Extraction of phenolic compounds and antioxidant activity from garlic husk using carbon dioxide expanded ethanol

Garlic has been used as functional food and traditional medicine for many centuries. However, the garlic husk, which contributes 25% of garlic bulk, was regarded as agricultural waste. Recent studies have found that the extract from garlic husk contains phenolic compounds with antioxidant and anti-bacterial activities, which can be applied in food and pharmaceutical industries. In order to reduce the draw back of conventional methods, carbon dioxide expanded ethanol (CXE) was used to extract phenolic compounds from garlic husk. The extraction was carried out in ranges of temperature (50–200 °C), CO₂ flow rate (0.5–2 mL/min) at constant pressure (10 MPa). The conventional Soxhlet extraction was also done to investigate the efficiency of CXE over conventional method. The high amount of phenolic compounds of 56.26 mg GAE/g of dried garlic husk and antioxidant activity (IC₅₀) of 0.41 mg/mL was obtained at temperature of 200 °C and CO₂ flow rate of 0.5 mL/min. The five major phenolic compounds identified from CXE method were garlic acid, 4-hydrobenzoic acid, caffeic acid, p-coumaric acid, and trans-ferulic acid.