Adulteration of Olive Oil.
—By reason of its great value as an edible oil and its high price there is no one of the edible oils which has been subjected to such a systematic and extensive adulteration. By reason of the resemblance in general character of many of the edible vegetable oils to olive oil, adulterations of the most extensive character may be practiced without indicating to the eye any change in composition. Nearly all the edible vegetable oils have the light amber tint which is characteristic of many grades of olive oil, and the difference between the color of the olive oil and other edible oils is not greater than the difference between the tints of the various olive oils themselves. The connoisseur of extremely delicate taste is usually able to distinguish by the taste any given edible oil from olive oil. If, however, any given edible oil be mixed with olive oil in small proportions not exceeding 25 to 30 percent, even the skilled taster will be deceived. In such cases only the chemist who has much skill and practice is able to detect the adulteration.
Adulteration with Cottonseed Oil.
—In the United States the principal adulteration of olive oil is with cottonseed oil. This is an oil which has already been described as of high nutritive value and to which no objection can be made from any hygienic or dietetic point of view. It is made in great quantities in the United States, and when subjected to the most careful refining processes can be offered to the consumer at a price probably not greater than one-fifth that of high-grade olive oil. It becomes the ideal material with which to adulterate olive oil. This adulteration extends often to complete substitution, the oil in question, though represented as olive oil both by the dealer and the label, containing no trace whatever of that substance. Such bare-faced substitution has apparently almost passed away under the quickening ethical sense of the manufacturer and merchant and the character of the national and state laws. Many of the oils which are used to adulterate olive oil have a greater specific gravity, hence whenever the specific gravity of an olive oil at 15 degrees goes above .917 it is ground for suspicion of adulteration though by no means a positive proof. The presence of cottonseed oil in olive oil is easily detected by the Halphen test, which has already been described. In Europe a very common method of adulteration is with sesamé oil, the properties of which are described below. Peanut oil is also extensively used for the same purpose. These two oils are easily detected when mixed with olive oil. The sesamé oil is distinguished by the color reaction to be described. Peanut oil is distinguished by the saponification of the oil, separation of the fatty acids, and consequent crystallization of the arachidic acid, which produces a crystalline form which is readily recognized by an expert. Rapeseed oil and poppy-seed oil are also extensively used as adulterants in Europe, but not very extensively in this country. Nearly all the oils which are employed in the adulteration of olive oil have high iodin numbers, and therefore whenever an iodin number is above 89 or 90 it may be regarded as a suspicious circumstance. There are, however, many genuine olive oils which would be condemned as adulterated if this test alone were employed. In addition to the oils mentioned, small quantities of castor oil, lard oil, fish oil, and even of petroleum oil, have been found as adulterants in olive oil. These, however, occur very infrequently, and it is not likely that they have been employed in this country.
If the examination shows that a given sample is free of cottonseed, sesamé, and peanut oil, and other characteristics in the sample are those of olive oil, it may be safely accepted as a pure sample.
Color of Olive Oil.
—The color of the freshly expressed olive oil is usually green or dark from the chlorophyl and other coloring matter derived from the olive. When refined and ready for commerce the oil is of a yellowish-green tint usually. Sometimes the oil obtained from the first pressing is almost colorless, but as a rule an amber-green tint is observed in most of the commercial varieties. Lower grade oils are often decidedly green, but still edible, due to the admixture of chlorophyl from the green olive employed. The flavor of olive oil is a pleasant and agreeable one, but differs greatly in oils from different sources. The further north the oils are produced the less pronounced the flavor and the sweeter the taste. The more southern oils, such as are obtained in the south of Italy and Spain, have a stronger and more pronounced flavor which, however, is very much prized by those accustomed to it. Large quantities of olive oil are produced also in the French and other possessions in the north of Africa. These, however, have a stronger flavor than those produced upon the continent of Europe and are not so highly prized when used alone. Olive oil is almost free of stearin, being composed chiefly of olein with some palmitin. The amount of free acid in olive oil varies with the character of the olives employed and the age of the oil. On long standing, without becoming rancid, olive oil develops a large quantity of free acid. It is a common supposition that rancidity in an oil depends upon the development of free fatty acid, but this is not the case. If an oil be free of rancidity it may contain a large percentage of free acid without becoming inedible. It is not uncommon to find in olive oil as high as 3 percent or more of free acid. This is due to the fact that in the refining of olive oil alkalies are not usually employed, and therefore any free acid which the natural olive possesses is not neutralized by the alkalies, as is the case in the refining of cottonseed oil and some other vegetable oils.
Constituents of Olive Oil.
—Olive oil consists almost exclusively of olein and palmitin. There is very little, if any, stearin in the highest grade oil. If all the solid fatty acid at ordinary temperature be regarded as derived from palmitin, the quantity of palmitin may be regarded as varying from three to 20 percent, according to the origin and character of the sample. While the olein and palmitin, therefore, may be regarded as the principal constituents of olive oil, there are others, also, existing in smaller quantities. The quantity of free fatty acid varies very greatly in olive oil. It is highly important that the oil be separated from the pomace as speedily as possible, since any fermentation of the pomace increases the quantity of free fatty acid. The largest number of high-grade oils contain less than three percent of free fatty acid, but a larger quantity, as has been stated, does not render the oil inedible unless actual fermentation has taken place producing rancidity. Rancidity appears to be the result of the generation of other acids than oleic, and also aldehyds, formic, butyric, acetic, and œnanthylic acids have been found. Olive oil is a typical non-drying oil and therefore shows a less rise in temperature when mixed with sulfuric acid than other vegetable oils. The specific gravity of olive oil at 15 degrees may be placed at the average figure of .917. It sometimes falls as low as .912 and rises as high as .919. It absorbs from 80 to 90 percent of its weight of iodin. In some samples the weight of iodin absorbed is less, falling as low as 77 percent, but this is only in very extraordinary cases. Occasionally it goes above 90 percent. Probably the number 87 would represent about the mean percentage of iodin absorbed by most edible oils.