New insights into non-extractable phenolic compounds analysis.

Area of Science:

• Food Chemistry
• Nutritional Science
• Analytical Chemistry

Background:

• Phenolic compounds (PC) are often studied as extractable phenolic compounds (EPC), overlooking non-extractable phenolic compounds (NEPC).
• NEPC remain in food matrices post-extraction and require hydrolysis for analysis, playing a significant role in the colon through microbial fermentation.
• Understanding NEPC composition is vital for elucidating their health effects.

Purpose of the Study:

• To review and critically evaluate analytical methods for non-extractable phenolic compounds (NEPC) in foods.
• To identify challenges and propose optimized strategies for accurate NEPC analysis.
• To emphasize the importance of NEPC in the context of dietary intake and health benefits.

Main Methods:

• Evaluation of 182 studies published in the last five years focusing on NEPC analysis.
• Discussion of critical analytical steps: exhaustive EPC extraction, hydrolysis, quantification, and identification.
• Comparison of analytical techniques, including spectrophotometry, liquid chromatography (LC) with diode array detection (DAD), and LC-tandem high-resolution mass spectrometry (HRMS/MS).

Main Results:

• Exhaustive EPC extraction prior to hydrolysis is essential to prevent NEPC overestimation.
• Aggressive hydrolysis methods can alter NEPC structure, necessitating optimized conditions based on research objectives.
• The Folin-Ciocalteu method is prone to overestimation; LC-DAD is recommended for quantification, and LC-DAD-HRMS/MS for identification, often using representative standards.

Conclusions:

• Accurate NEPC analysis requires meticulous methodology, including exhaustive EPC extraction and optimized hydrolysis.
• LC-DAD and LC-DAD-HRMS/MS are the preferred techniques for NEPC quantification and identification, respectively.
• Combining manual data handling with bioinformatics tools enhances NEPC identification accuracy.