Microbiological insight into cold-pressed oils by cultural and metataxonomic analysis

Abstract

In recent times, cold-pressed oils have become more popular due to their health benefits and flavours. They are produced by the non-blended and chemically-free cold extraction process from various plant seeds such as rapeseed, black cumin or hempseed. The purpose of this study was evaluation of bacterial composition of cold-pressed oils available in retail stores in Poland with the use of culture dependent and independent techniques. We detected bacteria within almost half of the studied samples originating from three different producers. Among culturable bacteria the most frequently represented phylum was Firmicutes, following by Actinobacteria and Proteobacteria. Especially, spore-forming bacilli belonging to the Bacillus cereus group, B. megaterium, and B. simplex were identified. In turn, the investigation of the whole microbial community of the unrefined oils revealed that Cyanobacteria and/or Proteobacteria dominated in all samples. Despite detected low number of culturable bacteria, mainly associated with plant and soil origin, the differences in the microbiome patterns between oils were showed, which might result from specific microbial composition of particular plant's seeds. Our results indicate that the pressing process does not kill all bacteria and shapes the microbiome of the finished product, thus the extend research in the field of oil microbiology in the future is needed.