Changes in microbial diversity of brined green asparagus upon treatment with high hydrostatic pressure

Abstract

The application of high hydrostatic pressure (HHP, 600MPa, 8min) on brined green asparagus and the changes in bacterial diversity after treatments and during storage at 4°C (30days) or 22°C (10days) were studied. HHP treatments reduced viable cell counts by 3.6 log cycles. The residual surviving population did not increase during storage at 4°C. However, bacterial counts significantly increased at 22°C by day 3, leading to rapid spoilage. The microbiota of green asparagus was composed mainly by Proteobacteria (mainly Pantoea and Pseudomonas), followed by Firmicutes (mainly Lactococcus and Enterococcus) and to a less extent Bacteroidetes and Actinobacteria. During chill storage of untreated asparagus, the relative abundance of Proteobacteria as well as Enterococcus and Lactococcus decreased while Lactobacillus increased. During storage of untreated asparagus at 22°C, the abundance of Bacteroidetes decreased while Proteobacteria increased during late storage. The HHP treatment determined a reduction of the Proteobacteria both early after treatment and during chill storage. In the HHP treated samples stored at 22°C, the relative abundance of Pseudomonas rapidly decreased at day 1, with an increase of Bacteroidetes. This was followed by a marked increase in Enterobacteriaceae (Escherichia) simultaneously with increase in viable counts and spoilage. Results from the study indicate that the effect of HHP treatments on the viability of microbial populations in foods also has an impact on the dynamics of microbial populations during the storage of the treated foods.