Effects of drying techniques on nutritional composition, digestibility, and antioxidant activity of Rumex obtusifolius L.

Rumex obtusifolius L., a wild medicinal plant rich in bioactive compounds, exhibits antioxidant, antimicrobial, and pharmacological properties, which may be modulated by processing and digestion. This study investigated the effects of oven-drying (O) and freeze-drying (F) on nutritional composition, total phenolics (TPC), flavonoids (TFC), and antioxidant activity (ABTS, DPPH, FRAP) in inflorescence (IO, IF), leaf (LO, LF), stem (SO, SF), and root (RO, RF). F produced powders with lower browning index and moisture; protein was highest in L (29%) and R; lipids in R and S (5–10%); fiber was greatest in S (75%). O favored fiber retention in stems and roots; F in inflorescences (54% total). LO had the highest K, Mg, Na, Cu, Mn, and S; IO the highest Ca and Li; roots the highest Fe. highest TFC (1287 mg CE/100 g O; 860 mg CE/100 g F), and antioxidant activity was verified in IO, followed by R, L, and S. In vitro digestion showed increases (>100%): TFC-RO gastric (+284%), TPC-RO gastric (+181%), DPPH-RF gastric (+207%), ABTS-SO gastric (+284%) and intestinal (+335%), ABTS-SF intestinal (+450%), ABTS-LF intestinal (+454%), and FRAP-LO gastric (+133%). Inflorescences exhibited degradation to phenolic and antioxidant activities <50% bioaccessibility, and minimal retention to RO (TPC +8%, FRAP +2%). Drying method and plant part strongly modulate the release and transformation of bioactive compounds during digestion. Optimizing plant part selection, drying technique, and understanding digestive bioaccessibility in R. obtusifolius can enhance nutrient and antioxidant release, supporting functional food innovation and sustainable use of underutilized botanical resources.