Optimization of the extraction process and in vitro antioxidant capacity analysis of selenium-containing proteins...

Current research lacks established approaches to concurrently achieve a high extraction yield with preserved bioactivity and to synergistically enhance plant selenium content and protein quality through agronomic practices. This study tested whether alkaline extraction maximizes selenoprotein yield without compromising antioxidant activity and whether foliar selenium application increases both fruit selenium content and the antioxidant capacity of extracted proteins. The fruits of the selenium-hyperaccumulator plant Cynanchum thesioides and its variant were utilized as experimental materials to systematically explore the differences in nutritional components and selenium (Se) content among various fruit types. The extraction conditions for Se-containing proteins using five distinct strategies were optimized via Response Surface Methodology (RSM), focusing on the extraction mechanism of alkaline extraction and the in vitro antioxidant activities of the derived Se-containing proteins. The findings revealed that the large fruits of the variant contained the highest selenium content (1.06 ± 0.02 mg/kg, n = 3). Under the optimal alkaline extraction conditions (solid-to-liquid ratio of 1:22.7, temperature of 44.62 °C, and NaOH concentration of 0.243 mol/L), the extraction yield of Se-containing proteins was 5.9 3 ± 0.15 mg/g (n = 3), significantly higher than those obtained by other methods (P < 0.05). Foliar application of selenomethionine (2 mg/L) significantly enhanced the selenium accumulation in the fruits to 1.92 ± 0.11 mg/kg (n = 3) and improved the antioxidant efficacy of the alkaline -extracted proteins. At a concentration of 5 mg/mL, the extract demonstrated strong antioxidant activity, with scavenging rates of 53.74% for superoxide anion (O₂⋅-), 68.73% for hydroxyl radical (⋅OH), and 62.58% for DPPH radical (DPPH⋅), along with a ferric reducing antioxidant power (FRAP) value of 1.33 ± 0.05 AU. This study offers a theoretical foundation and application prospects for the development of C. thesioides Se-containing proteins as antioxidant dietary components or functional food ingredients, encapsulating both extraction mechanisms and the functional activities.