ICUMSA News n°28 – 1996

Message from the President

Since raising the question of whether ICUMSA should consider a permanent Secretariat I have had two important contributions from the Chairmen of the US and French National Committees. Dr Rearick expressed the view that a matter of this importance should be discussed and voted on at Berlin in 1998. I responded that I thought it important that if the prevailing view was against the Secretariat proposal then candidates for the Presidency needed time to obtain the support of their employing companies and their National Committees before an election at the Berlin meeting. At any rate I am interested in having the matter debated now and suggested that the US National Committee might like to state the case for a Secretariat in an issue of ICUMSA News.

Mr. Cuer reported the feelings of the French National Committee, firstly by saying that if operating a Secretariat resulted in an increased levy this would be unpopular. They also doubted whether ICUMSA would be significantly enhanced by a Secretariat.

Secondly, they praised the role of Mr. Dutton in providing a link with international organisations and his management of publications. The French National Committee nominated Dr. Paul Mottard, now a consultant but formerly Chief Chemist at Groupement Technique de Sucrerie (GTS) to be Mr. Dutton’s successor upon his retirement from the Publications Manager role.

Since the original Secretariat proposal came from the Canadian National Committee, I have asked them to describe their concept. Malcolm Faviell writes “Our model for ICUMSA in the next century would be a competent paid Secretariat who looks after the day to day administration of ICUMSA. To monitor the performance of the Secretariat and provide direction there should be a Board of, say, half a dozen or so, elected Directors, headed by a chairman rather than the current President system. We would envisage the Board and Chairman to be elected (or re-elected) at ICUMSA’s four yearly Sessions. In the first instance the Secretariat would be hired (or fired) by the Board. The only drawback to the proposal is the cost. The alternative may be to go on the way we are going, and I believe that may be harder and harder to achieve!”

In essence, the Canadian model would be that most of the present duties of the President/General Secretary, Treasurer and Publications Manager would be carried out by a paid Secretariat.

I think that if the Secretariat debate is to be progressed it is important that everyone have a clear view of what the Secretariat concept involves. We have invited the US National Committee to state their view since they were the first to support a proposal by Dr. Margaret Clarke to have the Secretariat housed within Sugar Processing Research Institute Inc. (SPRI). If there are other proponents of a Secretariat, we invite them to place before us their concepts so that we may consider the pros and cons.

Progress Report on General Subject 1: Raw Sugar

by R. M. Urquhart, Referee for General Subject 1

At the 21st Session of ICUMSA the major Recommendations on General Subject 1 concerned ash, fine grain and polarisation. Several of the Recommendations related to the use of Near Infrared (NIR) wavelengths for polarisation analysis.


Various workers [1, 2, 4] have reported on the use of a NIR method for polarisation analysis and on the differences obtained between the NIR and ICUMSA methods, both current and earlier, using lead clarification. These workers have reported the bias between the methods in different ways with some comparing the NIR results in °Z with the lead clarified results in °S including a 0.1 deduction for the “equivalent dry lead” procedure. If the results of the NIR method are compared with the current Official ICUMSA method GS1/2/3-1 all three workers obtained lower average results with the NIR method.

Part of the bias between the two methods could be due to the standardisation of the NIR instrument. Paton et al [2] showed there was a difference of 0.06 °Z between a pure sucrose solution read in the two instruments (NIR lower), suggesting that the quartz plate values predicted by Bünnagel’s formulae may be in error by this amount. This would not be surprising because Bünnagel’s formulae were based on data at 10 wavelengths extending from 408 to 655 nm, and extrapolation to 880 nm may not be accurate. Studies are being undertaken under Subject 4: Polarimetry and Quartz Plates to provide data for the accurate calibration of quartz plates at NIR wavelengths.

However, at least as important as the bias itself is the variability that occurs between different sugars. Some sugars or groups of sugars can be significantly above or below the average. Sugars at either end of the range will be advantaged or disadvantaged by the use of the NIR procedure. The reasons for the variability from one sugar to another are not well understood but are thought to relate, at least in part, to the presence of optically active polysaccharides, and whether or not these are removed by lead clarification.

Recently published results from Colonial Sugars Inc. in Louisiana by Wilson [4] have again shown the variability that occurs for different sugars. One of the conclusions from the work is that certain non-sugars impact on the polarisation values obtained using the NIR method. Wilson discusses the effect of dextran. This is known to be highly dextrorotarory with a specific rotation about three times that of sucrose. However, it is largely removed by lead clarification [3].

The use of the NIR method without lead clarification will therefore give a higher polarisation than would otherwise be the case for the same raw sugar without dextran. As recommended at the 21st Session, further work is needed to establish the effect of different levels of non-sugars (and possibly the reducing sugars) in lead-clarified and unclarified solutions.


At the past two Sessions of ICUMSA the need for a raw sugar gravimetric ash method based on a single incineration has been discussed. Two such methods seem worthy of consideration.

The first is a method developed by Walkidia and Armando Perdomo (WAP) and was discussed at the 21st Session of ICUMSA under Subject 16. This method was reported as giving the same results as the Official ICUMSA procedure, on 45 Cuban raw sugar samples with an ash content ranging from about 0.09 to 0.70%. The second method is that used by the Australian sugar industry for many years. This method uses 5 g sample, charring with 2 ml of sulphuric acid and incineration at 525 °C until completely ashed. This normally takes 75 to 90 minutes. The repeatability for the method is 0.03 units for raw sugars between 0.20 and 0.60% ash. However, the method is frequently used for raw sugars down to 0.10% ash with similar precision.

A recent study by Nguyen et al. [5] carried out using the Australian Industry’s method and the ICUMSA conductivity method (GS1/3/4/7/8-13) showed that the ICUMSA method gave an overall result which was 12.5% higher. The Australian Industry’s method deducts 10 % for sulphation and when allowance is made for this, the two methods agree well. Another similar study by Chou et al. [7] carried out at the New York Sugar Trade Laboratory (NYSTL) and Domino Sugar has found that the ICUMSA conductivity ash method (GS1/3/4/7/8-13) gave good agreement with the US Contract 14 double sul phated ash method. The agreement between the ICUMSA conductivity method and the other two methods, one involving single, the other double incineration, would seem to indicate a good chance of successfully developing a method based on a single incineration.


In the study by Nguyen et al. cited above [5] a new procedure for colour measurement involving dissolution of the raw sugar in a 0.01 mol/l MOPS (4-morpholine propane sulphonic acid) buffer to give a solution at pH = 7.0, filtration through a 0.45 mm syringe filter and reading of the solution absorbancy at 420 nm in a 1 cm cuvette was also reported. The method has been used on raw sugars with ICUMSA colours in the range from about 1000 to 4000 and provides a simple and rapid procedure. The results of the work are to be published in the Sugar Journal and it is proposed to collaboratively test the method on raw sugars.

Fine Grain

At present there is no Official method for the determination of fine grain, mean aperture and coefficient of variation in raw sugars. The problem lies with specification of a simple, robust procedure for preparing sugars by dry sieving. Recent work by Paton and Player [6] compares the level of agglomerates in raw sugar, before and after washing, using a modified HSPA (Hawaiian Sugar Planters Association) method, and a washing procedure with methanol and propan-2-ol which is used in the Australian sugar industry. Comparisons were also made with the level of agglomerates in laboratory affined raw sugars prepared using the Amstar procedure. Except for sugars below about 98.0 °Z the results show little change in the level of agglomerates in raw and washed sugars using either of the washing procedures or laboratory affination. With low °Z sugars the overall levels of agglomerates were higher than in the higher °Z sugars and all methods reduced the levels, with the modified HSPA procedure giving the largest reduction.

It is not clear whether a suitable washing procedure should or should not reduce agglomerates. This may depend on whether or not this occurs in factory affined sugars. However, these procedures do offer methods for washing raw sugars and one or other could be collaboratively tested.

If a suitable procedure for washing and drying of raw sugars prior to sieving analysis cannot be found then it may be necessary to rely on instrumental techniques to determine crystal size characteristics.


1 Altenburg, W.; Chou, C.C. (1991): Zuckerind. 116, 1041–1046

2 Paton, N.H.; Player, M.R.; Urquhart, R.M.; Duong, M. (1993): Zuckerind. 118, 705–709

3 Bradbury, G.A.; Urquhart, R.M.; Curtin, J.H.; McCowage, R.J. (1986): Sugar Journal 48 (8), 11–13

4 Wilson, T.E. (1996): Int. Sugar Journal (98), 169–174

5 Nguyen, H.H.; Rowe, G.S.; McCunnie, K.A.; Player, M.R. (1996): Proc. Aust. Soc. Sugar Cane Technol. 341–349

6 Paton, N.H.; Player, M.R. (1996): Proc. Aust. Soc. Sugar Cane Technol. 334–340

7 Chou, C.C.; Mercene, S.; Altenburg, W. (1996): Proc. Sugar Ind. Technol., in press

Progress Report on Subject 6: Spectrophotometry

by Giorgio Mantovani, Referee for Subject 6

A first Report on this Subject was presented at Colorado Springs during the 20th Session and a second one at the 21st Session in Havana in 1994. Both of these Reports detailed the relevant publications which were collected with the cooperation of the limited number of the Associate Referees, but it was impossible to carry out any ring tests. The Recommendations proposed at the end of both of the Reports and finally adopted have practically remained unchanged:

1. As recommended by the Referee for General Subject 2, the Miller-Ihli method is officially adopted for the determination of lead in white sugar and the new HGA/AAS methods proposed by ILSI and AOAC International for the determination of arsenic and copper in white sugar are to be collaboratively tested.

2. The method for the determination of formaldehyde in white sugar, as described in the Appendix of the Report, is Tentatively adopted.

3. Near infrared spectrophotometric methods should be further studied.

4. The Blue number method and fluorimetric analysis for the determination of α-amino nitrogen should be further studied.

The President expressed his interest in seeing that what was proposed in Recommendation 4 could be brought to a conclusion during the next 4 years.

The list of Associate Referees for Subject 6 received from the ICUMSA General Secretary includes exactly twice the number of names which have been available for the previous two Sessions. Therefore, it would be possible, via some private communications, to rely upon that decisive number (eight) of laboratories to carry out ring tests. Moreover, it would even be possible to utilise the cooperation of some laboratories which may not necessarily be related to one of the Associate Referees.

There are now 23 months before the 22nd session in Berlin and this is the moment to get in touch with the Associate Referees, to arrange a work programme, to collect available literature data and to consider the possibility carrying out a ring test.

Concerning Subject 6, any programme must be necessarily related to the four Recommendations mentioned above. The first is to be dealt with under General Subject 2 (see ICUMSA News No. 26, January 1996).

As far as Recommendation 2 is concerned, the importance of formaldehyde has gradually diminished recently as a result of experiments carried out on alternative compounds which seem to give good results. However, formaldehyde usage still remains relatively high in some countries so that it could be worth either experimentally confirming the method approved by the Danish Official Food Control Agency or by testing another.

Regarding Recommendation 3, after having been proposed in Cannes at the 19th Session, the NIR technique underwent great development in the sugar industry in spite of some doubts, such as:

”Should ICUMSA be interested in methods that are based on apparatus which requires standardisation with a series of samples which have in turn already been analysed by other methods?”.

Such a technique has been widely adopted and utilised and increasingly sophisticated devices are available for measuring a great number of parameters in the sugar industry. Together with Professor Vaccari, Referee for Subject 5: “Dry Substance”, the author is continuing experiments of extending the employment of such technique to a number of applications. Many other laboratories around the world are involved in research of NIR spectroscopy and, in particular, the Sugar Processing Research Institute Inc. in New Orleans, USA, where Dr. Margaret Clarke and her colleagues are carrying out many analyses on cane and beet products.

Recommendation 3 states that “Near infrared spectrophotometric methods should be further studied”. Up to now, no collaborative tests have been recommended and this is reasonable. This is because of the difficulties related to the comparison of data from equipment having different characteristics and performance.

On the other hand, the NIR technique is very attractive and capable of giving interesting results even when applied to quite different sugar industry areas. Thus, looking through the Proceedings of the last ICUMSA Session held in Havana, one can find NIR spectroscopy utilisation in beet processing, cane juices, dry substance, moisture, molasses, raw sugar and specialty sugars.

From the literature one can observe that the fluorimetric method using phthalaldehyde seems to give good results. This could be compared with the results obtained using the traditional Blue number for the determination of α-amino nitrogen. The problem is to find at least eight laboratories having suitable equipment and being able to carry out the relevant experiments.

A circular letter addressed to the Associate Referees of Subject 6 is ready to be mailed with the proposals and comments discussed above. Assuming they reply promptly, it would then be possible to organise a fruitful collaborative exercise. Moreover, bearing in mind the distribution of ICUMSA News around the world, including its inclusion in a number of sugar magazines, we hope to receive suggestions, comments and, in particular, cooperation from anyone interested in this Subject and possibly not even involved in the work of our Commission.

Reference Liquids for Refractive Index

by H. Winkler, Referee for Subject 13: Refractive Index

In view of the steadily increasing number of enquiries from German industry, the Laboratory of Imaging Optics of the Physikalisch-Technische Bundesanstalt (PTB) decided to initiate work in order to make available certified liquid standard samples (reference liquids) for the range of the unit of measurement “refractive index”.

Early in 1997, certified reference liquids having the following technical data will be made available:

Range of refractive index                                          1.334 to 1.53

Wavelengths                                                              546, 589 and 644 nm

Temperature for the refractive index                        20 °C

Sample volume per package and certificate             10 cm3

Certified precision                                                     1 x 10–5

Hydrocarbons will be used as the reference liquids. Care has been taken in selecting these samples to ensure that no highly poisonous substances are used.

In the future it is also intended to certify the refractive index values for a temperature of 25 °C and to extend the temperature range continuously.

Editor: Rud Frik Madsen, Strandpromenaden 28, DK-4900 Nakskov, Denmark – Phone: +45 5392 1675 – Fax: +45 5495 1675.