Influence of Temperature–Time Controlled Water Extraction on Water‐Soluble Antioxidant, Polyphenol, Metal Ions, and Spectroscopic Properties of Juniper Herbal Tea

ABSTRACT This study describes the water‐soluble antioxidant activity, total polyphenolic content, metal ions, and spectroscopic features of juniper ( Juniperus communis L.) herbal tea. The UV– vis . absorption and fluorescence (FL) emission spectra of the water and ethanol (EtOH) extracts of the juniper fruits were examined. Juniper fruit water extracts prepared at varying temperatures (70°C–100°C) and times (20–80 min) were analyzed for total antioxidant activity and total polyphenolic content. Increasing extraction temperature and time significantly enhanced the antioxidant activity and total phenolic content of juniper herbal tea, as demonstrated by response surface modeling. The response surface methodology revealed that the antioxidant activity ( R 2 : 0.9490) and total phenolic content ( R 2 : 0.9902) were best described by the cubic model, indicating non‐linear, interactive, and curvature effects between the studied variables. Ideal extraction conditions were identified at 100°C for 80 min, yielding a desirability score of 0.964 for maximizing bioactive compound recovery. The water extract exhibited the highest antioxidant activity (1660 mg/100 g as ascorbic acid equivalent) and the greatest water‐soluble polyphenolic content (1845 mg/100 g as gallic acid equivalent). The metal ion contents of the water extract were found to be 38.49 mg/100 g for K(I), 10.12 mg/100 g for Mg(II), 5.35 mg/100 g for Ca(II), and 2.11 mg/100 g for Na(I). It is recommended that juniper fruit herbal tea can be prepared by boiling the fruits in water at 100°C for 80 min to maximize antioxidant activity, polyphenolic content, and K(I) and Mg(II) levels.