Vitamin Analysis: Methods with emphasis on B-vitamin microbiological assays MCQs With Answer

Vitamin Analysis: Methods with emphasis on B‑vitamin microbiological assays MCQs With Answer

This quiz collection is designed for M.Pharm students studying MPA 104T Food Analysis, focusing on analytical approaches for vitamins with special emphasis on microbiological assays used for B‑vitamins. The questions cover principles of microbiological assays, choice of test organisms, sample preparation and extraction, growth media and detection formats (turbidimetric, plate, agar diffusion), standardization, validation parameters, interferences, and comparison with chemical methods like HPLC. These MCQs aim to deepen understanding of method selection, assay performance, troubleshooting and regulatory considerations relevant to quantitative determination of B‑vitamins in complex food and pharmaceutical matrices.

Q1. Which principle best describes the basis of microbiological assays for quantifying B‑vitamins?

• Direct spectrophotometric absorption of vitamin chromophores
• Proportional growth response of a microorganism to the vitamin concentration
• Chromatographic separation followed by mass spectrometry
• Electrochemical oxidation current proportional to vitamin level

Correct Answer: Proportional growth response of a microorganism to the vitamin concentration

Q2. Which microorganism is classically used for microbiological assay of vitamin B12?

• Lactobacillus rhamnosus
• Escherichia coli
• Lactobacillus delbrueckii subsp. lactis
• Enterococcus faecalis

Correct Answer: Lactobacillus delbrueckii subsp. lactis

Q3. What is the main advantage of turbidimetric microbiological assays over plate assays?

• Higher selectivity for vitamers
• Ability to directly measure optical growth for rapid quantitation
• No need for calibration with standards
• Less sensitivity to matrix effects

Correct Answer: Ability to directly measure optical growth for rapid quantitation

Q4. For folate (vitamin B9) microbiological assays, which pre‑treatment is commonly required to convert polyglutamate forms to monoglutamate?

• Saponification with strong base
• Enzymatic deconjugation with conjugase (folate deconjugase)
• Direct dilution in water without treatment
• Oxidation with potassium permanganate

Correct Answer: Enzymatic deconjugation with conjugase (folate deconjugase)

Q5. Which of the following is a critical validation parameter for microbiological assays determining B‑vitamins?

• Retention time reproducibility
• Limit of detection and limit of quantitation, linearity, precision and recovery
• Signal‑to‑noise ratio at m/z 100
• Column efficiency (theoretical plates)

Correct Answer: Limit of detection and limit of quantitation, linearity, precision and recovery

Q6. Why are microbiological assays still used despite the availability of HPLC and LC‑MS methods for B‑vitamin analysis?

• They are always faster than chromatographic methods
• They measure biologically active vitamin equivalents and are cost‑effective for routine labs
• They do not require any calibration standards
• They can directly distinguish all vitamers with high specificity

Correct Answer: They measure biologically active vitamin equivalents and are cost‑effective for routine labs

Q7. Which factor most commonly causes positive bias in microbiological assays for B‑vitamins when analyzing fortified foods?

• Incomplete extraction of the vitamin
• Presence of growth‑promoting matrix components that mimic vitamin activity
• Use of sterile technique during dilution
• Low incubation temperature

Correct Answer: Presence of growth‑promoting matrix components that mimic vitamin activity

Q8. In a turbidimetric microbiological assay, what is the typical relationship between optical density (OD) and vitamin concentration in the working range?

• OD decreases linearly with increasing vitamin concentration
• OD is independent of vitamin concentration
• OD increases in a sigmoidal or linear fashion with vitamin concentration within the calibrated range
• OD oscillates unpredictably due to microbial metabolism

Correct Answer: OD increases in a sigmoidal or linear fashion with vitamin concentration within the calibrated range

Q9. Which B‑vitamin is most commonly assayed microbiologically using Lactobacillus casei or Lactobacillus rhamnosus strains?

• Vitamin B1 (thiamine)
• Vitamin B2 (riboflavin)
• Vitamin B6 (pyridoxine)
• Folate (vitamin B9)

Correct Answer: Folate (vitamin B9)

Q10. What is the recommended way to prepare samples containing protein‑bound B‑vitamins prior to microbiological assay?

• Direct inoculation without any extraction
• Acid hydrolysis followed by neutralization or enzymatic treatment to release the bound vitamers
• Heating to 50°C for 5 minutes only
• Filtration through 0.45 µm without chemical treatment

Correct Answer: Acid hydrolysis followed by neutralization or enzymatic treatment to release the bound vitamers

Q11. Which microbiological assay format is most suitable for high‑throughput screening of multiple samples for B‑vitamin content?

• Plate count colony forming unit assay
• Turbidimetric assay in microtiter plates measuring OD
• Agar diffusion well assay on large plates
• Thin layer chromatography bioautography

Correct Answer: Turbidimetric assay in microtiter plates measuring OD

Q12. During assay standardization, why is it important to prepare a standard curve using the same biological matrix as the samples when possible?

• Matrix matched standards reduce matrix effects and give more accurate quantitation
• It reduces microbial contamination
• It prolongs the shelf life of standards
• It eliminates the need for blanks

Correct Answer: Matrix matched standards reduce matrix effects and give more accurate quantitation

Q13. Which of the following conditions is most important to control during the incubation phase of a microbiological vitamin assay?

• Light intensity above the plate
• Incubation temperature and time to ensure consistent organism growth response
• Magnetic field strength in the incubator
• Orientation of culture tubes in the rack

Correct Answer: Incubation temperature and time to ensure consistent organism growth response

Q14. What is the primary limitation of microbiological assays when distinguishing between vitamers of the same B‑vitamin?

• Microbial growth response often cannot differentiate between vitamers with similar biological activity
• They always degrade labile vitamers
• They cannot detect any vitamers in fortified samples
• They provide too much structural information

Correct Answer: Microbial growth response often cannot differentiate between vitamers with similar biological activity

Q15. Which practice helps minimize interference from antibiotics or antimicrobial residues present in sample extracts for microbiological assays?

• Omitting sterilization of media
• Purifying extracts or performing additional cleanup such as solid‑phase extraction
• Increasing inoculum size regardless of interference
• Shortening incubation time to under 1 hour

Correct Answer: Purifying extracts or performing additional cleanup such as solid‑phase extraction

Q16. What does expression of results in International Units (IU) for certain B‑vitamins reflect in microbiological assays?

• Mass concentration in mg/L only
• Biological activity relative to an international reference standard
• Volume of sample required for the assay
• The number of microbial cells produced

Correct Answer: Biological activity relative to an international reference standard

Q17. Which validation experiment assesses whether other sample components affect the accuracy of the microbiological B‑vitamin assay?

• System suitability test
• Spike recovery or matrix effect study
• Blank run with sterile water only
• Column pressure test

Correct Answer: Spike recovery or matrix effect study

Q18. In comparing HPLC and microbiological assays for B‑vitamins, which statement is TRUE?

• HPLC always measures biological activity while microbiological assays measure individual vitamers
• Microbiological assays measure total biologically active equivalents, while HPLC separates and quantifies individual vitamers
• Both methods are identical in sample preparation and specificity
• HPLC cannot be used for fortified foods

Correct Answer: Microbiological assays measure total biologically active equivalents, while HPLC separates and quantifies individual vitamers

Q19. Which parameter must be checked to ensure linearity in a microbiological assay standard curve for a B‑vitamin?

• That the optical density is inversely proportional to concentration across the entire range
• That response (growth or OD) is directly proportional to vitamin concentration within the defined working range
• That all standards show zero growth
• That the incubation time varies for each standard

Correct Answer: That response (growth or OD) is directly proportional to vitamin concentration within the defined working range

Q20. Which regulatory or standardization body methods are commonly referenced for validated microbiological assays for vitamins in foods?

• USP, AOAC and ISO methods for vitamin microbiological assays
• IEEE protocols for electrochemical sensors
• EPA methods for air quality only
• Pharmacopoeial methods for antibiotics only

Correct Answer: USP, AOAC and ISO methods for vitamin microbiological assays

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