Star Anise Oil

Trans-Anethole (CAS 104-46-1) is the dominant phenylpropene in star anise oil, commonly accounting for approximately 80–90% or more, and provides the sweet anise, licorice-like, and warm-spicy character that makes it the key GC marker for odour quality and composition (Sharafan et al., 2022, Molecules). Our minimum anethole specification of 87% falls within the common composition range of commercial star anise oil; because trans-anethole melts at approximately 21°C, oils rich in anethole may become cloudy, crystallise, or solidify at low temperature, so freezing point is a useful supporting indicator of composition and storage behaviour but does not replace GC analysis. Trans-Anethole can isomerise under light and elevated temperature to the toxicologically more concerning cis isomer, so the oil should be stored tightly closed, protected from light, and away from prolonged heat exposure; cis-anethole is normally present only at trace levels in natural star anise oil but should still be monitored by batch GC (Sharafan et al., 2022, Molecules). Trans-Anethole carries a skin-sensitisation classification (H317), but the hazard classification, cosmetic use level, and labelling obligations of complete star anise oil must be assessed from its actual composition, target product, and local regulations rather than inferred directly from the SDS of the isolated substance.

In China, food-grade natural anethole is normally produced from star anise oil by high-efficiency fractionation and/or freeze crystallisation; GB 1886.167-2015 requires not less than 99.0% trans-anethole and sets a limit for cis-anethole (National Health and Family Planning Commission of China, 2015, GB 1886.167-2015 National Food Safety Standard—Food Additive Anethole). The oil can first be cooled to crystallise the higher-freezing trans-anethole, while more terpene components, anisaldehyde, and other lower-freezing constituents remain in the mother liquor; crushing and centrifugation of the crystals then provide a higher-purity crude anethole fraction. An optimisation study by Lu and co-authors used freeze crystallisation at approximately 5°C for 20 hours with separation of approximately 20-mesh crystals, followed by rectification at approximately 666.61 Pa and 140°C, reporting 99.8% purity and 94.1% overall recovery; these are process-development reference values, not fixed conditions for every plant, and should be adjusted for feed anethole content, crystallisation behaviour, heat transfer, and target recovery (Lu et al., 2009, Food and Fermentation Industries). For high-purity grades, freeze crystallisation primarily enriches anethole and reduces the rectification load, while vacuum rectification removes remaining close-boiling components; final release should be based on batch GC results for trans- and cis-anethole rather than freezing point alone.

The connection between star anise and oseltamivir phosphate comes from shikimic acid in the star anise fruit, not from star anise essential oil; shikimic acid is a water-soluble, non-volatile metabolite, whereas the steam-distilled oil consists mainly of volatile constituents such as trans-anethole (Sharafan et al., 2022, Molecules). Shikimic-acid content and practical extraction yield from dried star anise fruit vary with origin, batch, and process, with public sources commonly reporting a commercial extraction range of approximately 3–7%; shikimic acid is then converted through multistep chemistry to oseltamivir phosphate (Ghosh et al., 2012, Process Biochemistry). Early industrial routes used natural (−)-shikimic acid as the starting material and involved epoxide and azide chemistry, while shikimic acid can now also be supplied through engineered Escherichia coli fermentation to reduce dependence on seasonal star anise feedstock (Federspiel et al., 1999, Organic Process Research & Development; Sagandira et al., 2020, Pharmaceuticals). Bulk star anise oil should therefore be sourced and described for its trans-anethole content, odour, and food or fragrance use; unless a separate, validated shikimic-acid extraction and pharmaceutical-intermediate supply chain is involved, it should not be claimed as a Tamiflu or oseltamivir pharmaceutical intermediate.