Sugar Inversion

Sugar inversion is the chemical conversion of saccharose into glucose and fructose. This process is enhanced by acids and high temperatures.

Saccharose is subject to sugar inversion which changes the composition of the beverage. Since many soft drinks are produced using beet or cane sugar as a sweetener, this chemical reaction has to be closely monitored as the beverage composition gradually changes with progressing sugar inversion.
Measuring the degree of sugar inversion plays a very important role for the production and quality control before, during, and after the production process and is relevant for producers and bottlers of soft drinks with sugar.

1 What is sugar inversion?

Fig. 1: The sugar inversion process
Fig. 1: The sugar inversion pro

The inversion of beet or cane sugar is the chemical conversion of saccharose in solution into glucose and fructose. This process is enhanced by acids and high temperatures T. The angle of rotation of polarized light sent through the solution changes during the process of inversion.

2 What happens during sugar inversion?

The disaccharide sucrose is split up into a 1:1 mixture of the monosaccharides fructose and glucose, one molecule of sucrose consuming one molecule of water. As a consequence, the density of the solution increases with progressing degree of inversion, and the volume decreases. Figure 1 shows the process of sugar inversion.

3 Why is the reaction called “sugar inversion”?

Saccharose solutions rotate the plane of polarized light. The angle at which the plane of polarized light is rotated is specific for each sugar and depends on its concentration. An aqueous solution of saccharose is dextrorotatory. It causes a specific rotation of +66.5°. The specific rotation of glucose is +52.5°, but fructose is strongly levorotatory (-92°). While inverting, the specific rotation gradually undergoes a change in direction of polarized light from +66.5° to -19.7°. The inverted solution is levorotatory and displays a specific rotation of -19.7°.

formula 1

4 Why worry about sugar inversion?

Generally, soft drinks are produced by mixing concentrate with water at a defined ratio. Sucrose in the concentrate inverts during storage: the concentrate’s density increases, its volume decreases. The weight of glucose and fructose together after full inversion is 360,32 g/mol whereas the weight of saccharose before inversion is 342,30 g/mol.

formula 2

Fig. 2: Monitoring sugar inversion during production
Fig. 2: Monitoring sugar inversion during production

The °Brix fresh value will increase by about 5% after full inversion. Thus, Fresh Brix = Inverted Brix * 0.95.

For a correct mixing ratio of the syrup with water, the sugar content of the syrup must be known. If the recipe for soft drink production is based on the fresh (not inverted) concentrate, partial or full inversion of the product will cause under-dosing of the concentrate. If the recipe asks for inverted concentrate and the concentrate is still fresh, overdosing of the concentrate will be the consequence.

Hence, as Figure 2 illustrates, the progress of sugar inversion must be known before and during soft drink production. To do so, two options exist: the traditional method of forced inversion followed by calculation of °Brix fresh and °Brix inverted, or the instrumental method.

°Brix fresh:       °Brix value before inversion
°Brix inverted:   °Brix value after full inversion

 

5 How to track the progress of sugar inversion

5.1 The traditional method: forced inversion

Forced inversion is a wet chemical method and requires the following steps1:

  • Degas the sample (if carbonated).
  • Add acid.
  • Place the sample in a preheated water bath (90 °C, 1 hour).
  • Allow the sample to cool.
  • Measure the density of the sample.
  • Use an appropriate conversion procedure (e.g. a polynomial function) to calculate the °Brix fresh or °Brix inverted from the measured density.

 

If the degree of inversion is also required, the density is measured twice: once after degassing before inversion and once after inversion. The total time consumption per sample is 60 to 120 minutes.

5.2 The instrumental method

The instrumental method combines density and sound velocity measurements since these two properties are affected differently by the ongoing inversion process. These properties are used as an input for an algorithm which will provide information about concentration sugar fresh, concentration sugar inverted, and the degree of inversion. The instrumental method requires the following steps:

  • Degas the sample (if carbonated).
  • Inject the sample into the measuring cells of the analytical instrument.
  • Press <Start>.

The total time consumption including degassing is 5 to 10 minutes.

External links

Soft Drink and Syrup Analysis: Soft Drink Analyzer M
Analysis of inverted regular soft drinks with PBA-SI Generation M
Inline Brix Measurement, Diet Beverage Analysis and CO2 Measurement: Cobrix 5
Online Brix Measurement in Soft Drinks: Brix Monitor
MCP 200/250/300/500 Sucromat Automatic Saccharimeter
http://www.softdrinksinternational.com/
http://www.drinktec.com

Notes

1 All steps described can be seen as a general guideline and might be adapted according to company-internal standards.

References

  1. Shachman, M., The Soft Drinks Companion: A Technical Handbook for the Beverage Industry, CRC Press 2005
  2. Soft Drinks International – January/February 2016, Can sugar get any sweeter?
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