The impact of fermentation on the antioxidant activity and bioactive components in crucifers

Abstract

Crucifers have been widely recognized for their chemical components contributing to their pharmacological benefits. This study investigated the changes in glucosinolate (GSL) and isothiocyanate (ITC) levels in five cruciferous vegetables—alugbati (Basella rubra), cabbage (Brassica oleracea var. capitata), mustard (Brassica juncea), radish (Raphanus sativus var. longipinnatus), and Napa cabbage (Brassica rapa ssp. pekinensis)—following a 14-day fermentation period using high-performance liquid chromatography (HPLC). Furthermore, the effects of fermentation on the antioxidant activity of the vegetables were also determined using the DPPH assay. Results showed that raw extracts had high GSL levels, with concentrations ranging from 19.55 to 384.07 µmol/g, while fermented samples obtained lower GSL levels ranging from 6.90 to 49.16 µmol/g. An increase in the ITC contents was observed in both raw and fermented samples after subjecting to hydrolysis in the presence of exogenous myrosinase enzyme. DPPH assay revealed that raw vegetables exhibited varying antioxidant activities with IC₅₀ < 200 ppm.  Raw cabbage showed the strongest antioxidant activity with IC₅₀ = 25.32 ± 3.96 ppm, while the rest of the raw samples only exhibited intermediate activity with IC₅₀ values ranging from 50 to 100 ppm. On the other hand, fermented vegetables exhibit IC₅₀ values ≥ 200 ppm, indicating weak antioxidant activities. Therefore, the results from both chromatographic and DPPH assays indicate that fermentation further decreases the metabolite concentration and antioxidant capacity of the vegetable samples due to the chemical degradation of bioactive components.  Controlled and monitored fermentation conditions play crucial roles in preserving GSL, ITC, and other bioactive components in crucifers.