Front-face synchronous fluorescence spectroscopy coupled with PLSR for rapid quantitative analysis of Chinese...

Chinese five-spice powder is a cornerstone of Chinese cuisine, yet its commercial formulations frequently deviate from traditional recipes, leading to quality-fraud issues that necessitate rapid, non-destructive control methods. This study pioneers the application of front-face synchronous fluorescence spectroscopy (FFSFS) combined with partial least squares regression (PLSR) for simultaneous quantification of all five constituents: star anise, Sichuan pepper, fennel seed, cinnamon stick, and clove bud. One hundred lab-made calibration samples and twenty external validation samples were prepared across typical formulation ranges. FFSFS spectra (λ_ex = 250-600 nm, Δλ = 30-200 nm) were acquired using front-face geometry to mitigate scattering effects. Variable importance in projection (VIP) scores identified 2188 key variables, with highest scores mapping to flavonoid emissions (λ_ex = 450-600 nm, Δλ = 80-180 nm) and secondary clusters linked to protein tryptophan and phenylpropanoid markers. Principal component analysis (PCA) achieved clear species discrimination based on these fluorophore signatures. The mass fraction (wt%) of all five target constituents was simultaneously quantified by PLS2 which yielded component-specific accuracy: star anise and Sichuan pepper were predicted with high fidelity (R²_p = 0.830 and 0.825; RPD = 2.1), while fennel seed, cinnamon, and clove showed moderate predictability due to matrix interference and weak fluorescence. VIP analysis elucidated the chemical origins of these performance differences, linking model robustness to fluorophore abundance and stability. This FFSFS-PLSR framework provides the first rapid, non-targeted fingerprinting method for five-spice powder quantification, offering a powerful quality control tool with clear pathways for enhanced performance.