Honey (play /ˈhʌni/) is a sweet food made by bees using nectar from flowers. The variety produced by honey bees (the genus Apis) is the one most commonly referred to and is the type of honey collected by beekeepers and consumed by humans. Honey produced by other bees and insects has distinctly different properties.

Honey bees transform nectar into honey by a process of regurgitation, and store it as a primary food source in wax honeycombs inside the beehive. Beekeeping practices encourage overproduction of honey so the excess can be taken from the colony.

Honey gets its sweetness from the monosaccharides fructose and glucose, and has approximately the same relative sweetness as that of granulated sugar. It has attractive chemical properties for baking, and a distinctive flavor that leads some people to prefer it over sugar and other sweeteners. Most microorganisms do not grow in honey because of its low water activity of 0.6.However, honey sometimes contains dormant endospores of the bacterium Clostridium botulinum, which can be dangerous to infants, as the endospores can transform into toxin-producing bacteria in the infant's immature intestinal tract, leading to illness and even death[4] (see Health hazards below).

Honey has a long history of human consumption, and is used in various foods and beverages as a sweetener and flavoring. It also has a role in religion and symbolism. Flavors of honey vary based on the nectar source, and various types and grades of honey are available. It is also used in various medicinal traditions to treat ailments. The study of pollens and spores in raw honey (melissopalynology) can determine floral sources of honey. Because bees carry an electrostatic charge, and can attract other particles, the same techniques of melissopalynology can be used in area environmental studies of radioactive particles, dust or particulate pollution

Formation

A honey bee on calyx of goldenrod

Honey natural sugars are dehydrated to prevent fermentation, with added enzymes to modify and transform their chemical composition and pH. Invertases and digestive acids hydrolyze sucrose to give the monosaccharides glucose and fructose. The invertase is one of these enzymes synthesized by the body of the insect.

Honey bees transform saccharides into honey by a process of regurgitation, a number of times, until it is partially digested. The bees do the regurgitation and digestion, as a group. After the last regurgitation, the aqueous solution is still high in water, so the process continues by evaporation of much of the water and enzymatic transformation.

Honey is produced by bees as a food source. In cold weather or when fresh food sources are scarce, bees use their stored honey as their source of energy.[8] By contriving for bee swarms to nest in artificial hives, people have been able to semidomesticate the insects, and harvest excess honey. In the hive (or in a wild nest), there are three types of bees:

  • a single female queen bee
  • a seasonally variable number of male drone bees to fertilize new queens
  • some 20,000 to 40,000 female worker bees.[9]

The worker bees raise larvae and collect the nectar that will become honey in the hive. Leaving the hive, they collect sugar-rich flower nectar and return.

In the hive, the bees use their "honey stomachs" to ingest and regurgitate the nectar a number of times until it is partially digested.[10] Invertase synthesized by the bees and digestive acids hydrolyze sucrose to give the same mixture of glucose and fructose. The bees work together as a group with the regurgitation and digestion until the product reaches a desired quality. It is then stored in honeycomb cells. After the final regurgitation, the honeycomb is left unsealed. However, the nectar is still high in both water content and natural yeasts, which, unchecked, would cause the sugars in the nectar to ferment.[8] The process continues as bees inside the hive fan their wings, creating a strong draft across the honeycomb, which enhances evaporation of much of the water from the nectar.[8] This reduction in water content raises the sugar concentration and prevents fermentation. Ripe honey, as removed from the hive by a beekeeper, has a long shelf life, and will not ferment if properly sealed.[8]

Physical and chemical properties

Crystallized honey. The inset shows a close-up of the honey, showing the individual glucose grains in the fructose mixture.

The physical properties of honey vary, depending on water content, the type of flora used to produce it [pasturage], temperature, and the proportion of the specific sugars it contains. Fresh honey is a supersaturated liquid, containing more sugar than the water can typically dissolve at ambient temperatures. At room temperature, honey is a supercooled liquid, in which the glucose will precipitate into solid granules. This forms a semisolid solution of precipitated sugars in a solution of sugars and other ingredients.

The melting point of crystallized honey is between 40 and 50 °C (104 and 122 °F), depending on its composition. Below this temperature, honey can be either in a metastable state, meaning that it will not crystallize until a seed crystal is added, or, more often, it is in a "labile" state, being saturated with enough sugars to crystallize spontaneously.[11] The rate of crystallization is affected by the ratio of the main sugars, fructose to glucose, as well as the dextrin content. Temperature also affects the rate of crystallization, which is fastest between 13 and 17 °C (55 and 63 °F). Below 5 °C, the honey will not crystallize and, thus, the original texture and flavor can be preserved indefinitely.[12]

Since honey normally exists below its melting point, it is a supercooled liquid. At very low temperatures, honey will not freeze solid. Instead, as the temperatures become colder, the viscosity of honey increases. Like most viscous liquids, the honey will become thick and sluggish with decreasing temperature. While appearing or even feeling solid, it will continue to flow at very slow rates. Honey has a glass transition between -42 and -51 °C (-44 and -60 °F). Below this temperature, honey enters a glassy state and will become an amorphous solid (noncrystalline).[13][14]

The viscosity of honey is affected greatly by both temperature and water content. The higher the humidity, the easier honey will flow. Above its melting point, however, water has little effect on viscosity. Aside from water content, the composition of honey also has little effect on viscosity, with the exception of a few types. At 25 °C (77 °F), honey with 14% humidity will generally have a viscosity of around 400 poise, while a honey containing 20% humidity will have a viscosity of around 20 poise. Viscosity increase due to temperature occurs very slowly at first. A honey containing 16% humidity, at 70 °C (158 °F), will have a viscosity of around 2 poise, while at 30 °C (86 °F), the viscosity will be around 70 poise. As cooling progresses, honey will become more viscous at an increasingly rapid rate, reaching 600 poise around 14 °C (57 °F). However, while honey is very viscous, it has rather low surface tension.[15][16]

A few types of honey have unusual viscous properties. Honey from heather or manuka display thixotropic properties. These types of honey enter a gel-like state when motionless, but then liquify when stirred.[17]

Since honey contains electrolytes, in the form of acids and minerals, it exhibits varying degrees of electrical conductivity. Measurements of the electrical conductivity are used to determine the quality of honey in terms of ash content.[16]

The effect honey has on light is useful for determining the type and quality. Variations in the water content alter the refractive index of honey. Water content can easily be measured with a refractometer. Typically, the refractive index for honey will range from 1.504 at 13% humidity, to 1.474 at 25%. Honey also has an effect on polarized light, in that it will rotate the polarization plane. The fructose will give a negative rotation, while the glucose will give a positive one. The overall rotation can be used to measure the ratio of the mixture.[16][18]

Honey has the ability to absorb moisture directly from the air, a phenomenon called hygroscopy. The amount of water the honey will absorb is dependent on the relative humidity of the air. This hygroscopic nature requires that honey be stored in sealed containers to prevent fermentation. Honey will tend to absorb more water in this manner than the individual sugars would allow on their own, which may be due to other ingredients it contains.[18]

Like all sugar compounds, honey will caramelize if heated too much, becoming darker in color and eventually burning. However, honey contains fructose, which caramelizes at lower temperatures than the glucose.[19] Honey also contains acids, which act as catalysts, decreasing the caramelization temperature even more.[20] Of these acids, the amino acids, which occur in very small amounts, play an important role in the darkening of honey. The amino acids form darkened compounds called melanoidins, during a Maillard reaction. The temperature at which caramelization begins varies, depending on the composition, but is typically between 70 °C (158 °F) and 110 °C (230 °F). The Maillard reaction will occur slowly at room temperature, taking from a few to several months to show visible darkening, but will speed-up dramatically with increasing temperatures. However, the reaction can also be slowed by storing the honey at colder temperatures.[21]

Unlike many other liquids, honey has very poor thermal conductivity, taking a long time to reach thermal equilibrium. Melting crystallized honey can easily result in localized caramelization if the heat source is too hot, or if it is not evenly distributed. However, honey will take substantially longer to liquify when just above the melting point than it will at elevated temperatures.[16] Melting 20 kilograms of crystallized honey, at 40 °C (104 °F), can take up to 24 hours, while 50 kilograms may take twice as long. This time can be cut nearly in half by heating at 50 °C (122 °F). However, many of the minor substances in honey can be affected greatly by heating, changing the flavor, aroma, or other properties, so heating is usually done at the lowest temperature possible for the shortest amount of time.

Acid content

The average pH of honey is 3.9, but can range from 3.4 to 6.1. Honey contains many kinds of acids, both organic and amino. However, the different types and their amounts vary considerably, depending on the type of honey. These acids may be aromatic or aliphatic (non-aromatic). The aliphatic acids contribute greatly to the flavor of honey by interacting with the flavors of other ingredients. Gluconic acid, for instance, is a flavor enhancer. The aromatic acids, such as malic acid, come mostly from the flowers, adding to the aroma and taste of the honey.

Honey can contain up to 18 of the 20 amino acids. However, amino acid content is almost negligible in honey, accounting for only 0.05–0.1% of the composition. The main amino acid is proline.

Organic acids comprise most of the acids in honey, accounting for 0.17–1.17% of the mixture. Gluconic acid is the most prevalent. Gluconic acid is formed by the actions of an enzyme called glucose oxidase. Other organic acids are minor, consisting of formic, acetic, butyric, citric, lactic, malic, pyroglutamic, propionic, valeric, capronic, palmitic, and succinic, among many others.

Modern uses

As a food and in cooking

The main uses of honey are in cooking, baking, as a spread on bread, and as an addition to various beverages, such as tea, and as a sweetener in some commercial beverages. According to the The National Honey Board (a USDA-overseen organization), "honey stipulates a pure product that does not allow for the addition of any other substance...this includes, but is not limited to, water or other sweeteners".[34] Honey barbecue and honey mustard are common and popular sauce flavors.

Honey is the main ingredient in the alcoholic beverage mead, which is also known as "honey wine" or "honey beer". Historically, the ferment for mead was honey's naturally occurring yeast. Honey is also used as an adjunct in some beers.

Honey wine, or mead, is typically (modern era) made with a honey and water mixture with a pack of yeast added for fermentation. Primary fermentation usually takes 40 days, after which the must needs to be racked into a secondary fermentation vessel and left to sit about 35–40 more days. If done properly, fermentation will be finished by this point (though if a sparkling mead is desired, fermentation can be restarted after bottling by the addition of a small amount of sugar), but most meads require aging for 6–9 months or more in order to be palatable

In medicine

Historically, honey has been used by humans to treat a variety of ailments, from gastric disturbances to ulcers, wounds and burns, through ingestion or topical application, but only recently have the antiseptic and antibacterial properties of honey been chemically explained. Different honeys have different properties, which was known since ancient times. Much scientific research has been done, with emphasis of late on fighting infections in wounds. [66] The antibacterial mechanisms know to date are H2O2, methylglyoxal(MGO), bee defensin-1, the osmotic effect and the pH. [67]

In Ayurveda, a 4000-year-old medicine originating from India, honey is considered to positively affect all three primitive material imbalances of the body. "Vaatalam guru sheetam cha raktapittakaphapaham| Sandhatru cchedanam ruksham kashayam madhuram madhu|| "It has sweetness with added astringent as end taste. It is heavy, dry and cold. Its effect on doshas (imbalances) is that it aggravates vata (air / moving forces), scrapes kapha (mucus / holding forces) and normalizes pitta (catabolic fire) and rakta (blood). It promotes the healing process." Some wound gels which contain antibacterial raw honey and have regulatory approval are now available to help treat drug-resistant strains of bacteria (MRSA). One New Zealand researcher says a particular type of honey (manuka honey) may be useful in treating MRSA infections.[68])

As an antimicrobial agent honey is useful in treating a variety of ailments. Antibacterial properties of honey are the result of the low water activity causing osmosis, chelation of free Iron, its slow release of hydrogen peroxide,[69] high acidity,[70] and the antibacterial activity of methylglyoxal.[71]

Honey appears to be effective in killing drug-resistant biofilms which are implicated in chronic 

source : wikipedia

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نوشته شده در تاریخ سه شنبه 13 تیر 1391    | توسط: علی عظیمی    | طبقه بندی: مواد وبدن انسان، داروها،     | نظرات()