An exemplary embodiment of the present disclosure is directed towards a method for fermenting an onion (Allium cepa) skin with Aspergillus kawachii. Another exemplary embodiment of the present disclosure is directed towards a composition comprising fermented onion skin extract for inhibiting cancer cell growth and a method for preparing that composition. Quercetin is one of the main component of Allium cepa species. Fermentation of the onion skin enhances the quercetin content. The quercetin extracted and purified from the fermented onion skin extract inhibits the cancer cell growth.
