Squalene, fatty acids, and minor oil constituents in silflower (Silphium integrifolium) oils from nine varieties grown in Minnesota

Our previous study found that silflower ( Silphium integrifolium Michx.) seed oil had a squalane content and great potential as a new edible oil. The current study aimed to examine the squalene level and other properties with thirty silflower oils from nine genotypes grown in three locations in Minnesota in 2022 and 2023. Oil contents of 30 different seeds determined by hexane extraction of unhulled seeds were 19.41–25.92 %, and squalene levels in oils were 2.98–4.07 %. Two major fatty acids, linoleic acid (C18:2) and oleic acid (C18:1), were 66.52–73.62 % and 15.25–20.32 %, respectively. Contents of α-tocopherol, total phenolics, chlorophyll, free fatty acid, and total polar compounds contents were 277.5–765.6 μg/g, 16.29–33.97 mg GAE/100 g oil, 179.2 mg/kg - 977.6 mg/kg, 0.07 % - 0.53 %, and 5.21–11.18 %, respectively. Correlations between oil properties and growing conditions during two different growing seasons, P1 (90 days until flowering) and P2 (flowering to harvest), were analyzed. Oil content had a positive correlation with P1 temperature. Squalene content in oil was higher with lower P1 precipitation and higher P2 maximum temperature and precipitation. Oleic acid content increased, and linoleic acid content decreased when P2 temperature and precipitation were high. In general, α-tocopherol, total phenolics, free fatty acids, and total polar compounds negatively correlated with P1 temperature and precipitation while chlorophyll level had the opposite trend. This study provides more data on the properties of silflower oil and preliminary insight into the factors affecting these properties. • Squalene levels in 30 silflower oils were 2.98–4.07 %. • Oil content determined by hexane extraction of unhulled seeds ranged from 19.41 % to 25.92 %. • Contents of linoleic acid and oleic acid were 66.52–73.62 % and 15.25–20.32 %. • Content of α-tocopherol was 277.5–765.6 μg/g. • Squalene content was affected by precipitation and temperature.