Evaluation of bacterial contamination on three different surfaces within domestic refrigerators

The objectives of this study were to analyze the number of microorganisms, fungal composition and the correlation between bacterial enrichment and air quality on three internal surfaces (the inner wall, shelf, and basket) of domestic refrigerators. The results showed that the inner wall had a significantly lower number of coliforms (P < 0.05), and the range was 0.2−2.5 log MPN cm−2. The total bacterial counts and psychrophilic bacterial counts on three internal surfaces in the same refrigerator tended to be consistent. Moreover, the inner wall owned a simpler bacterial community structure. At the genus level of fungi, the dominant flora of both the inner wall and shelf were Saccharomyces spp. and Candida spp., while Saccharomyces spp., Candida spp. and Fistulina spp. took superiority in the basket. Specifically, Shannon index and Simpson index, which represent the bacterial community diversity, were the lowest on the wall, and six bacterial species on the inner wall had relative abundance higher than 0.5% of the total operational taxonomic units (OTUs), while for the shelf and basket, there were 12 and 11 bacterial species respectively. Also, there was a significant negative correlation in the basket between the chao1 index and PM2.5. This study could provide guidance for the sanitation and recommend adequate packaging of foods stored in refrigerators.