Capítulo 3. Funcionalización de las MNPs-1 con ácidos nucleicos y
3.4 Materiales y métodos
Surface active agents of cationic type are expected to remove colloids from raw juice substantially when added to the normal purification process. Use of Cetyl pyridinium bromide to juice in the defecation of juice gave promising results in the laboratory experiments conducted by N.A. Ramaiah as regards removal of colouring matter and colloids.10 Perhaps cheaper surface active additives may bring about further improvement in sulphitation process, in regard to removal of colloids.
8. FLOCCULANTS
A number of synthetic flocculating agents have come into use in the last two decades.
These flocculants are synthetic high molecular weight polyacrylamides which are partially hydrolysed. Their efficacy as settling aids depends on the molecular weight which ranges between 7 to 10 million and the degree of hydrolysis. These compounds can be either anionic, cationic or nonionic, and serve as bridges among particles of precipitate and thus bring about formation of bigger aggregates of floes. They are added as 0,05 to 0.1% solution in water at the rate of 2 to 5 parts per million parts of juice, to the treated juice in the pipe connecting flash tank to clarifier. A number of these polyacrylamides have come into market and their use has become absolutely essential when dealing with refractory juices or during periods of difficult settling as experienced in Deccan. Moreover their regular use in the process with installation of trayless clarifier has reduced the time of juice retention to 15 to 60 minutes. For improving settling rate and increasing the clarifier through put the addition of synthetic flocculant is essential.
Thus the introduction of synthetic polyacrylamide as settling aids has been a significant advance in the process of clarification.
In Indian industry Separan A.P. 30 and Sedipur were introduced in sixties and were found very effective in rapid settling of sulphitation treated juice in Deccan during periods of high mud trouble which coincided with high recover)' month of the season.
Since then a number of new synthetic flocculants have been introduced, under different trade names. Large scale trials in a sugar mill in Deccan by D.P. Kulkarni in early sixties showed that the polymer separan AP30 when added to suphited juice at the rate of 5 ppm. increased the rate of settling 2 to 4 times reducing the final mud volume by 20-40%.11 Thus, besides rapid rate of settling the final mud volume reduction is achieved by these flocculants. The choice of suitable polymer for use on large scale should be decided by actual settling tests in the laboratory.
9. ENZYMES
Enzymes are biological catalysts, consisting of protein molecule and are industrially produced from microorganims. They are specific in their action and leave no undersirable residue in the final product. In sugar manufacture in the strictest sense they
CLARIFICATION 99
are not employed in juice purification process; nonetheless their addition in the stages preceding or succeeding clarification to overcome the problems in processing created by the presence starch and dextran, is essential.
(A) Amylase—Starch is a polysaccharide composed of amylose and amylopectin in the ratio of 1: 4, out of which the amylose exerts depressing effect on the filterability of raw sugars. The starch granules are solubilised at 70°C and very little of it is eliminated in purification process either by defecation or sulphitation. Because of its melassigenic effect and the contribution to increase in viscosity in pan boiling starch content above certain level 400-500 ppm. is considered undesirable. Moreover much of the starch finds its way to sucrose crystals and starch content in sugar beyond 150 ppm. creates problems in filtration in the refining of raw-sugar. Enzyme Amylase hydrolyses starch at temperature 60°-70° and pH 6.5, into oligosaccharides and other polysaccharides according to studies conducted in South African factories.12 An a amylase Termamyl of Novo A/c enzyme is recommended to be added at the entry point of the second body of the evaporator, since it is suitable and effective at 90°-95°C. The enzyme is diluted ten times before use. If a particular type of amylase is effective at 70°-80°C in its action on starch it is added at the entry to the last but one vessel of evaporator. Perk recommended withdrawal of syrup from 3rd body of quadruple into a tank with thermostatic control and retention of the same in contact with enzyme for 20 minutes for efficient starch hydrolysis before the syrup is taken into last vessel of the evaporator.13
(b) Dextranase—Dextran is produced by bacteria Leuconostoc Mesenteroides in canes which are crushed after prolonged postharvest delay and in even in mills. Dextran is a long chain polymer of glucose molecules joined together by alpha 1:6 linkage and possesses very high molecular weight (5 x 106). It increases viscosity in boiling and contributes to higher loss of recoverble sugar. At the crystallisation station dextran inhibits the growth along B axis of the sucrose crystals which elongate along the 'C axis. According to the findings of Tilbury elongation of sucrose crystals of 2.3 is noticed in 'C' massecuite boiling with dextran level of 1.3% solid, as against normal 1-1.2.14 Use of specific enzyme dextranase results in partial reduction of dextran concentration and the residual dextran is of lower molecular weight which does not affect the crystallisation by increasing viscosity or suppressing the growth of crystals along B axis. The dextranse enzyme is effective at pH 4.5-5.5 and temperatures 50-60°C, conditions which make its addition essential at raw juice stage before heating. The optimum reaction time is 15-20 minutes, while the dosage is 10-20 ppm.
of juice for hydrolysis of dextran.
The dextranase is commercially produced from certain strain of Penicillium, and its use or choice should be governed by consideration of cost. This enzyme can solve the problems emanating from introduction of dextran generated from staling of cut cane at the expense of sugar in the process and it is essential that greater emphasis is laid on preventing this dextran formation by control of post-harvest delay in processing and good mill sanitation.
10. DIATOMACEOUS EARTH
Diatomaceous earth or Kieselguhr is essentially an inert filter aid with practically no power of absorbing impurities in sugar bearing materials. It was used in Java for improving filtration of settled muds after defecation or sulphitation. The important characteristics of good quality Kieselguhr are
(i) improving filterability of sugar bearing liquors or juices,
(ii) it should not contribute soluble matter when mixed with water.
In short it should be real inert filter aid. On account of the costs involved now a days, raw or plantation white sugar plants do not use this material but in refineries it is employed in all Alteration operations - particularly the decolourisation stage.
CLARIFICATION 101 REFERENCES
1. K. Douwes Dekker, Principles of Sugar Technology, Ed. P. Honig Part 1 p. 374,380.
2. Ibid p. 379.
3. Ibid p. 383.
4. D.P. Kulkarni, Proc. Deccan Sugar Tech. Assn. India, 1967 p. 147-160.
5. E. Hugot Handbook of Cane Sugar Engineering, 1972 p. 431.
6. S.C. Gupta N.A. Ramaiah, S.K.D. Agarwal & K.K. Mathur, Proc. Sugar Techn. Assn. of India 1971 p. 99-127.
7. D.P. Kulkarni, unpublished work.
8. cf. Cane Sugar Handbook by Meade & Chen Ed. 10,1977 p. 183.
9. O.S.. Mallea Proc. I.S.S.C.T. 9th Congress 1956 p. 406-418. also Ibid p. 408.
10. N.A. Ramaiah, Proc. Sugar Tech. Assn. India 1961, p. 119-128.
11. D.P. Kulkarni, Proc. Deccan Sugar Tech. Assn. India 1967p. 147-160.
12. cf. Cane Sugar Handbook by Meade & Chen 10th Ed. 1977 p. 137.
13. Manufacture of Sugar from Sugarcane by C.G.M. Perk, 1973 p,57.
14. R.H.TiIbury, Proc. I.S.S.C.T. XIV Congress 1971 p. 1452.