A Review on Phytochemical Constituents and Pharmacological Activities Of Brassica Oleracea Var Gongylodes

Abstract

Kohlrabi (Brassica oleracea var. gongylodes), a nutrient-rich cruciferous vegetable, has attracted growing scientific interest due to its diverse phytochemical profile and wide range of pharmacological activities.This review highlights the current knowledge on the chemical constituents and pharmacological activities of kohlrabi, emphasizing its potential therapeutic applications. Kohlrabi is particularly abundant in glucosinolates, isothiocyanates, flavonoids, phenolic compounds, vitamins, and minerals, which contribute to its antioxidant, anti-inflammatory, antimicrobial, antiulcer, anticancer, antidiabetic, antihypertensive, and hepatoprotective effects. The bioactive compounds, especially sulforaphane and erucin, have shown promising chemopreventive and cytoprotective properties in various in vitro and in vivo studies. Additionally, kohlrabi exhibits immunomodulatory and lipid-lowering activities, supporting its role in metabolic health.Although kohlrabi exhibits promising bioactivity, clinical evidence is still scarce. Comprehensive research, especially human clinical trials, is necessary to confirm its therapeutic efficacy and clarify its mechanisms of action. This review provides a comprehensive overview of kohlrabi as a functional food with significant pharmacological prospects.

Keywords

Introduction

• Plant Type           : Biennial by nature but cultivated as an annual crop.
• Color        : pale green, purple, or white depending on the variety
• Leaves                  : Lobed and slightly crinkled in appearance. Similar to leaves of cabbage and other Brassicas.
• Stem (Knob)        : Bulbous, turnip-shaped, and grows just above ground. Most distinctive and commercially valuable part of the plant.
• Flowers    : Small and yellow, appear in the second year if plant is allowed to complete its biennial life cycle. Not usually seen in cultivated crops as they are harvested before flowering.
• Root System        : Typically consists of a fibrous root system in Brassica crops.
• Edible Part          : The swollen stem (knob), which develops just above the cotyledons due to thickening of tissue.Leaves are also edible and resemble those of other Brassica oleracea members.
• Growth Habit: Thrives in cool and temperate climates.Requires well-drained, fertile soil with adequate moisture and sunlight.
• Propagation         : Grown from seeds, either directly sown or transplanted as seedlings.

Geographical distribution:

Kohlrabi (Brassica oleracea var. gongylodes) is believed to have originated along the northern coast of Europe and has been cultivated for a long time in the Mediterranean basin. From there, its cultivation gradually spread to Western Asia and Western Europe. Today, it is widely grown in several parts of the world. In South Asia, it is mainly cultivated in India, Pakistan, and Iran, where it holds agricultural importance. In the Middle East, it is considered an important crop in Egypt and is widely cultivated in Syria. In Iraq, its cultivation is limited to small areas, primarily in the holy Karbala province and to a lesser extent in the provinces of Babylon and Baghdad. In Europe, countries like Belarus and other northern European nations grow it on a large scale, and its cultivation has expanded across many European regions. In North America, the United States of America is known for large-scale cultivation of kohlrabi. Additionally, its presence has increased in several Middle Eastern and Asian countries, reflecting its growing agricultural and dietary importance across different climatic and geographical zones ^[9]. In India, kohlrabi is extensively cultivated in Jammu and Kashmir and West Bengal, while it is grown to a lesser extent as a rare exotic vegetable in certain regions of Maharashtra, Assam, Uttar Pradesh, and Punjab ^[1].

Chemical constituents: ^[10,11]

1. Glucosinolates and Their Hydrolysis Products

Kohlrabi is a rich source of glucosinolates, which are sulfur-containing compounds typical of Brassicaceae vegetables. These compounds are enzymatically hydrolyzed by myrosinase into biologically active products such as isothiocyanates, nitriles, and indoles, known for their anticarcinogenic, antimicrobial, and anti-inflammatory activities.

Major glucosinolates in kohlrabi:

• Gluconasturtiin
• Glucoraphanin
• Sinigrin
• Glucoiberin
• Glucobrassicin

2. Phenolic Compounds

Kohlrabi contains high levels of phenolic acids, which possess strong antioxidant and anti-inflammatory effects.

Common phenolics found:

• Caffeic acid
• Ferulic acid
• p-Coumaric acid
• Chlorogenic acid
• Sinapic acid

3. Flavonoids

Flavonoids are plant pigments with antioxidant and cardioprotective properties. In kohlrabi, especially the purple variety, flavonoid content is significant.

Important flavonoids:

• Kaempferol
• Quercetin
• Myricetin
• Anthocyanins (especially in purple-skinned kohlrabi)

4. Other Phytochemicals

• Alkaloids – minor compounds that may contribute to the plant’s therapeutic actions.
• Tannins – known for their antioxidant and antimicrobial effects.
• Saponins – exhibit hypocholesterolemia, antioxidant, and immunomodulatory activities.
• Terpenoids – contribute to aroma and possess anti-inflammatory properties.
• Phytosterols – help reduce cholesterol levels and support cardiovascular health.

Pharmacological activity:

1.Antioxidant activity:

Kohlrabi exhibits significant antioxidant activity, with leaf extracts consistently outperforming tuber extracts in various assays. Extracts prepared using ethanol, methanol, acetone, and water revealed that the leaves possess higher total phenolic content and stronger antioxidant potential. Regular consumption of fresh kohlrabi leaves, such as in salads, may enhance the body's antioxidant defense by effectively neutralizing free radicals, making them valuable for use in health supplements and nutraceutical formulations ^[12].

2.Antidiabetic activity:

Kohlrabi  exhibits promising antidiabetic activity, particularly through its ability to inhibit Protein Tyrosine Phosphatase 1B (PTP1B), a negative regulator of insulin and leptin signaling pathways. PTP1B is highly expressed in insulin-responsive tissues such as the liver, muscle, and adipose tissue, and its elevated levels have been linked to insulin resistance commonly observed in obesity and type 2 diabetes mellitus. In this context, inhibition of PTP1B represents a valuable therapeutic strategy. Methanolic extracts of both Red Kohlrabi (RK) and Green Kohlrabi (GK) cultivars, along with their respective fractions, demonstrated significant PTP1B inhibitory activity in vitro. Notably, the RK extract exhibited stronger inhibition, indicating its potential as a natural source of PTP1B inhibitors and supporting its use in the management and prevention of diabetes mellitus ^[13].

3.Anti-inflammatory activity:

Both red and green cultivars of kohlrabi exhibit dose-dependent anti-inflammatory activity, with the red kohlrabi (RK) extract showing particularly strong effects. This activity is primarily attributed to the high phenolic content, which enhances the antioxidant potential of the extracts. Phenolic compounds and flavonoids present in kohlrabi are known to act as effective anti-inflammatory agents. These bioactive compounds, due to their strong antioxidant properties, may help prevent diabetes mellitus (DM) and its associated complications. Notably, RK extract significantly inhibited the expression of pro-inflammatory proteins such as inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), both of which are typically elevated during inflammatory responses. Earlier studies attributed the anti-inflammatory activity of kohlrabi to isothiocyanates, but more recent research has shown that phenolic compounds also play a significant role in producing these effects ^[13].

4.Anticancer activity:

Previous studies have supported the cytotoxic effects of Brassica vegetable extracts against the proliferation of various cancer cell lines. Among the cruciferous vegetables tested—cabbage, cauliflower, kohlrabi, and radish—all exhibited notable antiproliferative activity. Specifically, the purple peel of kohlrabi (Brassica oleracea var. gongylodes) showed significant dose-dependent antiproliferative effects on human cancer cell lines, including HepG2 (liver), HCT-116 (colon), and A549 (lung) cells. Notably, kohlrabi extract exhibited over 40% inhibition of proliferation in colon cancer cells. These findings suggest that kohlrabi may possess bioactive constituents, such as flavonoids, which could contribute to its potential role in cancer prevention ^[14]. Kohlrabi is a rich source of phytochemicals, primarily glucosinolates and indoles. Among the isothiocyanates (ITCs) present in kohlrabi flesh, the most notable are methylthiobutyl ITC (erucin) and sulforaphane (SFN), the latter of which has been recognized as a promising anticarcinogenic compound ^[15].

5.Antibacterial Activity:

The methanolic extract of kohlrabi leaves exhibited broad-spectrum antibacterial activity, effectively inhibiting all tested Gram-positive (Bacillus anthracis, Bacillus subtilis, Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa, Escherichia coli, Salmonella enterica) bacterial strains. The antibacterial potential was evaluated using micro-dilution and agar disk diffusion methods, with MIC, MBC, and IZD values assessed. Gentamicin served as the positive control, and all tests were conducted in triplicate. These results suggest that kohlrabi leaves are a promising source of natural antibacterial agents due to their richness in bioactive compounds ^[16].

6.Hepato protective activity:

Kohlrabi  exhibits significant hepatoprotective activity, mainly due to its rich content of antioxidants such as phenolic compounds, flavonoids, and isothiocyanates like sulforaphane. These bioactive compounds help reduce oxidative stress, inhibit inflammation, and stabilize liver cell membranes by lowering elevated liver enzymes (AST, ALT, ALP) and enhancing antioxidant enzymes (SOD, CAT, GPx). Experimental studies have shown that kohlrabi extracts can protect against chemically induced liver damage, restore normal liver histology, and improve overall liver function, suggesting its potential as a natural hepatoprotective agent ^[17].

7.Antihyperlipidemic activity:

Kohlrabi has shown promising hypolipidemic activity, primarily due to its rich content of glucosinolates, isothiocyanates, dietary fiber, and phenolic compounds. These bioactive constituents help reduce serum lipid levels by lowering total cholesterol, triglycerides, low-density lipoprotein (LDL), and improving high-density lipoprotein (HDL) levels. Studies in animal models have demonstrated that kohlrabi extracts can significantly reduce lipid accumulation in the liver and bloodstream, thereby preventing hyperlipidemia-associated disorders such as atherosclerosis and cardiovascular diseases. The antioxidant properties of kohlrabi also contribute to its lipid-lowering effects by inhibiting lipid peroxidation and improving hepatic lipid metabolism ^[18].

8. Antifungal activity:

The crude protein extract from kohlrabi (Brassica oleracea var. gongylodes) seeds has shown strong antifungal activity against several phytopathogenic fungi, including Botrytis cinerea, Fusarium oxysporum, Alternaria longipes, and Magnaporthe oryzae. This activity is mainly due to a defensin-like peptide, BGAP (~8.5?kDa), which was isolated and characterized from the seeds. BGAP displayed broad-spectrum antifungal properties and remained stable under various stress conditions such as heat, pH changes, exposure to metal ions, and organic solvents, demonstrating its potential for practical use. Its antifungal mechanism is thought to involve disruption of fungal cell membranes or interference with enzymatic functions, though this is yet to be fully understood. These results highlight the potential of kohlrabi seed-derived peptides as natural antifungal agents for use in agriculture and food preservation ^[19].

9.Antiulcer activity:

Kohlrabi, a member of the Brassicaceae family, has been traditionally valued for its nutritional and therapeutic properties. Recent studies suggest that kohlrabi may possess antiulcer activity, primarily attributed to its antioxidant, anti-inflammatory, and cytoprotective effects. The presence of phytochemicals such as glucosinolates, isothiocyanates, flavonoids, and phenolic compounds plays a crucial role in mucosal protection. These bioactive compounds helps to Neutralize gastric acid,Enhance the production of gastric mucus,Reduce oxidative stress in the gastric lining,Suppress inflammation and inhibit Helicobacter pylori growth. Although direct antiulcer studies on kohlrabi are limited, related research on Brassica vegetables and animal models shows gastroprotective effects, suggesting a promising potential for kohlrabi as a natural antiulcer agent. Further in vivo and clinical studies are needed to confirm its efficacy and mechanisms ^[20].

CONCLUSION:

Kohlrabi is an underutilized cruciferous vegetable with a promising phytochemical profile and a wide range of pharmacological activities. Rich in glucosinolates, flavonoids, anthocyanins, and other bioactive compounds, it exhibits significant antioxidant, antimicrobial, anti-inflammatory, anticancer, antihypertensive, hypolipidemic, hepatoprotective, and immunomodulatory properties. Preliminary studies also suggest potential antiulcer activity, warranting further exploration. Despite its diverse therapeutic potential demonstrated in in vitro and in vivo models, clinical evidence remains limited. Therefore, more comprehensive preclinical and human studies are essential to validate its efficacy, determine safety profiles, and explore its mechanisms of action. The current findings support the potential of kohlrabi as a functional food and a source of natural therapeutic agents in the prevention and management of various chronic diseases

ACKNOWLEDGEMENT: I would like to express my sincere gratitude to Bharathi Education Trust, Bharathinagara, Mandya, Karnataka, for their valuable support. I am also thankful to Sir.Harshithkumar K N for his immense support and encouragement throughout this review.

Conflict of Interest: No conflict of interest.

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