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

Authors: Hwang, Hong-Sik; Liu, Sean; Moser, Jill; Singh, Mukti; VAN TASSEL, DAVID - The Land Institute

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2024
Publication Date: 1/25/2024
Citation: Hwang, H., Liu, S.X., Moser, J.K., Singh, M., Van Tassel, D.L. 2024. Composition and oxidative stability of silflower (Silphium integrifolium) seed oil and its potential as a new source of squalene. Journal of the American Oil Chemists' Society. https://doi.org/10.1002/aocs.12814.
DOI: https://doi.org/10.1002/aocs.12814

Interpretive Summary: Perennial crops are known to have many advantages over annual counterparts such as deeper rooting depth, better drought tolerance, and less tillage required. They can reduce soil erosion, increase nutrition retention, store carbon dioxide, and enhance agricultural sustainability. Silflower is a perennial plant in the sunflower family native to the central United States. Previous studies have revealed that it has a great potential as a good protein source and a new oilseed crop. This study analyzed the composition of silflower oil and examined its oxidative stability to evaluate the feasibility as a new healthy edible oil. The oil extracted from silflower seeds in this study was found to have 86.2% unsaturated fatty acid, which was similar to sunflower oil. It also contained high amounts of polar substances and phenolic compounds, which may be beneficial to human health. It was found that silflower oil oxidized faster than sunflower oil. However, this study developed some methods that can slow down the oxidation of oil. In addition, noteworthily, 4.89% squalene was isolated from silflower oil. Use of squalene in nutraceutical, cosmetic, pharmaceutical, and vaccine industries is growing fast due to its antioxidant, anticancer, immune stimulating, and skin-smoothing activities. Currently shark liver oil is the most common source, but industries are seeking alternative sources because of the international concern on overfishing as well as potential risks of toxic compounds in the oil. The current best plant sources of squalene are olive oil and amaranth oil, which contain 0.15-0.75% and 6-8% squalene, respectively. Therefore, the high content of squalene in silflower oil indicates the potential application of this oil as a promising alternative source of squalene. The information provided by this study will help to utilize silflower oil as a new edible oil and as a great plant source of squalene.

Technical Abstract: 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% (w/w), 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% (w/w), 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.