CONCLUSIONS
Silflower oil was extracted from unhulled silflower seeds with hexane and compared with the oil extracted from unhulled sunflower seeds. The oil content in unhulled silflower seeds was 15.2 % (w/w), and its fatty acid composition was very similar to that of sunflower oil. Silflower oil had high contents of TPC (12.35%, w/w), total phenolics (1.12 mg GAE/g oil), and chlorophyll (1002.8 mg/kg). It should be noted that it had a high squalene level (4.89%, w/w, isolated yield) indicating its potential application as a new plant source of squalene. Crude silflower oil had lower radical scavenging activity and oxidative stability than crude sunflower oil as indicated by ABTS assay, OSI, and TGA. The chlorophyll level of silflower oil was lowered, but still high (725.5 mg/Kg) after refining by a general refining process involving degumming, alkali refining, and bleaching with Fuller’s earth. The oxidative and thermal stabilities of silflower oil decreased after the refining process.
Further treatments with bentonite, sepiolite, and Tonsil® significantly lowered the chlorophyll level to 4.2, 474.5, and 38.5 mg/kg, respectively. Some aspects of oxidative stability improved by these bleaching agents. For example, the ABTS assay increased by treatments with bentonite and Tonsil®, the OSI slightly increased by Tonsil®, and the thermal stability determined by TGA increased by all three bleaching agents.
More studies should be conducted to understand the factors affecting the oxidative stability of silflower oil and to further improve the oil quality. Oils from unhulled and hulled seeds may have different properties, crop year and harvest time may affect the level of chlorophyll, and different extract methods may result in different oil properties. With the given seeds and the oil extracted under the experimental conditions used in this study, it could be concluded that silflower oil, which can be produced from the perennial plant with many advantages such as higher drought tolerance and less tillage required, has a great potential as a new edible oil. This study also found that silflower oil can be a great plant source of squalene.