Determination of rancidity in cosmetics MCQs With Answer

Introduction: This collection of MCQs on the determination of rancidity in cosmetics is designed for M.Pharm students studying Herbal and Cosmetic Analysis (MPA 204T). It covers fundamental concepts of hydrolytic and oxidative rancidity, analytical tests (peroxide value, anisidine, TBARS, acid value, Rancimat, Schaal test), instrumental approaches (SPME-GC-MS, UV spectrophotometry, DNPH derivatization), and practical aspects such as antioxidant selection, metal chelation, and factors accelerating oxidation. Questions emphasize interpretation of results, choice of appropriate assays for primary and secondary oxidation products, and stability testing of emulsions and oils in cosmetic formulations. The set aims to deepen understanding required for lab practice and quality assessment of cosmetic raw materials and finished products.

Q1. What best describes oxidative rancidity in cosmetic oils?

• Hydrolysis of triglycerides by water producing free fatty acids
• Peroxidation of unsaturated fatty acids leading to hydroperoxides and volatile carbonyls
• Microbial degradation of oils producing foul odors
• Saponification of oils with alkali forming soap

Correct Answer: Peroxidation of unsaturated fatty acids leading to hydroperoxides and volatile carbonyls

Q2. Which analytical test is primarily used to quantify primary oxidation products in oils?

• Anisidine value
• Peroxide value
• TBARS (Thiobarbituric acid reactive substances)
• Acid value

Correct Answer: Peroxide value

Q3. What is the conventional unit for reporting peroxide value in cosmetic oils?

• mg KOH/g
• g iodine/100 g
• meq O2/kg
• ppm MDA

Correct Answer: meq O2/kg

Q4. Which assay is most suitable for assessing secondary oxidation products (aldehydes) formed during oil rancidity?

• Peroxide value
• p-Anisidine value
• Iodine value
• Saponification value

Correct Answer: p-Anisidine value

Q5. What is the correct formula for calculating the TOTOX value used to estimate overall oxidative status?

• TOTOX = Peroxide value ÷ Anisidine value
• TOTOX = 2 × Peroxide value + p-Anisidine value
• TOTOX = Peroxide value + 2 × p-Anisidine value
• TOTOX = Peroxide value × p-Anisidine value

Correct Answer: TOTOX = 2 × Peroxide value + p-Anisidine value

Q6. Which antioxidant is commonly used in cosmetic formulations to retard oil oxidation?

• Hydrochloric acid
• Butylated hydroxytoluene (BHT)
• Sodium chloride
• Sorbitan monooleate

Correct Answer: Butylated hydroxytoluene (BHT)

Q7. The Rancimat method determines oxidative stability by measuring which of the following?

• Change in sample viscosity with time
• Conductivity increase of distilled water due to volatile oxidation products
• Absorbance at 600 nm of the oil sample
• pH change of the oil phase

Correct Answer: Conductivity increase of distilled water due to volatile oxidation products

Q8. Which factor most strongly accelerates oxidative rancidity in cosmetic oils?

• Storage in amber glass bottles at low temperature
• Presence of trace transition metals such as iron and copper
• Complete removal of oxygen from headspace
• Addition of natural tocopherols

Correct Answer: Presence of trace transition metals such as iron and copper

Q9. Formation of conjugated dienes during early stages of lipid oxidation is typically monitored by UV absorbance at which wavelength?

• 450 nm
• 700 nm
• 233 nm
• 540 nm

Correct Answer: 233 nm

Q10. The TBARS assay is primarily used to measure which oxidation marker in oils and formulations?

• Hydroperoxides
• Conjugated dienes
• Malondialdehyde (MDA) and related secondary carbonyls
• Free fatty acid content

Correct Answer: Malondialdehyde (MDA) and related secondary carbonyls

Q11. Which parameter specifically indicates hydrolytic rancidity in fats and oils?

• Peroxide value
• Acid value (free fatty acids)
• Iodine value
• Anisidine value

Correct Answer: Acid value (free fatty acids)

Q12. For profiling volatile aldehydes and ketones formed during oxidation of cosmetic oils, which analytical technique is most appropriate?

• SPME-GC-MS (headspace solid-phase microextraction followed by GC-MS)
• High-performance liquid chromatography with refractive index detection
• Iodometric titration
• Gravimetric analysis

Correct Answer: SPME-GC-MS (headspace solid-phase microextraction followed by GC-MS)

Q13. A higher iodine value in an oil indicates which of the following regarding rancidity susceptibility?

• Lower unsaturation and lower susceptibility to oxidation
• Higher unsaturation and greater susceptibility to oxidative rancidity
• Higher free fatty acid content causing hydrolytic rancidity
• Greater thermal stability of the oil

Correct Answer: Higher unsaturation and greater susceptibility to oxidative rancidity

Q14. To inhibit metal-catalyzed oxidation in a cosmetic emulsion, which additive is commonly used as a chelating agent?

• EDTA (ethylenediaminetetraacetic acid)
• Glycerol
• Propylene glycol
• Stearic acid

Correct Answer: EDTA (ethylenediaminetetraacetic acid)

Q15. The Schaal oven test is used to evaluate oxidative stability by holding samples at elevated temperature. What does it accelerate?

• Hydrolytic rancidity only
• Both oxidative reactions and generation of secondary volatiles to simulate shelf aging
• Neutralization of acids
• Polymerization of surfactants

Correct Answer: Both oxidative reactions and generation of secondary volatiles to simulate shelf aging

Q16. Which class of fatty acids is most susceptible to oxidative rancidity in cosmetic oils?

• Saturated fatty acids (e.g., stearic acid)
• Monounsaturated fatty acids (e.g., oleic acid)
• Polyunsaturated fatty acids (e.g., linoleic, linolenic acids)
• Trans fatty acids

Correct Answer: Polyunsaturated fatty acids (e.g., linoleic, linolenic acids)

Q17. Which derivatization reagent is widely used to detect and quantify carbonyl compounds (aldehydes/ketones) formed during lipid oxidation?

• p-Anisidine reagent
• 2,4-Dinitrophenylhydrazine (DNPH)
• Thiobarbituric acid (TBA)
• Phenolphthalein

Correct Answer: 2,4-Dinitrophenylhydrazine (DNPH)

Q18. During progressive oxidation of oils, how does peroxide value typically change over time?

• It continuously decreases as oxidation proceeds
• It remains constant throughout oxidation
• It increases during early stages and may decrease later as peroxides decompose to secondary products
• It only changes after formation of free fatty acids

Correct Answer: It increases during early stages and may decrease later as peroxides decompose to secondary products

Q19. In oil-in-water cosmetic emulsions, where is lipid oxidation most likely to initiate?

• Bulk aqueous phase far from droplets
• Oil–water interface (droplet surface) where pro-oxidants and antioxidants interact
• Inside the continuous oil phase only
• At the container cap without contact with formulation

Correct Answer: Oil–water interface (droplet surface) where pro-oxidants and antioxidants interact

Q20. Which volatile oxidation product is often used as a sensitive chemical marker correlating with sensory perception of rancidity?

• Hexanal concentration (volatile aldehyde)
• Water content (%)
• pH of the formulation
• Viscosity at 25°C

Correct Answer: Hexanal concentration (volatile aldehyde)

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