PROCESSING

SUCROSE LOSS IN THE MANUFACTURE OF THE CANE SUGAR

Margaret A, Clarke, Earl J. Robeps,mary A. Godshall, Mary A. Brannan, Frank G. Carpenter and Emory E. Coll

Cane Sugar Refining Research Project, Inc. Southern Regional Research Center, SEA, USDA

New Orleans, Lousidna, U.S.A.

ABSTRACT

The loss of recoverable sucrose in sugarcane harvesting, raw sugar. manufacture and sugar refining is a serious economic problem to the entire sugar industry. Chemical and microbial destruction of sucrose begin sometime even before harvesting, and continue through factory and refinery, and during storage of raw and refined sugars. In this pa- per, the various causes of sucrose loss, including inversion, thermal destruction, alkaline degradation, and microbial action are dekribed, and factors responsible for pathways of sucrose destruction are discussed. Problems other than sucrose loss, such as colorant formation and microbial polysaccharide development, are investigated. The quantities of sucrose loss under various conditions in process, and methods for the estimation of sucrose loss are discussed. An overall picture of sucrose loss, the reasons and results from field to factory and refinery is presented.

INTRODUCTION'

The loss of sucrose, a t all stages from sugarcane in the field to refined sugar in the bag, i s a serious economic problem to the sugar industly. The overall loss, from preharvest to final product, i s estimated a t between 5% and 35%, varying with geographical and technol,ogical criteria. At this, time, when increasing costs and decreasing availability of land are worldwideproblerns, it is of great benefit to the industry to cut-these losses to the lowest possible levels.

A 'considerable amount of lost sucrose is recoverable through readily avail- able measures; of this amount, certain losses, which may initially seem easier to maintain than to recover, lead to increasing complications in subsequent processing. In addition to the loss of recoverable sucrose per se, and the potential income thereby-lost, technical problems are created by the products of-chemical, microbiological and thermal sucrose loss.

M. A CLARKE E T A L 21 93

Microbiological deterioration, in field, factory and refinery, produces poly- saccharides, which decrease extraction and crystallization yields, increase viscosity and lower througput rates, and also produce color and acid forming compounds. Chemical and thermal sucrose breakdown also lower pH and produce colored compunds and color precursors. All of these non-sucrose compounds must be removed in processing, and all have a melassigenic effect, i.e., they carry sucrose with them to molasses, which increases the loss of recoverable sucrose. The costs of additional processing to remove the degradation products increase the economic burden of sucrose loss.

A critical analysis of the causes of sucrose loss is essential to identify the areas where losses may be cut back, and sucrose yield increased. In this paper, physical losses will not be discussed. These include direct losses due to poor cane-harvesting techniques, storage or transport of cane or sugar, spillage, sucrose lost to waste waters, waste muds and adsorbents. The causes, and the means of elimination of these losses are well known, though if these latter were better practiced, the extremely high rates of losses in some areas could be reduced to a more acceptable figure. The various types of chemical, thermal and microbiological loss, their effects and remedies will be discussed.

MICROBIOLOGICAL CAUSES OF SUCROSE LOSS

I '1 Dextran Formation

The major microbiological cause of sucrose loss is the formation of dextran by Leuconostoc mesenteroides, primarily, by L. dextranicum, to some extent, and by other slime-forming bacteria (Imrie and Tilbury12, Moroz12). Apart from the loss of sucrose to dextran formation, dextran causes an increase in solution viscosity which creates problems in evaporators and vacuum pans. Dextran also causes elongation of the sucrose crystal, along the C-axis (the so-called needle- grain) which makes purging of the centrifugals difficult and increases losses to molas~es and wash water. Dextran also gives artificially high pol values, since i t is dextrorotatory.

The degree of branching depends on the strain of bacteria that produced the dextran (13), and many of the differences in properties of various dextrans are due to these structural differences. Not all strains of L. mesenteroides will grow in sucrose solution, and of those that will, none will synthesize dextran over 600C, or at high Brix.

I

I ,

Dextran is a general name for polysaccharides that are polymers of glucose. The straight chains contain a-I, 6-linked glucose moities, with a-1,3 and a-1-4 linkages at the branching points. A t least 50% to 60% of the linkages must be a.1,6 to define a dextran. There is a wide range of molecular weights, from a few thousand up to several million.

PROCESSING

Dextran is synthesized from sucrose by the enzyme dextransucrase shown in Fig. 1, where a linear chain is represented. Although the variously branched dextrans behave in similar ways and cause similar problems in sugars, the variation in molecular structure and molecular weight make quantitive analysis confusing and difficult. The question of analysis ((2011 e t al5t6) . has caused confusion in the literature with regard to levels of dextran that bring about problems in the refinery. Haze-forming tests are generally used, with some sort of alcohol pre- cipitation. However, if interfering substances (e.g. starch, protein) are not eliminated (Meade and ~hen le ) , the high haze levels observed will not accurately reflect the dextran levels present that cause needle-grain and other problems to develop.

Growing linear dextran chain I

Fructose

FIGURE 1. Synthesis of dextrap from sucrose

I t will be noted in Fig. 1 that for every molecule of sucrose consumed, only the glucose portion is used in dextran formation, while a fructose moiety remains. This fructose subsequently decomposes into organic acids and colorant compounds, causing a decrease in pH, which in turn increases the rate of inversion, leading to further sucrose loss, and further formation of acids and colorants from the newly formed invert sugar. In addition to the fructose breakdown products, byproducts of the enzymic dextran formation are acetic and lactic acids, mannitol, and probably ethanol (~ i rschmul ler l~) , all of which enhance the problems of pH drop, colorant formation and increased sucrose loss to molasses later in processing.

M. A. CLARKE ET A L 21 95

To calculate losses from dextran formation, an average 25% yield of dextran is assumed (~irschmullerlo). Levels of dextran found in raw sugars are shown in Table 1, with the respective sucrose losses incurred to produce these dextran levels, and the amounts of fructose and acids (about 30% yield) formed. Dextran levels of 500 ppm (0.05%) are on the high side of average and above this' level needle-grain formation will be a problem. These are levels found by a detailed haze analysis, with interferences eliminated (Coll et a15v6)

TABLE 1. Dextran levels and sucrose loss in raw sugars

Sucrose lost Fructose formed Acids formed Dextran, % ( Ib/ton sugar) (Ib/ton sugar)

0.05 0.20 (4.4 Ibs) 2.2 Ibs 0.07 % 0.1 0.40 (8.81 Ibs) 4.4 Ibs 0.14 % 0.5 2.0 (44 Ibs) 22 I bs 0.7 %

I I t must be emphasized that these amounts of sucrose represent only those lost directly to dextran formation. Three to five times these levels may be lost later in processi~g, because of the other organic materials formed conjointly with dextran.

Additional micr-obiological causes of sucrose loss

In addition to dextran-forming organisms, many other bacteria, fungi and molds exist in cane fields, factories and refineries (Meade and Chenq5, Skoel et Damaged, includingfreeze-damaged cane, burnt caneand chopper-harvested cane dre particularly susceptible to growth of yeasts and bacteria. Especially notice- able, because of their end products found in sugars, are yeasts of the Saccharo- myces species, which produce ethanol, and the butyric-acid producing Clostridium thermosaccharolyticum. In addition to consuming sucrose, these organisms have end products that create more processing and marketing problems.

The sucrose loss caused by microbial action can be minimized or eliminated by proper handling and sanitation. These points are amplified in a later section of this paper.

THERMAL SUCROSE LOSS

The breakdown of sucrose by heat, to form polymeric and/or colored com- pounds occurs during storage of sugars, juices and syrups; this i s generally known as caramel formation. The reactions that take place are essentially the same in solid sugars and in process liquors, since most of the breakdown takes place in the

PROCESSING

molasses or syrup coating of the crystal, where there is sufficient water for the chemical reaction to occur. The fact that sugar losses on storage increase with in- creasing temperature of storage i s well known.

Fig. 2 shows the pol of stored raw sugars of various types with increasing temperature (Muro et a/19120, ~ r i e s t e r ~ ~ ) . In extreme cases (Priester221, where sugar was piled at high temperature, as much as five degrees of pol loss have been observed in five days. This loss was not all due to thermal decomposition; chemical decomposition, of which thermal decomposition is a special case, i s also res- ponsible. The pol drop is accompanied by color formation; in fact it is preceded by color formation, because in either syrup or stored crystal sugar, increase in color i s noted before sucrose 1,qss i s observable. It must be remembered that pol drop can be a deceptive measure of sucrose loss. I f sucrose is first inverted, and the fructose and glucose so formed are further reacted at unequal rates, the pol can appear arti- ficially high, if fructose disappears more rapidly than glucose, or artificially low, if glucose disappears more quickly than fructose. The former is the usual case in refineries; the latter in raw sugar factories (Clarke and Brannan4, Morel du Boil and Schaffler' 7 ) .

//1; High quality

70 9 0 110 130 1 5 0 0 ~ Temperature of storage

FIGURE 2. Pol loss of sugars on storage at different temperatures. Numbers -

on curves indicate number of literature reference

I M. A. CLARKE ET A L 21 97

1.t i s well known that ap increase in color indicates a loss of sucrose, but every few quantitative estimates have been made to relate color formed to sucrose loss, because there is such an extremely complex and diverse family of color-forming reactions, and such a wide range of intensity or degree of color in the reaction pro- ducts. The majority of the sucrose decomposition reaction prodhcts are not, in fact, colored.

A very approximate estimate (Flemings et a / ) that 20% of glucose ends up as colored compounds gives a factor of five, for molecules of sucrose lost per every six carbons of colorant compound formed. When the melassigenic factor of three to five molecules of sucrose lost to molasses with each molecule of color i s considered, then for an average colorant molecular weight of 6001, where 40% of this mole-, cular weight is carbon:

5 x 600 x.4 + (3 to 5) = 19 to 22 molecules of sucrose

72 (mol. wt, of 6 carbons) I I

have been lost.

A quantitative value for color in refined sugar of 3 ppm (Smith*') gives an estimate of 300 ppm in raw sugar; this agrees quite well with a value of 1% colorant in mill syrup solids (Smith et A 50 Brix syrup would contain 0.5%colorant, and the raw sugar from more than, 0.05%, or 500 ppm. So, on a weight basis, one ton of raw sugar is estimated to contain 0.5 kg. colorant. At the above mentioned molecular weight of 600 g and the ration of I9 to 22 molecules of sucrosct lost for each molecule of sucrose formed, this gives as an extremely general estimate, 15.8 to 13.3 molecules or 5.4 to 6.3 kg sucrose per ton of raw sugar (0.5% to 0.6%) lost in the formation and subsequent removal of this colorant. This approximation 'igngres the facts that (1) some color comes from plant sources, and i s not manu- factured from sucgose; (2) there is a wide molecular weight for colorant, from less than 100 to several thousand; (3) a great deal of colorant is removed by absorb- ents and clarifying agents and does not go to molasses; (4) colorant is continually being formed throughout processing; (5) since high molecular weight color is select- ively occluded in the crystal (Roberts and Godshall24), a higher proportion of low molecular weight color goes to molasses and (6) not all sugar color is formed through glucose.

This colorant includes not only that made from thermal sucrose loss, but also that from chemical decomposition, which is more properly discussed in the following section.

CHEMICAL SUCROSE LOSS

The chemical degradation of sucrose includes thermal degradation to caramel.

21 98 PROCESSING

type products as discussed above. There are two general divisions of chemical degradation: those under acidic conditions and those under basic conditions. The optimum pH for sucrose stability is between 8 and 8.5.

Acidic Conditions

The initial reaction is inversion of sucrose to glucose and fructose. In cane juice, this can be catalyzed by invertase enzyme and in any environment by low pH. lnvertase enzyme is inactivated by an increase in temperature to 800C or more, and acid inversion is inhibited by raising the pH above 6. There is always some invert present, and these reducing sugars deteriorate further through many series of reactions to form'colorant compounds, colorant precursors, and non-colored organics, with yet again the attendant problem of the melassigenic effect of non- sucrose compounds (Feather and Harris7, Fleminget aI8, parker2').

The rate of inversion has been the subject of many studies (Clarke and ~rannan3.4, G'oodacre and Coombsg), using either measurement of invert formed (Barnett and O'Connor, and Parker21) or of sucrose lost (Clarke and Brannan314,), or acid consumed. There has been some controversy about rates of inversion depending on the experimental method used to follow the reaction. The rate i:; generally considered to depend on temperature and theconcentrationlof hydrogen ion, sucrose, and water.

The invert sugars are comparatively stable in acid solution, but there is con- tinual color formation due, in part, to oxidation through several intermediates to 5-hydroxymethylfurfural (HMF) and to its colored decomposition products. Other pathways of color formation in acid solution include condensation of HMF with amino acids to form nitrogen-containing brown compounds, and the conden- sation of glucose with amine compounds, to form a product which, after under- going an Amadori rearrangement, i s polymerized to form the familiar brown Mail- lard reaction products, or melanoidins (Ramchander and Feather23). These color problems at low pH occur upon destruction of sucrose in cane juice, or anywhere else in processing where there is a localized temporary area of low pH.

Basic Conditions

Sucrose degradation under basic conditions i s not as serious as that under acid conditions from the point of view of direct sucrose loss, but it is more serious from the point of view of color formation, with the increased processing and loss to molasses thereby entailed. Color formation under basic conditions is an extremely complex field.

Alkaline degrddation of sucrose to reducing sugars i s probably the first reaction step (Shaw etaI27, Whistler and ~ e ~ i l l e r ~ ~ ) , although there is some contention thatglucose and fructose are not found in base hydrolysis (Parker2I ). ,

M. A. CLARKE ET AL

The major products of alkaline degradation are organic acids, especially lactic acid - which tends to lower pH - and polymeric colored products, either melan- oidins, or compounds formed through a series of saccharinic acids, a series of reactions that i s catalyzed by calcium ions (Carpenter and Roberts2. Hodgell, Parker21 ).

The presence of reducing sugars in an alkaline medium is the optimum for color formation, i.e., the worst situation for processing. This situation is obtained when cane juice is allowed to remain at acid pH for some time before the pH i s raised. In this case, the lime is said to destroy the invert; it does, but the desiruct- ion reactions create color. In addition, invert in solution will react with amine compounds, from protein breakdown, to form melanoidins. Excess lime will also catalyze breakdown of sucrose to organic acids (Montgomeryl7).

SUMMARY

In summary, the stages of sugar production are considered, with regard to the possible problem areas for sucrose loss, and measures that may be taken to prevent those losses.

Cane Harvesting

The most serious losses here occur when cane is allowed to become stale

before being taken to the mill. lnvertase enzyme inverts sucrose, and the pH drop which begins on cutting - or when cane is damaged - also causes sucrose to invert. Organic acids produced Trom invert degradation further decreases the pH. Leuconostoc mesenteroides infection and production of dextran proceed most rapidly under acid conditions, using up sucrose quickly. Dextran production rate increases with increasing ambient temperature and wetness. The amount of dextran present in chopper-harvester cane has been shown to increase from effect- ively none to 25% on Brix, when the cane is held for 24 hours (Keniry et al l4).

The remedies here are apparent: to minimize burn-to-acid and cut-tocrush times as much as possible. It i s often asked i f there i s not a biocide that can be used to get rid of L, mesenteroides. The organism is so prevalent - in most soils, air and water around the world - that such a biocide would have to be used in impractical- ly wide application. Efficiency in harvesting prevents are growth of the organisms, and conserves the sugar lost to i t s growth.

Losses of sucrose in this area can range from 5% to 25% and even higher; where cane is extremely deteriorated, it may not be possible to make sugar at all, but only molasses.

Raw Sugar Mil l

Deterioration of cane in the mill yard can le vere sucrose loss ,(Colt

2200 PROCESSING

eta15), but here again the remedy is obvious: efficient harvesting procedures com- bined with minimum storage times for cane, under optimum conditions of sani- tation.

Storage of cane juice is another potential cause of severe loss, particularly for any holding period before the pH i s raised. Over-compensation for pH drop by overliming only increases the problems of chemical sucrose loss and color forma- tion. Storage of juice or syrup at any stage a t elevated temperatures affords potential sucrose loss. An ever-present problem is dextran formation, which can be prevented only by good housekeeping, minimum storage of low Brix solutions and use of bactericides.

p, ,_ In storage of ra'w!sugar, and in transport, chemical or thermal sucrose loss

i s incurred when the sugar is stored at too high a temperature, i.e. i f it is not cooled to 100°F before piling. The drier the stored sugar, the less deterioration will occur, but the low temperature i g the most important factor(29).

Losses here, other than physical losses such as sucrose to bagasse, generally run from 3% to 80%.

Cane Sugar Refinery

In most refineries, the pH of liquors and syrups is generally between 7 and 9, a stable range for sucrose. However, chemical sucrose loss occurs in stored sweet- waters, once again by the self-catalyzing destruction of invert to organic acids, Recent studies (Clarke and ~ r a n n a n ~ ~ ~ ) , u s i n ~ high pressure liquid chromatographic techniques, indicate that there is some chemical sucrose loss in clarification, parti- cularly during carbonation, where invert is formed and destroyed within the carbonation system. Other recent studies, using radioactive tracer techniques Goodacreg), show sucrose loss of 0.004% to over 0.04% in neutral or alkaline pH liquors. There is always chemical, including thermal loss when sucrose i s held at high temperatures, even in high Brix solutions at neutral pH (Clarkeand Brannan3). The potential for dextran formation is s t i l l present, particularly, in low Brix solutions and low purity sweetwaters. Chemical, thermal and microbiological losses are generally kept below 2% in modern refineries.

CONCLUSION

In this paper the nature and reasons for sucrose loss, by thermal, microbio- logical and chemical means, have been followed from the cane field through the refinery. Particular emphasis has been placed on control of losses because of poly- saccharide formation and incorrect pH.

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inversion of sucrose. J. Chem. Soc. B. pp. 11 63-1 165.

2. Carpenter, F.G. and E.J. Robert (1975). Colorant formation under refining conditions. Proc. 1974 Tech. Sess. Cane Sugar Refin. Res. 106-1 15.

3. Clarke, M.A. and M.A. Brannan (1978). Sugar losses by inversifjn. Proc. Sugar I nd. Technol. pp. 333-367.

I 4. (1979). Sucrose losses through decomposition in refinery liquors. Proc. 1978. Tech. Sess. Cane Sugar Refin. Res. pp. 149-

5. Coll, E.E., E.J. Roberts, and M.A. Clarke (1978). Deterioration of sugarcane: Levels of dextran and polysaccharides in process streams at two Louisiana sugar factories. Sugar J. 41 : 21-25.

6. 1979. Detran problems in sugar production. Proc. 1978 Tech. Sess. Cane Sugar Refin. Res. pp. 92-106.

7. Feather, M.S. and J.F. Harris (1973). Dehydration in acid solution. Adv. Carbohydr. Chem. & Biochem. 28: 161-224.

8. Fleming, M., K.J. Parker and J.C. Williams (1968). Aspects of the chemistry of the browning fraction of reducing sugars. Proc. ISSCT, 13: 1782-1 800.

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9. Goodacre, B.C., G.L. Martin and J. Coombs (1978). Sucrose dehydration under alkaline conditions - an isotopic method for the estimation of "sugarloss" in refin~ng processes. Sucrerie Belge 97:305-315.

10. Hodge, J.E. (1953). Chemistry of browning reactions in model systems. J. Agric. Food Chem. 1 :928-943.

11. Hirschmuller, H. (1953). Chemical properties of sucrose. In Honig, P., Prin- ciples of Sugar Technology. pp. 1-1 7. Elsevier, Amsterdam.

12. Irnrie, F.K.E. and R.H. Tilbury (1972). Polysaccharides in sugarcane and i t s products. Sugar Technol. Rev. 4:291-363.

t, ' 6 *,

13. Jeanes, A., W.C. Haynes e t a/. (1954). Characterization and clarification of ,dextrans from ninety-six strains of baqeri'a. J. Am. Chern. Soc. 76: 5041-

> ' $ T i . "

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5052.

14. Keniry, K.S., J.B. Lee and C.W. Davis (1967). Deterioration of mechanically harvested chopped-up cane. Part 2. The rate of dextran formation. 1nt:Sugar. J. 69: 357-360.

15. Meade, G.P. and J.C.P. Chen (1977). Cane Sugar Handbook, 10th edition. Wiley Interscience, New York, p. 405.-

16. Montgomery, R. (1953). Observations on alkaline degradation of sugars. Ind. Eng. Chem. 45: 1144-1 147.

17. Morel du Boil, O.G. and:@,J. Schaffler (1979). Non-sucrose changes during sugar processing. Proc. 1978 Tech. Sess. Cane Sugar Refin. pp. 107-135.

18. Moroz, R. (1953). Methds and procedures for the analyses of micro-organisms in sugar. In Honig, P., Principles of Sugar Technology, v. Ill, pp. 373-452.

19. Muro, M. e t a/. (1974). Study on the deterioration of sugar. Sugar Ind. Abstr. 78-395.

20. (1976). Sucrose losses during storage of raw cane sugar. Sugar Ind. Abstr. 77-569.

21. Parker, K.J. (1970). Chemical problems in the sucrose industry. Sucr. Belge, 89:119-126.

22. Priester, H.R., Jr. (1978): Raw sugar quality considerations at Savannah Sugar Refinery. Proc. 1976 Tech. Sess. Cane Sugar Refin. Res. pp. 183-185.

23. Ramchander, S. and M.S. Feather (7975). Studies on the mechanism of color formation in glucose syrups. Cereal Chem. 52: 166-173.

24. Roberts, E. J. and M.A. Godshall (1979). Some observations on high mole- cular weight colorants in sugar. Proc. 1978 Tech. Sess. on Cane Sugar Refin. Res. pp. 68-80.

25. Shaw, P.E., J.H. Tatum and R.E. Berry (1969). Base catalyzed sucrose degra- dation studies. J. Agric. Food Chem. 17: 907-908.

26. Skoel, R.D., J.N. Hogu and A.B. Rizzuto (1978). Microbiology of sugar: A taxonomic study. Proc. 1977 Tech. Sess. Cane Sugar Refin. Res. pp. 82-99.

27. Smith, N.H. (1978). Fractionation of sugar colorants by high pressure liquid chromatography. Proc. 1977 Tech. Sess. Cane Sugar Refin. Res. pp. 19-34.

M. A. CLARKE E T AL

28. Smith, P., D. Linecar and N.H. Paton (1979). Techniques for the isolation of cane sugar colorants. Proc. 1978 Tech. Sess. Cane Sugar Refin. Res. pp. 81-91.

29. Symposium on Raw Sugar Quality Standards. 1969. Proe. 1968 Tech. Sess. Cane Sugar Refin. Res. pp, 138-159.

30. Whistler, R.L. and J.N. BeMiller (1958). Alkaline degradation of polysaccha- rides, Adv. Carb. Chem. 13: 289-330.

31. Williams, J.C. (1976). Porperties of colorants produced by the degr;dation of reducing sugars: Commr. lyo. Tech. Sucr. 1975: 319-327.

PERDIDAS DE SAGAROSA EN LA FABRICACION DE AZUCAR DE CAKA

Margaret A. Clarke, Earl J. Roberts, Mary A, Godshall, Mary A. Brannan, Frank G. Carpenter y Emory E. Coll

La pCrdida de sacarosa recuperable durante la cosecha de caiia, la fabricacihn de crudo y la refinacibn conseituye un serio problema econ61nico en toda la industria azucarera. La destrucci6n q6irnica y rimicrobiologica de la sacarosa empieza a veces antes de la cosecha, y continua en la fabrica y la refineria, asi como durante el almacena- miento del =&car cruda y la refinada. En este trabajo se describen las varias caum de p6rdidas de sacarosa, incluyendo inversion, destruc- cion temica, degradacion alcalina y acbion microbiana y tambien se discuten 10s factores que conducen a la destrucci~n de sacarosa. Se investiga, adem& problemas distintos a la destruccion de sacarosa como son la formation de colorantes y el desarrollo microbiano de pollisaciridos. Se discuten las cantidades de sacarosa p6rdidas bajo dis- tintas conciiciones del proceso asi como mktodos para estimar estas pkrdidas. Hay una referencia especial a m6todos de angisis por croma- tografi'a gaseosa y lfquida para azhcares, colorantes y pslisaciridos. Se presenta un cuadro general de p6rdidas de sacarosa, sus causas y resultados, desde el campo hasta el engenio y la refineria.