Development of Soy Protein-Based Bioplastics as Controlled-Release Systems for Iron Biofortification in Crops

Introduction. Improving nutrient-use efficiency (NUE) is essential for sustainable food production. Controlled-release fertilizers (CRFs) allow gradual nutrient delivery synchronized with plant requirements. Biodegradable matrices from renewable resources are promising carriers. Soy protein isolate (SPI), an abundant by-product of the soybean oil industry, can be valorized to develop bioplastics for agricultural applications. This study evaluates SPI-based matrices as controlled iron-delivery systems and for crop biofortification in horticulture.

Materials and Methods. SPI was plasticized with water, glycerol or mixtures (5–15wt%), and iron sulphate heptahydrate (5wt%) as micronutrient. Tablets were produced by compression molding (300 bar). Materials were characterized by FTIR, thermogravimetric and dynamic mechanical analyses, water uptake and SEM microscopy. Selected formulations were evaluated in pepper plants to assess plant growth and iron bioavailability.

Results and Discussion. Water-plasticized systems exhibited higher stiffness and lower swelling, whereas glycerol increased flexibility and water absorption but with greater soluble matter loss. Release profiles were biphasic, showing a rapid initial stage followed by sustained delivery. Crop assays demonstrated improved plant growth and leaf coloration compared with unfertilized controls. Several formulations promoted higher iron accumulation in plant tissues, highlighting their potential as sustainable tools for crop iron biofortification.

Conclusions. SPI-based bioplastics are promising biodegradable carriers for CRFs. Their application improves NUE, supports crop iron biofortification and valorizes agro-industrial by-products, contributing to more sustainable food production systems.

Funding sources: This research is part of the project with reference SOL2024-31712, cofounded by UE - Ministerio de Hacienda y Función Pública-Fondos Europeos-Junta de Andalucía-Consejería de Universidad, Investigación e Innovación. Authors acknowledge the financial support of Agencia Andaluza de Cooperación Internacional para el Desarrollo through the project “Fortalecimiento de las capacidades de investigación e innovación tecnológica de la UNAH para el desarrollo de cultivos biofortificados mediante el uso de matrices bioplásticas enriquecidas con micronutrientes como fertilizantes sostenibles (Honduras)” (expedient 2025UC005).