Rutin Degradation and Bioactivity Alterations in Capparis spinosa L. Fruits Subjected to Traditional Salting: A Comparative Study of Fresh and Salt-Cured Extracts

Capparis spinosa L. (caper) fruits are valued for their high content of bioactive flavonoids, particularly rutin, which exhibits significant antioxidant and pharmacological properties. Traditional salting is widely employed for caper preservation, yet its impact on phytochemical stability remains inadequately characterized.This study evaluated the effects of solvent polarity and traditional salting duration on rutin content, antioxidant capacity, and antimicrobial activity of Syrian C. spinosa fruits collected from the Hama Governorate. Soxhlet extraction was performed using ethanol (polar, ε = 24.3), chloroform (intermediate, ε = 4.8), and n-hexane (non-polar, ε = 1.9) on fresh and salt-cured (1 week, 2 weeks, 1 month) fruits. Rutin was quantified by HPLC-DAD with comprehensive method validation (linearity r² = 0.9994; recovery 98.7 ± 2.1%; LOD 0.85 µg/mL; LOQ 2.18 µg/mL). Antioxidant activity was assessed by DPPH radical scavenging assay. Antimicrobial activity was evaluated against Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853 using agar well diffusion. Fresh ethanolic extracts exhibited the highest rutin content (64.84 ± 2.31 µg/mL; 356.1 ± 12.7 µg/g dry weight; 1,935.3 ± 68.9 µg/g extract), which decreased significantly by >94% after one month of salting (3.71 ± 0.42 µg/mL; 20.4 ± 2.3 µg/g dry weight; 192.5 ± 21.7 µg/g extract; p < 0.001). Ethanolic extracts demonstrated superior antioxidant activity (IC₅₀ = 166.27 ± 8.45 mg/L) compared to chloroform (230.31 ± 12.18 mg/L), hexane (982.37 ± 45.62 mg/L), and ascorbic acid standard (320.65 ± 15.33 mg/L). A strong negative correlation was observed between rutin content and IC₅₀ values (r = -0.947, p < 0.001). Antimicrobial screening revealed distinct solvent-dependent profiles: chloroform extracts showed the strongest activity against P. aeruginosa (17.0 ± 0.82 mm inhibition zone), while ethanolic extracts were inactive against E. coli (0 mm). Chloroform and hexane extracts produced equivalent zones against E. coli (12.0 ± 0.55 mm). Traditional salting causes severe degradation of rutin and compromises antioxidant potential in caper fruits. These findings suggest that alternative preservation methods warrant investigation for maintaining the nutraceutical value of processed caper products, though their efficacy requires empirical validation.