INDUSTRIAL AND ENGINEERING CHEMXTRY
778
lasses where the excessive amount of salts prevents crystallization of cane sugar.
Sample 1 Sample 2 Total solids Ash Total acid a s citric Undetermined
COMMERCIAL ACIDLIQUORS In order to compare the composition of the citric acid liquors obtained in this investigation with that of the concentrated mother liquors produced in citric acid factories, two sainpIes taken from lead crystallizing pans were analyzed. Sample l came from a pan containing liquor that had been reworked four times. This means that the mother liquor had been removed from a batch of crystals, mixed with some fresh acid liquor, reduced to 38" BaumB, and allowed to crystallize. This was repeated four times, so that Sa'mpIe 1 contains an accumulation of salts, sulfuric acid, and other impurities from five lots of acid liquor. Sample 2 had been reboiled three times. After liquors have been reworked more than three or four times, they yield such poor crops of crystals that it is customary to return them to the neutralizing tanks and recover the acid as citrate of lime. The composition of these saniples was as follows:
Vol. 15, No. 8 %
70
74.09
72.4R
67.81
65.29
3.oi 3.27
.4.OS
3.11
A determination of totaI sulfates indicated that about 3 per cent of the total acid was sulfuric. These results show that, for approximately the same acid content, the dialyzed liquors (Table V) contain over 10 per cent more of total solids than the factory liquors made by the decomposition of calcium citrate with sulfuric acid. The factory liquors had such a low viscosity that the crystals could be readily removed and washed. The quantity of ash present, together with the small quantities of other constituents, is not great enough to prevent crystallization. ACKNOWLEDGMENT The author wishes to express his appreciation of the valuable assistance of E. M. Chace, chemist in charge, Laboratory of Fruit and Vegetable Chemistry, under whose supervision the work was conducted.
T h e . Relation of Alcohol Precipitate to Jellying Power of Citrus Pectin Extracts' 9
By Ruth Johnstin and Minna C. Denton OFFICE OF HOMEECONOMICS, U. s. DEPARTMENT OF AGRICULTURE, WASHINGTON, D.
C.
-
N ORDER to ascertain
filtered through C 1 0 h The amount of alcohol precipitate is not a reliable measure of lvhether a relationship effectiue pectin, as shown by comparisons of pectin solutions prepared The combined filtrates amounted to 600 grams. could be established in the open kettles and in an autoclaue. . Extracting in the autobetween the pectin content, Determinations based upon jellying power giue the only satisclaw required considerable as determined by the usual factory means of estimating effectiue pectin content at present known to us. study before a procedure alcohol precipitation methwas adopted which gave od, and the jellying power, Citrus pectin extracts prepared in an autoclaue at 5 pounds solutions that were consida study has been made of a pressure for 30 minutes had 25 per cent less jellying power than simered comparable with those large number of Pectin exilar extracts prepared in the open kettle. Prepared in the open kettle. tracts prepared from the The addition of acid in open-kettle extractions of orange peel If Pectins are unstable a t white Peel of citrus fruits. produced a n extract of about 100 per cent greater jellying power the temperature of boiling The work has involved the than when no acid was used. water, i t seems reasonable consideration of such details to suppose that they would as the preparation of the peel, the proportion of water to peel, the number of extrac- be less stable a t higher temperatures. However, if the tions, the methods of filtration, concentration, and storage heating period could be shortened, something might be of the extracts, and their use in combination with different gained by extracting in an autoclave. This idea seemed fruits and fruit juices in the making of jams and jellies. The to be substantiated by the fact that autoclave extracts results have shown that it is possible to prepare fairly con- always gave a higher weight of alcohol precipitate than sirncentrated pectin solutions from citrus peel, which can be ilar ones prepared in the open kettle. By reducing the proportion of water and opening the petused for making clear, transparent jellies without subjecting cock during cooling, it was possible to effect a concentration the extracts to a process of purification. The investigation has been confined to a study of pectin on the pomace equal to that obtained in the open-kettle procsolutions prepared in the open kettle and in the autoclave, ess. Three extractions were made in every case, using 330 cc, of water to 226.7 grams of peel. The combined filtrates vith and without the addition of acid. amounted to 600 grams. Extractions were made with presEXTRACTION sures varying from 3 to 20 pounds and heating periods ranging The method of procedure adopted in this series of experi- from 10 to 40 minutes. Although there are several referments for open-kettle cooking, was as follows: 226.7 grams ences in the literature to the use of the autoclave in making of ground, white peel of oranges were extracted three times, pectin extracts, which suggest its use as a means of increasing using a liter of distilled water for each extraction. The heat- pectin yield, yet in no case has it been possible to prepare ing was carried on in shallow pans of such a size that a con- by this method a pectin solution which had as great jellycentration to about one-half the original volume could be ing power as comparable extracts obtained by open-kettle accomplished in less than 20 minutes. The material was heating. Fellenberg2 called attention to the fact that protopectin 1 Presented before the Division of Agricultural a n d Food Chemistry a t t h e 65th Meeting of the American Chemical Society, New Haven, Conn., changes to pectin more rapidly in acid than in neutral solu-
I
April 2 t o 7, 1923, under the title, "Experimental Studies of Citrus Pectin Gels "
9
Biochem. Z.,85, 118 (1918).
IhTDUSTRIAL A Y D EXGI NEERIXG CHEMISTRY
August, 1923
tion. The writers had observed that lemon peel, which has a natural total acidity two to four times greater than that of oraiige peel, is always much more completely disintegrated a t the end of the extraction process. I n view of Fellenberg's statement, it seemed that the more thorough breaking up of the tissue might be due to the greater acidity of the lemon peel. With this idea in mind, a series of experiments was conducted similar to the ones just described, with the exception 'that 0.1 N citric acid mas used instead of distilled water. Comparisons of the extracts prepared by these different methods were based upon results obtained with the same lot of citrus fruit. This precaution was necessary since the pectin content varies within wide limits depending upon the variety and maturity of the fruit. DETERMIXATION OF PECTIK CONTEXT The pectin content of these extracts was determined directly by the * alcohol precipitation method and indirectly by measuring their jellying power or the amount of extract requird to form a jelly with a definite weight of sugar and acid. Seither of these methods, as a t present applied, can be regarded as entirely satisfactory. The alcohol precipitation method gives widely differing results with the same extract, depending upon variations in manipulation. Alcohol also precipitates substances other than pectin, such as vegetable gums and hemicelluloses. The Campbell alcohol method gives consistently higher results than the method adopted in thet,e experiments, which involves two precipitations. Estimations of pectin content based upon jellying power are subject to error because of the lack of a definition of what constitutes a jelly and of a standard method of measuring gel strength. I n making use of this method an arbitrary standard had to be selected for the sake of comparison, as has been done by other investigators. The details of the process were as follows: A series of four to six jellies was made with each pectin solution, using 84 grams of sugar, amounts of pectin extract ranging from 20 to 80 gram, enough 1 N citric acid to bring the total acidity to 1.3 grams, and enough distilled water to bring the volume to 150 cc. The mixture was then concentrated by boiling to 104" C., weighed, and poured into molds 1.25 inches deep and 2.75 inches in diameter. The weight of jelly a t the concentration of 104" C. was usually 140 *0.5 grams. The jellies therefore contained 60 per cent sugar and 0.9 per cent total acidity. The molds were loosely covered and allowed to stand 24 hours at room temperature before being turned out. The standard gel was one barely stiff enough to retain its shape when removed from the mold, and it gave no immediate evidence of syneresis. The member of each series which corresponded to this standard was selected, and the amount of pectin extract which had been used in this jelly was taken as a measure of jellying power of the extract. ORANGEPECTIN EXTRACTS PREPARED IN OPEN KETTLEAND AUTOCLAVE Acid in Extract Grams Grams Alcohol Extract Used in of Jelly of Jelly Precipitate (Calcd. a s Sugar Making per per Serial in Jelly Jelly G r a m of Gram of in Extract Citric) No. 7 0 G. G. Extract Peel METHOD % 150 Open kettle 0,347 0..67 54 70 2.0 5.2 Distilled water 0,890 151 Open kettle 1.90 84 27 5.2 13.7 0 . 1 N acid 0.565 154 Autoclave 5 0.057 84 90 1.5 3.9 Ibs. 30 min. Distilled water 155 Autoclave 5 0,960 1.270 84 60 2.3 6.0 Ibs. 30 min. 0 1 At acid 152 Autoclave 20 1,690 0.120 84 90 N o jelly lbs., 30 min. Distilled water 153 Autoclave 20 1.770 1.52 84 io N o jelly Ibs., 30 min. 0 . 1 A: acid
TABLE I-RESULTS
Table I gives the results obtained in one series of experiments with orange pectin extracts. A comparison of the figures in Columns 3 and 7 shows the disagreement between the quantity of alcohol precipitate and jellying power. Heating in the autoclave increases the amount of soluble matter in the extracts, yet when subjected to a jellying test these extracts prove to be quite deficient in jellying properties. Extracts in other series prepared a t 10 and 15 pounds pressure for the same and shorter periods of time were similar in jelly-making strength to Kos. 1.52 and 153. Doubtless, the instability of the pectin bodies a t the high temperatures in the autoclave accounts for these results. It seems likely that the alcohol precipitate in this case consists chiefly of partially decomposed pectins, pectic acid, and possibly some hemicelluloses, which do not contribute to the jellying properties. The temperature reached in the ordinary process of making jelly from the pectin extracts (104" C.) seemed to bring about practically no destruction of pectin. Determinations of alcohol precipitate in jellies made according to the formula previously mentioned, agreed very closely with the value calculated from the aniount of pectin extract used.
EFFECTOF ACID The favorable effect of acid in extracting orange pectin is shown in Table 11, which gives results of two series of experiments. TABLE 11-RESULTS
WITH T W O TYPICAL ORANGE PECTIN PARED WITH AND WITHOLT ACID
EXTRACTS PRE-
Acid in Extract Grams Grams Alcohol Extract Su,gar Used in of Jelly of Jelly Precipitate (Calcd. a s in Making per per Serial in Extract Citric) Jelly Jelly Gramof Gram G. G. No. METHOD 7" 9% Extract of Peel 125 Open kettle 0182 0.09 84 40 3.50 9.2 Distilled water 138 Open kettle 0.79 0.085 84 40 3.48 9.1 Distilled water 124 Open kettle 1.30 84 1.70 20 7.0 18.0 0 . 1 N acid 139 Open kettle 1.24 84 1.24 20 7.0 18.0 0 . 1 N acid
It will be observed that in these extracts prepared with acid, increase in alcohol precipitate is accompanied by increasing jellying power, although not exactly in the same proportion. The fact that the acid extracts have 100 per cent greater jellying power whereas the alcohol precipitate shows an increase of only about 75 per cent over the distilled water extracts, seems to indicate that in the presence of acid not only is a larger quantity of pectin produced, but likenrise ' a more effective pectin as regards jellying power. The effect of acid on lemon peel extracts is not so marked, probably because of the greater natural acidity of the lemon. Lemon extracts in general contained a smaller percentage of alcohol precipitates; yet, their jellying power averaged about 20 per cent higher than that of the average orange peel extracts. This seems to be due to a difference in kind rather than in amount of pectin present.
WITH
. ..
779
OTHERFACTORS INFLUENCING JELLYING POWER T o what extent the jellying property of these pectin extracts is affected by the foreign matter present, it is impossible to say. Pectin, as determined by the method used in these experiments, represents a very small percentage of the total solids extracted, and it is not unlikely that the other substances present may affect the character of the gel. It seems very probable also, in view of the recent work of that the apparent variations in jellying power may be due in part to differences in the hydrogen-ion concentrations of the gels. Even though the total acidity was kept at a constant value, there may have been considerable difference in 8
Delamaare Agr. Expt. S t a
, Tech. Bzdl 134.
I N D V S T R I A L A X D ENGINEERING CHE-MIXTRY
'780
hydrogen-ion concentration due to the buffer effect of other substances in solution. Fellenberg2 mentions the fact that the viscosity of pectins decreases with decreasing methoxyl content. In this connection it may be of interest to note that the acid pectin extracts of high jellying power had greater viscosity than did autoclave extracts in which the jellying properties were greatly reduced.
CONCLUSION The true explanation for the discrepancies which have been pointed out involves a knowledge of the pectin bodies both as regards their constitution and their colloidal nature, which a t present is not available.
Vol. 15, 9 0 . 8
As a result of unfinished tests with purified pectins, the writers concluded that quantitative relations in sugar-pectinacid gels cannot be correctly interpreted, nor can any great advance be made in the study of the colloidal properties of these solutions until there are available for careful experimentation pectins of a high degree of purity and of welldefined composition. When the relation of jellying power to composition is.once established, a very satisfactory method of estimating effective pectin content, based upon jellying power, can be developed. Such a method, to be capable of general application, will require an accurate device for measuring gel strength under carefully standardized conditions.
Jellying of Sorghum Sirup' Effect of Malt Diastase upon the Filtration of Sorghum Juice By Sidney F. Sherwood OFFICE OF SUGAR PLANT
INVESTIGATIONS,
BUREAUO F
PLANT
INDUSTRY, WASHINGTON, D. C.
T
Starch seems to be largely responsible for the jellying of sorghum The following sirups were HE cause of jellying sirup and for the extreme dificulty in filtering sorghum juice, espeprepared from juice from of sorghum sirup, a characteristic well cially after it has been heated. Preliminary treatment of the juice Silver Top, Folger's Early, known to manufacturers, with malt diastase greatly increases the rate of filtration and preSugar Drip, Early Rose, has not yet been explained. oents the 'j'ellying" of the finished sirup. Early Amber, and Red Amber sorghum, grown a t Although much of the sirup Arlington Farm, Va., in produced seems to have no jellying characteristics, jellying may occur a t any time, 1922. The quantity of starch in the juice was not deterordinarily becoming manifest either immediately after the mined, but all the juices gave a positive reaction with iodine, finished sirup has become cold or after the cold sirup has and when preserved with mercuric chloride and allowed to setbeen stored for some time. Jellied sirup varies from a tle exhibited in the settlings a starch layer or band. The slightly slimy material to a gelatinous semisolid resembling tables are based upon nine series of determinations and the ordinary table jelly prepared from fruit juices. Sirup of this results are in entire agreement with similar investigations character is highly unsatisfactory to both the dealer and made in previous seasons. the consumer. SIRUPA-Approximately 900 cc. of juice plus 1 ounce of kieselMany of the sirups made from different varieties of sweet guhr (3 per cent by weight), heated to 98" C., and filtered a t sorghum in connection with some breeding experiments and once. SIRUPB-Approximately 900 cc. of juice plus 1 ounce of kieselvarietal tests on sweet sorghums conducted by this laboratory stirred, and filtered a t once without heating. (project in charge of H. B. Cowgill, agronomist, under the guhr, SIRUPC-Approximately 900 cc. of juice heated t p 98' C., direction of C. 0. Townsend, pathologist in charge of office), cooled to 40' C., 10 cc. of malt extract added, permitted to stand had a jelly-like consistency. The starch content of 15 for 1hour, 1 ounce of kieselguhr added, and filtered at once. SIRUPD-Approximately 900 cc. of juice heated t o 98" C., samples of juice expressed from 15 varieties of sorghum cooled to 40" C., 10 cc. of malt extract added, permitted to stand a t maturity varied from 0.142 per cent (1.3 pounds per 100gal- for 1 hour, 1 ounce of kieselguhr added, heated to 98" C., and lon of juice) to 0.852 per cent (7.8 pounds per 100 gallon), with filtered a t once. SIRUPE-Identical with Sirup D, except that 20 cc. of malt an average of 0.366 per cent (3.3 pounds per 100 gallon).2 Starch seems to be largely responsible for the jellying pro- extract was used. pensity and for the extreme difficulty hitherto experienced The rate of filtration of these juices is shown in Fig. 1. in filtering sorghum juice, especially after it has been heated. Apparently, pseliminary treatment of the juice The effect of the diastase upon starch in the juice was inwith small quantities of malt diastase greatly increases the vestigated further by adding ordinary cornstarch to juice obrate of filtration and prevents jellying. tained from Early Rose and Red Amber sorghum. Starch was added at the rate of 15 grams per gallon (3.3 pounds per EXPERIMENTAL 100 gallon), the average of the figures given for starch conFreshly ground malt was mixed with water in the proportion tent of normal sorghum juice. Some of this juice was of 26 grams to 200 cc., stirred frequently during 1 hour, and treated with kieselguhr and with malt extract in the followfiltered through filter paper. The resulting extract was per- ing proportions: fectly clear. A Buchner funnel, 6 inches in diameter, was fitSIRUPF-Approximately 900 cc. of juice, heated to 98" C., ted with a single thickness of closely woven cotton cloth, which t o 40"C., permitted to stand for 1 hour, 1 ounce of kieselwas then faced with a layer of kieselguhr approximately 2 cooled guhr added (3 per cent by weight), heated to 98" C., and filtered mm. thick. The juice was kept thoroughly stirred while a t once. SIRUPG-Approximately 900 cc. of juice, heated to 98' C., being poured bn the filter, so as to build up an even cake, and cooled to 40" C., 20 cc. of malt extract added, permitted t o stand vacuum was maintained at a closely constant rate for all for 1 hour, 1 ounce of kieselguhr added, heated to 98" C., and runs. filtered a t once. 1 2
Received March 3, 1923. THISJOURNAL, 16, 727 (1923).
The rate of filtration of these juices is shown in Fig. 2.
