REPORT ON THE SEPARATION OF VEGETABLE PROTEIDS. By H. SNYDER, Associate Referee. The work on the separation of vegetable proteids has been confined to a study of the literature on the subject. No attempt has been made to correlate the literature, and only a general summary is given. No samples were distributed for the cooperative work, as previous investigations have shown that in the case of cereals, as in wheat, closely agreeing results can be secured when skilled analysts work on the same sample and follow a definite course of procedure. There is such an extensive overlapping of the proteids as to solubility that it is doubtful whether accurate analytical methods can be devised for the absolute determination of any one proteid. The water-soluble, dilute saltsoluble, and alcoholic-soluble proteids can be determined with a reasonable degree of accuracy, but each solvent has a tendency to yield a mechanical mixture rather than an individual proteid. In the case of some of the cereals, however, a solvent may extract an individual proteid with a high degree of purity. In the studies that are being made of the synthetic and ultimate composition of proteids, pure proteids are secured by special treatment not admissible in quantitative work. The object is to secure a pure proteid, and the mechanical losses due to the overlapping of the solvent can be disregarded. At the present time it would seem best, in the determination of vegetable proteids, to designate the products as water-soluble, salt-soluble, or alcoholsoluble proteids, designating the proteid by the solvent rather than by the specific names suggesting individual proteids, except in special cases, as in wheat, where the alcohol-soluble proteid is mainly gliadin. There is much need of an improved method for the determination of proteid and nonproteid nitrogen. While the determination of total nitrogen has reached a high degree of perfection, that for the determination of proteid nitrogen is defective. Stutzer's albuminoid nitrogen method does not make a sharp distinction between proteid and nonproteid nitrogen in many substances. Instances occur where the copper proteid is soluble owing to secondary reactions. In the presence of a large amount of starch the filtration and washing of the precipitate often require hours, rendering the accuracy of the results questionable. It would seem best first to direct attention to the improvement of the methods for the determination of proteid and nonproteid nitrogen rather than of individual proteids. The analytical and synthetical work that is being done bids fair to give, in the near future, important results, and then it will be possible to devise rational methods for the separate determination of the various component proteids. To analyze accurately a complex compound, its composition must first be determined. It is therefore recommended that the referee on vegetable proteids give special attention to the study of methods for the determination of proteid and nonproteid nitrogen. The association adjourned to meet at 2.30 p. m. THURSDAY-AFTERNOON SESSION. On the suggestion of Doctor Frear, the recommendations in the president's address calling for changes in the constitution were referred to the committee on amendments to the constitution for recommendations. In the absence of Mr. Woll, Mr. Bartlett, the associate referee, presented the report on dairy products. REPORT ON DAIRY PRODUCTS. By F. W. WOLL, Referee. The referee was requested, by a vote of the association, to continue the study of the analysis of condensed milk with special reference to the determination of lactose, sucrose, and fat in the sweetened product. The following explanatory letter, together with two carefully prepared samples of sweetened and unsweetened condensed milk, were sent to 22 different stations where chemists had signified their willingness to cooperate in the work outlined by the referee. MADISON, WIS., March 28, 1907. DEAR SIR: As stated in my circular letter of the 12th instant, the cooperative work on dairy products, Association of Official Agricultural Chemists, for this year will be along two lines: I. Analysis of condensed milk, with special reference to the determination of sucrose and lactose in the sweetened product. The provisional methods for analysis of condensed milk adopted tentatively at the last convention of the association are as follows: Preparation of sample: Mix thoroughly by transferring the contents of a can to a large evaporating dish and stirring with a pestle. Weigh 40 grams into a 100 cc flask, transfer thereto by washing, and make up to the mark with water. Total solids: Dilute a measured portion of the above 40 per cent solution with an equal amount of water, use 5 cc of the diluted mixture, and proceed as in the case of milk analysis. Ash: Ignite the residue from the total solids, cool, and weigh. Protein: Determine nitrogen by the Kjeldahl or Gunning method in 5 cc of the 40 per cent solution and multiply it by 6.25. Lactose: Dilute 5 cc of the 40 per cent solution to about 40 ce and add 0.6 cc of Fehling's copper solution; nearly neutralize with sodium hydrate solution and make up to 100 cc. Filter through a dry filter and determine the lactose in an aliquot by the gravimetric and polariscope methods. Sucrose: Determine (a) gravimetrically and (b) by difference, by deducting the milk solids (lactose, protein, fat, ash) from the total solids. Fat: Determine by (a) double-extraction method (Circular 32, page 6, Bureau of Chemistry, U. S. Department of Agriculture) and (b) Babcock centrifugal method, using either Leach's modification (Food Inspection and Analysis, page 49) or Farrington's (Wisconsin Station Report 17, page 86). II. The Gottlieb method for the determination of fat in milk. The directions for the Gottlieb method are as follows (Landw. Vers. Sta., 1892, 40: 1-27): Ten cc of milk are measured into a glass cylinder inch in diameter and about 14 inches long (see Land. Vers. Sta., 40: 6; a 100 ce burette or a eudiometer tube will do); 1 cc concentrated animonia is added and mixed thoroughly with the milk. The following chemicals are next added in the order given: 10 cc of 92 per cent alcohol, 25 ce of washed ether, and 25 ce petroleum ether (boiling point below 80° C.), the cylinder being closed with a moistened cork stopper and the contents shaken several times after the addition of each. The cylinder is then left standing for six hours or more. The clear fat solution is next pipetted off into a small weighed flask by means of a siphon drawn to a fine point (see Fig. 6, loc. cit.), which is lowered into the fat solution to within 0.5 cm of the turbid bottom layer. After evaporating the ether solution in a hood, the flasks are dried in a steam oven for two to three hours and weighed. This method is applicable to new milk, skim milk, buttermilk, whey, cream, cheese, condensed milk, and milk powder, but has been found of special value for determining fat in skim milk, buttermilk, cheese, and condensed milk. In the case of products high in fat a second treatment with 10 cc each of ether and petroleum ether is advisable in order to recover the last trace of fat. Chemists are asked to make comparative fat determinations in a number of samples of skim milk and buttermilk by this and the official method of fat determination in milk. * * * The referee is indebted to the Borden Condensed Milk Company, New York City, N. Y., who furnished the samples of milk, together with what they believe to be "fair average analyses" of the two products. TABLE I.-Results as reported by Borden Condensed Milk Company. The results Eight reports of the work done on these samples were received. of the analyses given in the following pages have been arranged for the sake of convenience under three headings: (1) Solids, protein, and ash in condensed milk. (2) Fat in condensed milk. (3) Sugar in condensed milk. SOLIDS, PROTEIN, AND ASH IN CONDENSED MILK. TABLE II.-Solids, protein, and ash in sample No. 9, sweetened condensed TABLE III.-Solids, protein, and ash in sample No. 123, unsweetened condensed G. E. Patrick: The solids obtained by drying a milk of any kind will vary from 0.1 to 0.2 per cent, according to the method of drying, i. e., whether dried rapidly or slowly, at high or low temperature. In the work here reported samples were dried first on the steam bath and then in boiling-water oven, at atmospheric pressure. P. H. Smith and E. B. Holland: Moisture: Dried 15 cc of a 20 per cent solution on quartz sand in a flat-bottomed dish at a low temperature until bulk of the water was expelled, then completed at 100°C. Ash: Evaporated to dryness 25 cc in a platinum dish with 5 cc of concentrated nitric acid and burned to white ash. Protein: Employed the Kjeldahl-Gunning method, using 5 cc of solution. James M. Doran: Solids: Determined according to the provisional method of the association, evaporating first over steam bath and later drying in water oven to constant weight. Protein: Determined nitrogen in aliquot of diluted milk (corresponding to about two grams of the original sample) by the Gunning method. Geo, A. Olson: Solids: Determined in the Babcock asbestos tube until constant in weight. Protein: Determined by the straight Kjeldahl method. Milk first dried in steam oven and finally incinerated in muffle furnace. Ash: DISCUSSION OF RESULTS. The results for protein and ash on the whole are fairly concordant. This, however, can not be said of those for solids. The difference in solids alone-3 per cent is sufficient to throw the analyses of the various ingredients out of balance. FAT IN CONDENSED MILK. TABLE IV.-Fat in sample No. 9, sweetened condensed milk. Adams paper coil method, 20 per cent solution, first extraction, 8.44; second, 0.08. First extraction, 8.22; second, 0.31; third, 0.08. e Modified method, 7.65. TABLE V.-Fat in sample No. 123, unsweetened condensed milk. Adams paper coil, 40 per cent solution, first extraction, 8.11; second, 0.01. e Modified method, 7.40. REMARKS BY ANALYSTS. G. E. Patrick: For comparison, fat was determined by the Adams method on a 40 per cent solution of the sweetened condensed milk, giving a result-the mean of triplicates-about 0.3 per cent lower than by the same method on a 20 per cent solution, as given above. In the Gottlieb method for fat the Rohrig tube, mentioned in last year's report, has been used continuously with the greatest satisfaction. We consider the Gottlieb method the best known for the determination of fat in milks. Geo. A. Olson: Adhered to methods as described in circular letter. P. H. Smith and Edw. B. Holland: Method (A). Extracted the pulverized solids with dry ethyl ether in a continuous extractor before and after washing to remove sugars. Method (B). Washed solids with water to remove sugars and extracted with ethyl ether. Results higher, with a considerable saving of time and work. James M. Doran: One to one and a half grams of the original sample was used for the Gottlieb method and allowed to stand over night before siphoning. The Adams-Soxhlet method gave low results after three days' extraction. It appeared to be unsatisfactory owing to the length of time required to obtain results. · DISCUSSION OF RESULTS. As stated last year, the double-extraction method increased the per cent of fat in both sweetened and unsweetened milk. The Gottlieb method generally gives higher results than any one of the other methods employed. The lack of agreement in the different methods of estimating the fat may be, in part, due to the variations in the samples. SUGAR IN CONDENSED MILK. TABLE VI.-Sugar in sample No. 9, sweetened condensed milk. |