The turnip is a vegetable plant, belonging to the same family as the rutabaga and cabbage. It is grown for its root, which is consumed as a vegetable. According to the varieties, it offers different shapes, elongated or rounded, and various colours ranging from white to pale yellow, often tinged with purple at the base of the leaves. This vegetable is the flagship ingredient in soups.
History of turnip
It is generally said that the turnip came from the Mediterranean basin. However, several vegetable plants belonging to the same species (Brassica rapa) originated in China. One of the assumptions currently under consideration is that it would have came from two independent varieties for this species. The first would have came from the more western regions (Europe, India and Central Asia) and it would include turnip, rutabaga and shuttle (now called rapeseed or canola). The second, would instead come from East Asia, and would include the many varieties of “Chinese cabbage” grown for their roots or leaves: ta-tsoi, Hon Tsai Tai, Mibuna, Mizuna, Komatsuna, Pac Choi, Bok choi, Pai lo lo, etc.
The Greeks and Romans knew many varieties of turnips. In the first century A.D., Pliny the Elder described, under the names of Rapa and Napus, turnips of elongated, flat and round form. At the same time, the vegetable was used in France for food for both humans and farm animals. Later, it will become an important food of the English that will boil or roast its roots, leather its leaves and prepare its young stems in salad.
The turnip was introduced in America by Jacques Cartier in 1541. with lettuce and cabbage, it will be the first vegetable of the old world to be grown in new France. The Amerindians will adopt it and quickly grow it.
Most turnip varieties have white flesh while the rutabagas is usually yellow, although the opposite is sometimes true. On the other hand, they can be differentiated for sure by their leaves: those of the rutabaga are smooth like those of the cabbage, while those of the turnip are rough and hairy.
It seems that the rutabaga was born from a spontaneous cross between a kale and a turnip (hence the name of turnip that is given to him on occasion). It is likely that this crossing has occurred in Europe, but we do not know when exactly. In any case, the first specimen was discovered at the end of the Middle Ages. This is not mentioned in the books before 1620, when a Swiss botanist will give a detailed description. The English name of Swede turnip suggests that it is in Sweden, or in one of the neighbouring countries, this hybrid was born.
Turnip is a vegetable of the family of the Diamondbacks, bulbous and white flesh; Its leaves are also edible. In Quebec, what is often called “turnip” is in fact the rutabaga, related to the turnip, but to the more yellow flesh. The Rutabaga is also known as the “Siam cabbage”.
Active principles and properties
For vegetables in general and the Brassicas
Several epidemiological studies have shown high consumption of vegetables and fruit decreases the risk of cardiovascular disease, certain cancers and other chronic diseases. Some mechanisms of action have been proposed to explain this protective effect; The presence of antioxidants in vegetables and fruits could play a role in it.
With regard to the vegetables of the family of the brassicas (among other things turnip and rutabaga, broccoli, and cauliflower), epidemiological studies show their regular consumption could help to prevent certain cancers such as lungs, ovaries and kidneys cancers (in the latter case, among woman). In addition, a study showed frequent consumption of brassicas (more than 30 times per month) was associated with a lower blood concentration of homocysteine, an amino acid constituting a risk factor for cardiovascular disease, when its concentration is too high in the blood. Finally, a study exploring cognitive function among older women found those who consumed the most often crucifers had a lower cognitive decline than those who consumed the least often, a result for the moment still preliminary.
For turnip and rutabaga
Glucosinolates. These compounds are mainly found in the crucifers, including turnip and rutabaga. Glucosinolates are biologically inactive, but when the food undergoes physical transformations (chopped, chewed, etc.), the glucosinolates come into contact with an enzyme present in the food, called myrosinase. Glucosinolates can then be transformed into active molecules called isothiocyanates: many of these molecules would help limit the development of cancer. Cooking reduces the activity of myrosinase, reducing the ability to transform glucosinolates into active compounds. However, intestinal bacterial flora can also be part of the transformation of glucosinolates into isothiocyanates, which could partially compensate for the loss of myrosinase activity in cooked foods.
Phenylethyl isothiocyanate (PEITC). This active isothiocyanate is derived from the transformation of gluconasturtiin, a glucosinolate which contains turnip and rutabaga. In an in vitro research study, PEITC has notably decreased the development of cancer cells and certain metastases. However, other studies are essential to ascertain whether these properties can be applied to humans, but especially if the consumption of turnip or rutabaga provides the same benefits as the PEITC itself.
Antioxidants (turnip leaves). Antioxidants are compounds that protect the body’s cells from damage caused by free radicals. The latter are highly reactive molecules that would be involved in the development of cardiovascular diseases, certain cancers and other diseases related to ageing. The turnip leaves are rich in antioxidants, some of which have been the subject of research.
Lutein and zeaxanthin. The turnip leaves are among the best sources of lutein and zeaxanthin, two antioxidant compounds of the family of carotenoids. Indeed, a cup of raw turnip leaves contains 12 154 μg of lutein and zeaxanthin. As a comparison, 125 ml (½ cup) of cooked kale, a vegetable very rich in lutein and zeaxanthin, contains 12 532 μg. Lutein and zeaxanthin accumulate among other things in the macula and the retina of the eye, thus protecting it from oxidative stress that could cause damage. In fact, the regular consumption of lutein and zeaxanthin is associated with a lower risk of macular degeneration and cataract, two eye diseases. We are also beginning to think that these compounds could help prevent certain cancers, especially those of the breast and lung, and contribute to the prevention of cardiovascular disease. It should be noted, however, that studies on the cardiovascular level are still limited and sometimes contradictory.
Isorhamnetine. A recent study noted that turnip leaves contained a high amount of flavonoids, a large family of antioxidants: this amount would be even three to ten times higher than in most other brassicas. Among these flavonoids, the researchers found mainly derivatives of isorhamnetine, which are not found in several other brassicas. Studies of Isorhamnetine from other plants (mustard leaves, ginkgo biloba) showed in vitro and in animals some benefits, such as a decrease in blood glucose concentration, antioxidant protection in tissues and the reduction of the activity of enzymes related to the development of cancerous cells. However, the effect of this compound has not yet been studied among humans. In addition, no studies appear to have verified whether the root of turnips and rutabaga also contain them.
Irritable Bowel Syndrome. Some people with irritable bowel syndrome may feel, in varying degrees, intolerance towards certain foods. There are times when intolerance concerns the crucifers such as turnips or rutabaga. By limiting or avoiding fermentable foods such as those in the Brassica family, people with this syndrome can alleviate their symptoms (abdominal pain, bloating, diarrhea). When the symptoms are mild, or during periods of “remission”, it is sometimes possible to gradually reintegrate these foods, always respecting individual tolerance.
Interaction of the crucifers with certain medications. Indoles, naturally occurring compounds in the brassicas, may notably diminish the action of certain analgesics such as products containing acetaminophen (Tylenol, Atasol, Tempur) and other drugs combining a mixture of active ingredients (Benylin, Contac, Robaxacet). People who consume a large amount of brassicas should take this into consideration.
Brassicas and thyroid cancer: a link between the two?
The crucifers contain naturally thioglucosides, substances believed to be related to thyroid gland cancer among animals. For this reason, scientists questioned the possibility that these vegetables would be associated with thyroid cancer among humans. These researchers carried out a meta-analysis of studies from many countries and comprising more than 5 000 people. They showed that a high consumption of brassicas was not be associated with a higher risk of thyroid cancer.
Selection and conservation
The leaves can be purchased more easily in the spring or early summer when the young turnip boots arrive on the market.
Asian grocery stores offer all kinds of varieties of B. Rapa leaves, throughout the year. Otherwise, you will be able to obtain canned turnip leaves.
Freshly cut, the leaves remain in the refrigerator for a few days. Prepare them as soon as possible after purchase, as they tend to wither.
The roots are kept in the cellar or in the refrigerator for a long time.
In Europe, sauerkraut is made with the roots cut. You can also use the leaves for cooking a sauerkraut.
Although the leaves of all types of turnips or rutabagas can be consumed, some varieties have been crossed in particular for this purpose. The “Shogoin”, in particular, whose roots are also edible, and the “Seven Top” which are consumed only with the foliage. They are sown early in the spring, then at the end of the summer, for a second harvest. Space the plants 5 to 10 cm.
If one finds the taste of the turnip or the rutabaga too pronounced, one can try to cultivate the variety “Oasis”, a hybrid whose flavor reminds the one of the melon.
Unlike other varieties, “Shogoin” flowers and forms its seeds from the first year. So you can easily harvest the seeds and sow them the following year, which will allow them having a good amount of greenery, the plant being very prolific. Treat the seeds with hot water (66 ° C for 25 to 30 minutes), cool them in cold water and dry them.
Turnips arrive at maturity in 40 to 80 days, depending on the varieties and size to which they are harvested. For rutabagas, it is necessary to count at least 90 days. It is recommended to sow them no later than three months before the first big frosts.
The cabbage fly is the main predator to dread in the vegetable garden. It lays its eggs at the foot of the plants. The larvae grows by digging tunnels into the root and feeding on the flesh of the vegetable. Various solutions exist to fight it.
-Sow turnips and rutabagas alternating with lettuce, because the fly does not like the smell of the latter.
-Cover light agrotextiles seedlings, allowing the most light to pass (85%) and leave it throughout the plant growth. This solution is suitable for fresh weather, but in the heat, it will have to be removed, at the risk that the plants will not burn. Put the fabric back as soon as the weather is refreshed.
-A weekly watering with wood ash diluted in water is very effective both against the cabbage fly and against various other unwanted insects that may attack it.
Ecology and Environment
In addition of growing quickly and giving a very good yield, the turnip and the rutabaga are an excellent fodder for the livestock. For nearly 600 years in the case of turnips, and almost as much in the rutabaga, they were cultivated as forage roots. However, at the beginning of the twentieth century, farmers turned away from this practice because it required too much labour, especially for the harvesting and storage of heavy roots (a forage turnip can weigh up to 40 kilos).
People had to wait for the 1970s to be interested again, when they discovered instead of harvesting the roots and bringing them to the cattle, they could bring the cattle to the field and feed them with roots, which significantly reduced the costs of manpower. Especially since their culture requires only a small amount of harrowing work, and sometimes even none, which reduces costs and protects the soil from erosion. The selection of varieties whose roots grow partially off the ground makes it easier for animals to have access to the underground part of the plant. Depending on the region, this grazing system can be practiced in the summer or fall, and even in winter, turnips and rutabagas are relatively cold-resistant.