Combining High-Pressure Processing and Supercritical Carbon Dioxide for Inactivation of Listeria innocua

The effect of high-pressure treatment with supercritical CO2 on the inactivation of Listeria innocua in a fish soup was investigated. The soup was inoculated with L. innocua, packaged in modified atmosphere with 50:50 or 95:5 CO2:N2, high-pressure processed (300, 350, 400 and 600 MPa, 2 min) under subcritical (T 304 K) and stored at 4 °C for up to 53 days. Treatment at 400 and 600 MPa had a significant (p < 0.05) effect on L. innocua under both supercritical and subcritical conditions. In contrast, pressurization at 350 MPa and supercritical conditions were needed to significantly (p < 0.05) inactive L. innocua. Increased levels of CO2 in the headspace significantly (p < 0.05) reduced the bacterial load during processing, and supercritical conditions had a significant (p < 0.01) interaction with both CO2 levels and pressure. Increased storage time gave significantly increased levels of L. innocua at 400 and 600 MPa. In addition, high levels of CO2 significantly decreased (p < 0.001) growth. However, 350 MPa under supercritical conditions seemed to set the L. innocua in a permanent lag phase, with slow and steadily decreasing numbers of bacteria during storage. All the design variables resulted in significant inactivation of L. innocua, and supercritical conditions combined with high levels of CO2 inhibited the recovery of L. innocua to a large degree.publishedVersio

Independent and combined effects of high pressure, microwave, soluble gas stabilization, modified atmosphere and vacuum packaging on microbiological and physicochemical shelf life of precooked chicken breast slices

publishedVersio

Effect of the Application of Ultrasound to Homogenize Milk and the Subsequent Pasteurization by Pulsed Electric Field, High Hydrostatic Pressure, and Microwaves

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Survival of Five Strains of Shiga Toxigenic Escherichia coli

The ability of foodborne pathogens to exhibit adaptive responses to stressful conditions in foods may enhance their survival when passing through the gastrointestinal system. We aimed to determine whether Escherichia coli surviving stresses encountered during a model dry-fermented sausage (DFS) production process exhibit enhanced tolerance and survival in an in vitro gastrointestinal model. Salami sausage batters spiked with five E. coli isolates, including enterohaemorrhagic E. coli strains isolated from different DFS outbreaks, were fermented in a model DFS process (20°C, 21 days). Control batters spiked with the same strains were stored at 4°C for the same period. Samples from matured model sausages and controls were thereafter exposed to an in vitro digestion challenge. Gastric exposure (pH 3) resulted in considerably reduced survival of the E. coli strains that had undergone the model DFS process. This reduction continued after entering intestinal challenge (pH 8), but growth resumed after 120 min. When subjected to gastric challenge for 120 min, E. coli that had undergone the DFS process showed about 2.3 log10⁡​ lower survival compared with those kept in sausage batter at 4°C. Our results indicated that E. coli strains surviving a model DFS process exhibited reduced tolerance to subsequent gastric challenge at low pH

The complete genome sequence of Listeria monocytogenes strain S2542 and expression of selected genes under high-pressure processing

Objectives The study aims to generate the whole genome sequence of L. monocytogenes strain S2542 and to compare it to the genomes of strains RO15 and ScottA. In addition, we aimed to compare gene expression profiles of L. monocytogenes strains S2542, ScottA and RO15 after high-pressure processing (HPP) using ddPCR. Results The whole genome sequence of L. monocytogenes S2542 indicates that this strain belongs to serotype 4b, in contrast to the previously reported serotype 1/2a. Strain S2542 appears to be more susceptible to the treatment at 400 MPa compared to RO15 and ScottA strains. In contrast to RO15 and ScottA strains, viable cell counts of strain S2542 were below the limit of detection after HPP (400 MPa/8 min) when stored at 8 degrees C for 24 and 48 h. The transcriptional response of all three strains to HPP was not significantly different.Peer reviewe

High-pressure processing-induced transcriptome response during recovery of Listeria monocytogenes

Background High-pressure processing (HPP) is a commonly used technique in the food industry to inactivate pathogens, including L. monocytogenes. It has been shown that L. monocytogenes is able to recover from HPP injuries and can start to grow again during long-term cold storage. To date, the gene expression profiling of L. monocytogenes during HPP damage recovery at cooling temperature has not been studied. In order identify key genes that play a role in recovery of the damage caused by HPP treatment, we performed RNA-sequencing (RNA-seq) for two L. monocytogenes strains (barotolerant RO15 and barosensitive ScottA) at nine selected time points (up to 48 h) after treatment with two pressure levels (200 and 400 MPa). Results The results showed that a general stress response was activated by SigB after HPP treatment. In addition, the phosphotransferase system (PTS; mostly fructose-, mannose-, galactitol-, cellobiose-, and ascorbate-specific PTS systems), protein folding, and cobalamin biosynthesis were the most upregulated genes during HPP damage recovery. We observed that cell-division-related genes (divIC, dicIVA, ftsE, and ftsX) were downregulated. By contrast, peptidoglycan-synthesis genes (murG, murC, and pbp2A) were upregulated. This indicates that cell-wall repair occurs as a part of HPP damage recovery. We also observed that prophage genes, including anti-CRISPR genes, were induced by HPP. Interestingly, a large amount of RNA-seq data (up to 85%) was mapped to Rli47, which is a non-coding RNA that is upregulated after HPP. Thus, we predicted that Rli47 plays a role in HPP damage recovery in L. monocytogenes. Moreover, gene-deletion experiments showed that amongst peptidoglycan biosynthesis genes, pbp2A mutants are more sensitive to HPP. Conclusions We identified several genes and mechanisms that may play a role in recovery from HPP damage of L. monocytogenes. Our study contributes to new information on pathogen inactivation by HPP.Peer reviewe

Extending shelf life of desalted cod by high pressure processing

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Teknologiutvikling for økt lønnsomhet i rekenæringen. Høytrykksprosessering som metode for tining og modning av fryste reker (AP4)

I prosjektet er det gjort forsøk for å undersøke om høytrykksprosessering (HP) kan benyttes for å korte ned modningstiden på reker. To delstudier er foretatt: (1) om HP kan benyttes for å modne rekene på kortere tid, evt. uten bruk av modningslake, og (2) om HP kan benyttes for å tine og modne reker i ett trinn. Forsøkene viste at reduksjon i modningstid ned mot 510 timer kombinert med høytrykksprosessering vil kunne gi lignende utbytte som dagens modning på cirka 20 timer. Modning av reker i modningslake kombinert med HP gav et høyere utbytte enn modning av reker i ferskvann kombinert med HP. Det ble ikke påvist at HP, med de testede betingelser, kan benyttes til å tine reker direkte fra frossen tilstand. Det var en tendens til at reker etter HP var enklere å pille enn ubehandlede kontroll-reker, og andelen hele reker etter pilling var høyere for de høytrykksprosesserte rekene

Rapport/Report 2/2014, English Summary

-I prosjektet er det gjort forsøk for å undersøke om høytrykksprosessering (HP) kan benyttes for å korte ned modningstiden på reker. To delstudier er foretatt: (1) om HP kan benyttes for å modne rekene på kortere tid, evt. uten bruk av modningslake, og (2) om HP kan benyttes for å tine og modne reker i ett trinn. Forsøkene viste at reduksjon i modningstid ned mot 510 timer kombinert med høytrykksprosessering vil kunne gi lignende utbytte som dagens modning på cirka 20 timer. Modning av reker i modningslake kombinert med HP gav et høyere utbytte enn modning av reker i ferskvann kombinert med HP. Det ble ikke påvist at HP, med de testede betingelser, kan benyttes til å tine reker direkte fra frossen tilstand. Det var en tendens til at reker etter HP var enklere å pille enn ubehandlede kontroll-reker, og andelen hele reker etter pilling var høyere for de høytrykksprosesserte rekene.High pressure processing (HPP) has been used on several types of commercial seafood. This study was done to explore whether HPP can be used in the maturation process of Norwegian coldwater shrimps. Two different approaches has been tested: (1) if HPP can be used to lower the maturation time of shrimps, and (2) if HPP can be used for combining thawing and maturation in one step. The experiments showed a reduction in the maturation step from 20 to 510 hours if HPP was used. Maturation in brine compared to tap water during HPP gave a higher yield. Under the tested conditions, HPP was not proven to be used for direct thawing of frozen Norwegian coldwater shrimps. There was a trend that shrimps after exposure to HPP was easier to pill compared with untreated control-shrimps, and the amount of whole shrimps after pilling was higher for shrimps exposed to HPP

Rapport/Report 2/2014, English Summary

-I prosjektet er det gjort forsøk for å undersøke om høytrykksprosessering (HP) kan benyttes for å korte ned modningstiden på reker. To delstudier er foretatt: (1) om HP kan benyttes for å modne rekene på kortere tid, evt. uten bruk av modningslake, og (2) om HP kan benyttes for å tine og modne reker i ett trinn. Forsøkene viste at reduksjon i modningstid ned mot 510 timer kombinert med høytrykksprosessering vil kunne gi lignende utbytte som dagens modning på cirka 20 timer. Modning av reker i modningslake kombinert med HP gav et høyere utbytte enn modning av reker i ferskvann kombinert med HP. Det ble ikke påvist at HP, med de testede betingelser, kan benyttes til å tine reker direkte fra frossen tilstand. Det var en tendens til at reker etter HP var enklere å pille enn ubehandlede kontroll-reker, og andelen hele reker etter pilling var høyere for de høytrykksprosesserte rekene.High pressure processing (HPP) has been used on several types of commercial seafood. This study was done to explore whether HPP can be used in the maturation process of Norwegian coldwater shrimps. Two different approaches has been tested: (1) if HPP can be used to lower the maturation time of shrimps, and (2) if HPP can be used for combining thawing and maturation in one step. The experiments showed a reduction in the maturation step from 20 to 510 hours if HPP was used. Maturation in brine compared to tap water during HPP gave a higher yield. Under the tested conditions, HPP was not proven to be used for direct thawing of frozen Norwegian coldwater shrimps. There was a trend that shrimps after exposure to HPP was easier to pill compared with untreated control-shrimps, and the amount of whole shrimps after pilling was higher for shrimps exposed to HPP