Postharvest microbial shifts of avocado, Persea americana Mill., fruit washings using broad-spectrum surface sanitiser and peracetic acid disinfectants

Microbiome studies have more recently enabled scientists to gain a better understanding of microbial populations, diversity and richness of species, population shifts due to interventions and finally persistence of microorganisms in different environments. The fruit surface provides a unique microbial site for bacterial attachment and survival due to the specific surface structures and ever-present exudates directly linked with ripening. Natural microbial populations provide a protective base against postharvest pathogens causing spoilage or foodborne pathogens i.e. Salmonella spp. and Listeria monocytogenes which is a food safety concern. Retaining fruit quality and safety is thus reliant on efficient sanitizing that will not disrupt the natural microbial balance but prevent pathogen persistence. The study aimed to determine the reliability of commercial fruit washings and the impact thereof on the bacterial microbiomes and the effectiveness of sanitizers to retain the pathogen free status of fruit. Sixty avocado fruit were sampled two times, weekly at the commercial food processing plant during the harvesting season (June - October 2016) and out of season (December 2016 - February 2017) for microbial analysis (DNA extraction and Illumina sequencing). Operational taxonomic units reflected on important phyla i.e., Proteobacteria, Bacteroidetes, Actinobacteria, Firmicutes and Acidobacteria. Diverse bacterial communities were associated with avocado fruit and differences in relative abundance of taxa were found between stored and washed fruit. Bacterial taxa associated with the avocado carpoplane were more diverse in season than out of season fruit that was first cold stored, these findings indicate that microbial diversity decreases during fruit storage. The fruit washing step contributes to the bacteria naturally found on the avocado carpoplane, it was noted that washed fruit had a more complex and unique bacterial taxa in both sampling periods, compared to unwashed fruit.