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What are the dextrose equivalent values (DE) of lactose, and other common sugars?

Some data like the values for sucrose (0), maltodextrin (x<20), maltose (52), and glucose (100) can be found at different places on the net, but others such as lactose are not as easy to come by.

An answer containing the DE values of common sugars, including lactose and fructose would be appreciated.

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Dextrose equivalent $(DE)$ is a measure of the amount of reducing sugars present in a sugar product, expressed as a percentage on a dry basis relative to dextrose (glucose). Commercial sugar products are generally characterized by their dextrose equivalent $(DE)$ value (Ref.1). The theoretical definition of $DE$ is given by:

$$DE = \frac{\text{Reducing power of Syrup Solids}}{\text{Reducing power of D-glucose}} = \frac{\text{# of Reducing-End Groups in Syrup Solids}}{\text{# of Reducing Groups in D-glucose}} $$

However, number of reducing Groups are inversely proportional to the molecular weight of solid products (Ref.1 and Ref.2).

$$ \therefore \ DE(\%) = \frac{M_\mathrm{glucose}}{M_n} \times 100 \tag1$$

where $M_\mathrm{glucose}$ is the molecular weight of D-glucose and $M_n$ is the "molecular weight" of syrup solids. Keep in mind that this is the theoretical definition of the $DE$. The standard method of determining the $DE$ is the Lane-Eynon titration, based on the reduction of copper(II) sulfate in an alkaline tartrate solution, an application of Fehling's test. To see the deviation between theoretical and Lane-Eynon determination, Ref.1 has given following examples:

$$\begin{array}{l c r} \text{degree of polymerization} & \text{theoretical }\%DE & \text{*Lane-Eynon* }\%DE \\ \hline 1\text{ (D-glucose)} & 100 \text{ (by definition)} & 100 \text{ (by definition)} \\ 2\text{ (maltose)} & 52.6 & 58 \\ 3& 35.7 & 39 \\ 4 & 27.0 & 30 \\ 5 & 21.7 & 24.2 \\ 6 & 18.2 & 20.8 \\ \hline \end{array}$$

Following are three common sugars (lactose and maltose, dimers of glucose; and sucrose, a dimer of fructose and glucose):

Common sugars

As indicated by green circles, only lactose and maltose have at least one reducing end remaining while sucrose have none. Thus, $\%DE$ of sucrose is zero. Since, both lactose and maltose are dimers of glucose and they have identical molecular weights. Hence, according to the equation $(1)$, both of them have the identical theoretical $\%DE$, which is $52.6\%$ (see the chart from Ref.1). To determine Lane-Eynon values of them, you shoud do appropriate titration of analysis (e.g., Ref.1 and Ref.2).


Late edit:

As requested by OP, I have searched for $\%DE$ value for fructose. Evidently, fructose is also a reducing sugar (Ref.3) since all monosaccharides are reducing sugars. Thus, since fructose has the same molecular weight as glucose, its theoretical $\%DE$ should be $100\%$.


References:

  1. M. G. Fitton, "Rapid Determination of Dextrose Equivalent by Cryoscopy," Starch 1979, 31(11), 381-384 (DOI: https://doi.org/10.1002/star.19790311107).
  2. Y. Rong, M. Sillick, and C. M. Gregson, "Determination of Dextrose Equivalent Value and Number Average Molecular Weight of Maltodextrin by Osmometry," J. Food Sci. 2009, 74(1), C33-C40 (DOI: https://doi.org/10.1111/j.1750-3841.2008.00993.x).
  3. Although D-fructose would appear to be nonreducing, it readily undergoes keto-enol tautomerism at high $\mathrm{pH}$ to form a mixture of D-glucose and D-mannose: M. H. El-Rafie, Hanan B. Ahmed, and M. K. Zahran, "Facile Precursor for Synthesis of Silver Nanoparticles Using Alkali Treated Maize Starch," International Scholarly Research Notices 2014, Article ID 702396 (DOI: https://doi.org/10.1155/2014/702396).
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  • $\begingroup$ +1. Thx for your answer. I added a query about “fructose” at the end of the question. Would you be able to also give a DE figure for that? $\endgroup$ Sep 2 at 23:20
  • $\begingroup$ @Constantthin: Fructose is not a reducing sugar so $\%DE$ should be zero like sucrose. $\endgroup$ Sep 2 at 23:24
  • $\begingroup$ It may be so, but do you have a reference to back up that? This website: bionity.com/en/encyclopedia/Reducing_sugar.html says it is. Is the author(s) wrong? $\endgroup$ Sep 2 at 23:44
  • $\begingroup$ @Constantthin: I have added value for fructose. based on the reference sited. $\endgroup$ Sep 5 at 18:16
  • $\begingroup$ @Constantthin: It's possible. The $\mathrm{pH}$ of blood is 7.4, a little basic. With enzymes capable of doing so, fructose can isomerize. In Lane-Eynon $DE$ determination, the solutions are basic so it has non-zero value. $\endgroup$ Sep 6 at 15:54

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