Sensory-Driven Formulation Optimization, Physicochemical Properties, Antioxidant Activity, and Structural Characterization of Erythritol-Based Green Tea Cookies

Although green tea is a well-known source of polyphenols with pronounced antioxidant properties, few studies have explored its use in erythritol-based baked products. In this study, an erythritol-based green tea cookie (GTC) was developed using green tea powder (GTP), butter, and erythritol. The formula was then optimized by single-factor experiments and a Box–Behnken response surface design. The optimal formulation contained 7.88 g GTP, 72.13 g butter, and 39.63 g erythritol, with a predicted sensory score of 80.35, while the validated sensory score was 81.07 ± 1.87 as evaluated by 12 trained panelists. The optimized cookies exhibited a 4.5-fold increase in total phenolic content compared with the control butter cookies (BC) and significantly enhanced antioxidant activity, with a ferric reducing antioxidant power (FRAP) value of 96.06 mg AAE/g dry weight (DW). GTP also modified the color and textural attributes of the cookies. Scanning electron microscopy (SEM) revealed a denser and more homogeneous microstructure than that of the control butter cookies (BC), with the pore area fraction reduced from 17.8% to 8.0%. Fourier transform infrared (FTIR) analysis indicated a redistribution of protein secondary structural elements, suggesting possible structural rearrangement. Overall, these findings demonstrate that GTP enhances the antioxidant capacity and modifies the quality attributes of erythritol-based cookies, providing a potential approach for developing functional erythritol-based products.