Acetic Acid Synergizes With Calcium Chloride to Enhance Thermal Stability of Carrots: Mechanisms of Pectin Cross-Linking and Cell Wall Reinforcement.

Abstract

Thermal processing, an effective strategy for salt reduction and preservation, is prone to causing texture deterioration (softening) in processed fruits and vegetables. Previous studies have reported that exogenous calcium and organic acids can serve as texture enhancers for plant-based foods during cooking, mitigating texture damage from thermal treatment. Therefore, this study aimed to investigate the effect of 0.4% acetic acid synergized with 0.5% calcium chloride treatment (AAI+CC) on improving the hardness of thermally processed carrots. The results showed that carrots pretreated with this combination exhibited optimal heat stability, with their cell wall structural integrity being less affected by heating. Through the determination of pectin methylesterase (PME) activity, total calcium content, and methyl esterification degree, it was found that AAI+CC effectively activated endogenous PME activity. This activation promoted the cross-linking of divalent calcium cations (Ca2+) with pectin to form an "egg carton" structure, thereby stabilizing the cell wall network. Additionally, immunolabeling and physicochemical analyses further revealed that the synergistic treatment effectively retarded pectin solubilization and depolymerization induced by β-elimination reactions. As a result, pectin chains became entangled during gelation, forming a more compact molecular conformation. These findings not only enhance the understanding of thermal processing texture in carrots but also provide a reference for the food industry to develop green quality-control technologies for thermal processing of fruits and vegetables.