The Phytochemical Screening and Biological Properties of Brassica napus L. var. napobrassica (Rutabaga) Seeds

Abstract

Rutabaga, also known as swede and scientifically classified as Brassica napus napobrassica, is a biennial edible root vegetable that belongs to the Brassica genus and is widely cultivated in North Europe and North America. The present study highlights both the phytochemical profile and the in vitro biological properties of rutabaga seed extracts obtained through maceration using solvents of increasing polarity, namely, cyclohexane (CYHA), dichloromethane (DCM), ethyl acetate (EtOAc), methanol (MeOH), and water (H₂O). HPLC-DAD was used to identify and quantify phenolic compounds, while volatile compounds were detected using GC-MS. The in vitro antioxidant capacity of the rutabaga seed extracts was evaluated through DPPH free radical scavenging activity. The in vitro anti-inflammatory activity (15-lipoxygenase (15-LOX) enzyme) was determined spectrophotometrically at the same concentration. Additionally, the cytotoxicity of the seed extracts was evaluated against human colon adenocarcinoma cells (Caco-2) and human embryonic kidney cells (HEK-293) using the MTT assay. The rutabaga seed extracts obtained from EtOAc, MeOH, and H₂O were particularly rich in reducing sugars, ranging from 189.87 to 473.75 mg/g DW. The MeOH extract displayed the highest concentration of both sugars and polyphenols. Phytochemically, the HPLC-DAD analysis revealed the presence of four phenolic compounds in the tested extracts, including (±) synephrine, gallic acid, p-coumaric acid, and trans-ferulic acid, newly discovered in rutabaga organs. Moreover, a total of ten volatile compounds were identified through GC-MS analysis, both before and after derivatization. At a concentration of 50 µg/mL, the methanol extract exhibited high antioxidant activity with 52.95% inhibition, while CYHA, DCM, and EtOAc exhibited moderate anti-15-LOX activity with less than 30% inhibition. Except for DCM and aqueous extracts, rutabaga seeds did not exhibit any anti-proliferative potential against Caco-2 cell lines. Interestingly, no cytotoxicity was registered for any of the seed extracts against the normal cell line HEK-293. Overall, the obtained data highlight the potential utilization of rutabaga seeds as a source of bioactive compounds in various fields, including pharmaceuticals, nutraceuticals, and functional foods.

Keywords: GC-MS; HPLC-DAD; chemical profile; in vitro bioactivity; maceration; rutabaga seeds.

Figure 1

HPLC-DAD chromatograms at 280 nm of rutabaga seed extracts (CYHA: cyclohexane, DCM: dichloromethane, EtOAc: ethyl acetate, MeOH: methanol, water: H₂O): (±) synephrine (1), gallic acid (2), p-coumaric acid (3), and trans-ferulic acid (4). Imp: impurity of mobile phase.

Figure 2

GC-MS chromatograms of rutabaga seed extracts (CYHA: cyclohexane, DCM: dichloromethane, EtOAc: ethyl acetate).

Figure 3

Antioxidant assay of rutabaga seed extracts at 50 µg/mL and vitamin C at 4 µg/mL. Results are mean ± SD (n = 3). The presence of distinct letters on the histograms indicates a significant difference between extracts according to Tukey’s test (significance level of p ≤ 0.05).

Figure 4

Cell viability of HEK-293 after 48 h treatment with 50 µg/mL and 5 µg/mL of rutabaga seed extract. Tamoxifen was tested at 100 µM. Results are mean ± SD (n = 3). The histograms’ different letters indicate significant difference according to Tukey’s test (p ≤ 0.05).

Figure 5

Principal component analysis “loading plot” of the total phenolic content (TPC), the antioxidant activity (DPPH) and biological activities (anti-inflammatory activity: 15-LOX), and the cytotoxic activity (Caco-2 and HEK-293) of rutabaga seed extracts.

Figure 6

Principal components analysis “score plot” of rutabaga seed extracts (CYHA: cyclohexane, DCM: dichloromethane, EtOAc: ethyl acetate, MeOH: methanol, water: H₂O).

Figure 7

Principal components analysis “Biplot” of the total phenolic content (TPC), the antioxidant activity (DPPH), biological activities (anti-inflammatory activity: 15-LOX), and cytotoxic activity (Caco-2 and HEK-293) of rutabaga seed extracts.