Comparative evaluation of quercetin content in three varieties of Allium cepa using TLC densitometry

Introduction: Herbal medicines are known for their multiple compounds which are responsible for their bioactivity. This creates a challenge in establishing quality control standards for raw materials and the standardization of finished herbal drugs. Currently, there is a common practice of selecting one or more compounds as markers for purposes of identification and quality assessment. In the present study a TLC densitometric method for determining the quantity of quercetin in extracts of outer scales of three different commercial varieties of Allium cepa (onion) was validated according to the ICH guidelines with respect to linearity, sensitivity, precision and accuracy. Materials and Methods: The test samples of all three varieties of A. cepa were prepared with methanol (90%). Similarly, the flavonoid rich fractions of each variety were prepared by fractionation with ethyl acetate. The methanol (90%) extract and flavonoid rich fraction of each variety were subjected to standardization using TLC densitometric analysis using quercetin as a marker compound. Results: The TLC densitometric studies show that the quercetin content was found to maximum in L28 variety of onion. Conclusion: This is a simple and precise method for evaluating the quality of onion extracts. This may be used in future to determine the quantity of the marker – quercetin, and help in standardization of A. cepa extracts.