Synergistic Approach for Disinfestation of Heat-Resistant Fungal Conidia in Grain Spawn Production: Combining Cold Plasma and Sodium Hypochlorite Treatments

Abstract

Abstract Heat-resistant fungal conidia are a common source of contamination and can cause significant difficulties in producing spawns. In this study, Aspergillus tubingensis (A. tubingensis) and Aspergillus flavus (A. flavus), frequent microbial contaminations of wheat grain spawn, were identified and isolated. Their conidia were treated with NaOCl and cold plasma to determine the effectiveness of these treatments in reducing contamination. Optical emission spectroscopy (OES) analysis of the plasma showed dominant emissions from the N2 second positive system and N2+ first negative system, while reactive oxygen species (ROS) spectral lines were undetected due to collision-induced quenching effects. The findings of the study show that A. flavus conidia are more resilient than A. tubingensis conidia when exposed to NaOCl and plasma treatments. The combined treatment of cold plasma and NaOCl had a synergistic effect, resulting in the inactivation of A. flavus and A. tubingensis conidia after just 30 and 10 seconds of plasma exposure, respectively. Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive X-ray Spectroscopy (EDXS) were utilized to investigate the effect of treatments on the form and element composition of the conidia surface. Treatment of conidia with NaOCl and cold plasma caused significant changes in the elemental composition of the conidia surfaces, with a considerable increase observed in the levels of Na, O and Cl, as well as N elements for both conidia. When lower concentrations of NaOCl were employed, the conidia size was found to be reduced. However, at higher concentrations and after plasma treatment, the conidia were ruptured and, in some cases, pulverized. These findings indicate that the combined treatment is a promising approach for the disinfestation of heat-resistant fungal conidia.