Investigation of The Effects of The Different Extraction Conditions on Phenolic Compounds Extraction from Onion Skin

Onion skin, which is a waste from the onion cultivation and processing industry, is one of the richest natural sources of phenolic compounds. In this study, the onion skin was extracted using different solvents and extraction times at various solid:solvent ratios to optimize the total phenolic compounds (TPC) and total flavonoid compounds (TFC) of the onion skin extract. The greatest content of TPC (61.29 mg GAE/g) and TFC (56.83 mg QE/g) of the extracts were obtained with 50% ethanol (ethanol/water; v/v) in 0.2 g/10 mL solid:solvent ratio. The highest TPC value was detected at the end of 90 minutes for 0.2 g/5 mL (55.25 mg GAE/g) and at the end of 120 minutes for 0.2 g/10 mL (60.14 mg GAE/g), while the highest TFC (51.06; 56.55 mg QE/g) value for both solid:solvent ratios were detected at the end of 120 minutes. It was found that the TPC and TFC of the onion skin were strongly influenced by the extraction condition. The findings of this study show that onion skin extract is a good source of phenolic compounds and emphasize that the extraction parameters used in obtaining onion skin extract are important.