Influence of Common Cooking Methods on Polyphenolic Composition and Antioxidant Activity of Amaranthus dubius

Abstract

Red spinach (Amaranthus dubius) is a nutrient-dense leafy vegetable known for its high content of polyphenolic compounds and antioxidant activity. However, the stability and bioavailability of these bioactives may be influenced by thermal processing. This study evaluated the effects of three common cooking methods; stir-frying, blanching, and steaming on the total phenolic content (TPC), total flavonoid content (TFC), betacyanin levels, and antioxidant activity of red spinach. Antioxidant potential was assessed using the DPPH radical scavenging assay, while phenolic constituents were profiled via high-performance liquid chromatography (HPLC). Stir-frying significantly enhanced antioxidant activity, achieving the highest DPPH scavenging value (50.79%), alongside increased TPC (86.40 mg GAE/100 g) and TFC (88.21 mg QE/100 g) compared to other treatments. Steaming also improved phenolic retention, particularly preserving rutin, which recorded the highest concentration (10.39 mg/l) compared to other treatments. In contrast, betacyanin levels remained statistically unaffected across treatments. Overall, stir-frying demonstrated superior efficacy in enhancing antioxidant capacity and polyphenolic content. These findings provide valuable insights for optimizing cooking methods to maximize the nutritional quality of red spinach.