Inactivation of Aspergillus niger and Erwinia carotovora in onion (Allium cepa L.) bulbs subjected to pulsed ozone treatment

Abstract

A number of microbes are responsible for the spoilage of onion, notably black mold rot caused by Aspergillus niger and soft rot caused by Erwinia carotovora. This research investigates the efficacy of gaseous ozone for the inactivation of A. niger and E. carotovora inoculated on onion bulbs. Ozone concentrations of 0.21, 0.42, and 0.64 mg L−1 were applied to the inoculated bulbs in pulsed mode. The reduction in microbial load of A. niger and E. carotovora varied from 0.47 to 2.31 log CFU g−1 and 0.72 – 2.99 log CFU g−1 respectively. With an increase in concentration and number of exposures, the efficacy of ozone on microorganisms increased. SEM analysis revealed structural disintegration of bacterial cells and fungal spores with the severity of ozone application. Cellular leakage from the microbial cell determined spectrophotometrically confirmed the SEM observations. Geeraerd tail model (Radj2: 0.990–0.994, ERMS: 0.931–0.595 × 10−1) was found to be most suitable to describe the survival curve of A. niger; whereas, the Weibull model (Radj2: 0.988–0.991, ERMS: 1.102–0.701 × 10−1) fitted best to survival data of E. carotovora.