Walnut
A walnut is the edible seed of any tree of the genus Juglans (family Juglandaceae), particularly the Persian or English walnut, Juglans regia. They are accessory fruit because the outer covering of the fruit is technically an involucre and thus not morphologically part of the carpel; this means it cannot be a drupe but is instead a drupe-like nut.
November 18, 2019
Description
Walnuts are the round, single-seed stone fruits of the walnut tree. They ripen between September and November in the northern hemisphere. The brown, wrinkly walnut shell is enclosed in a husk.[1] Shells of walnuts available in commerce usually have two segments (but three or four-segment shells can also form). During the ripening process, the husk becomes brittle and the shell hard. The shell encloses the kernel or meat, which is usually in two halves separated by a membranous partition.[1] The seed kernels – commonly available as shelled walnuts – are enclosed in a brown seed coat which contains antioxidants. The antioxidants protect the oil-rich seed from atmospheric oxygen, preventing rancidity.[2]
Chemistry
Walnut hulls contain diverse phytochemicals, such as polyphenols, that stain hands and can cause skin irritation. Seven phenolic compounds, including ferulic acid, vanillic acid, coumaric acid, syringic acid, myricetin, and juglone, were identified in walnut husks; juglone had concentrations of 2-4% fresh weight.[3]
Walnuts also contain the ellagitannin, pedunculagin.[4] Regiolone has been isolated with juglone, betulinic acid and sitosterol from the stem bark of J. regia.[5]
Storage
Walnuts, like other tree nuts, must be processed and stored properly. Poor storage makes walnuts susceptible to insect and fungal mold infestations; the latter produces aflatoxin – a potent carcinogen. A batch that contains mold-infested walnuts should be entirely discarded.[2]
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