ICUMSA News n°11 – 1991

Message from the President

New Subject numbers and Referee appointment

At the 20th Session at Colorado Springs, it was foreshadowed that some Subjects should be eliminated while others could be combined. The Steering Committee has considered these matters and decided to eliminate immediately the Refereeships involving Apparatus and Reagents, Ion Selective Electrodes and to eliminate Rheology at the end of the current Session. The Committee decided that Polarimetry and Quartz Plates should be combined in a single Refereeship while Enzymatic and Immunological Methods should be split into separate Subjects. The previous Subject of Ion Chromatography will become the more general Subject of Chromatographic Techniques for NonSugars.

The President has sought to appoint Referees for the various Subjects though at this time not all positions have been filled. The new Subject numbers and Referees already appointed are set out in Table 1.

Table 1: Subjects and Referees for 21st Session

General RefereeshipsReferee
1 Raw SugarRJ McCowage
2 White SugarCW Harvey
3 Speciality SugarsR W Plews
4 Molasses
5 CaneMA Brokensha
6 BeetW Mauch
7 Cane Sugar Processing0 L Crees
8 Beet Sugar ProcessingJ P Lescure
9 Starch-Derived SweetenersDB Whitehouse
1 Constitution and By-LawsMR Player
2 Oligosaccharides and PolysaccharidesK Thielecke
3 Method Format, Collaborative Testing and Treatment of DataMA Godshall
4 Polarimetry and Quartz PlatesA Emmerich
5 Dry SubstanceG Vaccari
6 SpectrophotometryG Mamovani
7 Colour Turbidity and Reflectance MeasurementS Akoglu
8 Chromatographic Techniques for SugarsKJ Schäffler
9 Chromatographic Techniques for Non-SugarsP Bourlet
10 Enzymatic MethodsE. Burzawa
11 DensityF Spieweck
12 RheologyR Broadfoot
13 Refractive IndexK J Rosenbruch
14 MicrobiologyR Strauß
15 Reducing SugarsJ Laursen
16 AshJ P Ducatillon
17 Immunological Methods


The Proceedings of the 20th Session are being prepared by Mr  J V Dutton as Editor/Manager of the Publications Department and assisted by the General Secretary, Mr R J McCowage and former Associate Referee, Dr Milan Vender who is now doing the typesetting. Copies will be available early in the new year and details of how to place orders are expected to be advertised in some sugar journals in February 1991.

21st Session Programme for General Subject 1 –

Raw sugar

by Referee R J McCowage

During the 20th Session of ICUMSA the methods of analysis required for raw sugar were identified and, for each, the urgency of review was established. The high priority methods were those which were currently in use in the international trade of raw sugars, either to establish a base value or to apply quality incentives. There were eleven methods in this category: polarisation, reducing sugars, sulphated ash, conductivity ash, moisture, colour, pH, fine grain, dextran, standard affination and temperature.

At the commencement of the 20th Session, a review of methods for the above analyses revealed that only the polarisation procedure met the IUPAC guidelines for collaborative testing. During the last Session, General Subject 1 Associate Referees participated in testing the methods for sulphated ash, conductivity ash, pH and colour, while Subject 17 Associates performed similar work on a method for raw sugar moisture. All of these methods now meet the requirements for Official status.

The programme for the 21st Session will involve the selection and collaborative testing of methods for reducing sugars, fine grain, dextran, standard affination and – temperature. Additionally, following a request by representatives of the USA sugar industry during the Colorado Springs meeting, the priority of a method for the starch content of raw sugar has been upgraded and work will be undertaken to develop and test a suitable procedure. Considerations relating to these tests are discussed in tum below.

Reducing Sugars

There are two Official reducing sugar methods mainly used in the beet industry – the Berlin Institute and Ofner methods. The cane industry uses the Lane and Eynon and Luff-Schoorl methods. While modem instrumental methods are not yet widely used, there is increasing interest in HPLC and GLC techniques for determining glucose and fructose.

It is the goal of the Commission to reduce the number of Official methods for a particular product. Your Referee would like to have agreement on adopting only one of the four traditional methods named above for the analysis of all raw sugar, or, if this is not possible, one method for cane raw sugar and one for beet raw sugar. Since there is obviously interest in knowing the content of the individual species, glucose and fructose, we should support the development of robust instrumental methods, with a view to one of these eventually replacing the traditional method adopted.

Since the international trade mainly involves raw cane sugar and the Lane and Eynon method is the procedure mostly used, comment is sought regarding the acceptability of adopting this method for Official purposes. If this is agreed to, a collaborative test programme will be organised to fulfill the IUPAC requirements.

Fine Grain

Crystal size is an important quality criterion for raw sugars in international trade. Its determination has been addressed by ICUMSA however, no Official method is available to determine the fine grain content of raw sugar.

The residual film of syrup on raw sugar crystals means that they cannot be sieved in their natural state. The syrup film must firstly be removed. In 1954 a procedure involving a methanol/ethyl ether washing and air-drying before sieving was Tentatively adopted. This was replaced by the Hawaiian Sugar Producers’ Association (HSPA) procedure in 1970, again adopted Tentatively. In the HSPA procedure, the raw sugar is washed four times in a saturated sucrose solution, once in methanol, and once in isopropanol. The washed sugar is dried under vacuum. Little work appears to have been done to further promote the method. At the 1974 ICUMSA Session, problems with conglomerate formation when using the HSPA method were reported. However, there seemed to be a deviation in the temperature at which the washed sugars were dried, when these results were obtained.

In 1978, Vignes [1] reported a modified sample preparation method which aimed at removing the syrup film from the crystals, without the formation of conglomerates during the drying step. The method incorporated three washes with sucrose saturated methanol, followed by three washes with sucrose saturated isopropanol. The washed crystals were firstly dried under vacuum in a rotary film evaporator and then in a oven at l l0’C. The elimination of the rotary vacuum drying step was shown to produce conglomerates and a higher MA and lower CV.

In 1982, ICUMSA recommended that further work should be carried out on the grist determination, particularly with a view to developing a method which minimises conglomerate formation during the washing and drying. A similar Recommendation was made in 1986. Clearly the matter of a satisfactory crystal washing and drying procedure for raw sugar prior to sieving, needs to be resolved. Your Referee proposes to conduct work at CSR’s laboratory with a view to defining a best procedure for preparing raw sugar for sieving. When this is completed, it would be desirable to have another laboratory corroborate the findings before a full-scale collaborative test was conducted. Any members with an interest in this work should contact the Referee so that plans can be drawn up with full consultation.


The CSR dextran assay was adopted Tentatively in 1974 for the determination of dextran-like substances in raw sugar. Collaborative test results were reported in 1982 and 1986 but the method was rejected on the basis of unsatisfactory reproducibility and its Tentative status was withdrawn in 1986.

During the early 1980’s there was considerable interest in dextran measurement and a number of alternative procedures were reported in the literature. The Roberts [2] procedure, which has been accepted by the AOAC, is the most widely used of these procedures, although concerns have been raised about the specificity of the test, and its overall reproducibility is only equivalent to that of the haze test.

During the 20th Session, work has been conducted in the United States and in Australia on immunoassay procedures for dextran. The work in Australia focussed on measurement in raw sugars and used a competitive assay technique based on dextran coated tubes. While the approach showed good initial promise it was found to be impossible to obtain reproducible results with the format being used. The Audubon Sugar Institute in the United States has also been working on a dextran test based on an immunoassay approach.

The matter of dextran measurement in raw sugars is still of particular significance to the raw sugar trade. Your Referee proposes to·search the deficiencies in the CSR dextran assay, with a view to making it robust enough to satisfy the criteria for acceptance in a collaborative test. If this is successful, this method will again be brought forward for adoption by the Commission as its Official method. It is not intended that this initiative preclude others from developing alternative dextran procedures. It is believed that there will always be some interest in the CSR haze method whether or not it becomes an Official ICUMSA method. However, further work on enzymatic or immunological methods is encouraged and your referee would be pleased to assist any members with an interest in this area.

Standard Affination

Few reports exist on small-scale affination methods. ICUMSA has methods for completely removing the syrup layer from cane and beet raw sugars for the main purpose of grist analysis or determination of crystal properties, but has no procedure reflecting what happens in refinery affination. Chen [3] lists three affination procedures: Honig-Chen, No. 10 Contract and HSPA methods. The latter is simply the procedure for preparing raw sugar for grist analysis.

The first two methods have the disadvantage that they require a relatively specialist and expensive centrifuge with a specification which virtually limits the choice to a single brand name. In the past ICUMSA has adopted a policy of not specifying nor endorsing particular brand names, so these are reasons which make it difficult to give Official recognition to either of these two affination methods.

With these problems in mind, work was carried out in Australia in an attempt to develop an affination procedure which does not require centrifugation. A procedure based on mingling the sugar with propylene glycol and displacing this by vacuum filtration and an alcohol wash. This appeared to be quite successful and the results are to be published shortly.

Members are invited to comment on the above situation and indicate whether they have enthusiasm for developing an ICUMSA affination procedure which meets both the technical requirements of the interested parties and the policy concerns of our Commission.


ICUMSA has not previously addressed the matter of raw sugar temperature measurement. Furthermore, there is little in the literature in this regard. While measuring raw sugar temperature may appear, at face value to be trite, there are a number of issues related to equilibration time, heat capacities of sugar and the thermometric probe, choice of temperature-sensing device,- and lead/stem effects which can cause erroneous results. For this reason, guidelines for temperature measurement in raw sugar need to -be set.

Following recent experience in Australia, your Referee expects to publish a paper on this subject shortly and members will be invited to comment on the appropriateness of the Australian approach for international application.


There is increased interest in starch in the USA following increased levels in some of their mainland raw sugars. Godshall, Clarke and Dooley [4] have reported work on methods. ICUMSA debated the subject in the 1970’s but did not adopt a procedure. The topic needs to be reactivated, and members interested in pursuing such work are invited to contact the Referee.

Official Methods and New Methods Book

There is further work to be done on the accepted Official methods. An alternative to the use of lead is required for the polarisation procedure, the possibility of using a single incineration in the sulphated ash procedure needs to be explored, as do the use of buffers and methods to improve filtration rates in the colour method. This work will primarily be the responsibility of the relevant scientific Referees is to be sought.

Mention should also be made of the need to rewrite methods in standard format for inclusion in the new Methods Book. This will be an important objective for the 21st Session and the assistance of relevant scientific Referees is to be sought. were designated ‘high priority’. One of the first tasks was to validate these methods by collaborative testing to IUPAC standards. Progress to date includes:


I Vignes, E.C. (1978): Proceedings JSSCT, 2563-2568

2 Roberts, EJ. (1983): ISJ, 85, 10-13

3 Chen, J.C.P. (1985) : “Cane Sugar Handbook”, 11th Edition; John Wiley and Sons, New York, 819-820

4 Godshall, M.A.; Clarke, M.A., and Dooley, C.D. (1990): SPRI Conference Proceedings (in press)

A review of progress in General Subject 2 – White Sugar

by Referee Dr C W Harvey


Following the successful meeting of delegates to the 20th Session of ICUMSA held at Colorado Springs, it is appropriate at this time to review progress, outline goals for the next Session and give some indication of the direction and longer term aims for this Subject.

Achievements in the 20th Session

The Report presented to the 20th Session identified those white sugar methods that are contained within legislation and that are considered very important to users and producers of white sugar. These methods were designated ‘high priority’. One of the first tasks was to validate these methods by collaborative testing to IUPAC standards. Progress to date includes:

1. Visual appearance of white sugar

The assessment of visual appearance of white sugar using the Braunschweig colour-type series was confirmed as the Official ICUMSA method, there being sufficient data from previous collaborative tests to validate the procedure. Discussion at the 20th Session indicated a need for an instrumental technique for measuring visual appearance. It is suggested that such a method should be developed within the Refereeship for Colour, Turbidity and Reflectance Measurements.

2. White sugar solution colour

The method for solution colour Officially adopted in 1978 required that the sugar solution be adjusted to pH 7.0 but gave no instructions on how to make this adjustment. During the 20th Session an extensive international collaborative test on the determination of solution colour using TEA buffer to control pH at 7.0 was successfully carried out and this is now the Officially adopted method.

3. Polarisation of white sugar

‘n co-operation with the Referee for Polarimetry, Dr A Emmerich, an international collaborative test was carried out on the Braunschweig method for polarisation of white sugar without clarification. The successful outcome of the test led to it being raised from Tentative to Official status. Further, the current ‘Raw Sugar Polarisation Method’ was Officially adopted for sugars needing clarification.

4. Conductivity ash

Following the successful collaborative testing of the conductivity ash method using 28% d.s. solutions by the Referee for Ash, Dr J P Ducatillon, that method’s Official status was confirmed.

5. Particle size

Although specifications for particle size are not included within legislation, the particle size distribution of white sugar is often of great importance to commercial users. Because of the diverse requirements of commercial users and the variations that exist within national standards for sieves, it has been recognised that a single international validated procedure is not required nor is it practical to carry out. Therefore, it has been decided to describe a method that will provide basic particle size data using sieves conforming to national standards, include a specification for the sieve-shaking equipment, and standard methods for evaluating results but leave the choice of evaluation method to the user.

The next four years

Recommendations approved at the 20th Session proposed that work in the current Session be devoted to:

1. Sulphur dioxide

Work already commenced on the rosaniline method for sulphur dioxide in white sugar will continue.

2. Methods for loss on drying, insoluble matter

The Referee for Method Format, Collaborative Testing and Statistical Treatment of Data, Mrs M A Godshall has advised that the collaborative tests carried out in previous Sessions on the methods for loss on drying and insoluble matter do not reach the standards set by IUPAC. Both will be included in this Session’s collaborative test programme.

3. Reducing sugars

There is insufficient data to validate either the methods of Knight & Allen for low levels of reducing sugars or the Berlin Institute and Ofncr methods for higher levels of reducing sugars. It is intended to add methods for reducing sugars to the collaborative test programme, after consulting the Referee for that Subject on the most suitable techniques.

4. Arsenic, Copper and Lead

The existing ICUMSA methods for arsenic, copper and lead need to be revised in collaboration with the Referee for spectrophotometry. These methods will be collaboratively tested after modification.

Future Directions

At the same time that the validation of high priority methods is being undertaken, consideration will be given to the adoption of new methods already being studied by Referees of the relevant Subjects. Attention will also be directed to the validation of quality assurance methods, which, until now have been regarded as lower priority.

Reliable validated methods are essential to produce accurate analytical data, but of equal importance is that laboratories applying these methods perform them competently. Your Referee is interested in discussing whether the Commission should concern itself with quality assurance procedures for laboratories carrying out tests on sugar products using Official methods.

Editor: Dr. R. Pieck, Klein Spanuit 9, B-3300 Tienen, Belgium, January 1991 – Tel. +32 16 / 81 24 36 – Telex 222 51 – Telefax: +32 16 / 82 03 17.