Acid hydrolysis conditions do affect the non-extractable phenolic compounds composition from grape peel and seed

Area of Science:

• Food Chemistry
• Plant Biochemistry
• Analytical Chemistry

Background:

• Non-extractable phenolic compounds (NEPC) represent a significant portion of plant phenolics.
• Understanding NEPC extraction is vital for assessing their bioavailability and bioactivity.
• Grape processing by-products are rich sources of valuable phenolic compounds.

Purpose of the Study:

• To investigate the impact of hydrolysis conditions on the extraction and composition of NEPC from grape peel and seed powder.
• To determine optimal hydrolysis parameters for maximizing NEPC yield and diversity.
• To explore the differential release of NEPC classes based on hydrolysis conditions.

Main Methods:

• Systematic variation of hydrolysis parameters: temperature (50-90 °C), hydrochloric acid concentration (0.1-15.0%), and time (5-20 min).
• Analysis of NEPC composition and concentration in extracted samples.
• Evaluation of the balance between NEPC release/extraction and degradation.

Main Results:

• Specific conditions (e.g., 1.0-8.0% HCl, 65-80 °C) yielded extracts with higher NEPC concentrations and compound diversity.
• Hydrolysis conditions significantly influenced the release of different NEPC classes.
• Non-extractable proanthocyanidins were favored by intermediate conditions, while hydrolysable tannins and hydroxybenzoic acids required harsher conditions.

Conclusions:

• Hydrolysis conditions are critical for modulating NEPC concentration and composition from grape matrices.
• Tailoring hydrolysis parameters allows for targeted extraction of specific phenolic classes.
• Accurate assessment of NEPC's biological effects necessitates consideration of matrix-dependent compositional variations.