|Illustration of components of the carob tree (Ceratonia siliqua).|
Ceratonia siliqua, commonly known as the carob tree, St John's-bread, or locust bean (not to be confused with the African locust bean) is a species of flowering evergreen shrub or tree in the pea family, Fabaceae. It is widely cultivated for its edible pods, and as an ornamental tree in gardens. The ripe, dried pod is often ground to carob powder, which is used to replace cocoa powder. Carob bars are available in health-food stores as a substitute for chocolate, particularly for vegans and others who want to avoid dairy products.
The carob tree is native to the Mediterranean region, including Southern Europe, Northern Africa, the larger Mediterranean islands; to the Levant and Middle-East of Western Asia into Iran; and to the Canary Islands and Macaronesia. The word carat, a unit of mass for gemstones and a unit of purity for gold alloys, was possibly derived from the Greek word kerátion literally meaning a small horn, and refers to the carob seed as a unit of weight.
The Ceratonia siliqua tree grows up to 15 metres (49 ft) tall. The crown is broad and semi-spherical, supported by a thick trunk with brown rough bark and sturdy branches. Leaves are 10 to 20 centimetres (3.9 to 7.9 in) long, alternate, pinnate, and may or may not have a terminal leaflet. It is frost-tolerant to roughly 20 degrees F.
Most carob trees are dioecious, some are hermaphrodite. The male trees don't produce fruit. The trees blossom in autumn. The flowers are small and numerous, spirally arranged along the inflorescence axis in catkin-like racemes borne on spurs from old wood and even on the trunk (cauliflory); they are pollinated by both wind and insects.
The fruit is a legume (also known less accurately as a pod), that can be elongated, compressed, straight or curved, and thickened at the sutures. The pods take a full year to develop and ripen. The ripe pods eventually fall to the ground and are eaten by various mammals, thereby dispersing the seed. The seeds contain leucodelphinidin, a colourless chemical compound.
Habitat and ecology
The carob genus, Ceratonia, belongs to the Fabaceae (legume) family, and is believed to be an archaic remnant of a part of this family now generally considered extinct. It grows well in warm temperate and subtropical areas, and tolerates hot and humid coastal areas. As a xerophyte (drought-resistant) species, carob is well adapted to the ecological conditions of the Mediterranean region with 250 to 500 mm of rainfall per year.
Carob trees can survive long drought periods but to grow fruit they need 500 to 550 mm rainfall per year. Trees prefer well-drained, sandy loams and are intolerant of waterlogging, but the deep root systems can adapt to a wide variety of soil conditions and are fairly salt-tolerant (up to 3% NaCl in soil). After irrigation with saline water in summer carob trees could possibly also recover during rainfalls in winter. In some experiments young carob trees could uphold basical physiological functions at 40 mmol NaCl/L.
Not all legume species can develop a symbiosis with Rhizobia to use atmospheric nitrogen. For carob it remains unclear if it has this ability: Some findings suggest that it is not able to form nodules with Rhizobia  while in another study trees have been identified more recently with nodules containing bacteria believed to be from the Rhizobium genus. However measuring the 15N-signal in plant tissue did not support that carob trees in the field can use atmospheric nitrogen.
Although used extensively for agriculture, carob can still be found growing wild in eastern Mediterranean regions, and has become naturalized in the west. The carob tree is typical in the southern Portuguese region of the Algarve, where it has the name alfarrobeira (for the tree), and alfarroba (for the fruit), as well as in southern Spain (Spanish: algarrobo, algarroba), Catalonia and Valencia (Catalan: garrofer, garrofa), Malta (Maltese: Ħarruba), on the Italian islands of Sicily and Sardinia (Italian: carrubo, carruba), Croatian islands near Split, and in Southern Greece, Cyprus as well as many Greek islands such as Crete and Samos. The common Greek name is (Greek: χαρουπιά, charoupia), or (Greek: ξυλοκερατιά, ksilokeratia), meaning "wooden horn". In Turkey, it is known as "keçiboynuzu", meaning "goat's horn". In Israel it's called "Haroov" (חרוב),known as "life saving tree - kav kharoovin". The various trees known as algarrobo in Latin America (Albizia saman in Cuba and four species of Prosopis in Argentina and Paraguay) belong to a different subfamily, Mimosoideae.
Carob is mildly sweet and is used in powdered, chip or syrup form as an ingredient in cakes and cookies, and as a substitute for chocolate by vegans and others who want to avoid dairy products. Carob bars are widely available in health food stores. Chocolate contains theobromine, which is poisonous to some mammals, but carob does not and is therefore used to make chocolate-flavored treats for dogs.
Carob pod meal is used as an energy-rich feed for livestock, particularly for ruminants, though its high tannin content may limit its use. The pulp is about 48–56% sugars and 18% cellulose and hemicellulose. There are some differences in sugar content between wild and cultivated types: sucrose = c. 531 g/kg dry weight in cultivated varieties and c. 437 g/kg in wild varieties. Fructose and glucose levels do not differ between cultivated and wild carob. Carob pulp is sold as flour or chunks.
The production of Locust bean gum (LBG), a thickening agent used in the food industry, is the economically most important use of carob seeds (and of the carob as a whole). It is produced from the endosperm, which accounts for 42–46% of the seed and is rich in galactomannans (88% of endosperm dry mass). For 1 kg LBG 3 kg of kernels are needed which come from approximately 30 kg carob tree fruit. Galactomannans are hydrophile and swell in water. LGB is used as a thickening agent, stabilizer, gelling agent or as a substitute for gluten in low-calorie-products. If galactomannans are mixed with other gelling substances like carrageenan they can be used to thicken food. This is used extensively in canned food for animals to get the jellied texture.
The embryo (20-25% of the seeds weight) is rich in proteins (50%) and its flour can be used in human and animal nutrition. The testa (30–33% of the seeds weight) is the seed coat and consists of cellulose, lignin and tannin.
In Cyprus, carob syrup is known as Cyprus's black gold, and is widely exported. In Malta, a syrup (ġulepp tal-ħarrub) is made out of carob pods. This is a traditional medicine for coughs and sore throat. A traditional sweet, eaten during Lent and Good Friday, is also made from carob pods in Malta. However, carob pods were mainly used as animal fodder in the Maltese Islands, apart from times of famine or war when they formed part of the diet of many Maltese. In the Iberian Peninsula, carob pods were used mainly as animal fodder, especially to feed donkeys.
Carob syrup is also used in Crete, Greece as a natural sweetener and considered a natural source of calcium. It contains three times more calcium than milk. It is also rich in iron, phosphorus and natural fibers (Due to its strong taste, it can be found mixed with orange or chocolate).
Crushed pods may be used to make a beverage; compote, liqueur, and syrup are made from carob in Turkey, Malta, Portugal, Spain and Sicily. Several studies suggest that carob may aid in treating diarrhea in infants. In Libya, carob syrup (there called rub) is used as a complement to Asida. The so-called carob syrup made in Peru is actually from the fruit of the Prosopis nigra tree.
Ornamental use of the carob tree
Ceratonia siliqua is widely cultivated in the horticultural nursery industry as an ornamental plant for planting in Mediterranean climate and other temperate regions around the world, as its popularity in California and Hawaii shows. The plant develops a sculpted trunk and ornamental tree form when 'limbed up' as it matures, otherwise it is used as a dense and large screening hedge. When not grown for legume harvests the plant is very drought tolerant and part of 'xeriscape' landscape design for gardens, parks, and public municipal and commercial landscapes.
- Spain 40,000 (F)
- Italy 30,841
- Portugal 23,000 (F)
- Greece 22,000 (F)
- Morocco 20,500 (F)
- Turkey 14,218
- Cyprus 5,186
- Algeria 3,136
- Lebanon 2,300 (F)
(F) = FAO estimate
Cultivation and orchard management
The vegetative propagation of carob is restricted due to its low adventitious rooting potential, which could be improved by using better grafting-techniques such as air-laying. Therefore seeds are still widely used as the propagation medium. The sowing occurs in pot nurseries in early spring and the cooling- and drying-sensitive seedlings are then transplanted to the field in the next year after the last frost. Carob trees enter slowly into production phase. Where in areas with good growing conditions the cropping starts 3–4 years after budding, the nonbearing period can take up to 8 years in regions with marginal soils. Full bearing of the trees occurs mostly at a tree-age of 20–25 years where the yield stabilizes. The orchards are traditionally planted in low densities of about 25–45 trees/hectare. Hermaphrodite plants or male trees, which produce no or fewer pods respectively, are usually planted in lower densities in the orchards as pollenizer.
Intercropping with other tree species is widely spread. There is not much cultivation management required. Only light pruning and occasional tilling to reduce weeds is necessary. Nitrogen-fertilizing of the plants has been showed to have positive impacts on yielding-performance. Although it is native to moderately dry climates, two or three summers irrigation will greatly aid the development, hasten the fruiting, and increase the yield of a carob tree."
Harvest and post-harvest treatment
The most labour-intensive part of carob cultivation is harvesting which is often done by knocking the fruit down with a long stick and gathering them together with the help of laid out nets. This is a difficult task because at the same time the trees are flowering and care has to be taken not to damage the flowers. Research to get the fruit to ripen more uniformely or also for cultivars which can be mechanically harvested (by shaking) is recommended in the literature.
After harvest carob pods have a moisture content of 10–20% and should be dried down to a moisture content of 8% so the pods don't rot. Further processing is done to separate kernels (seeds) from the pulp. This process is called kibbling and results in pieces of carob pods (kibbles). Processing of the pulp includes grinding for animal feed production or roasting and milling for human food industry. The seeds have to be peeled which happens with acid or through roasting. Then the endosperm and the embryo are separated for the different uses.
Pests and diseases
There are only few pests known to cause severe damage in carob orchards therefore it has traditionally not been treated with pesticides. Some generalist pests like the larva of the leopard moth (Zeuzera pyrina L.), small rodents like rats (Rattus spp.) and gophers (Pitymys spp.) can cause damage occasionally in some regions. Only some cultivars are severely susceptible to mildew disease (Oidium ceratoniae C.). One pest directly associated with carobs is the larva of the carob moth (Myelois ceratoniae Z.) which can cause extensive post-harvest-damage.
Cultivars and breeding aims
Most of the approximately 50 known cultivars are of unknown origin and only regionally distributed. The cultivars show high genetic and therefore morphological and agronomical variation. No conventional breeding by controlled crossing has been reported but there has been done selection from orchards or wild populations. Domesticated carobs (var. edulis) can be distinguished from their wild relatives (var. silvestris) by some fruit-yielding traits like building of greater beans, more pulp and higher sugar contents. Also there was an genetic adoption of some varieties to the climatic requirements of their growing-regions. Though there was a partially successful breaking of the dioecy, the yield of hermaphroditic trees still can't compete with that of female plants as their pod-bearing properties are worse. Future breeding would be focused on processing-quality-aspects as well as on properties for better mechanization of harvest or better yielding hermaphroditic plants. The use of modern breeding techniques is restricted due to low polymorphism for molecular markers.
The word carob comes from Middle French carobe. It may have come from the Ancient Greek where the word seeds were used as units of weight (karat) or is alleged to be taken into Europe from Arabic خَرُّوبٌ (kharrūb, "locust bean pod"), which derives from Akkadian language kharubu. Ceratonia siliqua, the scientific name of the carob tree, derives from the Greek kerátiοn (κεράτιον), "fruit of the carob" (from keras [κέρας] "horn"), and Latin siliqua "pod, carob." The term "carat", the unit by which precious metal and stone weight is measured, is also derived from the Greek word kerátiοn (κεράτιον), alluding to an ancient practice of weighing gold and gemstones against the seeds of the carob tree by people in the Middle East. The system was eventually standardized, and one carat was fixed at 0.2 grams.
In late Roman times, the pure gold coin known as the solidus weighed 24 carat seeds (about 4.5 grams). As a result, the carat also became a measure of purity for gold. Thus 24-carat gold means 100% pure, 12-carat gold means the alloy contains 50% gold, etc.
Subsistence on carob pods is mentioned in the Talmud: Berakhot reports that Rabbi Haninah subsisted on carob pods. It is probably also mentioned in the New Testament, in which Matthew 3:4 reports that John the Baptist subsisted on "locusts and wild honey"; the Greek word translated "locusts" may refer to carob pods, rather than to grasshoppers. Again, in Luke 15:16, in the Parable of the Prodigal Son, when the Prodigal Son is in the field in spiritual and social poverty, he desires to eat the pods that he is feeding to the swine because he is suffering from starvation. The use of the carob during a famine is likely a result of the carob tree's resilience to the harsh climate and drought. During a famine, the swine were given carob pods so that they would not be a burden on the farmer's limited resources.
Use of the carob plant dates back to Mesopotamian culture (modern day Iraq). The carob pods were used to create juices, sweets, and were highly prized due to their many uses. The carob tree is mentioned frequently in texts dating back thousands of years, outlining its growth and cultivation in the Middle East and North Africa. The carob tree is mentioned with reverence in "The Epic of Gilgamesh", one of the earliest works of literature in existence.
The Jewish Talmud features a parable of altruism, commonly known as "Honi and the Carob Tree", which mentions that a carob tree takes 70 years to bear fruit; meaning that the planter will not benefit from his work, but works in the interest of future generations. In reality, the fruiting age of carob trees varies (see under cultivation).
Ceratonia siliqua in native habitat (Sardinia, Italy).
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- Tree and images
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- PDF (1.32 MB) (English)
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