Synergistic regulation of drying quality in star anise (Illicium verum Hook. f.) through thermal and non-thermal pretreatments: Roles of structural modification and enzyme influence

Blanching is widely applied as a pretreatment for drying star anise, yet how different pretreatment routes regulate enzyme activity, tissue structure, and final quality remains insufficiently clarified. Here, hot-water blanching (HB), alkaline blanching (AB), radio-frequency treatment (RF), high pressure processing (HPP), and alkaline-assisted HPP (AHPP) were comparatively evaluated, with freezing incorporated as a non-thermal pretreatment option. Drying behavior, water-state redistribution, color development, enzyme activities, bioactive compounds, and aroma-related attributes were assessed to elucidate structure-function relationships. Freezing-assisted pretreatments provided the most consistent improvement in dehydration, reducing the overall drying time from ∼19 h (untreated) to 13–15 h and markedly decreasing residual bound/immobilized water after drying. AHPP resulted in the highest essential oil yield (1.92-fold), while freezing combined with HPP produced the highest redness parameter ( a ⁎  = 14.96), closer to market-typical coloration. Although HB fully inactivated PPO and POD, it led to substantial color deterioration. Total phenolic and flavonoid contents decreased significantly after AHPP ( p < 0.05 ), likely due to enhanced diffusion/leaching losses. Overall, the results indicate that pretreatments modulate enzyme activities and quality primarily through controlled structural alteration, and freezing-assisted strategies offer a practical route to improve drying efficiency while tuning key quality attributes of dried star anise.