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close this bookJojoba: A New Crop for Arid Lands (BOSTID, 1985, 100 p.)
View the document(introduction...)
View the documentAcknowledgments
View the documentPreface
View the document1 Introduction and Summary
View the document2 The Plant
View the document3 Production
View the document4 Jojoba Oil
View the document5 Uses
View the document6 Markets
View the document7 Commercial Uncertainties
View the document8 Jojoba Industry Needs
View the document9 Research Needs
Open this folder and view contentsAppendixes
View the documentAdvisory Committee on Technology Innovation
View the documentBoard on Science and Technology for International Development

4 Jojoba Oil

In 1935, research chemists at the University of Arizona found that the oil in jojoba seeds was totally unlike that secreted by any other plant. Conventional oilseed crops, such as soybean, corn, olive, and peanut, produce glyceride oils, in which fatty acids are connected to a glycerol molecule. Jojoba oil, on the other hand, contains no glycerides or glycerol. It is composed of fatty acids connected directly to fatty alcohols.

No other plant is known to produce liquids of this type (In recent years, loose claims that meadowfoam produces this kind of oil have been reported. However, it produces a glyceride oil much like rapeseed oil; to convert it into a jojobalike oil takes a series of chemical transformations). Jojoba apparently evolved unique enzymes and biosynthetic pathways to produce and metabolize (during seed germination) its unusual lipid. The chemical structure of the oil does not vary appreciably with plant type, growing location, soil type, rainfall, or altitude. For instance, plants throughout California and Arizona produce oil of virtually the same composition.

Most seeds contain between 45 and 55 percent oil, and average about 50 percent - more than twice the amount found in soybeans and somewhat more than in most oilseed crops. Extracting the oil is a straightforward process done with standard mechanical presses used for separating oil from peanuts, cottonseeds, soybeans, and other oilseeds. The presses extract about 76 percent of the oil in the first run and an additional 6-10 percent in a second pressing. Although all the remaining oil can be removed by solvent extraction, this is commercially impractical at present because too little seed is available to warrant its use. Experiments have shown that jojoba can also be extracted using carbon dioxide in the "supercritical process."


Physical Properties

A light-gold fluid, raw jojoba oil has few impurities, and for most purposes requires little or no refining. It contains no resins, tars, or alkaloids - and only traces of saturated wax, steroids, tocopherols, and hydrocarbons. Neutralizing is usually unnecessary because the oil is normally low in free fatty acids. Bleaching is also usually unnecessary, but simple commercial techniques (for instance, filtration through fuller's earth) can be used to remove yellow pigments and produce a colorless product. For cosmetic and pharmaceutical use, the oil is frequently pasteurized to kill microorganisms.


Jojoba oil’s chemical structure is similar to that of sperm oil, but it is radically different from that of other vegetable oils. Of some 15000 plant oils tested at the U.S. . Department of agriculture, only jojoba had the liquid fatty acid/fatty alcohol ester structure. The straight chain alcohols and straight chain acids that form the esters chain acids that form the esters each have one double bond


The oil content in jojoba seeds varies from less than 30 percent to more than 60 percent. Selecting plants that yield seeds with a high oil content is a target for jojoba breeders. It is not easy to accomplish because both the female bush and the pollinating plant have an effect on inducing the high-oil trait in the seeds. For this histogram, oil contents were measured by wideline nuclear magnetic resonance. This is a nondestructive technique, allowing individual high-oil seeds to be selected and then planted out. (Information from L. Anderson, R. D. Benson, and W. O'Brien)

Jojoba oil is easy to work with. It is nontoxic and biodegradable. It dissolves readily in common organic solvents such as benzene, petroleum ether, chloroform, carbon tetrachloride, and carbon disulfide, but it is immiscible with methanol and acetone.

For many industrial needs, the oil has promising physical properties: high viscosity index, high flash and fire points, high dielectric constant, and high stability. It has low volatility and its composition is little affected by repeated heating to remarkably high temperatures - up to 570°F (300°C), for instance.

TABLE I Properties of Jojoba Oil (a)

Freezing point

10.6-7.0°C

iodine value

82

Melting point

6.8-7.0°C

Saponification value

92

Boiling point at 757 mm under N2

398°C

Acid value

2

Smoke point (AOCS Cc 9a-48) (b)

195°C

Acetyl value

2

Flash point (AOCS Cc 9a-48) (b)

295°C

Unsaponifiable matter

51%

Fire point (COC)

338°C

Total acids

52%

Heat of fusion by differential




scanning calorimetry

21 cal/g

Iodine value of alcohols

77

Refractive index at 25°C

1.4650

Iodine value of acids

76

Specific gravity, 25/25°C

0.863

Average molecular weight of wax esters

606

Viscosity




Rotovisco (25°C)




MV-1 rotor in MV cup

35 cp



Plate and cone with Pk-1

33 cp



Brookfield, spindle #1, 25°C

37 cp



Cannon-Fenske, 25°C

50 cp



Cannon-Fenske, 100°C

27 centistokes



Saybolt, 100°F

127 SUS (c)



Saybolt 210 deg C

48 SUS (b)



a) Oil from expeller-pressed jojoba seeds starts to freeze at 10.6°C (51°F). It solidifies into a thick paste at 7°C. Frozen oil, allowed to warm up, melts at 7°C (45°F).
b) Smoke and flash points determined according to the official method, Cc 9a-48, of the American Oil Chemists' Society.
c) Saybolt Universal seconds.
SOURCE: T. K. Miwa.


Jojoba oil also has good keeping qualities and an exceptional shelf life. This is apparently due to the presence of natural antioxidants (alpha-, gamma-, and delta-tocopherols), which occur in concentrations of about 50 ppm. In practical terms, these antioxidants keep the oil from becoming rancid, and companies processing raw jojoba oil are reporting very low acid values (0.2-0.3), even without neutralization.

In one experiment, seeds analyzed 25 years after harvest showed no change in composition. It appears, therefore, that the dry seeds can be stored without deterioration or chemical changes.


Chemical Properties

For a raw natural extract, the oil is remarkable for its molecular uniformity: it is 97 percent linear wax esters. (The remainder comprises free fatty alcohols and acids, and tocopherols.) It also has an amazing internal homogeneity - more than 87 percent of the esters present are combinations of acids and alcohols with chain lengths of 20 or 22 carbon atoms. By contrast, common vegetable oils have fatty acids whose carbon chain lengths are mostly 16 and 18.

The esters are composed almost entirely of straight-chain acids and alcohols. The acids are a mixture of eicosanoic (C20) and docosanoic (C22), with small quantities of palmitoleic (C18) and oleic (C16). The alcohols are a mixture of eicosanol and docosanol, with smaller quantities of hexacosanol and alcohols of lower molecular weight.


Jojoba oil esters are made up of fatty alcohols and fatty acids that are predominantly 20 or 22 carbon atoms long. Compared with most vegetable oils, the carbon chain lengths are remarkably uniform. (Information from T.K. Miwa)

The acids and alcohols that make up jojoba oil each have a single double bond. Moreover, all double bonds are in the W9 position (i.e., between carbon 9 and carbon 10, counting from the methyl end). This is a remarkable molecular purity, and the double bond position is different from that usually found in vegetable oils.

The nature of the oil can be grossly changed by reactions at the double bonds and ester functions, and many new products can result. One research laboratory in Israel, for example, has produced more than 40 different jojoba-based chemicals that appear to have commercial industrial applications.(Information from A. Shani and J. Wisniak)



Jojoba oil can be transformed into a remarkable array of products. Research chemists have already produced more than 40 different compounds of potential commercial significance. Many of these conversions are simple, cheap, and can be readily made on an industrial scale. Once jojoba oil becomes available in quantity, it promises to be a new raw feedstock for the chemical industry. (Based on information from P. Landis, A. Shani, and J. Wisniak)


TABLE 2: Alcohol / Acid Structures of Jojoba Oil Determined by Gas Chromatography and Mass Spectrometry

As in other natural oils, the double bonds in fresh jojoba oil are all in the cis configuration. However, they can be easily isomerized (twisted around in space), using as catalysts traces of selenium, nitrogen oxides, or active earth. This produces an equilibrium mixture with 20 percent cis and 80 percent trans double bonds. This simple process dramatically transforms the liquid into a soft, opaque cream resembling face cream. It can be stopped at various intermediate degrees of isomerization, resulting in a family of pastelike waxes with melting points of 50°-140°F (10°-60°C). This process can, for example, provide soft solids that melt on contact with human skin. These soft solids, therefore, could be attractive to the pharmaceutical and cosmetics industries. Their other properties also differ from those of cis-jojoba oil and they offer a promising field for experimentation.


Jojoba Wax

Hydrogenation (commercially called "hardening") is one of the most well-known transformations of fats and oils. Hardened vegetable oils are ingredients in shortening and margarine. Hardening jojoba oil through hydrogenation produces a crystalline wax.(To chemists, liquid jojoba oil is also a wax and they call the hard solid "hydrogenated jojoba oil." In this report, we use the words jojoba oil and jojoba wax to distinguish the liquid from the hydrogenated solid) This lustrous, pearly white, crystalline solid has properties like those of beeswax, candelilla, carnauba, and spermaceti - all of which waxes are commercially in demand and subject to steeply rising costs and uncertainties of supply.

The hydrogenation process can be carried out with standard equipment used in the fats industry. It can be stopped part way to produce a range of soft-to-hard waxes, as desired.

Composed essentially of pure wax esters with no double bonds, jojoba wax is made up of saturated C20 and C22 fatty acids and alcohols. X-ray diffraction has shown that the ester molecules are lined up in hexagonal arrays, but the samples are not completely crystalline, probably because the slightly differing lengths of the carbon chains prohibit perfect ordering.

Jojoba wax is now available in quantities adequate for industrial purposes, and it appears to have considerable commercial promise. Hard waxes are in demand, but most are from wild species whose supplies are intermittent, haphazard, or declining. Carnauba wax, which is laboriously scraped from fronds of a palm that grows in Brazil, is in erratic and dwindling supply, and its price (fueled by greatly increased labor and transportation costs) is rising. Candelilla, another cuticular wax, is obtained by boiling the stems of a wild shrub found in Mexican deserts. Its supply, too, is uncertain, and for the same reasons. Spermaceti (the saturated form of sperm oil) was once an important hard wax, but its use in the United States and most other countries has been banned since the 1970s because of the sperm whale's endangered status.


TABLE 3 Properties of Industrial-Grade Jojoba Oils

Typical

Pure Grade

Gardner color

Maximum - 9

Odor

Typical fatty

Acid value

Less than 1.00

Saponification number

90-95

Iodine value:

80-85

Total plate count

Less than 50/gram

Melting point

7°-9°C

Flash point

295 deg C

Fire point:

338°C

SOURCE: T. K. Miwa.


Hardness is one of jojoba wax's most outstanding characteristics. It is harder than beeswax but is slightly softer than carnauba. In fact, the hardness (which industrial chemists register-by melting point) of fully hydrogenated wax approaches that of the "king of waxes," carnauba. Its melting point is about 158°F (70°C). Although this is slightly lower than that of carnauba, it is higher than that of most other waxes. Moreover, jojoba wax is sparkling, white, and crystalline, and in many applications may be superior to the yellow amorphous waxes such as carnauba.

Because it is produced from liquid, unsaturated oil, which is more readily and cheaply purified than a solid such as carnauba, hydrogenated jojoba wax can be made exceptionally pure. Where crystallinity is a disadvantage, jojoba wax can easily be made amorphous by adulterating it with small amounts of other waxes.

Jojoba oil's double bonds offer chemical functionality that can be put to advantage to produce partially hydrogenated oils. This change produces a range of soft plastic waxes melting at temperatures up to 140°F (60°C). This offers alluring possibilities for industry because an array of soft white waxes and creams with a range of melting points can be produced to a given melting-point specification.

Jojoba wax has the capability to form a "gel" with many other chemicals. It has been found to improve the physical structure of many cosmetic products through special coupling mechanisms that allow two previously incompatible materials to be used together in the same formula. (Information from J. H. Brown)