Correlation Analysis between Color and Metabolites of Illicium verum (Star Anise) Treated with Different Blanching Processes

In response to the problems of low efficiency and unstable quality in the traditional processing of star anise, this study systematically explored the impact of different blanching techniques on the “color-metabolite” correlation network of star anise and analyzed the correlation between color parameters and characteristic metabolites. An electronic nose and gas chromatography-mass spectrometry (GC-MS) were used to analyze the effects of six blanching techniques (boiling water, steam, microwave blanching alone and combined with sweating) on the odor and color of star anise. Non-targeted GC-MS-based metabolomics was used for analysis of volatile metabolites, and the non-volatile metabolites shikimic acid, total phenols, and total flavonoids were quantitatively detected. The results showed that a total of 69 volatile metabolites were identified across the six blanched samples. Using variable importance in projection (VIP) value > 1 as the threshold, orthogonal partial least squares discriminant analysis (OPLS-DA) identified 24 differential metabolites to effectively distinguish star anise treated with different blanching techniques. The relative contents of the characteristic components trans-anethole ((83.93 ± 8.33)%) and anisaldehyde ((1.55 ± 0.45)%) were the highest in the sample treated with microwave blanching combined with sweating. Traditional boiling water blanching effectively retained shikimic acid ((90.35 ± 0.84) mg/g) and total phenols ((68.00 ± 4.10) mg/g), and maintained the diversity of volatile metabolites (48). The total flavonoid content in microwave-treated star anise was 57.8% higher than that star anise subjected to traditional boiling water blanching, but the number of volatile metabolites was smaller (17). Pearson’s correlation analysis showed that the color parameters L* and b* were positively correlated with trans-anethole, anisaldehyde, anisole, total phenols, and shikimic acid (P < 0.05), and a* was positively correlated with total flavonoids (P < 0.05). In terms of color and odor, star anise processed by microwave blanching and steam blanching met the standards for da-hong star anise. Microwave blanching optimized the color and flavor, while boiling water blanching was more conducive to the retention of active components. The color values L*, a*, and b* can be used as indicators for process optimization, providing a basis for the targeted production of star anise products with highly active components or superior sensory characteristics.