Microencapsulation and characterization of algal extracts with biopesticide properties

The adverse effects of chemical pesticides, commonly used to enhance crop yield in agriculture, on environmental and human health have necessitated the search for sustainable biological alternatives. The antibacterial activity of microalgae against plant pathogens has highlighted their potential as bio-based pesticides. In this context, 70% methanolic extracts obtained from Chlamydomonas CC124 mt and Scenedesmus sp. AQUAMEB-57 —cultivated strains from the Algae and Cyanobacteria Culture Collection of Bursa Technical University—were shown to exhibit antibacterial activity against the plant pathogens Pseudomonas syringae pv. tomato and Clavibacter michiganensis. This study aimed to develop bio-pesticide formulations by encapsulating these microalgal extracts through two different microencapsulation techniques to enhance their controlled release, bioavailability, and active compound stability. The encapsulation processes were optimized using the Taguchi factorial design method with the L8 (27) orthogonal array. For the ionotropic gelation method, the independent variables included alginate concentration, CaCl₂ concentration, dropping height, dropping speed, stirring speed, stirring time, and gelation bath temperature. For the emulsification method, parameters such as alginate concentration, alginate:CaCO₃ ratio, aqueous:oil phase ratio, Tween80:oil phase ratio, emulsification stirring speed, gelation stirring speed, and gelation time were selected. In the ionotropic gelation method, optimization was based on average particle size and sphericity factor, while in the emulsification method, particle size distribution and span value were calculated. Statistically significant models were obtained for all responses, and the influence of each parameter on microparticle characteristics was determined. At the optimal formulation conditions, encapsulation efficiency (EE) and loading capacity (LC) of the microalgal extracts were evaluated. Physicochemical, thermal, and morphological characterizations were carried out using Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM), respectively. In vitro release studies of the extracts were conducted using a defined sampling and separation protocol. The antibacterial activity, minimum inhibitory concentrations (MIC), and release profiles of microparticles produced by both methods were assessed in vitro using the microdilution method against Pseudomonas syringae pv.tomato. As a result, the microencapsulation of algal extracts with bio-pesticide properties led to the development of thermally stable formulations that maintained antibacterial efficacy and achieved prolonged, effective dosing through controlled release. This approach contributed to reducing environmental risk and economic loss compared to conventional pesticide applications. Moreover, encapsulated systems demonstrated enhanced thermal stability over free extracts while preserving their bioactivity.