/?. C . B u c k a * t d t M . o 4 . M o tt& u t EASTERN R EG IO NA L RESEARCH LA BORATORY
U. S. DEPARTMENT O F AGRICULTURE PHILADELPHIA 18, P A.
M
ANY atte m p ts have been m ade to produce an apple sirup of satisfactory flavor for food uses. An apple sirup developed in this laboratory has found industrial application as a m oisture-retaining agent because of its high levulose content (1, 7). I t is objectionable for food uses, however, because of a slightly b itte r aftertaste due to th e calcium m alate formed in th e liming process.
T he ability of ion exchangers to remove acid an d basic constituents from solution sug
gested th eir possible use in preparing an edible sirup. Rem oval of malic acid prior .to liming w ould prevent th e form ation of calcium m alate.
I t was th o u g h t th a t ion exchanger treatm en t m ight also reduce the lead and arsenic contents.
A num ber of applications of ion exchangers to process industries have been reported. Englis and Fiess (3) sta te th a t elim ination of th e acid an d m ineral constituents from artichoke ex
tra c t by ion exchangers produced a sirup of im proved quality and flavor. T hey found th a t th e ash content was reduced to about two thirds of its original value by one cation exchanger trea tm e n t an d to one fourth by two tre a t
m ents. Aside from th e effect b n the p H value of the extract, no d a ta were reported on the actual am ount of acid constituents removed by th e anion exchanger. Io n exchangers removed 87% of nonsugar solids from beet an d sugar cane juices {11, 14)', th ey were slightly more effective in removing inorganic th an organic impurities. T he trea tm e n t also resulted in an increased p u rity an d higher yields of sugar.
T he usual procedures for m aking apple sirup include neutralization of th e acid w ith lime,
calcium carbonate, or alkali carbonate (i, %, 4, 5, 7, 10). This treatm en t, however, im p arts undesirable flavors. H aines (6) added sugar to dilute the acid, which is common practice in preparing m any fruit sirups. T he apple sirup developed in this laboratory an d used as a tobacco hu m ectan t (1, 7) is prepared by liming apple juice to a pH value of 8.0-8.5 to hydrolyze and precipitate th e pectin, heating to 80° C., filtering, reacidifying to a pH value of 5.0-5.5 to im prove color an d flavor an d prevent alkaline oxidation of sugars, and concen
tratin g under vacuum to a to ta l solids content of approxim ately 75% . T he procedure described in this paper is similar, w ith the addition of ion-exchanger tre a tm e n t before the l i m i D g step.
EXPERIMENTAL PROCEDURE
Before being passed through th e exchanger beds, the juice was trea ted w ith activ ated carbon1 and filtered w ith th e aid of dia- tomaceous earth of m edium porosity to rem ove colloidal m aterial th a t m ight be absorbed by th e exchanger w ith consequent reduc
tion of its effective capacity. T he clear filtrate was th en treated
Figure 1. 4-Inch Exchanger Columns of Standard Pyrex Pipe and Flanges, with Saran Fittings; (Above) Means of Attaching Saran Fittings to Pyrex Pipe
w ith the ion-exchanger m aterials as described. A fter being treated , it was heated to 57° C. (135° F.) and limed u n til a flocculent precipitate appeared, usually a t a p H value of 8.0 to 8.5. I t was th en filtered, reacidified w ith citric acid to a p H of 5.0 to 5.5, an d evaporated under vacuum to 75% to ta l solids.
Glass columns of 1-inch (25-mm.) and 4-inch (100-mm.) inside diam eters were used for exchanger beds. T he volum es of the beds were approxim ately 200 ml. an d 7.5 liters, respectively.
T he 1-inch columns were set up in th e conventional m anner (9).
T he 4-inch columns (Figure 1) were constructed of sta n d ard 5- foot lengths of 4-inch Pyrex piping. T he ends were closed by Saran flanges cut from a Vs-inch sheet, backed by a Vi-inch steel plate, and bolted to the piping w ith C om ing companion flanges.
T he d a ta reported here were obtained w ith th e 1-inch laboratory columns, although sim ilar results were obtained w ith the 4-inch columns.
1 L a te r w ork h a s sh o w n t h a t ca rb o n tr e a t m e n t is u n n ecessary a n d t h a t passage of screened (150-mesh) b u t u nfiltered ju ice th r o u g h th e exchangers reduces th e c a p a c ity b y o n ly 10 to 1 5 % . B efore th is p ro ce d u re ca n be rec o m m e n d ed , h o w ever, f u r th e r w ork m u s t be d o n e to d ete rm in e w h eth e r th is r ed u c tio n is cu m u la tiv e o r c o n s ta n t.
I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 37, No. 7 becom es necessary, a two-step (cation-anion) or a three-step (anion- cation-anion) exchanger treatment must b e used. A s much as 9 6 % per square foot of cross-sectional area. T his q u a n tity of regener- a n t was probably in excess of th e am ount actually needed b u t was used to ensure com plete regeneration. T o regenerate the cation beds, tw o volumes of 2% , or one volume of 4% , hydro
chloric acid per volume of exchanger were found sufficient. T he excess of regenerant was rinsed o u t downflow w ith w ater. T he rinse w ater for th e anion beds was softened b y passage through a cation exchanger to avoid precipitation of insoluble carbonates by h ard w ater. T he progress of th e reaction as th e juice passed anion exchangers th ere was a gradual change, an d the end p oint of th e run capacity, in term s of equivalents of ions rem oved, is n o t practical in th e case of apple juice because of its complex an d varying removed a slightly sm aller am ount, as T able I shows.
Table I. A sh Removed from A p p l e Juice by Cation Exchangers
July, 1945 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 637
Figure 4 . Effective Capacities of Cation and A nion Exchangers T he capacity of a cation exchanger natu rally
varied w ith the ash content of the juice. T he tests ju st described were conducted on the same lo t of juice; for different juices the capacities ranged from 10 to 40. the average being between 15 and 20.
T he capacities of the different anion ex
changers for the sam e juice varied over a wide range (Figure 4). T he rapid drop in pH value shown by curves C and D indicates th a t the capacities of these two exchangers were low.
Capacities of A and B were nearly equal and considerably higher th an those of C and D.
Ju i c e s o f Di f f e r e n t Ac i d i t y. Juices hav
ing a malic acid content ranging from 0.12 to 0.49% were used w ith anion exchanger A (Figure 5). T he capacities ranged from 12 to 40 volumes and, in general, varied inversely w ith the acidity of the influent. However, the relation was n o t exact enough to use acidity as a means of predicting capacity. T he reversal of order betw een juices V and VI m ight have been due to q ualitative differences in the anions of the juices and their differential adsorption by the exchanger. T he following generality m ay be permissible and useful: F or apple juices of average acidity, 0.3 to 0.4% , the capacities of goed anion exchangers range from 15 to 20.
M ETHO DS FOR USING I O N EX CH AN G E RS
Three methods of treatin g apple juice have been tested: (I) single trea tm e n t w ith an anion exchanger; (II) trea tm e n t w ith a cation exchanger followed b y trea tm e n t w ith an anion exchanger;
and (III) trea tm e n t first w ith an anion exchanger, th en w ith a catioD exchanger, and lastly w ith a second anion exchanger (sug
gested by F . I. L. Lawrence). Consideration was given to two other possible m ethods. One consisted in trea tin g a limed juice by m ethod I I . T his imposed a heavy load on the cation ex
changer, owing to th e added calcium, an d was therefore aban
doned. T he other involved th e use of a pectin-hydrolyzing en
zyme before th e anion exchanger trea tm e n t in m ethod I, b u t this proved more expensive th a n th e liming process and also produced darker sirup.
T he sim plest treatm ent is a single passage of the juice through an anion exchanger (m ethod I). Figure 3A shows typical curves for pH an d acidity of successive portions of the effluent juice; Figure 6 shows th e percentage of acid removed from the combined effluent. From the th irte en th volume of the effluent, only ab o u t 50% of the acidity of the influent had been adsorbed, whereas from the combined 13 volumes about 82% of the acid had been removed. This represents an
adsorption of about 47.5 grams of malic acid per liter, or 3 pounds per cubic foot of exchanger.
Since m ost of th e free acid is removed by this treatm en t, only 0.020 to 0.025%
lime is necessary to bring the pH value to 8.5 to hydrolyze the pectin, as com
pared w ith 0.25 to 0.30% required with
o u t anion-exchanger treatm en t. This liming process causes no increase in ash content; in fact a slight reduction m ay occur, probably because the added lime is precipitated as calcium pectate. Con
siderable color is occluded in th e pectin precipitate. A fter the juice is filtered, only a sm all am o u n t of citric acid is necessary to ad ju st th e pH value to
betw een 5.0 and 5.5 before concentration. Removal of the malic acid prevents the form ation of calcium m alate and thus pre
vents the b itte r afte rtaste characteristic of sirups prepared w ith
o ut this treatm en t. T he sirup contains the n a tu ral ash b u t has little flavor other th an sweetness. Addition of the recovered volatile constituents of the juice produces a sirup w ith a pleasing apple flavor.
Although m ethods I I and I I I effect a more complete removal of arsenic as compared w ith m ethod I, flavor im provem ent is n ot sufficient to justify th eir use unless arsenic removal is necessary.
Rem oval of arsenic is discussed in a later section.
In m ethod I I passage of the juice through the cation exchanger before passage through the anion exchanger converts combined acid to free acid an d perm its m ore complete adsorption of the anions. F.gure 2 shows the ash, acidity, and pH values of the effluents from th e cation and anion exchangers. T he cation- exchanger trea tm e n t reduced the ash content by about 90% and increased th e acidity from 0.43 to 0.64%. T he increase in acidity reduced the volume of juice which could be trea te d by the anion exchanger in the next step, only four volumes passing through
Figure 5. Effective Capacities of A n ion Exchanger A with Juices of Different A cid ity
pH OF I N F L U E N T
N EX C H A N GE R S
I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 37, No. 7 m ethod I I , by operating the first anion exchanger to a greater de
gree of satu ratio n and using the second one as a scavenger to ad sorb the acid th a t passed through the first. T he acidity and pH value of the effluent from the second anion exchanger were so low th a t a pH value of 5.0 for the combined effluent was n ot practical
centration of juice to sirup, it was considered ad
visable to determ ine the extent of lead and arsenic removal by ion exchanger treatm ent. W illits and T ressler (IS) found th a t the base exchange m aterial Zeo-Karb reduced the lead content of m aple sap from as m uch as 36 p.p.m . to 1 p.p.m.
or less. Lead is not so great a problem as arsenic, however, inasm uch as the liming process for pre
cipitation of pectin removes alm ost all of the lead. In one instance liming w ithout an anion exchanger treatm en t reduced the lead from 0.004 to 0.0002 grain per pound; in another case, after an anion exchanger treatm ent, liming reduced i t from 0.005 to less th an 0.0001 grain per pound.
Passage through anion exchangers generally re
m oved 20 to 50% of the lead, probably by pre
cipitation as th e hydroxide, since the pH in
creased as the fru it acids were removed. A cation exchanger removed only a bout 50% of the lead, possibly because of its presence in an un-ionized form.
Arsenic analyses were m ade on th e juices (Table I I) b u t were calculated to the basis of a sixfold concentration of juice to finished sirup, since the tolerance applies to the la tter. A lthough m ost of the samples were low in arsenic, th ey exceeded th e tolerance, especially sam ple 1, which was pressed from peels an d cores.
Since single passage of juice through an anion exchanger (m ethod I) removed a sm all an d variable am o u n t of arsenic, th is m ethod would n o t be satisfactory for juice containing excessive am ounts.
However, adequate w ashing of the fru it before pressing m ight m ake this simple tre a tm e n t satisfactory. T o ensure a m ore com
plete rem oval of arsenic, other ion exchanger trea tm e n ts could be used.
In m ethod I I passage of th e juice th ro u g h th e cation ex
changer prior to passage th rough the anion exchanger increased th e adsorption of arsenic. Exchangers of m an u factu rer A re
moved 50 to 80% of th e arsenic; exchangers of m an u factu rer B removed a sm aller an d more variable am ount.
By th e three-step trea tm e n t (m ethod I I I ) , exchangers of
generation as ordinarily practiced com pletely removes the arsenic from the exchanger. R em oval, however, m ig h t be effected by seventy-five cycles w ith no noticeable loss in capacity.
A C K N O W L E D G M E N T
The authors wish to acknowledge th e assistance of Infilco, The P e rm u tit Com pany, R esearch P ro d u cts C orporation, and The
July, 1945 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 639
Resinous P roducts & Chemical Com pany, which furnished the exchangers and gave helpful advice in carrying o u t the experi
m ents. T he contributions of C lara D ay R ehrig and N ancy O’Connell Buck (formerly of this laboratory), who assisted in the analytical determ inations and routine tests, are also ac
knowledged.
LITERATURE CITED
(1) Bradshaw , M . A., and M ottern, H . H „ Bur. of Agr. Chem. and Eng., Mimeograph Circ. ACE180 (1942); Fruit Products J ., 21, 356-8 (1942); Food Industries, 14, No. 12, 62-3 (1942).
(2) C harley, V. L. S., H opkins, D. P ., and Pollard, A., Fruit Prod
ucts J ., 21, 300-1 (1942).
(3) E n g l is , D. T., a n d F ie s s , H . A., In d. En q. Ch e m., 34, 864-7 (1942).
(4) Gore, H . C., U. S. D ept. Agr., Y earbook, pp. 227-44 (1914).
(5) Gore, H . C., U. S. P a te n t 1,141,458 (1918).
(6) H aines, C. W ., U. S. P a te n t 1,965,286 (1934).
(7) M ottern, H . H ., and M orris 3rd, R . H ., Bur. of Agr. and In d . Chem., Mimeograph Circ. AIC37 (1944).
(8) M yers, F . J „ I n d . E n q . C h e m . 35, 859-863 (1943).
(9) P e rm u tit Co., M im eograph, Suggestions for E x p tl. Use of Ion Exchangers in Process Industries, 1942.
(10) Poore, H . D ., Fruit Products J ., 14, 170-3, 201-3 (1935).
(11) Rawlings, F. N ., and Shafor, R. W ., Sugar, 37, N o. 1, 26-8 (1942).
(12) Resinous Products & Chemical Co., “ T he A m berlites” (1941).
(13) Tiger, H . L ., and Sussman, S., I n d . E n o . C h e m . , 35, 186-92 (1943).
(14) W eitz, F . W ., Sugar, 38, N o. 1, 26-31 (1943).
(15) Willits, C. O., and Tressler, C. J., Food Research, 4, N o. 5, 461-8 (1939).