# The Gelation Mechanism of an Apple Polysaccharide at Ambient Temperature as Induced by Ca2+

## TL;DR

This study shows how apple polysaccharide can form gels at room temperature when calcium is added, making it a potential substitute for gelatin in food.

## Contribution

The novel contribution is the discovery of Ca2+-mediated electrostatic screening as the gelation mechanism for apple polysaccharide.

## Key findings

- Ca2+ at 4.5 mmol·L−1 induces gelation of apple polysaccharide at 0.5% concentration across pH 3.0–8.0.
- Gel melting occurs around 33 °C, and pH changes do not significantly affect gel formation or melting.
- ITC and EPR measurements show no direct binding of Ca2+ to the polysaccharide chains.

## Abstract

In this study, an apple polysaccharide (AP) that exhibited a gelatin-like gelation behavior has been reported, with the gelation mechanism being further revealed. It was found that a suitable amount of Ca2+ addition (4.5 mmol·L−1) induced the formation of AP gels at 0.5% (w/v) polymer concentration in a wide pH range (3.0–8.0) by holding the polysaccharide solution at 4 °C. However, no gel was formed in the absence of Ca2+. Meanwhile, all gels melted around 33 °C upon reheating, and the change in pH did not significantly affect the formation and melting processes of the AP gels. Furthermore, ITC and EPR measurements indicated no detectable binding of Ca2+ to AP chains. Thus, the gelation mechanism was explained as Ca2+-mediated electrostatic screening, whose presence facilitated AP chain–chain association and ultimately triggered network formation. Our results suggested that AP may exhibit high potential as a possible gelatin substitute in food production.