Non-thermal Plasma Inactivation of Bacillus Amyloliquefaciens spores

Bacterial spores have remarkable resistance to a variety of harsh conditions, causing spoilage in food industry and becoming the primary bacterial agent in biowarfare and bioterrorism. In this study, inactivation mechanisms of Bacillus amyloliquefaciens (BA) spores by non-thermal plasma (NTP) were investigated by using Fourier-transform infrared spectroscopy (FTIR) as a major tool to exam spores after NTP treatment. Chemometric techniques, such as multivariate classification models based on soft independent modeling of Class Analogy (SIMCA) and Principal Component Analysis (PCA), were employed to identify functional group changes in FTIR spectra. The IR absorbance bands correlated to dipicolinic acid (DPA) decreased after NTP treatment indicating that DPA released and then reacted with reactive species generated by NTP and it was confirmed by nuclear magnetic resonance (NMR). Also IR absorbance bands corresponding to protein structure changed. FTIR combined with UV-Vis spectroscopy was used to monitor spore germination. Large amount of DPA released in a short time when spores germinated at 50°C, showing that DPA released in response to heating. NTP treated spores could germinate with little DPA release due to sub-lethal effects induced by plasma. Also an empirical model based on Weibull distribution was established to describe the spore germination process showing that NTP treated spores exhibited abnormal germination pattern. Inactivation mechanisms of NTP with air as feed gas was compared with high-pressure, wet heat, chemical treatment using chlorine dioxide (CD) and NTP with argon as feed gas. The results showed that few chemical changes in spores after autoclave and high pressure treatments, though protein structure changed. CD and NTP with air as feed gas inactivated spores by oxidation. DPA released after NTP with argon as feed gas treatment and it is possible that UV and charged particles accounts for the inactivation. This study provides in depth insight into the inactivation mechanism of NTP and information for optimizing NTP process.