Physicochemical properties of Gac (Momordica cochinchinensis (Lour.) Spreng) seeds and their oil extracted by supercritical carbon dioxide and soxhlet methods

Gac seeds are high in oil, but there are few studies on its extraction and characteristics. This study aimed to characterise Gac seeds and investigate the physicochemical properties of Gac seed oil extracted with supercritical carbon dioxide (SC-CO₂) and hexane (Soxhlet). The Gac seed kernel accounted for 66.4 ± 2.7% of the seed weight, and 53.02 ± 1.27% of it was oil. The SC-CO₂ oil had a higher quality than the Soxhlet oil for important criteria, such as peroxide (0.12 ± 0.02 vs. 1.80 ± 0.01 meq O₂/kg oil), free fatty acid (1.74 ± 0.12 vs. 2.47 ± 0.09 mg KOH/g oil) and unsaponifiable matter (33.2 ± 1.5 vs. 52.6 ± 2.4 g/kg) values, respectively. It also had a better colour (light yellow vs. dark greenish brown) and a higher antioxidant capacity measured with the DPPH (52.69 ± 0.06 vs. 42.98 ± 0.02 µmol Trolox equivalent/g oil) and ABTS (2.10 ± 0.12 vs. 1.52 ± 0.06 µmol Trolox equivalent/g oil) assays. However, a higher yield (53.02 ± 1.27 vs. 34.1 ± 0.8%) was obtained for the Soxhlet oil. Unless refined, the oils would not be edible due to their high unsaponifiable matter, but the SC-CO₂ oil would need less refining. Alternatively, the high unsaponifiable matter in the oil, especially in the Soxhlet oil, may make it useful for medicinal purposes.