Physiological and Medicinal Properties of Castor Oil

Castor plant is a member of the Euphorbiaceae family that spreads throughout the tropical regions of the world. Increasing demand of biodiesel and other medicinal and industrial applications for vegetable oil have increased processing and production of castor oil worldwide. Ricinoleic acid is the most important component of castor oil.

It has a variety of effects on the gastrointestinal tract, including inhibition of water and electrolyte absorption, stimulation of water secretion into the intestinal lumen and depression of small bowel contractile activity. Conjugated fatty acids from castor oil have attracted much attention as a novel type of biologically, physiologically and pharmaceutically beneficial functional lipid.

Castor oil is well–known for numerous health properties being the most important medicinal oil as a cleansing laxative and purgative. Moreover, root and leaves of castor plant is also useful as an ingredient of different prescriptions for nervous diseases. Recently, FDA has been approved castor oil as a direct food additive for using as a flavoring agent and/ or adjuvant. On the obtained reports and versatile application of castor oil in pharmaceuticals, cosmetics, biodiesel, paint, soap and recently in food industry has led to much research being done on castor oil.

Introduction

Castor plant was probably one of the first crops cultivated by early man who used the oil extracted from the seeds for a wide variety of applications including lamp. The castor is a perennial shrub mainly cultivated as an oilseed crop.

Castor plant is a member of the Euphorbiaceae family that spread throughout the tropical regions of the world. Early taxonomists tried to classify castor based on phenotypic differences into several subspecies but most botanists now believe all castor belong to the same species. Castor accessions show significant differences in branching, height, growth habit or colour and many of these phenotypic traits are simply inherited) and most accessions will readily intercross.

Castor plant is a coarse perennial, bearing large, alternate, palmately lobed leaves, flowers in huge terminal clusters. The seeds are also varicolored in prickly or smooth three–membered capsules.

In tropical climates the plant heights is commonly of 30 to 40 feet with stems three to six inches in diameter. In temperate climates it behaves as an annual plant, and heights of three to eight feet are more common. Here, a brief review of the most important physiological and medicinal properties of castor oil is given.

Castor Bean Seed

There are different varieties of castor bean seeds that contain about 45–55% oil. After the extraction of castor oil, the remaining material is called the castor bean pomace, which has about 36% protein. The castor bean pomace contains also a highly toxic and heat sensitive ricin and albumin and a powerful allergen protein fraction which is more heat resistant.

The size and external markings of seeds from different cultivated varieties differ but average seeds are of an oval, laterally compressed form. The smaller, annual varieties yield small seeds and the tree forms yields large seeds. They have a shining, marble–grey and brown, thick, leathery outer coat, within which is a dark– coloured, thin, brittle coat A large, distinct, leafy embryo lies in the middle of a dense, oily tissue.

Moisture content, foreign material, leaves and cracked or broken beans are considered for improving of grading the castor seeds. Ideally, castor beans should be stored at less than 7% moisture due to reduction of post contamination during storage period.

Castor Oil

China, India and Brazil produced the majority of the world’s castor oil in 2005 and 2006. Ethiopia, Thailand and Par aguay have also contributed relatively minor amounts for castor oil pr oduction. Total world production of castor seed was about 1 million ton/year during the year 2005 .

The changes of castor oil prices and variability in production has made the international market for castor oil very unstable. Increasing demand of biodiesel and other medicinal and industrial applications for vegetable oil have increased processing and production of castor oil worldwide.

Recently, FDA has also been approved castor oil as a direct food additive for use as a flavoring agent and/ or adjuvant. The joint FAO/ WHO expert committee reported that castor oil is safe for use in food as a carrier solvent and/or release agent. The Committee has been established an acceptable daily intake (ADI) of 0–0.7 mg/kg/day.

Castor seeds accumul ate abou t 45–55% oi l i n t he for m of triacylglycerol (TAG) that serves as a major energy reserve for seed germination and seedling growth. Castor is an important oilseed crop that produces an oil rich in ricinoleic acid (18:19c–12OH; about up to 90%), an unusual hydroxy fatty acid with conjugated unsaturation. The hydroxy group imparts unique chemical and physical properties that make castor oil a vital industrial raw material for industrial applications.

Due to the presence of the toxic ricin and potent allergenic 2S albumins in the seed, the general approach is to generate a safe castor crop by blocking expression of the ricin and 2S albumins in seed to produce r icinoleate from temperate oil seeds. Castor oil is obtained from extracting or expressing the seed of a plant.

The castor oil is not only a naturally–occurring resource; it is inexpensive and environmentally friendly. Castor oil is viscous, pale yellow non–volatile and non–drying oil with a bland taste and is sometimes used as a purgative. It has a slight characteristic odour while the crude oil tastes slightly acrid with a nauseating after–taste. Relative to other vegetable oils, it has a good shelf life and it does not turn rancid unless subjected to excessive heat. It is noteworthy that the quality of seed oil is hardly affected by the variation in good or poor seeds.

The castor oil and the chemical intermediate prepared are used in pharmacology and in the production of such industrial products as protective coatings, paints, synthetic, textiles, plasticizers, jet engine lubricants, hydraulic fluids, soaps and detergents, resins, waxes, cosmetic, anti–fungal products and a variety of valuable derived products.

In spite of being one of the most important industrial oils in world market, the development of alternative castor oil profiles other than high ricinoleic acid is needed for covering a wider range of market niches, not only in the industrial but also in the food sector.

A natural mutant of castor with seed oil characterized by high oleic acid and low ricinoleic acid content has been recently developed. The recent isolation of a natural mutant of castor bean with high oleic acid and low ricinoleic acid concentration opens up new potential uses for castor oil.

Oil Extraction

Production and processing of castor oil consist of: collection of castor seeds when the capsules drying, open and discharging the seeds. The seeds are then cleaned, decorticated, cooked and dried prior to extraction.

Cooking is done in order to coagulate protein, which is necessary to permit efficient extraction and to free the oil for efficient pressing. It is done at 80°C, under airtight conditions. After cooking, the material is dried at 100°C, to reach a moisture content of approximately 4% .

The oil is obtained from the seeds by two principal methods: pressing and solvent extraction. The extraction of oil from castor seed is by one or a combination of mechanical pressing and solvent extraction. In mechanical pressing, the seeds are crushed and then adjusted to low moisture content by warming in a steam–jacketed vessel.

Thereafter, the crushed seeds are loaded into hydraulic presses and they are pressed by mechanical means to extract oil. Extracted oil is filtered and collected in a settling tank. Material removed from the oil, called foot, is fed back into the stream of fresh material. Material discharged from the press, called cake, contains 8 to 10% oil. However, mechanical pressing will only remove about 40–50% of the oil present and the remaining it can be recovered by solvent extraction.

The oil from mechanical pressing has light colour and low free fatty acids. In the solvent extraction method, the crushed seeds are extracted with a solvent in a soxhlet or commercial extractor. Solvents used for extraction include heptane, hexane and petroleum ethers.

Oil Refining

If necessary from, it is usual to refine the crude oil obtained from solvent extraction and also mechanical pressing. The main aim of refining is to remove colloidal matter, free fatty acid, colouring matter and other undesirable constituents, making the oil more resistant to deterioration during storage.

Main steps of vegetable oil refining includes: (A) removing colloidal matter by settling and filtration, (B) neutralizing the free fatty acid by NaOH, (C) removing coloured components by bleaching agents and (D) deodorizing by tr eatment with steam at low pressure and high temperature. The common method of refining used for edible oils is applicable to castor oil. Refining of castor oil can be attributed to the fact that some impurities and other components are removed during oil refining.

Moreover, the pH value of the crude oil which is found to be 6.11 indicate that the oil is more acidic compared to 6.34 pH obtained for the refined oil. This may be as a result of degumming and neutralization carried out during the oil refining process.

Castor Oil Properties

Castor oil physical and chemical properties can vary with the method of extraction. Cold–pressed castor oil has low acid value, low iodine value and a slightly higher saponification value than solvent–extracted oil and it is lighter in colour.

Physicochemical properties of castor oil are centered on high content of ricinoleic acid and the three points of functionality existing in the molecule.

These include: (1) the carboxyl group which can provide a wide range of esterifications, (2) the single point of unsaturation which can be changed by hydrogenation or epoxidation or vulcanization, and(3) the hydroxyl group which can be acetylated or alkoxylated, may be removed by dehydration to increase the unsaturation of the compound to give semi–drying oil.

The hydroxyl position is very reactive and the molecule can be split at that point by high–temperature pyrolysis and by caustic fusion to yield useful products of shorter chain length. The presence of hydroxyl group on castor oil gives extra stability to the oil and its derivatives by preventing the formation of hydroperoxides.

Results revealed that ricinoleic acid comprises over 85% of the fatty acid of castor oil. According to Ogunniyi (2006), other fatty acids present are linoleic (4.2%), oleic (3.0%), stearic (1%), palmitic (1%), dihydroxystearic acid (0.7%), linolenic acid (0.3%) and eicosanoic acid (0.3%). The oil is characterized by high viscosity although this is unusual for a natural vegetable oil. It can be linked mainly to hydrogen bonding of its hydroxyl groups.

It is also soluble in alcohols in any proportion but it has only limited solubility in aliphatic petroleum solvents. Although castor oil is a unique naturally– occurring polyhydroxy compound, a limitation of the oil is the slight reduction of its hydroxyl value and acid value on storage; both values may change by about 10% if stored for about 90 days. The reduction of these values is due to the reaction between hydroxyl and carboxyl groups in the oil molecule to form estolides.

Conjugated Fatty Acid From Castor Oil And Its Health Aspects

 

Castor oil has only one double bond in each fatty acid chain. Therefore, it is classified as non–drying oil. However, it can be dehydrated to give semi–drying or drying oil which is used extensively in paints and varnishes.

As the name implies, dehydration involves the removal of water from the fatty acid portion of the oil. Being a polyhydroxy compound, its hydroxyl funct ionali ty can be reduced through dehydration or increased by interesterification with a polyhydric alcohol. The dehydration process is carried out at about 250°C and in the presence of catalysts  and under an inert atmosphere or vacuum.

Under this condition of dehydration, the hydroxyl group and an adjacent hydrogen atom from the C–11 or C–13 position of the ricinoleic acid portion of the molecule is removed as water. This yields a mixture of two acids, each containing two double bonds but in one case, they are conjugated.

The presence of an acid containing conjugated double bonds results in an oil resembling tung oil in some of its proper ties. Thus, castor oil, which is non–dr ying, can be treated and converted into a semi–drying or drying oil known as dehydrated castor oil (Ogunniyi, 2006). Production of conjugated linoleic acid (CLA) isomers from castor bean oil by Villeneuveet al . (2005) is studied.

Recently, CLA especially its isomers has attracted much attention because of its beneficial effects, including reduction of carcinogenesis, arteriosclerosis and body fat.Conjugated fatty acids from castor oil have attracted much attention as a novel type of biologically and physiologically beneficial functional lipid.

The unique activities of CLA have been intensively studied and CLA expected to be an important potential material for pharmaceuticals and dietary supplements. According to results, CLA inhibits the initiation of mouse skin carcinogenesis mouse forestomach and rat mammary tumorigenesis.

Moreover, CLA has been reported to be effective in preventing the catabolic effects of immune stimulation and to change the low–density lipoprotein/high– density lipoprotein cholesterol  ratio in rabbits. In addition, the effects of CLA on human’s body composition such as fat loss and lean gain are attracting increasing attention.

In recent years, CLA, as a dietary supplement, is produced through chemical isomerization of linoleic acid, which results in the by– production of unexpected isomers. However, recent studies have revealed that each isomer can have different effects on metabolism and cell functions, and acts through different cell signaling pathways.

Today, complex mixtures of isomers which are produced through alkaline isomerization of linoleic acid are used for production CLA commercial isomers. It is appeared that in production of CLA for pharmacological or nutraceutical purposes, an isomer– selective and safe process is required. The introduction of biological reactions to CLA production will solve these problems.

Toxicological Studies

The leaves, seeds and extracted oil of the plant contain the toxic protein ricin, highly allergenic storage proteins and the alkaloid ricinine which can inhibit protein synthesis in body glycoprotein cytotoxin present in the seeds and oil extracted from castor plant. The presence of ricin in the high protein meal of castor remaining after oil extraction can be affected on its value as an animal feed.

Ricinine is a bitter white crystalline alkaloid extracted from the seeds of the castor–oil plant. It appears to be a naturally occurring insecticide in castor bean which has a relatively low human toxicity. The researchers mentioned a negative correlation between the concentration of ricinine and oil in castor seeds. It was also reported that environmental factors such as high temperature enhance the concentration of ricinine during seed maturation.

A decrease in ileal water absorption can be concluded with ricinoleic acid in intestinal elution resulted in at intraluminal ricinoleate concentrations of 0.5 mm or higher. It has been reported that at 2.0 mm or higher, there was net water secretion in the jejunum. The absorption rate of ricinoleate was approximately half that of oleic acid.

As is well approved, the fresh castor seeds are very poisonous for humans. There is no agreement about the lethal rate of castor seed and it can be varying in humans, for example, from the possible previous protracted ingestion of oil. If castor seed is accidentally ingested, it can lead to abdominal pain, diarrhea and vomiting.

Therefore, as little as 1 mg of ricin can kill an adult.The symptoms of poisoning are nausea, diarrhea, fever, cyanosis, vomiting, perspiration revealed that oil injected in high doses can induce vasodilatation and lymphangitis. The pulp of the seeds contains allergens (glycoproteins) which in particularly sensitive persons can promote strong al ler gic reactions such as coryza, conjunctivitis, dermatitis, eczema and bronchial asthma.

CONCLUSION

There is no doubt that castor oil is a valuable plant. This is evident from the researches that much has been carried out about the oil and its component. In the present chapter, the physicochemical, physiological, medicinal and toxicological properties of castor oil have been outlined. Generally, it is considered that non–edible vegetable oils should be exploited as far as it is possible so that edible oils can be used for human’s consumption.

This is especially very important in developing countries where food safety and security poses a challenge. Safety data especially to castor oil/ricinoleic acid are limited. However, ricinoleic acid constitutes up to 90% of the fatty acid content of castor oil. Therefore, available results on castor oil component are relevant and have been discussed.

These data indicate bolus doses of 10–15 g or higher of undiluted castor oil to have pharmacological effects on the human gastrointestinal tract. Castor plant is one of the most important medicinal plants which are used in pharmaceuticals, cosmetics and hygienic industries in developed countries.

It is approved that conjugated fatty acids from castor oil have attracted much attention as a novel type of biologically and physiologically beneficial functional lipid. The versatile application of castor oil in pharmaceuticals, different industries and recently in food industry has led to much research being done on castor oil.