Composition and oxidative stability of silflower (Silphium integrifolium) seed oil and its potential as a new source of squalene

Silphium integrifolium Michx. (silflower), a perennial plant, is of great interest as a potential new oilseed crop due to its long, strong, deep, extensive root systems, which can prevent erosion, capture dissolved nitrogen, and out-compete weeds eliminating the need for frequent irrigation and herbicide uses. In this study, oil was extracted from unhulled silflower seeds, and its composition and oxidative stability were evaluated. The oil content in unhulled silflower seeds was 15.2% (wt/wt), and its fatty acid composition was similar to that of sunflower oil. The level of total polar compounds (TPC) in the oil was 12.3% (wt/wt), and the content of total phenolics was 1.12 mg gallic acid equivalent (GAE)/g oil. Noteworthily, 4.89% squalene was isolated from silflower oil indicating its potential application as an alternative source of squalene. Silflower oil had lower oxidative stability as indicated by the oxidative stability index (OSI) at 110°C and thermogravimetric analysis (TGA), presumably due to its high level of chlorophyll (1002.8 mg/kg). Even after a typical refining process involving degumming, alkali refining, and bleaching with Fuller's earth, silflower oil contained 725.5 mg/kg chlorophyll, and its oxidative stability was not improved. Further treatments with bleaching agents including bentonite, sepiolite, and Tonsil® lowered the chlorophyll level to 4.2, 474.5, and 38.5 mg/kg, respectively, and some aspects of oxidative stability were improved and better than those of refined sunflower oil. This study presents the potential of silflower oil as new edible oil and a great plant source of squalene.