116 Analyst, February, 1968, Vol. 93, $p. 116-117 A Critical Evaluation of the A.O.A.C. Method for the Determination of Milk Protein in Milk Chocolate when Applied to Crumb Chocolate BY R. J. MOT2 (Mars Limited, Confectionery Dicision, Dundee Road, Slough, Bucks.) Comparatively small differences in manufacturing temperatures of chocolate crumb may lead to unreiiable results when using the A.O.A.C. method for the determination of milk protein in crumb chocolate. A COLLABORATIVE study1 was recently carried out by the members of the Technical Com- mittee of the Office International du Cacao et du Chocolat on the determination of milk protein in milk chocolate, by using the A.O.A.C. methodJe in which the amount of protein precipitated from an oxalate solution with tannic acid is measured.The results obtained by the committee cast doubts on the suitability of that method for milk chocolate made by the “Crumb Process,” which is used for producing most of the chocolate in the U.K. and, to an increasing extent, on the European Continent. This crumb process differs from that used by American manufacturers in that it subjects the wet “crumb paste” to elevated temperatures, usually under reduced pressure. EXPERIMENTAL Crumb batches were prepared, one set, A, by heating portions for different lengths of time at 95°C and the other set, B, by heating for the same length of time at different temperatures. TABLE I RECOVERY OF NITROGEN FROM EXPERIMENTAL CRUMB A, HEATED FOR THE INDICATED TIME AT 95” c Heating time, hours 0 1 2 4 6 Protein-nitrogen by A.O.A.C.method, per cent. 1-25 1-26 1-25 1.20 1.11 Total nitrogen, per cent. . . .. . . 1.71 1.71 1-71 1.70 1-72 TABLE I1 RECOVERY OF NITROGEN FROM EXPERIMENTAL CRUMB B, HEATED FOR 2 HOURS, AT THE INDICATED TEMPERATURES Not Approximate heating temperatures heated 104OC 122OC 13OOC 14OOC Protein-nitrogen by A.O.A.C. method, per cent. 1.23 1.20 0.43 0.16 0.12 Total nitrogen, per cent. . . . . . . 1.89 1-66 1-66 1.65 1.55 Total fat, per cent. . . . . . . . . 15.8 15-7 16.9 15.9 16.9 Lactose, per cent. . . . . . . . . 11.9 11.4 11.1 11.0 10-8 Recovery of fat and lactose The samples were analysed for total nitrogen and protein-nitrogen before, and after, drying, according to the A.O.A.C. method. The results are listed in Tables I and 11. 0 SAC; Mars Ltd., Copyright Reserved.February, 19681 MOT2 117 DISCUSSION As seen in Fig.1, a slight but significant loss of protein-nitrogen resulted from increasing the heating time while maintaining the temperature at about 95”C, whereas increasing the dry temperature led to the loss of a considerable proportion of protein-nitrogen. Because the loss of total nitrogen under the various heating conditions was comparatively small, it is concluded that heating reduced the solubility of protein in sodium oxalate solution. As the conditions of crumb making vary between chocolate manufacturers, the results obtained by the A.O.A.C. method for milk protein in their products will also vary. Crumb drying temperature, “C Fig. 1. Relationship between crumb-drying temperature and resulting losses of protein- nitrogen (A.O.A.C.- nitrogen), lactose and total nitrogen based on the composition of the same crumb dried in wucuo at room temperature over phosphorus pentoxide : A, protein-nitrogen; B, lactose; and C, total nitrogen The use of the A.O.A.C. method would therefore appear to be unsatisfactory for charac- terising accurately the milk content of a large proportion of chocolate in the absence of detailed information on the manufacturing process used. However, losses of lactose are probably not more than 5 per cent. under the normal range of conditions of crumb making, and the lactose content of a crumb chocolate may form, together with other results, a more reliable basis of determination of milk content. REFERENCES 1. 2. Int. Choc. Rev., to be published. Horwitz, W., Editor, “Official Methods of Analysis of the Association of Official Agricultural Chemists,” Tenth Edition, Association of Agricultural Chemists, Washington, D.C., 1966, p. 187. Received August 18th, 1967