JUICE PURIFICATION. FUNDAMENTAL CHEMISTRY 185 assist in the agglomeration of calcium carbonate particles in the carbona
tion sludges, and by means of ion exchange21 even take part in the forma
tion of natural alkalinity, and thus in the deliming of second carbonation juices.
Pectins.
Soluble pectins are,in
principle, partly esterified polygalacturoruc acids. They are very easily saponified, and split into shorter chains.
Formation of acid or neutral salts is made possible by the.ir behavior as polyacids. Apparently their lime salts are only slightly dissociated, 80 that calcium pectates, which are rather insoluble, can have different residual charges, ranging from distinctly negative to neutral, and even positive.2'.I
It is highly probable that colloidal micelles of pectins may behave as cation exchangers.2l• 23 The larger-rnoleculed pectins, if due precautions are not taken, will form, on liming, voluminous, colloidal, strongly-hydrated precipitates j even highly viscous jelly-like solutions, settling and filtering with great difficulty. Decomposition products of lower molecular weight, produced in the beets, or during the liming of the juices, seem to influence the crystallization of sucrose, and to form turbidities in white sugar solu
tions which are difficult to
'filter
off.Pectins are strongly optically active, and difficult to clarify with lead acetate, thus increasing the error of apparent purities, and simulating sucrose losses.
On the other hand, they may, by ion exchange, increase the natural alkaliDity. In the agglomeration of calcium carbonate particles in first carbonation muds they seem to play an important part,2.4 and there are strong indications that they may further the precipitation of proteins, for example,
in
the "scalrung" of cassettes.Polyphenols.
These are responsible� for at least one group of coloring substanoes, the pH-sensitive "amethyst" colorg28 so frequently obtained inover-gasSed first carbonation juices. •
Tyrosine.
The formation of dark blue colors in raw juice has been ascribed to the action of tyrosinase on tyrosine. 'ZlSaponins.
These have been held responsible for the foaming of raw juices and especially waste waters, such as pulp and pulp-press waters.They seem to be normally eliminated ,during the purification of beet juices.
Nitrogenous Bases.
Betaine is an example. They act as buffers, and may simulate natural ,alkaJ.inity in second carbonation, depressing the ionization of carbonic acid, and hence enhancing the deliming of juices.Again,
they are able to bind carbonic acid as"" carbaminatea. When volatile, like N(CH.)" they may cause loss of alkalinity." They are probably lIlelassigenic. .Ammonia.
Ammonia is the most important nitrogenous base, being186 BEET-SUGAR TECHNOLOGY
chiefly responsible for loss of alkalinity. The NHt ion is an acid (NHt � NHa + H+, pK = 9.5), and therefore ammonium salts may invert even alkaline, warm sucrose solutions, and cause corrosion of evaporators.15 A certain loss of alkalinity, may, however, be desirable in strongly alkaline juices and sirups.
Iron, Aluminum.
These are practically eliminated by lime, but, if originally present in the form of salts, probably increase the amount of lime salts. Iron may catalyze oxidation reactions wIth formation of color, and lead to grayish�wbite sugars.Sodium, Potassium.
These form the major part of the cations in the raw juice. They are strongly melassigemc,9. 10 and their presence advaUM ta.geous only so far as they serve to produce the necessary natural alkalinity.Silicic Acid.
In colloidal form, originating from certain types of limestone, silicic acid has been reported to pass through the purification, and to give rise eventually to very disagreeable incrustations in the evaporators.
Lime�
If prepared by the burning or calcination of limestone, OaO is amorphous, highly dispersed, having lost 44 percent of its weight without a corresponding loss of volume; colloidal,29 since its solubility depends strongly on its method of preparation and the amount of solid phase present30 (see Fig. 7-5) ; and its sohitions in sugar can be ultrafiltered.31 Though its reaction with water is strongly exothermal, it is apparently still able to dissolve in the cold without hydration, and to give more concentrated solutions than those prepared from Oa(OHh.
Calcium Hydroxide.
Trus is used in the sugar industry in the form of milk of lime-a suspension of Ca(OH) 2 in water. Its physical properties depend on the conditions of slaking. Like OaO, it first goes into colloidal solution, in ,which it is stabilized by sucrose.32, 33 Its solubility is therefore not constant, but is determined by the previous history of the calcium hydroxide, the amount of the solid phase present, the temperature, and the concentrations of sucrose and nODSugars. Lower temperatures and higher concentrations of sucrose and nonsugars increase the solubility.MThe influence of temperature is very marked. The heating of a cold, sugar-lime solution, such as a juice defecated at room temperature thus leads easily to a supersaturatep. solution of ealcium hydroxides and a turbidity or precipitate is formed, which generally redissolves on cooling.
The composition varies greatly according to
detalls
of procedure, the presence of Oa(OR):! in the solid phase, and other factors.as Generally more or less sucrose is co-precipita.ted in the form of saccharates, decomposing oo1y slowly, Still
more
complicated phenomena take place if such solutions are carbonated,The second dissociation constant of calcium'hydroxide indicates that it is but·a
moderately
strong ba.se: pK2=
12.5.36• 87 This is very important,JUICE PUElFlCA.TION . PUNDA.MENTA.L CHEMISTRY 187 since the concentration of Ca+!- is rapidly diminishing even at relatively low pHJ where the dissociation of carbonic acid and sucrose is still ' very incomplete. This is another example of the many factors lowering the activity of Ca ...
LO
<J, C,.o ADDE.D • ...
Figure 7-5. Solubility of CaO in sugar solutions. The influence of the amount of solid phase. (Wat6rman.-van Akm, 1911).
, 'Z. !Io 5 10 1'2. 14- '='kt 5UCRQ5E IN SOLUTION
Figure 7-6. Solubility of Ca(OHh in sugar solutions. The influence of sng&r CottC8Dtration.
(Lan!loZt-B6m&t6m Tool
.. 1-168) .pea""'.
There ... no methods to determine it rapidly and with any&mOUJ;lt of precision, even though it is enormously important in physiology.
In a 17 percent sugar solution, containing 0.3 to 0.5 percent caO, only from 2 to 8 percent of the total amount of lime exists as Ca+<-. n
The first measurements of the pCa++ in sugar beet juices" from thin