Encapsulated Zataria multiflora's essential oil inhibited the growth of Aspergillus flavus and reduced aflatoxins levels in contaminated pistachio nut

Abstract

The essential oil of Zataria multiflora Boiss. (ZEO) was prepared using a British Pharmacopeia-type hydrodistillation apparatus. The ZEO was encapsulated with a natural polymer, chitosan (CS) by oil-in-water emulsification, and ionic cross-linking techniques. The shape and size range of the encapsulated particles were evaluated by Atomic-Force Microscopy (AFM) and Dynamic Light Scattering (DLS) and FT-IR spectroscopy. The AFM analysis of the ZEO encapsulated nano-particles (CS-ZEO) showed spherical shape particles with inner cavities. The mean size of CS-ZEO particles was 293 ± 17 nm according to DLS analysis. The chemical constituent of the oil was analyzed by GC-MS and thymol acetate (32.4%), carvacrol acetate (19.0%), γ-terpinene (18.5%), and ρ-cymene (14.5%) were reported as its major constituents. The non-encapsulated ZEO in the synthesis process was determined to calculate the encapsulation efficiency and loading capacity of the prepared CS-ZEO which were 87.4% and 6%; respectively. In vitro antifungal activity of ZEO and CS-ZEO in growth media against Aspergillus flavus was evaluated with the decrease in fungal mycelial mass. On the other hand, the HPLC results showed the reduction of aflatoxins B1 levels by 95% and 92% at concentrations of 0.8 mg/mL of ZEO and 6.7 mg/mL of CS-ZEO, respectively. The above-mentioned effective concentrations of the ZEO and CS-ZEO, were applied to pistachio samples, which reduced 90.5% and 99.0%, of the aflatoxin B1 levels, respectively compared to non-treated samples. Therefore, we suggest here, the CS-ZEO as a possible natural fungicide with an effective mechanism of lowering aflatoxins production in the contaminated pistachio.