Inactivation of Salmonella , Listeria monocytogenes and Escherichia coli O157:H7 inoculated on coriander by freeze-drying and supercritical CO 2 drying

Coriander, either fresh or inoculated with three strains of Escherichia coli O157:H7, Salmonella or Listeria monocytogenes, was treated with supercritical CO2 (scCO(2), with and without drying) or freeze-dried. After drying in scCO(2) for 150 min at 80 bar and 35 degrees C, the aerobic plate count, yeasts and molds, and the Enterobacteriaceae were reduced by 2.80, 5.03, and 4.61 log CFU/g, respectively. The total count of mesophilic aerobic spores was not significantly reduced by the treatment. Freeze-drying induced lower reductions with 1.23, 0.87, and 0.97 log CFU/g, respectively. After treatment at 100 bar and 40 degrees C without drying, inoculated strains of E. coli O157:H7, Salmonella, and L. monocytogenes were inactivated by > 7.37, > 4.73 and 4.99 log CFU/g, respectively. After drying in scCO 2 for 150 min at 80 bar and 35 degrees C, the strains were reduced by > 5.18 log CFU/g. Freeze-drying resulted in lower reduction with maximum 1.53, 2.03, and 0.71 log CFU/g, respectively. This study indicated that scCO(2) can be used for drying while offering a good inactivation of E. coli O157:H7, Salmonella, and L. monocytogenes as well as most of the bacteria in the vegetative form naturally occurring on coriander. Industrial relevance: Although dried foods are considered microbiological stable foods and show adverse conditions to microbial growth, they may still host pathogenic microorganisms, which may proliferate upon sufficient rehydration. Highly contaminated commodities such as herbs and spices can pose a threat to consumer health if not processed carefully. There is therefore a need to develop or improve drying techniques which can provide dried foods while reducing the initial contamination to acceptable levels in a single process. CO2 is a cheap, accessible solvent, with a low critical point (31 degrees C, 73.8 bar). Moreover, in the supercritical region, CO, exhibits potent microbicidal properties. Therefore, supercritical CO2 drying could be a valuable alternative nonthermal technique for conventional drying methods, such as air-drying or freeze-drying, when medium to high value-added food products with high initial contamination are involved

Microbial inactivation efficiency of supercritical CO2drying process

Conventional drying of spices, as hot air treatment, often needs an additional downstream inactivation step to decrease the microbial load of the dried product and improve its microbial safety and microbial quality. In this regard, the present work explored the possibility to dry and decontaminate food in a single step using supercritical carbon dioxide (scCO(2)) as a drying agent. A case study was focused on the drying of herbs and the antimicrobial effects were evaluated on the naturally present microbiota. For this purpose, experiments were carried out on coriander leaves using a high pressure vessel at 10 MPa, at two different temperatures (40 and 50 degrees C) with drying time of 0 and 150 min to establish the influence of each parameter on the microbial inactivation. Yeasts and molds appeared to be the least resistant to scCO(2) as they could never be detected after the treatment (<2 log CFU/g). Mesophilic bacteria were also significantly reduced, up to 4 log CFU/g, but remained above the limit of quantification. The quality of the dried product was comparable with the quality of air-dried samples in terms of phenolic constituents. Overall, the results indicated that scCO(2) drying was a promising green drying technique combining both drying and microbial inactivation in a single step with a relevant impact on safety and costs