Salt
From Wikipedia, the free encyclopedia
Salt, also known as table salt or rock salt (halite), is a crystalline
mineral that is
composed primarily of sodium chloride
(NaCl), a chemical compound belonging to the larger class of ionic salts.
It is absolutely essential for animal life, but can be harmful to animals and plants in excess.
Salt is one of the oldest, most ubiquitous food seasonings and salting is an
important method of food preservation.
The taste of salt
(saltiness) is one of the basic human tastes.
Salt for human consumption is
produced in different forms: unrefined salt (such as sea salt), refined
salt (table salt), and iodized salt.
It is a crystalline solid, white, pale pink or light gray in color, normally
obtained from sea water or rock deposits. Edible rock salts may be slightly grayish
in color because of mineral content.
Because of its importance to
survival, salt has often been considered a valuable commodity during human
history. However, as salt consumption has increased during modern times,
scientists have become aware of the health risks associated with high salt
intake, including high blood pressure in sensitive individuals. Therefore, some health
authorities have recommended limitations of dietary sodium, although others
state the risk is minimal for typical western diets.
History
While people have used canning and
artificial refrigeration to preserve food for the last hundred years or so, salt has
been the best-known food preservative, especially for meat, for many thousands
of years.[1]
A very ancient saltworks operation has been discovered at the Poiana Slatinei
archaeological site next to a salt spring in Lunca, Neamţ County,
Romania. Evidence indicates that Neolithic
people of the Precucuteni
Culture were boiling the salt-laden spring
water through the process of briquetage
to extract the salt as far back as 6050 BC.[2]
The salt extracted from this operation may have had a direct correlation to the
rapid growth of this society's population soon after its initial production
began.[3]
The harvest of salt from the surface of Xiechi Lake
near Yuncheng in Shanxi, China dates back to at least 6000 BC, making it one of the
oldest verifiable saltworks.[4]:18–19
Salt was included among funeral
offerings found in ancient Egyptian tombs from the third millennium BC, as were salted birds
and salt fish.[4]:38 From about 2800 BC, the Egyptians began exporting salt fish
to the Phoenicians
in return for Lebanon cedar, glass, and the dye Tyrian purple;
the Phoenicians traded Egyptian salt fish and salt from North Africa
throughout their Mediterranean trade empire.[4]:44
In Africa, the Tuareg have
traditionally maintained routes across the Sahara especially for the transportation of salt by Azalai (salt caravans). In 1960, the caravans still carried some
15,000 tons of salt a year but this trade has now declined to roughly a third
of that figure.[5]
Salzburg, Hallstatt, and Hallein lie within 17 kilometers (11 mi) of each other on the
river Salzach in central Austria in an area with extensive salt deposits. Salzach literally
means "salt water" and Salzburg "salt city", both taking
their names from the German word Salz meaning salt. The equivalent Celtic word was Hall, and Hallstatt was the site of the
world's first salt mine.[6]
The town gave its name to the Hallstatt culture
that began mining for salt in the area in about 800 BC. Around 400 BC, the
townsfolk, who had previously used pickaxes and shovels, began open pan salt making. During the first millennium BC, Celtic communities grew
rich trading salt and salted meat
to Ancient Greece and Ancient Rome
in exchange for wine and other luxuries.[1]
The word salary
originates from Latin: salarium
which referred to the money paid to the Roman Army's
soldiers for the purchase of salt.[7][8][9]
The word salad literally means "salted", and comes from the ancient Roman
practice of salting leaf vegetables.[4]:64
In 1930, Mahatma Gandhi
led at least 100,000 people on the "Dandi March" or "Salt Satyagraha",
in which protesters made their own salt from the sea, which was illegal under British rule,
as it avoided paying the "salt
tax". This civil disobedience inspired millions of common people, and elevated the Indian
independence movement from an elitist struggle to a
national struggle.[10]
Forms
of salt
Unrefined
salt
Different natural salts have
different mineralities depending on their source, giving each one a unique flavor.
Fleur de sel,
a natural sea salt from the surface of evaporating brine in salt pans, has a
unique flavor varying with the region from which it is produced. In traditional
Korean cuisine, so-called "bamboo salt"
is prepared by roasting salt[11]
in a bamboo container
plugged with mud at both ends. This product absorbs minerals from the bamboo
and the mud, and has been claimed to increase the anticlastogenic
and antimutagenic
properties of doenjang (a fermented bean paste).[12]
Unrefined sea salt contains small
amounts of magnesium and calcium halides and sulfates, traces of algal
products, salt-resistant bacteria, and
sediment particles.[13]
The calcium/magnesium salts make unrefined sea salt hygroscopic
(it gradually absorbs moisture from air if stored uncovered) and confer a
faintly bitter overtone. Algal products contribute a mildly "fishy"
or "sea-air" odor, the latter from organobromine compounds. Sediments, the proportion of which varies with the source,
give the salt a dull gray appearance. Since taste and aroma compounds are often
detectable by humans in minute concentrations, sea salt may have a more complex
flavor than pure sodium chloride when sprinkled on top of food. When salt is
added during cooking however, these flavors would likely be overwhelmed by
those of the food ingredients.[13]
The refined salt industry cites
scientific studies saying that raw sea and rock salts do not contain enough iodine salts to prevent iodine deficiency diseases.[14]
Refined
salt
Refined salt, the most widely used form, is mainly composed of
sodium chloride. Food grade salt accounts for only a small part of salt
production in industrialized countries (3 percent in Europe)[15]
although worldwide, food uses account for 17.5 percent of salt production.[16]
The main bulk is sold for industrial use where it has great commercial value as
a necessary ingredient in many manufacturing processes. A few common examples
include the production of pulp and
paper, the use as a mordant in the dyeing of textiles and the
making of soaps and detergents.[17]
The manufacture and use of salt is
one of the oldest chemical industries.[18]
Salt can be obtained by evaporation of sea water,
usually in shallow basins warmed by sunlight;[19]
salt so obtained was formerly called bay salt, and is now often called sea salt
or solar salt. Rock salt deposits are formed by the evaporation of ancient salt
lakes,[20]
and may be mined
conventionally or through the injection of water. Injected water dissolves the
salt, and the brine solution can
be pumped to the surface where the salt is collected. The raw salt is then
refined to purify it and improve its storage and handling characteristics.
Purification usually involves recrystallization. In this process, a brine
solution is treated with chemicals that precipitate most impurities (largely
magnesium and calcium salts). Multiple stages of evaporation are then used to
collect pure sodium chloride crystals, which are kiln-dried.[21]
Table
salt
In many cuisines around the world,
salt is used in cooking, and is often found in salt shakers
on diners' eating tables for their personal use on food. Table salt is refined
salt, which contains about 97 to 99 percent sodium chloride.[22][23][24]
It usually contains additives that make it free-flowing, anticaking agents such
as sodium aluminosilicate or magnesium carbonate. Some people put a desiccant,
such as a few grains of uncooked rice[25]
or a saltine cracker,[26]
in their salt shakers to absorb extra moisture and help break up salt clumps
that may otherwise form. Table salt has a particle density
of 2.165 g/cm3, and a bulk density
(dry, ASTM D 632
gradation) of about 1.154 g/cm3.[27]
Additives
in table salt
Most table salt sold for consumption
contain additives which address a variety of health concerns, especially in the
developing world. The identities and amounts of additives vary widely from
country to country.
Iodine
and iodide
Iodine is important to prevent the
insufficient production of thyroid hormones
(hypothyroidism), which can cause goiter, cretinism
in children, and myxedema in adults.[28]
Iodine-containing compounds are added to table salt. Iodized salt is
thus table salt mixed with a minute amount of potassium iodide,
sodium iodide, or sodium iodate.
A small amount of dextrose may also be added to stabilize the iodine.[29]
Iodized salt is used to help reduce
the incidence of iodine deficiency in humans. Iodine deficiency affects about two billion
people and is the leading preventable cause of mental retardation.[30]
The practice began in 1924.[31]
Iodine deficiency commonly leads to thyroid gland
problems, specifically endemic goiter, a disease characterized by a swelling of the thyroid
gland, usually resulting in a bulbous protrusion on the neck. Iodized table
salt has significantly reduced disorders of iodine deficiency in countries
where it is used.[32]
The amount of iodine and the
specific iodine compound added to salt varies from country to country. In the
United States, the Food and
Drug Administration recommends [21 CFR 101.9
(c)(8)(iv)] 150 micrograms of iodine per day for both men and women. US iodized salt
contains 46–77 ppm (parts per million), whereas in the UK the iodine content of
iodized salt is recommended to be 10–22 ppm.[33]
Fluoride
A lack of fluorine in the
diet is the cause of a greatly increased incidence of dental caries.[34]
Fluoride salts can
be added to table salt with the goal of reducing tooth decay, especially in
countries that have not benefited from fluoridated toothpastes and fluoridated
water. The practice is more common in some European countries where water fluoridation is not carried out. In France, 35 percent of the table
salt sold contains added sodium fluoride.[35]
Anti-caking
agents
Sodium ferrocyanide, also known as yellow prussiate of soda, is sometimes added
to salt as an anticaking agent. The additive is considered safe for human
consumption.[36][37]
Such anti-caking agents have been added since at least 1911 when magnesium carbonate was first added to salt to make it flow more freely.[38]
The safety of sodium ferrocyanide as a food additive was found to be
provisionally acceptable by the Committee on Toxicity in 1988.[36]
Other anticaking agents sometimes used include tricalcium phosphate, calcium or magnesium carbonates, fatty acid salts (acid salts),
magnesium oxide, silicon dioxide,
calcium silicate, sodium aluminosilicate, and calcium aluminosilicate. Both the European Union and the United States Food and
Drug Administration (FDA) permitted the use of aluminum in the
latter two compounds.[39]
Iron
In "doubly fortified
salt", both iodide and iron salts are added. This additive alleviates iron deficiency anemia, which interferes with the mental development of an
estimated 40 percent of infants in the developing world. A typical iron
source is ferrous fumarate.[35]
Other
additives
Another additive, especially
important for pregnant women, is folic acid
(vitamin B9), which gives the table salt a yellow color. Folic acid
helps prevent neural tube defects (NTDs) and anemia, which affect young mothers, especially in
developing countries.[35]
Salty
condiments
In many East Asian cultures, salt is
not traditionally used as a condiment.[40]
In its place, condiments such as soy sauce,
fish sauce
and oyster sauce tend to have a high sodium content and fill a similar role
to table salt in western cultures. They are most often used for cooking rather
than as table condiments.[41]
Health
effects
Chloride and sodium ions, the two major components of salt, are needed by all
known living creatures in small quantities. Salt is involved in regulating the water content (fluid balance)
of the body. The sodium ion itself is used for electrical signaling in the
nervous system.[42]
Salt consumption has increased
during modern times and scientists have become aware of the health risks
associated with high salt intake, including high blood pressure
in sensitive individuals. Therefore, some health authorities have recommended
limitations of dietary sodium, although others state the risk is minimal for
typical western diets.[43][44][45][46][47]
The United States Department of Health and Human Services recommends that individuals consume no more than 1500–2300 mg
of sodium (3750–5750 mg of salt) per day depending on age.[48]
Salt is sometimes used as a health
aid, such as a high salt diet being used in the treatment of dysautonomia.[49]
Acute
effects
Too much or too little salt in the
diet can lead to muscle cramps, dizziness, or electrolyte disturbance, which can cause neurological problems, or death.[50]
Drinking too much water, with insufficient salt intake, puts a person at risk
of water intoxication (hyponatremia).[51]
Death can occur by ingestion of
large amounts of salt in a short time (about 1 g per kg of body weight).[52]
Deaths have also resulted from attempted use of salt solutions as emetics, forced salt intake, and accidental confusion of salt with
sugar in child food.[53]
Long-term
effects
The effect of salt consumption on
long term health outcomes is controversial.[54]
Some associations include:
- Stroke
and cardiovascular
disease.[55]
- High blood pressure:
Evidence shows an association between salt intakes and blood pressure
among different populations and age range in adults.[56]
Reduced salt intake also results in a small reduction in blood pressure.[54]
- Left
ventricular hypertrophy
(cardiac enlargement): "Evidence suggests that high salt intake
causes left ventricular hypertrophy, a strong risk factor
for cardiovascular disease, independently of blood pressure effects."[56]
"...there is accumulating evidence that high salt intake predicts
left ventricular hypertrophy."[57]
Excessive salt (sodium) intake, combined with an inadequate intake of
water, can cause hypernatremia.
It can exacerbate renal disease.[50]
- Edema:
A decrease in salt intake has been suggested to treat edema (fluid
retention).[50][58]
- Stomach cancer
is associated with high levels of sodium, "but the evidence does not
generally relate to foods typically consumed in the UK."[59]
However, in Japan, salt consumption is higher.[60]
However, a meta-analysis published
in The Journal of Hypertension found no strong evidence that reducing
salt intake affects the risk of heart attack, stroke or death in people with
normal or high blood pressure.[61]
Furthermore, the Journal of the American Medical Association has
reported that those excreting less salt (thus, presumably ingesting less) were
at increased risk of dying from heart disease.[61]
In 1994, the British Medical Journal published a randomized double blind, placebo controlled study examining 100 Dutch middle-aged and
elderly subjects with mild to moderate hypertension. A low sodium, high
potassium, high magnesium mineral salt was used at the table and in foods given
to the intervention group, with the control group using ordinary table salt in
their foods and at the table. Over a 24-week period, the researchers found a
reduced blood pressure in the intervention group, with mean blood pressure
falling by 7.6 mm Hg (systolic) and 3.3 mm Hg (diastolic) in the
mineral salt group compared with the control group.[62]
However, critics have pointed out that it is possible that some of the subjects
may have changed their dietary habits due to being able to distinguish the
mineral salt from table salt because of the difference in taste.[63]
According to The Mayo Clinic
and Australian Professor Bruce Neal, the health consequences of ingesting sea
salt or regular table salt are the same, as the content of sea salt is still
mainly sodium chloride.[64][65]
Recommended
intake
Recommended intakes of salt are
usually expressed in terms of sodium intake. Salt (as sodium chloride) contains
39.3 percent of sodium by weight.
Country
|
Description
|
Sodium
intake
mg per day |
Salt
intake
mg per day |
Authority
|
Remarks
|
United Kingdom
|
RNI: 1600
|
RNI: 4000
|
However, average adult intake is
two and a half times the RNI. SACN states, "The target salt intakes set
for adults and children do not represent ideal or optimum consumption levels,
but achievable population goals." The Food
Safety Authority of Ireland
endorses the UK targets.[57]
|
||
Canada
|
An Adequate Intake (AI) and
Upper Limit (UL) recommended for persons aged 9 years or more.
|
AI: 1200–1500
UL: 2200–2300 |
AI: 3000–3750
UL: 5500–5750 |
||
Australia and New Zealand
|
An Adequate Intake (AI) and an
Upper Level of intake (UL) defined for adults
|
AI: 460–920
UL: 2300 |
AI: 1150–2300
UL: 5750 |
Not able to define a recommended
dietary intake (RDI)
|
|
United States
|
An Upper Limit (UL) defined for
adults. A different upper limit defined for the special group comprising
people over 51 years of age, African Americans and people with hypertension,
diabetes, or chronic kidney disease (regardless of age).
|
UL: 2300
UL for special group: 1500 |
UL: 5750
UL for special group: 3750 |
The Food
and Drug Administration itself
does not make a recommendation, but refers readers to the dietary guidelines
given by this authority.[71]
|
A 2009 meta-analysis
found that the sodium consumption of 19,151 individuals from 33 countries fit
into the narrow range of 2,700 to 4,900 mg/day. The small range across
many cultures, together with animal studies, suggest that sodium intake is
tightly controlled by feedback loops in the body, making recommendations to
reduce sodium consumption below 2,700 mg/day potentially futile.[72]
Labeling
UK: The Food Standards Agency defines the level of salt in foods as follows: "High
is more than 1.5 g salt per 100 g (or 0.6 g sodium). Low is 0.3 g salt or less
per 100 g (or 0.1 g sodium). If the amount of salt per 100 g is in between
these figures, then that is a medium level of salt." In the UK, foods
produced by some supermarkets and manufacturers have 'traffic light' colors on
the front of the pack: red (high), amber (medium), or green (low).[73]
USA: The FDA Food Labeling Guide
stipulates whether a food can be labeled as "free" "low,"
or "reduced/less" in respect of sodium. When other health claims are
made about a food (e.g., low in fat, calories, etc.), a disclosure statement is
required if the food exceeds 480 mg of sodium per 'serving'.[74]
Campaigns
Consensus Action on Salt and Health
(CASH)[75]
established in the United Kingdom in 1996, actively campaigns to raise
awareness of the harmful health effects of salt. The 2008 focus includes
raising awareness of high levels of salt hidden in sweet foods that are
marketed towards children.[76]
In 2004, Britain's Food Standards Agency started a public health
campaign called "Salt – Watch it", which recommends no more than 6g
of salt per day; it features a character called Sid the Slug
and was criticised by the Salt Manufacturers Association (SMA).[77]
The Advertising Standards Authority did not uphold the SMA complaint in its adjudication.[78]
In March 2007, the FSA launched the third phase of their campaign with the
slogan "Salt. Is your food full of it?" fronted by comedienne Jenny Eclair.[79]
The University of Tasmania's Menzies
Research Institute maintains a website to educate
people about the problems of a salt-laden diet.[80]
In Australia, the "Drop the Salt! Campaign" aimed to reduce the
consumption of salt by Australians to 6g per day over the course of five years
ending in 2012.[81]
In January 2010, New York City
launched the National Salt Reduction Initiative, modeled after an initiative in
the United Kingdom. The campaign calls on food makers to voluntarily reduce the
amount of sodium in their foods, from 20 percent reduction in peanut butter
to a 40 percent reduction in canned vegetables, with an overall goal of
reducing sodium in packaged and restaurant foods by 25 percent by 2015.[82]
A number of major food producers have taken up the challenge and pledged to
reduce the sodium content of their food. Pepsi is developing a "designer salt" that's slightly
more powdery than the salt it regularly uses. The company hopes this new form
of salt will cut sodium levels by 25 percent in its Lay's potato chips.[83]
Nestlé's prepared
foods company, which produces frozen meals, announced that it will reduce
sodium in its foods by 10 percent by 2015.[84]
General Mills announced that it will reduce the sodium content of
40 percent of its foods by about 20 percent by 2015.[85]
In the United States, taxation of
sodium has been proposed as a method of decreasing sodium intake and thereby
improving health in countries where typical salt consumption is high.[86][87]
Taking an alternative view, the Salt Institute, a salt industry body based in
North America, is active in promoting the use of salt,[88]
and questioning or opposing the recommended restrictions on salt intake.[89]
Lowering
salt in diet
It is a misconception that sea salt
has a lower sodium content than table salt, — they are both basically sodium
chloride.[64][90][91]
A low sodium diet reduces the intake of sodium by the careful selection of
food. This aim can also be achieved by the use of a salt substitute,
and Potassium chloride is widely used for this purpose. Although recommended
limits for potassium are higher than for sodium, potassium has its own health
disadvantages, and it is advised that such a salt substitute not be used by
those taking certain prescription drugs.[92]
Another possibility being researched is the use of seaweed granules
in the manufacture of processed foods as an alternative to salt.[93]
Production
The world's oceans are a virtually
inexhaustible source of salt and this abundance of supply means that reserves
have not been calculated.[94]
The evaporation of seawater
is the method of choice in areas of high evaporation and low precipitation.
Elsewhere salt is extracted from the vast sedimentary deposits which have been
laid down over the millennia from the evaporation of seas and lakes. These are
either mined direct,
producing rock salt (halite), or are extracted in solution by pumping water into the
deposit. In either case the salt may be purified by mechanical evaporation in
pans under vacuum.[95]
In 2002, total world production (of
sodium chloride in general, not just table salt) was estimated at 210 million tonnes, the top five producers being the United States (40.3
million tonnes), China (32.9), Germany (17.7), India (14.5), and Canada (12.3).[96]
During the period 2003 to 2008, global production of salt increased by 12% per
year, and China took over as the largest producing nation as its chemical
industry expanded.[94]
Non-dietary
uses
Apart from its use in the human
diet, sodium chloride is widely used in industry and is one of the largest
inorganic raw materials used by volume. Its major chemical products are caustic soda
and chlorine and these
are used in the manufacture of PVC, plastics, paper pulp and many other inorganic and organic compounds. Salt itself
is used as a food preservative, flavouring agent, in minerals for livestock,
for de-icing, for snow control, as a water softening agent and in many
industrial processes.[94][95]
Usage
in religion
In the Hebrew Bible,
thirty-five verses mention salt,
[97]
one of which being the story of Lot's wife,
who was turned into a pillar of salt when she looked back at the cities of Sodom and Gomorrah (Genesis 19:26) as
they were destroyed. When the judge Abimelech destroyed the city of Shechem, he is
said to have "sown salt
on it," probably as a curse on anyone who would re-inhabit it (Judges
9:45). The Book of Job contains the first mention of salt as a condiment.
"Can that which is unsavoury be eaten without salt? or is there any taste
in the white of an egg?" (Job 6:6)[97]
In the Christian New Testament,
six verses mention salt. In the Sermon on the Mount, Jesus referred to his followers as the "salt of the earth".
The apostle Paul also encouraged Christians to "let your conversation
be always full of grace, seasoned with salt" (Colossians 4:6).[97]
Salt is mandatory in the rite of the
Tridentine Mass.[98]
Salt is used in the third item (which includes an Exorcism) of the
Celtic Consecration (cf. Gallican Rite)
that is employed in the consecration of a church. Salt may be added to the
water "where it is customary" in the Roman Catholic rite of Holy water.[98]
In Judaism, it is
recommended to have either a salty bread or to add salt to the bread if this
bread is unsalted when doing Kiddush for Shabbat. It is
customary to spread some salt over the bread or to dip the bread in a little
salt when passing the bread around the table after the Kiddush.[99]
To preserve the covenant between their people and God, Jews dip the Sabbath
bread in salt.[100]
In one of the Hadith recorded in Sunan Ibn Majah,
the Islamic Prophet Muhammad is reported to have said that: "Salt is the master of
your food. God sent down four blessings from the sky – fire, water, iron and salt".[101]
Salt is considered to be a very
auspicious substance in Hinduism and is used in particular religious ceremonies like
housewarmings and weddings.[101]
In Jainism, devotees offer raw rice and a pinch of salt before a deity to
signify their devotion and it is sprinkled on a person's cremated remains
before the ashes are buried. [102]
In Wicca, salt is symbolic of the element Earth. It is also believed
to cleanse an area of harmful or negative energies. A dish of salt and a dish
of water are almost always present on an altar. The salt is mixed with the water to consecrate
it, in effect producing holy water. This mixture is used in a wide variety of
rituals and ceremonies.[103]
In the native Japanese religion Shinto, salt is used for ritual purification of locations and people (harae, specifically
shubatsu), such as in sumo wrestling,
and small piles of salt called morijio (盛り塩?, pile of salt) or shiobana (塩花?, salt flowers) are placed in dishes by the entrance of
establishments for the two-fold purposes of warding off evil and attracting
patrons.[104]
In Aztec mythology, Huixtocihuatl
was a fertility goddess who presided over salt and salt water.[105]
The ancient Egyptians, Greeks and
Romans invoked their gods with offerings of salt and water. Some think this to
be the origin of Holy Water in the Christian faith.[100]
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