Impact of Water Activity on the Inactivation and Gene Expression of Listeria monocytogenes during Refrigerated Storage of Pressurized Dry-Cured Ham.

Listeria monocytogenes population and the expression patterns of three virulence (plcA, hly, and iap) and one stress-related (sigB) genes in dry-cured ham with different water activity (aw) values (0.92, 0.88, and 0.84) and treated with high pressure processing (HPP, 450 MPa/10 min and 600 MPa/5 min) were monitored throughout 30 days (d) at 4 °C. The antimicrobial effect of HPP at 600 MPa against L. monocytogenes S4-2 (serotype 1/2b) and S12-1 (serotype 1/2c) was greater in dry-cured ham with aw values of 0.92, with reductions of 2.5 and 2.8 log units, respectively. The efficacy of HPP treatments decreased at lower aw values. Regarding gene expression, L. monocytogenes strains responded differently to HPP. For strain S4-2, the four target genes were generally overexpressed in dry-cured ham immediately after HPP treatments at the three aw values investigated, although the extent of this induction was lower in the samples pressurized at 600 MPa and with aw values of 0.84. For strain S12-1, the expression of all target genes was repressed at the three aw values investigated. The antimicrobial efficacy of HPP against L. monocytogenes could be compromised by low aw values in food products. However, no growth of HPP-survival cells was observed during refrigerated storage in low-aw dry-cured ham, and the overexpression of virulence and stress-related genes decreased.

Occurrence of Toxigenic Fungi and Mycotoxins during Smoked Paprika Production.

'La Vera' smoked paprika is a traditional Spanish product regulated under a protected designation of origin. Mycotoxins are possible contaminants in paprika, yet there is little information about mycotoxin production during the processing of smoked paprika. In this study, samples of dried peppers collected from six traditional dryers from four producers were evaluated for physicochemical parameters, mycotoxins, and mycotoxin-producing fungi. The moisture content and water activity of the peppers ranged from 11.0 to 16.3% and 0.513 to 0.611, respectively, with significant differences among the dryers (P ≤ 0.05). Culture methods revealed fungal counts of 2.6 to 5.7 log CFU/g, with significant differences among the dryers (P ≤ 0.05), and real-time PCR revealed aflatoxin-producing fungi (2.00 to 3.42 log CFU/g) in all dryers. However, mycotoxins were not detected in dried pepper samples. Sixty-seven mold species isolated from dried peppers were identified by sequencing of the ITS1-5.8S rRNA-ITS2 region and characterized by mycotoxigenic ability. Four isolates of Penicillium expansum, four isolates of Penicillium thomii, and one isolate of Aspergillus parasiticus were producers of patulin, penicillic acid, and aflatoxins, respectively. Toxigenic fungi were inoculated onto smoked dried peppers and stored at 84, 91, 94, and 97% relative humidity (RH) at 20°C for 30 days. Patulin was not detected under any of these conditions. Penicillic acid was detected in dried samples stored at 91 to 97% RH, although the optimum condition was isolate dependent. Aflatoxins G2, B1, and B2 were detected at 91 to 97% RH, with the highest concentrations at 94% RH. According to our results, hazard analysis critical control point systems should be used to control the drying and storage conditions of dried peppers until the milling step to avoid rehydration, which encourages fungal growth and mycotoxin production.

Effect of selected strains of Debaryomyces hansenii on the volatile compound production of dry fermented sausage "salchichón".

Different biotypes of Debaryomyces hansenii, characterized by mitochondrial DNA (mtDNA) restriction analysis, were inoculated in dry fermented sausages to evaluate their influence as single starter culture on volatile compound generation throughout the ripening process. Similar evolution of physicochemical parameters and microbial population was observed in both uninoculated and inoculated sausages. The tested biotypes modified the volatile compound profile of sausages specially in esters, branched alcohols and aldehydes. The biotype of D. hansenii with the E mtDNA restriction pattern is the most suitable to be used as starter culture since it produced volatile compounds involved in flavour development of dry-cured meat products such as 3-methylbutanol, 3-methylbutanal and 2-propanone. Moreover, the use of D. hansenii strains with the B, C2 and E mtDNA restriction patterns, as a mixed starter culture, should be also considered to generate low amount of sulphur compounds in dry-cured meat products.