Influence of processing on star anise quality: Appearance, chemical composition, and bioactivity

Star anise has been used as a spice for thousands of years, yet the effects of processing on its appearance and quality remain unclear. In this study, we systematically evaluate the effects of pretreatment (pre-blanching) and drying methods (sun, shade, and hot-air drying) on the appearance, phytochemical composition, antioxidant activity, and quality formation mechanism of star anise. The key finding is a temperature-dependent trade-off: low-temperature drying (sun, shade, and hot air drying ≤60 °C) produced brown samples with low brightness (L*) and yellowness (b*), accompanied by markedly lower levels of total flavonoids, phenolics, tannins, and epicatechin. In contrast, high-temperature treatments (pre-blanching and hot-air drying ≥80 °C) yielded yellowish-brown samples with substantially higher bioactive compound contents, along with correspondingly stronger antioxidant activity. In addition, odor was unaffected by pre-blanching but was absent in hot air dried samples, indicating that drying method governs volatile retention. Mechanistically, high temperature inactivated peroxidase while releasing bound phenolics, thereby suppressing enzymatic browning and promoting phenolic accumulation. Correlation analyses confirmed that L* and b* positively correlated with phenolic content and antioxidant activity. Overall, processing temperature, rather than pretreatment, is the primary determinant of star anise quality. High temperature processing (pre blanching or hot air drying ≥80 °C) is an effective strategy to produce star anise with superior phenolic profiles and antioxidant capacity, albeit at the cost of characteristic odor loss.