Rancidity of oils MCQs With Answer is a focused study resource designed for B. Pharm students to master lipid stability and degradation. This introduction covers essential concepts such as oxidative rancidity, hydrolytic rancidity, lipid oxidation mechanisms (initiation, propagation, termination), primary and secondary oxidation products, and key analytical tests like peroxide value, anisidine value, TBARS and Rancimat. You will also learn factors influencing rancidity—unsaturation, light, heat, metal ions—and prevention strategies including antioxidants, chelators and packaging. The content is practical for pharmaceutical excipient selection, formulation stability studies, and quality control. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What is rancidity in oils?
- Microbial contamination of oils
- Hydrocarbon polymerization
- Degradation of lipids producing off-flavors and odors
- Increase in oil viscosity without chemical change
Correct Answer: Degradation of lipids producing off-flavors and odors
Q2. Which are the main types of rancidity?
- Oxidative, hydrolytic and enzymatic rancidity
- Thermal and catalytic rancidity only
- Microbial and photochemical rancidity only
- Hydrogenation and polymerization rancidity
Correct Answer: Oxidative, hydrolytic and enzymatic rancidity
Q3. During autoxidation initiation step what occurs?
- Formation of stable ketones from fatty acids
- Homolytic cleavage producing free radicals by hydrogen abstraction
- Termination by radical recombination
- Conversion of peroxides to aldehydes
Correct Answer: Homolytic cleavage producing free radicals by hydrogen abstraction
Q4. What are primary oxidation products of oil autoxidation?
- Short-chain aldehydes and ketones
- Free fatty acids
- Lipid hydroperoxides (peroxides)
- Polymeric crosslinked oils
Correct Answer: Lipid hydroperoxides (peroxides)
Q5. Which analytical test primarily measures primary oxidation products?
- Anisidine value
- Peroxide value
- TBARS assay
- Acid value
Correct Answer: Peroxide value
Q6. The peroxide value is usually expressed in which units?
- mg KOH/g oil
- meq O2/kg oil
- % w/v
- ppm Fe
Correct Answer: meq O2/kg oil
Q7. Which test is used to detect secondary oxidation products like aldehydes?
- Peroxide value
- Anisidine value (p-anisidine)
- Iodine value
- Saponification value
Correct Answer: Anisidine value (p-anisidine)
Q8. What does the TBARS assay measure?
- Conjugated dienes
- Malondialdehyde and related substances
- Peroxide radicals directly
- Total fatty acid composition
Correct Answer: Malondialdehyde and related substances
Q9. What does the acid value indicate in oils?
- Degree of unsaturation
- Amount of free fatty acids
- Peroxide concentration
- Presence of heavy metals
Correct Answer: Amount of free fatty acids
Q10. Hydrolytic rancidity primarily produces which products?
- Lipid hydroperoxides
- Free fatty acids and glycerol
- Short-chain aldehydes like hexanal
- Crosslinked polymers
Correct Answer: Free fatty acids and glycerol
Q11. Which enzyme commonly causes enzymatic or hydrolytic rancidity?
- Lipase
- Protease
- Amylase
- Peroxidase
Correct Answer: Lipase
Q12. Which fatty acid is most susceptible to oxidative rancidity?
- Palmitic acid (saturated)
- Oleic acid (monounsaturated)
- Linoleic acid (polyunsaturated, two double bonds)
- Stearic acid (saturated)
Correct Answer: Linoleic acid (polyunsaturated, two double bonds)
Q13. Which is more susceptible to oxidation: linolenic acid or oleic acid?
- Oleic acid
- Both are equally susceptible
- Linolenic acid (more double bonds)
- Neither undergoes oxidation
Correct Answer: Linolenic acid (more double bonds)
Q14. Photooxidation involves which reactive species?
- Singlet oxygen
- Carbon dioxide radicals
- Sodium radicals
- Hydrazine radicals
Correct Answer: Singlet oxygen
Q15. Which metal ions accelerate oil oxidation as pro-oxidants?
- Iron and copper
- Calcium and magnesium
- Sodium and potassium
- Gold and silver
Correct Answer: Iron and copper
Q16. Conjugated dienes formed during early oxidation absorb at approximately which wavelength?
- 232 nm
- 600 nm
- 450 nm
- 700 nm
Correct Answer: 232 nm
Q17. The Rancimat test is used to measure what parameter?
- Induction period or induction time for oxidation
- Acid number of oil
- Viscosity at 25°C
- Heavy metal contamination
Correct Answer: Induction period or induction time for oxidation
Q18. Which antioxidant is a commonly used synthetic chain-breaking antioxidant in oils?
- EDTA
- BHT (butylated hydroxytoluene)
- Sodium benzoate
- Citric acid
Correct Answer: BHT (butylated hydroxytoluene)
Q19. Which natural antioxidant is widely found in vegetable oils?
- α-Tocopherol (vitamin E)
- Saccharin
- Parabens
- Ascorbyl palmitate only
Correct Answer: α-Tocopherol (vitamin E)
Q20. Chelating agents like EDTA reduce rancidity by:
- Absorbing oxygen physically
- Binding transition metals that catalyze oxidation
- Converting peroxides to acids
- Lowering oil temperature
Correct Answer: Binding transition metals that catalyze oxidation
Q21. Which value gives a combined estimate of primary and secondary oxidation (commonly used)?
- Totox value
- pH value
- Saponification value
- Refractive index
Correct Answer: Totox value
Q22. The formula for Totox value is:
- Totox = PV + AV
- Totox = 2 × PV + AV
- Totox = PV − AV
- Totox = PV/AV
Correct Answer: Totox = 2 × PV + AV
Q23. Which volatile compound is a common marker for oxidation in sunflower oil?
- Hexanal
- Benzene
- Acetone
- Phenol
Correct Answer: Hexanal
Q24. During advanced oxidation, peroxide value may decrease because:
- Peroxides evaporate intact
- Peroxides decompose into secondary products
- Oxygen is completely consumed and peroxides crystallize
- Peroxides convert back to unsaturated fats
Correct Answer: Peroxides decompose into secondary products
Q25. Which instrumental technique is commonly used to identify volatile oxidation products?
- FTIR only
- Gas chromatography-mass spectrometry (GC-MS)
- Atomic absorption spectroscopy (AAS)
- Polarimetry
Correct Answer: Gas chromatography-mass spectrometry (GC-MS)
Q26. Iodine value indicates:
- Acidity of oil
- Degree of unsaturation (double bonds) in fatty acids
- Peroxide concentration
- Presence of antioxidants
Correct Answer: Degree of unsaturation (double bonds) in fatty acids
Q27. Which packaging condition helps prevent rancidity in pharmaceutical oils?
- Transparent containers exposed to light
- Packaging under nitrogen and opaque containers
- Storing at high humidity and temperature
- Adding metal lids without liners
Correct Answer: Packaging under nitrogen and opaque containers
Q28. Which statement about antioxidants is true?
- All antioxidants act by chelating metals
- Chain-breaking antioxidants donate hydrogen to lipid radicals
- Antioxidants increase peroxide formation
- Antioxidants only work at very high concentrations
Correct Answer: Chain-breaking antioxidants donate hydrogen to lipid radicals
Q29. Which fatty acid position is most easily abstracted to form radicals during autoxidation?
- Terminal methyl group
- Bis-allylic methylene hydrogen (between two double bonds)
- Carboxyl carbon
- Glycerol backbone
Correct Answer: Bis-allylic methylene hydrogen (between two double bonds)
Q30. Enzymatic rancidity is frequently due to contamination by:
- Heat only
- Microorganisms producing lipases
- Heavy metals in packaging
- UV light exposure
Correct Answer: Microorganisms producing lipases
Q31. Which condition typically slows down oxidative rancidity?
- Increased unsaturation
- Higher storage temperature
- Storage in presence of oxygen and light
- Low temperature and exclusion of oxygen
Correct Answer: Low temperature and exclusion of oxygen
Q32. Which assay specifically reacts p-anisidine with aldehydes to quantify secondary oxidation?
- Peroxide value assay
- Anisidine value assay
- Iodine value test
- Saponification number
Correct Answer: Anisidine value assay
Q33. A high peroxide value combined with a low anisidine value suggests:
- Late stage oxidation predominates
- Early or primary oxidation predominates
- Nothing — both values are unrelated
- Only hydrolytic rancidity is present
Correct Answer: Early or primary oxidation predominates
Q34. Which compound is an example of a secondary oxidation product causing off-odor?
- Hydroperoxide
- Aldehyde (e.g., hexanal)
- Triglyceride
- Saturated fatty acid
Correct Answer: Aldehyde (e.g., hexanal)
Q35. Which analytical measure would you use to estimate free fatty acids formed by hydrolysis?
- Peroxide value
- Acid value (acid number)
- Conjugated diene assay
- Rancimat induction time
Correct Answer: Acid value (acid number)
Q36. Which factor does NOT typically increase the rate of rancidity?
- Presence of antioxidants
- Light exposure
- High degree of unsaturation
- Trace metal contamination
Correct Answer: Presence of antioxidants
Q37. In pharmaceutical formulations, rancid oils can affect:
- Color only, but not stability
- Drug stability, potency and organoleptic properties
- Only the dissolution rate of solids
- Only packaging integrity
Correct Answer: Drug stability, potency and organoleptic properties
Q38. Which method quantifies malondialdehyde formed during lipid peroxidation?
- TLC separation only
- TBARS (thiobarbituric acid reactive substances)
- Peroxide titration with iodide
- Iodine value determination
Correct Answer: TBARS (thiobarbituric acid reactive substances)
Q39. Which antioxidant is lipid-soluble and commonly used in oil-based formulations?
- Ascorbic acid (water soluble)
- BHA (butylated hydroxyanisole)
- Sodium metabisulfite only
- Citric acid only
Correct Answer: BHA (butylated hydroxyanisole)
Q40. Which practice is recommended to reduce rancidity during manufacturing?
- Use open-air high-temperature mixing
- Store under inert gas and use antioxidants
- Expose oils to sunlight for sterilization
- Add transition metals to stabilize oils
Correct Answer: Store under inert gas and use antioxidants
Q41. Gas chromatography analysis of oxidized oils primarily detects:
- Non-volatile triglycerides only
- Volatile oxidation products like aldehydes
- Total peroxide number directly
- Saponification value numerically
Correct Answer: Volatile oxidation products like aldehydes
Q42. Why might antioxidants show pro-oxidant activity under some conditions?
- They are always stable and never pro-oxidant
- At high temperatures or in presence of metal ions they can form radicals
- Because antioxidants remove oxygen completely
- Only if used without chelators they evaporate
Correct Answer: At high temperatures or in presence of metal ions they can form radicals
Q43. Which measurement is most appropriate to monitor initial oxidative changes in an oil during storage study?
- Anisidine value only
- Peroxide value and conjugated diene assay
- Microbial count
- Sodium content
Correct Answer: Peroxide value and conjugated diene assay
Q44. Lipid peroxidation in biological membranes often leads to:
- Improved membrane fluidity only
- Loss of membrane integrity and cellular damage
- Immediate repair without consequences
- Conversion to stable triglycerides
Correct Answer: Loss of membrane integrity and cellular damage
Q45. The presence of conjugated trienes is typically monitored at what wavelength?
- 270 nm
- 100 nm
- 360 nm
- 520 nm
Correct Answer: 270 nm
Q46. Which statement about peroxide value trends during prolonged oxidation is correct?
- Peroxide value remains constant throughout
- Peroxide value may rise initially then fall as peroxides decompose
- Peroxide value always decreases from the start
- Peroxide value is irrelevant to oxidation stage
Correct Answer: Peroxide value may rise initially then fall as peroxides decompose
Q47. Which of the following is NOT a practical approach to prevent oil rancidity in dosage forms?
- Addition of appropriate antioxidants
- Light-protective, oxygen-impermeable packaging
- Storage at elevated temperatures to speed curing
- Use of metal chelators to bind trace metals
Correct Answer: Storage at elevated temperatures to speed curing
Q48. Which physical property often changes as a result of lipid oxidation?
- Color, odor and flavor deterioration
- Increase in freezing point exclusively
- No change in organoleptic properties
- Becomes magnetic
Correct Answer: Color, odor and flavor deterioration
Q49. Photooxidation differs from autoxidation mainly because it:
- Requires enzyme catalysis
- Involves singlet oxygen generated by photosensitizers
- Produces only saturated fatty acids
- Is unaffected by light intensity
Correct Answer: Involves singlet oxygen generated by photosensitizers
Q50. Rank susceptibility to oxidation: linolenic, oleic, linoleic — which is correct from most to least?
- Oleic > linoleic > linolenic
- Linolenic > linoleic > oleic
- Linoleic > linolenic > oleic
- All have equal susceptibility
Correct Answer: Linolenic > linoleic > oleic
