Production of a Palatable .Artichoke Sirup I.
General Procedure
F. A. DYKINS,E. C. KLEIDERER, U. HEUBAUM, V. R. HARDY, AND D. T. ENGLIS University of Illinois, Urbana, Ill. liminary endeavor, and NTEREST in a conimerThe present widespread interest in the growing Willaman (14) has given concial production of levulose of levulose-yielding crops, and the efforts toward s i d e r a t i o n to the idea. It is has become v e r y general the production of crystalline levulose, have led to recognized that the success of during the past few years. The a n attempt to prepare a palatable sirup f r o m such a project from a commerpeculiar properties of the sugar Jerusalem artichokes without going through a c i a l s t a n d p o i n t is rendered which make the p r o d u c t i o n dubious at the present time bedesirable ( g ) , and the sources process of crystallization. cause of the low cost of highfrom which it may be derived Artichoke tubers, sliced and dried shortly after grade sucrose, as well as of sirups (i), have been recently reviewed. harvesting, are most satisfactory for the diffusion with which a levulose sirup must The problem has received attenprocess for the removal of the water-soluble compete. The manufacture of tion in this laboratory at inmaterial, which gives the best results of the various these e x i s t i n g p r o d u c t s has tervals ( 2 , 3 ,0 , 1R),and recently reached a high stage of developa consistent effort has been dimethods tried. For defecation of the extract, a ment and efficiency. The prorected t o w a r d its s o l u t i o n . simple treatment with Super-eel, followed by duction of refined sugars has The object of p r a c t i c a l l y all filtration, gices best final sirups. Hydrolysis come about several years after, investigations in the field has of the solution of the polysaccharide material is and essentially as a result of, the been to prepare the crystalline accomplished by catalysis with hydrochloric acid preparation of sirups of a palatlevulose. Although, in general, able quality which have been a direct crystallization i s t h e under pressure, which results in a minimum of gradually improved. The proeasiest method of purification of added salt in the final product and avoids certain duction of a palatable sirup from a sugar w h e n it is the major troublesome precipitates and objectionable feaJerusalem artichokes was the obc o n s t i t u e n t of a s o l u t i o n , tures involcing other acids. Reduction in the ject of these experiments, and it owing to the extreme solubility ash content as a result of electrodialysis of the is hoped and believed that the of l e v u l o s e and tJhe effect of successful accomplishment will certain impurities upon its tendextract has also proved advantageous. After a likewise contribute greatly to the ency to crystallize, this operapartial concentration of the hydrolyzed extract, attainment of the final goaltion has not yet been possible it is neutralized, heated with active char, filtered, pure levulose at a low cost. It for the separation of this sugar and finally concentrated to a solid content satisis b e l i e v e d , too, that having from the raw juices. factory f o r table use. some characteristics d i f f e r e n t One p r o c e d u r e , which has from existing sirups, such as high been employed successfully by A sale of the product in the community has solubility of its major constituJ a c k s o n and a s s o c i a t e s (8) resulted in a favorable response on the part of the ent, little tendency to crystalfor use upon the extract of the consumers. lize, better k e e p i n g q u a l i t y , Jerusalem artichoke, involves higher sweetening power, and a h v d r o l v s i s , defecation, a n d preliminkry precipitation of the sugar as the calcium salt. distinct flavor of its own, artichoke sirup will find a consuming The calcium levulate is then subjected to carbonation, and public to which it will have an appeal. A consideration of the procedures followed in the various the sugar is crystallized directly. The methods employed by McGlumphy and co-workers (10) and Golovin, Bryuk- methods developed for the crystallization of pure levulose, hanova, and Fridinan ( $ ) are essentially the same. The cost reveals that in no case is the crystallization effected from a of production is relatively high, and the yields are as yet sirup which may be said to be of a palatable nature. A palatable artichoke sirup must be of reasonably high sugar not all that is to be desired. Hoche ( 7 ) , using chicory as the source, accomplished a purity, low ash content, suitable color, and pleasing taste. purification of the raw extract by precipitation of the inulin, COMPOSITION AXD AVAILABILITY O F RAW M A T E R I A L the polysaccharide form of the sugar, by chilling the solution. This material was then hydrolyzed and the lerulose crystalThe artichoke, similar to other sugar-yielding plants, is a lized from the resulting sirup. Apparently Hoche has defined seasonable crop. It will require either an intensive campaign the conditions for the preparation of both the inulin and the of a few weeks to work up the entire crop, or some means of levulose carefully. The reported yields are low and are storing and preserving the crop until used must be developed. probably due to the fact that a relatively small fraction of The simplest storage plan is to leave the tubers in the ground. the levulose-yielding material is removed in the first opera- I n climates where the ground freezes, these tubers cannot be tion. Although the methods mentioned accomplish the used until spring. A second method is to dig the tubers and separation of the crystalline sugar, extensive utilization of the store them during the winter in pits. The third method, product will be limited by the high cost of production. which is perhaps most expensive, is to store the artichokes Levulose sirups have been mentioned as more or less inci- under definite conditions of temperature and humidity. dental products in attempts to prepare the pure sugar. Traub ( I S ) has defined these conditions as 32' to 35" F. However, an effort to make a high-quality palatable sirup (0' to 1.7" C.) and a relative humidity of 89 to 92 per cent. has received little attention. Cockerel1 (1) reported a pre- A comparative study of these three methods of storage has 937
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been made. It has recently been reported that another method of preservation of artichokes involving a supplementing of the thin periderm of the tubers with a coating of certain chemicals has been employed elsewhere. The problem of storage is one of preventing spoilage and conserving moisture content. In the case of the storage of artichokes, however, loss of sugar material is not only due to spoilage, but also to chemical changes taking place in the tubers. In agreement with Traub ( I J ) , analyses a t regular intervals demonstrated that there was a steady loss of fructose-yielding polymers with a corresponding increase in the glucose-yielding polymers. Thus, not only does the ratio of levulose to total sugars decrease, but the ratio of levulose t o glucose decreases a t a much faster rate. These chemical changes during storage greatly alter the character of the sirups subsequently prepared from the tubers. I n order to avoid the losses mentioned, attention -,vas turned to the practicability of drying the tubers. Shaffer (12) and Dawson (3) have previously made some studies in this laboratory on the drying of sliced artichoke tubers and chicory roots. McGlumphy and co-workers (IO) have also reported experiments of this nature. This work on the drying of the sliced tubers has been continued, and the dried material has been used as the principal source from which the extract for sirup-making has been prepared.
EXTRACTION OF WATER-SOLUBLE PORTION The initial extracts were made from fresh tubers, using both cold and hot water. The composition of the extracts obtained was much the same in each case. However, hot water extracted a greater quantity of the soluble material and was used for the following experiments. When the fresh tubers were sliced and extracted in a diffusion battery, an extract of only about 12 per cent solids could be obtained. This dilute extract required concentrating before proceeding with the sirup manufacture. To avoid this concentration, the sliced tubers, or Eometimes the whole tubers, were steamed and then pressed in a hydraulic press. This procedure gave an extract of about 16 per cent solids. While this method involved less subsequent concentration, difficulties encountered during the concentration indicated that some of the other methods of extract preparation which had been employed were more satisfactory. The decision to preserve the artichoke material by drying contributed materially to the solution of the problem of extract preparation. I n the experimental diffusion battery, which consisted of six cells of a capacity of 12 pounds (5.4 kg.) each, the draw from the fifth cell gave an extract of 30 to 35 per cent solids; the draw from the sixth cell gave an extract of 35 to 40 per cent solids. Further continuation of the diffusion builds up an extract too viscous to handle. An extract of about 35 per cent solids proved best for the process. HYDROLYSIS OF POLYSACCHARIDE MATERIAL The extent of the hydrolysis obtained by the various methods is not the only criterion for judgment of the hydrolysis when the goal sought is a palatable sirup. The quantity of sugar formed should, of course, be a high proportion of that obtainable, but several other factors must be taken into consideration: type of acid used, character and amount of ash added as a result of neutralization, development of color, amount of caramelization, and, finally, flavor and palatability of the finished sirups. Hydrolysis of the polysaccharide material may be effected by any one of several procedures. Kleiderer and Englis (9) in this laboratory, have obtained nearly complete hydrolysis
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of inulin by use of carbon dioxide and sulfur dioxide a t a pressure of 1000 pounds per square inch (70.3 kg. per sq. cm.) a t 150" C. for 60 minutes. Using nitrogen under the same pressure a t 160" C., hydrolysis was effected in 120 minutes. I n the latter experiment, caramelization was noted. The bombs used in this work were of small capacity, and work on a larger scale a t high pressures has not been attempted. Since the catalysis of the hydrolysis is probably due chiefly to the hydrogen ion, an extensive study was made of the effect of time, temperature, hydrogen-ion concentration, and concentration of solids in the extract upon the extent of conversion. A consideration of many factors involved indicated that an extract of about 35 per cent solids was most satisfactory for sirup production. Further work then depended on the adjustment of the time, temperature, and p H such that a good hydrolysis was obtained and the resultant sirup palatable. The acids used to lower the pH of the extracts naturally divide themselves into two groups: (1) acids whose anions can be removed after hydrolysis by the formation of an insoluble precipitate when neutralized-e. g., sulfuric, orthophosphoric, carbonic, and sulfurous acids; (2) acids whose anions must remain in the hydrolyzed extract, usually as the sodium salts-e. g., hydrochloric and various organic acids. Studies were made using various amounts of the different acids a t different temperatures and for different times. Suitable hydrolyses were easily obtained. In the first group of acids, since the anion is to be removed later by precipitation, the amount added may be comparatively large. Therefore hydrolyses with this group may be effected a t low temperatures. While some of these procedures have shown promise of producing a palatable sirup, due to the success attained with another procedure, further work on these methods has been deferred. A consideration of the use of hydrochloric acid indicates a t once that the chloride ion must be left in the sirup. Neutralization with soda would form sodium chloride, a certain amount of which would not be objectionable in the finished sirup. Owing to the low caramelization temperature and the sensitiveness of levulose to destruction by acid, the specification for an analytical procedure is that the solution should never be heated above 70" C. when it is 0.22 N in mineral acid (8). By decreasing the amount of acid added, it is qossible to increase the temperature without much destruction of levulose. Experiments were made a t 70" and a t 100" C., but the acid required for hydrolysis gave such large amounts of sodium chloride on neutralization that the sirups obtained were excessively salty. Accordingly the temperature was increased and the amount of acid added decreased. This required that the further experiments be carried out in an autoclave. Tests were made using different pressures. The optimum conditions for hydrolysis were indicated to be a pressure of 25 pounds per square inch (1.8 kg. per sq. cm.) for 20 minutes a t a pH of 4.2, using an extract of 30 to 35 per cent solids. Another method of accomplishing the acidification of the extract is by means of electricity. The hydrolysis may then be carried out under pressure as was done with the extract acidified with hydrochloric acid. Preliminary work on this method has been done in this laboratory by Heubaum (Oa). Further work is in progress. This method has the advantage of acidifying the extract without the addition of acid, thus reducing the ash content of the finished sirups. Treatment in the electrodialytic apparatus also reduced the colloid content of the extract by about 40 per cent as determined by the basic dye test of Paine and Balch (11). Experiments with this method on a small scale have proved highly successful, and further tests are being made to see if the method will be applicable to large-scale production.
August, 1933
I' SIT R Y I K D U S T R I A L A K D E N G I N E E R I N G C €I E &
An examination (of the possible means of hydrolysis with reference to the convenience and cost, as well as to the character of the finished sirups, led to the selection of the use of hydrochloric acid and pressure. DEFECATION
AKD SEUTRALIZATION
Any defecation procedure requiring the addition of chemicals also requires that these chemicals be subsequently removed by the formation of an insoluble precipitate which can be filtered out. Otherwise there will be a sizable increase in the amount of ash. A considerable proportion of the colloidal material is removed from artichoke extracts simply by heating and filtration, and some is removed by coagulation during the acidification and hydrolysis. I n general the defecation of sugar solutions is effected by raising the pH somewhat above 7 by the addition of some base, usually lime. The use of lime for the defecation of artichoke extracts has been investigated. In the procedure employing acids whose anions are left in the sirup, the use of calcium is evidently not permissible. I n the other series of procedures, lime defecation may be carried out in two ways: (1) direct treatment of the artichoke extract with lime, filtration, neutralization of the lime with acid, filtration, and subsequent acidification and hydrolysis; (2) hydrolysis of the extract and subsequent treatment with lime to neutralize the acid and to effect defecation. The action of the lime is twofold. It neutralizes the charge on the colloid particle and causes its precipitation. Also, when neutralized by an acid such as sulfuric or phosphoric, the insoluble precipitate which forms adsorbs the colloidal impurities. This is especially important when phosphoric acid is used. Judging the defecation on the basis of nitrogen removal, the first procedure is the better. In agreement with the work a t the Bureau of Standards, this method has been observed to cause loss of about 12 per cent of sugar-yielding material. It is questionable whether the additional removal of the nitrogenous material is worth this loss of the polysaccharides. Since any excess of basic defecating agent must be neutralized, the subject of the acids used for the hydrolysis may be discussed in greater detail a t this time. When the acids are of the removable type, such as sulfuric or phosphoric, neutralization may be accomplished by using the hydroxides or carbonates of calcium, strontium, or barium. I n each case an insoluble precipitate forms which may be filtered from the sirup. One cannot avoid having present a saturated solution of the insoluble precipitate a t the dilution a t which the filtration is carried out. The viscosity of the sugar solution also prevents completeness of precipitation, and, when the sirup is finally concentrated to 82 per cent solids, a precipitate slowly forms which settles out on long standing. Because of the extreme insolubility of barium sulfate, good sirups were obtained when this method was used, but the feasibility of using sirups whose preparation involves barium compounds remains to be investigated. The strontium sirups were fairly good, but deposited some precipitate on standing. The calcium sirups deposited an appreciable amount of precipitate and also acquired a peculiar bitter taste, which is believed to be due to the calcium ion and must be eliminated before the sirups may be used. When an acid of' the nonremovable type, such as hydrochloric, is used to accomplish the hydrolysis, defecation by lime is not permissible owing to the accumulation of soluble calcium chloride in the sirup and the bitter taste believed to be due to the calcium ion. I n this procedure no defecating agents are added and the only defecation accomplished is that of the various filtrations and that due to the coagulation of colloids by the acid and during hydrolysis. The hydrochloric acid may be neutralized by either sodium
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hydroxide or sodium carbonate, the latter generally being used because of convenience and lower cost. This procedure leaves sodium chloride in the sirup, and the process has been developed so that the sodium chloride present is less than 0.8 per cent. This amount is not objectionable to the taste. CONCENTRATION, FILTRATION, AND DECOLORIZATION I n initial attempts, filtration of the extract proved difficult. By heating the extract with Super-Cel and then filtering through a press, the cloths of which had been previously coated with the filter aid, satisfactory results were obtained. The difficulty experienced with extracts from fresh material was much more pronounced than that with extracts from the dry material. The extract may be neutralized immediately after hydrolysis and the concentration carried out in a copper vacuum sugar pan. To reduce the amount of acid to be neutralized, and thus the ash content of the finished sirup, a concentration of the acidified extract was carried out previous to neutralization in glass-lined equipment under reduced pressure. Both the acidity of the condensate and the diminished amount of alkali required for neutralization indicated the value of this type of concentration. After being concentrated to 60 per cent solids and neutralized, the sirups were treated with Carborafi. Two and sometimes three treatments were required for proper decolorization. The final concentration was to a sirup of 82 per cent solids. At this concentration there is no danger of spoilage, and the viscosity is about the same as that of other marketed sirups. SEMIPLANT-SCALE PRODUCTION For the operation of the semiplant scale unit, only the sliced and dried artichoke material was employed. For the purpose of extraction, a larger diffusion battery was constructed. The cells consisted of six 27-gallon galvanized cans. I n the side of each, just above the bottom of the can, a hole was drilled and a lock nut soldered so that a sill cock could be screwed into place. Previous to the introduction of the dried material, a piece of copper wire screen was placed on the inside of the can over the opening from the sill cock. Having filled the battery with dried material, t o the first cell water a t boiling temperature was added. After standing a short time, the extract was drawn off into a large bucket and poured into the next cell. Fresh hot water was then added to the first cell, and the drawing off and pouring forward of the liquid repeated until the complete battery was in operation. The temperature of the extract was maintained at 70" to 80" C. by occasionally heating the draw from one of the cells in a jacketed kettle before pouring into the next cell. When a cell was exhausted, it was immediately emptied and refilled with dried chips. In case of stoppage a t the outlets, the valve stem of the sill cock could be quickly removed, and, by thrusting a small rod against the screen, the flow could be started again. Although the unit was a somewhat crude affair, it cost little and gave satisfactory results. Each cell had a capacity of 35 pounds of the dried material, and the battery under normal working conditions delivered about 200 pounds of 35 per cent extract per hour. The subsequent operations were essentially the same as has been specified for the small-scale experiments. The extract of 30 to 35 per cent solids, coming from the diffusion battery, was filtered with the aid of Super-Cel, using a small Shriver filter press. The filtered extract was acidified with hydrochloric acid to a pH of 4.2. The acidified extract was then transferred to a copper
N E E R I N G C I l E M I STW Y
convertor haviug a (:apitcity of 40 gallons (151.6 liters), Steam was introduced until a pressure of 25 pourids per square inch (1.8 kg. per sq. cm.) wzs reached. This pressure was maintained for about 20 minutes, and the hydrolyzed extract then bluwn off. During the conversion tliere was a 10 per cent dilution of the extract oiviirg to the steam. The extent of the hydrolyris tinder t11e.e &ditiotis was 80 to 90 per cent of the hydrolyzable material. The acidified and converted extract was then traitsferred to a glass-lined vacuum sugar pail and concentrated to a derisity of 60 per cent solids. Ihring this concentration some hydrochloric acid i m s lost in the distillate, thereby reducing the amount OS alkali required for neutralizxtion. The sirup was ivitbdrnwii from the pan and neutralized with soda to a pII of 5.4, the course of the neutralization lieirig followed by nieaiis of the quinligdrone elect,rode. The neutralized sirup was filtered and treated with Carboraffin to reduce the color tu a value approxiniating that of an average maple sirup. The resulting sirup WBB returried to tlic pan arid concent,rated to 82 per cent solidi;. The sirup has been marketed in this commimity tlirouglr the agency of the University Agricultural Sales Room A number of users have expressed Favorahle comments. The principal uses thus far hare been as a general tahle sirug aid in cooking recipes in wliich a colorcd sirup mag be used. Ot,lier tests.. dcoeiidine more snecificallv 011 the exocotional . progcrties of Iev~~Iosc, are imm being made.
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ACKNOWLEDGMENT This mvestigation was made possible through a special appropriation by the University of Illinois for a study of the growing and utilization of new agricultural products. To Roger Adams who has sponsored this uroiect and whose aid a n i encouragement have been chiefly responsible for the resnits obtained the authors wish to express their appreciation. ~~1TEllAl'UP.ECITED
Hmf.MO.Bull., 8 , 243 (ISIU). (2) Cohen. B.S. Thesis. Unir. of Ill., 1Y29. (3) Usweon, M.S. Thesis, Univ. of 111.. 1928. (4) Golovin, Uryukhaiiovn. and Fridman,J. S u g a i l n d . (U.S. S. R.). 3, 140 (192'3). (5) Harding,?'. S., Bugw. 25,406(1923). (6) Hardinp. W. T., I5.S. rheais, Univ. of Ill., 1'321 ( 6 8 ) Heiibaiirn, Pacts About SUWT. 28. to be uublishc!d (1933). (7) Hoehe. Z. Ver. deut. Zuckwind. 76. UT:I (1936). (8) Jackson, Siisbeo. and l'mfiitt. Bur. Standards, Sei. Paper 519 (1) Cockerell. CaILJ. Comm.
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(Y) lilcidorer and Englis, Ino. ENG.CIIE&
