Reinforcement of soy protein-based bioplastics as potential sustainable packaging solutions

· Thermal treatment conditions play a key role in protein bioplastics. · Post-thermal treatment improves mechanical properties but not the absorptive capacity. · The incorporation of different proteins promotes a reduction in water uptake capacity. · Glyoxal and enzymatic crosslinking led to better mechanical properties. · The results open up a potential for the application of these matrices in the packaging industry. Due to the substantial amount of plastic waste in the environment, scientists are seeking new alternatives to traditional plastics. Bioplastics are considered to be important in addressing this issue despite their significant drawbacks, such as poor mechanical properties and higher costs. In order to reduce their price, agri-food waste and by-products can be used as raw materials (e.g., soy protein), promoting a circular economy; and by incorporating different reinforcement methods, it is possible to develop materials with improved mechanical and barrier properties. The aim of this work is to improve the properties of soy protein/glycerol injected bioplastics by incorporating different biopolymers (gelatin and saccharose) or applying different crosslinking methods (physical, chemical or enzymatic crosslinking through thermal treatment, glyoxal or transglutaminase, respectively). These materials were evaluated by physicochemical, mechanical, and functional tests. The results confirmed an improvement in the mechanical properties of the reinforced protein-based bioplastics, showing an increase in their stiffness and a decrease in their deformability, reducing their capacity to absorb water. In any case, these results support the modification of the properties compared to the reference systems.