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.