Ascorbic Acid from Walnut Hulls A. A. BLOSE, J. B. STARK, G. G. PURVIS, JEAN PEAT, AND H. L. FEVOLD' Western Regional Research Laboratory, Albany, Calif.
In studies on recovery of ascorbic acid from waste green hulls within the limits of error natural sources of aswalnut hulls, an over-all yield of crystalline product of of the animal test. Spurious 25 to 50% was obtained. Experimental details are precorbic acid is the immature vitamin C (or nonvitamin C walnut or its green hull. This sented for the following steps: extraction in dilute aqueous reductants which respond to sulfur dioxide solution; purification of the extract by abfact was discovered by Gherthe indophenol test) has been ghelezhiu in 1937 (2), and sorption on, and elution from, anion exchange resin; estimated by the method of several studies (8, 7' , 9) have and crystallization from the concentrated, decolorized Wokes et al. (IO) t o be less eluates. Pilot plant scale extraction operations were than 15% of the total apconfirmed and extended the original observations. The conducted. Economic analysis of the extraction process parent ascorbic acid measured immature walnut develops a indicates that the process is marginal unless other use photocolorimetrically. Analcan be made of the equipment during the off-season. maximum of 2 t o 2.5y0 ascoryses for ascorbic acid and bic acid on the wet basis (I6 other constituents of walnut hulls obtained from commerto 20% dry basis) just before hardening of the shell. From this maximum the concentration decia1 hullers over three harvesting seasons are given in Table 1. creases gradually to about 0.370 (wet basis) during the final 3 Extraction and Stabilization Methods. LABORATORY SCALE months of ripening. Bukin ( 1 ) has reported a procedure for reINVESTIQATIONS. Since most mechanical hullers break the hulls covery of ascorbic acid from whole immature walnuts, involving away in discrete pieces, the cellular structure is not damaged and four solvent fractionation steps and giving a 20% yield of very little loss of ascorbic acid takes place in the process of hullcrystalline product. ing. In the frozen state (0' F.) the ascrobic acid in the hulls is In recent years the Western Regional Research Laboratory has quite stable over periods of I year or longer. However, a t atmosconducted a project on possible utilization of waste walnut hulls pheric temperature the destruction of ascorbic acid is fairly rapid as a aource of ascorbic acid. At least 50,000tons of hulls are proHulls held a t normal temperatures in open air lost more than two duced yearly in California alone. A considerable portion is availthirds of their ascorbic acid within 8 hours. When hulls were disable in central locations, because walnuts are harvested with hulls integrated in distilled water by means of a Waring Blendor, there intact and hulled by machin'es. A study of the development of was an 85% loss within 30 minutes. This rapid destruction is unascorbic acid in several commercial varieties of Persian walnut in derstandable from estimations of ascorbic acid oxidase in walnut central California during the growing sebson has been reported hulls, from which it has been concluded that, a t room temperature elsewhere (4). and p H 5, it should require not more than 70 minutes t o destroy The present report is concerned chiefly with a relatively simple all of the ascorbic acid in disintegrated hulls containing 1% of the chemical process, which involves extraction of hulls and stabilizavitamin. In the intact hull tissue, physical separation of oxidase tion of the mcorbic acid in aqueous sulfur dioxide, purification of and limited supply of oxygen are probably limiting factors in the extracts by synthetic resin anion exchangers, and crystallization rate of oxidation of ascorbic acid. from the concentrated resin eluates. Large laboratory experiments and pilot plant scale extraction operations have been TABLE I. CONSTITUENTS O F WALNUT HULLS conducted. Cost estimates of investment and capital charges for Moisture-Free Basis, % several of the initial steps in this process have been made and have Constituent Crude fiber 20.3 been summarized in the Discussion section of this paper. The Nitrogen 1 1 commercial development of the process is not attractive at presReducing sugars 16.2 Total sugars 16.2 ent. As is frequently the case with waste-recovery problems, Ash 17.6 this unfavorable cost is largely due to the seasonal production of T a n n i n analysis walnuts but is exaggerated because ascorbic acid is so unstable Total extractives 54.4 Soluble extractives 53.7 that cheap storage of the hulls is not possible. Obviously, the Nontanmns 45.3 Tannins high capital charges would be reduced if the equipment could be 8.4 T a n n i n purity, 8.4/53.7 15.6 used for some other purpose during the 10 or 11 months of the Moisture 81-8970 year that hulls are not available. Such a possibility is not in sight Ascorbic 'acid, 0.4-0.8% wet basis; 2.5-5.0% molsture-free at present. Nevertheless, the results of both the economic and technical studies should be of value to those interested in wasterecovery problems in general and may be of direct value if changThe ascorbic acid in the hulls was completely stabilized a t room ing conditions make it possible t o combine the recovery of ascortemperature for 5 months, and longer, by covering the packed bic acid with other processes. hulls with a 1.5% aqueous solution of sulfur dioxide. Experiments designed to determine the minimum concentration of sulfur EXPERlMENTAL WORK dioxide necessary to stabilize the ascorbic acid over short periods Ascorbic acid content of the hulls as received from the mechanirequired for chemical processing revealed that a concentration of cal huller is adversely affected by delayed harvest, unusually hot 0.1% sulfur dioxide (pH of mixture, 3.9) gave adequate protection for 20 hours at room temperature. weather, or rain. Determination of ascorbic acid was made accordh g to the photocolorimetric 2,6-dichlorophenol-indophenol dye After precautions are taken to prevent oxidation, by excluding oxygen and/or inactivating the natural oxidases, extraction of the test as described by Loeffler and Ponting (6). This method gives results which agree with guinea pig vitamin C bioassays (4)of the ascorbic acid from the walnut hull tissue in aqueous solution can be accomplished in a variety of ways. Approximately two thirds 1 Present address, Quartermaster Food & Container Institute for the of the total solids of the walnut hull are water-extractable. Since Armed Foro-, 1849 West Pershing Road, Chicago 9, Ill.
0
N E of t h e r i c h e s t
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387
INDUSTRIAL AND ENGINEERING CHEMISTRY
388
TABLE 11. HOTCOUNTERCURRENT EXTRACTION OF HULLS Vol Extract Extractant Concn. of Ascorhic Acid, Exposure per Kg. Mg./100 311. Experit o Hulls, Wet Ilulls, Fresh Final ment Min. Liters hulls extract 150 200 172 90 0.8 145 330 0.7 9s 330 90 450 95 400 0.7 120 309 75 0.8 303 120 450 0.8 75 391 180 434 0.8 50 200 4 At time of initial exposure t o hot extractant, hulls were a t room temperature. Bath Temp., C.a
the hulls contain 85 to 90% water, the maximum theoretical concentration of ascorbic acid in the extract is essentially the same as that in the wet hull, and the practically attainable concentration, even by the use of the countercurrent extraction principle, is considerably below this level There is little differential extraction of ascorbic acid compared to the other soluble solids; hence the ratio of ascorbic acid to total solids in the first extract is only a little greater than in the succeeding extracts. The rate a t which equilibrium is reached with respect to concentration of ascorbic acid between walnut-hull tissue and extractant a t room temperature varies from 3 days for large pieces of hull to 2 minutes for hulls disintegrated in a Waring Blendor Because of retention of solution in the walnut tissue or pulp, a batch procers of extraction and filtration requii es several volumes of eutractant. Countercurrent extraction methods were investigated and found satisfactory when applied t o the uncut hulls a t temperatures of 75" to 90" C. To verify the stability of ascorbic acid in the hot sulfur dioxide solution, the total amounts of ascorbic arid in mixtures of blended hull and aqueous sulfur dioxide mere dehermined after stated periods a t room temperature and a t 95 ' t o 100' C. Heating for 30 minutes gave no loss in any case; heating for GO minutes resulted in an average loss of 14%. The general procedure used in the laboratory scale hot countercurrent extraction experiments mas as follows: Hulls, as received from R mechanical huller, were preserved in 0.2% aqueous sulfur dioxide (sufficient solution to cover closely packed hulls) at 2" C. for 1 to 3 days prior to extraction. The drained hulls were packed into six stainless steel cylindrical extractors, which were connected in seriei: during the extraction period, Hot 0.2% aqueous sulfur dioxide solution was forced under air pressure through the series of extractors immersed in a steam-heated water bath. Each extractor was placed in the bath only when the preceding one had been filled with the progressing extract. When the extract had passed through the sixth extractor, samples were taken for analysis. The results (Table 11) show that a t 90' to 95 C (bath temperature) the final extract reached its maximum theoretical ascorbic acid content within 1.5 to 2.5 hours. Two hours a t 75' C gave over 80% of maximum, whereas 3 hours at 50' C. gave less than 50y0of the maximum theoretical ascorbic acid concentration. O
The 0.2% aqueous sulfur dioxide extract of walnut hulls, prepared by either hot or cold extraction, is relatively stable with respect t o its ascorbic acid content. When extracts were concentrated tenfold in vacuo and stored (with 0.2% sulfur dioxide present) in full, stoppered bottles a t room temperatures for 2 months, there was no loss in ascorbic acid during the concentration or storage period. Storage for 7 months resulted in a 20 t o 25% loss. Ascorbic acid represents only 5 to 8% of the total moisture-free solids in the extract. The substances that accompany ascorbic acid are quite soluble; it has been found that they do not precipitate during vacuum concentration to 8, 20, or 35% solids and prolonged chilling a t 3' C. PILOTPLANT SCALE STUDIES.During two walnut-processing seasons, extraction studies were made on a pilot plant scale with a continuous, countercurrent extractor which was modeled after an
Vol. 42, No. 2
orange peel extractor developed a t this laboratory. Hulls were taken directly from a hulling machine and were fed continuously into one end of the extractor. The hulls were moved through the extractor by a conveyer screw and were discharged a t the opposite end. Water passed countercurrently t o the hulls. The extract was preserved with 0.2% by weight of sulfur dioxide, and the treated extract was stored in wooden tanks. The extractor consisted of a redwood trough containing a &inch pitch, 16-inch diameter, helical screw conveyer mounted on a 4.5inch diameter shaft. The total length of the screw was 16 feet, and the effective length for extraction was 15 feet. The screw fitted the trough closely, leaving approximately 0.25 inch of clearance at the sides and around the bottom. Along the sides of the trough (near the upper edges) lengthwise wooden strips were fitted to the shape of the screw to prevent short-circuiting of liquid during operation a t high liquid levels in the extractor. Covers were placed over as much of the trough as possible during operation to minimize exposure of the liquid to air and to minimize heat losses. The extractor was heated by direct injection of steam from small holes drilled in two 0.5-inch diameter tubes, running lengthwise and located in the bottom of the extractor trough. All metal parts of the extractor were fabricated from stainless steel to minimize destruction of ascorbic acid by metallic contamination. No special provision for liquid flow was made in the screw or the extractor. Horevcr, the operation indicated that, if the unit were scaled up to a screw of larger diameter, increased opportunity for liquid flow along the screw would be necessary. From a process standpoint, successful operation was obtained during both seasons. Minor precautions were necessary to keep the extractor operating smoothly; otherwise no difficulties were encountered. Boiling in the extractor caused disintegration of hulls and interfered with movement of hulls along the screw. Hulls were also found to expand slightly on soaking and heating, forming plugs between screw flights unless an even feed rate was maintained. Suitable conditions for extracting ascorbic acid from green xalnut hulls, .ivith the extractor described here, are as follows: Extractor position Extractor screw speed, r.p.m. Liquid depth i n extractor, inohea Extraction temperature, F. Hull feed rate Ib./hour Water flow raie Ib./hour Steam f l o w rate: lb./hour Extract flow rate, Ib./hour Approx. hull retention time, min. Average recovery of ascorbic acid % Soluble solids extraction rate, lb./hour
Level 11/a 13 200-210 420-480 300-420 120 420-540 30 70-80 18-24
Purification with Ion Exchange Resins. Various methods have been used for the isolation of ascorbic acid from plant extracts. These have generally involved organic solvent fractionations, heavy metal srtlt precipitations, or both. Attempts to apply these procedures to the sulfited walnut-hull extract in the laboratory indicated that these methods were too indirect and inefficient to have commercial possibilities in competition with the synthetic ascorbic acid. Matchett et al. (6) a t this laboratory had developed a method for the separation of tartaric acid from grape wastes by means of synthetic organic ion exchange resins. In this same period, Mottern and Buck (8) discovered a process for the recovery of ascorbic acid from citrus and other natural products by the use of ion exchange resins, which was subsequently patented. Working along these same lines a more direct method for purification of ascorbic acid in the hull extract was found in adsorption of the vitamin from the extract on anion exchange resin and elution of the vitamin and other organic acids with dilute inorganic acid solutions. DIRECT USE OF ANION EXCHANGE RESININ A C I D C Y C L E . In a preliminary evaluation of the resins, hull extract was first passed through a cation exchange resin in the hydrogen cycle to transform all salts to their corresponding acids and then through anion exchange resin in the alkaline cycle to adsorb the ascorbic acid and
INDUSTRIAL A N D ENG INEERING CHEMISTRY
February 1950
other organic acids. However, it was discovered t h a t anion exchange resin in the acid cycle adsorbs ascorbic acid directly from hullextract. The resin was prepared by treatment with 2 N hydrochloric acid, followed by thorough washing with distilled water to a p H of 2.7 in the wash. I n contrast t o adsorption in the alkaline cycle, which required pretreatment with cation exchange resin, the adsorption in the acid cycle was accomplished on untreated extract, thus resulting in a much simpler process. Fifty ml. of 0.2oJ, aqueous sulfur dioxide extract of fresh hulls were passed through 25 grams of Amberlite IR-4 in the acid cycle, followed by 50 ml. of distilled water to wash out the residual unadsorbed material and 300 ml. of 0.1 N hydrochloric acid to elute adsorbed acids. Values for pH, amount of ascorbic acid, and proportion of ascorbic acid t o total solids in the fractions are given in Table 111. There was an over-all recovery of 89% for total solids; of the total ascorbic acid 70% appearedin the eluates a t an average purity of 63%. The resin in this experiment was allowed t o adsorb only one fourth of its maximum capacity for ascorbic acid.
TABLE111. PASSAGE OF HULL EXTRACT THROUGH ANION EXCHANGE RESININ ACIDCYCLEAND ELUTION WITH 0.1 N H C I P
Hull extract @adsorbed fraction tiluates 1st 2nd 3rd 4th 5th 6th
P
Total, Mg.
4.0 3.22
118.5 5.9
2.61 2.45 2.40 2.26 1.92 1.44
10.1 19.3 33.1 30.2 5.6 0.9
Ascorbic Acid Mg./ Dry basis 100 ml. % ’ 237.0 7.8 5.9 0.6 19.8 35.7
64.8
60.4 11.1 1.8
10.9 52.6 97.6 54.9
4.4 0.1
CAPACITY OF ANIONEXCHANGE RESIN. The capacity of the resin to adsorb ascorbicacid from the hull extract was arbitrarily defined as the amount that could be passed through a column of resin before effluent concentration of ascorbic acid exceeded 20% of influent concentration. Values are expressed in mg. of ascorbic acid per ml. of regenerated backwashed drained resin bed volume. One ml. of drained resin contained approximately 0.25 gram of dry resin. Four lots of resin (Amberlite IR-4 and IR-4-B) gave values falling within the range of 9 to 11 mg. of ascorbic acid per ml. of bed volume. Capacities for other methods of resin development, bssed on single experiments, were: hull extract on anion exchange resin in alkaline cycle (pH 8), 1.5 mg. per ml., and hull extract through cation exchange resin and then on anion exchange resin in a1 Cali l e cycle, 7.5 mg. per ml. An increase in concentration, on a volume basis, of ascorbic acid in the influent, effected by vacuum concentration of the hull extract, had no apparent influence on capacity, probably because the ratio of ascorbic acid to other adsorbable acids in the extract is not changed by such a concentration. However, when the concentration of ascorbic acid in the influent was increased in relation to the total solids, by the addition of pure ascorbic acid, there was a marked increase in capacity, as follows: hull extract a t 208 mg. of ascorbic acid per 100 ml., capacity 11 mg. per ml.; hull extract plus ascorbic acid a t 566 mg. per 100 ml., capacity 21 mg. per ml. ; hull extract plus ascorbic acid a t 908 mg. per 100 ml., capacity 26 mg. per ml.; hull extract plus ascorbic acid a t 1500 ml. per 100 mg., capacity 41 mg. per ml. Apparently the efficiency of the resin-adsorption step depends on the concentration of ascorbic acid in the original hulls. Because the initial cost of resin is relatively high, it is essential to know the number of cycles the resin can undergo before its performance is irreversibly impaired.
For this purpose, a column containing 110 grams (dry weight) of Amberlite IR-4 anion exchange resin was subjected t o successive cycles of regeneration with 3 to 6 liters of 2 N hydrochloric acid, washing with 40 liters of distilled water, saturation and de-
389
termination of capacity at 20y0 “break-through” with hull extract (0.28% ascorbic acid, 0.2T0 sulfur dioxide), washing with 500 ml. of distilled water, and elution with 2 liters of 1 N hydrochloric acid. Rate of flow through the column for absorption and elution was about 10 ml. per minute. Fifty successive cycles were run, and the capacities at 20% break-through were measured. Values at intervals of ten cycles are given in Table IV.
TABLE IV.
DECREASE IN RESIN CAPACITY OVER FIFTY CYCLES Capacity of Resin Mg. Ascorbic Acid per Ml.’Bed Vol.
Cycle No. 1 10
15 8
20a 30
6
7.5
40a
4
45 50
7.5 4
a Cycle waa followed by treatment with sodium hydroxide and distilled water before usual hydrochloric acid regeneration process.
Treatment of the resin with sodium hydroxide solution appears to improve the capacity temporarily. A reasonable explanation for the decrease in capacity is that some anion in the hull extract, with a stronger affinity for the resin than either ascorbate or chloride ion, gradually builds up on the resin and reduces its capacity for ascorbic acid. The following experimental evidence suggests that the sulfate ion contributes to this effect. Sulfate in appreciable quantities (0.015 millimole per milliliter) was found in sulfited hull extract. When sulfuric acid was used in place of hydrochloric acid for the development of the anion exchange resin in the acid cycle, the capacity of the resin for ascorbic acid dropped from 11 to 4 mg. per ml. It is well known t h a t the sulfate is adsorbed preferentially t o chloride on anion exchange resin and this difference is apparently reflected in the equilibrium between ascorbate and sulfate as compared with equilibrium between ascorbate and chloride on the resin. Large scale laboratory experiments on resin adsorption and elution. The resin step was subjected t o large scale laboratory trials on hull extract prepared in the field with tap water, a t nearly full capacity of the resin. General characteristics are illustrated in the following typical run (Table V): To a column containing 6.7 kg. (dry weight) of Amberlite IR-4 (previously run through three cycles) 14 liters of I N hydrochloric acid were added and then tap water slowly for 48 hours. Nineteen liters of hull extract, containing 115 grams of ascorbic acid at a purity of 5.5T0, were passed through the resin, followed by 38 liters of distilled water. Elution was effected with 152 liters of 0.2 N hydrochloric acid made from distilled water. The capacity of the resin was approximately 5.5 mg. per ml. of bed volume, and the bed was loaded t o 4.2 mg. per ml. Maximum purity of 47% was obtained in eluate 3, whereas the maximum concentration of ascorbic acid on a volume basis occurred in eluate 4 a t 0 13%. The marked decrease in capacity encountered when small scale laboratory experiments with distilled water were attempted on a larger scale with t a p water can probably be attributed to effect of sulfate in the tap water. A carefully controlled comparison was
TABLE V. LARGESCALELABORATORY USE OF ANIONEXCHANGR RESININ ACIDCYCLEWITH TAPWATER
Hull extract Unadsorhed Plus wash Eluate No. 1 2 3 4 5 6 7
8
Ascorbic 4cid Dry hasis. Grams/liter %
PH
Total Gram;
4.5 3.8 2.6
115.0 1.5 6.5
6.0 0.08 0.34
5.5 0.2 2.9
9.3
0.49 0.47 0.76 1.33 0.72 0.24 0.17 0.13
30.6 35.8
2.3 2.3 2.2 1.8 1.3
.... .. ...
8.9
14.4 25.3 13.6 4.6 3.3 2.5
47.3
30.9 8.4 3.9 6.3 5.4
INDUSTRIAL A N D ENGINEERING CHEMISTRY
390
made to determine the magnitude of t11i.s effect. T v o 65-gram columns of anion exchange resin were carried through successive cycles of adsorption and elution of hull extract in idcntical manner, with the exception that tap water was used throughout (extraction, adsorption, elution, and regeneration) in one case and distilled water in the other. The complet,e treatment from one cycle to the next consisted of regeneration v,ith 3 lit,ers of 2 N hydrochloric acid, Tyashing with 20 liters o€ w-ater to pH 2.7, saturating x-ith hull extract, to more than 20% broak-through, washing with 1 liter of water, and elution with 2 liters of 1.0 N hydrochloric acid, Ti%-enty-onecycles mere run for each of the two columns (Table VI). Marked deterioration of performance with tap mater suggests that a t least one, and possibly more, of the steps in the resin process require the use of distilled or deioniwd water.
Vol. 42, No. 2
elution. The first portion of effluent from each cclumn, representing wash and containing practically no ascorbic acid, was discarded. Eluates from columns 111 to VI, inclusive, \+ere scparat,ed, for each column, into two lots-the high purity eluatca occurring up to the point, of maximum purity and the remainciei coming off thereafter. The high purit'y fraction was removed as product; the remaining eluates were used to elutc the next column. The net load for each column was obtained by subtracting the ascorbic acid in the water washes, which were discarded, from the ascorbic acid in the load of huli extract. The purities of the products from foul. successive coluinns (Table l:II), compared to the avera.ge purity of eluates in Table V, indica t)t, thc. feasibility and advantages of a c o n h u o u s cycle of elution.
CHARACTERISTICS OF THE ELUATES. A typical hydrochloric acid eluate, containing 1.5% ascorbic acid, 0.2% sulfur dioxide, and 3.9y0 total solids, was stored in screwcap glass vials in the dark. After 2 months there was a 9% loss of ascorbic acid a t 5 O C. and a 247, loss a t 22 C. Eluates were fed to rats by stomach tube in amount,s as high as 400 mg. of moisture-free solids per kg. of body COMPARISON O F USE O F TAPTJrATER AKD DISTILLED weight pcr day for 14 days wit,hout ill effect. On an equivalent 'rAH1,IG VI. m A T E R IN I b S I X STEP basis this dosege would supply over one hundred. times the recomOver-all hlax. Zoncn. Max. P u r i t y mended daily requircnient of ascorbic acid for a 70-kg. man. Capacity, Recovery Ascorbic Acid .Iscorbic Acid Cycle Mg. Ascorbic Ascorbic i n Eluates, in Eluates, Isolation of Ascorbic Acid from Eluates Obtained in ResinKO. ~Acid/Ml. Acid, % % "0 Elution Step. ORGAXiC SOLVESTFRACTIONITIOKS. The method DisDisDisDisTap tilled Tap tilled Tap tilled T a p tilled of Bukin ( , I ) , mhich was reported to give a 20% yidd of crystalline ascorbic acid from immature walnuts containing 13 % ascorbic acid on a dry basis, was applied to walnut huli extracts, containing 5 to 7% ascorbic acid (dry basis) and also to resin eluatcs wit,h 25 t o 40y0 ascorbic acid (dry basis). Purification was obtained in both caws, but no crystallizatioii vias achieved in the The data presented thus far on the adsorption and elution step final step. demonstrate a sevenfold, or greater, increase in purity of a subGlacial acetic acid solutioris of the eluates, ii-itli 35 to 45y0 stantial portion of the ascorbic acid in the hull extracts. Howascorbic acid (dry basis), were fractionated by t,he stepwise adever, the concentration of ascorbic acid by volume in the eluates dition of ethyl ether and isopropyl ether. ImpuriLies were prefwas disappointingly lorn. This concentration can be increased to a erentially removcd in the early precipitate fractions, resulting in limited extent by increasing the concentration of the eluting acid a yield of 25% of crystalline ascorbic acid in the final precipitates. but only a t the expense of the purity (percentage of ascorbic acid, However, this method involved the use and recovery of relatively dry basis). Attempts to use other inorganic acids (sulfurous, large volumes of ethers and was discarded in favor of the simple sulfuric, phosphoric) gave no improvement over the use of hydrocryslallization by concentration of the charcoal-treated eluate, chloric acid. which is described: -
_
_
_
I
ELUTION THROUGH SERIES OF RESINC O L U M ~ WITH REMOVAL O F PRODUCT AT EACH STEP
TABLE VII.
xet ~
Column I 11 Ill l,V
Y'I
~
Mg. Ascorbic Acid/Ml. Bed Vol.
5.2 6.6
7.7
8.0 5.5
5.2
Acid Removed a s Product ~Ascorbic d , 70 of Purity, % ascorbic net load acid, dry basis N o remoral N o removal 39
E. .
97 100
The eluates from t,he resin column are light yellow in color. On concentration to 40 to 6070 solids, they develop a brown coloration, which can be removed by the following procedure: eluattw obtained by the multistage elution technique were treated with sulfur dioxide to a concentration of 1% and passed tbrough a filter pad of Korit A, previously washed with 1% sulfur dioxide solution. The minimum quantity of Korit A necessary for decolorization mas used. In three experiments the percentage recovery of ascoroic acid ranged from 85 t o 90%.
dR -"
47 43
l M LOADING ~AKD ELUTING ~ OF RFGSIX ~ CoLmms. ~ Inspectionof the resin elution data (TablesIIIand V) shows that both concentration and purity of eluates rise to a maximum and then fall off, the maximum concentration usually occurring after maximum purity. The hydrochloric acid concentration increases throughout the elution. I t would be desirable to recover the vitamin C in the less pure fractions a t a higher concentration and purity by recycling through a series of freshly loaded columns. Thus the h a 1 eluates from one resin column, containing relatively high proportions of hydrochloric acid and the more strongly held organic acids of the hull, could be used to elute the ascorbic acid from resin columns freshly loaded with hull extract. Experiments involving the use of six resin columns were designed to evaluate such an elution procedure. Six columns in the hydrochloric acid-developed cycle were loaded with hull extract and washed with distilled water. The Erst column was eluted with 0.2 N hydrochloric. Columns I1 and I11 were eluted with the eluates of the preceding column, in order, plus enough 0.2 Ai hydrochloric acid to complete the
~ R Y S T A L L I Z A T I O ~ ~ ~decolorized . eluate containing 23 grams of ascorbic acid a t a purity of 36% was concentrated to about 70% 3olids and allowed to crystallize at, 40" F. for several days. The with absolute alcohol and ~crystals were ~ washed~ several times ~ ~ dried, while the mother liquor and washings were concentrated and chilled to give a second crop of crystals. Yields of 8.8 and 2.7 grains of ascorbic acid were obtained in the first and second crops of crystals, which totaled 11.5 grams, or a 50% yield from the decolorized eluat,e. Reworking of the second mother liquor would probably increase the over-all yield of crystalline product.
DISCU SSlON
The over-all yield from this process can be estimated conservatively a t 25%. Recovery of ascorbic acid in the extraction step can be made practically quantitative, but the most economical point would be somewhat lower. A reasonable estimate of the recovery in the resin step should be based on the amount that could be recovered a t a purity of 3570 or more. With a multistage elution scheme, t'he percentage should range from 70 to 80. Yields in decolorization and crystallization should be 40 to 70%, depending on feasibility of reworking the second mother liquors. A serious practical disadvantage is the very dilute solutions encountered, first in the hull extract, where the 85 to 90% water in the hulls is the limiting factor, and second in the resin eluates,
February 1950
a
INDUSTRIAL AND ENGINEERING CHEMISTRY
where the low capacity of the resin for ascorbic acid is limiting. Means of circumventing these two difficulties would materially increase the economic feasibility of the process. There is a good possibility that characteristics of the anion exchange resin could be modified to give a much greater capacity for ascorbic acid. A preliminary economic study of the process as it might be applied to a typical walnut-growing district, was made at this laboratory. Based on the availability of 5000 tons of hulls (containing 25 tons of ascorbic acid) in a localized area over a 30-day period, and a 25% yield, it was estimated t h a t recovery of $100,000 worth of ascorbic acid per year would require a capital investment of $300,000 which is too high to make the process attractive commercially. Of this $300,000, $175,000 is required for equipment to recover and concentrate the walnut-hull extract. This rather high cost of extraction and concentration equipment is a consequence of the large volumes of dilute solutions that would be handled during only 1 month of the year, and the corrosive nature of the solutions*which necessitates stainless steel or other resistant material. Lengthening of the processing season by a n inexpensive method of storing green hulls and increasing the over-all yields would materially decrease the ratio of capital investment to annual value of product.
39 1
clude: H. D. Lightbody, W. B. Van Arsdel, W. D. Ramage, J. H. Thompson, A. H. Brown, and P. W. Kilpatrick. The late Clyde Barnum provided technical information and assistance in the procurement of raw materials, and A. W. Christie, Grant Burton, C. C. Anderson, Edward Bunker, and others in the California Walnut Growers Association gave helpful assistance. LITERATURE ClTED (1) (2)
Bukin, V. N., and Garkina, I. N.,B i o k h i m i y a , 7, 59 (1942). Gherghelenhiu, A. K., B u l l . A p p l i e d B o t a n y Genetics P l a n t
Breeding ( L e n i n g r a d ) , Suppl. 84, 206 (1937). (3) Hennig, K., and Ohske, P., Biochem. Z., 306, 16 (1940). (4) Klose, A. A., Peat, Jean, and Fevold, H. L., P l a n t Physiol., 23, 133 (1948).
(5) Loeffler, H. J., and Ponting, J. D., IND. ENG.CHEX.,ANAL.ED., 1 4 , 8 4 6 (1942).
(6) Matchett, J. R., Legault, R. R., Nimmo, C. C., and Notter, G. K., IND. ENG.CHEY.,36, 851 (1944). 152, 447 (7) Melville, R., Wokes, F., and Organ, J . G., -\'ahre, (1943).
( 8 ) Mottern, H. H., and Buck, B. E., U. S. Patent 2,433,583 (June
ACKNOWLEDGMENT
15, 1948).
V. F. Kaufman of this laboratory made the economic study and supplied the cost data. Hans Lineweaver determined the ascorbic acid oxidase in walnut hulls. Others in the Western Regional Research Laboratory t o whom the authors are indebted in-
(9) Pyke, M., Melville, R., and Sarson, H., N a t u r e , 150, 267 (1942). (10) Wokes, F., Organ, J. G., Duncan, J., and Jacoby, F. C., Biochern.
J., 3 7 , 6 9 5 (1943). RECEIVED June 13, 1949.
Isothermal and Isobaric Degassing of Ice Cream ALFRED LACHMANN, E. L. JACK, AND D. H. VOLMAN University of California, Davis, Calif. T h e effect of degassing ice cream of definite composition has been studied. The air liberated from the ice cream structure was measured quantitatively under controlled temperature and pressure conditions. I t has been observed that the amount of air liberated from the ice cream is related to both the temperature and the pressure to which the ice cream is subjected. This relationship can be used for a determination of the strength and permeability of a particular ice cream structure.
T
HE degassing of ice creams isothermally and isobarically has
been investigated with particular reference to the amount of air liberated and its relation to the strength and permeability of the ice cream structure. When air escapes from ice cream a decrease of ice cream volume is observed at certain pressures and temperatures. The amount of air liberated depends partly on the structural strength and permeability of an ice cream of fixed composition. The strength of the structure may be weakened by a multitude of factors. I n addition t o the composition of ice cream, the manufacturing procedures are of great importance and can influence the stability of the ice cream mix. Homogenization pressure, different freezing techniques, percentage of incorporated air (overrun-Le., the increase in volume of the ice cream over the volume of mix expressed as per cent of the volume of mix), temperature changes in hardening room and storage cabinet are only some of the factors which play a great part in the structure of the final ice cream product. On the basis of results of a large number of investigations, various theories have been proposed interpreting the weakening of the ice cream structure (1-13).
From all the studies it is to be expected that fracture of air cells enclosed in the ice cream structure would be accompanied by diffusion of the incorporated air from the ice cream. The diffusion rate is related t o the rigidity and permeability of the particular ice cream structure. Therefore, the change of' external temperature and pressure and its effect on ice cream in relation to the amount of air liberated can give information about the strength and imperviousness of ice cream if the volume of air liberated a t selected temperatures and pressures is measured quantitatively. No publication of this type of investigation has been reported. APPARATUS
Figure 1 shows the apparatus used in the investigations. It is composed of the reaction chamber containing a weighed amount of ice cream of a definite composition. This vessel has the shape of a large test tube with a capacity of approximately 350 t o 375 ml. Its opening is wide enough to allow an easy drawing of the ice cream into the container from the freezer unit. A Dewar flask filled with an alcohol-dry ice mixture provides the cooling at the desired experimental temperature. The gas buret of 50-ml. volume graduated in 0.1 ml. is used to measure the volume of air liberated. It is immersed in a water jacket to keep the temperature constant during the investigation. The bottom of the buret is connected with a mercury reservoir permitting pressure regulation by manipulation of the stopcock. With this arrangement no leveling bulb is necessary, With a water aspirator, the desired pressure is obtained and measured by the attached mercury manometer. PROCEDURE
PREPARATION OF ICECREAM. Fresh cream of 30 t o 35% fat, milk, skim milk, and condensed skim milk of approximately 35y0 total solids were the milk products used for the experimental mixes. The composition of the ice cream mix was as follows:
