Effects of different Forsythia suspensa leaf drying methods on volatile profile, taste-active compounds, and functional properties of millet-forsythia biscuits

Introduction: leaf biscuits. This study aimed to evaluate the influence of different drying techniques on the flavor profile, taste-active compounds, microstructure, and antioxidant capacity of these biscuits. Methods: Four drying methods-sun drying (SD), vacuum freeze drying (VFD), vacuum drying (VD), and hot air drying (HAD)-were compared. Volatile compounds were analyzed using dichloromethane extraction coupled with GC-MS and principal component analysis (PCA). Aroma and taste profiles were assessed with an electronic nose (E-nose) and electronic tongue (E-tongue). Free amino acids, texture, microstructure (SEM), and antioxidant activities (DPPH and ABTS assays) were also measured. Results: A total of 86 volatile compounds were identified, with aldehydes, alcohols, and ketones as the major contributors. VFD samples had a 28.4% higher total volatile peak area than HAD samples, with better preservation of C6-C9 aldehydes and aromatic compounds. PCA of E-nose data explained 86.7% of variance and clearly distinguished among drying treatments. Taste analysis showed HAD samples had higher overall taste intensity, while VFD samples preserved taste-active amino acids, including glutamic acid and aspartic acid (18.6% and 14.2% higher than HAD, respectively). Texture analysis indicated HAD increased hardness by 21%, whereas VFD improved crispness and cohesiveness. SEM images revealed that VFD maintained a uniform porous structure, whereas HAD caused structural collapse. VFD samples exhibited the highest antioxidant activity (DPPH 67.29%). Discussion/conclusion: Differences in quality were attributed to the drying mechanisms. VFD minimized thermal degradation and volatile loss, preserving native compounds and bioactive substances. VD provided intermediate preservation, limiting oxidation but causing some compositional changes. HAD promoted lipid oxidation and Maillard reactions, while SD led to gradual oxidation and volatile loss. Vacuum freeze drying effectively enhanced flavor, umami amino acid content, microstructure, and antioxidant activity, providing valuable guidance for optimizing functional cereal-based product processing.