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Analysis of Carbohydrates - Classical carbohydrate methods

4 important questions on Analysis of Carbohydrates - Classical carbohydrate methods

How does a refractometer work?

It bives a Bx value. This stands for 1 gram sucrose per 100 gram sample.
It measures the refraction index of a sample.
VERY fast method!

Influenced by presence of other compounds for instance organic acids
Value influenced by composition of sample.
not very specific

How does a colour assay work?

A sample with carbohydrates is boiled in sulphuric acid. Therefore it undergoes a degradation into furan derivatives which react with phenolic compounds. These will give a colour and you can measure it with a spectrophotometer.

However some sugar molecules might have more affinity to bind with the phenolic compound which introduces a error.

So it can be used as a indication but is not very specific.

How does the Nierle Tegge assay go?

Reducing Suger is oxidized by Cu2+ to a sugar acid and a Cu+.

The Cu2+ is present in a EDTA complex. When the reaction occurs you will get a free EDTA complex.
The amount of free EDTA can be quantified with a titration with Cu2+.

Unfortunately not all sugars react the same and therefore the results are a rough estimation.

What is the dextrose equivalent (DE)?

DE=(moles reducing sugar / moles of glucose building blocks) * 100%

DE does not necessarily provide information about the distributor of maltodextrin present.

Easy to standardize by adding glucose