Some of the Health Attributes of Onions

09/05/2011 12:26:00 AM by Joel Canestrino – Onion Breeder

Joel CanestrinoHello there, the Short-Day onion breeder for Hazera in the United States here. My breeding program is in New Mexico, just a few miles south of Las Cruces. Many plant breeders work on only one or two commodities for their entire career becoming experts not just on the breeding and genetics of their crops, but also the culinary uses, processing, marketing, seed production and agronomy of their crops as well.

The development of agriculture in the Levant dates to 10,000-12,000 years before present. Production of domesticated onion was recorded nearly 5,000 years ago in Egypt. The Russian botanist Nikolay Vavilov described the Pamir Mountain region of southern Tajikistan as the area of origin for onions in 1916. The bulb onion, Allium cepa, is known only as a domesticated species. Its wild progenitor is uncertain, like so many other domesticated crops that were extensively modified by the plant breeders of antiquity. The eastern Mediterranean is considered an area of diversity for domesticated onion species. The UNFAO lists onion as the second most important vegetable crop, by tonnage, in the world, second only to tomatoes. Onions are grown over a much wider geographic range than are tomatoes, spanning over 170 countries.

Onions are used as a fresh vegetable, pickled vegetable, dehydrated spice and as a medicinal herb. From a nutritional standpoint, onions do not have a lot to commend them. They are low in fat, but also low in protein and carbohydrates. They are only a moderately good source of Vitamin C, Vitamin B6, Folic acid and potassium. They are low in salt and relatively high in dietary fiber. Onions are valued for the low-calorie, flavor punch they add to almost any dish. In southern New Mexico we could not imagine enchiladas without a liberal amount of spicy green chile sauce and freshly chopped onions sprinkled on top. Onions are packed with all sorts of beneficial “phytochemicals” in addition to traditional vitamins and nutrients. For centuries, onions have been highly valued for their medicinal qualities by many cultures.
The three main families of compounds which give onions their beneficial health attributes are flavonoids, fructans and organosulfur compounds. Quercetin, and to a lesser extent kaempferol, are the primary flavonoids in onion. Quercetin pigments yellow onions and is concentrated in the outer, dry tunicate skins and in the first several fleshy scales. The pigment anthocyanin is found in red onions and is the same pigment that gives red wine its color. White onions are largely devoid of quercetin and anthocyanin. The flavonoids are considered to have powerful anti-oxidative activity via metal ion chelation and inhibition of lipid peroxidation. Epidemiological studies indicate that regular consumption of red and yellow onions can reduce the incidence of stomach, bladder, colon, breast, ovarian and brain cancer, moderate the symptoms of diabetes, reduce the incidence and severity of cataracts and reduce inflammations and coronary heart disease via their flavonoid content. Tea and apples are also high in quercetin, but the quercetin in onions has a higher bioavailability. The flavonoids in onions are more heat-stable than the organosulfur compounds, light cooking actually improves their bioavailability.

The health attributes associated with the organosulfur compounds in onions are concerned mostly with antibacterial activity, leading to reduced stomach and colorectal cancers and onion induced anti-platelet activity (OIAA). OIAA is associated with a reduction in cardiovascular disease and stroke. To get the full health benefits of the organosulfur compounds in onions it is better to eat pungent onions raw, the organosulfur compounds are quickly degraded by cooking and are present in lower concentrations in mild onions. There are three primary alkenyl cysteine sulphoxide (ACSO) flavor precursors in onions. Alliinase, an enzyme, is contained in the vacuoles of the cells and the ACSOs are in the cytoplasm. When the onion is macerated, the enzyme will react with the ACSO’s to form volatile sulfur compounds such as thiopropanal S-oxide, the tear inducing lachrymatory factor. Onions that are boiled or cooked whole will denature the alliinase before it can react with the ACSO flavor precursors, resulting in a very mild flavor.

Fructans are the primary storage carbohydrate in onions. Onions do not produce starch and usually only have small amounts of the “sweet” sugars glucose, sucrose and fructose. Fructans are thought to not only serve as storage carbohydrates for the onion, but also protect the onion against drought and cold stress. The primary fructan in onions is inulin. The human digestive tract does not have enzymes to digest inulin in the small intestine, but bifidobacteria in the large intestines do, thus inulin is considered a source of semi-soluble fiber in the diet. In the small intestine, inulin serves as an insoluble bulking agent slowing digestion, lessening the impact on glycemic index and binding to lipids. In the large intestine, inulin and other oligosaccharides from onion are pre-biotics that stimulate the growth of pro-biotic (beneficial) bacteria in the intestinal tract.

Globally, per capita onion consumption is around fifteen pounds a year, but is as high as seventy pounds a year per person in Libya. Onions have been an important part of traditional folk medicine in China and India for centuries. As part of a health conscious diet, onions add tons of flavor and very few calories. Their potential to reduce blood clotting and improve digestion is no longer disputed by modern medicine. They are easy to grow in the garden and inexpensive to purchase in the grocery store. By adding colorful, flavorful fresh vegetables and fruits to every meal the health benefits of natural, whole foods can be enjoyed by the entire family.