Nut (fruit)
|
Chestnuts are both botanical and culinary nuts |
From Wikipedia, the free encyclopedia
A
nut is a fruit composed of a hard shell and a seed, where the hard-shelled fruit does not open to release the seed (
indehiscent).
In a culinary context, a wide variety of dried seeds are often called
nuts, but in a botanical context, only ones that include the
indehiscent
fruit are considered true nuts. The translation of "nut" in certain
languages frequently requires paraphrases, as the concept is ambiguous.
Most seeds come from fruits that naturally free themselves from the shell, unlike nuts such as
hazelnuts,
chestnuts, and
acorns,
which have hard shell walls and originate from a compound ovary.
Culinary usage of the term is less restrictive, and some nuts as defined
in food preparation, like
almonds,
pecans,
pistachios,
walnuts, and
Brazil nuts, are not nuts in a botanical sense. Common usage of the term often refers to any hard-walled, edible kernel as a nut.
Botanical definition
A nut in
botany is a simple dry
fruit with one
seed (rarely two) in which the
ovary
wall becomes very hard (stony or woody) at maturity, and where the seed
remains attached or fused with the ovary wall. Most nuts come from the
pistils with
inferior ovaries (see
flower) and all are
indehiscent (not opening at maturity). True nuts are produced, for example, by some plant families of the
order Fagales.
- Order Fagales (NOT all species produce true nuts)
A small nut may be called a
nutlet.
Nutlet may refer to one of the following. In
botany, this term specifically refers to a
pyrena or pyrene, which is a
seed covered by a stony layer, such as the kernel of a
drupe.
Walnuts and hickories (Juglandaceae) have fruits that are difficult to
classify. They are considered to be nuts under some definitions, but are
also referred to as drupaceous nuts. "Tryma" is a specialized term for
hickory fruits.
In common use, a "tree nut" is, as the name implies, any nut coming
from a tree. This most often comes up regarding allergies, where some
people are allergic specifically to peanuts (which grow on a bush),
others just to nuts that grow in trees.
Culinary definition and uses
A
walnut,
left, and its seed,
right, having been removed from its pericarp.
Korean Pine seeds — unshelled, and shell, above; shelled, below
A nut in
cuisine is a much less restrictive category than a nut in botany, as the term is applied to many
seeds that are not botanically true nuts. Any large, oily kernels found within a shell and used in food are commonly called nuts.
Nuts are an important source of nutrients for both humans and
wildlife. Because nuts generally have a high oil content, they are a
highly prized food and energy source. A large number of seeds are edible
by humans and used in cooking, eaten raw, sprouted, or roasted as a
snack food, or pressed for oil that is used in
cookery and
cosmetics.
Nuts (or seeds generally) are also a significant source of nutrition
for wildlife. This is particularly true in temperate climates where
animals such as
jays and
squirrels store
acorns and other nuts during the autumn to keep from starving during the late autumn, all of winter, and early spring.
Nuts used for food, whether true nut or not, are among the most common
food allergens.
Raw
mixed nuts, sold as a snack food. This is a "fancy" mix, meaning that it does not include peanuts.
Some fruits and seeds that do not meet the botanical definition but are nuts in the culinary sense are:
Nutrition
Nuts are very often high in nutrients because they are the source of
energy for the new plant. Most nuts contain a considerable quantity of
fat and vitamins and are rich in essential amino acids. The high energy
density makes nuts a very filling food.
A graph detailing the nutritional properties of nuts and oily seeds.
Several
epidemiological studies have revealed that people who consume nuts regularly are less likely to suffer from
coronary heart disease (CHD). Nuts were first linked to protection against CHD in 1993. Since then many
clinical trials have found that consumption of various nuts such as
almonds and
walnuts can lower serum
LDL
cholesterol concentrations. Although nuts contain various substances
thought to possess cardioprotective effects, scientists believe that
their Omega 3
fatty acid profile is at least in part responsible for the
hypolipidemic response observed in clinical trials.
In addition to possessing cardioprotective effects, nuts generally have a very low
glycemic index (GI). This is a result of their high fat and protein content and relatively low carbohydrate levels.
Consequently, dietitians frequently recommend nuts be included in diets prescribed for patients with
insulin resistance problems such as
diabetes mellitus type 2.
One study found that people who eat nuts live two to three years longer than those who do not. However, this may be because people who eat nuts tend to eat less
junk food.
Nuts contain the
essential fatty acids linoleic and linolenic acids, and the fats in nuts for the most part are
unsaturated fats, including
monounsaturated fats. Many nuts are good sources of vitamins E and B
2, and are rich in protein, folate, fiber, and essential minerals such as magnesium, phosphorus, potassium, copper, and selenium.
Nuts are most healthy in their raw form.
The reason is that up to 15% of the healthy oils that naturally occur in nuts are lost during the roasting process.
Raw or unroasted walnuts were found to have twice as many
antioxidants as other nuts.
Although initial studies suggested that antioxidants might promote
health, later large clinical trials did not detect any benefit and
suggested instead that excess supplementation of antioxidants is
harmful.
Nutrition Content
Table lists the nutrition content per 100 grams of raw nuts.
Almonds |
21.26 |
50.64 |
3.881 |
12.214 |
32.155 |
Walnuts |
15.23 |
65.21 |
6.126 |
47.174 |
8.933 |
Dry Roasted Unsalted Peanuts |
23.68 |
49.66 |
6.893 |
15.694 |
24.64 |
Pistachio |
20.61 |
44.44 |
5.44 |
13.455 |
23.319 |
Other uses
The nut of the
horse-chestnut tree (
Aesculus species, especially
Aesculus hippocastanum), is called a
conker in the
British Isles. Conkers are inedible because they contain toxic
glucoside aesculin. They are used in a popular children's game, known as
conkers,
where the nuts are threaded onto a strong cord and then each contestant
attempts to break their opponent's conker by hitting it with their own.
Horse chestnuts are also popular
slingshot ammunition.
Historical usage
Nuts, including the wild
almond,
prickly water lily,
acorns,
pistachio and
water chestnut, were a major part of the human diet 780,000 years ago.
Prehistoric humans developed an assortment of tools to crack open nuts during the
Pleistocene period.
Aesculus californica was eaten by the
Native Americans of
California during famines after the toxic constituents were leached out.