Optimization of process variables for industrially scalable encapsulation of salicylic acid in an environmentally friendly setting

Abstract

Encapsulated phytohormones are gaining attention as a novel palliative treatment for plants to cope with environmental stress. Exogenous treatments using encapsulated salicylic acid (SA) promote plant stress tolerance while enabling normal growth and development. Several methods exist to produce encapsulated active molecules, and recently, spray drying has emerged as a particularly appealing process for formulating these compounds. However, phytohormone encapsulation has not been properly established yet. In a previous study, silica/chitosan SA encapsulated samples were formulated at different ratios, and their physical, chemical, and kinetic characteristics were analyzed, resulting in a promising antifungal product. However, it is unknown whether the encapsulated SA is affected in its structure and, thus, in its properties due to the spray temperature. Therefore, to decrease the spray temperature, silica/chitosan SA samples were formulated using a water-acetone mixture, and their characteristics studied and compared with the samples previously formulated in water.

This study reveals the dispensability of using an organic solvent to reduce the spray-drying temperature during atomization, as the antifungal potential of the silica/chitosan-encapsulated SA samples does not improve. Acetone- and water-based encapsulates effectively inhibited the mycelial growth of two necrotrophic fungi (Alternaria alternata and Penicillium digitatum) by approximately 50 %. However, avoiding the use of organic solvents in the formulation mitigate associated issues such as environmental impact, safety, health and toxicity concerns, cost, regulatory compliance, material compatibility, and handling.

Furthermore, the water-based encapsulation process was optimized through a fractional randomized experimental design. Six process variables at two levels were selected: i) solid content, ii) milling speed, iii) milling time, iv) spray temperature, v) feed rate, and vi) airflow, resulting in 16 randomized experiments that allowed the establishment of optimal conditions for the encapsulation of SA. This optimization enables the reduction of raw material loss and production costs, fostering environmental sustainability.