Tricalci x r n I? as a Caki ig In1 ibitor in Salt and Sugar
2’lic cfl;cieruy of tricalciuni phosphate ac a cuke inhiliilor iri sull and sugar is deperiderrl ripoil jour nmjor mriables iri. chemical arid physical composition: ratio of CaO lo P801, irnn and a h i n u m phosphate content, degree I$ Iiydrulion, orid particle size. Tricaleiuni phos~~lrule made to come witlun, cerluia h i t s g o w n i n g those variables has lwen found lo prevent caking in salt arid sugar M e r ffiriii other commonly used fillers. The addilion of this special grudc of trimlciuni phospliute to salt and sugar favorably affects their physical ehuraclcrislics and iniprot3es their nulrilive value.
I
1‘ K4S luiig l m n knowi that the objectionable teiidcnq to cake on the part of salt, sugar, and other powdered food products can be reduced by the addition of srnall amounts of certniri materials to these iroducts. T l i e number of substances tliat ciin be used fur tliis purpose is limited, because notliiiig cini Lie added to food products that lias not becn proved to be either harmless or beneficial to the Irealtli, and only a few arc actually in grneral use. Recent bii~chenricai research lrss sliuivn that calcium pliosplintes supply essential elements nlricli may not be abundantly present in thr: average iiictnry. Blooin ( 1 ) reported tlist dicalciinn phosphate lras been used sui in children’s diets fur ricket,s prevention without the use of vitainin U. 1,aMer (4)state: “Many American dietaries are below tlio minimum requir(:nients desirable for adult: largely because of an uriduly large proport.ion of sugars, white flour, and processed corn meal fronl wliicli the naturally occurring forms oS calcium arid plrospliorus have becn remo\wj in manufacture;” and Surtlier “Certain inorganic salts of calcium and pliosphorns can fuiiction as well ae organic Sorms in meeting defieienaies of tlicse elements.” Stecnbock arid .Tones (9) Sound that varions calciinn salts, including tricalcium pliosjihate, supply inorganic elements available Sor bone-building in rats. Hoppert’s work (S) on the nutritive value OS leavened bread arid biscuits indicates that the residual salts in seis-rising flours, vliich are largely composed of di- a i d tricaleiuin pliospliate, assist growth mid bone developnent. McCollum (6‘) and Sherman (8) have stressed the importance of calcium and phosphorus intake on tooth development and caleifieation. Tricalcium phosphate has hcen nsetl to prevent caking in salt (commercial sodium chloride) for a number of years, and in view of recent dietary consideratimi i t has seemed ilrsirable to determine the comparative cfiieit.iieg nf different
grades of trimilciuni pliiq~liate,diciilciiini phospiiate, and utlirr usable matr:riala 21s anticaking agents in salt arid sugsr.
C.\KIZO 811 f i ~ & ~griuird materials exliilit a teriilenc>- to cake; the extent of caking may vsry froiii t l i e Sornmtioii uf friable, loosely bound agglomerates to hard, rucklike bodies niolded by the eoiitaincr iii n-hidi tliey sre p:icked. The extent of caking is deixndent on several factors, in miiich are included the inlim:nt properties of the niaterial, and the tcmperat.ure, liuniiditg, lengtli of t,inie, and method of storage. Cakiiig is most, prevalent, in materials that are pliysically tiuinidity affeotcd by compar:tti’;cly small changes in rclat.i~-s and temperature These may result in alterntioris in the degree of hydration and crystal structure of individual particles, or, as is the case in tlic cakiiig of salt and sugar, tlisre need not ne( arily ire a incasuralilc change in the 1 clmacter of iiidividnrtl particles roniiwsitinn or ph> Salt and rrl@ir rimy lie sed :is mildly iiygroscopic materials wliiclr under cnrt,ain coxmintrations of truinidity al,sorb surface niuisture; sncli absori)ed moisture is not t,iglitly lield, and decrease in himiidity of the surroondings canscs evaporation. Tlie authors’ interpretation uf tlie nieclianisrn iniulved in tlic eiiking of salt aiid sugar comprises two steps. With tlie absorption of appreciable amounts of water, there is soon t i film of salt or sugar solut,ion nii the surface of indi-
I I?
. I 3 1 h 1.
Ft~t,ww,),1933
A
N 1)
vidual crystal?. So loiig as this exccns moisture is present, caking does nut ta,ke place. When water is evaporated from what is then probably a saturated solution of the Inaterid, there is a cemmting of adjaernt crystals, aiid caking residts. Witti this fundamental coitccption uf caking, it was reawned that a innterial that wonld he effer:tive as a filler or cake inhibitor niight be otic that was equally or inore hygroscopic than the material being filled, ur perhaps a i j u i t e inert substance in a fine state of suhdivisioii tiint, when tlioroughly disseminated tliroughout the salt or sugar, irould act as a buffer, tending to hold t.lrc particles apart. and 1mveiiting the bond forniation that is pictured as ileing cawed by tho evaporation or coiicnitr;tti~,n of the sorrounditig filrri r d solution.
"r
SA I
!.$:I oil ii, 20-gralu sample, R g:siti in iveigili uf 1 1 1.1, i(img. gi\ satisfactory results. Aftw saturating, tlie piute and sarnlili:~:are rimored front 1,Im desiccator and dried in tho same c ~ o nfor 2 liours at, 40" C. with the plate in tnotiurr.
l"lI,I,El?.S
In the invesbigation instigated to find ai1 improved cnke inhibitor, attcntion was first given to salt as the product wlrich then n'as coiisidered the inore trnublesome. It wns sann fourid that a rapid test was needed that would rliow quickly the relative effect of diffcrmt materials on the ixkiiig of SRlt,, without liaviiig to resort to a long storage period uridw varying conditions iif tempcratitre and humidity. A i m p l e piece of npparatus (Figure 1 ) has heell evolved
q.\+rtir.~~rn,Na*,
WI*&ri
AN,j
'TO M A K E 'rnr,:hI.c:,"M
I',,r,s,,,30nrc; L'lrosP,r:,r~;
A Siirtiier sumriation giving t,he vi~luesin T:ilk I may lit! takiiig thc P/C value of a standard sarnplc as 100. Wit,li a satisfactory riieaiis r i i inducing caking, tests haw been ninde to deterniirre the relative eakc-inhibiting pro1)ertios of various materials. These were mixed vitli a n d k n o m conirricrcial grade of table salt in tlic proportion of 1.5 grains per 100 of salt, and tested as just described. The salt osed in all the tests was a refined grade oi table salt, IIIIL~E,
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It is evident from these tests that tricalcium phosphate and basic magnesium carbonate show distinct advantage over other materials tested. The difference in behavior of the two samples of tricalcium phosphate suggested that variations in the composition or physical characteristics of tricalcium phosphate from different sources affected the cake-inhibiting properties. It is known
CONSTRANT-TEMPERATURf E L E C T R I COVEN
URATED SOLUTION DlUfi CHLORIDE
FIGURE1. ACCELERATED CAKING APPARATUS
CHEMISTRY
aluminum phosphate, respectively. Caking tests showed a marked improvement in the cake-inhibiting properties, with the batch containing 6 per cent of aluminum phosphate a t least equal to sample 4252. The samples containing iron phosphate were decidedly off-color, and the addition of iron phosphate as an accelerator was therefore considered impractical. The improvement shown by the addition of aluminum phosphate to tricalcium phosphate suggested a test with pure aluminum phosphate. It was found inferior to any of the samples of tricalcium phosphate as a cake inhibitor. A series of experimental batches containing varying proportions of aluminum phosphate from 2 to 31 per cent were prepared, and all samples were found distinctly superior to 4252. Certain disagreement in duplicate tests appeared in the order of effectiveness of the experimental samples, but in each case the material containing 7 per cent aluminum phosphate gave somewhat better results, with only slight differences in samples containing from 3 to 11 per cent aluminum phosphate.
IGNITION Loss
that products which are accepted as tricalcium phosphate may vary considerably in chemical composition and physical make-up, and it was therefore reasoned that, by first determining the influencing factors and by controlling these within definite limits, a tricalcium phosphate might be made that would possess improved anticaking effect.
Having shown that the particle size was influential but not the governing criterion of effectiveness in a cake inhibitor, the relative water-absorbing capacities of different samples of tricalcium phosphate and their relation to cake inhibiting were investigated.
1-
PARTICLESIZE
Following one of the original premises, a study JTas made of the effect of particle size on the anticaking properties of tricalcium phosphate. Particle size was determined on various samples by the sedimentation method described by Calbeck and Harner (2). The percentage distribution of particle size was calculated, and rectangular histograms (Figures 3 to 7) were made for comparison. Caking tests of phosphates shown in Figures 3 to 7 were made by the procedure just described and the order of effectiveness showed: SlMPLE
4252 1-A (1 milled) 4188-A (4188 milled)
ORDER 1 2 3
4158-A 1-A 4252 4188 1
8" STANDARD TYLER SCREEN
SAMPLE ORDER 4188 4 1 5
This shows that, whereas reducing the particle size of a given product improves its anticaking properties (compare 4188 and 4188-A, and 1 and 1-A), there are still other factors that make sample 4252 superior. Since equal quantities by weight of the several materials were added to salt, and since the density of the different grades was known to vary, the specific area was calculated on all samples, and it was found that materials having the greatest specific area or smallest particle radius spread are not necessarily the best cake inhibitors. This is shown as follows: SAMPLE
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R.ADIUS
SP. ARE.+.
&f icrons 4.2-2.35 4.3-2.32 12 . 6 - 2 . 4 11.9-2.24 21.2-4.1
0.3918 0.3651 0.3493 0.3253 0.2489
C.4KIh-5
TEST
3 2 1 4
5
IRON AND ALUMINUM PHOSPHATES The outstanding chemical difference between sample 4252 and the others tested was in the impurities present as iron and aluminum phosphate, and experimental batches were made containing 6 per cent of mixed iron and aluminum phosphates, 6 per cent of iron phosphate, and 6 per cent of
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FIGURE2. VIBRATED SCREEN FOR CAKING EVALUATION
Caking tests of calcined and uncalcined tricalcium phosphate showed the calcined material inferior as a cake inhibitor. This was not due to possible loss of water-absorbing properties as was supposed, because absorption tests by exposure of the two materials to humid atmosphere and under normal conditions showed the calcined product to be more hygroscopic. Further experiments with samples of tricalcium phosphate varying in water content from below 6 and over 12 per cent ignition loss showed that those having an ignition loss between 6 and 12 per cent were most efficient in preventing caking. It would appear, therefore, that tricalcium phosphate
February, 1933
INDUSTRIAL AKD ENGINEERING CHEMISTRY
143
possessing a water content equivalent to that of definite mono- or dihydrates is the more effective cake inhibitor. RATIOOF CaO
TO
P205
Tricalcium phosphate sold as such may vary appreciably in chemical composition. This applies not only to what may be considered minor components, but to the Figure 4. Sample 4188 CaO and PzOj as well. I n addition to Figure 3. Sample 4252 IO, , , I natural variations caused by differences in water and impurities contained, there A 2 are appreciable differences in the percentage and molecular ratio of CaO to Pd& found in different samples and all classified as tricalcium phosphate. I n Table I it was shown that dicalcium p h o s p h a t e is poor as a cake inhibitor, Figure 6. Sample 4188 milled and. since variations in ratio of CaO to PzOs affect the p e r c e n t a g e of di- and tricalcium present, it would appear that a tricalcium phosphate with a low ratio of CaO to P& w o u l d be i n f e r i o r for Figure 5. Sample 1 preventing caking. I n Table I1 are shonn the percentage ratios of CaO to P205 present as di- and FIGURES 3 TO 7. DISTRIBUTION OF basic phosphates in various s a m p l e s of PARTICLE SIZE tricalcium phosphate and their relation to comparative values in c a k i n g tests. I n d e t e r m i n i n g t h e CaO a n d P205 I ' present as di- and basic phosphates, the CaO found by direct analysis was corPfRCLNT Br NLICHT rected for CaO present as chlorides, sulFigure 7. Sample 1 rniiled fates, c a r b o n a t e s , and m o n o c a l c i u m phosphate; and the Pzo5 was corrected for that present as monocalcium (soluble Pz05)and iron and sample X-343, but an appreciable increase was effected aluminum phosphates. compared with the original X-625. The higher mole ratio of CaO to P205than required for the hydroxyphosphate TABLE11. 1 t . 4 ~ 1 0 OF ~ CaO AND P205 indicates absorption of calcium hydroxide by the basic RATIOCaO: PzOs MOLE &KlSG phosphate. I Y BASIC EQCIV. RATIO TEST S.4MPLE PEOSPH.4TE CaO: PZOI R.ATIXG On a caking test this material was found somewhat inferior /O to sample X-343 but better than the original X-625. It 1 34 X-343 3.40 1.31+ X-683 3.36 appears, therefore, that the optimum ratio of CaO to Pzo5 1 28 X-625 3.24 is in the range of the calcium hydroxyphosphate. A prac1.28 X-677-1 3.24 X-684-3 3.11 1.23 tical consideration is that, under ordinary manufacturing 1.20 X-684-2 3.02 conditions, it is difficult to make a tricalcium phosphate This shows a definite relationship between CaO:P?05ratio more basic than the calcium hydroxyphosphate that will and anticaking efficiency. not show free lime. Traces of free lime in a product to be The third column (Table 11) of mole ratios s h o w that all used in salt are conceivably undesirable. these samples contain an excess of CaO over that required for tricalcium phosphate, and that it is desirable not only RESULTSO F S.4LT TESTS to eliminate dicalcium phosphate, but also for the phosphate to be more basic than theoretical tricalcium phosphate. This investigation therefore shows that the efficiency of It is worth noting that the samples which were found most tricalcium phosphate as a salt filler is dependent upon four effective in preventing caking approach a mole ratio corre- major factors (namely, ratio of CaO to P206, iron and alumisponding to the so-called calcium hydroxyphosphate [3Ca3- num phosphate content, degree of hydration, and particle (P0&Ca(OH)2] with a mole ratio of CaO to P20a of 3.33 size), that a t least three of these factors, all of which can be or a percentage ratio of 1.31. readily controlled in the course of manufacture, must be The fact that sample X-343 exceeded in this ratio and within definite limits. still seemed somewhat better in preventing caking suggested The first three factors may be readily determined in the that increasing the ratio of CaO to P205still farther to ap- laboratory by known analytical procedures. The determiproach a possible tetracalcium phosphate [Ca3(P0J2 CaOH) ] nation of particle size by the sedimentation method is tedious (7) with a mole ratio of C'aO to P& of 4, would show further and too long for use as a routine control. Apparent density, improvement . siftings through fine screens from 200 to 400 mesh, and a A quantity of basic phosphate was prepared from sample suspension index are reliable measures of bulk and particle X-625 by the method described by Lorah, Tartar, and Wood size which can be established as routine laboratory tests. ( 5 ) . This showed a mclle ratio of 3.41 and a percentage The suspension index makes use of the same principles emratio of 1.42. The basicity is only slightly higher than on ployed in the sedimentation test and consists of noting the
-+I
CI
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layer of settled powder after a definite time from an alcohol suspension made in a graduate of definite dimensions. The better tricalcium phosphate fillers will show an apparent density under 0.3; a t least 96 per cent will pass a 400-mesh screen, and the suspension index will not be less than 19 by the method adopted in this laboratory. Tricalcium phosphate meeting the. specifications established by these tests is found to be a more efficient filler for fine salt than other materials tested. Magnesium carbonate is found to be next in efficiency on the fine and granu-
Vol. 25, No. 2
the rate of flow, as do the lower percentages of magnesium carbonate. The addition of even 0.5 per cent tricalciuni phosphate materially increases the rate of flow. From 3.5 to 4 per cent of magnesium carbonate is needed to attain the same rate of flow given by 1 per cent tricalcium phosphate. The addition of larger amounts of starch affects the rate of flow slightly, and it is doubtful whether any amount of starch would equal the effect of 1 per cent tricalcium phosphate. Projecting the starch curve on the gradient indicated, it would intersect the value for 1 per cent tricalciuiii phosphate somewhere around 46 to 50 per cent starch. TURBIDllY
- - W s FILLER
FIGURE 8.
]?ATE
FLOWOF CONDITIONED SUGAR
OF
lar type salts, and it shows some superiority as a filler in vacuum pan or cubical crystal salt. Salt filled with tricalcium phosphate retains the original sparkle that is desired by cracker manufacturers who sprinkle it over their products. Magnesium carbonate makes the salt chalky and gives it a flat nhite appearance. SUGAR FILLERS
The irriprovenients effected in the cake-inhibiting properties of salt filled with the special tricalcium phosphate suggested a filler for granulated and fine powdered grades of its use sugar.
CAKINGTESTS A series of accelerated caking tests with basic magnesium carbonate, starch, and the special grade of tricalcium phosphate showed that tricalcium phosphate was superior t o starch and that basic magnesium carbonate compared favorably with tricalcium phosphate. To check the effect as shown by the accelerated test, one-pound (0.5-kg.) cartons of XXXX sugar were filled with varying percentages of the three fillers mentioned. These were stored for 53 days under a pressure of approximately 1 pound per square inch (0.07 kg. per sq. cm.) and under the normal weather conditions prevailing in St. Louis between the latter part of May and the middle of July. It was found that 1 per cent of special grade tricalcium phosphate was superior to 3 per cent basic magnesium carbonate and distinctly superior to 5 per cent starch. Kone of the cartons filled with special grade tricalcium phosphate showed caking. A conclusion from the progress report of the investigator on this project states: “One-half of one per cent of tricalcium phosphate X-343 completely prevented the formation of any lumps in XXXX powdered sugar on standing 53 days.”
RATEOF FLOW I t was observed when preparing the various samples of filled sugar that those containing tricalcium phosphate possessed unusual free-flowing properties. The samples filled with 2 per cent or more of magnesium carbonate also exhibited increase in flow; those containing starch had a tendency to cling and form semi-plastic agglomerates. The effect of the three fillers on the rate of flow of sugar is illustrated in Figure 8. This shows the time required for the flow of 110 cc. of the filled sugar. Starch actually impedes
Because tricalciuin phosphate is essentially insoluble, it as believed that water solutions of filled sugars might be objectionably turbid, and comparative turbidities were made of sugars filled with starch, niagneqium carbonate, and tricalcium phosphate. One-gram samples of the filled sugars were dissolved in distilled water and made up t o 50 cc. in S e s s l e r tubes; these were compared with the standard turbidity samples containing barium carbonate as the turbidifier. In e q u a l a m o u n t s b y weight, magnesium carbonate _gave the most t u r b i d and PERCENT FILLER starch the least turbid sohF~~~~~ 9. TURBIDITY OF tion. In the a m o u n t s of \VATER S O L U T I OOFSUGAR ~S f i l l e r r e q u i r e d t o prex-ent C O N T A I N I ADGI F F E R E N T COI\IDITIOYERS caking effectively, tricalcium p h o s p h a t e g a v e the least turbid and starch the most turbid solution. This is illustrated in Figure 9. The circles on the curves represent the amounts of each filler required for equivalent anticaking effert as found by the dorage te
EFFECTo s I c r s c ; ~ Fine pon-dered sugar is used extensiTely in riiakiiig icings for cakes. Behavior of sugars Containing the three conditioners was investigated. Observations made under the direction of C. D. hIorison a t t,he American Institute of Baking on samples of icing sugars received under code (identity of filler unknown to the diser\-er) suggest the following conclusions: Cold icings made n-ith sugar containing tricalcium phosphate
