Synergistic Effect of Pectin-Calcium Ion-Sugar Combination on the Hardening of Low-Sugar Preserved Kiwifruit

The purpose of this study was to investigate the synergistic effect of a mixed aqueous solution of pectin, calcium ion and sugar on the hardening of low-sugar preserved kiwifruit. The effects of different treatments (purified water (control), 1% pectin, 1% pectin + 0.3% CaCl₂, 1% pectin + 0.3% CaCl₂ + 20% sucrose, and 1% pectin + 0.3% CaCl₂ + 10% stevia) on the quality of preserved fruits were systematically evaluated by measuring the solid content, texture characteristics, water activity, drying kinetics, retention rate of reduced ascorbic acid, and microstructure. The results showed that the combined treatment significantly improved the hardening effect: the pectin + calcium ion system formed a dense gel network through ion crosslinking, and resulted in a higher solid content when compared with the control group. Texture analysis showed that the pectin + CaCl₂ + stevia group had a cutting force of 5915.71 g, and the elasticity and supporting capacity were the best. Low-field nuclear magnetic resonance (NMR) and drying curves showed that sucrose and stevia delayed the loss of water activity and improved the drying efficiency (the moisture content was reduced to 20% after 5 hours). Scanning electron microscopy (SEM) confirmed that hardening treatment with the mixed solution led to the formation of a uniform gel network, supporting the walls of cells disrupted by cryopreservation. The pectin + CaCl₂ + stevia group showed the lowest loss of reduced ascorbic acid and outstanding antioxidant activity. In conclusion, the combined treatment (1% pectin + 0.3% CaCl₂ + 10% stevia) demonstrates significant advantages in improving the hardening effect, maintaining the nutritional quality, and meeting the demand for low-sugar products. This study provides a theoretical basis and process reference for the development of functional preserved fruits.