R O B E R T S. GADDIE1
All commercial g r a n u l a t e d sugars contain traces of acid-insoluble sub- stances which p r e c i p i t a t e in acidified a q u e o u s solution a n d which, at suffici- ent c o n c e n t r a t i o n , show up as a white flocculent precipitate. T h e floc present in beet sugar is composed of a m i x t u r e of s a p o n i n a n d its derivatives, of fats, a n d of various o t h e r adsorbed minerals a n d colloids. ( 1 )2 Because these substances gradually p r e c i p i t a t e in certain c a r b o n a t e d beverages a n d acidified p h a r m a c e u t i c a l syrups, it is necessary that sugar be p r o d u c e d as free as possible from these floc-formers.
C e r t a i n i n f o r m a t i o n of a very general n a t u r e on the concentration of floc in t h e g r a n u l a t e d sugars p r o d u c e d by the seven factories of the Utah- I d a h o Sugar C o m p a n y was o b t a i n e d d u r i n g the 1952 a n d 1953 campaigns.
T h e general n a t u r e of the i n f o r m a t i o n was d u e in large p a r t to the extreme qualitative value of the t h e n k n o w n tests. In 1953, Walker a n d Owens, working on this p r o b l e m , f o u n d a fairly large percentage of the acid-insoluble constituents in beet sugar to be s a p o n i n a n d Dr. W a l k e r devised a m e t h o d of analysis for this c o m p o n e n t . Even t h o u g h the m e t h o d h a d n o t been published a n d h a d , in fact, n o t been tested thoroughly, W a l k e r very kindly m a d e available all the i n f o r m a t i o n he h a d on the p r o b l e m . W i t h our a d a p t a t i o n of this test it was d e t e r m i n e d that a measure of saponin con- centration in a sugar gave an excellent measure of t h a t sugar's tendency to p r o d u c e floc in susceptible beverages. T h e m a x i m u m safe concentration of four p . p . m . for sugar g o i n g i n t o these susceptible beverages (2) was further d e t e r m i n e d . W i t h these facts established, it was decided to make exhaustive tests on sugar from all seven of the U t a h - I d a h o factories d u r i n g the 1954 campaign a n d a t t e m p t , w i t h i n the practical limits of full scale o p e r a t i o n and on p r e s e n t knowledge, to control the saponin concentration in the final sugar.
T h e n u m b e r of analyses which could be m a d e was limited by the two spectrophotometers available. However, a m i n i m u m of three samples, rep- resenting three to six strikes of sugar from each factory each day, was analyzed.
A study of these analytical results showed t h a t each factory's sugar produc- tion fell i n t o o n e , a n d only o n e , of three classifications. Typical examples of these three are shown in T a b l e 1.
Table 1.—Saponin Concentration in Sugar Samples from Three Different Factories.
Factory A B C
No. of Samples 2 3 2 2 9 8 631
Saponin Maximum
2 4 3 17
Concentration Minimum
6 0 1
p p m
Average 14
1 6
1General Chemist, Utah-Idaho Sugar Co., Salt Lake City, Utah.
2Numbers in parentheses refer to literature cited.
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T h e results gave q u a n t i t a t i v e confirmation to d e d u c t i o n s arrived at from the general i n f o r m a t i o n o b t a i n e d t h e two previous years.
a. Sugar from some factories always contains relatively high concentra- tions of saponin, (A in T a b l e 1) .
b. Sugar from some factories always contains very low c o n c e n t r a t i o n s of saponin, (B in T a b l e 1) .
c. S a p o n i n c o n c e n t r a t i o n in sugar from some factories varies within wide limits (C in T a b l e 1) .
Because the saponins are only o n e of m a n y non-sucrose constituents in purified beet juice a n d because very efficient sugar-end o p e r a t i o n nearly always results in i m p r o v e d sugar quality, it is logical to suppose t h a t saponin concentration in g r a n u l a t e d sugar w o u l d be lowered by high p a n purities, precision sugar b o i l i n g t e c h n i q u e to avoid crystal agglomerates a n d as n e a r perfect separation of m o t h e r l i q u o r from crystals as possible. On this supposi- tion it was decided to try this p r o c e d u r e at Factory C ( T a b l e 1) . S t a n d a r d liquor purities were held up to n e a r 93.0, h i g h raw sugar p u r i t y was main- t a i n e d at 98.5 to 99.0 a n d sufficient wash water was a p p l i e d at the centri- fugals to b r i n g the color i n d e x of t h e sugar to the lowest practical value.
T y p i c a l results are shown in T a b l e 2. Colors are given in terms of reference basis u n i t s (3) .
T a b l e 2.—Saponin Concentration in Selected Sugar Samples from Factory C.
Sample No. White P a n Purity 1 92.5 2 92.8 3 92.1 4 92.6 5 92.9 6 91.9 7 93.1 8 93.1 9 92.5 10 92.2 11 93.2
Color Index 3 4 29 3 4 3 4 2 7 2 2 17 13 17 19 19
Saponin 12 8 11 10 6 3 3 1 1 2 1
Variations i n p a n p u r i t y w i t h i n the limits a t which o p e r a t i o n s were c o n d u c t e d d i d n o t have any m e a s u r a b l e effect on floc, b u t floc concentra- tion at this factory was found to be almost directly p r o p o r t i o n a l to color i n d e x . However, in o r d e r to o b t a i n a sugar with a color i n d e x below 22, it was sometimes necessary to wash w i t h as m u c h as 26 q u a r t s of water per m a c h i n e . T h i s w o u l d fill up t h e w h i t e side in a b o u t 24 h o u r s a n d so would have to be d i s c o n t i n u e d temporarily. T h r o u g h o u t most of t h e campaign, however, it was possible to o b t a i n sugar c o n t a i n i n g less t h a n four p.p.m.
s a p o n i n by washing to such a color i n d e x .
As soon as results from the work at factory C were available, identical conditions were established at factory A w h e r e s a p o n i n c o n c e n t r a t i o n had b e e n r u n n i n g consistantly high. All o p e r a t i n g conditions were directed toward the p r o d u c t i o n of an extremely even, relatively coarse grain in the
V O L . I X , N o . 2, J U L Y 1956 191 vacuum p a n s , a n d as n e a r perfect washing in the white centrifugals as could be o b t a i n e d . In spite of these efforts, results o b t a i n e d at Factory C could n o t be d u p l i c a t e d in Factory A, even for short periods. T h e r e seemed to be no correlation whatever between s a p o n i n concentration a n d any o t h e r physical or chemical characteristic of t h e sugar. T h i s is illustrated in T a b l e 3.
Table 3.—Saponin Concentration in Selected Sugar Samples from Factory A.
Sample No. White Pan Purity Percent Ash Color Index Saponin p.p.m.
1 93.1 .0050 17 12 2 93.8 .0054 20 8 3 93.6 .0058 23 13 4 93.4 .0038 24 15 5 93.3 .0040 35 8 6 93.5 .0044 35 10 7 93.5 .0046 36 6
Periodic samples of sugar were m a d e i n t o a massecuite, p u r g e d , a n d washed in t h e laboratory centrifugal with what would be equivalent in factory practice to 40 q u a r t s of hot distilled water p e r m a c h i n e w i t h o u t effecting a decrease of m o r e t h a n 1 or 2 p . p . m . of saponin.
Since t h e s a p o n i n s are highly surface-active, adsorbing agents such as activated carbon should remove at least a p o r t i o n of those left in the purified juice (4) . T h e r e f o r e , the a d d i t i o n of activated carbon (Darco S51) to the s t a n d a r d l i q u o r was started. T h e first 48 hours, .3 p o u n d s p e r ton of beets was a d d e d . F o r the n e x t 48 hours this was increased to .5 p o u n d s a n d 48 hours later to .6 p o u n d s p e r ton of beets. At this p o i n t , the s t a n d a r d l i q u o r filters h a d a b o u t reached the limit of t h e i r capacity a n d higher carbon addi- tions were n o t practical. D u r i n g these periods, sugar boiling was carefully watched a n d 2.5 q u a r t s of centrifugal wash water p e r m a c h i n e were used.
No decrease in average s a p o n i n c o n c e n t r a t i o n in the sugar was effected by any of these carbon a d d i t i o n s . A d s o r b i n g agents, such as activated carbon, have selective a d s o r p t i o n p r o p e r t i e s which do n o t confine themselves to the saponins. Because of this, Sabine predicted, a n d o u r work has shown, that in m a n y cases the q u a n t i t y of carbon which would probably be r e q u i r e d would raise p r o d u c t i o n costs h i g h e r t h a n could be justified.
S a p o n i n s all form emulsions with oil (6) . In testing the solubility of the sugar beet saponins in t h e various c o m m o n defoamers used in sugar m a n u f a c t u r i n g , M c G i n n i s (7) , found t h a t they were least soluble in Balab.
Therefore, for a p e r i o d of 24 hours, all foam oils (except Balab) were taken out of the process a n d B a l a b used as sparingly as possible. Saponin con- centration in the sugar p r o d u c e d d u r i n g this p e r i o d r a n g e d from 6 to 13 P-p.m.
T r i t e r p e n e s form insoluble c o m p o u n d s with heavy metal ions (4) . T h i s explains the h i g h ( a b o u t 9 5 % ) e l i m i n a t i o n from diffusion juice, as the cal- cium complex, w h e n lime is a d d e d at the carbonators. H o p i n g to take f u r t h e r a d v a n t a g e of this p r o p e r t y , two things were tried. First, milk of lime e q u i v a l e n t to a b o u t .15%" C a O on beets was added to the filtered 1st carbonator j u i c e g o i n g to 2 n d c a r b o n a t i o n . T h i s was c o n t i n u e d for 3 days
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a n d when no decrease in floc was o b t a i n e d the second e x p e r i m e n t was started. T h i s consisted of a d d i n g fresh milk of lime e q u i v a l e n t to a p p r o x i - mately . 0 7 % C a O on beets to the s t a n d a r d l i q u o r at the high melter. T h i s was then sulfured to pH 7-8 to 8.0 using liquid S O , a n d filtered on the s t a n d a r d l i q u o r presses using .6 p o u n d s filteraid p e r ton of beets. After a 72 h o u r r u n in which no significant decrease was effected in the average s a p o n i n c o n c e n t r a t i o n in the sugar, this p r o c e d u r e was also d i s c o n t i n u e d . It is highly p r o b a b l e that m e t h o d s of processing influence, to some extent, the c o n c e n t r a t i o n of saponins in the final sugar. Eis, et al (4) have shown, t h a t even at the same factory, the c o n c e n t r a t i o n of t r i t e r p e n e s in diffusion juice is widely variable. A l t h o u g h 95-97% is e l i m i n a t e d in carbon- ation, in cases of high t r i t e r p e n e incidence, the removal is still i n a d e q u a t e .
References
(1) W A L K E R , H O W A R D G. J R . , a n d O W E N S , H A R R Y S. 1953. B e e t sugars; acid insoluble constituents in selected samples. Agr. a n d F o o d C h e m . 1:450.
(2) W E S T , R O B E R T R . a n d G A D D I E , R O B E R T S. 1956. D e t e r m i n a t i o n of s a p o n i n in g r a n u l a t e d sugar: m e t h o d of H. G. W a l k e r a d a p t e d to r o u t i n e control. J o u r n . Amer. Soc. Sugar Beet T e c h . 9:146-152.
(3) Bottler's Sugar Survey (1952)
(4) Eis, F. G., C L A R K , L. W., M C G I N N I S , R. A., a n d A L S T O N , P. W. 1952.
Floe in c a r b o n a t e d beverages. I n d . & Eng. Ch. 44:2844.
(5) SABINE, F. M. 1952. T h e floe p r o b l e m in beet sugar. Proc. Amer. Soc.
Sugar Beet T e c h . p p . 760 763.
(6) M C I L R O Y , R. J. 1951. T h e p l a n t glycosides. E d w a r d A r n o l d & C o m p a n y , L o n d o n , p . 64.
(7) M C G I N N I S , R. A. Private communication.