Comprehensive Quality Assessment of Brassica napus L. Seeds via HPTLC, LC-QToF, and Anatomical Investigation

Abstract

The Brassicaceae family, commonly referred to as cruciferous plants, is globally cultivated and consumed, with the Brassica genus being particularly renowned for its functional components. These vegetables are rich sources of nutrients and health-promoting phytochemicals, garnering increased attention in recent years. This study presents a comprehensive microscopic, chromatographic, and spectroscopic characterization of Brassica napus L. seeds from Kazakhstan aimed at elucidating their morphological features and chemical composition. Microscopic analysis revealed distinct localization of flavonoids, total lipids, and alkaloids. High-performance thin-layer chromatography (HPTLC) analysis of seed extracts demonstrated a complex chemical profile with significant quantities of non-polar compounds in the hexane extracts. Additionally, methanolic extracts revealed the presence of diverse chemical compounds, including alkaloids, flavonoids, and glucosinolates. The chemical composition exhibited varietal differences across different Brassica species, with B. napus L. seeds showing higher concentrations of bioactive compounds. Furthermore, liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-QToF-MS) analysis provided insights into the chemical composition, with sinapine isomers, feruloyl, and sinapoyl choline derivatives as major compounds in the seeds. This study contributes to a better understanding of the chemical diversity and quality control methods' approximations of B. napus L. seeds, highlighting their importance in functional food and nutraceutical applications.

Keywords: Brassicaceae; flavonoids; histochemistry; microscopy; phytochemistry; quality control.

Figure 1

Micro-morphology and histochemistry of seeds of B. napus. (A,B) Scanning electron microscopic observation of seed and close view of the surface texture, respectively. (C) Stained with TBO. (D) The same section is viewed under UV. (E) Stained for flavonoids and viewed under UV (arrows indicate). (F) Stained for total lipids with Fluorol Yellow 088 (arrows indicate). (G) The section was stained with Nadi reagent for acidic lipids (arrows indicate this). (H) Dragendorff reagent stained for alkaloids (arrows indicate). (I,J) Cotyledon stained with Lugol’s Iodine for starch grains (arrows indicate). (K) Cotyledon stained for total lipids with Sudan III (arrows indicate). (L) Cotyledon under UV. hi, hilum; re, reticulation; ep, epidermal layer; pa, palisade layer; al, aleurone layer. The cross-section of the seed epidermis has three layers, namely, the outer epidermal layer, palisade, and aleurone cell layer. The outer epidemical layer is a thin, single layer, followed by the palisade layer, which is thick and composed of sclerenchymatous cells. In the third layer are oval to elongated cells filled with aleurone grains (C,D). Flavonoids were present in the palisade layer (E), and the same cells were composed of total lipids (F) and yielded a positive reaction to acidic lipids with Nadi stains (G). The Dragendorff reagent confirmed the presence of alkaloids (H). There was an absence of the endosperm region; thus, this seed belongs to the non-endospermic seed group. The interspace was fully occupied by the cotyledon, which serves as the food storage organ. The cotyledon is conduplicate, filled with very minute starch grains (I,J) and total lipids (K,L). No calcium oxalate crystals were present in the seed.

Figure 2

Scanning electron micrograph of the Brassica species. (A,B) B. napus (Red Russian Kale), (C,D) Brassica rapa, (E,F) Brassica juncea, (G,H) Brassica oleracea, (I,J) Brassica nigra, and (K,L) Brassica mixed sample.

Figure 3

Chromatogram of different Brassica seeds’ hexane extracts. Lanes 11–15 are selected samples at a higher concentration.

Figure 4

Chromatogram of methanolic B. napus seed extract in different concentrations.

Figure 5

TCC chromatograms (positive and negative ion mode) for B. napus seed (methanolic) extracts.