New method for determining total dietary fiber by liquid chromatography

Area of Science:

• Food Science
• Analytical Chemistry
• Biochemistry

Background:

• The Prosky method is a standard for determining total dietary fiber (TDF).
• Limitations exist in the Prosky method's ability to quantify all soluble dietary fiber (SDF) components, particularly low molecular weight fractions.
• Liquid chromatography (LC) offers advanced analytical capabilities for complex carbohydrate analysis.

Purpose of the Study:

• To investigate the molecular weight limitations of the Prosky method for soluble dietary fiber (SDF) determination.
• To develop and validate enhanced LC-based methods for more accurate TDF quantification.
• To compare TDF values obtained by the Prosky method with those from novel LC approaches.

Main Methods:

• Utilized liquid chromatography (LC) to analyze soluble dietary fiber (SDF) fractions based on molecular weight and degree of polymerization.
• Employed a modified Prosky method with MES-TRIS buffer, followed by LC analysis of the filtrate to quantify low molecular weight SDF (LMSDF).
• Developed a second LC method for direct TDF determination after enzymatic hydrolysis, quantifying LMSDF using glucose as an internal standard.

Main Results:

• Confirmed that the Prosky method accurately quantifies SDF with an average degree of polymerization of 12 or higher.
• LC-based methods yielded higher TDF values for rice, soybean flour, and pressed barley compared to the Prosky method (approx. 6%, 3.5%, 3.5% higher, respectively).
• The second LC method demonstrated high accuracy and effectiveness in determining LMSDF.

Conclusions:

• The Prosky method has limitations in capturing the full spectrum of SDF, especially lower molecular weight components.
• LC-based analytical strategies offer a more comprehensive and accurate approach to TDF and SDF quantification.
• These findings have implications for accurate nutritional labeling and food composition analysis.