Another and better method of determining the nitrogen is by Kjeldahl’s[195] process. It has been frequently subjected to modifications, but was originally carried out as follows. 0·25 grammes of the nitrogenous substance (cacao preparation) is heated on the sand bath together with 20 ccm of concentrated sulphuric acid and a little quicksilver, till the solution becomes colourless or only of a very pale yellow. After diluting with about 200 ccm of water, it is made alkaline by the addition of soda lye (which must of course be entirely free from nitrogen, the same remark applying to the sulphuric acid used) and, potassium or sodium sulphide being added, it is then distilled, and the ammonia given off collected and determined as above described. As this method also determines the total amount of nitrogen, an allowance must be made for the nitrogen in the theobromine and caffeine before multiplying the result by 6·25. This modification is still to be recommended as the best and most reliable.
In rare cases an excessive amount of albumen may be due to the admixture of earth-nut cake or gelatine. As to the detection of the latter adulteration, see page [254]. Bileryst[196] says that earth-nut cake can be recognised by its high percentage of albumen content, amounting to between 45 and 47 percent.
Investigation of Milk and Cream Chocolate
12. Investigation of Milk and Cream Chocolate. The tests bearing on these products really constitute a chapter in themselves, which has acquired special importance owing to the great popularity they enjoy and the consequently greatly increased production. According to the unanimous opinion of the Association of German Chocolate Manufacturers and the Free Union of German Food Chemists, expressed when considering the respective claims of such chocolates, it is chiefly if not exclusively a matter of determining the percentage of milk or cream, which ought not to be below 12·5 or 10%, always supposing the milk or cream to be a substitute for sugar, and this means therefore that the quantity of cacao material in the chocolate product should on no account sink below 32%. (Cf. p. 283 No. 3. Abs. 5.) The method employed in the investigation is generally the same as that suggested by Laxa in his treatise on “Milk Chocolates”[197] although it has been considerably improved by Baier and his colleagues.[198] It is here a matter of working backwards from the determination of the fatty and nitrogenous components (or caseine) to the amount of milk or cream in the chocolate. This presents a certain amount of difficultly as it is not only necessary to determine the milk, but also to establish that neither skimmed or whipped material (either in part or entirely) has been employed. Yet it is possible here to proceed with absolute certainty, as Baier[199] convincingly demonstrates, by taking into consideration the relative proportion of milk fat, called caseum or caseine.
If it is desired finally to characterise the respective chocolates, determinations of the quantity of milk fat present and the amount of milk product used become essential. Baier gives both as calculable (cf. footnote 1)[200], the Reichert-Meissl number of the total fat being ascertained, and from this, subtracting the R.-M. number of the cacao fat present[201] the quantity of milk fat, finally the amount of caseine, milk sugar, mineral matter and other factors. No details of this somewhat extensive calculation are proved in the original.[202] We give the following regulations (Laxa-Baier) for carrying out the determination of the caseine, together with the necessary formula.
20 grammes of fine divided chocolate are loosely introduced into a Soxhlet’s extracting apparatus, and there extracted with ether for a period of 16 hours. Of the residue, 10 grammes are used for testing in connection with caseine, and this after the ether has evaporated. These are mixed up in mortar with gradual and even addition of a 1% solution of sodium oxalate, so that no lump formations occur, and then brought into a marked carboy of 250 ccm capacity, until 200 ccm of the sodium oxalate solution have been used. The carboy is then provided with an asbestos net, and heated by means of a flame from the under side, until its contents are brought to boil. The mouth of the carboy is covered with a small funnel which has been hermetically sealed at its narrower end. Then boiling oxalate solution is poured into the vessel up the bend, and it is then allowed to stand over till another day, shaking however being often repeated, then filled with sodium oxalate solution up to the mark, agitated with a regular motion, and then filtered through an ordinary filter. To 100 ccm of this solution 5 ccm of an uranous acetate solution (5% strong) and drop by drop and with repeated stirring a 30% solution of acetic are added until there is a deposit. (This will require from 30 to 120 drops, according to the amount of caseine present.) Then an extra 5 drops of acetic acid can be added. This causes the deposit to stand out clearly from the liquid matter and it can be readily separated by centrifugalising. Afterwards it can be washed out with 100 ccm of solution, of which 5 ccm are uranous acetate and 3 ccm acetic acid 3 % strong, until the sodium oxalate can no longer be seen on adding calcium chloride (i. e. after about three repeated centrifugalisations). The contents of the tube are then rinsed on to the small filter by means of the wash fluid, stirred in a Kjeldahl carboy with concentrated sulphuric acid and copper oxide, and the quantity of nitrogen found converted into caseine by multiplying with the factor k = 6·37.—Bearing in mind the quantity of fat, the percentage of caseine in the original chocolate is calculated.[203]
In the following:
b = signifies the total of fatty content of the chocolate[204],
a = the Reichert-Meissl number of the total fat,
and K = the amount of caseine as established by the Laxa-Baier method (nitrogen contents times 6·37).
| 1. | F = (a-1) b / 27 | Further: 1. The desired quantity of fatequal is to the R.M.N. a, of the total fat lessthat of the cacao fat (1·0) multiplied by thetotal amount of fat and divided by the average R.M.N. for butter fats = 27. |
| 2. | a) E = 1·11 K | 2. The total amount of albumen E is equal to the amount of caseine K multiplied by1·11, as this constitutes about 90% of the former; and as the albumen E, milk sugarM and the mineral constituents A (Ash V) are present in the milk in the proportion of100 : 132 : 21·4, this yields the formula given in b & c. |
| b) M = ( 1·11 K - 132) / 100 | ||
| c) A = (1·11 K - 21.4) / 100 | ||
| 3. | T = F + E + M + A | 3. The total quantity of milk stuff T isequal to the total of fatty contents, albumen, milk, sugar and ash. |
| 4. | x = Q · k | 4. The fatty constituency of the originalmilk or cream to be calculated from the formula x = Q times k, where Q is thequotient resulting when the amount of fat F is divided by that of caseine K, and kthe normal caseine consistency of average milk preparation. Or it varies as the numbersk1 etc. indicate in the case of 10% cream and so forth. Higher percentagesthan those given do not come into consideration. |
| Q = F / K | ||
| k = const. | ||
| In the case of milk: | ||
| k1 = 3·15 | ||
| k2 = 3·05 | ||
| k3 = 2·7 | ||
| k4 = 2·5 |
c. Microscopic-botanical investigation.