RSM-Based optimization of phenolic extraction from black tea and encapsulation with maltodextrin through multiple drying techniques

This study aimed to optimize the extraction of phenolic compounds from black tea (Camellia sinensis) and evaluate their encapsulation using maltodextrin via freeze drying, convective drying, and microwave drying. Response surface methodology (RSM) with a central composite design was employed to investigate the effects of liquid-to-solid ratio (10 to 20 mL/g), extraction temperature (45 to 75 °C), and extraction time (40 to 80 min) on total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity. Optimal extraction conditions (16.30 mL/g, 63.53 °C, 68.99 min) yielded 161.92 milligrams of gallic acid equivalent per 100 grams (mg GAE/100 g) TPC, 154.67 milligrams of quercetin equivalent per 100 grams (mg QE/100 g) TFC, and 82.95% DPPH scavenging activity, with strong model predictability (R2 > 0.96) and low error metrics. Encapsulation significantly influenced bioactive retention, with freeze drying achieving the highest TPC (145.25 ± 1.22 mg GAE/100 g), production yield (81.39 ± 3.50%), and encapsulation efficiency (85.67 ± 2.21%), followed by microwave and convective drying. Microstructure analyses revealed that freeze drying preserved phenolics by forming porous, stable microcapsules, while convective drying caused collapse and bioactive loss. Overall, RSM-optimized extraction with maltodextrin encapsulation proved most effective for stabilizing black tea phenolics in functional and nutraceutical products.