Effect of Tannic Acid Concentration on the Physicochemical, Thermal, and Antioxidant Properties of Gelatin/Gum Arabic-Walled Microcapsules Containing Origanum onites L. Essential Oil

It has long been known that oregano herbs have wide uses and industrial applications due to their high antioxidant activities and other activities of the main essential oil compound, carvacrol, but these compounds are sensitive to oxidation. Gas chromatography-mass spectrometry (GC-MS) analysis was performed to identify the volatile compounds of Origanum onites L. (OOEO), and the main volatile component of OOEO was determined as carvacrol (69.60%). This study aims to develop OOEO-loaded microcapsules by complex coacervation using gum arabic (GA) and gelatin (GE) as wall materials and different concentrations of tannic acid (TA) as a cross-linker. The OOEO microcapsules cross-linked using 2% TA have the highest loading capacity, microencapsulation yield, and efficiency with 36.39%, 83.75%, and 89.61%, respectively. The Fourier transform infrared spectra of the complex coacervates showed characteristic carvacrol peaks, one of the main components of OOEO, indicating that OOEO was successfully encapsulated in the polymer matrix. Thermal gravimetric analysis data revealed that cross-linking with TA affects the thermal stability of the microcapsules attributed to electrostatic interactions between the microcapsule wall and TA. With increasing TA concentration, GE/GA-walled microcapsules exhibited decreased aggregation with increased particle size and absolute zeta potential. This new approach to the production of OOEO-loaded microcapsules provides a high yield strategy with improved physico-mechanical properties and antioxidant activities.