Enhanced angiotensin-converting enzyme inhibition and antioxidant activities through synergistic green tea and black rice extracts

The study investigated the synergistic effects of green tea extract (GTE) and black rice extract (BRE) on total phenolic content, flavonoid content, antioxidant activities and angiotensin-converting enzyme (ACE) inhibition. The influence of GTE concentrations (14.64–85.36 % w/w) and pH levels (3.59–6.41) was analyzed by regression and response surface methodology. Optimized conditions of synergistic effect (85.36 % w/w GTE and 14.64 % of BRE at pH 6.0) yielded the highest antioxidant activities (DPPH IC₅₀ = 0.112±0.015 mg/mL, ABTS = 89.14±1.58 mmol TE/100 g, FRAP = 373.66±3.42 mmol Fe²⁺/100 g), the highest total phenolic (120.98±1.60 mmol GAE/100 g), flavonoid contents (15.28±1.07 mmol QE/100 g) and ACE inhibitory activity (IC₅₀ = 6.125±0.106 μg/mL). Therefore, this condition was selected to produce the combined extract for determining the combination index (CI). The CI was 0.349±0.075 for DPPH and 0.505±0.019 for ACE inhibition, indicating confirmation of a synergistic effect. These findings suggest that the combined extract could serve as a valuable functional ingredient, enhancing access to bioactive-rich resources for nutritionally supportive and sustainable diets. With potential applications in food systems and healthcare, this agro-ingredient may contribute to improved access to resources for blood pressure management and non-communicable disease (NCDs) prevention, aligning with broader goals in nutrition and health equity.