Citrus Fruit

Citrus fruit belong to the Rutaceae family (subfamily of the Aurantioideae), which is divided into three types: Citrus, Fortunella (Kumquat) and Poncirus Trifoliata. There are only three types of genera and eighteen defined species, but other natural mutations exist. This is the reason why citrus fruit and especially the numerous hybrids are widely spread throughout the world. From a botanical point of view, the fruit is a hesperidium: a berry whose pulp is divided into four sections containing seeds. The pulp contains only a cellulosic matter, while the juice contains carbohydrates, citric and tartaric acid, proteins, vitamin C, lipids, carotenoids and chrolophyll.

Citrus fruit: A history

Citrus originate in China and India, the Poncirus from Korea and China whilst the Fortunella come exclusively from China. The first written documents on citrus can be traced to neighbouring areas. The Far East is therefore the starting point for the development of citrus growing in neighbouring countries. Citrus arrive in India, Indochina, the South China Sea islands, the Philippine islands up to the Indian ocean. From China, citrus also travel as far as Japan: the new satsuma mandarins, which account for 80% of Japan’s citrus production derives from the Chinese guanxi. It would appear that this mandarin had been imported into Japan in 1500, that it adapted so quickly to the new land and that it fast became a common product.

In India, the first information on citrus fruit goes back to the first writings in Sanskrit, an Indo-European language imported by the Aryans between 2000 and 1000 BCE. In Sanskrit, both cedar and lemon were translated as jambila, this word appeared for the first time in the Vajasaneyi samhita, written a little before 800 BCE. The absence of any Sanskrit word to describe the orange validates the hypothesis that it had been imported into India from China 2,000 years ago with the migrations from Yunnan to the Bramaputra valley. It has since been proven that India had cultural and commercial contact with Mesopotamia, which is crossed by the Tigris and the Euphrates. It is surprising to note that despite its climate, which was unsuitable for citrus growing, Babylonian farmers were skilful enough to get round this obstacle.

It is highly probable that citrus growing was spread via Afghanistan and Pakistan and then onto the West. Another piece of evidence concerning the migration of citrus to the West is provided by the sacred Hebrew books: the frequency with which the cedar is mentioned suggests that the Jews were already familiar with citrus fruits at least with the cedar before the Christian era. In Greece, the cedar is quoted in different texts. In some papyrus, it is referred to as kitron,in other 6th century texts such as those by Galeno the term kitrion or kitreos is used. Theophrastus (372-287 BCE.) in his work “Historia plantarum” describes the cedar specifying that it’s a plant, which is found in Persia and the land of the Mede. We find another reference in the “Deipnosophistae » written by Athenaeus which goes back to 200 CE. In his « History of Libya » he tells the story of Juba, King of Mauritania who claims that the Libyans called the fruit « Apple of the Hesperides » If we draw our conclusions from these discoveries, it would seem that the Greeks didn’t know of any citrus besides the cedar, even if Alexander the Great’s expeditions, during which he was accompanied by researchers-botanists, reached as far as the valleys of the Punjab. (India)

In Ancient Rome, the cedar was called malus medica, and then citrus. The first reference to citrus in literature goes back to the 2nd century BCE with the work of Cloanzio Vero, followed a century later by Oppio , the botanist who talks about it in his book « De Silvestris Arboribus”. Theocritus from Syracuse who lived in the 2nd century BCE doesn’t even mention it. In the Middle Ages, during the Crusades, the French discovered citrus and popularised them in their lands. Even the Marine Republics contribute to the spreading of citrus fruit.

By the 12th, 13th and 14th centuries, citrus fruit was widespread throughout Italy, Spain and the South of France. We suppose that it was neither the Arabs nor the Marine republics that introduced the sweet orange to Europe but rather the Portuguese. One of the words used to describe the sweet orange at the time was “Portugal”, similar names are still used today in Greek, Turkish and Arabic During the Renaissance, citrus fruit was grown and known almost everywhere. This we know thanks to numerous written accounts and pictorial representations. in particular in “still life.” In Italy, the South has the best climate for citrus growing. In the central and northern areas citrus fruit is traditionally grown in earthenware pots, which are exposed to the sun during the summer season and transferred to a protected area away from the cold in the winter. This same method was also adopted in France and the Germans, the Belgians and the Dutch subsequently followed in the example. At the end of the 18th Century, citrus fruit growing spread to America, transported by Europeans during the colonisation of the continent. After several decades, new citrus varieties were discovered in the West, including bergamot, grapefruit, the Mediterranean mandarin, the Clementine and the tangerine. The bergamot probably originated from a spontaneous hybridisation, whilst the grapefruit was discovered in Barbados and described by Griffiths Hughes in 1750 whereas in 1789, Patrick Browne described the grapefruit discovered in Jamaica: both of them baptised it “forbidden fruit”.

Citrus fruit: structure

All varieties of citrus fruit are similar in structure varying only in size and shape. Lemons are usually oblong with the major axis following the stalk; mandarins are fattened at the top and bottom with their major axis being on the equatorial line whilst the majority of oranges are round. Size based on the equatorial diameter of the fruit is also varied. Differences don’t only exist among species but also exist within varieties of the same species requiring the use of specific equipment to best transform the fruit and in some cases preliminary procedures to classify fruit according to grade.

The skins are made up of an epidermis of epicuticular wax with blotches. The quantity of wax depends on the variety, climatic conditions and growth rate. This layer normally contains a microflora made up mainly of fungus and bacteria, which are more copious in damp climates. This justifies the need for appropriate washing of the fruit before proceeding to extract juice and essential oils. This washing minimises the risk of contamination arising from the fruit surface. It is necessary to use a washing brush in water or a detergent or disinfecting solution (usually with 25ppm of chlorine). Under the epidermis, we find the flavedo, characterised by its yellow, green or orange colour. The flavedo contains the oliferous vesicles on the inside and are very fine and fragile; the essential oil contained within can be collected by scraping on the flavedo layer. Under the flavedo, we find the albedo made up of tubular-like cells and which combine together to constitute the tissue mass compressed into the intercellular area. The albedo’s thickness varies according to the type of citrus and the growing methods used. It is absolutely necessary to adjust the extractors to compensate for the albedo layer thickness, especially to obtain the best quality possible. The albedo is rich in flavonoids, which, if transferred to the juice make it particularly bitter. Next we discover the fruit’s endocarp and the carpels in which the juice containing vesicles are to be found, and which from a synthetic biology point of view should be considered as the liquid released by the cytoplasm and by the vacuoles in the vesicles’ internal cells. A spongy tissue similar to that of the albedo forms the fruit’s core.

Vitamins found in citrus fruit

Aside from vitamin C (ascorbic acid) which is, without doubt, the most abundant vitamin in citrus fruit (a glass of orange juice provides 60% of the recommended intake. the other vitamins are: folacine, vitamin B6, Thiamine, riboflavin, Biotin, Panothenic acid and vitamin A type composites. The average quantities present in fresh orange juice are shown in the chart below.

Vitamin	Unit/100 ml
Ascorbic Acid	mg	35 – 56
Thiamine	mg	60 – 145
Riboflavine	mg	11 – 90
Niacin	mg	200 – 300
B-6	mg	25 – 80
Folacin	mg	120 – 330
Pantothenic Acid	mg	130 – 210
Biotin	mg	1 – 3
Vitamine A	IU	190 – 400

Six different scientific studies compared seven juices containing 100% fruit: apple, grape, pink grapefruit, orange, pineapple and prune. The analysis showed that the citrus fruit juices in particular the grapefruit and orange, were richer in nutritional components per calorie than the others.

Fruit varieties

The citrus family is very big and includes dozens of varieties, many of which are used in food; those, which are not edible, are used in the cosmetic industry for their essential oils. Here’s a list of the most important varieties of citrus fruit, their use and their properties.

– Orange tree: This evergreen, which originates in China and Japan, was introduced to Italy by the Arabs in the 14th century. The orange contains citric acid, sugar, vitamins and mineral salts for the production of marmalades, juices, essential oils and perfumes. There is a red variety, the blood orange that unfortunately is becoming more difficult to find because of the increased availability of the seedless variety. The top perfume houses use the expensive orange blossom essential oil.

– Bitter orange tree: The fruit of this variety is inedible in its uncooked state and mainly used for the production of marmalades, whilst its leaves and flowers are used for essential oil extraction.

– Bergamot tree: The fruit of this variety is inedible in its uncooked state and mainly used for the production of marmalades, whilst its leaves and flowers are used for essential oil extraction.

– Citron tree (citrus medica): Originating from Persia and called a “cedro” in Italian, this tree should not be confused with its gymnosperm homonym known as the Lebanon cedar or the Atlas cedar ( cedrus atlanticus.) The fruit of this tree can weigh up to 1kg. It is used in the production of preserves and for the extraction of oil used in perfumes, medicine and in the liqueur industry. The fruit is used by practising Jews in rituals during the Feast of Tabernacles.

– Chinotto (myrtle-leaved orange tree): Cultivated in areas around the Mediterranean, it looks like a little orange with a slightly bitter taste, and it weighs between 40 – 50 grams. It is used in the production of sweets and drinks (often caramel-coloured).

– Lemon tree: This evergreen is characterized by its oval leaves and yellow fruit. The lemon is the main citrus fruit for edible or industrial purposes. The fruit juice, rich in citric acid and vitamin C, is used as an astringent, antiscorbutic and thirst quencher. The lemon is also widely used in the liqueur industry and in perfume production. Not forgetting the detergent industry, which uses lemon-derived products. In antiquity, lemon juice was used as an anti hemorrhagic remedy and disinfectant whist sailors used it to fight against scurvy (insufficient intake of vitamin C) during long sea crossings.

– Lime tree: Due to its sensitivity to cold, the lime is mainly cultivated in tropical and subtropical areas. The fruit, which is small and very acid, is mainly used in juice or in cocktails. Lime is also used in perfumes and detergents. Always green, and flowering all year round, provided it lives in suitable conditions, it is often used as an ornamental plant.

– Fortunella or Kumquat: This fruit is relatively uncommon; small with a sweetish peel is edible, contrary to other citrus fruit. Its unusually sweet peel makes it particularly interesting in the production of preserves.

– Pomelo: This is only grown in Thailand and has no commercial or industrial use. It’s used locally in food preparation and the production of preserves.

– Mandarin tree: This green shrub originates in China. The fruit resembles the orange but on a smaller scale. It’s fruit juice, rich in vitamin C, is used in the liqueur industry. Its use is currently on the decrease due to the Clementine, which is lower in calories and more popular with the consumer.

– Clementine tree: This natural hybrid, which comes from Tunisia, has a fruit, which, like all citrus fruit is rich in vitamin C.

– Grapefruit tree: The fruit of this tree resembles the yellow-coloured lemon; it originates in India and is rich in vitamin C and fibres. In the 1990’s in the U.S.A. a pink grapefruit, hybrid of the orange, rich in vitamins C and A, made its appearance. It’s considered important from an industrial and commercial point of view because it is consumed fresh and used fin the preparation of juice and drinks. The pink varieties are used almost exclusively for eating fresh as the fruit’s carotenoids make it difficult for juice preparation.

It was the Arabs who first discovered techniques for extracting essential oils and the Italians discovered perfume producing techniques on a large scale with fruit peel and flower petal extracts Naples and Sicily developed these techniques and from there, the first exotic perfumes were created which went on to be widely successful throughout Europe. From a food and dietary point of view, citrus fruit is extremely important in food production and industry. To obtain a maximum of benefits from freshly squeezed citrus juices, it is always advisable to drink them immediately as once it comes into contact with oxygen light and heat, vitamin C rapidly deteriorates.

Fruit yield

The table below shows the percentage of the different parts, which make up the fruit and the variations depending on fruit type:

	orange	lemon	mandarin	grapefruit
skin %	21.5 – 38.1	32.0-46.6	25.6-33.0	33.6-36.4
pulp %	61.9-78.6	53.4-67.9	67.6-73.6	63.6-67.3
juice %	23.8-51.0	21.6-27.0	32.5-38.6	30.0-33.6

Aside from type and variety, juice yield depends also on ripeness, growing methods, meteorological factors and extraction systems.