Analysis of Indigestible Dextrin Powder (LB-802.5)

Dietary fiber has preventive effects on dyslipidemia, constipation, obesity, etc. In Japan, indigestible dextrin is approved to be labeled as a Food for Specified Health Uses (FOSHU). This labeling system was started in 1991. The Japanese Director-General of the Consumer Affairs Agency approves certain food products to label their effects.
The enzyme-HPLC method is used for the analysis of samples containing a large amount of low-molecular-weight water-soluble dietary fiber, such as indigestible dextrin. The enzyme-HPLC method used in this application, analysis of commercially available indigestible dextrin powder, refers to the FOSHU standards. It enrolls a series of sample pretreatment and an HPLC analysis (the sample pretreatment used was modified slightly from the method described in FOSHU standards). OHpak LB-802.5, a column for aqueous SEC was used for the HPLC analysis. The determined dietary fiber fraction peak area and the glycerin internal standard peak area are compared to obtain their ratio.
*According to the Japanese “Food Labeling Standards”, Low-molecular-weight water-soluble dietary fibers are defined as compounds retained less than maltotriose (red dotted line).

Sample pretreatment

1. Dissolve 1 g of powder sample in 50 mL of 0.08 M phosphate buffer (pH6.0)
2. Add 0.2 mL of α-amylase. Make sure the pH is 6.0 ± 0.5 (in this application, it was pH6.3)
3. Let it react at 90 ℃, with shaking for 30 minutes.
4. After cooling, add 0.2 mL each of protease and amyloglucosidase. Make sure the pH is 6.0 ± 0.5 (in this application, it was pH6.3)
5. Let it react at 60 ℃, with shaking for 30 minutes.
6. Heat at 100 ℃ (water bath) for 10 minutes.
7. After cooling, add 5 mL of 10-times water-diluted glycerin.
8. Make up to 100 mL with water. Obtained is the enzyme-treated solution.
9. Pass 50 mL of enzyme-treated solution through an ion exchange resin* at 50 mL/h.
   *A mixture of Amberlite™ IRA-67 and Amberlite™ 200CT (DuPont™); 25 mL each
10. Pass through a No.9 ion exchange resin, using approximately 150 mL of water (to obtain 200 mL of effluent)
11. Concentrate using a rotary evaporator.
12. Make up to 20 mL with water.
13. Filter using a 0.45-µm membrane filter. Use this as an injection sample.

Sample: 20 μL
Pretreated indigestible dextrin powder

1. Dietary fiber fraction
2. Glucose
3. Glycerin (Internal standard)

Column：Shodex OHpak LB-G 6B (6.0 mm I.D. x 50 mm) + LB-802.5 (8.0 mm I.D. x 300 mm) x 2
Eluent： H2O
Flow rate：0.5 mL/min
Detector： RI
Column temp.：80 ℃

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