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Die Prinzipien der Melasseanalyse

To ensure quality standards in molasses trading, it is important that the industry accepts methods of analysis which will give consistent and reproducible results in different laboratories. The purpose of this information sheet is to describe the standard methods of analysis, their procedures and value in day-to-day operations.

Fact file

  • Tate & Lyle recommends classical methods of analysis for proven results and ensuring quality standards for commercial organisations.
  • Methods described in this sheet are recognised by the International Commission for Uniform Methods of Sugar Analysis (ICUMSA) and the Association of Official Analytical Chemists (AOAC).
  • Sugars in molasses are principally sucrose and reducing sugars glucose and fructose, while the residual material consists of organic non-sugar matter, inorganic constituents and water.
  • Because molasses contains both reducing sugars and sucrose, the content of original reducing sugars is determined separately from total reducing sugar content.
  • The Lane Eynon method for determining sucrose content in molasses is preferred by Tate & Lyle because it will give more easily reproducible results.
  • To determine dry matter content, Tate & Lyle recommends drying in a vacuum oven at 65 degrees Celsius for 18 hours with very pure dried sand as an extender.
  • Tate & Lyle research has shown the value of the Karl Fischer method for determining dry matter.

The methods described are recognised by the International Commission for Uniform Methods of Sugar Analysis ( ICUMSA ) and the Association of Official Analytical Chemists ( AOAC ). Only those methods with high degrees of reproducibility and repeatability are included for discussion. Tate & Lyle recommends classical methods of analysis because they are the proven ways for producing results for commercial organisations. Our research also includes instrumental analysis with GLC and HPLC to determine individual sugar content, but these methods are not regarded as a substitute for the classical methods described below.

Composition of cane molasses

The sugar content of molasses includes sucrose as well as reducing sugars. Sucrose is a disaccharide which, when hydrolysed, splits up into two monosaccharides - glucose and fructose ( also known as dextrose and laevulose ).

The original sucrose is equivalent to 0,95 of the reducing sugars formed ( 342 parts of sucrose will produce 360 parts of reducing sugars after hydrolysis ). Sucrose does not reduce cupric ions in alkaline solutions ( such as Fehling's solution) but the reducing sugars do, hence their name. Molasses contains both reducing sugars and sucrose, so that the original reducing sugars are determined first and then the total reducing sugars after hydrolysis.

The residual material consists of organic non-sugar matter, inorganic constituents and water. Included in the organic non-sugar constituents are nitrogen-containing materials, and in reporting analysis, nitrogen content, multiplied by 6,25, is referred to as protein content. Protein content measured in this way may vary, but typically averages around 4 %.

Reporting sugar content

Sugar content is often reported as the total of sugars as invert (TSAI), although individual sugars can also be reported as total sugars as sucrose (TSAS), or total of sucrose and invert, or as total sugars or total sweetening matter (TSM). If sucrose is represented as S%, invert content by I%, the reporting method is as follows:

Determination of sugar content

Lane Eynon double reduction method

The Lane Eynon method is used to determine sucrose content in molasses. It is preferred by United Molasses because it will give more easily reproducible results in different laboratories. The company's version of the constant volume modification analysis is now an official ICUMSA method. This method does rely on inversion, and it is known that under certain conditions of high acidity and high temperature, sugars may be destroyed.

Because of the different methods of inversion employed by laboratories, recommended conditions, which avoid destruction of sugars and to ensure reproducibility of results, have been chosen. Frequent standardisation of Fehling's solution against pure invert sugars is also recommended.

The volumetric method of Lane Eynon is well known in the sugar industry. However, some non-sugars, especially calcium, which possibly form a complex with glucose and fructose, can influence the results. The effect is eliminated by sequestering the calcium with sodium ethylenediamine-tetra-acetate

 

 

Luff-Schoorl method standardisation

The EC has directed that the Luff-Schoorl method is accepted as standard for determination of sugars in feedstuffs. However, the Luff-Schoorl reagent varies in pH value from 9.3 to 10.1, giving sugar recoveries ranging from 98% to 103%.

EC regulations require the reagent pH to be "approximately 9.4" but no instructions are given should this not be the case. Although ICUMSA now recommends a modified reagent to give standardised results, United Molasses' own research of published data indicates variations in pH even where extreme care is taken in making the reagent, hence United Molasses' preference for the Lane Eynon analytical procedure.

Determination of dry matter

Vacuum oven method

The UK Feeding Stuffs Analysis Regulations (1982) specify oven drying at 100 degrees Celsius to determine dry matter. This is unsuitable for liquid products such as molasses, because sugars will at this temperature become caramelised, volatiles other than water will be lost and skin will form on the surface, preventing quantitative water loss.

While older methods employ extenders such as sand with heating at atmospheric pressure to determine moisture content, Tate & Lyle recommends very pure, acid washed and dried sand as an extender and drying in a vacuum oven at 65 degrees Celsius for 18 hours.

Karl Fischer method

Although vacuum oven drying is preferred, investigations by Tate & Lyle have shown the value of the Karl Fischer method. Given the high moisture content of molasses, only small sample weights (0,2g) are possible, while daily calibration of reagent is essential. Although over a large number of samples, the differences between the two methods are quite small, individual results may vary quite widely.

The analysts training service

Drawing on the expertise and sophisticated laboratory facilities, Tate & Lyle can offer customer laboratory staff a full training service in their internationally approved molasses analysis techniques. Qualified analysts will take your staff step-by-step through the recognised procedures and their comparative value in today's day-to-day commercial operations.

Monitoring for higher standards

As part of its service to customers throughout Europe, Tate & Lyle operates ring tests to ensure that laboratories are producing consistent and reproducible results. Through a ring of participating client, commercial and independent laboratories, customers receive both their own test results and those of third parties which remain unidentified as a control. This comparative approach enables customers to monitor laboratory results and identify potential difficulties with particular analysis methods. To learn more about the ring test service, contact the Tate & Lyle technical department in Burton-on-Trent or your local Tate & Lyle area manager.


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