October 15, 1932
/
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
ACRKOWLEDGMENT The authors wish to express their gratitude to J, M. Gailles, Jr*, Of the Research Laboratory Of Chemistry of the Massachusetts Institute of Technology, for photographs of the spectrum.
373
LITERATURE CITED (1) Edwards, J. D., Bur. Standards, Tech. P a m 89. (2) Edwards, J. D., Ibid., Tech. Paper 94. ( 8 ) Weaver, E. R., Palmer, P. E., Ledig, P. G . , Pickering, S. F., and Frantz, 3. W , J. IKD.E m CHEM.,12, 359-66 (1920). RECBIVED April 2, 1932.
Determination of Hydrophyllic Colloid Content of Cane Juice E. A. FIEGER AND A. R. CHOPPIN,Louisiana S t a t e University, Baton Rouge, La. HE ability of certain plants to resist droughts and others to resist low or freezing temperatures has long interested scientific observers. Gortner ( 1 ) and Newton (4) and later Newton and his co-workers (5) explain the resistance of plants to the desiccating effect of drought or low temperatures as due to their ability to hold water in a "bound" condition by means of hydrophyllic colloids which the resistant plants or varieties have elaborated. They believe the hydrophyllic colloids in Xerophytic plants prevent excessive moisture losses during severe desiccation such as is induced by periods of drought. Likewise, in the case of winter hardy plants, which are not killed by temperatures considerably below 0' C., these colloids prevent streaming of water from the interior of the cells to the intercellular spaces where it may form ice crystals and injure the plant. It has been previously shown that the type of material of which these colloids are composed is probably polysaccharides, such as pentosans in the case of drought-resistant plants, and protoplasmic proteins in the case of frost-resistant plants, However, since both of these classes of substance may act as hydrophyllic colloids, we may use the same mechanism for measuring both these phenomena. Any method, then, which will measure either the amount of hydrophyllic colloids in the plant or the amount of water bound by these colloids will be of value in increasing our knowledge of the physical conditions of the constituents of the plant sap. This knowledge may be of value also as a means of distinguishing those varieties of canes which are the most resistant to low temperature. Also, any increase in our knowledge of the conditions of the colloids in cane juice may be of value in sugarhouse practice. With these objectives in view, investigations were undertaken in the fall of 1930 in an attempt to determine the cold resistance of the various new varieties of sugar canes which have been introduced into Louisiana within the past few years. In 1922 Newton and Gortner (4) proposed a method for determining the per cent of bound water in plant juice, which is based upon the observation that the depression of the freezing point of a plant juice, upon the addition of sufficient sucrose to make a molal solution of it in the total water present in the juice, is greater than the theoretical amount which should be obtained. This excess depression they explain on the assumption that all the water in the juice is not free to dissolve the sucrose, and therefore the actual concentration is somewhat greater than the apparent molal concentration. The assumption is also made, based upon Scatchard's (6) work, that sucrose in molal concentration forms the hexahydrate. If sucrose hexahydrate is formed in solution, then we will have one mole of sucrose hexahydrate dissolved in 1000 - (18 X 6) or 892 grams of water, which gives a depression of 2.085' C. instead of the value 1.86' C. I n their original paper, Newton and Gortner use
the following formula for calculating the grams of bound water:
where dT1 = freezing point depression of freshly expressed juice dT0 = freezing point depression of juice after addition of sucrose Km = 2.085' C. on basis that sucrose forms hexahydrate In a later publication Newton and co-workers (5) have modified this formula by changing the value of Km from 2.085' C. to the value experimentally obtained by determining the freezing point of a molal solution of the sucrose in distilled water. This change was found necessary because the various lots of sucrose used gave values for molal solutions somewhat higher than this theoretical value of 2.085' C. I n applying the method of Newton and Gortner to cane juices, several correction factors must be introduced. By determining the freezing points of sucrose solutions of varying concentrations, the increments of increase of the freezing point with increasing amounts of sucrose in solution are not constant. This is brought out in Table I. TABLEI. FREEZING POINTS OF SUCROSE SOLUTIONS SUCCESSIVE ADDITIONS OF SUCROSE
SUCROSE ADDED Mole
TO
Av. INCREASE IN FREEZINQ POINT DEJPRESSION DUE 0.25-MOLE SUCROSE
c.
1 Rt,
n.2R
0.546
2nd 3rd 4th 5th 6th 7th 8th
0.25
0.533 0.533 0.543
0.25 0.25 0.26 0.25 0.25
0.25
0.555 0.562
0.572 0.583
Accordingly the depression of the freezing point of sucrose solutions has been plotted against concentration, as shown in Figure 1. Then by knowing the sucrose content of the cane juice, by use of the graph, the depression of the freezing point due to the sucrose present in the juice can be obtained. Likewise the depression of the freezing point can be determined for the total amount of sucrose after the addition of a moIe of sucrose. By this means then, errors due to the fact that the freezing point depressions of sucrose solutions are not directly proportional to concentration can be eliminated. By the use of this method it will be noted that the freezing point of the original juice has been divided into two factors: that due to the sucrose present, and that due to the nonsucrose solutes. A second correction must be introduced as pointed out by Moran and Smith (3) and applied by Grollman (2), and one which Newton and Gortner failed to take into consideration. However, the correction of Grollman-i. e., multiplying dT1 by 1000/892-cannot be applied successfully to juices
ANALYTICAL EDITION
3 74
which are high in sucrose, such as cane juice, or even some samples of winter wheats which may contain as high as 6 per cent sucrose. As mentioned previously, the abnormally high depressions of the freezing points of sucrose solutions are explained on the basis that the sucrose is hydrated. This means, then, that sucrose is removing water from solution. I n a cane juice, which contains solutes other than sucrose, the addition of sucrose to the juice will cause the nonsucrose solutes to be dissolved in an amount of water different from that in which they were dissolved in the original juice. Since the
Vol. 4, No. 4
experimental mill. The brix, sucrose content, freezing point depression of the original juice and the juice plus a definite amount of sucrose were determined on each sample. The freezing point determinations were made using the Beckman set-up, the usual precautions being observed. The samples were collected beginning October 27 to December 12. TABLE11. AVERAGEVALUESOF BOUND WATER
--
Av. BOUNDWATER SUCROSZFormula 1 Formula 2 Sucrose
CAN^
P.0.J. P.O.J P.0.J. (7.0. P. 0.J. C. P.
Total
% 38 36M 213 281 234 807
8.79 10.20 10.10 17.00 11.60 12.00
38.3 48.8 42.0 50.2 46.6 46.3
12.7 14.0 10.0 16.4 11.6 12.0
143 125 133 121 126 127
166.7 139.0 143.0 136.4 136.6 139.0
Since the values of bound water for a given variety of cane varied rather widely for samples collected during the season, the average values have been tabulated and are shown in Table 11. There is no apparent correlation between bound water content and the ability of the various varieties to withstand frosts or freezing temperature as calculated by this method (Formula 2). Since Newton and Gortner have shown a correlation between winter hardiness and bound water for wheat plants, their formula (Formula 1) was applied to the data without again showing any correlation. low
Freezing Pomt Depr~ssion
FIGURE 1. DEPRESSION OF FREEZING POINTOF SUCROSE SOLUTIONS vs. CONCENTRATION degree of hydration of sucrose varies with the concentration, a graphical method was also used in making this correction for changes in the amount of solvent water. Figure 2 was obtained by plotting depressions of the freezing point of sucrose solution against amount of solvent water, which can be readily calculated by using the formula: 1.86 X 1000 X M Solvent water = dTM
molal concentration of sucrose d T M = depression of freezing point of sucrose solution of M concentration
where M
=
The depression of the freezing point due to the nonsucrose solutes can now be corrected for changes in the amount of solvent water caused by the addition of sucrose to the cane juice. This can be calculated as follows: dTz (dTi - dT4) X Wi/Wz where dTz = depression of freezing point of non-sucrose solutes corrected for sucrose change in solvent water dTl = depression of freezing point of original juice dTa = depression of freezing point due to sucrose in original juice VI = amount of solvent water in original juice W 2 = amount of solvent water after addition of one mole of sucrose to juice
The formula for calculating bound water then becomes:
+
(dTz dTs) Grams bound water = dTo (2) dTo - dT1 where dTo = freezing point depression after addition of sucrose dTl = freezing point depression of juice dTz = freezing point depression of nonsucrose solutes corrected for change in solvent water dTa = freezing point depression due to total sucrose present after addition of one mole of sucrose W Z = grams free water in juice after addition of sucrose
wz
The experimental determinations were carried out on samples of juice obtained from the various new varieties of canes which have been introduced into Louisiana. The juice was expressed from representative samples by means of an
6001
I
f
I
2
I
3
I
4
Freezing Point Depression
I
5
I
FIGURE 2. DEPRESSION OF FREEZING POINT. OF SUCROSE SOLUTIONS vs. AMOUNT OF SOLVENT WATER The amount of water of hydration of the sucrose in the original juice is also included in the table. The amount of water held by the sucrose is tremendously greater than that held by the colloids. I n the last column is tabulated the total bound water content. Although these values are in the approximate order of hardiness of the cane varieties toward frost, there is not sufficient difference between them to be significant. It appears as a logical explanation, then, that the production of sucrose by plants as cold weather approaches is an extremely effective means of protection. For the cane plant, a t least, we need not postulate the production of colloids, since the production of sucrose is equally as effective if not more so. This is borne out by the rapid increase in sucrose content and purity with the advent of low temperatures in the fall. LITERATURE CITED (1) Gortner, R. A., “Outlines of Biochemistry,” Wiley, 1929. (2) Grollman, A., J. Gen. Physiol., 14, 681-83 (1931). (3) Moran, T., and Smith, E. C., Trans. Faraday Soc., 26, 695 (1930). (4) Newton, R., and Gortner, R. A., Botan. Gar., 74, 442-6 (1922). (5) Newton, R., and Martin, W. M., Can. J. Res., 3, 3 3 6 4 2 7 (1930). (6) Scatchard, G., J. Am. Chena. Soc., 43, 2406-18 (1922). RECEIVED April 6, 1932. Presented before the Division of Sugar Chemistry at the S3rd Meeting of the American Chemioal Society, New Orleans, La., March 28 to April 1, 1932.
