers to:
The liquid by‑product of fermentation
A mixture of sugars released from complex carbohydrates
The gas produced
The solid residue
Explanation - Hydrolysate is the result of enzymatic or acid hydrolysis of polysaccharides into fermentable sugars.
Correct answer is: A mixture of sugars released from complex carbohydrates
Q.74 During a continuous fermentation, what parameter indicates that the system is at steady state?
Constant pH
Constant temperature
Constant product concentration
All of the above
Explanation - Steady state means all key variables remain stable over time.
Correct answer is: All of the above
Q.75 What is the main benefit of using a high‑volume bioreactor for microbial fermentation?
Lower mixing time
Higher cell density
Reduced oxygen transfer
Lower costs
Explanation - Large volumes allow more biomass to be produced per unit time.
Correct answer is: Higher cell density
Q.76 Which of the following is a typical by‑product of the fermentation of cassava?
Ethanol
Lactic acid
Acetic acid
Butyric acid
Explanation - Cassava starch is converted to sugars and fermented by yeast to produce ethanol.
Correct answer is: Ethanol
Q.77 Which of the following is a primary goal of scale‑up from a lab‑scale to an industrial‑scale fermentor?
Decrease product yield
Increase mixing efficiency
Reduce oxygen transfer rate
Limit cell density
Explanation - Scale‑up aims to maintain efficient mixing, mass transfer, and temperature control as volume increases.
Correct answer is: Increase mixing efficiency
Q.78 Which of the following best describes a 'plug flow' reactor?
A reactor where the liquid moves in a uniform stream
A reactor with perfect mixing
A reactor that uses plug flow for gas
A reactor that uses plug flow for heat transfer
Explanation - In a plug flow reactor, fluid elements move without back‑mixing, resulting in a gradient of residence times.
Correct answer is: A reactor where the liquid moves in a uniform stream
Q.79 Which of the following is a key factor influencing the oxygen transfer rate (OTR) in a bioreactor?
Temperature
Stirrer speed
pH
Biomass concentration
Explanation - Higher agitation increases interfacial area and turbulence, enhancing O₂ transfer.
Correct answer is: Stirrer speed
Q.80 What is the purpose of a sterilization step before inoculation in fermentation?
Increase nutrient concentration
Reduce product acidity
Eliminate competing microorganisms
Increase temperature
Explanation - Sterilization removes unwanted microbes, allowing the inoculated strain to dominate the culture.
Correct answer is: Eliminate competing microorganisms
Q.81 Which of the following is a typical product of the fermentation of soy milk?
Ethanol
Lactic acid
Acetic acid
Butyric acid
Explanation - Lactobacillus spp. ferment soy milk sugars, producing lactic acid used in soy yogurt.
Correct answer is: Lactic acid
Q.82 Which of the following is a key benefit of using a stirred‑tank fermentor?
Uniform mixing and temperature distribution
Low cost
No need for pH control
Inherent foaming reduction
Explanation - Stirred‑tank reactors provide consistent mixing, essential for homogeneous culture conditions.
Correct answer is: Uniform mixing and temperature distribution
Q.83 What does the term 'biomass concentration' refer to in a fermentation process?
Concentration of nutrients
Cell mass per unit volume
Concentration of product
Amount of oxygen dissolved
Explanation - Biomass concentration is a measure of how many cells are present in a given volume of culture.
Correct answer is: Cell mass per unit volume
Q.84 Which of the following is NOT typically used to control pH in a fermentor?
Acid injection
Base injection
Temperature control
Buffer addition
Explanation - While temperature affects metabolism, pH control uses acid, base, or buffers directly.
Correct answer is: Temperature control
Q.85 In a batch fermentation, when does the product formation phase usually begin?
Immediately after inoculation
After the lag phase
During the exponential growth phase
At the end of fermentation
Explanation - Product formation often starts after cells have adapted to the environment and begun exponential growth.
Correct answer is: After the lag phase
Q.86 Which of the following is a common measure of fermentation performance?
Yield
Color
Smell
Volume
Explanation - Yield quantifies how much product is produced per unit of substrate, indicating process efficiency.
Correct answer is: Yield
Q.87 In the production of cheese, which microorganism is primarily responsible for the development of the characteristic aroma?
Lactobacillus delbrueckii
Propionibacterium freudenreichii
Saccharomyces cerevisiae
Bacillus subtilis
Explanation - This bacterium produces propionic acid and CO₂, contributing to Swiss cheese flavor and holes.
Correct answer is: Propionibacterium freudenreichii
Q.88 Which of the following is a typical component of a fed‑batch feed solution?
Only water
High glucose concentration
Acidic buffer
High salt concentration
Explanation - Fed‑batch feeds often contain sugars to maintain growth without substrate inhibition.
Correct answer is: High glucose concentration
Q.89 What is the main purpose of a pH-stat controller in fermentation?
Automatically adjust temperature
Maintain constant pH by adding acid or base
Measure dissolved oxygen
Control agitation speed
Explanation - A pH-stat continuously monitors pH and automatically adds reagents to keep it within set limits.
Correct answer is: Maintain constant pH by adding acid or base
Q.90 Which of the following is a primary cause of foaming in yeast fermentations?
Low agitation
High sugar concentration
Low temperature
Low agitation
Explanation - High sugar increases viscosity and gas production, leading to foaming.
Correct answer is: High sugar concentration
Q.91 Which of the following is NOT a typical product of the fermentation of corn mash?
Ethanol
Acetone
Lactic acid
Methane
Explanation - Corn mash is mainly fermented to ethanol; methane is produced in anaerobic digestion, not typical here.
Correct answer is: Methane
Q.92 The term 'oxygen uptake rate' (OUR) is used to measure:
Oxygen solubility
Rate at which cells consume oxygen
Rate of oxygen transfer
Oxygen concentration
Explanation - OUR quantifies how much oxygen is being consumed by the culture per unit time.
Correct answer is: Rate at which cells consume oxygen
Q.93 Which of the following is a key factor influencing the product titer in a fermentation process?
Substrate concentration
Agitation speed
Inoculum density
All of the above
Explanation - All listed factors can affect how much product is produced per unit volume.
Correct answer is: All of the above
Q.94 In a packed bed reactor, how is the gas distributed to the packed bed?
By a gas sparger
By a liquid pump
By a vacuum
By passive diffusion
Explanation - A sparger introduces gas into the liquid to enable gas–liquid mass transfer within the bed.
Correct answer is: By a gas sparger
Q.95 What is the main advantage of using a plug flow reactor for the production of biofuels?
Uniform mixing
High residence time distribution
Gradient of residence times
Low energy consumption
Explanation - Plug flow reactors offer a gradient that can be beneficial for sequential reactions in biofuel synthesis.
Correct answer is: Gradient of residence times
Q.96 Which of the following is a typical product of lactic acid bacteria in the fermentation of kefir?
Lactic acid
Ethanol
Acetic acid
Methane
Explanation - Lactobacillus in kefir produce lactic acid, contributing to the drink’s tart flavor.
Correct answer is: Lactic acid
Q.97 Which of the following best describes the 'lag phase' in a microbial culture?
Time when cells die
Time when cells adapt to new conditions
Time when maximum growth occurs
Time when product is formed
Explanation - During the lag phase, cells adjust before entering exponential growth.
Correct answer is: Time when cells adapt to new conditions
Q.98 In a continuous fermentor, what does a constant product concentration indicate?
The system is not working
The system is at steady state
The feed concentration is too high
The temperature is too low
Explanation - Steady state is achieved when production and removal rates balance, keeping concentration constant.
Correct answer is: The system is at steady state
Q.99 Which of the following is a common use of a membrane in fermentation technology?
To increase stirring speed
To separate cells from the product
To measure temperature
To control pH
Explanation - Membranes allow selective separation, enabling continuous product recovery while retaining cells.
Correct answer is: To separate cells from the product
Q.100 What is the primary role of a temperature probe in a fermentor?
To measure dissolved oxygen
To monitor temperature
To inject nutrients
To stir the culture
Explanation - Accurate temperature measurement is essential for maintaining optimal microbial activity.
Correct answer is: To monitor temperature
Q.101 Which microorganism is typically used for the production of fermented soy sauce?
Lactobacillus casei
Aspergillus oryzae
Saccharomyces cerevisiae
Pseudomonas fluorescens
Explanation - A. oryzae is used in the koji step to produce enzymes that break down soy proteins and starches.
Correct answer is: Aspergillus oryzae
Q.102 In a bioreactor, what does 'dissolved oxygen (DO)' refer to?
Oxygen present in the gas phase
Oxygen that has dissolved in the liquid medium
Total oxygen in the system
Oxygen bound to proteins
Explanation - DO is the amount of oxygen that has dissolved in the culture medium, available for cell respiration.
Correct answer is: Oxygen that has dissolved in the liquid medium
Q.103 Which of the following is a typical product of the fermentation of cassava?
Ethanol
Lactic acid
Acetic acid
Butyric acid
Explanation - Cassava starch is converted to sugars and fermented to ethanol, used as biofuel.
Correct answer is: Ethanol
Q.104 What is the main purpose of a sterilization step before inoculation in a fermentation process?
Increase temperature
Reduce sugar concentration
Eliminate competing microorganisms
Add nutrients
Explanation - Sterilization removes unwanted microbes, ensuring that only the intended inoculum grows.
Correct answer is: Eliminate competing microorganisms
Q.105 Which of the following is a typical by-product of lactic acid fermentation of milk?
Lactose
Casein
Ethanol
Lactic acid
Explanation - Lactobacilli convert lactose to lactic acid, which curdles the milk and gives yogurt its flavor.
Correct answer is: Lactic acid
Q.106 In a fed‑batch process, the feed rate is often controlled by:
Manual addition
Computer‑controlled pumps
Gravity flow
Temperature changes
Explanation - Automated pumps allow precise control of substrate addition to avoid over‑feeding.
Correct answer is: Computer‑controlled pumps
Q.107 Which of the following best describes the 'mixing time' in a bioreactor?
Time required to add feed
Time to reach uniform temperature
Time needed for complete mixing of a tracer
Time to reach maximum cell density
Explanation - Mixing time is measured by the time it takes for a tracer to become uniformly distributed.
Correct answer is: Time needed for complete mixing of a tracer
Q.108 What is the main advantage of a membrane bioreactor over a conventional fermentor?
Lower cost
No need for downstream processing
Simultaneous cell separation and product recovery
Higher temperature tolerance
Explanation - Membrane bioreactors enable continuous removal of product while retaining cells, simplifying downstream steps.
Correct answer is: Simultaneous cell separation and product recovery
Q.109 Which of the following is a typical component of a minimal growth medium for Lactobacillus?
Glucose, salts, and vitamins
Only water
High protein concentration
High salt concentration
Explanation - Minimal media provide the essential nutrients needed for growth while limiting excess components.
Correct answer is: Glucose, salts, and vitamins
Q.110 Which of the following is NOT a typical measure of fermentation performance?
Yield
Product purity
Process time
Temperature
Explanation - Yield, purity, and time reflect performance; temperature is an operating parameter.
Correct answer is: Temperature
Q.111 Which of the following is a primary cause of foaming in yeast fermentations?
Low agitation
High sugar concentration
High temperature
Low pH
Explanation - High sugar increases viscosity and gas production, leading to foaming.
Correct answer is: High sugar concentration
Q.112 During the production of cheese, which microorganism is responsible for the development of the characteristic aroma of Swiss cheese?
Lactobacillus delbrueckii
Propionibacterium freudenreichii
Saccharomyces cerevisiae
Bacillus subtilis
Explanation - This bacterium produces propionic acid and CO₂, contributing to Swiss cheese flavor and holes.
Correct answer is: Propionibacterium freudenreichii
Q.113 Which of the following is a typical product of the fermentation of corn mash?
Ethanol
Acetone
Lactic acid
Methane
Explanation - Corn starch is fermented by yeast to produce ethanol used in fuel and beverages.
Correct answer is: Ethanol
Q.114 Which of the following is a key factor influencing the oxygen transfer rate (OTR) in a bioreactor?
Temperature
Stirrer speed
pH
Biomass concentration
Explanation - Higher agitation increases the interfacial area and turbulence, enhancing oxygen transfer.
Correct answer is: Stirrer speed
Q.115 Which of the following is a common method for measuring cell density in a fermentor?
Optical density
Coulter counter
pH measurement
Cell counting by microscopy
Explanation - Optical density (OD) at 600 nm is a quick proxy for cell concentration in liquid culture.
Correct answer is: Optical density
Q.116 Which of the following is NOT a typical component of a fed‑batch feed solution?
High glucose concentration
Buffering agent
Inhibitor
Nutrient salts
Explanation - Feed solutions are formulated to avoid inhibitors that would hinder growth.
Correct answer is: Inhibitor
Q.117 During a continuous fermentation, the system is at steady state when:
The product concentration fluctuates
The temperature is constant
The biomass concentration remains constant
Both product and biomass concentrations are constant
Explanation - Steady state implies all key variables remain unchanged over time.
Correct answer is: Both product and biomass concentrations are constant
Q.118 Which of the following best describes a plug flow reactor?
A reactor with perfect mixing
A reactor where fluid moves in uniform streams
A reactor that uses a sparger for gas
A reactor that uses a sparger for heat transfer
Explanation - In a plug flow reactor, the liquid elements flow as discrete 'plugs' without back‑mixing.
Correct answer is: A reactor where fluid moves in uniform streams