STUDIES ON CANE DETERIORATION IN AUSTRALIA

D. H. Foster, P. A. lnkerman and K. E. Mc Neil

Sugar Research Institute Mackay, Australia '

ABSTRACT

Recent work on cane deterioration in Australia is reviewed, During cane fires, temperatures rise above 80'6 throughout 20% of the upper portion of the cane stem resulting in appreciable loss of sucrose. Dilution of sugar in burnt cane sticks due to water uptake leads to an apparent sucrose loss. This dilution occurs chiefly in the outer portion of the stick where the greater proportion of vascular bundles are found. Uptake of water does not appear to be of any consequence in the first 24 hours after burning, but can be appreciable after this time.

No microorganisms are found inside sound green cane but high levels can be found in standing burnt cane. Surprisingly, microbial populations may be just as large in chopper-harvested green cane as in chopper-harvested burnt cane. In contrast, dextran and ethanol levels in the former are only a small fraction of the levels in the latter.

A variety of microorganisms are found inside green and burnt chopper-harvested cane and in cane that has been left standing in the field after burning. Species of Leuconostoc, Lactobacillus, Klebsiella, Enterobacter, Erwinia and Saccharomyces have been isolated.

For adsessment of cane deterioration between burning and cutting, measurement of collective changes in pH, apparent purity, C.C.S. and dextran concentration is desirable because there is no reliable relation- ship between the separate paramaters. The presence in burnt cane of acid-producing organisms other than Leuconostoc demonstrates why there is a poor correlation between pH and dextran.

Only the dextran-forming species of Leuconostoc and Lactobacillus produce a detectable "haze" with 50% (v/v) ethanol. Dextran is the only polysaccharide in chopper-harvested burnt cane which is produced in quantities sufficient to cause processing difficulties.

D. H. FOSTER ET AL

INTRODUCTION

The deterioration of sugar cane is brought about by a number of interacting processes. A summary of these processes i s presented in diagrammatic form in Fig. 1.

The overall effect i s a loss of sucrose accompanied by an increase in impurities. The latter further compound the effect by decreasing recovery.

Studies on cane deterioration in Australia covering the period 1969 to 1976 have been reviewed by lvin and ~oster". Since harvesting of cane is now carried

k b sucrose loss (chemical)

I Water uptake

Burn-to-cut Sucrose losses microbial plant enzymic chemical

Chopper-harvested canes

Water loss (evap)

Cut to crush delay

plant enzymic chemical

Crush - F~GURE 1. Sequence of processes which influence deterioration

out entirely by chopper-harvester and this is generally preceded by burning the cane approximately 12 to 40 hours prior to harvesting, the emphasis of the research was placed on the deterioration occurring between burning andcutting and crushing.

2206 PROCESSING

However, the degree of deterioration proved very difficult to measure in absolute terms. A number of parameters was investigated and used as indicators of deterioration, but none was completely satisfactory, In contrast, Keniry eta / " demonstrated that the dextran level of juice was an excellent indicator of the processing problems associated with deteriorated cane (see also Wells and ~ a m e s ~ ' and references therein). The successful application of dextranase during processing has confirmed this major role of dextran under Australian conditions (lnkermang ).

More recently, cons~deration has beeh given to the harvesting of green cane because of i t s obvious advantages such as:

1. Higher recoverable sucrose % cane resulting from the elimination of (i) sucrose losses between burning and cutting and reduction of losses between cutting and crushing (ii) sucrose losses due to the cane fire and (iii) dilution of juice due to water uptake by the root system.

2. Reduction of dextran formation to negligible amounts, and

3. Avoidance of the chore and nuisance of burning.

The chief disadvantages of green cane harvesting are the increased amount of cane left in the field with some varieties which are not free trashing14 and the reduced rate of harvesting which must be accepted to produce a trash-free product.

In this paper, recent studies on some of the parameters influencing deteriora- tion of sugar cane are reported viz. the initial burning of cane with the resultant effects of sucrose loss, water uptake and of deterioration brought about by long delays before harvesting. In addition, the above work is coniplemented by micro- bial studies on this cane (designated standing-burnt cane) and on green and burnt chopper-harvested canes.

It is worth noting that, at present, green cane comprises only a small percent- age of the total supply to Australian factories. Furthermore, i t is only of real impor- tance in the hot and wet northern areas where deterioration is rapid and where there is a danger of burnt cane being left in the field for long periods. Frequently the latter type of cane comprises the whole of the mill supply during wet weather.

QBSERVATIONS AND DISCUSSIONS

Burning of cane

(a) Temperature measurement

King and Sutherland (private communication) reported a maximum tempera- ture of 4 0 0 ' ~ on the cane surface in an intense fire. This maximum lasted for less than 3 seconds. Below the cane surface, a temperature as high as 70°c was recorded at a depth of about 0.3 mm. In comparison, Questel and ~ r e ~ ~ e r ' ' measured tem- peratures of 50 to 70°c in the center of stalks near the top.

In recent investigations at the Institute, ~ o s t e r ~ used thermocouples set in

D. H. FOSTER ET AL 2207

the cane about3 meters above ground level. The results are shown in Table 1.

The temperature in a moderate fire rose above 80°c for about 8 seconds a t a depth of 1.5 mm below the cane surface (Fig. 2). Thus, at least 20% of the ohter portion of the cane stalks (average diameter of approximately 25 mm) would have been subjected to temperatures above 80'~.

TABLE 1. Maximum temperatures inside cane during fires

Distance from cane surface (mm) 1 .O 1.5 2.0 2.5

Maximum temperature (OC) in:

Moderate fire 87 60

Poor fire 98 45

I b I I I I I

0 20 40 60 80 100 120

Time (seconds)

FIGURE 2. Temperature profiles inside cane in a moderate fire

(b) Sucrose loses

Even in a poor fire, 9 8 ' ~ was reached at a depth of 1 mm below the cane surface (Fig. 2). Thus, a large portion of the cane must be dehydrated and heated to a temperature which denatures enzymes and results in the formation of both colored and uncolored degradation products from sucrose. Furthermore, sucrose losses could be substantial in the most severe fires.

Investigation of these losses has just commenced at Sugar Research Institute, hence only preliminary results are available. Internodes from the top and bottom of 10 sticks of cane were selected before burning and 21 and 45 hours after burning. The top internodes were taken about 300 mm below the topoing point and the bottom internodes about 200 mm from the butt. Cane was sliced off the internodes to a depth of about 0.6 mm which amounts to about 10% of the internode weight. The core and rind portions were analyzed for pol, Brix and apparent purity. The results are given in Table 2.

TABLE 2. Apparent purity of juices from green and burnt cane

Internode Portion Apparent Purity of Juice a

Top: -

Green 92.3 91.6 93.6 88.5

Burnt 21 h 90.7 91.8 71.8 68.2

Bottom:

Green 94.3 94.6 74.5 75.5

Burnt 21 h 93.3 93.5 71.4 70.7

a Extracted by boiling for 3 hours.

Constitutes " 9 0 % of cane.

Constitutes " 10% of cane.

No significant change in the core portions was otserved. However, in the upper rind, the apparent-purity fell by 20 units. These changes occurred almost entirely in the first 21 hours after burning. Therefore, it i s assumed that they are

D:H. FOSTER ET AL 2209

1 I due to heat-induced chemical reactions.

The rind in the butt internodes had a much lower ini/tial purity and did not vary to any degree as a result of burning. This i s consistent with much lower tem- peratures at ground level. More detailed analvsis of sucrose and its degradation products will be made in future work.

Holder and stefano8 in Florida have claimed that yields of sucrose (%cane are 5% greater in cool burnt cane than in hot burnt cane. They reported a lower Brix and sucrose concentration'in hot burnt cane with no significant change in purity. These results suggested that there had been a substantial increase in water content.

Time burnt (hours)

h)

!2 b

0

TABLE 3. pH and ~ e x t r a n ~ levels in chopper-harvested cane during storageC

Time Mackay (October, 1977) Tully (November, 1977)

(days) Green (NCo12R) Burnt (NCo12R) Green (099l IR) Burnt (09012R) stored -.

In 1.;

bins PH dextran PH dextran PH dextran PH dextran

0 5.3 < 50 5.6 1 6 4 5.5 < 50 5.2 < 50 .

a All alcohol haze (50%, v/v) moved by dexttenase (Fuleher and lnkeman7). Concenbetims expressed in ppm on Brix. \O b Dm* and mutilated billets.. Mackay, 23-50%; Tully, green, 17%; burnt, 21% II

c -Metemlogicel dam: Mackay; 16-280~, 48-98% mi. humidity; Tully; 17-23O~, 34.98% =I. humidity. 0

d Burnt-mut delay 36 h. Dextran levels inside cane. B 5 Z G)

TABLE 4. Viable cell countsa for chopper-harvested canes after storage for two daysb

Burnt billas Green billets Types of Microorganisms Unwashed Sound Shattered Sound Shattered

Total bacteria d 4.3 x lo7 3.9 lo7 3.1 x 107 3.5 x lo7 5.2 x lo7 yeastse 3.8 x lo6 1.7 x 106 2.3 x lo6 3.8 x lo7 QX lo7

a Estimated (per m l of juice) after incubation for 48 h. Tully rials, November, 197Z See Table 3 for othr

a Estimated (per rnl of juice) after incubation for 48 hr.

Tully trials, November, 1977. See Table 3 for o&er relevant data

Sucrose tryptone agar plus 75 ppm sodium azide. d Plats count agar.

Wort agar plus 500 ppm aureomycin.

fcl Water uptake

The uptake of water by cane after burning isnow well recognized

Most of the water seems to be absorbed into the outer portion of the stick where the greater portion of the water-conducting vascular bundles are found. Experiments designed to explore this question were carried out several years ago in Mackay. NCo 310 canes,were taken at various times after burning and cut so as to provide outer (rind) and inner (core) fractions of equal weight. The difference in pol was determined and plotted as a function of time after burning (Fig. 3). The core fraction had a fiber content of about 6% while the rind fraction fiber was 16%. In addition, the pol of the latter diminished with time relative to the former in each of three series of measurements.

In order to explore water behavior after burning in gredter detail, a tech- nique has been developed (Fosterb) for sampling sticks from portion of a, field of cane and measuring properties which indicate water uptake precisely. Fifty sticks of cane were found to be sufficient to give a reproducible sample for measuring cane density. This parameter together with recordings of dimensional changes on sticks lefts standing in the field allows the calculation to be made.

Negligible dilution due to water uptake was observed in 7 measurements made over periods of 16 to 20 hours after burning. However, in 6ne of two mea- surements made over 45 hours, the cane took up 1% of water by weight in the last 24 hours. The degree to which this dilution depends on soil moisture, severity of burning and other factors has yet to be determined.

Further evidence for higher microbial deterioration in burnt cane was provided by Blake and ~ c ~ e i l ' . During a period of total conversion to the crushing of green cane billets, levels of ethanol in first mill juice fell to 15% of the levels obtained when crushing burnt cane.

These reduced levels reflect diminished deterioration by yeasts, enterobw- teria and Leuconostoc. The same roup of organisms present in standing burnt cane 9 have been isolated from chopped .burnt and green cane (McNeil and Inkerman, unpublished). Among the yea/its, Saccharom~c~s cerevisiae dominates although other species of Saccharomyces, Rhodotorula, Torulopsis and Candida are present.

Deterioration in standing burnt cane

Early studies on deterioration of cane le f t standing in the field before cutting has resulted in conflicting data. Young2' reported no significant loss in sugar content in standing burnt cane in less than 4 days. In contrast, woodZ0 found that cane which is burnt and left standing (even for one day before cutting) exhibits a more rapid decline in recoverable sugar percentage than cane which is burnt and cut immediately. The latter result emphasised the importance of burning only enough cane to meet the requirements of single day's harvest.

Preliminary investigations

A preliminary investigation was carried aut in the Babinda-Tully districts of

D. H. FOSTER E T AL 221 3

North Qheensland during the very wet crushing season of 1973 (Fulcher and lnkerman7). The findings which were confined mainly to measurement of dextran levels are summarized below:

1. The pH of first-expressed juice cannot be used to indicate the presence of, or concentration of dextran in the normal cane supply duriing wet weather. In contrast, in burnt chopper-harvested cane stored for long periods of time under the same climatic conditions, the expected relationship exists viz, high levels of dextran are accompanied by correspondingly low values of pH, apparent purity and C.C.S..

2. High levels of dextran were found in some "sound" burnt canes with burn-to- cut times of the order of 4 days; other canes which had been burnt for longer periods (6 to 7 days) contained little or negligible amounts of dextran.

3. The presence of dextran inside "sound" burnt cane was indicative of a heavy internal infection by Leuc~nostoc. This contradicted an earlier held view that "sound standing crops of cane, whether green or burnt, do not harbor Leuconostoc.' (EganS). Howevsr, in most probability, Egan was referring to burnt cane left standing in the field for less than 24 hours.

4. Dextran was not detected in sound upright or lodged green cane. However, diseased cane (or cane of "poor" quality; see Bacic et at . ' ) contained appre- ciable amounts of dextran. Consequently, it could serve as a source of micro-

,. bial infection of chopper-harvested cane.

Studies during the 1976 season

11 la) Confirmation of the previous work

I The results of Fulcher and lnkerman7 were confirmed during the 1976 crushing season by the studies of McNeil and lnkermanl and Back et a l l .

For example, McNeil and ~nkerman'~ examined random samples of burnt cane that had stood in the field for a t least 10 days after burning (Table 5). Analyses revealed that all samples exhibited some degree of deterioration. This assessment was made from the low values obtained for pH, apparent purity and C.C.S. com- pared to similar mill datajfor fresh burnt cane.

Dextran was detected in 4 of the 6 samples, two of which could be described as "sound". In comparison, samples 4 and 6 contained to dextran although obviously deteriorated i.e. if the other three parameters of deterioration were used for cam- parison.

The above results dehonstrated that the presence of dextran in standing burnt cane was variable. Therefore, dextran is not a reliable indicator of deterioration under these conditions (Bacic et al. ' ).

The levels of reducing sugars in stand~ng burrt cane have also been measured and shown to rise with an increase in the burn-to-cur time (Bacic eta / . ' ) . However,

2214 PROCESSING

in our opinion, the use of this parameter as a measure of deterioration i s unsatis- factory, because all of the microorganisms found inside standing-burnt cane (McNeil and lnkerman' ) can utilize reducing sugars as carbon sources.

(6) Relationship between dextran and pH

There appears to be little correlation between pH and dextran levels in standing burnt cane (Table 5). Similar conclusions were reached by Bacic et a/. I.

Generally, for a given pH in juice, there is less dextran in standing burrit cane than in stored chopper-harvested cane. Therefore, other microorganisms and possi- bly the plant contribute-more to the total acid production in standing burnt cane than do dextran-pr6xucing microorganisms. In contrast, the latter organisms dominate in stored (or "held-over") burnt chopper-harvested canes, and thereby must contribute substantially to the total acid production (EganS, Fulcher and lnkerman').

The presence, in burnt cane, of acid-producing organisms other than Leucon- nostoc (vide infra) demonstrates why there is a poor correlation between dextran 1 and pH except in the case of stored burnt chopper-harvested cane.

(c) Deterioration between burning and harvesting

Dextran levels and microbial counts increased rapidly in all samples during transport to the factory (Table 5 and 6). These latter results are indicative of fur- ther deterioration and demonstrate the rapidity with which standing burnt cane deteriorates between cutting and crushing, especially if harvesting were delayed for long periods of time (wood2').

In general, the measurement of deterioration by such individual parameters as pH, apparent purity, C.C.S. and dextran concentration is not reliable in many situations. Instead, the collective use of these parameters i s more meaningful, especially in the determination of a particular trend in deterioration.

(d) Polysaccharide synthesis by microorganisms

Leuconostoc was the only microorganism isolated which, when cultured on artificial cane juice medium ( ~ i l b u r y ' ~ ), produced a poSysaccharide in sufficient yield that could be detected by the method of Keniry et, a l l Z . Identification of dextran was confirmed by an enzymic method (Fulcher and lnkerman7).

Cane dextrans isolated from burnt-chopper-harvested and standing-burnt cane were shown to have similar physico-chemical properties viz. solubilities in ethanol, (Fig 1 in McNeil and lnkerman"), enzymic rate measurements (Fig 2 in McNeil and Ir~kerman'~), weight-average molecular weights 25 x lo6 Crees and Inkerman, unpublished) and structure - [95% d: - 1, 6 and - 5% d: - 1, 3 lin- keges; Leonard and ~ichards' 3 , Blake, unpublished]. In comparison, Covacevich and I3ichards3 reported a very similar structure to the above polysaccharides for all of the high molecular weight-dextran fractions that had been isolated fro^ a wide

TABLE 5. Analyses of burnt standing canea

Dextran Burn-to Cut-to pH App. Purity C.C.S. ,(ppm on Brix)

Sample ' Cut (days) (Crush (h) CUP crushd . . C U ~ crushd C U ~ crushd CUF crushd

Green Cane 5.2 90 13.5 < 50

Fresh c a n 8 < 1 10-18 5.2-5.4 89 15.2

a Meterol a Meterdogical data: rainfall, 119 mm; temperature, 26.930.6 (maw./ and 18-2!i0c, fminl; relative humid% 52-1- b Cane bckgrwnd; wll burnt, new growth in root area, NCo 310 varieties except for sample 2 (0871, sound except for a

k w @is in simples 3 and 6 and many */its h sample 5. c Analysis of fadm simples collected from the field d Andy& of factory samples of chqpper-harvested cane obtained from the same field e Estimated using average fiber content for each variety. f Sample at factory includes cane crushed with some 12 day-burnt cane g Normal facivty scy~ply of burnt chopper-harvested cane for period f o l l o w i ~ stale cane.

N TABLE 6. Numbersa and dominanp speciesC of microorganisms present in burnt standing cane 2

03

Internal Cut Crush Sample

d ,

Number umber^ Type type

1 . 6 ~ 10' E. cloace E. herbicola E. uredovora L. mesedteroides

1.7 x lo6 E. cloace K.-bneumoniae

1 . 0 ~ lo4 E. aerogenes E. herbicola

1.9 x los f L. rnesenteroides (1.8 x lo51g L. mesenteroides

Not examined

Not examined

Not examined

E. herbicolh Not examined

L. mesenteroides 1.5 x 1 o8 L. mesenteroides - - -

6 52 L.mesenteroides 4 . 5 ~ 1 0 ' . E. cloace 2.9 x 107 L. mesenteroides -0 n

L. mesenteroides 0 2 Gi

1 . 0 ~ lo6 12 Green Zero -, E. dissolvens z

0

Cane (Unwashed) E. cloace E. uredovora L. rnesenteroides a

;;I R

a Edtimated using the pour plate dilution technique. Isolated at the highest dilution of the viable cell count. Other organisms may have been present in smaller numbers.

Classified according to Bergey3 Manual o f Determinative Bacteriology (1974 edition).

Estimated per gram of tissue.

Estimated per m l o f juice.

Sub-sample with no splits.

Sub-sample with splits.

211 8 PROCESSING

range of Bueensland raw sugars. The authors ivere surprised at the high degree of structural consistency, since, in their opinion, the species of dextran-producing microorganisms would be expected to'vary among the different sites of biosyntkesis.

Bacic et a/.' reported a rise in the concentration of non-dextran polysacha- rides in juice from standing burnt canes during the latter part of the season. Though the nature of these polymers was not investigated, a microbial origin was suggested by the authors. However, it i s not known whether these polymers are of hny signi- ficance during processing as juices had not been subjected to clarification.

Microorganisms inside standing burnt cane

Large nu,mbers of microorganisms were insolated from within sound or cracked stal)/ding-burgt cane (Table 6). The number of organisms present was comparable with level?observed in burnt cane billets 3 days after cutting an an^) or after artificial inoculation ( ~ i l b u r y ' ~ ) . The low numbers of microorganisms in sample 6 suggest a possible role for the plant's down degradative enzymes in deterio- ration viz. invertase and other hydrolytic enzymes.

No microorganisms were detected inside freshly-cut green cane. However, the juice from this unwashed cane after crushing had a comparatively high cell count, presumably from microorganisms on the cane surface.

Leuconostoc mesenteroides was the dominant microorganism in standing burnt cane after chopper-harvesting and transport to the mill (~~an').Recent work indicates that dextran-fokming species of Lactobacillus are also present (McNeil, unpublished data).

Enterobacteria, particularly Enterobacter aerogenes, Enterobacter cloace, Enterobacter dissolvens, Erwinia herbicola, Erwinia uredovora and Klebsiella pneu- moniae dominate under different conditions. There is the probability that the motile species can invade standing-burnt cane more effectively than Leuconostoc.

Erwinia herbieola; in particular, has been reported as the dominant species of the epiphytic microflora of sugar cane (0weni6). ~ i l b u r y ' ~ reported most of the above species in cane juice but concluded that species other than Leuconostoc contributed little to overall deterioration. These studies suggest that this conclu- sion may not be valid, a t least for standing-burnt cane.

REFERENCES

1. Bacic, A., M. T. Covacevich and G. N. Richards (1977). Deterioration in burnt standing cane: a preliminary survey. Proc. Qd. Soc. ,Sugar Cane Tekh- nol., 44th Conf., 11-18.

2. Blake, J. D. and K. E. plcNeil (1978). A comparative study of alcohol con- centrgtions in green and burnt cane and the changes occurring during milling. Proc. Qd. Soc. Sugar Cane Technol., 45th Conf., 127;132.

D. H. FOSTER ET AL 2219

3. Covacevich, M. T. and G. N. Richards (1977). Studies on dextrans isolated from raw sugar manufactured from deteriorated cane. Part 1. Isolation, purification and structure of the dextrans. Int. Sugar J., 79: 3-9.

4. Egan, B. T. (1965). The infection process in sour Storage rdt. Proc. Qd. Soc. Sugar Cane Technol., 32nd Conf., 25-30.

5. . (1971). Post-harvest deterioration of sugar cane. Bur. Sugar Expt. Stns. Qd.

6. Foster, D. H. (1979). Trends in green cane procesqing. Proc. Aust. Soc. Sugar Cane Technol., 46th Conf.

7. Fulcher, R. P. and P. A. lnkerman (1974). Further studies on'the deteriora- tion of cane and cane juice. Proc. Wd. Soc. Sugar Cane ~echnol., 41st Conf., 161-169.

Holder, D. G , and R. P. De Stefano (1977). Influence of pre-harvest burn intensity on cane quality. Proc. Am. Soc. Sugar Cane Technol., 7, 58-60.

Inkerman, P. A. (1979). An appraisal of the use of dextranase. Proc. Int. Soc. Sugar Cane Technol., 17th Congress (these proceedings).

Ivin, P. C. and D. H. Foster (1977). Some aspects of cane quality affecting mill processing. Proc. ISSCT 16th Congress, 2701 -2710.

Keniry, J. S, J. B. Lee and C. W. Davis (1967). Deterioration of mechanically harvested chopped-up 'cane. Part 1. Dextran - a promising quantitative in- dicator of the processing quality of chopped-up cane. Int. Sugar J,, 71: 230- 233.

Keniry, J. S, J. B. Lee and V. C. Mahoney (1969). lmproverhents in the dextran assay of cane sugar materials. lnt. Sugar J., 71: 230-233.

Leonard, G. J. and G. N. Richards (1975). Uncertainties in the useof periodate oxidation for determination of dextran structure. Carbohyd. Res., 41: 143- 152.

Mason, V., D. H. Foster, R. A. James, R. N. Cullen and K. J. Meng (1978). An evaluation of cane harvester performance. Proc. Qd. Soc. Sugar Cane Technol., 45th Conf., 217-228.

McNeil, K. E. and P. A, lnkerman (1977). Preliminary studieson thedeteriora- Yion of long-standing-burnt cane. Proc. Qd. Soc. Sugar Cane Technol., 44th Cpnf., 19-27.

Owen, W. L. (1949). The microbiology of sugars, syrups and molasses. Minneapolis: Burgess Publishing Co. 1-275.

17. Questel D. D. and T. Bregger (1959). Internal temperatures in ore-harvested burned cane and mortality of the sugar cane borer. Proc. Int. Soc. Sugar Cane Technol., 10th Congress, 921-923.

18. Tilbury, R. H. (1968). Sour cane. Tate and Lyle Ltd. Research Centre, Annual Report, 32-35.

19. ( 1 9 7 0 ) . Ph.D. Thesis, University of Aston, Birmingham, England.

20. Wells, W. D. and G. P. James (1976). Rapid dextrans formation in stale cane and i t s processing consequences. Proc. Qd. Soc. Sugar Cane Technol., 43rd Conf., 287-293.

21. Wood, R. A. (1973). Deterioration losses: burnt cut cane vs. burnt standing cane. Proc. Sth. Afr. Sugar Techn~I. Assn. (June) 140-143.

22. Young, H. E. (1962). The deterioration of burnt standing cane and burnt cut cane. Proc. Int. Soc. Sugar Cane Technol. 1 I t h Congress, 307-31 1.

ESTUDIOS RECIENTES SOBRE DETERMINACION DE LA C-A EN AUSTRALIA

D. H. Foster, P. A. lnkerman y K. E. McNiel

RESUMEN

Se hace una revision de trabajo recientes sobre determinacion de la caiia en Australia.

Cuando se quema la, caiia, la temperatura sube por encima de 80°C en el 20% de toda' parte superior del tallo lo que causa una pCrdida de sacarosa. La ' dilucion del azucar en 10s tallos de la caAa quemada debido a la absorcion de agua causa un descenso aparente del contetido de sacarosa. Esta dilucion es mas marcada en la parte externa del tallo de la cual se encuentra la mayor parte de 10s vasos capilares. La absorcion de agua no parece ser importante en las primeras 24 horas despues de la quema, per0 puede ser significativa posteriormente.,

No se encuentran microrganismos dentro de la c a a verde y sana per0 se encuentran altos niveles en caila quemada dejada en pie. Es sorprendete que las poblaciones microbianas puedan ser tan elevadas en c a a cosechada a maquina verde como en la quemada. En cambio 10s niveles de dextran y etanol son m u c h ~ menos en la caiia cosechada verde comparada en la cosecha quemada.