Walnuts

Walnut (Juglans regia)
Parts & commercial forms: shelled kernels (whole/pieces; raw/roasted; salted/unsalted), walnut flour/paste (incl. partially defatted), walnut oil (virgin or refined).

The walnut is the edible seed of trees of the genus Juglans, mainly Juglans regia (the so-called Persian or English walnut), in the botanical family Juglandaceae. The tree produces a green outer husk that dries and opens, revealing a hard, woody shell, inside which there is the kernel with its characteristic “brain-like” shape, divided into two lobes. Walnuts are widely cultivated in temperate regions and have a long history of use as both food and traditional remedy.

As a food ingredient, the walnut is valued for its rich, slightly bitter, aromatic flavor and crunchy yet buttery texture. It contains a high amount of fats, with a relevant proportion of unsaturated fatty acids (including omega-3), plant proteins, dietary fiber, vitamin E, B-group vitamins and minerals such as magnesium, phosphorus, potassium and copper. In the kitchen, walnuts are used raw or toasted in salads, baked goods, sauces (for example walnut pesto), desserts, bread, cereals and yogurt toppings, as well as in savory dishes with cheese, vegetables, meat or pasta. Walnut oil, obtained by cold pressing the kernels, is also appreciated as a delicate condiment used mainly raw to preserve its aroma and nutritional properties.

Common name: Walnut (European/Persian walnut)

Parent plant: Juglans regia L. — common walnut or European walnut

Kingdom: Plantae
Clade: Angiosperms
Clade: Eudicots
Order: Fagales
Family: Juglandaceae
Genus: Juglans
Species: Juglans regia L.

Cultivation and growth conditions

Climate:
European walnut requires a temperate climate with warm, dry summers and cool winters.

• It tolerates winter cold down to about –10/–15 °C during dormancy.

• It is sensitive to late frosts, which can damage young shoots and inflorescences.

• It prefers well-ventilated environments, not prone to persistent atmospheric humidity.

Sun exposure:
Walnut requires full sun, which is essential for:

• good photosynthetic activity,

• proper hull (husk) development,

• correct nut ripening.

Shade and insufficient light reduce yield and nut quality.

Soil:
Walnut grows best in soils that are:

• deep (the taproot penetrates very deeply),

• well drained,

• medium-textured or slightly sandy,

• rich in organic matter,

• with pH between 6.5 and 7.5.

Heavy, clayey soils with waterlogging increase the risk of root diseases and reduce vigor.

Irrigation:
Water requirement is medium, especially:

• in spring (vegetative regrowth),

• during nut filling (summer).

Excess water causes nut drop, rots, and defects in the hull; water shortage can halt kernel development.

Temperature:

• Germination: 10–20 °C

• Optimal vegetative growth: 20–30 °C

• Flowers damaged below –1/–2 °C

• Heat stress above 38–40 °C

Strong temperature fluctuations negatively affect nut quality.

Fertilization:
Walnut responds well to balanced fertilization:

• Nitrogen: applied in moderate quantities to avoid excessive vegetative growth.

• Phosphorus: supports root development and flowering.

• Potassium: crucial for kernel quality, aroma, and storability.

The addition of organic matter improves soil structure and water-holding capacity.

Crop care:

• Formative pruning in the first years and light maintenance pruning later on.

• Removal of dead branches and suckers.

• Monitoring of major pests, such as:

  • walnut husk fly (Rhagoletis completa),

  • codling moth and other Lepidoptera,

  • mites.

• Control of key diseases:

  • bacterial blight,

  • collar and root rots,

  • anthracnose.

Good canopy aeration reduces disease pressure.

Harvest:
Harvest takes place between late summer and early autumn, when:

• the green hull (husk) splits and begins to detach,

• the shell has hardened,

• the kernel reaches its characteristic light color and full flavor.

Timely harvest is important to prevent darkening, off-odors, and quality loss caused by decomposing hulls.
After removal of the hull, walnuts are washed, dried, and graded.

Propagation:
Walnut is propagated by:

• seed (to produce rootstocks),

• grafting (to maintain cultivar characteristics and improve productivity).

Fruit cultivars are grafted onto selected rootstocks chosen for vigor, adaptability, and disease resistance.

Caloric value (dry kernels)
~650–660 kcal per 100 g (typical ≈ 654 kcal/100 g; varies with moisture/roast).

Average composition (per 100 g)

• Fat: ~60–65 g

• Protein: ~14–15 g

• Carbohydrate: ~13–14 g (of which fiber ~6–7 g, sugars ~2–3 g)

• Water: ~2–4 g

• Micronutrients: high Mn and Cu; plus Mg, P, Zn, K; folate; vitamin E (predominantly γ-tocopherol); polyphenols (incl. ellagitannins → gut-derived urolithins in capable individuals).

Fatty-acid profile (indicative, % of total fat)

• PUFA (PolyUnsaturated Fatty Acids—beneficial but balance overall): linoleic C18:2 Ω-6 ~35–50%; ALA C18:3 Ω-3 ~8–15% → strong plant Ω-3 source.

• MUFA (MonoUnsaturated Fatty Acids—generally heart-friendly): oleic C18:1 ~15–25%.

• SFA (Saturated Fatty Acids—best in moderation): palmitic C16:0 ~5–8%, stearic C18:0 ~1–3%.
  Health note: the meaningful ALA (Ω-3) supports cardiometabolic health; diet-wide Ω-6:Ω-3 balance still matters.

Sensory & technological properties

• Texture: crisp, then friable-buttery in mouth.

• Flavor: nutty-woody with sweet-lactic tones; roasting (110–150 °C) intensifies Maillard notes but raises oxidation susceptibility.

• Functionality: granules for toppings, flour for gluten-free bakery (needs binders), base for pestos/creams.

Walnut oil (brief)

• Virgin/cold-pressed: pronounced aroma; smoke point ~160–180 °C → best raw.

• Refined (RBD): milder flavor; smoke point ~220–230 °C → suitable for moderate heat.

• High PUFA → excellent for dressings, less ideal for prolonged frying.

Food applications

• Snacks (raw/roasted; honey/chocolate coated).

• Bakery/confectionery: brownies, cakes, cookies, nougat, pralines.

• Culinary: salads, pastas, herb-cheese pestos; plant beverages/creams with other nuts.

Nutrition & health (highlights)

• ALA (Ω-3): roughly 2–2.5 g per 30 g serving (~a small handful).

• May support a favorable lipid profile when walnuts replace fats high in SFA within a balanced dietary pattern.

• Fiber and polyphenols (ellagitannins → urolithins) contribute to satiety and gut functions (bioactivation varies by microbiota).

• Suggested portion: ~30 g/day; consider total calories.

Allergens & safety

• Tree-nut allergen → potential IgE-mediated reactions (can be severe): strict labeling and cross-contact control.

• Oxidation: high PUFA makes walnuts prone to rancidity (paint-like/pungent odor). Minimize light/heat/oxygen.

• Mycotoxins: manage moisture and shell integrity; rely on controlled drying/storage supply chains.

Quality & specifications (typical themes)

• Kernel moisture ≤3–4% for crunch and stability.

• Low peroxide/anisidine numbers (no rancid notes).

• Grading by size and defects (breaks, browning).

• Walnut flour: more oxidation-sensitive than cereal flours → use fresh lots; consider inert-gas packing.

Storage & shelf life

• Store cool, dark, airtight; ideally vacuum/inert gas.

• Refrigeration/freezing extends life (kernels pick up odors easily).

• Avoid prolonged light/air exposure after opening.

Troubleshooting

• Rancid notes: discard; prevent with lower temp, O₂-barrier packs, stock rotation.

• Loss of crunch: light re-dry/re-roast; deploy in moist recipes.

• Over-friable gluten-free bakes: add binders (xanthan/psyllium/eggs) and balance with starches.

Sustainability

• Widely cultivated (Mediterranean, U.S./California, Eastern Europe, Central Asia). Favor supply with traceability, responsible water/biodiversity management, and fair social practices.

Conclusion
Walnuts combine rich sensory appeal with a PUFA-forward profile featuring meaningful ALA Ω-3. With moderate portions, proper storage, and integration into a balanced diet, they deliver substantial nutritional and functional value across snacks, bakery, and savory dishes.

Lipid acronym mini-legend (quick reference)

• MUFA = MonoUnsaturated Fatty Acids: generally heart-friendly; improve lipid profile.

• PUFA = PolyUnsaturated Fatty Acids: include Omega-3 and Omega-6; beneficial, but keep a reasonable Ω-6:Ω-3 balance.

• SFA = Saturated Fatty Acids: limit/moderate; health impact depends on overall diet and replacements.

• ALA / EPA / DHA (Omega-3): beneficial for heart/brain; strongest evidence for EPA/DHA.

• TFA = Trans Fatty Acids: avoid; linked to higher cardiovascular risk.

• MCT = Medium-Chain Triglycerides: rapidly absorbed/oxidized; useful in specific contexts, but still count toward calories.

Studies

Walnut has a significant presence of components beneficial for human health, including fats, vitamins and proteins, including :

• omega3 fats
• omega6 fats
• alpha-linoleic acid
• vitamin B1
• vitamin B2
• Vitamin B6
• vitamin E
• polyphenols

All these substances effectively combat the high levels of harmful LDL cholesterol and promote the proper performance of the cardiovascular system (1).

Recent studies in the US have found that a daily intake of 3-4 nuts contributes to the human body, about :

• 5 grams of fiber
• 250 mg potassium
• 70 mg calcium
• 90 mg magnesium
• 3.5 mg vitamin E
• 150 mg sodium

Which benefits not only the cardiovascular system, but also the immune system.

Walnut has antioxidant, anti-inflammatory, antimicrobial and antifungal activities due in large part to the significant content of alpha-tocopherol (a compound of vitamin E), flavonoids, phenols, alkaloids, terpenoids, tannins, saponins and steroids (2).

Walnuts are an excellent source of vitamin E and magnesium. People who consume 3 nuts take folate, beta-carotene, vitamin K, lutein, zeaxantine, phosphorus, copper, selenium, potassium and zinc for about 1000 kcal (3).

This animal study supports the hypothesis that daily consumption of walnuts could suppress the growth and survival of breast cancer (4).

However, care should be taken to purchase bleached walnuts, as chemicals may be used in the bleaching process.

The walnut, collected from the tree or from the ground, should only be cleaned with a toothbrush to remove any incrustations of soil or parts of the hull.

The hull is used as a natural black dye and as a hair dye.

Furniture is made from high-quality walnut wood.

Walnut studies

References______________________________________________________________

(1) Damasceno NR, Pérez-Heras A, Serra M, Cofán M, Sala-Vila A, Salas-Salvadó J, Ros E. Crossover study of diets enriched with virgin olive oil, walnuts or almonds. Effects on lipids and other cardiovascular risk markers.   Nutr Metab Cardiovasc Dis. 2011 Jun;21 Suppl 1:S14-20. doi: 10.1016/j.numecd.2010.12.006. 

Abstract. Background and aims. Virgin olive oil (VOO) and nuts are basic components of the Mediterranean diet, a heart-healthy dietary pattern. Nuts have well known cholesterol lowering effects, while evidence is unclear for VOO. We designed a study in hypercholesterolemic patients to assess the effects on serum lipids and other intermediate markers of cardiovascular risk of replacing 40% of the fat in the background diet with VOO, walnuts or almonds. Methods and Results After a 4 week run-in period with a healthy diet, eligible candidates were randomized into three diet sequences in a crossover design, with a common background diet enriched with VOO, walnuts or almonds, lasting 4 weeks each. Outcomes were changes of serum lipids and oxidation and inflammation markers, measured by standard methods. Plasma fatty acids were determined by gas chromatography to assess compliance. In 18 participants completing the study (9 women, mean age 56 y, BMI 25.7 kg/m2), LDL-cholesterol was reduced from baseline by 7.3%, 10.8% and 13.4% after the VOO, walnut and almond diets, respectively (P = 0.001, Friedman test). Total cholesterol and LDL/HDL ratios decreased in parallel. LDL-cholesterol decreases were greater than predicted from dietary fatty acid and cholesterol exchanges among diets. No changes of other lipid fractions, oxidation analytes or inflammatory biomarkers were observed. Plasma fatty acid changes after each diet sequence supported good compliance. Conclusion. The results confirm the cholesterol lowering properties of nut-enriched diets. They also suggest that phenolic-rich VOO has a cholesterol lowering effect independently of its fatty acid content, which clearly deserves further study.

(2) Jahanban-Esfahlan A, Ostadrahimi A, Tabibiazar M, Amarowicz R. A Comparative Review on the Extraction, Antioxidant Content and Antioxidant Potential of Different Parts of Walnut (Juglans regia L.) Fruit and Tree. Molecules. 2019 Jun 5;24(11):2133. doi: 10.3390/molecules24112133. 

Abstract. As a valuable tree nut, walnut is a well-known member of the Juglandaceae family. The fruit is made up of an outer green shell cover or husk, the middle shell which must be cracked to release the kernel, a thin layer known as skin or the seed coat, and finally, the kernel or meat. The nutritional importance of walnut fruit is ascribed to its kernel. The shell and husk are burned as fuel or discarded away as waste products. In the past two decades, the evaluation of the phenolic content and antioxidant activity of different parts of walnut has received great interest. In this contribution, the recent reports on the extraction and quantification of phenolic content from each part of the walnut tree and fruit using different solvents were highlighted and comparatively reviewed. The current review paper also tries to describe the antioxidant content of phenolic extracts obtained from different parts of the walnut tree and fruit. Additionally, the antioxidant and antiradical activities of the prepared extracts have also been discussed.

(3) Tree nuts and peanuts as components of a healthy diet.  King JC, Blumberg J, Ingwersen L, Jenab M, Tucker KL.  J Nutr. 2008 Sep;138(9):1736S-1740S.

Abstract. Nuts have been part of the diet for thousands of years. In 2003, a Qualified Health Claim was approved, stating that eating 1.5 oz (42 g) of nuts per day may reduce the risk of heart disease. Usual intakes fall short of this recommendation. About one-third of Americans report consuming nuts (tree nuts or peanuts) on any one day. Seven percent of Europeans report eating nuts, but the amount eaten by European nut consumers (31 g/d) is larger than that of Americans (21 g/d). Nuts are an excellent source of vitamin E and magnesium. Individuals consuming nuts also have higher intakes of folate, beta-carotene, vitamin K, lutein+zeaxanthin, phosphorus, copper, selenium, potassium, and zinc per 1000 kcal. Regular nut consumption increases total energy intake by 250 kcal/d (1.05 MJ/d), but the body weight of nut consumers is not greater than that of nonconsumers. Nuts are an excellent source of phytochemicals (phyotsterols, phenolic acids, flavonoids, stilbenes, and carotenoids). The total phenolic constituents probably contribute to the total antioxidant capacity of nuts, which is comparable to broccoli and tomatoes. To improve guidance on the use of nuts in the diet, the position of nuts in typical food patterns needs to be addressed. The 2005 MyPyramid includes nuts in the meat and beans group. Yet, nuts are rarely consumed as meat substitutes. Because approximately 60% of the nuts consumed in the U.S. are eaten as snacks, emphasizing their use as a healthy snack may be more effective than inclusion within a food group.

(4) Hardman WE, Primerano DA, Legenza MT, Morgan J, Fan J, Denvir J. Dietary walnut altered gene expressions related to tumor growth, survival, and metastasis in breast cancer patients: a pilot clinical trial. Nutr Res. 2019 Jun;66:82-94. doi: 10.1016/j.nutres.2019.03.004.