I N D U S T R I A L A N D ENGINEERING CHEMISTRY
1138
recorded for the pure esters. The identification was completed by saponifying the ethyl esters and converting the acid thus obtained to the solid p-bromophenacyl ester and determining the melting point of the solid derivative (1). Mixed melting points were also taken with known p-bromophenacyl esters. The results are collected in Tables I1 and 111. T a b l e 11-Comparison of Physical Properties of E t h y l Esters from F a t t y Acids of Filter-Press C a k e w i t h Known E t h y l Esters B. P. ETHYL B. P. FRACAT 4-6 ESTER AT 5 n? MM.“ d TION MM. d: OF ACID
c.
c. 1 5 7 9 11
71-73 114-117 134-138 156-160 178-185
0,83528 1.4201 Caprylic 1.4332 Capric 1.4402 Lauric 1.4441 Myristic 1.4451 Palmitic
0.84328 0.85425 0. S4?25 0.827*5
89-92 108-108 128-132 152-166 175-180
0.87817b 1 . 4 1 8 2 ~ 0.862d 1,4238~ 0.86711Qa 1.4321f 0:6ibS28c
....
VOl. 21:
KO.11
prepared from the corresponding acids by the method of Judefind and Reid (1) and after purification were found to melt at the temperatures recorded in Table 111. These.esters were analyzed for bromine by the Parr bomb method: p-Bromophenacyl laurate. Calcd., 20.14; found, 20.07. p-Bromophenacyl myristate. Calcd., 18.80; found, 19.05 The lauric acid ester was more granular in appearance than the other esters. T a b l e 111-Melting UXKNOWK
FRACTIOKESTER
c.
J
P o i n t s of p - B r o m o p h e n a c y l Esters ~BROMOPHENACYL ESTEROF: hfIXED
c.
c.
66.0 59.0 77.0
68.0
1.4347 at34.3’
80.0
c.g
Obtained b y distilling esters that were available from fractionation of ethyl esters of coconut oil acids. b Cahours and Demarcay, Bull. soc. chim., [ 2 ] 34,. 482 (1850). c Determined on esters obtained from fractionation of ethyl esters of coconut oil acids. d Rowney, A n n , 79, 243 (1851). E Delffs Ibid. 92, 278 (1854). f Interdational Critical Tables, Vol. I, p. 255, McGraw-Hill Book Co., New York, 1926. o Ibid., Vol. I, p . 264.
The intermediate fractions are mixtures of those esters which were not completely separated by the distillations. This was not determined definitely except in the case of Fraction 3, which was shown to be a mixture of ethyl caprylate and ethyl caprate.
The p-bromophenacyl esters of lauric and myristic acids have apparently not been previously described. They were
(1) Judefind and Reid, J . Am. Chem. Soc., 42, 1048 (1920). (2) Verbeek. Seifensieder-Zlg.,48, 202 (1921); C. A . , 16, 2738 (1921).
a
Literature Cited
Factors Affecting Color in Sorghum Sirup’s’ J. J. Willaman3 and S . S . Easter‘ DIVISIONOF AGRICULTURAL BIOCHEMISTRY, UNIVERSITY OF hfINNESOTA, UNIVERSITY FARM, ST. PAUL, MI“.
Previous Work The main factors in quality in sorghum sirup are color and flavor. The color m u s t be a fairly light amsorghum sirups is Anderson ( I ) , in studying ber. The flavor m u s t be mild, b u t still characteristic s i m i l a r t o t h a t of the chemical changes caused of sorghum. Since t h e annual production of sorghum making cane sirup. It conby the clarification of sorsirup in t h e United States is about thirty million gals i s t s essentially in pressing ghum juice, noted the color lons; since a continually greater proportion of this is the juice from the stalks, of the sirup produced; but, being made on a large industrial scale where techclarifying with heat, filtering not having any color standnical control is available, rather t h a n on the farm; or settling, and evaporating ards, he could only compare and since very little information exists about t h e conto a sirup. Refinements in, h i s s a m p l e s among themtrol of color and flavor in the manufacture of the sirup, and control of, this process selves. He concluded that t h e present work was undertaken. are possible only in the larger the amount of color in the The Pfund color grader has been found to be adf a c t o r i e s e q u i p p e d with sirup varies directly with the mirably adapted for use in this industry. Reference laboratories. Under t h e s e amount of lime used and with (1) t h e tables and curves are presented herewith for conditions the control of the the time required for evapocalibration of this instrument against a spectrophoacidity and density of the ration. (2) t h e relation between color and density in tometer; sirup, the use of decolorizing Zerban and Freeland (9) sorghum sirup; (3) t h e relation between pH and dencarbons, the development of summarize the coloring matsity; and (4) t h e relation between pH and color. Frucsuperior strains of the plant, ter of sugar cane juice as tose has been found to be by far t h e most important the elimination of waste, and folloTs: is subjected to source of color when sorghum juice the utilization of by-products (1) Chlorophyll. This is of heat. Deductions are made concerning the control are possible and are being aclittle importance as it is not of color in the manufacturing process. complished ( 5 ) . soluble and is removed with the scums. The following is a contri(2) Anthocyanins. These are present in the rhd, are soluble bution to the control of color in the sirup. It deals largely cane juice, and are precipitated by large quantities of lime but with three phases of the question: (1) the measurement of in incompletely by small quantities. color in the juice and sirup; (2) the relation of the natural (3) Saccharetin. This is present as the “incrustating” pigments of the juice to pH; and (3) the production of color coloring matter of the cane pith. It is insoluble in acid solutions, but is soluble with a yellow color in alkaline solutions. from the sugars in relation to p H and to temperature.
HE process of making
T
-
Received June 18, 1929. Presented before the Division of Sugar Chemistry a t the 78th Meeting of the American Chemical Society, Minneapolis, Minn., September 9 t o 13, 1929. 2 Published, with the approval of the Director, as Paper 866, Journal Series, Minnesota Agricultural Experiment Station. * Now at New York Agricultural Experiment Station, Geneva, N. Y. 4 Now with Waconia Sorghum Mills Co., South Fort Smith, Ark. 1
The present work was done under a fellowship grant from the company, to which grateful acknowledgment is made. 5 The U. S . Department of Agriculture restricts the term “sorghum” to the grain varieties of Andropogon sorghum, and calls the saccharin varieties “sorgos.” The sorghum sirups described in the present paper were, of course, made from the saccharin types, but the older term is retained here because i t is the only one used in the industry.
November, 1929
I N D USTRIA.L A N D ENGINEERING CHEMISTRY
1139
taken. Between readings the electrodes were laid so that the gold bead of the electrode was covered by the diluted sirup. The Type K potentiometer was used in these determinations. The electrodes were washed with distilled water after the readli' ing a t 9 hours and the citrate buffer was determined to see if the electrodes were affected by the long contact with the sugar solution. At the end of 9 hours of continual contact with the diluted sirup, the 9 greatest difference between electrodes was -c 0.05 pH. This error was not great enough = to be considered in this work. These results gave confidence in the Bailey elecz6 trode and it was used for all hydrogen-ion determinations. It might be of interest to note that the Waconia Sorghum Mills have used this electrode for two seasons in their 3 factory control. RIATERIALS; POL-4RIZlTION AND INVERSION-The sorghum sirup used for the majority of the experiments was a highgrade, mild-flavored sample from the 1927 0 IJ u) OJ 109 ci concenlration "Pn degree3 Brix season. I t s color was 13.1, Brix 80°, ash F i g u r e 1-Relation between Color a n d C o n c e n t r a t i o n in Sorghum S i r u p 3.7 per cent, and sucrose 46 per cent. The other sorghum sirups used will be described (4) Color Produced b sugars at high temperature:. Fructose later. The sucrose was high-grade cane sugar. The glucose darkens most readily, glucose next, and sucrose least. In slightly was a light b r o m , crystalline, technical preparation. The acid solutions they do not form so readily as in neutral solutions. ( 5 ) Glucosates of alkalies and alkaline earths. These are invert sugar was prepared from the sucrose in the laboratory formed when reducing sugars are brought into contact with lime as follows: 1500 grams of sucrose were dissolved in 1500 cc. or similar alkaline substances and heated, are dark brown and of distilled arater. The solution was heated on a steam even almost black. bath and 10 cc. of concentrated phosphoric acid were added. (6) Iron salts of tannin and other fiolyphenols Iron is taken up from the machinery and reacts with soluble polyphenolic The heating was continued until the solution was 91.5 per cent substances in the juice, inverted according to Willaman's method of following inversion (6). They conclude that the chlorophyll and saccharfitin do not M e a s u r e m e n t of Color add any appreciable color because they are not soluble, and the glucosates have little opportunity to form because Until recently the most commonly used method of evaluatthe juice is slightly acid. Thus the main sources of color are the unprecipitated anthocyanins, the products formed ing the color of sirups was by means of the arbitrary set of standards described Wiley (7)* They are exby high temperatures on the sugars, and the effect of the polyphenols, mainly in connection with iron. Sorghum cane and sugar cane are so similar that it is reasonable to expect to find the same groups of coloring matter in one as in the other. Glucose and fructose are much more abundant in sorghum, and hence would be a more prolific source of their colored degradation products. I5
v1
L
9
YI
Methods
MEASUREMENT OF PH-The hydrogen-ion concentration was determined in large Bailey hydrogen elect1odes after having been shaken for a t least 3 minutes. This method was chosen as the work would cover a greater range of pH than the quinhydrone electrode would cover. The antimony electrode was found to be affected by the sugars so that it was not dependable. A Leeds and Northrup portable potentiometer and a normal potassium chloride calomel half-cell were used. Before accepting the Bailey hydrogen electrode] an experiment was carried out to show the truth or fallacy of the generally supposed idea that a hydrogen electrode will "poison" quickly in sugar solutions and require very frequent replatinizing. Five electrodes were used to find the effect of continued contact with a diluted sirup a t 17" Brix. The same supply of diluted sirup was used each time, and before each determination the electrode was refilled, hydrogen added, the shaking continued for 5 minutes, and the p H
Figure 2-Color
P r o d u c t i o n in Sorghum Sirup d u r i n g Evaporation
tremely unsatisfactory, since it is very difficult to make two sets alike and they fade rapidly. Furthermore, they can hardly be used with cloudy sirups. Recently the Pfund color grader was developed for honey. It has been found to be admirably adapted for use on sorghum sirup and molasses, especially when equipped with the modified scale for very dark samples (8). The instrument consists essentially of an amber-colored glass wedge and a hollow colorless glass wedge to contain the sample of sirup. The two wedges, one above the other, move in opposite directions in front of windows in the frame, through which the intensity of the color of the unknown may be matched
11-10
1-01. 21, No. 11
KO reference cell was used. Readings were taken from 460 to 680 mp, a t 20-mp intervals. At each point six readings were taken and averaged. The averaged readings were plotted and hmooth curves drawn among the points. The values in Table I were taken from the curves, and may be regarded as a reference table for the calibration of other wedges. At least it will be so regarded by the writers, since it is very desirable that any future wedges used by them read the same a5 the original. Table I-Reference Table for Calibration of Colored Wedge of H u n d Color Grader against Keuffel and Esser Spectrophotometer (I'alues are in terms of transmissivity) WAVE
LENGTH
2 5
SCALE R E A D I N G O N COLORIMETER 5 0 7 3 10 0
31.0 38.7 4 7 , .5 56.0 62.8 68.5 73.1 76.5 78.7 80.5 82.2 83.8
Figure 3-Relation
20.5 27.1 35.6 46.4
12.4 18.5 27.0 36.9
62.8 68.3 72.7 75.8 78.0 79.9 81.8
67.8 71.8 74.9 77.4 i0.6
0.3 5.8 13.2 22.3 32.4 42.5 51.4 58.1 63.3 67.6 71.4 74.8
5.9
11.9
;;:: 62.2
g5.9
12 5
19.8 29.7 39.8
49.3 .)I . O 62.9 67.3 71.8 73.9 76,9
between pH a n d Concentration i n Sorghum Sirup
ngaimt the standard wedge. The color uiiita are iii teriw of a centimeter scale, reading froiii 0 to 11. The instrument covers a wide range of color from a1nio.t mater white (zero on the scale does not correspond with complete lack of color in the wedge) to the color of a dark molasses. For a group of observers the accuracy has berii found to be 1 0 . 1 color unit a t the dark end and '10.2 at the light end. Practically all sirups arid juices so far encountered, including sonie rather cloudy ones, have berii easily evaluated. Standardization of Color Grader
i3iiicc one of the priiiie advantages of the l'fund color grader is the permanelicy of the colored wedge, and since this wedge is fixed in position in the instrument in relation to an arbitrary scale, it was considered desirable to calibrate the instrument against fundamental units. A Keuffel and Eqqer spectrophotometer was wed for this purpose.
7.L 0
0
F t 6
L
4
0
6
l i m t 01 h e o l i n q in hour3
Figure 5-Effect
0
6-4
$4 J.(1
D
of Heating o n Color Production i n 1.5' Brix Sorghum a t Various pH's
Relation between Color and Concentration
Figure 4-Relation between pH a n d Color i n Sorghum Sirup
R i t h the wedge in position in the instrument, pieces of paper were pasted on the wedge in such a way as to leave an open slit a t positions 2.5, 5.0, 7.5, 10.0, and 12.5 on the scale. The wedge was then removed, cleaned carefully. and then mounted in the spectrophotometer so that the upper beam of light mould pass through one of the slits.
I n order to tell whether color wa5 being produced in the mill processes, it was necessary t o know just how much color would be produced by concentration alone. Obviously. if there is color present in the juice, the intensity of thii color will increase with evaporation. In order to deal only with the effect of concentration, and not with the procev of evaporation, finished sirups were diluted in steps and the color and density taken a t each step. A wide range of quality in the sirups was desired, so the following were chosen: No. 1 was a dark sirup, diluted in the laboratory, treated with carbon, and reevaporated to a 'irup. It waq
Soveinber, 1929
I.VDUSTRIAL dIVD EAYGISEERISGCHE,l!ISTRY
light in color but with a sharp flavor. S o . 2 was a mild, \cry high-grade sirup from the 1925 crop, slightly darker than No. 1. hut with a much inore desirable flaxor. KO. 3 was a sample of 1926 sirup, dark and with a very poor flavor. I t had been treated with carbon in the factory procesb.. Yo. 4 WAS the rpitonie of poor sorglimii sirup. being very dark, gummyq and with a very poor flavor. It was made from frozen can?. S o . 5 , from the 1928 crop. ~ i B the s lightest and best flavored. The logarithms of the sirup densitiey (in degrees Brix) were plotted against the coloi values of these five sirups, and the results are shown in Figure I . Straight lines among the points of a given sirup seeiiied to be justified. These lines were practically parallei. The significance of the parallel log curves is that each >imp on dilution gives the same shaped color-density curve and that the curves are separated by the same difference in color throughout the range of concentrations. In other words, if two saiiiples of sirup show a difference of two color units a t 80" Brix, they will show the same color difference :it 10" Brix. The cotangents of the angles formed by these lines with the base line were calculated by dividing the log of the concentration by the color units. This w m done in order to havc a single value for each curTe. These value5 were averaged, giving a cotangent of 0.1171 as the al-erage For the five s i r u p . .In angle with cotangent 0.1171 mas drawn through the origin, as shown in the chart. This angle or line then represents the average relation between log of concentration mid color among these five sirups, and hence, presumably, among all sirups. The color of the theoretical sirup represented by this curve was calculated :it various concentrations by the formula: Log of concentration Cotangent 0 1171
=
This curve represents a sirup with a color of 16.2 a t 80' Brix. Since the density-color curves of all sirups are parallel. from this one curve the color was calculated for a series ot w u p s representing the whole range of color of sorghum >irups, and for all concentrations of these sirups. Thcae yalues are given in Table 11. This may be regarded as :i reference table for predicting the iioriiial increase in color of any sorghum sirup due to concentration alone. I11 applying it, the Brix and color of the initial juice are meaiured and from the table is read the expected color of the sirup a t 80" Brix. The difference between the predicted and tlit. actual color of the finished sirup represents the amount of color produced during the manufacturing process. Thih table should hold for any sorghum Firups encountered, for the range of color covered is from 7.0 to 17.0. It appearb in the table that a sirup of color 7.0 would be developed from n juice without color a t a Brix of 12.0. This, of course, anomalous. The explanation is that the color is too light to be read on the Pfuncl color grader, since the latter doc. indicate sonie color even a t zero on tlic scale. IC
Table 11-Reference ' B R I X ---------COLOR
Table for Predicting Color of Sorghum Sirup Various Concentrations I N DIJGRGES Prr VD------
color units
because thi. curve was derived from the formula Log of concentration Color units
=
cotangent
Figure 6-Change
1141
i n pH of Sorghum Juice during Heating
dt
1142
I N D U S T R I A L A N D ENGINEERING CHEMISTRY Color Production during Evaporation
Figure 2 represents an experiment to determine the actual color production in sorghum sirup during evaporation. It was carried out in the season of 1927 in a sorghum mill with vacuum evaporators. The juice samples were taken at intervals during evaporation, and Brix and color measured. The points on the curve represent the samples taken. The thick upper line is the smoothed actual curve, while the thin lower line is the theoretical color curve due to concentration alone, as obtained from Table 11. These curves show that considerable color is produced in the evaporator. The divergence of the curves indicates color being produced
/
Vol. 21, No. 11
A sample of high-grade sorghum was diluted t o 15" Brix, and the p H and color read. The p H was shifted with sodium hydroxide and phosphoric acid. The color was read a t the various pH's. The results, as plotted in Figure 4, lie in a fairly straight line. The dots and circles represent readings on the same sirup on two different days. A line with an angle of 45 degrees was drawn through these points. There is some evidence of an S-shaped curve shown by the points a t the extreme limits of the range in pH covered. However, the points lie well along the 45-degree angle within the practical range of pH, which is from 5.0 to 7.0. This chart shows that there is a change of one color unit with each change of one pH. The change in color appears to be more of a change in intensity than a change in tint as is the case with indicators used in titrations. The slight change in tint in the sorghum is from a somewhat yellowish tinge in acid solutions to a slight reddish tinge in alkaline solutions. The red tinge may be produced by glucosates. An attempt to isolate or determine the pigments in sorghum has not been attempted. Production of Color at Higher Temperatures
The above experiments were performed a t room temperatures. The effect of pH on color a t high temperatures was next determined. The temperatures decided upon were 60", 80', and 97" C. These cover the critical part of the mill process, for the juice may remain for several hours between boiling and 60" C. The pH's chosen were approximately 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, and 9.5. This range covered more than was needed for the mill practice, but a knowledge of the effect of high pH's appeared desirable. The stock sample of sorghum was diluted to 15' Brix and the pH adjusted nrith phosphoric acid and sodium hydroxide. Six test tubes containing about 50 cc. each were taken for each pH and immersed in a water bath a t a given temperature. Figure 7-Apparent and Calculated Change i n Color of Sorghum Sirup during Heating a t Various pH's
a t all times during the evaporation and the actual curve gives some evidence of auto-acceleration in production of color a t the higher concentations, beginning a t about 65' Brix. The finished sirup had a color of 10.8, while the color predicted from Table I1 should have been only 9.3. The difference of 1.5 is the added color due t o the process of evaporation. This was the first definite eyidence that color is produced in the evaporator. It was to find the cause of this color that this research was continued.
7.221
622 b19
6 9.Pb
Relation between pH and Concentration
Since the p H of sorghum sirup may be measured on occasion a t various concentrations, it was thought desirable to determine the change in pH as a sirup is concentrated or diluted. The results for a single sample are given in Figure 3. The slope of the curve will probably be found to vary with the buffer value of the sirup. This one curve is presented here as a preliminary example, since, so far as the writers are aware, this is the first time such a curve has been published. Relation between pH and Color The addition of acid or alkali to sorghum causes it to become lighter or darker, respectively. This change in color with a change in reaction is, as before mentioned, no doubt due to the anthocyanin pigments present which act as indicators. A knowledge of the amount of change in color per unit change of p H was essential so that samples a t different reactions could be compared or a correction applied when there was a change in pH.
60" 1.56
?e
Y
6.73 514
6
2
*
lrmc
b
d
hearing
in hours
8
0
iz
Figure 8-Effect of Heating on Color Production i n 15' Brix Glucose Solution a t Various pH's
Each test tube was filled to a definite marked volume and that volume maintained. The samples were allowed to stand in the bath 5 minutes before the time was recorded in order for them to reach the temperature of the bath. At the end of each hour a test tube was taken from the bath held a t 97" C. and a t the end of every 2 hours from the bath a t 60" and 80" C. The temperature varied as much as *2" C., but was constant most of the time. As soon as a sample was taken from the bath, it was cooled to 25" C. and the color and pH read. The color increase a t 60" C. was never more than 0.3 color unit, and the figures are not given here. At 97" and 80" C. there was considerable development of color; the results
I
I N D U S T R I A L AA'D ENGINEERING CHEMISTRY
November, 1929
4 -'
I
itme
Figure 9-Change
01 hrdlinq
tn hob?5
of pH i n 15' Brix Glucose Solutions during Heating
1143
of the relation between p R and color shown in Figure 4. A quantitative illustration of this may be of interest, taking, for example, the series of 97" C. The total increase of color in 6 hours a t a pH of 5.1 was 2.7, while a t pH 9.7 the increase was 2.3. If the sugars are oxidized more rapidly in alkaline solutions, the sample a t pH 9.7 should have produced considerably more color than the sample a t 5.1. Accompanying the color change was a decrease in pH of 3.9. According to Figure 2 this is equivalent to a decrease in color of 3.9 units. Therefore, this covert increase should be added to the apparent increase of 2.3, giving an actual increase of 6.2 color units. For practical purposes, of course, the apparent color is the important one. The compensating action of the concomitant decrease in pH is offered as the explanation of the fact that the change in color is apparently independent of the initial pH. These relations are brought out more strikingly in Figure 7. The lon-er line of each pair represents the measured change in color a t each initial pH for the total time of heating (12 hours a t 60" and 80" C. and 6 hours a t 97" C.). The upper line represents the calculated color change, on the basis of 1.0 unit decrease in color for 1.0 unit decrease in pH. This chart emphasizes the following facts: (1) The apparent total color production a t 60" C. is about 0.1 unit; a t 80" C., 0.6 unit; and a t 97" C., 2.6 units. (2) The apparent color produced over the entire heating period is practically independent of the initial pH, as these curves are flat throughout the pH range. (3) When these flat curves are corrected for the color they have lost due to the decreasing pH, we have an entirely different picture of the effect of the initial pH. The divergence of the curves in each pair represents color produced which never becomes apparent. In other words, if a t the end of the heating period each sample was adjusted to its original pH, we would have the upper, instead of the lower, curve. (4) The
are shown in Figure 5 . As would be expected, the highest temperature produced the most color. But the striking fact, and one which was wholly unexpected, is that a t any one temperature the increase in color is independent of the initial pH of the solution, since the curves are parallel. Thus, a t 60" C., the average increase in color was only 0.1 degree; a t 80"C. it is 0.6; a t 97" C. it is 2.7; and these values hold for all pH's from 5.0 to 9.7. Because of the well-known ' action of alkalies on sugars this result appeared a n o m a l o u s . The explanation, however, was found to lie in the change in p H which the solutions underwent during heating. T h i s i s brought out in Figure 6, in which the pH's are plotted against time of heating. The pH begins to decrease immediately; it continues to de- -, crease a t a slackening rate throughout the time A 2 of heating; the decrease is greatest a t the highest temperature and a t the highest pH's, and is -; C practically nil a t pH 5.1. It has been shown by Mathews ( 2 ) and Nef (3) that sugars are readily oxidized to acids in alkaline solutions, but that in acid solutions 71 the reaction is greatly retarded. They show also that fructose is oxidized more readily than 1 glucose. Paine and Balch (4)noted a change in I' p H in sugar cane juice during heating. They conclude that the change depends on the initial pH, the temperature, the period of heating, and the nature of the juice. The writers interpret the above results as , follows: At the higher pH's coloring matter is produced from the sugars. Acids are also produced, and these lower the pH. The lowering of the pH decreases the apparent color, because Figure 10-Effect i
i
6
1'
of Heating on Color Production in a 1 5 O Brix Invert Sirup a t Various pH's
I S D G S T R I d L ALVDE.\'GIL\TEERISG CHE.VI,STRY
1144
reason that the two curves meet a t pH 5.1 is that there is no decrease in p H at this initial reaction. To the sorghum sirup manufacturer this means that hc can adjust the initial pH of the juice to any desired point. and the only color change will be due to the effect of the pH on the indicator pigments, which amount5 to 1.0 unit of color for 1.0 unit of pH.
97
4
time
--
o i heo(ing
0
IO
in hOU1S
1-01, 21,
50.
11
A sample of technical glucose. which was crystalline. light, brown, and non-hygroscopic, was inade up t'o 15" Brix and the pH's adjusted as with the diluted sorghum. The same approximate pH's were used and the same technic in holding at 97", 80": and 60" C. Thc results for color production are given in Figure 8, and for change in pH ill Figure 9. There was a decided change of pH in every case. including pH 5.19 and 4.85. I n this it differed froin sorghum. ivhich did not change pH a t 5.1. This niay be due to thc buffering action of the ash constituents of the sorghum. The color production was small, even at 97" C. As in sorghum, however, the increase in color a t any one temperature was practically independent of t'he pH. Thus a t 97" C. the average increase in B hours was 0.7 unit; a t 80" and a t 60" C. in 12 hours it was 0.3 and 0.1, respectively. It will be noted, by comparing the colors a t various pH's a t zero time, that there is some change in color due to p H alone. :is in the case of sorghum (Figure 4). Hence the above apparent color values could be corrected for the bleaching cffect of the decreasing pH's, as was done in sorghum in Figure 7. The meagerness of the data, however, do not n.iirrant this.
,
Figure 11-Change i n pH of 15O Brix Invert S i r u p a t Various ptl's
Color Production by Various Sugars
It i:, to be as,uincd that the production of colur and of acids in the above experiments mas due to the lmakdown of sugars, in view of the well-known tendency of some wgars to do so in alkaline media ( 2 , 3, 4 ) . I n this caie it is of further iinportance to know the relative contril)iiticm of the various sugars present to the change5 rioted. There are three sugars-sucrose, glucose, and fructo\epresent in sorgh~iinin varying proportions. The biicrosc purity is usually highest a t the beginning of tlic seaion and lowest a t the end of the season, after the cane has been stored for some time. The reducing sugars, of course, appear inversely with the sucrose. ?tIathews ( 2 ) says that fructose is oxidized more rapidly than glucose. Zerbari and Freeland (9) say that fructose is oxidized most rapidly. glucose next, and sucrose least. They fail to say lion. uiuch more rapidly fructose is oxidized than the other sugarq* and they do not say anything about the amount of color pioduced. The next problem mas to show which w g a r wai responsible for the color and what proportion of color was due to each sugar, in order that the sorghum sirup ilianufacturer can know the importance of a control of inversion. This has not been stressed before in sorghum manufacture. although it is of utmost importance in the sucrose industry. A iainple of high-grade coniinercial sucrose was made up to 15" Brix and the pH adjusted with phosphoric acid and sodium hydroxide to 6.12 and 7.81. Using the same technic as with the diluted sorghum, these samples were held a t 97" C. for 6 hourq. They all remained colorless. The p H decreased 0.4 in the first and 0.8 in the second case. These pH's were not very definite, for the sucrose solution was poorly buffered.
b
initio1
$H
Figure 12-Relation between pH and Increase i n Color in Glucose and i n Invert Sirup
It appears, then, that glucose does not contribute much to color production in sorghum. Fructose was next examined. Since sufficient of the sugar itself mas not available, invert sirup war prepared as described above. It was used in a Concentration of 15" Brix, and was treated at the same temperature and the same pH's as were the above sirups. The results for color are given in Figure 10, and for change in p H in Figure 11. The curves for color production in invert sirup make a n entirely different picture from the others. Here the increase in color is not independent of the pH, but is greater the greater the pH. This hold. for all three temperatures.
Soveniber. 1929
114.5
I S D c-STRI.4 L, d S D E S G I S E E R I S G C H E V I S T R Y
The production of acids, as evidenced by decrcase in p H (Figure ll), is well marked at 9 i " C., but less so a t the other temperatures. It is irregular in many cases, owiiig probably to the lack of buffer salts. Another way of showing t'he strikingly different behaviur of invert sirup is to plot the increase in color (instead of t'lie actual color values) for the total time of heating against the initial pH. Such curves for sorghum have aheady been presented in the lower of each pair in Figure 7. Those for the others are given in Figure 12. The amount of total color production in sorghum and glucose is independent of the pH, but in invert sirup it increases w r y ra.pidly with increase in pH. The above differwces must be due to the fructose content of t'he invert sirup. Allowing for t,he amount of inversioii in both cases, the diluted invert sirup contained 6.9 per cent fructose and the sorghum 2.25 per cent. This greater des h c t i b i l i t y of fructose over glucose and sucrose is in accord with our general kno~vledgeof these sugars. It is obvious that marked inversion in sorghum juice is likely to he the cause of color development in the sirup-inaking process. Conclusions
for predicting the increase in color of sorghum juice clue to concentration alone, and by means of it color forniatioii during the process of evaporation may be detected. 4-The pigment,s of sorghum juice do not change color from acid to alkaline, but they change in intensity linearl~. d h the pH. 5-When diluted sorghum sirup is heated a t various pII'*. color and acids are produced. The amount of color is proportional to the temperature, hut is independent of the initial pH. This is largely due to the decrease in pH with i t > concomitant decrease in color intensity. 6-When glucose solubions are heated in t>hesaii~ci i i m i i ( ~ there is some increase in color and a decrease in pI-1. As iii sorghum, the color formation is proportional to the tmiper:iture and independent of the iiiit,ial pH. i-Invert sirup behaves quite differently, owing tu tlic, fructose. There is a very great increase in color, and thih increase is greater the greater the pH. Probably most colnr production in sorphnin sirup is due to tlie fructose present. 8-111 factory practice the most important factors in color production are the degree of inversion of the siicrow and the length of time and the temperature a t which the juiw is held, assuniing that, the reaction nevcr lwcoinc~salkalinc~.
1-The l'fund color grader is a highly satisfactory instriiinent for evaluat,ingthe color of sorghuni sirup. The colored glass wedge of one of these instruments has been calibrated (1) against a spectrophotometer. d reference table of t'his ( 2 ) calibration is given here. 13) ) 2-The Bailey hydrogen electrode is very satisfactory and ) dependable for measuring the pH of sorghum juice up to a density of about 55" Brix. (G) 3-Five samples of sorghum sirup showed a s~raight~-line ( i j relation between log of concentration (in degrees Brix) 14) and color value. .I reference table has been constructed (9)
Literature Cited Andersoti, J. I N D . I ~ N GCHGM., . 9, 492 (1917) hlathews, 3. Biol. Chrm., 6, 3 (1909). h-ef, A n n . . 403, 204 (1913). Paine and Balch, Facis .Ihoul S u g a r , 22, 338, 362, 336 ( 1 9 2 i ) . \villaman, Sugar, 24, 83 (1922); Chem. Me/ Enq.. 31, 314 Food I n d u s / v i e s , 1, 107 (1925). \Villaman, S I L ~ Q28, Y , 409 (1926). Wiley, r.S. D e p t . Agr., Bur. Chem., Bull. 93 (I'JOA). Willaman, IND.E s o . CHEM.,20, 701 (1925). Zerban and Freeland, Lotiisiana Expt. % I . . / 3 r i l / . 166 L1019).
IQ24,,
Acetonedicarboxylic Acid as a Leavening Agent' Edwin 0. Wiig I..\BORATORII:S OF CESERAI. CHEMISTRY, UXIVERSITY O F U'I~COSSIS X I A i > r s u s .
UTHORITIES disagree as to thr physio1op;ical actioii of the products left by baking powders in baked goods. Inasmuch :is all cnniiiion bakiiig powders leave saline cathartics, such as sodium tartrate, Iiochelle salt, disodium acid phosphate, or sodium sulfate, and since there is some question as t o the physiological effect of aluminum hydroxide, :i leavening agent that w-oultl leave no residue woii.ld precludc the possibility of any controversy aiitl would constitute an ideal baking powder. Some time after the completion of a study of the kinetirs of tlie decomposition of acetonedicarboxylic acid, it occurred to the author that this substance might serve as a leavening agent, since it readily decomposes into carbon dioxide.
A
Preparation and Testing rlcetonedicarboxylic acid was prepared by adding fuining sulfuric acid to citric acid ( 2 ) . The resulting acetonedicarboxylic acid was crystallized from ethyl acetate several times and then dried over calcium chloride. Cornstarch or other starch was dried by heating under reduced pressure in a flask on a steam bath. Starch and acetonedicarboxylic acid were then weighed and mixed so as to give a baking Presented before the Division of Agricultural and Food Chemistry a t the 77th Meeting of the American Chemical Society, Colt!rnbus, Ohio, April 29 t o May 3, 1929.
\\'IS.
ponder which noultl yield from 13 t o 15 per wilt carboii dioxide, the usual strmgtli of a coniniercial baking powder. Cukes, and in one caw, bread, were then baked using a commercial baking powder and some acetonedicarboxylic acid baking pn~vder. The same recipes were uscd and thc bailie oven condition^, the two products generally being liaketl side by side. I n every case the acetonedicarboxylic acid ponder r a i w l the product a s wc11 ah the cornmereid powder. Esperimeiitb iwre carried out to determme bhether t ~ rI l ~ t acetone was left in the product. A cake 1e:~vencdwith acetonedicarboxylic acid baking powler wah run tlirougl1 n food chopper, n-hich %as subsequmtly c~rrfullywasheti with water and the washings added to the ground c a k ~ A thin paste was made of the cake by adding a litrr of matc.1 and then steam-distilled until 200 to 300 cc. of distillat(, collected. A few d r o p of sulfuric acid were added to tlw distillate, which was then distilled until 30 cc. were collected On adding 10 cc. of this distillate to 25 cc. of a haturatetl solution of 2,4-dinitrophenylhydrazine in 2 ;V hydrochloric acid, no precipitation was obtained, while 0.005 cc. of acetoncl in 10 cc. of water gave a heavy precipitate. Hence not more than a trace of acetone can possibly be prewit, since it i\ readily volatilized at baking teinperatiire,i. Furthermore, small amount* of acctonc are knnn.n to be harmless ( 2 ) .
