Camellia Saponin-Enhanced Sodium Alginate Hydrogels for Sustainable Fruit Preservation

It is well known that food waste, especially perishable fruits, is one of the pressing issues worldwide, and as much as 50% of harvested fruits are wasted in developing countries as a result of poor preservation methods. Other traditional options such as plastic films or chemical preservatives are harmful to the environment and to our health. In this work, the limitations are overcome through the fabrication of an innovative camellia saponin/sodium alginate (CS/SA) composite hydrogel film that not only recycles agricultural waste but also improves fruit protection. CS/SA films were prepared by ionic crosslinking with CaCl₂ with different CS content (0-10% w/v, corresponding to 0-3.1 wt% in air-dried films). Detailed SEM, FTIR, XRD and rheological studies indicated that CS addition led to a gradual microstructural densification, stronger intermolecular interactions (involving hydrogen bonding and electrostatic complexation) and superior viscoelasticity, with the best performance at 8% CS (2.5 wt% in dried film). Mechanical tests confirmed that the stable CS/SA film showed higher tensile strength (152 kPa) and compressive strength (353 kPa) than pure SA (10 kPa) with a relatively low Young's modulus (0.82 MPa) and high elongation at break (116.33%), which could be easily peeled off from fruit surfaces-an essential benefit of this over stiff chitosan/alginate composites. Structure: The composite film exhibited lower porosity (103.2%), reduced moisture content (94.7%), a controlled swelling ratio (800%) and improved barrier property with a water vapor permeability of 1.3 × 10-6 g·m^-1·s^-1·kPa^-1 and an oxygen permeability of 1.9 × cm³·μm·m^-2·d^-1·kPa^-1. The 8% CS film showed very strong antioxidant activity (86% DPPH scavenging). Results of application tests on bananas and strawberries indicated that the ripening process was delayed by the CS/SA coatings, the decay rate was decreased from 99.9% (uncoated control) to 55.6% after 9 days, the weight loss was reduced to 29.3%, and the fruit's firmness and titratable acidity were maintained. This degradable, multifunctional hydrogel film has the potential to be a sustainable measure to simultaneously mitigate food waste, valorize agricultural byproducts, and protect the environment, which could offer substantial benefit for enhancing global food security as well as fruit shelf life.