Bioprocessing of citric acid MCQs With Answer

Bioprocessing of citric acid MCQs With Answer

This quiz set is designed specifically for M.Pharm students studying Bioprocess Engineering and Technology. It focuses on industrial and laboratory aspects of citric acid bioprocessing — covering microbial strains, substrates, fermentation strategies (submerged and solid-state), nutritional and environmental controls, metabolic regulation, scale-up factors, aeration/agitation effects, and downstream recovery including lime treatment and crystallization. Questions probe both theoretical foundations and practical considerations such as impurity removal, yield optimization, and contamination control. Use these MCQs to reinforce classroom learning, prepare for exams, and deepen understanding of process variables central to efficient, high-yield citric acid production.

Q1. Which microorganism is predominantly used in industrial citric acid production?

• Escherichia coli
• Penicillium chrysogenum
• Aspergillus niger
• Saccharomyces cerevisiae

Correct Answer: Aspergillus niger

Q2. Which substrate is most commonly used at industrial scale for citric acid fermentation due to cost-effectiveness?

• Pure glucose syrup
• Cane molasses
• Lactose from whey
• Glycerol from biodiesel

Correct Answer: Cane molasses

Q3. What fermentation mode is most widely employed in large-scale citric acid production?

• Solid-state fermentation (SSF)
• Submerged aerobic fermentation (SmF)
• Anaerobic batch fermentation
• Photofermentation

Correct Answer: Submerged aerobic fermentation (SmF)

Q4. What pH range is optimal for maximizing citric acid accumulation by Aspergillus niger?

• pH 6.5–7.5
• pH 4.5–5.5
• pH 2.0–3.0
• pH 8.0–9.0

Correct Answer: pH 2.0–3.0

Q5. Typical optimum temperature for Aspergillus niger citric acid fermentation is approximately:

• 10–15 °C
• 20–25 °C
• 28–32 °C
• 40–45 °C

Correct Answer: 28–32 °C

Q6. Which trace metal ion, when maintained at very low concentration, is known to enhance citric acid accumulation?

• Calcium (Ca2+)
• Manganese (Mn2+)
• Iron (Fe2+/Fe3+)
• Magnesium (Mg2+)

Correct Answer: Manganese (Mn2+)

Q7. High initial sugar concentration in the fermentation medium (e.g., 10–15% w/v) primarily contributes to:

• Enhanced biomass formation without product
• Osmotic stress preventing production
• Higher citric acid yield and product concentration
• Complete suppression of fungal growth

Correct Answer: Higher citric acid yield and product concentration

Q8. Which nutritional condition is deliberately limited to favor citric acid over biomass formation?

• Carbon source in excess
• Nitrogen source (ammonium/organic N)
• Excess phosphate
• High vitamin concentration

Correct Answer: Nitrogen source (ammonium/organic N)

Q9. Which downstream treatment is commonly used to remove proteins and other impurities by forming calcium salts prior to citric acid recovery?

• Activated charcoal adsorption
• Lime treatment (carbonatation)
• Solvent extraction with ethyl acetate
• Membrane ultrafiltration

Correct Answer: Lime treatment (carbonatation)

Q10. How is citric acid typically liberated from calcium citrate precipitate during purification?

• Neutralization with sodium hydroxide
• Acidification with sulfuric acid to form free citric acid and gypsum
• Direct crystallization from alkaline solution
• By thermal decomposition at high temperature

Correct Answer: Acidification with sulfuric acid to form free citric acid and gypsum

Q11. A realistic industrial yield of citric acid from sugar (g citric acid / g sugar) is approximately:

• 0.1–0.2 g/g
• 0.4–0.5 g/g
• 0.7–0.9 g/g
• 1.5–1.8 g/g

Correct Answer: 0.7–0.9 g/g

Q12. Accumulation of citric acid in Aspergillus fermentation is often associated with which metabolic effect?

• Activation of isocitrate dehydrogenase
• Inhibition of aconitase leading to citrate buildup
• Enhanced conversion of citrate to α-ketoglutarate
• Complete block of glycolysis

Correct Answer: Inhibition of aconitase leading to citrate buildup

Q13. Compared to submerged fermentation, solid-state fermentation (SSF) for citric acid production typically offers which advantage?

• Lower product concentration but better purity
• Higher water consumption and dilution
• Higher volumetric productivity and lower wastewater
• Requires strictly anaerobic conditions

Correct Answer: Higher volumetric productivity and lower wastewater

Q14. A critical process variable that must be optimized because citric acid production is strictly aerobic is:

• Agitation/aeration rate
• Light intensity
• Carbon dioxide sparging only
• Anaerobic headspace

Correct Answer: Agitation/aeration rate

Q15. Use of immobilized Aspergillus cells in citric acid production primarily provides which benefit?

• Faster genetic mutation rates
• Facilitates continuous operation and cell reuse
• Complete elimination of downstream processing
• Production under anaerobic conditions

Correct Answer: Facilitates continuous operation and cell reuse

Q16. What is the purpose of the carbonatation step (CO2 addition after lime treatment) in citric acid downstream processing?

• To oxidize citric acid to acetone
• To precipitate impurities as calcium carbonate for removal
• To directly crystallize citric acid
• To sterilize the fermentation broth

Correct Answer: To precipitate impurities as calcium carbonate for removal

Q17. Which insoluble byproduct is formed when calcium citrate is acidified with sulfuric acid during citric acid recovery?

• Calcium carbonate
• Calcium sulfate (gypsum)
• Calcium chloride
• Calcium phosphate

Correct Answer: Calcium sulfate (gypsum)

Q18. How is contamination by bacteria usually minimized during citric acid fermentations?

• By operating at near-neutral pH
• By maintaining very low pH (~2) which favors Aspergillus and inhibits bacteria
• By adding large amounts of antibiotics continuously
• By elevating temperature to 60 °C during fermentation

Correct Answer: By maintaining very low pH (~2) which favors Aspergillus and inhibits bacteria

Q19. Which genetic modification strategy is commonly pursued to enhance citric acid production in fungal strains?

• Overexpression of citrate exporter/transport proteins
• Deletion of glycolytic enzymes to stop sugar uptake
• Insertion of lactose-utilizing genes only
• Overexpression of bacterial nitrogenase

Correct Answer: Overexpression of citrate exporter/transport proteins

Q20. Which measurement is most indicative that a citric acid fermentation batch is complete and ready for downstream processing?

• Peak biomass concentration regardless of sugar
• Residual sugar concentration is very low and citric acid concentration plateaus
• Rapid rise in pH above 7.0
• Complete color change of the culture to bright green

Correct Answer: Residual sugar concentration is very low and citric acid concentration plateaus

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