OLIVE OIL

Olive Oil is extracted from the pericarp of the fruit of the _Olea Europea_. When pure, it exhibits a pale yellow or greenish colour, has a specific gravity of 0·9176, and possesses a faint, pleasant odour and a bland and agreeable taste. It is insoluble in water, very slightly in alcohol, but dissolves in about 1½ parts of ether. Olive oil boils at 315°, and begins to deposit white granules at 10°; at 0°, it solidifies to a solid mass which, by pressure, may be separated into tripalmetine and trioleine. Upon saponification, it is decomposed into oleic, palmetic, and stearic acids and glycerine. The best-known varieties of olive oil met with in commerce, in the order of their quality, are--Provence, Florence, Lucca, Genoa, Gallipoli, Sicily, and Spanish.[136]

Owing to the high price of the pure article, and perhaps to the difficulty experienced in detecting foreign admixtures, olive oil is probably more extensively adulterated than any substance of general consumption. The oils most employed as adulterants are those of cotton-seed, poppy, pea-nut, sesamé, rape-seed, arachis, and lard. Although the subject of the adulteration of olive oil has received the attention of numerous chemists, including several of exceptionally high standing, the results obtained, while of service in indicating the presence of some foreign oil, are unfortunately often of but little use in the positive identification of the particular adulterant used. Of the many methods of examination that have been suggested, the following are the most satisfactory:--

1. _Specific gravity._--The density of olive oil is lower than that of the majority of the oils with which it is mixed, and it is sometimes possible to detect the presence of the latter by means of this property, especially when they are contained in a considerable proportion. Cotton-seed oil differs more in specific gravity than the other oils generally employed as adulterants. Donny[137] applies the test by placing in the suspected sample a drop of olive oil of known purity which has been dyed with ground alkanet root, and observing whether it remains stationary. A more satisfactory method is to determine the density by the gravity bottle. The following tabulation gives the densities (at 15°) of olive and several other oils liable to be met with as admixtures:--

Olive oil ·914 to ·917 Poppy oil ·924 „ ·927 Cotton-seed oil ·922 „ ·930 Sweet almond oil ·914 „ ·920 Arachis oil ·916 „ ·920 Colza oil ·914 „ ·916 Sesamé oil ·921 „ ·924 Rape-seed oil ·914 „ ·916 Lard oil ·915

2. _Solidifying point._--Attempts have been made to utilise the fact that some of the oils added to olive congeal at a lower temperature than the pure oil. Thus, cotton-seed oil solidifies at -22°, ground-nut oil at -33°, poppy at -18°.

3. _Elaidin and colour tests._--Pure olive oil is converted into a solid mass when treated with various oxidising agents, the change being retarded by the presence of some of its adulterants. The test may be made in several ways:--

(_a_) Ten grms. of the sample are shaken with 5 grms. of nitric acid (sp. gr. 1·40) and 1 grm. of mercury, and the colour produced and time required for solidification noticed. In this manner the following results have been obtained:--

------------+----------------------+----------------- Oil. | Coloration. | Minutes for | | Solidification. ------------+----------------------+----------------- Olive | Pale yellowish green | 60 Almond | White | 90 Arachis | Pale reddish | 105 Rape | Orange | 200 Cotton-seed | Orange red | 105 Sesamé | Yellowish orange | 150 Beech-nut | Reddish orange | 360 Poppy | Red | Remains fluid. ------------+----------------------+-----------------

(_b_) Or a few pieces of copper foil are added to a mixture of equal parts of the oil and nitric acid, the liquor occasionally stirred, and then set aside. If the oil be pure, it will be converted into a nearly white buttery mass in from three to six hours; sesamé oil yields a red, cotton and rape-seed a brown, and beech-nut a reddish-yellow colour, the solidification being delayed from 10 to 20 hours, while poppy oil fails to solidify at all.

(_c_) Nine parts of the sample are oxidised by heating with one part of concentrated nitric acid, the mixture being well stirred; pure olive oil forms a hard, pale-yellow mass in the course of two hours; seed oils (including cotton-seed) turn orange-red in colour and do not become solid in the same time or manner.

(_d_) A portion of the sample is well mixed with one-fourth of its weight of chromic acid; if pure, the oil will be converted into an opaque mass.

(_e_) Introduce 2 c.c. of the sample into a narrow graduated glass cylinder, add 0·1 gramme potassium dichromate, next 2 c.c. of a mixture of sulphuric and nitric acids, shake well, and then add 1 c.c. of ether; shake again and allow the mixture to stand at rest. Lively effervescence and evolution of nitrous fumes soon take place, and the oil rises to the surface, showing a characteristic coloration. Olive oil exhibits a green colour, whereas in presence of 5 per cent. of sesamé, arachis, cotton-seed, or poppy oil, the colours will vary from greenish-yellow to yellow or yellowish red. The coloration is more readily observed upon agitating the mixture with water and, setting it aside for a short time.

(_f_) Several portions of the oil are placed upon a porcelain slab and separately treated with a few drops of concentrated sulphuric acid, nitric acid, and a solution of potassium dichromate in sulphuric acid, and notice taken of the colours produced, comparative tests being simultaneously made with olive oil of undoubted purity.

(_g_) The presence of sesamé oil is readily detected by the formation of a deep green colour when the oil is agitated with a mixture of equal parts of nitric and sulphuric acid.

(_h_) Upon mixing samples containing cotton-seed oil with an equal volume of nitric acid (40° B.) a coffee-like colour is produced. Olive oil gives a pale green, rape and nut, a pale rose, and sesamé oil a white-coloured mixture.

The presence of rape- and cotton-seed oils may also be detected as follows:--Dissolve 0·1 gramme silver nitrate in a very little water, and add about 4 c.c. of absolute alcohol. This solution is added to the sample of olive oil to be tested, the mixture well shaken and put aside for one or two hours; it is then to be heated for a few minutes. If cotton-seed or rape-seed oil is present, the oily stratum which separates on standing will exhibit a brownish-red or blackish colour, due to the reduction of silver. Olive oil fails to cause an appreciable coloration. Experiments made by the author with samples of olive oil containing 10 per cent. of cotton-seed and rape-seed oils furnished the following results:--On standing one hour, without heating, the mixture containing cotton-seed oil showed a slightly dark colour, that adulterated with rape-seed oil a decidedly dark colour; upon the application of heat, the former exhibited a dark-red colour, while the latter turned quite black.

_Maumené’s test._--This test is founded upon the fact that the elevation of temperature caused by mixing olive oil with strong sulphuric acid is considerably less than that produced with the oils commonly employed as its adulterants. With these latter an evolution of sulphurous acid generally takes place, which is not the case with pure olive oil. The best method of procedure is as follows:--10 c.c. of sulphuric acid (sp. gr. 1·844) are gradually added to 50 grammes of the sample, the mixture being constantly stirred with a small thermometer, and observations made of the maximum increase of temperature produced, as well as of the evolution of gas. When treated in this manner, genuine olive oil causes an elevation of about 42°; that given by various other oils, often added to it, ranges from 52° to 103°, and it is frequently possible to recognise their presence in admixtures by the high temperature produced. The following are the increases of temperature observed by L. Archbutt:--olive, 41-45; rape, 55-64; arachis, 47-60; sesamé, 65; cotton-seed (crude) 70; (refined), 75-76; poppy-seed, 86-88; menhaden, 123-128. In the Paris Municipal Laboratory an acid of 1·834 sp. gr. is used, and the following heating powers are regarded as standards:--For olive oil, 55·5°; for cotton-seed, 69·5° for nut, 62°; for sesamé, 66°; for poppy oil, 73°.

The application of Hubl’s test for butter (see p. 75) is one of the most useful means for the detection of foreign oils in olive oil. The iodine absorption number of the pure oil is considerably below that of its most common adulterants.

The prevalence of the adulteration of olive oil has been abundantly demonstrated. Of 232 samples examined by the New York and Massachusetts State Boards of Health, 165 (71 per cent.) were spurious. It is a notorious fact that large quantities of cotton-seed oil are exported from the United States to France and Italy, much of which returns home under the guise of the genuine product of the olive.

FOOTNOTES:

[136] It has been stated that American olive oil of superior excellence is made in the States of N.C., Miss, and Cal.; but this product does not, as yet, appear to be generally known on the New York market.

[137] Frens. Zeitsch. 3, 1864, p. 513.

Mustard is the product obtained by crushing and sifting the seeds of _Sinapis nigra_ and _Sinapis alba_, of the genus Brassicaceæ. In the manufacture of the condiment, both the black and white seeds are used. According to analyses made by Piesse and Stansell,[138] fine grades of the two varieties of mustard possess the following composition:--

--------------------+--------------+-------------- |Black Mustard.|White Mustard. --------------------+--------------+-------------- | per cent. | per cent. Moisture | 4·52 | 5·78 Fixed oil or fat | 38·02 | 35·74 Cellulose | 2·06 | 4·15 Sulphur | 1·48 | 1·22 Nitrogen | 5·01 | 4·89 Albuminoids | 30·25 | 30·56 Myrosin and albumen | 6·78 | 6·67 Soluble matter | 32·78 | 36·60 Volatile oil | 1·50 | 0·04 Potassium myronate | 5·36 | .. Ash | 4·84 | 4·31 Soluble ash | 0·98 | 0·55 --------------------+--------------+------------

Clifford Richardson regards the following proportions of the more prominent constituents of pure mustard flour as a basis for detecting adulterations:--

Per cent. Water 5·00 to 10·00 Ash 4·00 „ 6·00 Fixed oil 33·00 „ 37·00 Volatile oil 0·25 „ 1·00 Crude fibre 0·50 „ 2·00 Nitrogen 4·50 „ 6·00

The following results were obtained by Messrs. Waller and Martin from the examination of 14 samples of very low grade dry mustard, as found on the New York market:[139]--

Per cent. Moisture, ranged from 5·43 to 9·86 Fixed oil „ „ 6·81 „ 22·56 Total ash „ „ 2·05 „ 16·05 Soluble ash „ „ 0·15 „ 2·90 Insoluble ash „ „ 1·69 „ 13·15

Eight samples were coloured with turmeric, 4 with Martius’ yellow, 12 contained starch, and 5 showed the presence of calcium sulphate.

The article usually sold as mustard is a mixture of mustard farina, prepared from different varieties of the seed, with wheaten flour or starch, and turmeric. It is claimed by the manufacturers that pure mustard possesses too acrid a taste to be suitable for use as a condiment; and its admixture with the foregoing substances is so generally resorted to and recognised, that the New York State Board of Health, in 1883, legally sanctioned the practice, provided the fact is distinctly stated upon the label of the packages. Other prevalent forms of sophistication consist in the partial extraction of the fixed oil from the mustard before its introduction on the market, and in the addition of cocoa-nut shells, _terra alba_, and “Martius’ yellow” (potassium dinitronaphthalate). The latter colouring matter is specially objectionable, being poisonous in its action. The presence of organic admixtures is usually recognised upon a microscopic examination of the sample. The anatomical structure of mustard seed is described by Fluckigen and Hamburg in ‘Pharmacographia.’ Wheaten flour or starch is readily identified by the iodine test. The following methods are employed for the detection of turmeric:--

1. A portion of the sample is agitated with castor oil and filtered. In case turmeric is present, the filtrate will exhibit a marked greenish fluorescence.

2. Upon treating the suspected sample with ammonium hydroxide, an orange-red colour is produced in presence of turmeric. Or, the mustard is boiled with methylic alcohol, the extract filtered, evaporated to dryness, and the residue treated with hydrochloric acid; if turmeric be present, an orange-red coloration takes place, which changes to a bluish-green upon adding an excess of sodium hydroxide. In addition to the above qualitative tests, valuable indications regarding the purity of mustard are to be obtained by the determination of the proportions of fixed oil, sulphur, and ash contained in the sample under examination.

_Fixed Oil._--The amount of fixed oil is estimated by digesting a weighed portion of the mustard with ether in a closed vessel, filtering, and determining the weight of the residue left upon evaporating the ethereal solution to dryness over the water-bath. The oil possesses a specific gravity ranging from 0·915 to 0·920. The percentage of fixed oil in pure mustard is very considerable (usually over 34 per cent.), whereas the substances commonly added contain but a very small quantity. In case wheaten flour has been employed as an adulterant, the proportion of pure mustard (_x_) in a mixed sample, can be approximately calculated by the following formulæ, in which _y_ is the fixed amount of oil contained.[140]

(33·9_x_) / 100 + 1·2(100 - _x_) / 100 = _y_,

36·7_x_ / 100 + 2·(100 - _x_) / 100 = _y_.

In the absence of flour, a low percentage of fixed oil indicates the presence of exhausted mustard cake.

_Sulphur._--Blyth determines the total sulphur by oxidation with fuming nitric acid, diluting the liquid considerably with water, filtering and precipitating the sulphates formed by means of barium chloride. The proportion of sulphates (in terms of barium sulphate) found in the ash is to be deducted from the weight of the precipitate obtained; the remainder, multiplied by 0·1373, gives the amount of sulphur present in organic combination, and, as the quantity contained in this form in mustard is far greater than in any of the substances employed for its adulteration, the estimation is frequently very useful.

_Ash._--The amount of ash is determined in the usual manner, _i. e._ by the incineration of a weighed portion in a platinum capsule. Genuine mustard contains about 5 per cent. of ash, of which nearly 1 per cent. is soluble in water. In presence of inorganic impurities, the quantity of ash is naturally increased, while a proportion under 4 per cent. is usually considered an indication of organic admixture.

The composition of the ash of mustard seed is given below:--

Per cent. Potassa 16·15 Lime 19·24 Magnesia 10·51 Ferric oxide 0·99 Phosphoric acid 39·92 Sulphuric acid 4·92 Chlorine 0·53 Silica 2·48

The adulteration of mustard is very extensively practised. Of 18 samples bought at random in the shops and tested for the New York State Board of Health, 12 were found to be impure; of 88 samples, examined in the year 1884 by the Massachusetts State Board, 20 were compounds (labelled as such, but in a manner designed to deceive the purchaser). 37 were adulterated with flour, turmeric, and, in some cases, with cayenne, and 31 were found to be pure; in 1885, 211 samples were tested, of which 124 were sophisticated; of 27 samples tested by the National Board of Health, 21 contained foreign admixtures, consisting chiefly of wheat or flour and turmeric, but also including corn-starch, rice, cayenne, and plaster of Paris.

FOOTNOTES:

[138] ‘Analyst,’ 1880, p. 161.

[139] ‘Analyst,’ ix. p. 166.

[140] Blyth, op. cit.

Black Pepper is the dried unripe berry of _Piper nigrum_; white pepper, which is much less in use, being the same fruit deprived of its outer skin by maceration in water and friction. The more important constituents of pepper are an alkaloid (piperin), the volatile oil, and the resin, and upon these ingredients its value as a condiment depends. The partial composition of genuine pepper, as given by Blyth, is shown below:--

-----------+---------+---------+---------+---------+------------------- | | | | | Ash. | | | |Aqueous +---------+--------- Variety. |Moisture.| Piperin.| Resin. |Extract. |Soluble. | Total. -----------+---------+---------+---------+---------+---------+--------- |per cent.|per cent.|per cent.|per cent.|per cent.|per cent. Penang | 9·53 | 5·57 | 2·08 | 18·33 | 2·21 | 4·18 Tellicherry| 12·90 | 4·67 | 1·70 | 16·50 | 3·38 | 5·77 Sumatra | 10·10 | 4·70 | 1·74 | 17·59 | 2·62 | 4·31 Malabar | 10·54 | 4·63 | 1·74 | 20·37 | 3·45 | 5·19 -----------+---------+---------+---------+---------+---------+---------

The percentages of piperin, resin, extract, and ash are calculated on the sample dried at 100°. König’s analysis of pepper is as follows:--

Per cent. Water 17·01 Nitrogenous substances 11·99 Volatile oil 1·12 Fat 8·82 Other non-nitrogenous substances 42·02 Cellulose 14·49 Ash 4·57 to 5·00

Heisch[141] has analysed several varieties of pure and commercial pepper, with the following results:--

-------------------+-------------------------------------------------- |Water. | +-----+-------------------------------------- | |Total|Ash Soluble in Water. | |Ash. | +-------------------------------- | | | |Ash Soluble in Acid. | | | | +--------------------------- | | | | |Ash Insoluble. | | | | | +--------------------- | | | | | |Alkalinity | | | | | | as +---------- | | | | | |K_{2}O. |Piperin. | | | | | | +-----+-----+ | | | | | | | Alcoholic| | | | | | | | Extract.| | | | | | | +-------+ | | | | | | | |Starch.| | | | | | | | | +-+ | | | | | | | | | | -------------------+-----+-----+-----+----+-----+----+-----+-----+---- |p.c. |p.c. |p.c. |p.c.|p.c. |p.c.|p.c. |p.c. |p.c. {| 9·22| 4·35|1·54 |1·51|0·36 |0·72|48·53|10·47|4·05 Black berry {| to | to | to | to | to | to | to | to | to {|14·36| 8·99|3·34 |3·83|4·38 |1·57|56·67|16·20|9·38 | | | | | | | | | {|13·67| 1·28|0·217|0·84|0·22 |0· |76·27| 9·23|5·13 White berry {| to | to | to | to | to | to | to | to |to {|17·32| 8·78|0·618|2·80|0·69 |0·22|77·68| 9·73|6·14 | | | | | | | | | Fine ground (white)|13·90| 1·58|0·16 |0·90|0·52 |0·0 |75·31|10·66|4·51 Long pepper |12·15|13·48|2·28 |5·52|5·68 |0·53|58·78| 8·29|1·71 Adulterated ground |11·12|14·70|2·02 |4·07|8·61 |0·78|35·85|11·57|2·02 -------------------+-----+-----+-----+----+-----+----+-----+-----+-----

The same authority regards 50 per cent. of starch as the minimum standard for unadulterated pepper. The granules of pepper-starch are characterised by their exceedingly small size, being only about ·008 mm. in diameter.

The proportion of ash in genuine pepper seldom exceeds 7 per cent., of which not over 1/10th should consist of sand; but in the commercial article, the total ash often approximates 10 or 12 per cent., 40 or 50 per cent. of which is sand and other insoluble substances.