Chapter VIII: p. 108

=Sesame Oil.=—This oil also goes by the name of _teel oil_ and _gingelly oil_, and in commerce is sometimes described as _French salad oil_.

It belongs to the same class of oils (_semi-drying_) as cotton-seed oil, which it also resembles in its chemical composition.

It contains the glycerides of oleic, linolic, palmitic, and stearic acid. The solid fatty acids amount to about 14 per cent. of the total fatty acids, while, according to Farnsteiner, the linolic acid is about 12 per cent.

The unsaponifiable matter contains phytosterol, a body termed _sesamin_, and a compound of the nature of a phenol, termed _sesamol_. It is to the presence of this substance that the characteristic furfural reaction (see Baudouin’s test, p. 105) is due.

This active constituent may be removed from sesame oil by treatment with animal charcoal, and the oil may also be rendered inert by prolonged heating over boiling water.

Sesame oil has a pale yellow colour and a pleasant odour of the grain. It solidifies at a lower temperature (5° C.) than cotton-seed oil, and does not yield the large proportion of “stearin” given by the latter.

In the elaidin test it gives a reddish-brown partially solid mass of about the same consistency as the elaidin of cotton-seed oil.

Its iodine value (usually about 106) is somewhat lower than that of cotton-seed oil, except in the case of the oil from Russian seed, which has an iodine value of 114-115.

As is mentioned elsewhere, the addition of sesame oil to margarine is compulsory in Germany, Austria, and Belgium, so that the product possesses a “latent colour” which may be developed by the use of the Baudouin reagent.

In addition to its use as a salad oil, and in pharmaceutical preparations, sesame oil is employed as an adulterant of olive and almond oils; while, in turn, it is liable to be adulterated with arachis oil, cotton-seed oil, poppy oil, and rape oil.

The presence of the first may be detected by an estimation of the arachidic acid (p. 108), while Halphen’s test will show the presence of cotton-seed oil.

The other oils are detected by the general physical and chemical characteristics, and, in the case of rape oil, by the characteristics of its principal fatty acid, erucic acid.

=Cotton-Seed Oil.=—This oil, as has been already mentioned (p. 16), is expressed in enormous quantities in the United States, while there is a steadily increasing production in Egypt and India. In practice, a ton of cotton seed yields about 2½ cwt. of crude oil, which is then separated into “summer oil” and “foots” by refining (p. 23).

The bulk of the cotton-seed oil used for food in this country is derived from Egyptian seed, for the Indian oil is considered to have an unpleasant flavour.

Experiments made by Hooper, however, upon oils derived from American seed grown in India (_Ann. Report, Indian Museum_, 1910, 26), show that the fault lies with the method of screening the seed and the process of refining the oil.

He finds that by treating Indian oils with the amount of alkali corresponding to the acidity and giving a subsequent thorough washing with water, the whole of the colouring matter, the so-called “bloom,” and the acid taste are removed, and that the product has the light colour and bland flavour of refined Egyptian oil.

Thus by removing all dirt from the seed and delivering the seed in sound condition, and washing the oil to a sufficient extent after the refining with alkali, there appears to be no reason why oils from Indian seed should be in any respect inferior to Egyptian oils. Hooper’s experiments also indicate that as much “stearin” could be separated from Indian oils as from American or Egyptian oils.

Cotton-seed oil consists chiefly of the glycerides of oleic and linolic acids, the latter, as is indicated by the iodine value, being present in greater proportion than in olive oil, and amounting to about 17 or 18 per cent. of the total fatty acids. The glycerides of solid fatty acids which are present in solution, and separate out as “cotton-stearin” on chilling the oil, consist principally of those of palmitic acid with a small proportion of stearic acid (Hehner and Mitchell).

Owing to the presence of the large amount of linolic acid, cotton-seed oil belongs to the class of oils known as “semi-drying” oils, _i.e._ oils which thicken on exposure to the air, but, unlike the drying oils, do not form a dry film until after the lapse of a long time.

When exposed to a temperature of about 10° to 14° C., cotton-seed oil yields a deposit of the so-called “cotton-stearin” (_q.v._), while the entire oil becomes solid at about the freezing-point of water. The stearin, which is separated by filtration (p. 25), is a useful by-product, which is utilised in the preparation of margarine. The oil from which the “stearin” has been separated goes by the name of “winter” cotton-seed oil.

Oils which have been refined by treatment with alkali and separation of “stearin” have a mild taste and are practically devoid of free acids. They are widely employed both as salad oils and as substitutes for lard in cooking, but the bulk of the American oil is made up into margarine or used in the manufacture of soap.

Cotton-seed oil is a common adulterant of olive oil, and, owing to its forming a frequent ingredient of margarine, may find its way into butter.

In addition to the colour reactions, described on p. 107, it may be identified by the relatively high melting-point of its solid fatty acids (32° to 38° C.), and by its iodine value (112-115).

In the elaidin test (p. 107) it yields a butter-like mass of an orange colour, very different from the hard white elaidin produced by olive oil.

Cotton-seed oil contains about 1 per cent. of unsaponifiable matter consisting chiefly of phytosterol. The presence of cotton-seed oil in animal oils and fats may thus be confirmed by the phytosteryl acetate test (p. 101).

=Sunflower Oil.=—Enormous quantities of sunflower seeds are cultivated in Russia for the production of an edible oil, and most of the oil mills in that country are engaged in the industry.

The method of expression is similar to that used in this country for linseed. The seeds are first “screened” from dirt, particles of stalk, etc., and are then steamed and crushed to a paste, which is wrapped in hair-cloths and expressed in a hydraulic press. Expression by hand is still employed in some of the smaller mills.

When freshly obtained from clean seed, sunflower oil is a pale yellow fluid with a pleasant odour and flavour, but the second (hot) pressings are much darker in colour, and are used for illuminating purposes and in the manufacture of varnish.

Sunflower oil has good drying properties, though these are less pronounced than in the case of poppy or linseed oil. It consists of the glycerides of oleic, linolic, and palmitic acids, and probably contains a small amount of linolenic acid.

Its iodine value (about 130) is considerably higher than that of cotton-seed oil.

When used as a salad oil it has the advantage of keeping fluid to a very low temperature, but its drying capacity, which causes a film to form upon the surface when exposed to the air, is a drawback from which olive and similar non-drying oils are free.

Sunflower oil is occasionally employed as an adulterant of olive oil. It would be detected by the increase in the iodine value, and, according to Jean, by its having a slight reducing action upon silver nitrate in Bechi’s test (_q.v._).

=Poppy Oil.=—The oil expressed from the seeds of the poppy (_Papaver somniferum_), which is cultivated in Egypt and Asia Minor, has a mild, bland taste, and is sometimes used as an edible oil.

Its chief use, however, is as a drying oil for paints, for which its good drying capacity and its light colour make it particularly suitable.

It consists of the glycerides of oleic, linolic, and linolenic acids, with a small proportion of those of solid fatty acids, including stearic and palmitic acids.

It bears considerable resemblance to sunflower oil in its chemical and physical characteristics, as is shown by the following typical values:—

+--------+----------------+--------+--------+----------------+
| | Saponification | Iodine | Hehner | Solidification |
|Sp. gr. | Value. | Value. | Value. | Point. |
+--------+----------------+--------+--------+----------------+
| 0·926 | 194 | 140 | 95·4 | -15° to |
| | | | | -20° C. |
+--------+----------------+--------+--------+----------------+

If added in any considerable quantity to olive oil there would be an increase in the sp. gr. and iodine value of the latter.

=Maize Oil.=—This oil, which is also known as _corn oil_, is obtained from the germs of the maize or Indian corn (_Zea mais_), and is used to a limited extent as an edible oil.

It has a pale yellow colour, and a fragrant odour recalling that of the fresh grain.

It resembles cotton-seed oil in its composition, and contains the glycerides of oleic, linolic, and palmitic acids, together with an appreciable quantity of those of volatile fatty acids, as is indicated by its relatively high Reichert-Meissl value (4 to 4·5).

Like cotton-seed oil it belongs to the class of semi-drying oils, slowly forming a dry skin when exposed to the air in a thin film.

The following values have been recorded:—

+--------+----------------+--------+--------+---------------+
| | Saponification | Iodine | Hehner | Melting-point |
|Sp. gr. | Value. | Value. | Value. | of |
| | | | | Fatty Acids. |
+--------+----------------+--------+--------+---------------+
| 0·9245 | 190 | 122 | 93·6 | 17°-20° C. |
+--------+----------------+--------+--------+---------------+

The presence of cotton-seed oil, which is sometimes used to adulterate maize oil, would be shown by the characteristic colour reactions (p. 107). For the detection of maize oil in lard or in butter reliance would have to be placed upon the general analytical values and upon the results of the phytosteryl acetate test.

CHOCOLATE FATS

=Cacao Butter.=—In the manufacture of cocoa and chocolate a large proportion of the fat contained in the cocoa-bean is expressed, and forms a valuable by-product.

This fat, which is usually termed cacao butter, comes into the market in moulded slabs, weighing several pounds each.

It is a hard substance of a yellowish colour, having an aroma of cocoa, and, when broken, shows signs of crystalline structure.

Its flavour and high melting-point render it particularly suitable for the “cream” of chocolate creams, and large quantities of it are used for this purpose.

The chemical composition of cacao butter resembles that of other hard fats, the differences being due to a different proportion of the various glycerides.

It contains stearic, palmitic, lauric, and oleic acids, while arachidic, and a fatty acid termed theobromic acid, are also said to have been identified, though the presence of either is doubtful.

The hardness and high melting-point of the fat are due to the large proportion (about 40 per cent.) of stearic acid it contains.

The melting-point of the commercial product ranges from about 27° to 34° C.

The relatively low iodine value (usually between 32 and 36) indicates the presence of a much smaller amount of liquid fatty acids than of solid fatty acids, the former, according to Farnsteiner, consisting of oleic acid, and constituting 31 per cent. of the total fatty acids.

It has frequently been stated that cacao butter is not liable to become rancid. This, however, is not the case, for the fat, like other fats, does gradually decompose on exposure to light and air, though owing to its consistency and the low proportion of glycerides of liquid fatty acids present the process is not rapid, as in the case, for example, of cocoanut oil.

Cacao butter is frequently adulterated, the principal substances liable to be found being stearic acid, cocoanut oil, paraffin wax, beeswax, and various vegetable oils.

Cacao butter fetches too high a price to be used in the lowest grade of chocolate creams, and various substitutes are now sold.

=Cocoanut and Palm-Kernel Oil Stearins.=—Among the most common of these cheaper products are the “stearins,” obtained by expression from cocoanut oil and palm-kernel oil, both of which in their original condition are too soft, and melt at too low a temperature to be suitable for this purpose.

In preparing more solid fats these oils are melted and refined, then chilled down, and subjected to pressure in the cold in a hydraulic press. A fractionation is thus effected, the expressed portion, known as cocoanut or palm-nut olein, being much more fluid than the stearin left in the press, while the latter is more consistent than the original fat.

Thus while the melting-point of cocoanut oil is usually about 23° C., that of the separate is about 30° C.

The following results were obtained by Sachs (_Chem. Rev. Fett- u. Harz.-Ind._, 1908, xv. 30) in the examination of commercial samples of these stearins:—

LEGEND:
(A) = Saponification Value.
(B) = Reichert-Meissl Value.
(C) = Melting-point of Fatty Acids.
+----------------+--------------+-------+---+-----+------+---------+
| | |Sp. gr.| | | | |
| |Melting-point,| at |(A)| (B) |Iodine| (C) |
| | °C. |100° C.| | |Value.| |
+----------------+--------------+-------+---+-----+------+---------+
|Hard cocoanut | | | | | | |
| stearin |29·3 to 29·5 |0·8700 |252| 3·4 |4·0 to| 28·1 |
| | | | | | 4·5 | |
|Palm-nut stearin|31·5 to 32 |0·8700 |242| 2·2 | 8 |28·5-29·5|
+----------------+--------------+-------+---+-----+------+---------+

Frequently these products are rendered still more consistent by the addition of a small proportion of an animal stearin or some vegetable fat of higher melting-point, such as Japan wax.

Thus a commercial preparation consisting of a mixture of cocoanut stearin with 25 per cent. of Japan wax, melted at 34° to 35°·5 C., or approximately at the same temperature as a good specimen of cacao butter.

=Other Vegetable Fats.=—Of late years various exotic vegetable fats have been put upon the market as chocolate fats either in their pure state or in admixture with cocoanut or palm-nut stearins. These fats include dika fat, tankawang fat (Borneo tallow) and Illipé fat.

_Dika fat_, which is obtained from the seed kernels of _Mangifera gabonensis_ and other members of the same family, growing on the West Coast of Africa, is a hard fat, melting at about 39° C. (or higher than cacao butter), and having an iodine value (5) about the same as that of cocoanut oil.

_Borneo tallow_ (_tankawang fat_) derived from the seed kernels of _Shorea aptera_ and other members of the _Dipterocarpi_. The native method of separating the fat is to suspend the kernels in baskets above boiling water, and when soft, to express them in primitive presses. According to Sachs (_loc. cit._), Borneo tallow melts at 37°·5 C., and has an iodine value of 30-31.

_Illipé butter_ (_Mahua butter_), which is derived from the seeds of _Bassia latifolia_, is a yellow fat, large quantities of which are eaten in India.

Nine samples of the Indian product examined by Crossley and Le Sueur had melting-points ranging from 23° to 29° C., and iodine values of 58·4 to 67·8. The relatively low melting-point appears to depend upon the large proportion of glycerides of liquid fatty acids present, and this fat would probably yield a hard stearin on expression.

Other fats that might be used for this purpose, if they could be obtained in sufficient quantity, are shea butter, from the seeds of _Bassia Parkii_ (melting at about 25° C.); Mafura tallow, melting at 35° to 42° C.; Mkani fat, melting at about 40° C.; and Malabar or Piney tallow, produced by the East Indian tree, _Vateria indica_ (melting at about 37° C.).

Sachs (_loc. cit._) states that favourite substitutes for cacao butter consist of a mixture of two-thirds of palm-nut stearin with one-third of cocoanut stearin, and of a mixture of 40 per cent. of Borneo tallow with 60 per cent. of cocoanut stearin.