Evaluation of treatments to control Penicillium expansum in model apple handling systems

Pencillum expansum is a post-harvest fungal pathogen that causes spoilage losses during long-term apple storage. Apples that are infected with the organism also accumulate patulin, a carcinogenic mycotoxin that may contaminate processed apple products such as apple juice. Flotation tanks and storage bins are significant sources of P. expansum spores and are typical sanitation targets. Conventional sanitizers that are used to control this organism, such as sodium hypochlorite (NaOCl), have not been completely effective, and the efficacy of sanitizers on storage bin materials has not been fully explored. An understanding of sanitizer mechanisms of action could also support the development of optimal formulations to control P. expansum.; In this study, the susceptibility of P. expansum spores to NaOCl compared with electrolyzed oxidizing water (EOw) and chlorine dioxide (ClO2) was determined in aqueous suspensions, in a model flotation tank, and on wood and plastic surfaces. The effect of non-ionic surfactants on the efficacy of the sanitizers was also investigated by modifying each sanitizes with up to 0.1% VN of polyoxyethylene sorbitan monoolate (Tween 80), polyoxyethylene sorbitan monolaurate (Tween 20), or sorbitan monolaurate (Span 20). Physical and chemical changes caused by the sanitizers were evaluated using electron microscopy and Fourier transform infrared spectroscopy (FT-IR), respectively. The potential of FT-IR in discriminating heated-treated from untreated fungal spores, and to distinguish between several pathogenic fungal species, was also evaluated.; All the sanitizers inactivated the spores of P. expansum significantly in aqueous suspensions. NaOCl was improved by the addition of surfactants, while Tween 80 reduced the efficacy of EOw. Neither EOw nor NaOCl treatments prevented the decay of inoculated-wounded apples, but cross contamination by spores introduced into the model flotation tank was substantially reduced especially when NaOCl was modified with surfactants. The efficacies of EOw and NaOCl solutions depended on their oxidation-reduction potential (ORP). The effectiveness of treatments on wood surfaces was marginal and was not enhanced by the addition of surfactants. However, on plastic surfaces, modification with Tween 20 and Span 20 substantially improved the efficacy of all the sanitizers. Transmission electron microscopy images of treated spores revealed structural damage to spore organelles, but scanning electron microscopy did not reveal any differences between treated and untreated spores. FT-IR data suggested that NaOCl and ClO2 altered the protein and lipid components of the spores. FT-IR also successfully differentiated unheated spores from those that had been exposed to heat treatment up to 80°C, and species of Aspergillus and Penicillium were distinguishable using this technique. (Abstract shortened by UMI.)...