Biodegradable soy protein-based tablets for the controlled release of zinc

Controlled-release systems are gaining interest in the horticultural industry to supply fertilizers to crops. However, their manufacturing process increases their cost, making its industrialization difficult. In this context, compaction of powders could be a low-cost and easily industrializable alternative. Thus, the main objective of this work was the manufacture of soy protein-based tablets with zinc (micronutrient) incorporated using different compaction parameters (pressure: 333, 416 and 777 MPa; post-manufacture heat treatment: 4 and 24 h). Thus, the mechanical (dynamic compression tests) and microstructural properties (SEM and grain number) of the different tablets were evaluated to study the effect of pressure and temperature on them. In addition, water uptake capacity and micronutrient release were studied. The latter has been analyzed with the use of two theoretical models (Higuchi and Korsmeyer-Peppas) to evaluate which model is the most accurate for predicting the zinc release of the different tablets. The results presented in this work demonstrate the great utility of soy protein-based tablets for the controlled release of zinc. Thus, this process allows the incorporation of 116 g of Zn in a kg product that can be released under control (9-10 h in water). These products have great industrial potential due to their ease of processing and properties, making them economically competitive.