Extraction of Aconitic Acid from Sorgo EMIL K. VENTRE, J. A. AMBLER, H. C. HENRY', S. BYALL, AND H. S. PAINE2 U. S . Department of Agriculture, New Orleans, La. Aconitic acid in the sorgo plant occurs both as free acid and combined with the cations of the juice. The aconitate precipitated from sorgo juice contains magnesium as well as calcium. Efficient precipitation of the aconitate re-
quires concentration to a density of 50" to 60' Brix and heating to temperature above 75' C. Almost twice as much aconitate was precipitated by using lime and calcium chloride as by using lime alone.
A
acid in the juices. Likewise, for the 1942 season the titratable acidity calculated as aconitic acid was:
CONITIC acid (1,2,3-propenetricarboxylicacid) was discovered in 1820 in Aconitum napellus by Peschier (e), and 4nce then numerous investigators have reported aconitic acid in sugar cane juices and its products. The early literature contains only two references to the occurrence of aconitic acid in qorgo. Parsons ( 5 ) reported the calcium salt of aconitic acid deposited on the heating surface of evaporating pans used to concentrate sorgo juices which had previously been limed to neutrality. Wiley and Maxwell (10) reported a qualitative determination of the acids occurring in the sorgo plant and considered aconitic acid to be first in order of the proportions of the acids determined. These early investigators did not report the aconitic acid content of the sorgo juices and there was no reason to expect that the sorgo plant could be a source of aconitic acid. Ventre (7) and Ventre and Paine (9) reported that the calcium salt of aconitic acid interfered with the extraction of sucrose from the sorgo plant, and devised a method for separation of calcium aconitate as a by-product in manufacture of sugar from sorgo. Table I presents analyses of sorgo juices processed a t the pilot plant located a t the U. S. Department of Agriculture's Sugar Plant Field Station, Meridian, Miss., during the 1941 and 1942 seasons. Some runs consisted of only one variety, and other runs were of mixed varieties. 1941 was a normal growing season and all the runs were harvested in the dead-ripe stage of maturity. 1942 was a "late" season, and the sorgo was harvested in the ripe ytage of maturity. Table I shows a lower average percentage of Brix solids, a lower titratable acidity, and a lower aconitic acid content in the ripe stage as compared with the more mature deadripe stage, an indication that all three of these characteristics of the juices increased with maturity. There was considerable variation in the aconitic acid content of individual lots of the same variety through each season. This also applies to the titratable acidity; while in general it may be said that the titratable acidity increased when the aconitic acid content increased, the data in Table I do not give a smooth correlation. Titratable acidity measures the free acid content of the sorgo juice; it may consist entirely of aconitic acid or may consist of other acids that are known to occur in sorgo. If we calculate the average titratable acidity as aconitic acid and compare it with the average aconitic acid content of the juices, we find that aconitic acid cannot occur wholly as the free acid. This is evident if we take the free acidity of the 1941 season and calculate it as aconitic acid:
4.8 cc. X 0.0058 10 cc. X 1.078 X 0.1944
-
3.6 cc. X 0.0058 10 cc. X 1.072 X 0.1807
However, the total aconitic acid solids content was 2 X % , of which only (1.07 X 100)/2.85, or 37.54%, could occur as free aconitic acid. The more mature cane of the 1941 season had a lower ratio of free acid to total aconitic acid than the less mature cane of the 1942 season. The combined aconitic acid is easily liberated by mineral acids and is capable of reacting by double decomposition with other salts. Therefore, it would seem that the combined aconitic acid is present as soluble aconitates of the cations in the juice. Since
TABLEI. ACONITICACID, TITRATABLE ACIDITY,AND BRIX SOLIDSIN SORGO ~UICES
Dead-Ripe Stage of Maturity, 1941 Season Straight Neck & 6.0 Early Folger 8-15-41 18.60 4.5 8-19-41 17.77 S.A. 287C 4.5 8-20-41 18.12 S.A. 287C 5.2 8-26-41 19.37 S.A. 2870 6.4 8-28-41 20.16 S.A. 287C 9-3-41 6.0 17.78 Straight Neck ABC 19.43 5.0 9-5-41 Colman Y1 4.8 9-9-41 20.17 8.A. 287C Early Folger 16154 9-11-41 20.78 5 .9 & Red X 3.2 9-16-41 18.96 Iceberg 6 .3 9-18-41 21.48 S.A. 2870 3.6 9-22-41 18.58 Icebsrg & Red X 9-24-41 20.82 4.1 Collier 9-26-41 19.89 4.7 Straight Neck 5.8 9-29-41 19.74 ' S.A. 287C Average 19.44 4.8
2
1.33QJo
Present address, 1547 Eugene St., Baton Rouge, La. Present address, 25 Devon Way, Haatings-on-Hudson, N.
3.80 4.26 3.83 3.58 3.44 6.23 4.17 4.96 4.81 3.96 5.24 5.38 4.56 5.65 4.27 4.47
Ripe Stage of Maturity, 1942 Season 8-25-42 15.30 2.72 3.0 3.55 9-4-42 16.44 2.7 2.60 9-1-42 17.16 2.9 2.55 9-8-42 17.01 3.0 9-2-42 2.70 17.28 2.6 2.24 9-9-42 19.39 3.6 2.75 9-15-42 20.60 4.0 2.02 2.1 9-10-42 17.17 2.53 9-16-42 19.28 4.0 3.54 9-21-42 20.04 4.6 2.30 9-17-42 3.0 16.68 2.54 19.69 9-22-42 5.7 3.31 17.65 9-23-42 3.7 3.73 15.61 9-24-42 3.9 3.21 4.4 18.16 9-28-42 2.74 20.09 9-29-42 4.5 2.66 4.1 18.80 9-30-42 3.12 19.00 10-1-42 4.4 Average 18.07 3.6 2.85 !rhe determination of aconitic acid was the authors' adaptation of the color reaction of C. 8 Taylor J . Chem. Soc 11% 886 (1919)l a8 modified by 0. Furth and H. Herimann &iochem. Z.,280,448-57 (1935)l.
Red X S.A. 287C S A . 287C S.A. 287C S.A. 287C Straight Neck S.A. 287C Ga. Blue Ribbon S.A. 287C Straight Neok S.A. 287C Straight Neok S.A. 287C S.A. 2870 Straight Neok Straight Neok Straight Neok Straight Neck
The total aconitic acid per cent solids for this season was 4.47% of which only (1.33 X 100)/4.47 or 29.53% could occur as free 1
- 1.07%
Y.
201
202
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 38, No. 2
which plays a role in the precipitation of insoluble aeonitate
TABLE 11. FLOW SHEETOF ACONITICACID IN SUGARILIANU- from the juice. FACTURING PROCESS Table I11 gives some analyses of the insoluble aconitate ob(Juices treated with lime only; dead-ripe stage of maturity; average determinations of ten . pilot-ulant runs) . Aconitic % Brix Purity, .+id, % Material Solids 7c pH Brix Solids Raw juice= 19.70 71.30 4.85 4.68 4.92 Centrifuged juice 19.36 73.02 Cold limed juice 10:07 19:io 74:23 8.2 4:,53 Defecated juice Sirup 60.70 75.99 7.5 4.59 Defecated sirup 59.54 77.35 6.67 2.67 R a w juice average acidity, 4.9 cc. of 0.1 N NaOH per 10 cc.: average removal of aconitic acid by analysis, 42.93% of total acid; yield of washed and dried aeonitate, equivalent t o 40.77% of total acid.
the predominating cation in plant juices is potassium, it follows that the combined aconitic acid is probably present in thc juice in large part as potassium aconitate. METHOD OF EXTRACTION
For the most efficient utilization of the sorgo plant, the aconitic acid must be necessarily extracted as a by-product in the manufacture of the principal commercial constituent of the juicenamely, sucrose. Aconitic acid is remoyed from the evaporator sirup by heating the sirup above 75" C. and separating the aconitate precipitated, which is principally calcium aconitate. The principal influencing factor o n aconitic acid removal from sorgo juice from which the starch has been previously removed is the quantity of lime that may be added to the juice. The use of lime for the neutralization and clarification of the sorgo juices from which sugar is t o be extracted permits the introduction of a quantity of lime sufficient t o neutralize the free acid of the juices; however, it has just been shoxn that this amount of lime would only be equivalent to 29.53 to 37.547, of the amount required to combine with t,he total amount of aconitic acid occurring in the juices. The addition of lime much in excess of the quantity required t o neutralize the free acid results in such high alkalinities that the monosaccharides of t,he juices are decomposed with the formation in the juices of undesirable products. The liming of the juices should be controlled so that, when the sirup is heated, the pH drops to just below 7.0. It was found that sirups having a pH over 7.0 after being heated did not precipitate a granular aconitate but produced an amorphous precipitate that was water soluble and could not be recovered from the sirup. Table I1 presents a flov sheet of aconitic acid in the sorgo juices and sirups a t different stages of the sugar manufacturing process. The removal of aconitic acid was practically negligible previous to the heat treatment of the sirups. Theoretically, the calcium that could be introduced by ncut'ralization of the free acid was equivalent, on the average, to
4.9 cc. x 0.0058 1.33% aconitic acid 10 cc. x 1.080 x 0 . 1 9 m = which was
4.68
loo= 28.41% of total aconitic acid in juice.
Therefore. in these runs this value represents the average removal of aconitic acid as calcium aconitate to be expected by neutralization with lime. Howwer, the average removal actually obtained was 42.95y0. This increased removal over that which would be expected is undoubtedly due to the occurrence in raw sorgo juice not only of calcium but also of magnesium,
tained from sorgo and sugar cane products. The only recorded analysis of this material obtained from sorgo is by Parsons (6). Unfortunat,ely he did not dctermine aconitic acid directly, but assumed that it T-ias represented by the remainder left after all the mineral matter and "moisture" a t 125' C. had been determined. It is now knoivn ( 1 ) that, drying a t 125 ' removes only an indefinite portion of t'he water of crystallization from the aconitate. Consequently his "organic matter by difference" represents not only the aconitic acid present, but includes an uncertain amount of water, and his formulas for the aconit,atcs are in error. However, there is no'reason to suppose that his analyses of the mineral constit'uents are in error. He found a significant amount of magnesium oxide which, he believed, was probably present in the material as the oxide or hydrate, held in colloidal suspension in the juices after liming until occluded in the precipitate of calcium aconitate. Until recently it was generally accept'ed that the magnesium in the natural aconitates from both sorgo and sugar cane products is present as either the hydrate or t,he carbonate (6). The only other recorded analyses of such aconitates are given by McCalip and Seibert (4), as Table I11 sliom. They obtained their material from sugar cane products. These investigators reported much higher contents of magnesium oxide buit st,ated that no carbon dioxide was evolved when the insoluble sediments were dissolved in hydrochloric acid. Therefore, neither thc mngnesium nor t,he calcium could have been present as carbonate. During recent studies on aconitic acid, many analyses of the insoluble aconitates obt,aincd from sorgo and sugar cane products have been made; a few are given in Table 111. All of theso precipitates contained varying but significant percentages of magnesium but no detectable amounts of carbonates. By calculat,ing the percentages of the constituents of the aconit,ates as chemical equivalents and comparing the basic and the acidic equivalents (as in Table IV), it is evident that t>liecalcium oxide does not furnish enough basic equivalents to equal (Le., to neutralize) the acidic equivalent,s of the aconitic acid. Thercfore, the combinat,ion of the calcium oxide prehent with the aconit,ic acid present would leave an excess of the latter, or would result in the formation of an acidic aconitate. But either an excess of aconitic acid or an acidic calcium aconitate Tvould neutralize magnesium oxide or hydrate in suspension in t'hc original solution (1) since none of these possible react'ants is so insoluble that the basic ones would not neutralize the acidic ones in aqueous media such as juices and sirups. Therefore, Parsons' idea of the presence of free magnesium oxide in the insoluble aconitates is untenable. This is also shown by balancing the total major basic equivalents with t'he total major acidic equival e n t ~as ~ ,in Table IV. If the equivalents of the calcium and magnesium oxides are added and the acidic equivalents of the sulfur trioxide are subtracted from this sum, it is found that the remain8 Equivalents for Si02 are ignored, since silicic acid is but slightly acidic and its salts are highly hydrolyzed in dilute solution.
TABLE 111. ANALYSESOF INSOLUBLE ACONITATES FROM SORGO AND SUQABCANEPRODUCTS Aconitic CaO, MgO, MgOsa, SiOz, SOa, PzOs, Alkalies, Source Acid, % % F % % % % % h Trace 0.57 1.57 0.19 22.87 3.65 Sorgo ( 6 ) Trace 0.73 3.61 Trace 67.81 25.98 Sorgoc o:is 010 ... 0.14 23.9 3.3 Sorgo 59.3 0.07 0.03 0.37 39.2 23.4 3.8 Sorgo ... 6.61 5.76 23.96 Sugar caned 56.98 0.13 0.78 2:35 ... 4.08 9.78 15.66 Sugar cane (4) 56.21 ... Trace 3.58 0.66 1.25 11.98 Sugar cane (4) 57.44 13.58 a M 2 0 3 = total Fez03 MzOa, etc. b Organic matter by difierence 63.67%. C This analysis was made by tde late E. IC Nelson, U. S. Department of Agriculture. d Acknowledgment is made t o C. A. Fort, U. S. Department of Agriculture, for this analysis.
..
...
...
Moisture,
%
7 . 4 8 (125' C.) 8.18 (105' C.)
... ,..
February, 1946
INDUSTRIAL AND ENGINEERING CHEMISTRY
ing basic equivalents are practically equal to the acidic equivalents of the aconitic acid, which indicates that the insoluble aconitates are neutral salts. More recently Ventre and Paine (9) considered these materials as mixtures of calcium and magnesium aconitates. However, it has not been possible to remove the magnesium by leaching with water or with calcium chloride solutions. If the insoluble aconitates were physical mixtures, it should be possible to wash the very soluble magnesium aconitate (8) out and leave behind magnesium-free calcium aconitate. The facts given above lead to the conclusion that the natural insoluble aconitates must be double salts of aconitic acid with calcium and magnesium, or mixed salts of a more complex nature. This was confirmed by Ambler, Turer, and Keenan ( 1 ) by means of chemical and microscopical studies of insoluble aconitates prepared under different conditions from solutions containing varying proportions of calcium and magnesium. Solutions which contained no magnesium and which were maintained a t temperatures below 70" C. deposited crystals of the hexahydrate of tricalcium aconitate; but if kept a t temperatures above 80" C., they deposited the trihydrate of tricalcium aconitate. Solutions which contained amounts of magnesium greater than 6T0 of the weight of the calcium present deposited, a t temperatures up to 100" C., crystals which contained both calcium and magnesium and which were always hexahydrates. When these different crystalline preparations were examined under the microscope and compared with the natural insoluble aconitates, the crystals of the latter were different from those of the tri- and hexahydrates of tricalcium aconitate, but were identical in optical-crystallographic properties with the crystals containing both calcium and magnesium. A few of the laboratory preparations of the calcium-magnesium aconitate contained sufficient magnesium oxide (7.6, 7.1, 7.68% MgO; average 7.4%) t o correspond to the formula for dicalcium magnesium aconitate hexahydrate, CazMgAconz.6Hz0 (theoretical MgO = 7.27%), but most of them contained less magnesium oxide than this formula would require. However, all of them showed the same crystalline characteristics, and no crystals of either the tri- or hexahydrate of tricalcium aconitate could be detected in them. Specimens were prepared whose magnesium oxide content varied between 1.9 and 7.6%. I n each case, however, the sum of the equivalents of the calcium oxide and the magnesium oxide equaled the equivalents of the aconitic acid, as noted above in the cases of the natural materials. The results indicate that calcium and magnesium form a double salt with aconitic acid, and that this double salt can, and generally does, form homogeneous mixed crystals or solid solutions with tricalcium aconitate hexahydrate4. This explains the fact that it is impossible to separate the two salts by leaching or by any mechanical means. Solid solutions are more insoluble than either of the salts comprising them, and this accounts for the facts that dicalcium magnesium aconitate is so rarely formed and that tricalcium aconitates will not form if much magnesium is present in the solution. When the dry salts are heated, the crystals of tricalcium aconitate hexahydrate lose water of crystallization more easily than the crjstals of the calcium-magnesium aconitate hexahydrate. Whereas the former began to lose water a t 70" to 75" C., and lost four of the six molecules of water a t 120" C., the solid solutions did not begin to lose weight until heated to 80" C., and did not lose four molecules of mater until the temperature reached 140" C. Temperatures above 250" C. are required to remove the water completely from either of them. Crystals of tricalcium aconitate trihydrate lost no water when heated to 140°C. 4 I t may also be reasoned t h a t trimagnesium aconitate crystallizes with tricalcium aoonitate to form the series of salts heinn discussed. At present it is merely a n academic question as t o which is the correct way t o interpret t h e results. Practically, i t makes no material difference.
203
TABLEIV. EQUIVALENTS OF CONSTITUENTS OF INSOLUBLE ACONITATES
A Aconitic Acid
E
Source CaO Sorgo (6) 0.816 Sorgo" i:iSg 0.927 Sorgo 1.022 0,852 Sorgo 1 . 0 2 0 0.835 Sugar cane* 0.982 0.854 0.969 0,559 Sugar cane (4) Sugar cane (4) 0 , 9 9 0 0 , 4 8 4 a See Table 111, footnotec. b See Table 111, footnoted.
C
D
MgO 0.182 0.179 0.163 0,187 0.285 0.483 0.594
SOs
E (E
... ,..
0:OOl 0.165 0.102 0.031
+ C - D) 0,998 1.106 1.015 1.021 0.974 0.940 1.047
F
Ratio E/A 0:947 0.993 1.001 0.992 0.970
1,057
TABLE V. FLOWSHEETOF ACONITICACID IN SUGARMANUFACTURING
PROCESS
(Juices treated with lime and calcium chloride from typical pilot-plant run) Total P u i i t y of Aconitic yo Brix Sucrose, Acid, % Materiala Solids % Brix pH Biix Solids Raw juice 19,82 72.41 4.85 3.12 Limed juice 8.32 Defecated juice 19:08 76: 59 8.10 3:o Sirup 66.42 76,50 7.52 2.86 Defecated sirup 65.26 79,66 6.80 0.57 5 Calcium chloride added equivalent to 60% of total aconitic acid: aconitic acid elimination in sirup by analysis, 81.73% total aconitic acid in juice: yield of washed and dried aconitate, 12.96 pounds per ton of juice.
Both of the insoluble tricalcium aconitates and the calciummagnesium aconitate separate best, and in greatest yield, from solutions of pH 6.7 to 6.9. At pH 7.0 and higher they generally separate in a mass of very small amorphous spheres or droplets which are soluble in cold water ( 1 ) . This is especially true when they precipitate from sugar solutions of high Brix. I n this form it is impossible to wash them free from sugar before they dissolve. Sirups containing this amorphous form filter slowly because of the fineness of the particles. When a sirup containing such a precipitate of aconitates was maintained a t high temperature, the amorphous spheres slowly crystallized from the center out, forming spherical aggregates of minute radiating crystals. Complete transformation from amorphous to crystalline condition required several days, and as it proceeded, filterability became less and less. This confirms the observation made above that, when precipitating aconitate from sorgo and sugar cane products, care must be taken that the insoluble material does not separate a t a pH greater than 6.9. IMPROVED METHODS OF EXTRACTION
It has been shown that the amount of calcium which may be added to the juices by neutralizing the free acidity and yet not attack the monosaccharides is sufficient t o precipitate only an average of 42.9% of the total aconitic acid occurring in the juices, and that most of the aconitic acid in the juices must be in a combined form of the nature of a soluble aconitate. Therefore, the addition of more calcium in the form of a soluble salt should precipitate an increased amount of calcium aconitate. The combined use of calcium hydroxide for the neutralization of sorgo juices and of calcium chloride t o furnish soluble calcium to precipitate aconitate in excess of that obtained from neutralization of the free acids of the juice was studied and is the subject of a patent by Ventre, Ambler, Ryall, and Henry (8). Table V presents data from a typical sorgo juice treated by this method. The percentage of aconitate precipitated was 81.770, nearly double that obtained by the use of lime only. I n applying this process, if the juices did not normally contain some calcium and magnesium, the amount of calcium chloride to be added should be the equivalent of the difference between the free acids calculated as aconitic acid and the total aconitic acid contained in the juices. However, as has been pointed out, some of the cal-
204
INDUSTRIAL AND ENGINEERING CHEMISTRY
cium and magnesium naturally occurring in the juice is utilized in the formation of the insoluble aconitate with the result that the amount of aconitate precipitated is in excess of that t o be expected from neutralization of the free acids of the juices. The average was almost 43% of the total aconitic acid present. Therefore, i t is necessary t o add only a maximum of calcium chloride equivalent to 607, of the total aconitic acid contained in the juices. The use of calcium chloride and lime might be expected to cut down materially the amount of magnesium in the precipitated aconetate; however, in duplicate runs made in 1942 for comparison of the lime alone with the lime and calcium chloride treatments, the magnesium was not eliminated from the aconitate by use of calcium chloride, but 13 to 147, of the aconitic acid in the precipitated aconitate was in combination with magnesium. I n the sugar manufacturing process when juices are treated by lime only or by lime and calcium chloride, the aconitic acid content is not significantly changed until the sirup is heated. The removal of the aconitate from the sirup removes solids by both methods. I n the sirups made from juices treated with lime and calcium chloride, a slightly greater increase in purity is obtained than when lime only is used. This is attributed to the replacement of the aconitate radical, whose combining weight is 58, by
voi. 38, N ~ 2.
the chloride radical, whose combining weight is 35.5. As an example, potassium aconitate in the juices would be changed to potassium chloride and calcium aconitate, the latter being removed by precipitation. The remaining potassium chloride has a lower equivalent weight than the potassium aconitate originally present. LITERATURE CITED
(1) Ambler, J. A, 'Purer, J., and Keenan, G. L.,J . Am. Chem. Soc., 67, 1 (1945). (2) Buchner, Ann., 28, 243 (1838). (3) Guinochet, E., Compt. rend., 94, 455 (1882). (4) McCalip, M.A , and Seibert, A. H., IND. ENG.CHEM.,33, 637 (1941); Sugar Bull. 19, No. 17, 84 (1941). (5) Parsons, H. B., Am. C'hem. J.,4, 39 (1882). (6) Prinsen-Geeiligs, H. C., Arch. Suikerind., 41, 720 (1933). (7) Ventre, E. K., Sugar J . , 3,No. 7, 23 (1940). (8) Ventre, E. K., Ambler, J. A., Byall, Sam, and Henry, H. C., U.S. Patent 2,359,537 (Oct. 3, 1944). (9) Ventre, E. K., and Paine, H. S.,Ibid., 2,280,085 (April 21, 1942). (LO) Wiley, H. W., and Xaxwell, IT., A m . Chem. J . , 12, 216 (1890). PRESENTED on the program of the Division of Sugar Chemistry and Technology of the 1945 Meeting-in-Print, AMERXCAN CHauIcilL SOCIETY.Cocitribution 168 of the Agricultural Chemical Reeearch Division, U. 8. Department of Agriculture.
Yeasts from Wood Sugar Stillage E. F. IQURTH Oregon Forest Products Laboratory and Oregon State College, Corvallis, Oreg, Three strains of yeasts, Torula utilis No. 3, iMycotorula lipolytica (P-13), and Hansenula suaveolens Y-838, were grown on still waste liquor from the production of wood sugar alcohol. -411 three were found to utilize a large proportion of the unfermentable sugars and acids in the liquor, which indicates that these yeasts have possibilities for a practical utilization of such still waste liquors. The yield of dry Torula yeast may exceed 50% of the weight of sugar consumed, which indicates that components other than sugars are assimilated for yeast growth. Air diffusion was found to be an important factor in the rate of yeast growth and consumption of sugar. With proper aeration the assimilable sugar is consumed by Torula in 18 hours.
T
HE wood-sugar alcohol plant a t Springfield, Oreg., will have approximately one-half million gallons of still waste liquors for disposal each day. This dark colored liquor contains the unfermentable sugars (pentoses) , organic acids and salts, and miscellaneous other products resulting from the hydrolysis of Douglas fir wood. The primary hydrolysis products from wood are lignin, wood sugars, and acetic and formic acids. Secondary products, such as levulinic acid from the hexoses and furfural from the pentoses, are produced by further decomposition of the sugars during hydrolysis of the hemicelluloses and cellulose. Normally, softwoods give sugar mixtures that include glucose, galactose, mannose, arabinose, and xylose. The first three sugars are decomposed with brewer's yeast, Saccharomyces cerevisae, t o alcohol and carbon dioxide, whereas the pentoses are unaffected and remain in the spent beers. Distillation of the alcohol from the beers gives a liquor which is still high in biochemical oxygen demand. It is desirable t o find a use for this still waste liquor and simultaneously decrease its stream pollution load. For this purpose the feasibility of manufacturing feeding yeast by growing
species capable of utilizing the residual pentoses was investigated by the Oregon Forest Products Laboratory in cooperation with the U.S. Forest Products Laboratory and the Willamette Valley Wood Chemical Company. Torula utilis is of particular importance in Europe for the manufacture of fodder yeast and protein feeding stuffs. I t s high nutritional value has been established ( I , 3, 6). Yields of dry yeast of 35 t o 50% on wood sugar have been reported (4, 7 , fO), and Lechner (5)has obtained a yield of 46-4974 on xylose. I t s abilitj to utilize arabinose is reported t o be negligible ( 6 ) . The feasibility of growing fodder yeast on the still waste liquor raises several important questions. Among them are the yield of yeast that may be expected, the extent t o which the materials in the still waste liquor are assimilable, and the time required for their utilization by yeast. The fermentation of the fermentable sugars to alcohol is complete within 24 hours. Therefore, the utilization of the unfermentable sugars in a similar period IS desirable from the standpoint of plant operation. The still waste liquors used in this work were prepared from Douglas fir hydrolyzates fermented R ith brewer's yeast in the pilot plant of the U.S. Forest Products Laboratory. I n the pilot plant, wood waste, including some bark, was first subjected to hydrolysis a t 150' t o 185' C. with concentrations of 0.5 t o 1.0% of sulfuric acid. The hot wood sugar solutions were neutralized with lime t o a pH of approximately 5.0 under 35 pounds steam pressure and passed through a filter press t o remove the calcium sulfate sludge. After cooling and the addition of urea and NaHzPOl as nutrients, the wood sugar wort was adjusted to a pH of approximately 5.8 and fermented with a strain of Saccharomyces cerevisae. Fermentation of roughly 5% wood sugai worts was complete within 24 hours with 80 t o 837, utilieation oi the reducing sugar present. The yeast was recovered by centrifuging and re-used for the fermentation of the next batch of wood hydrolyzate.
