Methyl arachidate

Red pitaya fruit was obtained locally from the vicinity of Sepang, Malaysia. Red pitaya seeds were then manually separated from the red flesh and pulp in the lab. The seeds were cleaned and washed under running water until all the flesh and pulp were removed. The seeds were then dried, crushed into small particles in a mill and kept in a desiccator until further analysis. Liquefied CO₂ (99.9% purity) was supplied by Poly Gas Sdn. Bhd. in a pressurized deep tube cylinder. Immobilized lipase from Rhizomucor miehei (Lipozyme RM IM) was purchased from Novo Nordisk (Denmark). Oleyl alcohol (≥85% purity), n-hexane (≥99% purity) and isopropanol were supplied by Merck (Darmstadt, Germany). Reference standards of fatty acid oleyl esters, including oleyl palmitate, oleyl stearate, oleyl oleate, oleyl linoleate and methyl arachidate, were obtained from Sigma Aldrich (St. Louis, USA). MTT [(3-4,5 dimethyl triazole-2-yl)-2,5-diphenyltetrazolium bromide] was also purchased from Sigma Aldrich (St. Louis, USA), while reconstructed human epidermal model EpiDermTM (EPI-200) and 5% sodium dodecyl sulfate (SDS) solution were obtained from Mattek Corporation (Ashland, USA). All other chemicals were of analytical grade.