20th Session, 1990
Members attending the 19th Session at Cannes in 1986 would be aware that the United States National Committee extended an invitation to our Commission to hold the 20th Session in their country. We have now been advised by Mr John A. Richmond, Chairman USNC, that they propose to hold this meeting in Colorado Springs, Colorado, from 3rd to 8th June, 1990. The chairmen of national committees have been asked to provide Mr Richmond with an estimate of the numbers of members and accompanying spouses expecting to attend that meeting to assist planning. Readers contemplating attending the Colorado Springs meeting are urged to advise their chairman of national committee.
General Referee G9: Starch Derived Sweeteners
Following extensive discussions with people engaged in the starch derived sweetener industry, the President is pleased to announce that the position of General Referee for Subject G9 has been offered to Dr Brian Whitehouse, Manager Quality Assurance, Cerestar, Gruppo Perruzzi. Dr Whitehouse was nominated by the International Federation of Glucose Industries following discussions between their President, Mr J.P. Anemaet and Dr G. Rens and Mr J. Huberlant, representing ICUMSA. It is hoped that Dr Whitehouse will be able to create a good working environment permitting collaboration between the various organisations with an interest in this subject. We look forward to his contributing his thoughts on how this can be done in a future issue of ICUMSA News.
Adoption of New Sugar Scale
Members will be aware that extensive publicity was given to the change in sugar scale from “degrees S” to “degrees Z” effective 1 July 1988. In addition to the press release published in most sugar journals, letters were sent to the heads of international organisations affected by the change. There have been. some instances where organisations using the sugar scale have been slow to make changes either because of technical difficulties or an unwillingness to address the issues involved. National Committees and individual members are urged to do whatever they can to promote the adoption and understanding of the new scale. It would indeed be unfortunate if we have two scales, the old and new in widespread use after a reasonable transition period. Those who know their history would not wish to see a repeat of the experience with the 1932 International Sugar Scale and the Ventzke scale it replaced.
ICUMSA represented at other meetings
At a conference sponsored by UNIDO on sugar and diversification held in Havana, Cuba, from 26th to 30th September 1988, ICUMSA was officially represented by Vice President Dulce Martinez who described the latest developments of our Commission. Dr Roger Wood of the U.K. Ministry of Agriculture, Fisheries and Food presented a report on the analysis of sugars at the Inter-Agency meeting in Budapest on 10th and 11th November. The President, Dr Murray Player, represented ICUMSA at the 8th International Conference on legal Metrology in Sydney on 23rd to 28th October.
Working Group’s Review of Methods
by Mary An Godshall
In 1987, ICUMSA’s Working Group on Collaborative Studies recommended that all existing ICUMSA methods be reviewed to determine which ones ·met the collaborative testing requirements. The group also recommended adopting IUPAC guidelines for collaborative tests as the criteria for reviewing the methods. The guidelines were published in the September 1987 and February 1988 issues of ICUMSA News.
The Methods Review Committee is under the purview of Subject 3 and includes Mary An Godshall (USA), Chairman, Albert Emmerich (Germany), Günter Pollach (Austria), Charles Ivin (Australia) and Roger Wood (England). Several General Referees have contributed suggestions and conducted their own reviews, which have been very helpful to this study and are gratefully acknowledged.
Schneider’s Sugar Analysis ICUMSA Methods served as a basis for the review, and every attempt was made to update all methods based on subsequent recommendations that appeared in the 1978, 1982 and 1986 Proceedings. It became evident during the review that some methods have been subjected to much higher standards of acceptance than others. The Working Group also believes that ICUMSA should adopt a formal numbering system for its methods to obviate the difficulties caused by using a variety of names for the same method.
The review showed that only sixteen methods fulfilled all the requirements for international recognition. Twelve of these are official ICUMSA methods and the other four enjoy tentative status and would be candidates for elevation to official status at the next session in 1990. Of the official methods which have been adequately tested are some of great commercial significance namely, the international sugar scale [1] and the polarisation of raw sugar [2]. Lane and Eynon reducing sugar methods [3] were also approved though the working group commented that the repeatability and reproducibility should be calculated and reported for the constant volume method. The Schäffler GLC method for sucrose in molasses [4] was approved and this together with the United Molasses modification of the Lane and Eynon method for determining total sugars are important to the molasses trade.
Collaborative testing of methods for ash determination [5] have been satisfactorily conducted though the test data were not presented in the referees’ report. The method for lactic acid [6] still requires the reporting of repeatability and reproductibilty data. The methods for citric acid [7], visual appearance of white sugar [8] and direct determination of pH [9] were the official methods found to meet the IUPAC requirements.
The four tentatively approved methods which met international requirements for collaborative testing will be examined by general referees so that a case can be made for official recognition. They are the Dutton double polarimetric method for sucrose [10], the transamination method for lactic acid [ 11], calcium phosphate in powdered sugar [12) and moisture in raw sugar [13).
The remainder of the methods examined failed to meet international requirements either through there being insufficient collaborative test data or none at all. It was also thought that some methods should be deemed outdated on grounds that they have been replaced by other methods or have held tentative status beyond the allowed twelve years.
References
References are cited in abbreviated form. S-xx refers to page in Schneider, F. ed., (1979) “Sugar Analysis: ICUMSA Methods”, ICUMSA, Peterborough. The other notation refers to the Proceedings year/page/recommendation that pertains to the method.
1 1986/66/1
2 S-25, 1986/197/5
3 S-52, 1982/1351′)
4 1986/147/2
5 S-83, 1982/281/1, 1986/292/1, 1982/282/2, 1986/292/2
6 S-108
7 1982/326/1
8 S-129, 1982/375/4
9 S-131
10 S-30
11 1982/326/2
12 1986/230/5
13 1986/348/4
Subject 12 – Rheology
by Ross Broadfoot, Sugar Research Ltd, POB 689, Mackay, Queensland 4740, Australia)
Introduction
There are a number of areas where the measurement and definition of the rheological properties of materials within the sugar industry are of importance. For example, the rheology of the molasses, syrup, invert syrup, etc. may influence its market acceptance and traded product value. As well, in factory processing, viscosity is a prime consideration for pipeflow design for massecuite and molasses, crystallizer operation and crystal-mother liquor separation in centrifugals. It is also of importance in mathematical modelling of process steps such as evaporation, crystallization, centrifuging and drying. The generally non-Newtonian nature of massecuites and molasses makes the measurement and specification of the rheology of these materials more complex than would be the case for Newtonian solutions.
Viscosity measurement of sugar solutions
Instruments for viscosity measurements in sugar solutions and massecuites involve four principles of measurement:
1. Torque required to rotate an element at a fixed angular velocity in the sample. This is the basis of the rotating cylinder viscosimeter and is the only measurement procedure which has been officially adopted by ICUMSA. The method is an official procedure for molasses (not massecuite). Other rotational viscosimeters include those using the cone and plate configuration in either a rotating or oscillating mode.
2. Rate of fall of a calibrated sphere through the sample
3. Damping effect of the viscous medium on the vibration of a thin plate element within the sample
4. Rate of flow of the material under pressure through pipeline and orifices.
Because massecuites and molasses often exhibit pseudoplastic flow behaviour, i.e. the viscosity of the material reduces as higher rates of shear are applied, it is necessary to define the shear conditions under which the viscosity is measured.
The flow behaviour of a material under a shear force is generally presented graphically as a plot of shear stress against shear rate. For Newtonian fluids a constant proportionality exists between the shear stress τ and the shear rate γ in laminar flow:
τ = η γ,
where η viscosity of the fluid in Pa s.
Work for the 20th Session
The main objective being pursued is to provide standard techniques for obtaining rheological data of interest to the sugar industry. At this time the General referees involved with defining analytical methods for the various sugar products have not enunciated their requirements for viscosity measurements. It is expected that techniques for measuring the viscosity of molasses and massecuites will be called for. Until needs are defined there is no case for conducting collaborative tests of any of the available measurement techniques.
The Referee proposes to pursue the recommendations of the 19th Session which are principally concerned with establishing the pipeflow method as a standard technique for measuring the viscosity of massecuites. The Referee is anxious to hear from readers on industry needs for viscosity measurements so that the future programme for Subject 12 can be more sharply focussed. Editor: R. Pieck, Klein Spanuit 9, B-3300 Tienen, Januar 1989-Tel. +32 16/81 24 36-Telex 222 51 -Telefax +31 16/82 03 17