GENERAL FEATURES:
Components:
° 0.015% essential oil containing sulfide compounds: when the bulb is bruised by allinase are degraded in flavonoid disulfides;
° minerals (potassium, sodium, zinc, iron, calcium, phosphorus, vitamin C).
° fruffosan (10-40%), pectin, inulin
° glycolic acid
° polyphenols (tannins, pyrocatechol} trace-caffeic acid and chlorogenic
Onion (Allium cepa L.) is botanically included in the Liliaceae and species are found across a wide range of latitudes and altitudes in Europe, Asia, N. America and Africa. World onion production has increased by at least 25% over the past 10 years with current production being around 44 million tonnes making it the second most important horticultural crop after tomatoes. Because of their storage characteristics and durability for shipping, onions have always been traded more widely than most vegetables. Onions are versatile and are often used as an ingredient in many dishes and are accepted by almost all traditions and cultures. Onion consumption is increasing significantly, particularly in the USA and this is partly because of heavy promotion that links flavour and health. Onions are rich in two chemical groups that have perceived benefits to human health. These are the flavonoids and the alk(en)yl cysteine sulphoxides (ACSOs). Two flavonoid subgroups are found in onion, the anthocyanins, which impart a red/purple colour to some varieties and flavanols such as quercetin and its derivatives responsible for the yellow and brown skins of many other varieties. The ACSOs are the flavour precursors, which, when cleaved by the enzyme alliinase, generate the characteristic odour and taste of onion. The downstream products are a complex mixture of compounds which include thiosulphinates, thiosulphonates, mono-, di- and tri-sulphides. Compounds from onion have been reported to have a range of health benefits which include anticarcinogenic properties, antiplatelet activity, antithrombotic activity, antiasthmatic and antibiotic effects. Here we review the agronomy of the onion crop, the biochemistry of the health compounds and report on recent clinical data obtained using extracts from this species. Where appropriate we have compared the data with that obtained from garlic (Allium sativum L.) for which more information is widely available.
TEARS:
Onions are rich in vitamins and minerals. The characteristic smell of the cut bulbs is due to the abundance of sulfoxides, primarily the trans-tiopropanal-S-oxide. Slice the onions makes my eyes water because of precursors present in the cytoplasm , alkyl or alkenyl cysteine sulfoxide ( ACSO ) , after cutting are combined with allinase , an enzyme that is released from the vacuole , and the combination of these elements produces acids solfenici , pyruvate and ammonia. The acid sulfenico , if attacked by a second enzyme called Factor Lacrimathory Shyntase produces syn- propanethial S oxide , a molecule voltatile and water soluble , which is precisely the tear factor because , when it comes into contact with the aqueous humor on the bulb ocular , is transformed into sulfuric acid (image)
The contact with the sulfuric acid causes an immediate defense reaction by the eye, consisting in the production of tears , but the increased amount of secreted aqueous eye that does not transform a greater amount of propylene oxide in sulfuric acid , in a chain reaction.
It is just to reduce the amount of factor released tear that one of the solutions adopted to cut onions without tears is to do it under running water: the compound is very water-soluble so if it decreases the volatility.
The alliin lyase (or alliinase) is an enzyme belonging to the class of lyases present in plants of the genus Allium, such as garlic and onion. The alliin lyase is responsible for the catalysis of chemical reactions involved in the production of volatile compounds that give these foods the characteristic aromas, smells and tear properties. In particular, it catalyzes the following reaction:
an S-alkyl-L-cysteine S-oxide ⇄ an alkyl sulfonate + 2-aminoacrilato
The alliin lyase is part of the defensive system that these plants adopt to counter the herbivores. Normally, the alliin lyase is contained within the cells of the plant, particularly around the tissue forming the cribro-vascular bundles, but as a result of an injury caused by an animal that wants to eat it, this enzyme is released by producing irritating compounds. It all translates into a deterrent for animals. The same reaction occurs after cutting or pestamento onion and garlic for culinary purposes.
In garlic, a alliin lyase converts alliin to allicin. In onions, the enzyme acts on solfenici groups (-S-OH) of biomolecules by producing the compound CH3-CH2-CH = S +-O-.
Diuretic:
The diuretic action is due, in part, to the presence of potassium salts, substances cinarinosimilar and glycolic acid.
The diuretic action of glycolic acid is manifested not only in the elimination of water, but also in the elimination of chlorides and urea, an action that takes place after a certain latency (48-72 hours after dosing), and this because the action is kind of hepatorenal.
The activity in the liver would be demonstrated by the reduction of elevated blood parameters, such as the rate uremic, the values of prothrombin, serum cholesterol, and a fall in the ratio free cholesterol / esterified cholesterol, demonstrating an exaltation of esterification processes.
The increased bile secretion is attributable to the presence of caffeic acid and chlorogenic acid, substances cinarinosimili also equipped with a remarkable diuretic activity.
The diuretic action is essentially due to flavonoids and potassium salts. The presence of glycolic acid is responsible for the action hepatorenal attributed to the plant due to which there has been an improvement in the liver and kidney function that is reflected in particular on urogrenesi, diuresis and the power of concentration of the kidney. It would thus favored the elimination of chloride, urea, and generally of catabolites. To this is added the action of flavonoids which in addition to anti-inflammatory action that are to play at the level of the pelvis and the bladder are hepatoprotectors, antispasmodic, antibacterial, and diuretic.
Antiplatelet:
Onion has been shown to favorably modify the lipoprotein profile. However, research on its underlying mechanism is lacking. The present study investigated the interaction of dietary onion powder with the protein expression of key receptors and enzymes involved in cholesterol metabolism. Thirty-six male hamsters were randomly divided into three groups and fed a high-cholesterol control diet or the two experimental diets supplemented with 1% onion powder (OP-1) or 5% onion powder (OP-5), for a period of 8 weeks. It was found that onion dose-dependently decreased plasma total cholesterol (TC) level. The change in plasma lipoprotein profile was accompanied by a greater excretion of both fecal neutral and acidic sterols. Western blot analysis revealed that onion up-regulated sterol regulatory element binding protein 2 (SREBP-2), liver X receptor alpha (LXRα) and cholesterol-7α-hydroxylase (CYP7A1) with no effect on 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) and LDL receptor (LDL-R). It was concluded that the hypocholesterolemic activity of onion powder was mediated by enhancement of fecal sterol excretion and up-regulation of LXRα and CYP7A1.
antitrombotic
In vitro effects of an oily extract of onion were examined on the metabolism of arachidonic acid (AA) in human platelets. Onion was found to reduce the formation of thromboxane and lipoxygenase products from exogenous arachidonic acid in platelets; it did not inhibit the incorporation of AA into platelet phospholipids. While not affecting the platelet phospholipase activity it did reduce the formation of thromboxane B2 and lipoxygenase products in platelets that were prelabelled with arachidonic acid and then activated by A23187. This suggests that onion inhibits the formation of AA metabolites by exerting its effect at steps later than the liberation of AA. With concentrations of onion extract producing abolition of AA-induced aggregation, only partial inhibition of aggregation was observed with ADP- and epinephrine-induced aggregation. Onion did not inhibit A23187 induced aggregation. The results suggest that inhibition of platelet aggregation by onion is mediated largely by its effect on platelet thromboxane production.
Similarly to garlic, onion has anti-platelet activity and fibrinolytic activity due to sulfur compounds .
Of the latter , most of which are inhibitors of cyclooxygenase and lipoxygenase .
The onion contain a substance called rutin, able to prevent the formation of blood clots , those lumps , or emboli , which can cause heart attacks and strokes and that depend on a malfunction of the cardiovascular system . Well, the U.S. scholars at Harvard Medical School in Boston , found that rutin is able to block an enzyme called PDI ( protein disulfide isomerase ), involved in the formation of blood clots own . Robert Flaumenhaft , coordinator of the study published in the Journal of Clinical Investigation , explains the importance of the discovery : " Rutin has been shown to be the most powerfully anti- thrombotic compound we have ever tested in this model. The clots are formed both in the arteries than in veins. Blood clots in the arteries are rich in platelets, while those in the veins are rich in fibrin. This finding suggests that a single agent is able to treat and prevent both types of lumps " . Furthermore , the onion , as well as other foods that contain rutin , are not drugs , have no side effects and are excellent to be enjoyed , even if the next step of the researchers , will be to produce a molecule of rutin in synthesis by test on humans instead of other anti clot : "It ' a safe and inexpensive , can reduce recurrent clots that could help save thousands of lives."
Returning to the discussion of aspirin , this is a good anticoagulant also because it inhibits the production of thromboxane , a compound that promotes the aggregation of platelets . The thromboxane may be hindered in the same way from substances that occur naturally in garlic , or the ajoene and adenosine , the latter also widespread in the onions. The onions also avoid the accumulation of lipids in the blood , another aspect that can produce thickening and promote clotting.
The onion contains a compound called rutin, a glycoside flavonoico that acts as an anticoagulant both in the veins and in the arteries. Rutin , also known as quercetin 3 rutinoside or vitamin P does not intervene directly on the blood clot but on a class of enzymes called disulfide isomerase that are rapidly released from the cells when the blood clots within the vessels . In this way it effectively inhibits the accumulation of both platelet both the production of fibrin. Rutin is not found only in apples but also in oranges , grapefruits , lemons in in buckwheat , tea , red wine , in peppermint and cipolle.Analogamente Garlic has anti-platelet aggregation and fibrinolytic activity due the sulfur compounds .
Of the latter , most of which are inhibitors of cyclooxygenase and lipoxygenase .
A positive feature of the onion that is consumed in salads (which is impossible for garlic ) inhibits the growth of bacteria responsible for tooth decay
The onion ( but also the apples and tea, both black and green) also contain a substance called rutin, able to prevent the formation of blood clots , those lumps , or emboli , which can cause heart attacks and strokes and that depend on a malfunction of the cardiovascular system . Well, the U.S. scholars at Harvard Medical School in Boston , found that rutin is able to block an enzyme called PDI ( protein disulfide isomerase ), involved in the formation of blood clots own . Robert Flaumenhaft , coordinator of the study published in the Journal of Clinical Investigation , explains the importance of the discovery : " Rutin has been shown to be the most powerfully anti- thrombotic compound we have ever tested in this model. The clots are formed both in the arteries than in veins. Blood clots in the arteries are rich in platelets, while those in the veins are rich in fibrin. This finding suggests that a single agent is able to treat and prevent both types of lumps " . Furthermore , the onion , as well as other foods that contain rutin , are not drugs , have no side effects and are excellent to be enjoyed , even if the next step of the researchers , will be to produce a molecule of rutin in synthesis by test on humans instead of other anti clot : "It ' a safe and inexpensive , can reduce recurrent clots that could help save thousands of lives."
Returning to the discussion of aspirin , this is a good anticoagulant also because it inhibits the production of thromboxane , a compound that promotes the aggregation of platelets . The thromboxane may be hindered in the same way from substances that occur naturally in garlic , or the ajoene and adenosine , the latter also widespread in the onions. The onions also avoid the accumulation of lipids in the blood , another aspect that can produce thickening and promote clotting.
