Uniquely identifiable characteristics
Not to be confused with :
Sea Kale Beet (or Chard) [an edible plant with similar name] nor with Kale a cultivated and edible species of (Brassica oleraceae).
Sea Kale is sometimes grown as an ornamental garden plant (aren't all garden plants?). Although this is not the cultivated Kale grown for cooking, nevertheless it can be eaten and was eaten in the 18th Century, but it is easily damaged and deteriorates after harvesting so its popularity declined.
The leaves are glaucous-green and wavy and similar to those of another seaside plant Yellow Horned-Poppy but that has large yellow flowers and very long curved seed pods.
The coastal shingle plants
Sea Kale (Crambe maritima) Yellow Horned-Poppy (Glaucium flavum) and Rock Samphire (Crithmum maritimum) are thermophilous, growing well and increasing in numbers with warmer summers.
GLUCOSINOLATES IN SEA KALE
Epi Progoitrin is a Glucosinolate contained within the vacuoles of seeds, leaves and roots of many plants belonging to the Brassica Genus (as well as numerous other genera). Glucosinolates all consist of a glucose unit (top right) attached via a sulfur bridge to an organic group containing a nitrile unit (CN). The other end always terminates with a N-O-HSO3. Glucosinolates all behave in similar ways: they are innocuous whilst contained within the cells, but, once released, an enzyme (myrosinase, which is also liberated by the plant upon damage) releases the glucose unit whilst at the same time converting the N-O-HSO3 to the isothiocyanate group -N=C=S which remains bonded to the organic group, that is, it becomes a mustard oil. Mustard oils are quite toxic and also cause burning of the skin. The liberated Glucosinolates thus transformed act to deter insects and mammals from eating the plant containing them.
Unfortunately, this can include humans. Although about 30% of the isothiocyanate is broken down by cooking for 4 minutes until tender, a 76% decrease can be obtained by boiling for 20 minutes. For the occasional meal, Sea Kale is safe to eat when cooked but, eaten on a more regular basis, may precipitate problems caused by nitriles adversely acting upon the kidneys and liver. It is not called Progoitrin without reason; it can cause the disease Goitre.
Cooking incapacitates some of the myrosinase enzyme, thus partially preventing the conversion of non-toxic glucosinolates into toxic mustard oils.
Glucosinolates are numerous in plants; more than 120 occur in the many members of the Cabbage Family. Some have beneficial qualities - perhaps possessing therapeutic or prophylactic properties or having a chemo-protective role in the diet or use as pharmaceutical agents. Glucosinolates and/or their breakdown products have long been known for their fungicidal, bacteriocidal, nematocidal and allelopathic properties and recent research suggests some may be useful as chemo-protective agents in patients receiving chemotherapy for cancer.
GLUCOSINOLATES IN GENERAL
There are other glucosinolates with negative implications, perhaps being 'anti-nutritional' or goitrogenic such as Epiprogoitrin. The reason for the huge differences lies in the products resulting from the enzymatic decomposition of the specific glucosinolate in question. The end product could variously be Nitriles such as Epithionitrile, Thiocyanates, Isothiocyanates or Oxazolidine-Thione, besides the glucose unit which is always liberated. These differing breakdown products have widely varying properties. R is a radical.
Only CN groups attached to organic groups are called Nitriles such as Mandelonitrile; if attached to inorganic groups they are called cyanides, after the acid hydrocyanic acid, HCN. Over 120 different Nitriles occur naturally in the plant kingdom, but many are produced only on stress such as cooking. Synthetic nitriles are used in superglues, which polymerise on exposure to the slightest trace of moisture. Nitriles themselves can further degrade into Hydrogen Cyanide plus the organic radical, see Mandelonitrile and the Modus Operandi of Cyanogenic Glycosides.
The main difference between Thiocyanates and Isothicyanates is that the latter are not organic cyanides; the radical is not bonded to the sulfur atom but to the nitrogen atom and the carbon atom is not triple-bonded to the nitrogen atom, with the order SCN being reversed to NCS without any triple-bonds.
This compound, 5-allyl 1,3-Oxazilidine 2-thione, has thyroidal toxicity interfering with iodine uptake and induces the disease goitre. Indeed, its goitre inducing potential is greater that the related compound, 5-ethenyl 1,3-Oxazilidine 2-thione which is called Goitrin, which has one carbon atom fewer in the side chain.
Sea Kale also contains about 120µg/g of Calystegines, polyhydroxylated nortropanes, of which roughly 61% is Calystegine A5, 35% Calystegine B3, and 6% Calystegine A3.