Bioprocessing of vitamin C MCQs With Answer

Introduction: This quiz collection on Bioprocessing of Vitamin C is designed for M.Pharm students to deepen understanding of industrial and biotechnological routes for ascorbic acid production. It covers biochemical pathways, microbial strains, fermentation strategies, process parameters (pH, aeration, substrate feeding), co-culture systems, upstream and downstream considerations, analytical quality control, and regulatory implications for pharmaceutical-grade vitamin C. Questions emphasize mechanistic insights, scale-up challenges, and modern bioprocess innovations (e.g., direct 2-keto-L-gulonic acid fermentation, immobilization, oxygen transfer optimization). Use this set to test concept mastery, identify gaps, and reinforce practical reasoning required for designing and controlling vitamin C bioprocesses in a pharma environment.

Q1. Which microorganism is primarily used for the oxidation of D-sorbitol to L-sorbose in the classical Reichstein-type process?

• Ketogulonicigenium vulgare
• Gluconobacter oxydans
• Bacillus megaterium
• Aspergillus niger

Correct Answer: Gluconobacter oxydans

Q2. In modern two-step bioprocesses for vitamin C, which intermediate is produced biologically and then chemically converted to ascorbic acid?

• 3-keto-gluconate
• 2-keto-L-gulonic acid (2-KLG)
• L-ascorbate-2-phosphate
• Dehydroascorbic acid

Correct Answer: 2-keto-L-gulonic acid (2-KLG)

Q3. Which co-culture pairing is commonly used to increase 2-KLG yield from L-sorbose?

• Klebsiella pneumoniae with Saccharomyces cerevisiae
• Ketogulonicigenium vulgare with Bacillus spp.
• Pseudomonas putida with Rhizopus oryzae
• Gluconobacter oxydans with Aspergillus niger

Correct Answer: Ketogulonicigenium vulgare with Bacillus spp.

Q4. What is the primary role of Bacillus species in the Ketogulonicigenium–Bacillus co-culture used for 2-KLG production?

• Direct oxidation of sorbitol to sorbose
• Secretion of growth-promoting factors and removal of inhibitory compounds
• Conversion of 2-KLG to ascorbic acid enzymatically
• Suppression of oxygen transfer to favor microaerobic metabolism

Correct Answer: Secretion of growth-promoting factors and removal of inhibitory compounds

Q5. Which fermentation mode is most commonly applied to control substrate inhibition when producing L-sorbose or 2-KLG at industrial scale?

• Continuous culture with high dilution rate
• Fed-batch fermentation
• Batch fermentation with a single large substrate charge
• Chemostat at zero dilution

Correct Answer: Fed-batch fermentation

Q6. For aerobic oxidation steps in vitamin C bioprocessing, which bioreactor parameter is most critical to maintain high productivity?

• kLa (oxygen transfer coefficient)
• Light intensity
• Magnetic stirring field strength
• Carbon dioxide partial pressure

Correct Answer: kLa (oxygen transfer coefficient)

Q7. Immobilization of whole cells for sorbitol oxidation to sorbose offers which main advantage?

• Complete elimination of by-product formation
• Enhanced cell reuse and operational stability
• Avoidance of aeration requirements
• Promotion of genetic mutation to increase yield

Correct Answer: Enhanced cell reuse and operational stability

Q8. Which analytical method is most appropriate for quantifying 2-KLG and monitoring conversion during fermentation?

• Gas chromatography with flame ionization detection (GC-FID)
• High-performance liquid chromatography (HPLC)
• Atomic absorption spectroscopy (AAS)
• Infrared spectroscopy of dried biomass

Correct Answer: High-performance liquid chromatography (HPLC)

Q9. During scale-up of an aerobic vitamin C fermentation, which similarity rule is most commonly targeted to maintain process performance?

• Constant Reynolds number across scales
• Constant power input per unit volume (P/V)
• Constant volumetric mass transfer coefficient (kLa)
• Constant impeller tip speed

Correct Answer: Constant volumetric mass transfer coefficient (kLa)

Q10. Which enzyme activity in Gluconobacter is directly responsible for converting sorbitol to sorbose?

• Membrane-bound sorbitol dehydrogenase
• Lactonase
• 2-keto-L-gulonate oxidase
• Glucose isomerase

Correct Answer: Membrane-bound sorbitol dehydrogenase

Q11. What is a major downstream unit operation for obtaining pharmaceutical-grade ascorbic acid from fermentation-derived 2-KLG?

• Ion-exchange chromatography followed by crystallization
• Direct spray-drying of whole broth
• Simple filtration without purification
• Lyophilization of live culture

Correct Answer: Ion-exchange chromatography followed by crystallization

Q12. Which impurity control is particularly important for pharmaceutical vitamin C production compared to food grade?

• Removal of residual solvent traces
• Color control only
• Removal of heavy metals and endotoxins to tight limits
• Allowing higher water content

Correct Answer: Removal of heavy metals and endotoxins to tight limits

Q13. Which substrate is most commonly used as the initial feedstock in the classical biochemical route to vitamin C?

• Fructose
• D-sorbitol
• Cellulose

Correct Answer: D-sorbitol

Q14. What is the main advantage of direct microbial production of 2-KLG from glucose using engineered strains compared to the classic sorbitol route?

• Lower oxygen demand making aerobic control unnecessary
• Elimination of the chemical reduction/oxidation steps and simplified upstream integration
• Guaranteed zero by-product formation
• Requires no downstream purification

Correct Answer: Elimination of the chemical reduction/oxidation steps and simplified upstream integration

Q15. Which operating condition typically inhibits production of 2-KLG in co-culture due to oxidative stress sensitivity?

• Low dissolved oxygen below microaerobic levels
• Excessively high dissolved oxygen leading to reactive oxygen species formation
• Neutral pH around 7.0
• Moderate agitation with good heat removal

Correct Answer: Excessively high dissolved oxygen leading to reactive oxygen species formation

Q16. In designing medium for sorbitol-to-sorbose fermentation, which trace element is often critical for the activity of membrane dehydrogenases?

• Calcium
• Molybdenum
• Copper
• Zinc

Correct Answer: Copper

Q17. Which process analytical technology (PAT) measurement would be most useful for real-time control of aerobic vitamin C fermentations?

• Off-line plate counts every 24 hours
• On-line dissolved oxygen and real-time HPLC or NIR monitoring of substrates/products
• Periodic visual turbidity observations
• End-point titration only after harvest

Correct Answer: On-line dissolved oxygen and real-time HPLC or NIR monitoring of substrates/products

Q18. Which fermentation by-product, if accumulated, can inhibit 2-KLG formation and must be controlled?

• Acetic acid
• CO2
• Water
• Magnesium ions

Correct Answer: Acetic acid

Q19. During downstream processing, why is pH adjustment often required before crystallization of ascorbic acid?

• To neutralize and convert ascorbic acid to its sodium salt for better solubility
• To precipitate cells as living biomass
• To destroy 2-KLG residuals enzymatically
• To promote formation of ascorbic acid lactones that limit purity

Correct Answer: To neutralize and convert ascorbic acid to its sodium salt for better solubility

Q20. Which regulatory consideration is essential when producing vitamin C for parenteral pharmaceutical formulations?

• Only color and taste specifications
• Sterility assurance, pyrogen/endotoxin limits, and validated aseptic processing
• Allowance of microbial contaminants if within low counts
• No documentation required for endotoxin testing

Correct Answer: Sterility assurance, pyrogen/endotoxin limits, and validated aseptic processing

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