Chapter XIII: Part I: ; Analyst, 1905, 155). In this, 10 grms. of the fat, melted

Text size

and weighed at 60° C., are placed in a cylindrical vessel, and saponified by first stirring for ten minutes with 5 c.c. of potassium hydroxide solution, containing 120 grms. potassium hydroxide in 100 c.c., and then heating to 70°-80° for twenty minutes. The saponified fat is washed into a distilling flask with 200 c.c. of water, gently warmed until solution is complete, and the fatty acids liberated by adding 30 c.c. of phosphoric acid (sp. gr. 1·15), any carbon dioxide being removed by connecting the vessel with a pump for ten minutes.

The volatile fatty acids are then distilled off in the apparatus shown in Fig. 3, and to obtain comparative results, strict adherence to the form and dimensions given must be made. Two hundred c.c. are distilled over, the heat being regulated so that this takes about one and a half hours, and the distillate is allowed to stand until the following day, when it is filtered through a wet paper, the flask washed with 5 c.c. of water, which is also passed through the paper, and the soluble fatty acids titrated with standardised lime-water, with phenol-phthalein as indicator.

The filter is now washed with four successive quantities of 5 c.c. of alcohol, poured on drop by drop, and the washings collected in the receiver originally used. The condenser is next rinsed, first with 20 c.c. of alcohol, which should fill the tube when closed at its lower end, and a second time with 5 c.c. of alcohol, these washings being added to the remainder, and the whole titrated with the standard lime-water.

The results of both titrations are expressed as butyric acid, and the ratio

insoluble acids
———————————————— × 100
soluble acids

for pure butter should lie between 10 and 15, whilst for cocoanut oil it is 250-280. For butter containing 10 per cent. of cocoanut oil the figure is 19·8, and 15 per cent. cocoanut oil 24·1, for 20 per cent. cocoanut oil 27, and for 50 per cent. cocoanut oil 73·1. It is claimed that by this process the presence in butter of as little as 5 per cent. of cocoanut oil can be detected with certainty.

Two methods have been proposed, based on the precipitation of insoluble silver caprylate: (1) by Kirschner (_Zeit. Untersuch. Nahr. Genussm._, 1905, ix. 65-70), and (2) by Wijsman and Reijst (_Zeit. Untersuch. Nahr. Genussm._, 1906, xi. 267-271).

In the former process, 5 grms. of the fat are treated by the before-mentioned Reichert-Meissl-Wollny process so far as neutralising 100 c.c. of the filtered distillate with N/10 barium hydroxide solution. Half a grm. of silver sulphate is then added to the neutral solution, which is frequently shaken for one hour, and filtered, and 100 c.c. of the filtrate are transferred to a distilling flask. To this liquid are now added 35 c.c. of dilute sulphuric acid (2½ per cent.) and a few fragments of pumice, and the whole distilled until 110 c.c. of distillate have been obtained. This is filtered, and 100 c.c. titrated with N/10 barium hydrate solution, the number of c.c. required; calculated back to the 5 grms., giving what is termed the “second titration value.”

According to Kirschner, the percentage of butter fat in a mixture of butter and cocoanut oil may be calculated from the formula:—Percentage of butter fat = 4·319 S - 0·456 R - 2·15, where S = the second titration value, and R = the Reichert-Meissl figure. A similar formula is given for the percentage of cocoanut oil, which = 7·42 R - 8·116 S - 3·57. Wijsman and Reijst’s method, or the “_silver value_ method,” is performed by treating with silver nitrate (1) the Reichert-Wollny distillate; and (2) 250 c.c. filtered from 300 c.c. of distillate obtained from a further 5 grms. of fat, this being saponified, treated with acid, and 100 c.c. distilled off in the usual way, after which 100 c.c. more water are added from a tap funnel, and another 100 c.c. distillate collected, this being once more repeated.

In both cases the filtered solutions are neutralised with N/10 alkali, and 40 c.c. of N/10 silver nitrate solution added, the precipitated silver salt collected on a filter and washed until about 200 to 300 c.c. of filtrate have been collected, after which 50 c.c. of N/10 sodium chloride solution is added and the excess of chloride titrated back with N/10 silver nitrate solution, potassium chromate being used as indicator.

Eleven-tenths of the number of c.c. required in the first case, and six-fifths of that used in the second, give what are termed the first and second “silver values.”

In the case of pure butter all the caprylic acid should distil over in the first 110 c.c. so that the “second silver value” should not exceed the first, but with cocoanut oil the distillation of caprylic acid continues with the second and third 100 c.c. of distillate, so that the second silver value is greater than the first. The process has been adversely criticised by Jean (_Ann. de Chim. Anal._, 1906, ii. 121-124).

A useful qualitative test for the detection of even small quantities of cocoanut oil in butter is that due to Hinks (_Analyst_, 1907, 160). In this, 5 c.c. of the melted and filtered fat are dissolved in 10 c.c. of ether, and cooled to 0° C. for thirty minutes. The solidified glycerides are then rapidly filtered off, the filtrate evaporated, and the residue redissolved in 3 to 4 times its volume of boiling 96 to 97 per cent. alcohol. This is allowed to cool to the ordinary temperature, and then placed in a water-bath at 5° C., at which temperature it is kept for fifteen minutes. The alcoholic layer is filtered off into a tube cooled to 0° C., and the flocculent precipitate, which soon separates, is examined microscopically with a magnification of 250-300. Butter treated in this manner deposits round, granular masses, whereas cocoanut oil gives fine needle-shaped crystals. As little as 5 per cent. cocoanut oil may be detected by this process.

Ross (_Analyst_, 1908, 457) has attempted to make this process quantitative by determining the refraction of the residues obtained, but without success.

Palm oil in butter may be detected by the Liebermann-Storch reaction for rosin. Ten c.c. of the filtered fat are dissolved in 10 c.c. of acetic anhydride, and 1 drop of sulphuric acid (sp. gr. 1·53) added. The mixture is shaken, and, on standing, a blue liquid, having a greenish tint, separates, if palm oil is present.

=Soluble and Insoluble Fatty Acids—the Hehner value.=—A weighed quantity of about 5 grms. of the filtered butter fat is introduced into a strong 6 oz. bottle, and 50 c.c. of approximately N/2 alcoholic potassium hydroxide solution added, another 50 c.c. being also placed in an empty flask. The bottle is fitted with an india-rubber stopper, which is secured by wire, and is placed in a water-bath, being occasionally removed, and well agitated without bringing the liquid in contact with the stopper. After about thirty minutes, saponification is complete (this being shown by the contents of the bottle being free from oily globules), and the bottle is withdrawn and allowed to cool. The stopper is then removed, and the contents of the bottle transferred, by rinsing with boiling water, into a 10 oz. flask, which is placed, together with the flask containing only alcoholic potassium hydroxide solution, on a steam-bath.

As soon as all the alcohol has evaporated the contents of each flask are neutralised with N/2 hydrochloric acid, an excess of about 1 c.c. of acid being added, and a note made of the quantity used. The flask containing the butter fat is nearly filled with boiling water, and placed on the water-bath, a cork with a long upright tube being inserted. When the fatty acids have melted to a clear liquid on the surface of the water, the flask is removed and its contents allowed to become perfectly cold, when the fatty acids should solidify. By gently tapping the sides of the flask this cake is detached, and the liquid is poured through a filter into a large flask. This liquid should have a distinct odour of butyric acid, especially on warming.

The flask containing the insoluble fatty acids is again filled with boiling water, the cork and reflux tube inserted, and the liquid gently heated to the boiling-point, after which the flask is removed and thoroughly shaken until the melted fatty acids are emulsified with the water. The fatty acids are now allowed to separate again on the surface, solidified by cooling, detached by gently tapping, and the liquid filtered off as before. The process is repeated three times, or until the washings collected separately do not require more than 0·2 c.c. of N/10 sodium hydroxide solution for neutralisation.

The mixed washings are next diluted to one litre or other convenient volume, and an aliquot part titrated with N/10 sodium hydroxide solution, the number of c.c. required being calculated upon the whole liquid. This amount of alkali is that required to neutralise the excess of acid added after saponification, together with the soluble fatty acids, and the former may be known by titrating the excess in the blank experiment, so that the difference between these two titrations gives the alkali absorbed by the volatile fatty acids. These are usually expressed as butyric acid, C₃H₇COOH, the percentage of which may be found by multiplying the number of c.c. of alkali solution required to neutralise the soluble fatty acids by 0·0088 and by 100, and dividing by the weight of fat taken.

_The Insoluble Fatty Acids_ are determined by allowing the flask containing the solid cake to drain as completely as possible, melting the fatty acids, and pouring them on to the wet filter through which the solution of soluble fatty acids was passed. They are then washed on the filter with boiling water, and the funnel filter transferred to a small beaker and placed in the water-bath until all the fatty acids have filtered through. Flask, funnel, and filter paper are well washed with ether, the washings added to the filtered fatty acids, and the ether evaporated. The fatty acids are then dried in the oven at 100° C. until constant in weight, and from the weight obtained the percentage of insoluble fatty acids is calculated on the weight of butter fat taken. This is known as the Hehner value.

Butter should contain at least 5 per cent. of soluble fatty acids calculated as butyric acid, and the insoluble fatty acids should not exceed 89½, rarely 88½ per cent.

The following table contains results obtained by Thorpe (_Journ. Chem. Soc._, 1904, 254) on 357 samples of British butters:—

LEGEND:
(A) = Reichert-Meissl-Wollny Number.
(B) = Saponification Equivalent.
(C) = Refactometer Number at 45° C.
(D) = Soluble Acids per cent. on Fat.
(E) = Insoluble Acids per cent. on Fat.
(F) = Mean Molecular Weight of Insoluble Acids.
+----------+------+----------+-------+------+-----+------+-------+
| | | Specific | | | | | |
| Number | | Gravity | | | | | |
| of | (A) | at | (B) | (C) | (D) | (E) | (F) |
| Samples. | | 37·8° C. | | | | | |
+----------+------+----------+-------+------+-----+------+-------+
| 7 | 22·5 | 0·9101 | 255·4 | 42·0 | 4·3 | 90·1 | 266·9 |
| 17 | 23·5 | 0·9104 | 253·4 | 41·5 | 4·5 | 89·7 | 265·5 |
| 15 | 24·5 | 0·9108 | 251·3 | 41·5 | 4·7 | 89·4 | 265·0 |
| 27 | 25·5 | 0·9110 | 251·1 | 41·3 | 4·8 | 89·3 | 264·2 |
| 37 | 26·5 | 0·9113 | 248·9 | 41.0 | 4·9 | 88·9 | 261·9 |
| 51 | 27·5 | 0·9114 | 247·4 | 40·6 | 5·2 | 88·7 | 261·7 |
| 78 | 28·8 | 0·9118 | 245·7 | 40·1 | 5·4 | 88·4 | 260·9 |
| 56 | 29·5 | 0·9120 | 244·0 | 40·1 | 5·6 | 88·3 | 259·6 |
| 41 | 30·5 | 0·9123 | 242·4 | 39·9 | 5·8 | 87·9 | 260·1 |
| 18 | 31·3 | 0·9125 | 241·5 | 39·7 | 5·7 | 87·9 | 258·0 |
| 10 | 32·6 | 0·9130 | 241·2 | 39·4 | 6·0 | 87·7 | 257·8 |
| | | | | | | | |
| 357 | | | | | | | |
+----------+------+----------+-------+------+-----+------+-------+

=Casein (Curd).=—This may be estimated by transferring the dry butter used in determining the water to a dry filter of known weight, washing it thoroughly with ether or petroleum spirit until free from fat, and weighing the filter after drying at 100° C. The residue includes casein and salt, and the latter may be determined as described below, and subtracted from the total residue.

The amount of casein does not usually exceed 1 to 2 per cent., but cases are recorded when adulteration with casein has been practised, and as much as 5 to 6 per cent. found.

=Salt.=—For most practical purposes, the ash remaining after burning either the dried butter, or the residue insoluble in ether, may be taken as salt (sodium chloride). If desired, the sodium chloride may be estimated by extracting the butter with 10 to 20 c.c. of hot water in a separating funnel, separating the aqueous layer, repeating this about ten to fifteen times, and titrating the aqueous washings with standard silver nitrate solution, using potassium chromate as indicator.

The proportion of salt may vary from 0·5 for a fresh butter up to 11 per cent. for a salt butter, but should not go beyond the latter limit (see also p. 41).

=Colouring Matters.=—The natural colouring matter of butter, which is termed “lactochrome,” is insoluble in alcohol or glacial acetic acid, so that if on shaking the sample with either of these reagents a coloured extract is obtained, artificial colouring matter has undoubtedly been added.

Two general schemes have been devised for the detection of artificial colouring matters in butter or margarine: (1) devised by Leeds (_Analyst_, 1887, 150), in which the fat and colouring matter are first extracted with petroleum ether, and the colouring matter dissolved out of the ethereal extract with N/10 potassium hydroxide, and reprecipitated with dilute hydrochloric acid; and (2) that devised by Cornelison (_Journ. Amer. Chem. Soc._, 1908, 1478), who extracts the colouring matter directly by means of glacial acetic acid.

Leeds’ process is carried out by mixing 100 grms. of the sample with 300 c.c. light petroleum spirit (sp. gr. 0·638), separating the ethereal layer by means of a separating funnel, and washing it with 100 c.c. of water in successive small quantities. The ethereal extract is allowed to stand for fifteen to twenty hours surrounded by ice, and is then decanted from any separated “stearin” and shaken with 50 c.c. of N/10 potassium hydroxide solution. The alkaline extract is separated, made faintly acid with dilute hydrochloric acid, and the precipitated colouring matter filtered off, together with a trace of fatty acid, which is always dissolved out by the alkali. The colouring matter may then be identified by the tests given on the preceding page.

In Cornelison’s method 10 grms. of the melted fat are thoroughly shaken with 10 to 20 grms. of glacial acetic acid, at about 35° C., the mixture allowed to separate, and the acid liquid drawn off. The colour of the latter is noted, and portions treated with various reagents to identify the colouring matter. The table on p. 125 gives the results obtained with the colouring matters mentioned, incorporated with pure butter in the proportion of 1 part in 100,000.

PRESERVATIVES (see p. 46).

The amount of boron compound may be readily estimated by Richmond and Harrison’s modification of Thomson’s process. Twenty-five grms. of the sample are weighed into a 100 c.c. stoppered cylinder, and, after determination of the moisture present, sufficient water is added to bring the total volume of water up to such a quantity that 1 c.c. corresponds to 1 grm. of butter. From 10 to 15 c.c. of chloroform are now introduced, and the contents of the flask heated, shaken, and allowed to separate. An aliquot portion of the aqueous liquid is then removed by means of a pipette, evaporated to dryness, ignited, and the residue extracted with hot water. The extract is made neutral to methyl orange, boiled to expel carbon dioxide, half its volume of neutral glycerin added, and the mixture titrated with N/10 sodium hydroxide solution until pink to phenol-phthalein. Each c.c. of N/10 sodium hydroxide solution is equivalent to 0·0062 grms. of boric acid.

Another method, devised by Richmond and Harrison (_Analyst_, 1902, 181), is to weigh out 25 grms. of the sample in a beaker, add 25 c.c. of a solution containing 6 grms. of milk sugar and 4 c.c. of N/1 sulphuric acid, in 100 c.c. of water. The beaker is placed in a water-oven until the fat has just melted, and the contents are then stirred well, allowed to separate, and 20 c.c. of the aqueous liquor withdrawn. A few drops of phenol-phthalein are then added, and the liquid heated to the boiling-point, and titrated with N/2 sodium hydroxide solution until faintly pink, after which 12 c.c. of glycerin are added, and more N/2 sodium hydroxide solution run in until a faint pink colour is again obtained. The amount of alkali required in the second titration, less the alkali required to neutralise 12 c.c. of the glycerin, multiplied by 0·0368, gives the amount of boric acid in 20 c.c. of the aqueous extract, and the percentage may be calculated by multiplying by (100 + percentage of water in the butter), and dividing by 20. In an average butter the number of c.c. of N/2 sodium hydroxide solution used, multiplied by 0·2, approximates closely to the percentage of boric acid.

The best method of testing for benzoic acid, salicylic acid, fluorides, and [Greek: b]-naphthol is to extract the melted butter with a dilute solution of sodium bicarbonate, and to examine this extract for the various preservatives.

Thus, in testing for benzoic and salicylic acids, the alkaline extract is exactly neutralised with dilute hydrochloric acid, and a solution of ferric chloride added. If benzoic acid or a benzoate has been added, a buff-coloured precipitate will be immediately thrown down, and if salicylic acid has been employed, an intense violet coloration will be produced.

Numerous methods have been suggested for detecting even very minute admixtures of benzoic acid or benzoates, among which may be mentioned those of Halphen (_Journ. Pharm. Chim._, 1908, 201) and Robin (_Ann. de Chim. Anal. Appl._, 1908, 431).

Halphen’s test depends on the conversion of the benzoic acid into ammonium diamido-benzoate, which, in alkaline solution, has a brown-red colour. A quantity of the butter is melted with sufficient lime-water to render the aqueous liquor which separates distinctly alkaline. After cooling, the latter is separated, acidified with phosphoric acid, and extracted with ether. The ether is allowed to evaporate spontaneously, and the residue dried at the ordinary temperature, after which it is gently heated with 2 c.c. of concentrated sulphuric acid until completely dissolved. An addition of 0·2 c.c. of fuming nitric acid is now made, and the solution transferred to a dry test tube and heated carefully over a small flame until sulphuric acid fumes appear. After cooling, the mixture is diluted with 5 or 6 c.c. of water, which causes nitrous fumes to be evolved. When again cold, a saturated solution of sodium sulphite is added drop by drop until all yellow vapours have disappeared. Ammonia is then allowed to flow over the surface of the solution, and if benzoic acid is present, an orange-red coloration is produced, the intensity of which is proportional to the quantity of benzoic acid. In case no coloration is produced, the absence of benzoic acid may be confirmed by adding a drop of ammonium sulphide to the ammoniacal solution, when, if benzoic acid is present, a red coloration develops at the point of contact of the two liquids.

By Robin’s process it is claimed that as little as 12 parts per 100,000 of sodium benzoate may be detected with certainty. The test is carried out by shaking 25 grms. of the melted butter with a solution of 0·4 to 0·5 grm. of sodium bicarbonate in 50 c.c. of water, and 15 c.c. of 95 per cent. alcohol, and allowing the mixture to stand for ten minutes, after which the alcoholic layer is drawn off, acidified with 7 or 8 drops of hydrochloric acid, and heated to the boiling-point. It is then shaken with a little talc, and filtered, the cold filtrate extracted in a separating funnel with 40 c.c. of ether, and the ethereal extract washed once with a mixture of 20 c.c. of water, 5 c.c. of 95 per cent. alcohol, and 0·2 to 0·3 grm. of sodium bicarbonate. The alkaline alcoholic extract is evaporated on the water-bath, and the residue carefully warmed with a mixture of 5 c.c. of concentrated sulphuric acid and 10 drops of fuming nitric acid, until white fumes appear, after which the liquid is poured into 50 c.c. of water containing a small piece of turmeric paper. A yellow coloration indicates the presence of benzoic acid, which may be confirmed by adding ammonia solution until alkaline, then a few drops of ammonium sulphide solution, and shaking the vessel. In the presence of benzoic acid the colour changes from yellow to reddish orange.

=Fluorides.=—The presence of these may be detected in the absence of boric acid by evaporating a small quantity of the alkaline extract to dryness in a platinum crucible, igniting the residue, moistening it with a few drops of concentrated sulphuric acid, and covering the mouth of the crucible with a piece of glass, coated with paraffin wax, through which some marks have been scratched.

Fluorides may also be detected by applying the above process to the aqueous liquor, which separates when a sample of the butter is melted.

If boric acid is present, the fluoride is liable to be lost by volatilisation as boron fluoride. It is necessary, therefore, to separate the borate as calcium borate, by rendering the liquid alkaline with lime-water, evaporating it to dryness, and extracting the residue with dilute acetic acid, which dissolves calcium borate. The insoluble matter is then dried, and treated with concentrated sulphuric acid as described above.

MARGARINE, VEGETABLE BUTTER, OR OTHER BUTTER SUBSTITUTES

The analysis of these is a matter requiring a considerable amount of skill, and even when the analysis is made, very long experience is necessary before a right interpretation can be put upon the chemical and physical data obtained.

The only requirements for margarine under the Sale of Food and Drugs Act, 1899, are that the sample shall not contain more than 16 per cent. water or more than 10 per cent. of butter. The same restrictions as to preservatives apply to this as to genuine butter.

The amount of water is readily determined by the method given under “Butter” (p. 109). The method officially adopted by the Committee of the Society of Public Analysts for the estimation of butter is the Reichert-Meissl-Wollny process (p. 111), the maximum permissible limit for the Reichert-Wollny value being 4, and a Reichert-Wollny value of 7·1 being regarded as indicative of the presence of 20 per cent. butter fat.

In addition to the analysis of margarine to ensure compliance with these standards, it is often desirable to endeavour to determine the precise composition of a sample of artificial butter, such as the relative proportions of animal and vegetable fats, and the particular fats or oils of which they consist. It is here where only prolonged experience can decide what tests to apply and determine the correct interpretation to put upon the results obtained.

In an exhaustive analysis, the specific gravity, saponification value, iodine value, titre, and Reichert-Wollny-Polenské figures should always be determined, and such qualitative tests as Halphen’s for cotton-seed, Baudouin’s for sesame, the arachidic acid test for arachis oil, and the Liebermann-Storch test for palm oil applied.

The tests for colouring matters and preservatives are the same as for natural butter.

LARD

In addition to the tests mentioned in Chapter V. pp. 60 _et seq._, Halphen’s test for cotton-seed oil and Baudouin’s test for sesame oil should be applied, and, if thought desirable, arachis oil may be tested for by the arachidic acid method. The presence of as little as 2 to 3 per cent. cotton-seed oil may be detected by the phytosteryl acetate test (see p. 101), and the addition of maize oil, which is sometimes used for adulterating lard, will also be shown by the same method.

Preservatives may be detected, and, if present, estimated as described under “Butter.”

CHEESE

The composition of cheese is so variable that it is to be regretted there are no standards to which it should conform.

The proportion of fat may vary from 20 per cent. or less to 35 or 40 per cent., or, in a cream cheese, up to 75 per cent., while the water may be anything between 20 and 40 per cent.

The analysis of cheese should include determinations of the proportions of water, ash, fat, and nitrogen, and an examination of the fatty matter.

_Water._—This may be determined by drying a weighed quantity of about 5 grms. of the sample, cut in thin slices, in the oven at 105° C., until constant in weight.

_Ash._—The dried cheese, as obtained in the above determination, is ignited at as low a temperature as possible, and the residue weighed when the whole of the carbon has been burned away.

_Fat._—This may be determined approximately by grinding up 25 to 50 grms. of the dried cheese with ignited sand, and extracting the mixture in a Soxhlet apparatus with ether or petroleum spirit, the extract being collected in a weighed carbonic acid flask, from which the solvent is afterwards distilled off, and the residue dried in the oven at 105° C., and weighed.

A better method is that of Palmquist, which is a modification of the Rose-Gottlieb process. In this, about 1 grm. of the cheese is weighed into a Gottlieb tube, 10 c.c. of 2·5 per cent. ammonia solution added, and the mixture warmed on the water-bath, and shaken until a milky homogeneous solution is obtained. After cooling, 10 c.c. alcohol and 25 c.c. of ether are added, the tube being thoroughly shaken after each addition. An addition of 25 c.c. of petroleum spirit is then made, and the tube, after being again well shaken and inverted, is allowed to stand for a few hours for its contents to separate, after which the ethereal layer is siphoned into a weighed flask. A second extraction of the mass remaining in the tube is then carried out in an exactly similar manner, the ethereal extract being again siphoned into the weighed flask, the solvent distilled off, and the residue dried in the oven at 105° C., and weighed.

A larger quantity of the fat for its examination may be readily prepared by cutting up a quantity of the cheese, wrapping it in a piece of muslin, and suspending over a basin in an oven at 105° C. The clear fat collected should then be examined, and its Reichert-Wollny value, which should be similar to that of butter, determined. If the Reichert-Meissl-Wollny figure is abnormal, the fat requires further systematic examination by the processes mentioned under “Margarine” (p. 130), to detect foreign fats.

_Nitrogen._—This is estimated by heating 1 to 2 grms. of the cheese with concentrated sulphuric acid and a globule of mercury, as in the well-known Kjeldahl process. The proteins may be calculated by multiplying the percentage of nitrogen by 6·3.

CHOCOLATE

No standards have yet been legally fixed in this country for any of the various forms of chocolate, though such standards are in existence on the Continent, and are urgently needed in view of the large amount of adulteration practised in this industry. Not only is the natural fat of the chocolate replaced by other fats, such as cocoanut oil, and cocoanut stearin, or palm-nut stearin, and the chocolate adulterated with excessive husk or starch, but products are sold as milk or cream chocolate which have no right to such designations. Hence N. P. Booth presented to the International Congress of Applied Chemistry, held in London last year, the following proposed standards, which are not more stringent than those adopted by some Continental countries and by some of the Colonies:—

1. _Unsweetened Chocolate_ must be prepared exclusively from roasted, shelled, finely ground cocoa-beans, with or without the addition of a small quantity of flavouring matter. It should contain not less than 45 per cent. of cacao butter.

2. _Sweetened Chocolate._—A preparation consisting exclusively of the products of roasted, shelled, finely ground cocoa-beans, and not more than 65 per cent. of sugar, with or without a small quantity of harmless flavouring matter.

3. _Granulated or Ground Chocolate for Drinking Purposes._—The same definition as for sweetened chocolate should apply here, except that the proportion of sugar may be raised to not more than 75 per cent.

4. _Chocolate-covered Goods._—Various forms of confectionery covered with chocolate, the composition of the latter agreeing with the definition of a sweetened chocolate.

5. _Milk Chocolate._—A preparation composed exclusively of roasted, shelled cocoa-beans, sugar, and not less than 15 per cent. of the dry solids of full-cream milk, with or without a small quantity of harmless flavouring matter.

The analysis of chocolate should comprise determinations of the moisture, ash, fat, fibre, total nitrogen, and sugar, and an examination of the nature of the fatty matter and sugar.

In the case of milk chocolate or cream chocolate, the fatty matter should contain both cacao butter and butter fat, and the sugar should contain lactose.

The analysis is carried out as follows:—

_Water._—A weighed quantity of about 5 grms. is finely divided, and dried in the oven at 105° C., until constant in weight.

_Ash._—The dried product obtained in the determination of the moisture is cautiously burnt until all carbonaceous matter is volatilised. The proportion of ash should not exceed 1 to 1·5 per cent., unless the sample has been coloured with mineral colouring matter, such as ochre.

_Fat._—This may be estimated by extracting 5 grms. of the finely ground sample in an extraction thimble with ether or light petroleum spirit, by means of a Soxhlet apparatus. The extracting liquid is collected in a small weighed flask, which, when extraction is complete, is detached from the Soxhlet apparatus, the solvent distilled off, and the residual fat weighed, after being dried in the oven at 105° C.

Kreutz (_Zeit. Untersuch. Nahr. Genussm._, 1908, 584-586) recommends melting the sample with chloral alcoholate prior to extraction with ether. From 2 to 3 grms. of the chocolate are placed in a small flask with 3 to 4 grms. chloral alcoholate, and the mixture melted by heating on a water-bath. The hot mass is well stirred with 10 to 15 c.c. of ether, a further 35 c.c. of ether added, and, after thorough shaking, the mixture is filtered through a dry filter. The filtrate is passed through the filter again and again until perfectly bright, and the residue on the filter washed with ether three times. The ether is then distilled off, and any chloral alcoholate removed by heating the residue to about 75° C., under reduced pressure. The residue obtained is extracted with carbon tetrachloride and filtered to eliminate a little theobromine and colouring matter, the filtrate evaporated in a weighed flask, and the residue of fat dried in the oven at 105° C., and weighed.

For the examination of the fat a larger quantity may be prepared by simply shaking up about 15 to 20 grms. of the finely ground sample in a stoppered bottle with three or four successive quantities of petroleum spirit, allowing the mass to settle, pouring off the solvent, and evaporating it. The residual fat should then be examined for its refractive power, its Reichert-Meissl-Polenské values, its saponification value, its iodine value, and its titre.

Genuine cacao butter gives a refractometer reading at 35° C. of about 49°, has a Reichert-Meissl value of 1 or rather less, a saponification value of about 286-290, an iodine value of about 34, and a titre of about 48° C. Cocoanut oil has a refractive power of only about 37°, and is thus readily detected by this, as also by the much increased saponification value and reduced iodine value, and the increased Reichert-Meissl figure.

Cocoanut stearin also increases the saponification value, reduces the iodine value, and raises the Reichert-Meissl figure. Palm-nut stearin increases the saponification value, reduces the iodine number, and slightly raises the Reichert-Meissl figure, its own Reichert-Meissl value being about 2·2.

Of the other fats said to be used as substitutes for cacao butter, and mentioned in Chapter VII.

_Dika, or Gaboon Fat_, raises the saponification value, lowers the iodine value, but does not affect the Reichert-Meissl figure.

_Borneo Tallow, or Tankawang Fat_, has analytical values very similar to those of cacao butter.

_Illipé Fat_ has a much higher iodine value (54-60). (See also p. 87.)

_Fibre._—This is best estimated by Allen’s method (_Commercial Organic Analysis_, iii., Part II., p. 567), in which 2 grms. are freed from fat, and boiled for thirty minutes under a reflux condenser with 200 c.c. of water and 2½ c.c. of sulphuric acid. The liquid is filtered through linen, and the residue thoroughly washed with hot water and boiled with 200 c.c. of 1¼ per cent. solution of sodium hydroxide. The residue is filtered off, washed with hot water, alcohol, and ether, and dried at 110° C., and weighed. It is then ignited, and the loss regarded as crude fibre.

_Total Nitrogen._—This is estimated on about 2 grms. of chocolate by the Kjeldahl method. In an ordinary chocolate it is normally about 1 per cent., and in a milk chocolate slightly higher. In a plain chocolate the proportion of nitrogen, multiplied by 20, will give the percentage of fat-free cocoa.

_Sugar._—This may be determined in plain chocolate by means of a polarimeter, a 20 per cent. aqueous solution, which is clarified with lead acetate in the ordinary way, being used. In the case of milk chocolate the introduction of lactose complicates the determination slightly, but estimation of the copper-reducing power enables the lactose to be calculated, and an allowance made for its effect on the optical rotation.

Previous Next

Comments

Edible fats and oilsChapter XIII: Part I: ; Analyst, 1905, 155). In this, 10 grms. of the fat, melted

0%26 min left in chapter