Leek (Allium ampeloprasum var. porrum)

Description
The leek is a vegetable belonging to the Amaryllidaceae family, closely related to onion and garlic. It consists of a long cylinder formed by overlapping fleshy leaf sheaths; the edible part is mainly the white pseudostem, while the dark green leaves are more fibrous but can be used for stocks and flavouring. Its flavour is delicate, sweet and less pungent than onion, which makes it very versatile in many culinary preparations.

The species Allium also includes:

•     garlic (Allium sativum L.)
•     chives (Allium schoenoprasum L.)
•     onion (Allium cepa L.)
•     scallion (Allium fistulosum L.)

Indicative nutritional values per 100 g

• Energy: ≈ 60–65 kcal

• Water: ≈ 83–85%

• Carbohydrates: ≈ 14 g

  • of which sugars: 3–4 g

• Protein: 1.5–2 g

• Total fat: 0.2 g

  • SFA (saturated fatty acids; excess in the overall diet is associated with cardiovascular risk): traces

  • MUFA (monounsaturated fatty acids; generally favourable for lipid profile): traces

  • PUFA (polyunsaturated fatty acids; involved in cell membrane integrity and anti-inflammatory functions): traces

• Dietary fibre: 1.5–2 g

• Vitamins: vitamin C, vitamin K, folate, small amounts of provitamin A (β-carotene)

• Minerals: potassium, calcium, magnesium, traces of iron

Values vary with variety, growing conditions and part of the plant used (white vs green).

Key constituents

• Sulphur-containing compounds (typical of Allium species): alk(en)yl sulphides, thiosulfinates, responsible for characteristic aroma.

• Flavonoids, especially kaempferol and its glycosides.

• Carotenoids in the green leaves (lutein, β-carotene).

• Vitamin C, folate and vitamin K.

• Soluble fibres, including inulin and related fructans.

Production process

• Sowing or transplanting: usually from spring to early summer, directly in the field or after raising seedlings in nurseries.

• Growing: leeks need fertile, well-drained soils and regular irrigation.

• Blanching: during growth, soil is ridged up around the stems (“earthing up”) to increase the length of the white portion.

• Harvest: manual or mechanical, when plants reach the desired diameter and length.

• Post-harvest handling: removal of soil, trimming of roots and dark leaf tips, possible washing.

• Packaging: bunches, crates, or fresh-cut (washed and sliced leek) as fourth-range products.

Physical properties

• Pseudostem length: typically 20–40 cm.

• Colour: white at the base, grading to light and then dark green towards the leaves.

• Texture: crisp when raw, soft and creamy when cooked.

• High water-holding capacity.

• Good resistance to cold; leek is a typical autumn–winter crop in many climates.

Sensory and technological properties

• Aroma: gently sulphurous and “onion-like”, but milder than onion or garlic.

• Taste: slightly sweet, aromatic, without excessive pungency.

• Cooking behaviour:

  • becomes tender and creamy, ideal for puréed soups and veloutés;

  • excellent for light sautés as a base for many dishes;

  • green leaves are more fibrous but strongly aromatic, suitable for stocks and flavouring liquids.

• Technological versatility: suitable for stewing, grilling, baking, pan-frying, soups, risottos and quiches.

Food applications

• Aromatic base for sautés, stocks and sauces (as an alternative or complement to onion).

• Main ingredient in soups and puréed vegetable creams (e.g. leek and potato soup).

• Used in quiches, savoury tarts, gratins and flans.

• Pan-fried or braised as a side dish, in risottos, with fish or white meat.

• Green tops used for stocks, fumets and aromatic bundles (bouquet garni).

• Fresh-cut products (cleaned and sliced leek) for ready-to-use cooking.

Nutrition & health

• Source of soluble fibres (including inulin), which may support intestinal function and beneficial gut microbiota in the context of a balanced diet.

• Contains natural antioxidants (flavonoids and carotenoids) that contribute to protection against oxidative stress.

• Sulphur compounds from Allium vegetables are studied for potential benefits on cardiovascular and immune health (evidence is suggestive but not definitive).

• Low energy density makes leek suitable for light and weight-control diets.

• Provides folate and vitamin C, important for cell metabolism and immune function.

Portion note
Typical serving size: 80–100 g of leek as a vegetable side dish, or about 50 g when used mainly as an aromatic base.

Allergens and intolerances

• Leek is not among the major allergens listed in EU legislation.

• It may cause reactions in individuals sensitive to Allium species (garlic, onion, shallot, chive).

• The content of fermentable fibres (e.g. inulin) can cause bloating or discomfort in people with sensitive bowel or conditions like IBS or SIBO.

Storage and shelf-life

• Whole fresh leeks:

  • 1–2 weeks in the refrigerator, preferably in a perforated bag to avoid condensation.

• Fresh-cut leek (fourth-range):

  • about 4–7 days at 0–4 °C, depending on packaging and hygiene.

• Frozen:

  • 8–12 months if blanched and frozen under proper conditions.

• Avoid excessive moisture to prevent mould growth and softening.

Safety and regulatory aspects

• Must comply with EU limits for pesticide residues (MRL – Maximum Residue Level), contaminants and general hygiene.

• Proper cold-chain management is essential for washed, sliced products.

• Facilities must operate under GMP (Good Manufacturing Practices) and HACCP (Hazard Analysis and Critical Control Points) to ensure food safety.

Labelling

For fresh whole leek

• Name: “leek”.

• Country of origin.

• Commercial category and size class where applicable.

• Lot identification and storage indications.

For fresh-cut (fourth-range) products

• Ingredient list (e.g. “leek”).

• Use-by date.

• Net weight.

• Storage instructions (temperature and handling).

Troubleshooting

• Soft or brownish stem → degradation due to excessive humidity, prolonged storage or temperature abuse.

• Very strong, unpleasant odour → over-mature product or beginning spoilage.

• Yellowing leaves → oxidation or stress during cultivation/storage.

• Residual soil between leaf sheaths → insufficient washing; thorough cleaning is needed, especially near the root end.

Sustainability and supply chain

• Leek can be grown with low-impact agronomic techniques (crop rotation, targeted irrigation, integrated pest management).

• Good field yields and the possibility of using green tops for stock help reduce waste.

• All plant residues are fully compostable and suitable for organic-waste streams.

• Packaging is typically recyclable (cardboard crates, recyclable plastic film).

• Short supply chains improve freshness and reduce transport-related emissions.

Main INCI functions (cosmetics)
Although relatively uncommon, leek-derived extracts used in cosmetic formulations may provide:

• Antioxidant properties (due to flavonoids).

• Mild soothing and softening effects.

• Light skin-conditioning action in vegetable-based formulas.

• Purifying effect linked to sulphur compounds, in suitable and well-tolerated concentrations.

Conclusion
Leek is a versatile vegetable with a delicate but characteristic aroma and an interesting nutritional profile. Thanks to its combination of soluble fibre, vitamins and bioactive sulphur and flavonoid compounds, it fits well into balanced, plant-rich diets. Its layered structure and creamy texture after cooking make it ideal for numerous traditional and modern recipes. Proper management of cultivation, hygiene and cold chain is key to preserving quality, safety and sensory characteristics.

Mini-glossary

• SFA – Saturated fatty acids; dietary fats that should be moderated because of their association with increased cardiovascular risk.

• MUFA – Monounsaturated fatty acids; generally considered beneficial for blood lipid profile.

• PUFA – Polyunsaturated fatty acids; important for cell membranes and anti-inflammatory processes.

• MRL – Maximum Residue Level; legal limit for pesticide residues and certain contaminants in foods.

• GMP – Good Manufacturing Practices; operational standards ensuring hygienic and correct production.

• HACCP – Hazard Analysis and Critical Control Points; preventive system for identifying and controlling food-safety hazards.

Studies

These vegetables are consumed both as complements to main courses and as medicinal herbs in which there are useful components for health such as flavonoids, phenolic acids that exert an antioxidant activity.

The major component among the flavonoids is kaempferol (1) known for its anti-inflammatory, antidiabetic, cardioprotective properties.

The leek is among the herbs that have a solid scientific literature for curative effects of hemorrhoids (2).

Although in animal studies, leeks have been shown to exert hypoglycemic, hypolipidemic and can be considered a useful dietary supplement in diabetic patients (3).

Leek studies

References___________________________________

(1) .  Fattorusso E, Lanzotti V, Taglialatela-Scafati O, Cicala C. The flavonoids of leek, Allium porrum Phytochemistry. 2001 Jun;57(4):565-9.

Abstract. A phytochemical investigation of the extracts obtained from bulbs of leek. Allium porrum L. has led to the isolation of five flavonoid glycosides based on the kaempferol aglycone. Two of them are new compounds and have been identified as kaempferol 3-O-[2-O-(trans-3-methoxy-4-hydroxycinnamoyl)-beta-D-galactopyranosyl]-(1-->4)-O-beta-D-glucopyranoside, and kaempferol 3-O-[2-O-(trans-3-methoxy-4-hydroxycinnamoyl)-beta-D-glucopyranosyl]-(1-->6)-O-beta-D-glucopyranoside, on the basis of spectroscopic methods, including 2D NMR. The isolated compounds have been evaluated for their human platelet anti-aggregation activity.

(2)   Dehdari S, Hajimehdipoor H, Esmaeili S, Choopani R, Mortazavi SA. Traditional and modern aspects of hemorrhoid treatment in Iran: a review. J Integr Med. 2018 Mar;16(2):90-98. doi: 10.1016/j.joim.2018.01.002.

Caliskan, U. K., Aka, C., & Oz, M. G. (2017). Plants Used in Anatolian Traditional Medicine for the Treatment of Hemorrhoid. Records of Natural Products, 11(3).

Abstract:  Hemorrhoidal disease is a benign perianal disease, which is basically caused by vasodilation on pleux haemorrhoidalis vein, which affects mainly individuals at their active ages, and it is believed that the number of cases is much higher than the actual reported number. The majority of the patients’ complaints consist of pain, itching, bleeding and feeling of discomfort. Any patient with these symptoms requires a careful review of their personel history and a physical, digital examination. The treatment options are evaluated in a wide spectrum from conservative to surgical procedures. The main goal of the treatment is, in acute phase, relief of the symptoms quickly and in chronical phase prevention of the relapses. Before going to surgery, depends on the grade of the disease, human being very often apply local topical treatments, plant based intestinal regulators, plant based phlebotonics and anti-inflammatory drugs to improve or prevent the worsening of hemorrhoid. In this review, a brief information was given about hemorrhoid, in further the plants that were applied in traditional medicine, their latin, Turkish and common names, parts of the plants and their method of application in treatment of the symptoms in Anatolia. The data showed that herbal remedies included 170 from 60 different plant families used in the treatment of hemorrhoids. Although there are many natural based antihemorrhoidal preparations presence in the world, just a few safe antihemorrhoidal preparations prescribed in Turkey. This review will be a guide to discovery of different effective natural compounds from plants of different families such as Asteraceae, Lamiaceae and Rosaceae, which are highly rich in terms of antihemorhoidal compounds flavonoids and terpenes. 

(3)  Rahimi-Madiseh M, Heidarian E, Kheiri S, Rafieian-Kopaei M. Effect of hydroalcoholic Allium ampeloprasum extract on oxidative stress, diabetes mellitus and dyslipidemia in alloxan-induced diabetic rats.  Biomed Pharmacother. 2017 Feb;86:363-367. doi: 10.1016/j.biopha.2016.12.028.

Benedé S, Gradillas A, Villalba M, Batanero E. Allium porrum Extract Decreases Effector Cell Degranulation and Modulates Airway Epithelial Cell Function. Nutrients. 2019 Jun 8;11(6):1303. doi: 10.3390/nu11061303. 

Abstract. Allium genus plants, such as leek (Allium porrum), are rich sources of anti-inflammatory and anti-oxidant secondary metabolites; this is of interest because it demonstrates their suitability as pharmacological alternatives for inflammatory processes, including allergy treatment. The composition of methanolic leek extract (LE) was analyzed by GC-MS and LC-IT/MS, and the total phenolic content and antioxidant capacity were quantified by colorimetric methods. Its pharmacological potential was analyzed in human bronchial epithelial Calu-3 cells, human mast cells LAD2, and humanized rat basophiles RBL-2H3. LE exhibited a cytotoxic effect on Calu-3 cells and HumRBL-2H3 cells only at high concentrations and in a dose-dependent manner. Moreover, LE decreased the degranulation of LAD2 and HumRBL-2H3 cells. LE treatment also significantly prevented alterations in transepithelial electrical resistance values and mRNA levels of glutathione-S-transferase (GST), c-Jun, and NFκB after treatment with H2O2 in ALI-cultured Calu-3 cells. Finally, ALI-cultured Calu-3 cells treated with LE showed lower permeability to Ole e 1 compared to untreated cells. A reduction in IL-6 secretion in ALI-cultured Calu-3 cells treated with LE was also observed. In summary, the results obtained in this work suggest that A. porrum extract may have potential anti-allergic effects due to its antioxidant and anti-inflammatory properties. This study provides several important insights into how LE can protect against allergy.

Schliemann W, Kolbe B, Schmidt J, Nimtz M, Wray V. Accumulation of apocarotenoids in mycorrhizal roots of leek (Allium porrum). Phytochemistry. 2008 May;69(8):1680-8. doi: 10.1016/j.phytochem.2008.02.015.

Abstract. Colonization of the roots of leek (Allium porrum L.) by the arbuscular mycorrhizal fungus Glomus intraradices induced the formation of apocarotenoids, whose accumulation has been studied over a period of 25 weeks. Whereas the increase in the levels of the dominating cyclohexenone derivatives resembles the enhancement of root length colonization, the content of mycorradicin derivatives remains relatively low throughout. Structural analysis of the cyclohexenone derivatives by mass spectrometry and NMR spectroscopy showed that they are mono- and diglycosides of 13-hydroxyblumenol C and blumenol C acylated with 3-hydroxy-3-methyl-glutaric and/or malonic acid. Along with the isolation of three known compounds five others are shown to be hitherto unknown members of the fast-growing family of mycorrhiza-induced cyclohexenone conjugates.