Preservation of emulsions MCQs With Answer

Preservation of emulsions MCQs With Answer is an essential topic for B. Pharm students studying formulation stability, preservative selection, and microbial control in emulsified systems. This introduction covers preservation principles, preservative partitioning, preservative–emulsifier interactions, challenge testing (preservative efficacy test), regulatory expectations, and practical approaches to extend shelf-life. Keywords included: Preservation of emulsions MCQs, preservative efficacy, emulsion stabilization, microbial contamination, preservative partitioning, O/W and W/O emulsions, USP preservative tests, and formulation strategies. The content is tailored to help pharmacy students understand preservative choice, compatibility, and testing. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which phase of an oil-in-water (O/W) emulsion primarily requires antimicrobial preservation?

• The oil phase
• The aqueous phase
• The interfacial film only
• The vapor phase above the emulsion

Correct Answer: The aqueous phase

Q2. What is the main reason preservatives fail in some emulsions?

• Evaporation of the oil phase
• Partitioning of preservative into the oil phase
• Too high aqueous solubility of preservative
• Excessive emulsifier HLB value

Correct Answer: Partitioning of preservative into the oil phase

Q3. Which preservative is commonly used for acidic aqueous pharmaceutical emulsions and is most effective at low pH?

• Benzyl alcohol
• Sodium benzoate
• Chlorocresol
• Phenoxyethanol

Correct Answer: Sodium benzoate

Q4. USP <51> is most closely associated with which aspect of preservation?

• Oxidative stability testing
• Preservative efficacy (challenge) testing
• Determination of emulsion droplet size
• Packaging compatibility tests

Correct Answer: Preservative efficacy (challenge) testing

Q5. Which organism is commonly used in preservative efficacy tests as a gram-negative challenge organism?

• Staphylococcus aureus
• Pseudomonas aeruginosa
• Escherichia coli K12
• Bacillus subtilis

Correct Answer: Pseudomonas aeruginosa

Q6. What role does EDTA play when used with preservatives in emulsions?

• Acts as a primary preservative itself
• Chelates metal ions and enhances preservative activity
• Increases oil phase viscosity
• Neutralizes emulsifier charge

Correct Answer: Chelates metal ions and enhances preservative activity

Q7. Which preservative is a parabens class member frequently used in O/W emulsions?

• Methylparaben
• Sodium lauryl sulfate
• Thiomersal
• Formaldehyde

Correct Answer: Methylparaben

Q8. Phenoxyethanol is often chosen because it is:

• Highly volatile and evaporates quickly
• Effective over a broad pH range and compatible with many emulsifiers
• Only effective in W/O emulsions
• Strongly ionic and binds to proteins

Correct Answer: Effective over a broad pH range and compatible with many emulsifiers

Q9. Which factor most increases microbial growth risk in emulsions?

• Low water activity
• High oil content with no water phase
• Presence of nutrients in the aqueous phase
• Highly acidic pH below 3

Correct Answer: Presence of nutrients in the aqueous phase

Q10. In preservative selection, the term “partitioning” refers to:

• Distribution of preservative between oil and water phases
• Splitting of emulsion droplets into smaller sizes
• Division of packaging types
• Separation of preservative into vapour phase

Correct Answer: Distribution of preservative between oil and water phases

Q11. Which preservative is known for good activity against fungi and yeasts and is often combined with parabens?

• Propylene glycol
• Sorbic acid (sodium sorbate)
• Benzalkonium chloride
• EDTA

Correct Answer: Sorbic acid (sodium sorbate)

Q12. Why are W/O emulsions generally harder to preserve than O/W emulsions?

• Water phase is external in W/O emulsions
• Oil phase is external in W/O emulsions, reducing preservative availability in internal aqueous droplets
• W/O emulsions have no water content
• They freeze more readily

Correct Answer: Oil phase is external in W/O emulsions, reducing preservative availability in internal aqueous droplets

Q13. Which test monitors preservative performance by intentionally inoculating product with microbes?

• Stability accelerated test
• Preservative efficacy test (challenge test)
• pH stress test
• Viscosity trial

Correct Answer: Preservative efficacy test (challenge test)

Q14. Which antimicrobial class is ionic and often incompatible with anionic surfactants?

• Nonionic phenols
• Quaternary ammonium compounds (e.g., benzalkonium chloride)
• Parabens
• Organic acids

Correct Answer: Quaternary ammonium compounds (e.g., benzalkonium chloride)

Q15. How does increasing viscosity of the continuous phase affect preservative efficacy?

• Always increases preservative efficacy
• May hinder preservative diffusion and reduce efficacy
• Eliminates need for preservatives
• Causes immediate phase inversion

Correct Answer: May hinder preservative diffusion and reduce efficacy

Q16. Which preservative is alcohol-based and commonly used in combination with others to broaden activity?

• Isopropyl myristate
• Ethanol
• Glycerin
• Sorbitan monooleate

Correct Answer: Ethanol

Q17. Which is a regulatory concern when using formaldehyde-releasing preservatives?

• They have no microbial activity
• Potential toxicity and allergenicity risk and regulatory restrictions
• They are ineffective in acidic formulations
• They cannot be used in aqueous systems

Correct Answer: Potential toxicity and allergenicity risk and regulatory restrictions

Q18. Which of the following increases preservative activity by destabilizing bacterial cell walls?

• Using nonionic emulsifiers exclusively
• Incorporating chelators like EDTA
• Raising droplet size to >50 microns
• Adding inert oils

Correct Answer: Incorporating chelators like EDTA

Q19. What is the effect of pH on benzoic acid (sodium benzoate) preservative activity?

• More active at high pH (>8)
• More active at low pH (acidic) where undissociated acid form predominates
• pH has no effect
• Only active at neutral pH

Correct Answer: More active at low pH (acidic) where undissociated acid form predominates

Q20. Which test method is typically used to enumerate surviving microbes after challenge testing?

• Gas chromatography
• Plate count method
• Particle size analysis
• Refractive index measurement

Correct Answer: Plate count method

Q21. Which property of an emulsifier most influences preservative partitioning?

• Molecular weight only
• Hydrophilic–lipophilic balance (HLB)
• Color of emulsifier
• Melting point

Correct Answer: Hydrophilic–lipophilic balance (HLB)

Q22. Why might a preservative be ineffective in an emulsion despite being effective in simple aqueous solution?

• Because emulsions are sterile by default
• Because preservative may bind to emulsifier or partition into oil phase reducing free concentration
• Because water in emulsions has higher boiling point
• Because emulsions lack oxygen

Correct Answer: Because preservative may bind to emulsifier or partition into oil phase reducing free concentration

Q23. Which organism represents a fungal challenge organism commonly used in efficacy testing?

• Streptococcus pyogenes
• Aspergillus brasiliensis (formerly A. niger)
• Micrococcus luteus
• Clostridium perfringens

Correct Answer: Aspergillus brasiliensis (formerly A. niger)

Q24. What is a common consequence of preservative over-concentration in topical emulsions?

• Increased product viscosity
• Toxicity and skin irritation or sensitization
• Guaranteed microbial sterility without testing
• Complete phase separation

Correct Answer: Toxicity and skin irritation or sensitization

Q25. Which natural preservative is often limited by narrow spectrum and variable activity?

• Tea tree oil
• Phenoxyethanol
• Methylparaben
• Benzalkonium chloride

Correct Answer: Tea tree oil

Q26. What is the role of co-solvents like propylene glycol in emulsion preservation?

• Act solely as humectants with no effect on preservation
• Increase preservative solubility in aqueous phase and sometimes aid activity
• Cause immediate microbial growth
• Remove the need for emulsifiers

Correct Answer: Increase preservative solubility in aqueous phase and sometimes aid activity

Q27. Which preservative is cationic and may be inactivated by anionic excipients?

• Phenoxyethanol
• Benzalkonium chloride
• Methylparaben
• Sodium benzoate

Correct Answer: Benzalkonium chloride

Q28. What is “preservative efficacy test” acceptance primarily based on?

• Color change of formulation
• Log reduction of specific microorganisms over specified times
• Increase in viscosity after storage
• pH remaining constant

Correct Answer: Log reduction of specific microorganisms over specified times

Q29. Which factor does NOT typically affect preservative action in emulsions?

• Emulsifier identity
• Packaging material only
• pH of aqueous phase
• Presence of chelating agents

Correct Answer: Packaging material only

Q30. How does droplet size distribution influence preservative availability?

• Smaller droplets increase total interfacial area, potentially binding more preservative
• Droplet size has no influence
• Larger droplets always improve preservative efficacy
• Only affects color of emulsion

Correct Answer: Smaller droplets increase total interfacial area, potentially binding more preservative

Q31. Which of the following is a preservative resistance concern for Pseudomonas species?

• Pseudomonas cannot grow in emulsions
• Intrinsic resistance to some preservatives and ability to form biofilms
• Pseudomonas is easily killed by low preservative concentrations
• Pseudomonas only grows at freezing temperatures

Correct Answer: Intrinsic resistance to some preservatives and ability to form biofilms

Q32. Which analysis helps predict how much preservative remains in the aqueous phase?

• Partition coefficient measurement between oil and water
• Melting point analysis
• Odour threshold testing
• Thermal gravimetric analysis

Correct Answer: Partition coefficient measurement between oil and water

Q33. Which class of preservatives is commonly disallowed or restricted in many regulations due to sensitization?

• Parabens
• Isothiazolinones (e.g., MCI/MI)
• Benzoates
• Alcohols

Correct Answer: Isothiazolinones (e.g., MCI/MI)

Q34. What formulation approach can help improve preservative action in W/O emulsions?

• Add more oil to sequester preservative
• Use internal aqueous phase preservatives that partition into droplets plus interfacial active preservatives
• Remove water entirely
• Use only solid excipients

Correct Answer: Use internal aqueous phase preservatives that partition into droplets plus interfacial active preservatives

Q35. During development, why is preservative compatibility with active pharmaceutical ingredient (API) important?

• API may chemically react or inactivate preservative or vice versa
• API never interacts with preservatives
• Compatibility testing is only cosmetic
• APIs only affect color not preservation

Correct Answer: API may chemically react or inactivate preservative or vice versa

Q36. Which preservative is often restricted in pediatric topical products due to toxicity concerns?

• Phenoxyethanol
• Parabens
• Formaldehyde releasers
• Propylparaben

Correct Answer: Formaldehyde releasers

Q37. What is the main aim of aseptic processing in relation to preservative use?

• To allow removal of preservatives entirely
• To reduce initial bioburden so preservatives can maintain product long-term more effectively
• To sterilize oil phase only
• To change emulsion droplet charge

Correct Answer: To reduce initial bioburden so preservatives can maintain product long-term more effectively

Q38. Which of the following is a sign of preservative failure in a finished emulsion?

• Stable droplet size over time
• Visual microbial growth, off-odour, turbidity increase
• Lower melting point
• Constant pH

Correct Answer: Visual microbial growth, off-odour, turbidity increase

Q39. Which preservative works well at neutral to slightly alkaline pH and is often combined with others for broad spectrum?

• Sodium benzoate
• Phenoxyethanol
• Formaldehyde
• Acetic acid

Correct Answer: Phenoxyethanol

Q40. Which manufacturing practice reduces contamination risk during emulsion processing?

• Open cooling in ambient air
• Implementing cleanroom procedures and sterile equipment handling
• Using unfiltered water
• Adding preservatives after packaging

Correct Answer: Implementing cleanroom procedures and sterile equipment handling

Q41. How can surfactants reduce free preservative concentration?

• By increasing preservative volatility
• By forming micelles or associating with preservative molecules, sequestering them
• By converting preservative to gas
• Surfactants never interact with preservatives

Correct Answer: By forming micelles or associating with preservative molecules, sequestering them

Q42. What is the consequence of preservative adsorption to container surfaces?

• Increased preservative concentration in product
• Reduced effective preservative concentration and potential preservation failure
• Immediate sterilization of container
• No measurable effect

Correct Answer: Reduced effective preservative concentration and potential preservation failure

Q43. Which analytical approach helps determine if preservative remains active after accelerated stability?

• High performance liquid chromatography (HPLC) assay and residual activity testing
• Particle size analysis only
• Colorimetric pH strips
• Viscosity alone

Correct Answer: High performance liquid chromatography (HPLC) assay and residual activity testing

Q44. Which preservative is especially effective against gram-positive bacteria and has surfactant-like properties?

• Benzoic acid
• Benzalkonium chloride
• Propylene glycol
• Methylparaben

Correct Answer: Benzalkonium chloride

Q45. What is a benefit of combining preservatives in a formulation?

• Always increases toxicity
• Provides synergistic or broader spectrum activity and may reduce individual concentrations
• Makes preservative efficacy tests unnecessary
• Makes preservation effective only at freezing temperatures

Correct Answer: Provides synergistic or broader spectrum activity and may reduce individual concentrations

Q46. Which preservative is often used in oil-in-water emulsions because it partitions to the aqueous phase yet is lipophilic enough to act at interfaces?

• Benzyl alcohol
• Chlorhexidine
• Propylparaben
• Glycerin

Correct Answer: Propylparaben

Q47. What is the main limitation of using ethanol as the sole preservative in emulsions?

• High effectiveness against spores
• Evaporation leading to reduced concentration and limited long-term protection
• Inability to dissolve in water
• Causes phase inversion

Correct Answer: Evaporation leading to reduced concentration and limited long-term protection

Q48. Which parameter must be reported when submitting preservative efficacy data to regulators?

• Log reductions at defined time points and organisms challenged
• Only the pH of the formulation
• Only the brand name of preservatives
• Only viscosity changes

Correct Answer: Log reductions at defined time points and organisms challenged

Q49. Which preservative is commonly paired with EDTA to enhance activity against gram-negative bacteria?

• Parabens (methyl/propylparaben)
• Hydrogen peroxide
• Formaldehyde
• Mineral oil

Correct Answer: Parabens (methyl/propylparaben)

Q50. Which best practice helps ensure long-term preservation of an emulsion product?

• Rely solely on natural preservatives without testing
• Design preservative system based on partitioning, compatibility, challenge testing, and good manufacturing practices
• Store product at uncontrolled temperatures
• Use the minimum possible water content without evaluation

Correct Answer: Design preservative system based on partitioning, compatibility, challenge testing, and good manufacturing practices

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com