Impact of High-Hydrostatic Pressure Treatments Applied Singly or in Combination with Moderate Heat on the Microbial Load, Antimicrobial Resistance, and Bacterial Diversity of Guacamole

Abstract

Guacamole is an avocado sauce highly appreciated for its pleasant taste and nutritional value. The present study addressed the impact of high-hydrostatic pressure (HP) treatments on the product safety and bacterial diversity. Four HP treatments, 5 min each, were applied: (A) 450 megapascals (MPa) at 22 °C; (B) 450 MPa at 50 °C; (C) 600 MPa at 22 °C; (D) 600 MPa at 50 °C. Controls and treated samples were refrigerated stored for 50 days. The residual surviving fraction was lowest for the 600 MPa treatment at 50 °C. Bacterial growth on media supplemented with antibiotics (cefotaxime and imipenem) or the biocide benzalkonium chloride was detected only from control samples but not from HP-treated samples. High throughput sequencing analysis indicated that the bacterial diversity of control samples was dominated by members of Fam. Enterobacteriaceae, but it changed to a lactic acid microbiota during storage. HP-treated samples showed reduced relative abundances of Enterobacteriaceae and lactic acid bacteria and higher abundances of Pantoea, Ralstonia and Methylobacterium. Results from the study indicate that HP treatments of guacamole at 50 °C show higher microbial inactivation compared to 22 °C. However, all treatments reduced the levels of Enterobacteriaceae and penem-tolerant bacteria and provided product stability against acidification by lactic acid bacteria.

Antimicrobial Resistance, Biocide Tolerance, and Bacterial Diversity of a Dressing Made from Coriander and Parsley after Application of Treatments Using High Hydrostatic Pressure Alone or in Combination with Moderate Heat

“…Treatments with high hydrostatic pressure (HP) were applied as described in a previous study carried out on guacamole [ 34 ], using Stansted Fluid Power LTD HP equipment (SFP, Essex, UK) with water containing 10% propylenglycol as the pressurization fluid. The system included an electrical heating unit (SFP), which allowed us to apply the following treatment conditions at a gradually increasing speed up to 75 MPa/min followed by almost instant decompression: (A) 450 MPa at 22 °C; (B) 450 MPa at 50 °C; (C) 600 MPa at 22 °C; and (D) 600 MPa at 50 °C.…”

“…The procedures used for the microbiological analysis were the same as described in a previous study [ 34 ]. Controls and HP-treated batches (two bags each) were analyzed following HP treatments (time 0) and during the refrigerated storage period (days 2, 5, 10, and 20).…”

“…Microbial DNA was extracted as described in a previous study [ 34 ]. The pellets recovered from samples (5 mL) after centrifugation (13,500× g for 5 min) were resuspended in sterile saline solution (0.5 mL each) and treated with propidium monoazide (PMA™, GenIUL, S.L, Barcelona, Spain) [ 38 , 39 ].…”

“…The following standard procedure was used for DNA sequencing and analysis [ 34 ]. Amplification of the 16S rDNA V3–V4 regions was performed using the Illumina Metagenomic Sequencing Library Preparation protocol (Illumina, Inc., San Diego, CA, USA) with the primers (F)5′TCGTCGGCAGCGTCAGATGTGTATAAGAGACAGCCTACGGGNGGCWGCAG and (R)5′GTCTCGTGGGCTCGGAGATGTGTATAAGAGACAGGACTACHVGGGTATCTAATCC [ 40 ].…”

The Role of the Bacterial Community in Producing a Peculiar Smell in Chinese Fermented Sour Soup

“…A total of 20–30 ng DNA was used as a template; the PCR primers included the “CCTACGGRRBGCASCAGKVRVGAAT” sequence and “GGACTACNVGGGTWTCTAATCC” sequence and were designed by GENEWIZ Company (GeneWiz, South Plainfield, NJ, USA) to amplify the V3 and V4 variable regions. In addition, an index connector was added to the end of the 16S rDNA product by PCR for NGS sequencing [ 14 ]. The PCR parameters were as follows: predenaturation at 94 °C for 3 min × 1, denaturation at 94 °C for 5 s, annealing at 57 °C for 90 s, elongation at 72 °C for 10 s, and final elongation at 72 °C for 5 min for a total of 24 cycles.…”