Improved Method for Production of Sweet Potato Starch F. H. THURBER, Bureau of Chemistry and Soils, Washington, D. C. Alkaline su@te solutions have been found mat&' 5 minutes after the grindOLOR-PRODUCING highly satisfactory ,for the remoz,al of colored ing Period was completed, after compounds w h i c h a r e which it was passed over a shaker present in sweet potatoes compounds in fhe manufacture of sweet potato corered Tvith 200-mesh bolting impart a grayish yellow cast to starch w h i c h is inanufactured starch. The manufacturing lime has been cloth. The starch was then relowered to lhaf required for making high-grade covered from the starch milk by from them. I n order to compete white potato starch, the yield has been appremeans of a solid bowl centrifuge. successfully with imported white ciably incrflased, and a starch sf a high degree PURIFICATIoN. An alkaline potato starch, it is essential that M sweet potato starch c o m p a r e sulfite solution--0.00125 of p u r i t y arid excellent color has been produced. sulfur dioxide (o.oos per cent) favorably with this i m p o r t e d and 0.005 M sodium hydroxide starch in color. Balch and Paine (1) have developed a method for the production of high-grade (0.02 per cent)-was added to the crude starch in sufficient sweet potato starch having a satisfactory color. I n their amount to form an approximately 5 per cent suspension. process sulfur dioxide is added during the grinding period The starch was then tabled. After the first tabling, the in sufficient amount to keep the colored compounds in a starch in a number of runs appeared to be quite pure. Howreduced state, After the starch has been srreened and ever, to insure the production of a high-grade product, the tabled, the remaining colored impurities are washed out n i t h treatment with alkaline sulfite and the tabling process were dilute sodium hydroxide solution, The excess sodium hy- repeated. After the second tabling, in order to remove the droxide is then neutralized with acetic acid or sulfurous acid, excess alkali, the starch was taken up in sufficient water to form a 5 per cent suspension. The mixture was agitated after which the starch is washed and dried. I n continuing the work on this process, it was found that for 5 minutes and was then filtered. I n some runs a small a white starch was obtained when distilled water was used, American filter was used, but, since the process was not conbut that it was difficult to produce white starch with Wash- tinuous, leaf vacuum filters were found to be more coningkon city water. Water which had been pasaed through venient. a Permutit water softener gave somewhat better but not To complete the purification process, the starch vias entirely satisfactory results. Since cations such as Ca++, again taken up in water after which the mixture was acidified Mg++, and F e + + might form insoluble and thiis difficultly (pH 5 determined colorimetrically with bromocresol green). The s t a r c h was f i l t e r e d a g a i n , removable colored compounds with w a s h e d on the filter with w a t e r soluble colored products present in WASHED S W E E T P0,TATOES (pH 5), and dried a t a temperathe sweet potato, it was decided to A-KALINI SULPHITE-GRINDERi investigate the use of alkaline rei ture of 125' F. I S 1 SCREEN TYPE OF POTATOES. Kiln-dried ducing a g e n t s , such as s o d i u m 9 JLP W R C M Sancy Hall sweet potatoes that had sulfite and sodium sulfide, in roni 2 N D SCREEN nection with the p r o c e s s . The been in storage for approximately excess sodium ion might be expected PULP I S T M I X I N G TANK8 months were used in this investii NEUTRALIZER TAILINGSISTIABLE gation. The amount of alkaline to replace such ions as Ca++, MgA+, .i i CONCENTRATER Z N D MIX~NGTANK--E$K and F e + + and thus p r e v e n t the sulfite required varied s o m e w h a t t DRIER f o r m a t i o n of the objectionable, T A I L I N G S c 2 N D TABLE with different lots of potatoes. It c is expected that the quantity used difficultly removable colored prodWAREHOUSE SETTLING TANK WASHING TANK ). FILTER i may be somewhat d i m i n i s h e d ucts. Z N D STARCH i c Since some d i f f i c u l t y was enwhen f r e s h l y dug p o t a t o e s are NEUTRALIZER NEUTWALI ZER i countered with the precipitation of (. available. FILTER FILTER ferrous sulfide, only a few prelimi(. The flow diagram for the process STARCH DRIER nary runs were made with sodium 1 i is given in Figure 1. WAREHOUSE DRIER YIELD. The yield of starch from t sulfide. The method as finally deWAREHOUSE veloped, in which alkaline sulfites a typical run in which 444 pounds wereused, proved tobehighlysatisFIGURE 1. FLOW DIAGRAM FOR S W E E T P O T 4 T o of p o t a t o e s w e r e used w a s 64 STARCH MANUFACTURE factory; the manufacturing time pounds-14.41 per cent-of first was lowered to that required for grade starch (moisture content 13.8 the making of high-grade white potato starch, the yield was per cent) and 18 pounds-4.05 per cent-of second grade appreciably increased, and a starch of a high degree of pu- starch (moisture content 13.8 per cent). The total yield of rity and excellent color was produced. starch having a moisture content of 13.8 per cent was 82 pounds or 18.46 per cent. PROCEDURE MANUFACTURING DISCUSSIONOF RESULTS Sweet potatoes were ground in a hammer mill. The resulting pulp was treated during the grinding period with DATA. The results of tests which were made ANALYTICAL an equal weight of alkaline sulfite solution-0.02 M sulfur on this run and on three other typical runs are given in dioxide (0.128 per cent) and 0.085 M sodium hydroxide Table I. Hydrogen-ion concentration values with the (0.34 per cent). The pulp was allowed to stand for approxi- quinhydrone electrode were determined in a water suspension
C
---J---=~ ~~:'~\~~ FUGL
t : +
919
INDUSTRIAL AKD E N G I N E E R I S G CHEMISTRY
920
of the starch (ratio of starch to water, 1 to 5 ) ( 2 ) . Colorimetric determinations were made on the clear liquid from which the starch had been removed [as noted by Ripperton
YJSCOSITY.The maximum viscosity of this starch is higher than the maximum obtained on other sweet potato starches which have been examined under identical condii3 per cent paste was prepared and its viscosity tions ( 3 ) . ; determined with a Stormer viscometer in the manner described in a previous article (3). Figures representing the viscosities which were obtained are given in Table 11. The values are plotted on the curve in Figure 2 . The viscosity curve for corn starch is inserted merely for reference. TABLE 11.
VISCOSITY O F
TEJIP. TIME C.
060.
80-
99'don,N.
is97
l*O,V,N
(994
reon,*
~99'1
,o'm,N
CPPY
7 L ~ , = . C L i o A 7 U I~N ~ & 7,MZ
POTATO STARCH FIGURE2. VISCOSITYOF SWEET
( 2 ), measurements made with the quinhydrone electrode are somewhat lower than those made colorimetrically]. The ash and protein content are both exceptionally low.
DATAON SWEETPOTATO STARCH TABLEI. ANALYTICAL ASH %
AtoIBTuRE
%
'
P H
uinhydrone Chlorophenol eiertrode red
PROTEIN ( N X 6.25)
%
Vol. 23, No. 8
Xin.
3 PER CENT SWEET POTATO STARCH
PASTE
VISCOSITY
TEMP. TIME
Stormer units
C.
Min.
VISCOSITY
Stormer units
TEMP. TIME C.
Min.
VISCOGITY
Stormer units
COST OF CHEMICALS. Approximately 2 pounds of sodium hydroxide and 0.75 pound of sulfur dioxide were used in each run. Thus, the cost of chemicals should be somewhat under 0.1 cent per pound of dry starch. Although this chemical treatment adds an appreciable amount to the apparent cost of production, the yield is increased sufficiently so as actually to lower the cost of production per pound of starch. LITERATURECITED (1) Balch and Paine, ISD.ENG.CHEM.,23, 1205-13 (1931).
(2) Ripperton, Hawaii iigric. Expt. Sta., Bull. 63 (1931). (3) Thurber. IXD. ENG.CHEW,25, 565 (1933). RECEIVEDJanuary 21, 1933. Presented before the Diviaion of Sugar Chemistry a t t h e 84th Meeting of the American Chemical Society, Denver, Colo , August 22 t o 2 8 , 1932. This paper is Contribution 127 from the Carbohydrate Division, Bureau of Chemistry and Soils.
Increased Acidity Inhibits Corrosion Application t o Canning Prunes E. F. KOHNANAXD X. H. SANBORN,National Canners Association, Washington, D. C.
D
RIED prunes possess certain unique dietetic and nutritive characteristics that justify their occupying a definite place in our dietary. As in the case of all dehydrated products, however, the forethought that is necessary to have them ready for a given meal militates against their use. This would indicate the desirability of canning this fruit, for which dehydration would seem superfluous. Evidence in favor of canning the fresh prunes may be found in recently published data ( 3 ) which show that, while dehydration results in a loss of most of the vitamin C in prunes and a considerable portion of the vitamin A, this latter vitamin is unaffected in canning fresh prunes, and vitamin C is fairly well retained. DEHYDR-4TION ADDSTO FLAYOR I n recent years the Italian variety of prunes, grown largely in Oregon and Washington, has been canned in considerable amounts in the fresh state. The canned product has a brilliantly colored sirup, and the prune itself presents an attractive appearance. Its relative tartness is an advantage from the standpoint of flavor for canning it in the fresh state As will be understood from the contents of this paper, its relatively low p H tends to minimize its attack on the can. This variety of prune, however, is not produced in as large quantities as the French (Santa Clara) variety, grown in California. When the latter variety is canned fresh, the
color of the sirup is mediocre compared with that of the Italian variety and the prune itself is less attractive than the Italian variety. PvIoreover, the flavor is flat and inFipid. The French variety of prune needs to be dried to give it the most desirable flavor. Because of the desirability of having prunes ready to serve, there was a general movement among canners a few years ago to can prepared prunes-i. e., stewed dried prunes, ready t o serve. The losses encountered due to hydrogen swells and perforations, because of the excessive corrosive effect of the prunes on the can, were so great that the canning of this commodity has heen almost completely abandoned and it is now impossible to purchase it on the retail market. The losses are not quite as great in the larger sized cans, and certain governmental departments have continued to purchase them in this form. Because of their convenience, the Navy has purchased prunes in canned form only for a number of years in spite of the fact that large losses were encountered.
DEHYDRATION IKCREASES CORROSIVEEFFECTON CAN An investigation has disclosed the fact that drying or dehydrating prunes greatly increascs their corroiive effect on the can, thus giving rise to undue losses from hydrogen swells and perforations. This is definitely brought out in experimental packs represented in Table I. A word as to what constitutes "losses" in this connection will give a clearer
