410 The MITCHELL: THE DETERMINATION OF THE MARC CONTENT Determination of the Marc Content of [Vol. 75 Fresh and Dried Sugar Beets BY THOMAS J. MITCHELL SuNoPsrs-The marc content of the sugar beet is important on account of the volume error it introduces in the determination of the sugar in the beet. After a short reference to earlier work, some experiments on the estimation and effects of the marc in fresh and in dried cossettes produced from beets grown in Oxfordshire and Buckinghamshire are described. The volume correction for the normal saccharimetric weight (26 g.) of fresh beets was found to be close to 1.2 ml., with a specific gravity of 1-19 for the dry marc. In a series of 100-ml. mixtures of different weights of dried marc ( 1 to 8 g.) with a pure sucrose solution that itself polarised 36-9, the polarisations of the filtered mixtures showed increases that averaged 0.34 per gram of marc taken.The marc content of dried beet cossettes appears to be higher than might be expected from calculations from the marc in the fresh beets. CLAASSEN~ defined beet marc as the residue remaining after complete extraction of the sugar and the readily soluble non-sugars from the beet under conditions similar to those in the factory, the extraction being effected as rapidly as possible in order to avoid the formation of soluble substances from hemicelluloses, pectin, and the like.August, 19501 OF FRESH AND DRIED SUGAR BEETS 41 1 This marc, or insoluble cellular matter, is sometimes assumed to be present in a constant amount, 5.0 or 4.75 per cent., but this cannot be true, because the proportion of cellular matter varies considerably with climatic conditions, the age of the plant and the soil fertility.Claassen’s definition must therefore be regarded as empirical, and the marc cannot be regarded as the water-insoluble portion of the beet without further definition of how it is determined. The particle size of the beet pulp, the length and mode of treatment and in particular the quantity and temperature of the water used for extraction influence the result considerably. The temperature must be at least 60” C. to destroy protoplasm. The proportion of marc present in the sugar beet is important on account of the volume error caused by the presence of this insoluble matter in determinations of sugar in the beet by digestion methods.The corrections generally accepted are those of Rapp and Degener2 who assumed 4.8 per cent. as the average dry marc content of the beet, and 2.0 as the density of the marc, which gives a correction of 0-6 ml. per normal weight (26 g.). HeintzS found that dried sugar beet marc would absorb water from sugar solutions, and ScheibleI.4 later showed the presence of colloidal water in beet marc. He found an average of 2 4 ml. for the hydrated marc per normal weight of beet, this is much higher than the volume occupied by the dry marc. The principal corrections that have been proposed for the marc volume per normal weight of beet are shown in Table I. TABLE I Authority Stammer, K. .. .. Rapp, G., and Degener, P. . . Pellet, H. . ... .. Fribourg, C. . . .. .. Claassen, H. . . .. .. Sidersky, D. . . .. .. Spengler, O., and Brendel, C. Stan&k, V., and VondrAk, J . Muller, E., and Pucherna, J. Kopeckfr, 0. .. .. Spengler, O., and Paar, W. Bachler, F. R. . . .. Osborn, S. J. . . .. Spengler, O., Paar, W., and StanGk, V., and Pavlas, P. . . Muck, E. Carolan. R. J. . . .. Reference 2. ver. deut. Zucker-Ind., 1882,32, 634 Ibid., 1882, 32, 786 . . .. .. Ibid., 1906, 56, 903 . . . . .. “Analyse chimique,” Paris, 1907 . . 2. ver. deut. Zucker-Ind., 1916, 66, 359 “Manuel du chimiste de Sucrerie,” 2. vey. deut. Zucker-Ind., 1926,76, 880 Paris, 1909, p. 241 2. Zuckerind. Cechoslov., 1926-27, 51, Ibid., 1929-30, 54, 99 . . .. 2. ver. deut. Zucker-Ind., 1931, 81, 447 Ibid., 1933, 83, 342 . . . . ..101, 115 Facts about Sugar, 1934, 29, 191 . . Ind. Eng. Chem., Anal. Ed., 1934,6, 37 2. ver. deut. Zucker-Ind., 1937, 87, 594 2. Zuckerind. Cechoslov., 1937-38, 62, 357, 365 Int. Sugav J., 1944, 46, 179 . . .. Correction per normal weight, 0.6 0.80 0-75 - - 1.35 2.42 1.54 1.7 1.30 0-83 2.31 1.00 2.1 1.06 - Remarks Original method 4.8% of dry marc; density 2.0 Improved method of estimation 3.0 to 4.5% of dry marc, Av. 3.5 yo ; density 1.13 In presence of lead acetate In presence of lead acetate In presence of lead acetate Confirms work of Spengler, Paar and Muck (1937) METHODS OF ESTIMATING MARC IN SUGAR BEET- Stammer’s method-The finely divided sample (20 g.) is digested in a beaker with 300 to 400 ml. of cold water for 30 minutes. The liquid is sucked off and digestion and filtration continued until the filtrate is free from sucrose (by a-naphthol test).The residue is treated with boiling distilled water, collected on a dry weighed filter-paper; and washed with alcohol and ether. I t is dried first at low temperature and then at 100” to 110” C. to constant weight. The final residue is ignited and the ash weight deducted from the first weight. The difference, multiplied by five, gives the percentage of dry marc. CZaassen’s method-The ground pulp (25 g.) is placed in a beaker marked at 400 ml. and boiling water poured in up to the mark. After 2 minutes digestion the pulp is rapidly filtered on a Buchner funnel and returned to the beaker. The extraction is repeated three times, and the marc collected on a tared filter-paper, washed with a few ml.of alcohol and dried for 6 to 8 hours at 105” to 110” C. The calculation to percentage of dry marc is made as in Stammer’s method, but by multiplying by 4 instead of 5 .412 MITCHELL: THE DETERMINATION OF THE MARC CONTENT [Vol. 74 The amount of marc found by these methods depends primarily upon the temperature of digestion. During exhaustive hot water extraction certain normally insoluble pectins are known to undergo hydrolysis and pass into solution; other constituents may behave similarly. EXPERIMENTAL The data following were obtained in a study of sugar beets grown in Oxfordshire and Buckinghamshire and of fresh and dried cossettes prepared from them. Estimation of the specific gravity of dried beet cossettes and of the marc from them-A composite sample of dried cossettes taken over a 3 months' drying campaign was found to contain 7.5 per cent.of water and 64.4 per cent. of sugar by polarisation. The specific gravity was determined by weighing 5 g. of the fine cossette "flour" in light petroleum of sp.gr. 0.79216 at 20" C. The average of six tests gave 1.4300 at 20" C. Dried marc-A similar method applied to dried marc gave specific gravity 1.19012 as the average of six determinations. The specific gravity of sucrose at 20" C. is 1.5877. Check on specific gravity from the composition of dried beets-Assuming 64.4 per cent. of sucrose at sp.gr. 16877 and 7.5 per cent. of water in the dried cossettes, there would remain 28.1 per cent. of marc and soluble non-sugars which can be assumed to have a specific gravity of 1.19.On this basis- 64.4 at 1-5877/100 = 1.022 28.1 at 1-19/100 7.5 at 1.00/100 Total Weight 9er cubic foot of dried beet cossettes widely in weight per cubic foot according to Dried cossettes : 0.334 0.075 .. . . 1.431 - - - and of fresh beets-Loose dried cossettes vary how the slices are packed. Lb. per cu. ft. Cu. ft. per ton Composite sample over 7 days . . 14.9 150.8 Average from storage bins (3-months Stan6k and Sanderas .. .. 25.0 Fresh beet cossettes . . .. .. 26-2 composite sample). . .. .. 19.0 Fresh beets : 120.0 89.6 85.5 Washed beets (Claassen) . . .. 34-37 60-66 Direct estimation of marc in dried beet cossettes-The sample of dried cossettes was ground in an impact mill to a fine flour passing an 80-mesh sieve. A weighed amount was treated in a beaker with water at 50" C.using 100 ml. of water per 5 g. of sample. Digestion was continued for 5 minutes, and the pulp rapidly filtered off on a Buchner funnel. The pulp was returned to the beaker and the process repeated thrice. After the fourth digestion the marc was collected on a tared filter-paper and washed with water at 50" C. until there was no reaction with the a-naphthol test. - A final washing was given with The residue was dried at 105" C. for 6 hours and weighed; it was then No. 1 2 3 4 5 6 7 Cossettes weighed, g. 3 3 4 4 4 2 20 Average . . TABLE Marc, % 20.83 21.20 21.30 21.48 21-73 19.60 20.61 20.96 - I1 Ash, 2-07 2.43 2.43 2.40 2.60 2.60 2.50 2.43 % - a few ml. of alcohol. ashed and re-weighed. Ash-free marc, % 18.76 18.77 18.87 19.08 19.13 17-00 18.11 18.53 These beets were selected from a week's average delivery in early October at the beginning of a crop.August, 19501 OF FRESH AND DRIED SUGAR BEETS 413 TABLE I11 Method as for Table 11, but using proportions of a Cossettes No.weighed, g. 1 6.6 2 6.5 3 13.0 4 13.0 5 26.0 6 26.0 Marc, % 23.37 24-54 24.80 24-75 23-38 24-30 Ash, 2.59 2.7 1 2-46 2-63 2-55 2.42 % Ash-free marc, % 20.78 21.83 22-34 22.12 20.83 2 1-88 normal weight Correction per Volume normal weight occupied, of fresh beets, ml. ml. 1.16 1.16 2-43 1-22 4.67 1.17 In Table I11 the volume occupied by the dry ash-free marc was obtained by dividing the weight of marc found with each proportion taken originally by the specific gravity of the marc (taken as 1-19>. The correction per normal weight of fresh beets assumes a drying factor of 4.0 for dried cossettes, Le., 1 part of dried cossettes is equivalent to 4 parts of fresh beets.The beets used in this test were an average sample from a week's delivery in mid- December. Indirect estimation of marc volume error-About 50 g. of dried cossettes were continuously extracted with cold water for 9 hours until free from sugar (as shown by a-naphthol test). The resultant pulp was dried for 6 hours at 105" C. Various amounts of this dry marc were weighed into dry 100-ml. flasks which were then filled to the mark with a sucrose solution containing 96 g. per litre. Air was removed from the solutions before completing to volume. The solutions were filtered and read in a saccharimeter.The results are shown in Table IV. TABLE IV NO. 1 2 3 4 6 6 7 8 9 10 Dry pulp taken, g. 0 0.5 1.0 2.0 3.0 4.0 5-0 6.0 7.0 8.0 Polarisation reading, % 36.9 37.2 37.3 37-5 37.8 38.6 38.8 39.3 39.9 38.2 Polarisation reading calculated, 36.9 37.1 37.2 37.6 37-8 38.2 38.6 38.9 39.2 39.6 % Difference per g. of marc - 0.60 0.40 0.30 0-30 0.33 0.34 0.32 0.34 0.38 Their precision is limited by the accuracy possible in reading the saccharimeter. The calculated figures were obtained by using the specific gravity of 1.19 for the dried marc. The average difference per gram of marc, omitting No. 2, is 0.34. Average figures for the marc content of fresh beets and dried cossettes derived from them are given in Table V. The fresh beets were treated by Claassen's method, and the dried cossettes by the method used for Tables I1 and 111.An extraction temperature of 50" C. is permissible with dried cossettes because the protoplasm is no longer active. TABLE V AVERAGE MARC CONTENT OF BEETS Fresh beets Dried cossettes Number of samples . . .. .. 15 Minimum 99 99 .. . . 4.00 Maximum 99 99 .. . . 5.40 Average water content, % . . . . 78.00 Average percentage of marc . . .. 4434 20 22.45 19.60 26-70 7-50 The average percentage of marc in the fresh beets, calculated to a dry basis, becomes The latter value Owing to the difficulty of comparing 22-00, and calculated to 7.5 per cent. of water, becomes 20.35 per cent. is 2.1 per cent. below the percentage of marc found.414 JACKSON: A NEW METHOD FOR THE DETERMINATXON OF SODIUM [Vd. 75 fresh and dried samples, and to the limited accuracy of the method it is not possible to attach much importance to this difference; it may point to coagulation rendering insoluble certain constituents of the beet during t.he drying process. REFERENCES 1. 2. 3. 4. 5. Claassen, H., 2. ver. deut. Zucker-Ind., 1916, 66, 359. Rapp, G., and Degener, P., Ibid., 1882, 32, 786. Heintz, A., 2. anal. Chem., 1874, 13, 262. Schiebler, C., Ibid., 1879, 18, 176, 256. Stanek, V., and Sandera, K., Z . Zuckerind. Cechoslov., 1929, 525; Int. Sugar J., 1929, 31, 501. DEPARTMENT OF TECHNICAL CHEMISTRY THE ROYAL TECHNICAL COLLEGE GLASGOW September, 1949