Along with cabbage, Brussels sprouts and cauliflower, broccoli is an edible member of the Brassicaceae family, formerly known as the Cruciferae on account of the shape of their flowers which are cruciform and, to botanical historians, resembled a Maltese cross. However, not all of the Brassicaceae are green leafy vegetables, for swede, turnip and kohl rabi also belong to the family, and the wall-flower is a non-edible member. Other members of the family, for example, charlock (Brassica sinapis) are weeds. Containing more vegetable types than any other plant family, the members of the Brassica family are of huge economic importance and, among the family, all parts of the plants: flowers, leaves, stems and roots, may be cooked and eaten. Ten of the most common vegetables eaten by Man are, remarkably, a single species, Brassica oleracea; these including broccoli itself, kale, cabbage, cauliflower, Brussels sprouts and kohl rabi.
As may be inferred, 'broccoli' can take many forms but the vegetable we refer to as 'broccoli' pertains to the sprouting types which work on the 'cut-and-come-again' principle. Broccoli has many strong branches or arms growing out from the main stem and the very name 'broccoli' is Italian, deriving from the Latin braccium, meaning arm or branch. Roman farmers called broccoli 'the five green fingers of Jupiter'1. The Latin name Brassica comes from a Celtic word, 'bresic', meaning 'cabbage'.
Broccoli is believed to have originated in the eastern Mediterranean, and was cultivated and used in cooking by the ancient Greeks and Romans. Pliny the Elder, an Italian naturalist and writer, 23 to 79 AD, tells us the Romans grew and enjoyed broccoli during the 1st Century AD. The vegetable became a standard favourite in Rome where the variety called Calabrese was developed.
It is said that the Roman Emperor Tiberius, who reigned between 14 BC and 37 AD, had a son named Drusius who so loved broccoli that he ate it to the exclusion of all other foods. After following this diet for an entire month, his urine turned bright green thus causing his father to scold him severely for 'living precariously'.
It was introduced to Britain from Cyprus in the early 17th Century, before being introduced to the Americas.
Most of the 'cauliflowers' which are sold between October and June are really the more hardy broccoli. This is of a 'heading' type which forms a single large white head in winter or spring. This form may be cooked as one would a cauliflower.
Calabrese (also spelled calabresse), or Italian green sprouting broccoli, is a variety which originated in the Italian province of Calabria. It produces a medium-sized green central head which is usually available in March. This may also be cooked like cauliflower and served with melted butter.
Calabrese produces a crop of delicately-flavoured spears, and some varieties produce a succession of such spears stretching from early autumn until the first frosts.
The stems of these should be cut into short lengths, sliced thinly, and cooked, with their tiny heads, in boiling, unsalted water as for any green vegetable. Alternatively, they can be tied in bundles and cooked and served like asparagus, which they resemble in taste. Some people, although liking the heads, don't like the stems. Some supermarkets, for example, in Ireland provide hacksaws to allow customers to saw off the stems before buying. Apparently, the stems are a great favourite of guinea pigs, although they will cause them to smell a bit!
There are several varieties of calabrese, but one which is especially worthy of a mention is Romanesco. This is not only because of its taste, which is outstanding, but because it is beloved of mathematicians as being one of a number of plants which exhibit fractal geometry.
Fractals are complex shapes which look similar at a succession of different magnifications. They are ubiquitous in nature, occurring for example in coastlines, river courses, clouds, blood vessels in the lung, and in the branches of plants. Broccoli is a fractal because it branches off into smaller and smaller pieces, which are similar in shape to the original.
Purple Sprouting Broccoli
This is the variety most frequently grown in the home-garden, being quite hardy. Early purple sprouting and white sprouting broccoli come into season at the beginning of April. It grows well in heavy soils and in cold areas where little else can successfully over-winter. To prepare, the tiny heads should be cut off with about 2 inches (5cm) of stem and adjoining leaves, and cooked whole in boiling unsalted water, as one would any green vegetable.
If purchased from the greengrocer, there is often much stem and leaf with the heads. Remove and discard the really coarse stems. Shred the remaining stems and leaves and add to the pan before the green heads.
Why Do Some People Hate Broccoli?
On 22 March, 1990 the then President of the United States, George Herbert Walker Bush, when asked at a news conference why he had banned broccoli from menus served at the White House and on the Presidential aircraft, Air Force 1, famously retorted:
I do not like broccoli. And I haven't liked it since I was a little kid and my mother made me eat it. And I'm President of the United States and I'm not going to eat any more broccoli.
This so incensed Californian farmers that Apio Produce and the United Fresh Fruit & Vegetable Association sent letters from broccoli-growers together with 20,000lbs (about 9 tonnes; one truckload) of fresh broccoli from California to the White House as a response. Lady Barbara Bush, who likes broccoli, received the shipment in a formal ceremony on the White House lawn. Still President Bush refused to yield and the broccoli was donated to local food banks.
Sadly, Bush's sentiments are echoed by thousands of children. So, why do many people not like the taste of broccoli? It is principally due to a bitter taste imparted by chemical compounds known as 'glucosinolates' which are present in a variety of vegetables, especially Cruciferous vegetables.
Some people however, are less susceptible to this bitter taste and it has been found that this is due to them possessing different genetic versions of a taste receptor known as hTAS2R38. This receptor specifically determines people's perception of taste of plants that synthesise glucosinolates.
Such differences in taste receptors are well known. For example, some Researchers might recall an experiment to determine how many students in the class could taste a bitter substance known as phenylthiocarbamide (PTC). This and another compound, propylthiouracil (PROP), chemically resemble the glucosinolates found in plants.
It is thought that different versions of this taste receptor exist because it confers an evolutionary advantage in certain circumstances. Thus, it is known that iodine is necessary for proper function of the thyroid gland, but there are certain geographic regions (typically remote from the sea) where inorganic iodine levels are low. In such regions, endemic goitre (enlarged thyroid gland) can arise in response to the need to maintain levels of the thyroid hormone, thyroxine. Glucosinolates have been found to block the formation of organic iodine and the transport of iodine into the thyroid gland. In such circumstances, thyroid toxins such as glucosinolates can exacerbate problems with thyroid function, thus leading to problems such as retarded sexual maturation and mental retardation in low-iodine regions.
By testing the bitterness perceived by individuals possessing different versions of the hTAS2R38 taste receptor, researchers have obtained evidence to suggest that the receptor's gene has evolved in such a way that individuals avoid vegetables that can inhibit thyroid function.
Broccoli and Flatulence
Being high in complex carbohydrates, especially oligosaccharides such as inulin, broccoli, together with the other Cruciferous vegetables, are notorious flatulence-producing foods, where the flatus has an offensive odour. Gases present in flatus include carbon dioxide and hydrogen, which are odourless and produced by the bacterial fermentation of starches and complex oligosaccharides. The offensive odour is due to small amounts of hydrogen sulphide and methyl sulphide, produced by the action of sulphate-reducing bacteria on the sulphur compounds present in brassicas.
Health and Nutritional Benefits of Broccoli
Broccoli is one of the most nutrient-dense foods available, being particularly rich in vitamins A and K. Thus, containing 89.2 mg of vitamin C per 100g, one cup of cooked broccoli provides 100% of the Recommended Daily Intake of this vitamin.
Broccoli is rich in cholesterol-reducing fibre and in folic acid (folate), which is essential for the production of red blood cells. As folate deficiency is associated with developmental neural tube defects (NTDs), such as spina bifida, it is especially recommended for women who are planning a pregnancy or who are already pregnant. In men, folate has been shown to be required for a viable sperm count.
In terms of minerals, broccoli is a good source of iron, and so people suffering from anaemia should consider this as a useful addition to their diet. It is also rich in chromium, which is absolutely critical to the functioning of insulin - the hormone which regulates blood sugar levels.
It is, however, for its anti-cancer properties that broccoli is most renowned.
Like other members of the Brassicaceae, broccoli produces sulphur compounds, such as sulforaphane, which has both anti-cancer and antimicrobial properties. Sulforaphane causes the body to produce increased levels of 'detoxifying enzymes' which speed the removal of carcinogens from the body. They also kill abnormal cells and act as anti-oxidants. Sulforaphane has also been shown to be effective at inhibiting Helicobacter pylori2 growth, this organism being strongly linked to duodenal and gastric ulcers3, and to stomach cancer4.
Like cauliflower, cabbage and brussels sprouts, broccoli also contains compounds known as indoles. These help to prevent carcinogens from damaging DNA, the complex molecule which acts as the blueprint for the production of all living cells. They also block oestrogen receptors in breast cancer cells, inhibiting the growth of oestrogen-sensitive breast cancers.
Having an abundance of anti-oxidants such as beta-carotene, vitamin C and indoles, broccoli is said to be particularly effective against cancers of the lung, colon and breast. Tests have also shown that women who ate more broccoli are less prone to cancer of the cervix.
Sulforaphane, described above, is an isothiocyanate.
Isothiocyanates are formed when the vegetables are cut, chewed, digested, or otherwise damaged. This enables a sulphur-containing glucosinolate called sinigrin to be brought into contact with the enzyme myrosinase, resulting in the release of glucose and allyl isothiocyanate.
Scientists from Penn State University in Pennsylvania, USA have recently shown that low doses of a formulation containing isothiocyanates can reduce malignant melanoma in mice by up to 60%. Further tests on human skin cancer cells showed that the drug slowed growth by up to 70%. Malignant melanoma is the most deadly form of skin cancer and affects more than 8,000 Britons per year. It is possible that a sun cream based on an extract from broccoli could be on the supermarket shelves in the not too distant future.
As well as having anti-cancer properties, some isothiocyanates have been shown to have antiviral activity, and this may account for the effectiveness of broccoli in combating cervical cancer, which is associated with Human Papilloma Virus (HPV)5
A Note on Cooking Green Vegetables
It is said that excessive heating of food can result in a 50% reduction in vitamin levels, and 77% reduction in mineral levels. Spinach, for example, loses 19% of its iron content when cooked in unsalted water, and a further 30% of its iron if the water is salted. Furthermore, prolonged storage of green leafy vegetables can result in as much as an 80% reduction in their vitamin C content.
Sulforaphane is present in broccoli as sulforaphane glucosinolate (SGS) which, although having cancer chemopreventive activity itself, is low compared to that of sulforaphane. Sulforaphane is produced from SGS by the action of the enzyme myrosinase (thioglucoside glucohydrolase), also present in cruciferous vegetables and which is activated upon maceration of the vegetables. It had been thought that this enzyme is inactivated by over-cooking. However recent research (2010) has shown that the microflora in the colon produce enzymes that will release sulforaphane from SGS, thus making it available for absorption in the body. Nevertheless, it makes sense to use vegetables as freshly as possible, and to minimise cooking times.
Some simple rules are:
- Keep vegetables (and fruit) whole until required. Don't even wash, peel or slice them until then.
- Always add the vegetables to boiling water. If the vegetables are put into cold water and brought to the boil, this causes a greater loss and/or destruction of the nutrients than does quick boiling.
- Use the smallest volume of water possible, then use this for the preparation of sauces, soups and stocks.
- It is best to add salt 'at the table' to taste, rather than to the cooking water. For example, spinach is said to lose an extra 30% of its iron content when cooked in salted water, compared to unsalted water.
- Steaming is an excellent alternative to cooking in boiling water - and saves energy too!.