Title: Citric Acid-Stabilized Amorphous CaCO₃ as a High-Surface-Area Carrier for Functional Food Ingredients

Area of Science:

• Materials Science
• Nanotechnology
• Chemical Engineering

Background:

• Amorphous calcium carbonate (ACC) possesses a large specific surface area, making it suitable for functional material development.
• ACC's utility is limited by its rapid, spontaneous recrystallization into more stable crystalline forms (vaterite, calcite) within seconds.
• Developing stable, high-surface-area ACC is crucial for its practical application.

Purpose of the Study:

• To investigate the use of citric acid for stabilizing amorphous calcium carbonate (ACC).
• To achieve reproducible, high-surface-area ACC under controlled conditions.
• To demonstrate the potential of stabilized ACC as a platform for functional materials.

Main Methods:

• Systematic variation of citric acid concentration in a mixed ethanol/ethylene glycol medium.
• X-ray diffraction (XRD) to confirm the suppression of ACC crystallization.
• Brunauer-Emmett-Teller (BET) analysis to determine the specific surface area of synthesized ACC.
• Loading curcumin onto ACC to assess its dissolution behavior.

Main Results:

• Complete inhibition of ACC crystallization was achieved at citric acid concentrations above 0.39% w/v.
• ACC samples synthesized with 0.44-1.11% w/v citric acid exhibited high surface areas ranging from 600-700 m²/g.
• Enhanced dissolution behavior of loaded curcumin was observed, dependent on the ACC's surface area.
• A specific surface area threshold was identified for optimal cargo dissolution.

Conclusions:

• Citric acid effectively suppresses the recrystallization of amorphous calcium carbonate (ACC).
• Stable, high-surface-area ACC can be reproducibly synthesized using citric acid.
• The surface-area-to-cargo ratio is a critical factor for optimizing functional material formulations.
• Stabilized high-surface-area ACC presents a promising platform for advanced material design.