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BACKGROUND An innovative pilot-plant packaging was developed and evaluated for applying oregano essential oil (OEO) vapours in conditions of high vacuum for exploring the antimicrobial effect of essential oil vapours applied immediately before packaging of fish fillets. Farmed sea bream (Sparus aurata) fresh fillets have been used as a model for validating this new technology. These fillets, as a refrigerated product under modified atmosphere packaging (MAP), have a relatively short shelf life (12-14 days) mainly due to the fast microbial growth. The effects of conventional OEO dippings [pretreatment dipping (0.1% of OEO) of whole fish (T1) and filleted sea bream (T2)] were compared with the OEO application in vapour phase (67 μL L-1 ) under vacuum (5-10 hPa) immediately before MAP fillet packaging (T3). RESULTS T3/T2 samples showed the lowest microbial growth after 28 days at 4 °C, with loads up to 1/2.6 log units for Enterobacteria/lactic acid bacteria compared to untreated samples. The initial trimethylamine nitrogen (TMA-N) content (2.6 mg kg-1 ) increased in T1 and T2/T3 samples by 9.6 and 6/7 units, respectively, after 28 days. Quality Index Method (QIM) better reflected the fish fillets shelf life than texture and colour measurements. The shelf life of T3/T2 samples was established in at least 28 days (4 °C), while the QIM threshold (6) was exceeded after 7/21 days in untreated/T1 fillets. CONCLUSION The fish shelf life was extended with vapour OEO treatment using this new technology, similarly to OEO dipping treatment, according to QIM, corroborated by the microbial quality and TMA-N contents. © 2020 Society of Chemical Industry.

The current procedure used to slaughter gilthead seabream involves hypothermia in seawater with crushed ice, slurry ice. This method stresses the fish and negatively affects the quality and shelf life of the fresh product. Clove essential oil (CEO), one of the most effective anesthetics when handling fish, is not used for stunning at slaughter on an industrial scale, mainly due to its very low water solubility. The main objective of this study was to evaluate the use of very low doses (5–15 mg/kg ice) of CEO nanoencapsulated in β-cyclodextrin (β-CD), which is known to improve the water solubility of the essential oil, to reduce stress in farmed gilthead seabream at slaughtering. Postmortem plasmatic levels of different stress markers and the mRNA expression level of several immune- and stress-related genes were evaluated. In conclusion, CEO nanoencapsulated in β-CD used within the ice at slaughtering significantly decreases fish stress compared to the current procedure that uses only ice.

The use of vapour of essential oils (EOs) through an innovative pilot-plant packaging device was studied to preserve the quality of sliced mushrooms during storage. A mix of EOs (eugenol, bergamot EO, and grapefruit EO) was vaporized (100 and 125 µL L−1) and applied during packaging of sliced mushrooms under modified atmosphere packaging (MAP), then, the product quality was studied during cold storage up to 12 days. The highest colour changes of EOs125 samples, which were observed in the mushroom stipe, were not observed with the EOs100 atmosphere. Thus, the high polyphenoloxidase activity observed in untreated samples after 5–7 days was highly controlled with the vapour EOs atmospheres. Furthermore, the visual appearance scores of EOs100 samples were still over the limit of usability, while untreated samples were already below this threshold after 5 days of storage. A strong bacteriostatic effect was achieved with vapour EOs, reducing the Pseudomonas spp. (the main microbial genus in cultivated mushrooms) growth by ≈1.7 log CFU g−1, regardless of the EOs dose, after 12 days. The activity of phenyl ammonia lyase was also reduced up to ≈0.4 enzymatic units with the EOs100 treatment. Conclusively, packaging of sliced mushrooms under an atmosphere enriched with 100 µL L−1 EOs vapour highly controlled the quality loss of sliced mushrooms owing to their enzymatic inhibition and high bacteriostatic effect.

Active packaging including encapsulated essential oils (EOs) may highly increase the shelf life of horticultural products due to the higher antimicrobial activity of EOs in the vapour phase through a controlled release from the packaging. In that sense, the aim of the present study was to study the effects of an active packaging (a cardboard box including a βcyclodextrin (βCD) inclusion complex with an EOs mix) on the quality of bell peppers (green, red and yellow) during storage at 8 °C (90 % relative humidity) up to 18 d. The EO mix (carvacrol:oregano:cinnamon 70:10:20 v:v:v) was efficiently encapsulated within the βCD inclusion complex by 94 %. Green, red and yellow peppers packaged within the active box showed 1–2 lower log units of enterobacteria than the control (without the active coating) after 11–18 d. Furthermore, green/red and yellow peppers showed lower mould counts (approximately 1 log unit) than control samples at days 6 and 11, respectively. The decay incidence of samples was also highly controlled by the active packaging with percentages lower than 5 % after 18 d while control samples showed decay incidences of 10–15 %. The use of this active box did not negatively affect the physicochemical quality of peppers even showing red and green peppers of the active box better firmness than control samples after 18 d. The shelf life of peppers stored within the active box reached 18 d while samples stored with the control box were rejected. Carvacrol residues in peppers were very low (below 1 mg kg−1) avoiding off-flavours according to sensory results. Conclusively, this active packaging allowed to extend the shelf life of green, red and yellow peppers for at least 18 d at 8 °C.

Heat resistance determinations, necessary for the design of safe thermal treatments, are usually performed in batch systems, but those on continuous systems are more realistic. In continuous systems, samples and temperatures are only taken from the inlet and outlet. Therefore, microbial inactivation kinetics and heat-labile compound degradation on these systems remain a black box. A pilot-scale heat exchanger, with several temperature sensors and sampling tubes along the system, was built. The aims of this research were to determine the residence time distribution, the flow type, and the inactivation kinetics of Salmonella Senftenberg and Staphylococcus aureus on the heat exchanger. Microbial inactivation data were obtained both under isothermal and non-isothermal conditions and compared to those obtained in a batch system. Flow was estimated as turbulent. Under isothermal conditions, similar inactivation levels were reached for S. aureus in both equipments (batch or continuous). Under non-isothermal conditions, for both microorganisms, higher inactivation of the population was observed in the last step of the treatment in the heat exchanger than in the batch system. These differences could be attributed to faster heating rates in the heat exchanger. The heat exchanger used in this investigation is a suitable tool to understand microbial inactivation kinetics in continuous systems.

Cronobacter sakazakii is an opportunistic pathogen in neonates which can cause meningitis, septicaemia and enterocolitis related to the consumption of contaminated Powdered Infant Formula (PIF). C. sakazakii has an unusual ability to survive under dry conditions and it could be among the most thermotolerant members of the Enterobacteriaceae. Little is known about how Cronobacter species respond to heat stress and the mechanisms involved in the process. In the current study we determined the heat resistance of a particularly stress tolerant C. sakazakii strain, C. sakazakii DPC 6529, and monitored the behavior of a lux-tagged derivative under different reconstitution and handling scenarios in a commercial brand of PIF. Some of the molecular mechanisms involved in the heat stress response were investigated using a transposon mutagenesis approach. Survival curves of C. sakazakii DPC 6529 in Luria-Bertani (LB) broth and PIF at various temperatures (58, 60, 62 and 64 °C) displayed an upward concavity and were fitted to the non-linear Weibull model. While at the highest treatment temperatures heat resistance was lower in PIF than in LB broth, at lower temperatures no significant differences in heat resistance were observed. Experiments in real time with artificially inoculated PIF reconstituted at different water temperatures (50, 55, 60, 65, 70 °C) and cooled at different rates confirmed that C. sakazakii can survive for long time periods in powdered formula, and is capable of proliferating after reconstitution. The use of water at temperatures between 50 and 65 °C for reconstitution did not provide a significant inactivation of C. sakazakii cells. Reconstitution at 70 °C reduced the bacterium to levels below the detection limit, although survivors were able to proliferate and reached dangerous levels when the reconstituted product was stored for a long time at room temperature. The cooling rate had an important impact on survival and subsequent growth of C. sakazakii, which makes it advisable to avoid rapid cooling of baby formula. Transposon mutagenesis allowed the identification of some of the molecular mechanisms involved in the response of C. sakazakii DPC6529 to heat stress. Genes identified included the Ribosome Maturation Protein RimP and Outer Membrane Porin L (OmpL). Results suggest that de novo protein synthesis, and the uptake of cysteine for the formation of disulfide bonds for protein stabilization, are key processes.

An active cardboard tray coated with a water-based emulsion including encapsulated (in β−cyclodextrins (CDs)) essential oils (EOs) was used to study the quality changes of cherry tomatoes (flow-packaged using a macroperforated film) during storage up to 24 days at 8 °C. Commercial polyethylene and non-active cardboard trays were used as control materials. Firmness of samples was well maintained for 24 days, while decay incidence was reduced from 8% to

Application of essential oils (EOs) in vapour phase under vacuum conditions may increase the effectiveness of EOs to sanitize plant products. Different treatments with EOs vapor were studied in vitro and in vivo against saprophyte microflora and pathogens at laboratory, pilot plant and industrial scales. Vapor of carvacrol combinations with oregano and peppermint essential oils (80:20 v:v) showed the best microbial reductions up to 1.5 log units for mesophiles ( in vitro at laboratory scale), 0.9–3.9 log units for several isolated molds ( in vitro at pilot plant scale) and approximately 1 log unit for Listeria innocua ( in vivo at pilot plant scale). Particularly, carvacrol:oregano and carvacrol:peppermint vapors showed the highest mold log reductions (>3.3) for Botrytis cinerea , Alternaria alternata and Aspergillus niger while Fusarium spp. and Penicillium spp. showed lower reductions. EOs vapors concentrations lower than 0.5 mg L −1 did not achieve mold reductions higher than 0.2 log units while EOs vapors concentrations ≥10 mg L −1 did not increase the antifungal activity. Fresh cilantro treated at industrial scale with vapor of carvacrol:peppermint (less off-flavors than carvacrol:oregano) (80:20 v:v) at 8 mg L −1 under vacuum (adapting a vacuum cooling system) showed 0.8, 1.8 and 1.2 lower mesophiles, psychrophiles and enterobacteria log units, respectively, than untreated samples after 12 d at 2 °C of storage. Yeast and mold growth in cilantro was low throughout the studied period at storage temperature of 2 °C. Yellowing and browning of cilantro treated at 8 mg L −1 was also minimal, compared to the rest of treatments, after 12 d at 2 °C. In conclusion, the application of carvacrol:peppermint (80:20 v:v) vapor at 8 mg L −1 under vacuum in an industrial installation may extend the shelf life of fresh cilantro further than 12 d at 2 °C ensuring its microbial and visual quality.

The aim of this research was to evaluate the effect of thermal treatments (isothermal or nonisothermal) combined with nisin, a natural antimicrobial, on the survival and recovery of Clostridium sporogenes spores. The addition of nisin to the heating medium at concentrations up to 0.1 mg liter(-1) did not reduce the heat resistance of C. sporogenes. Without a thermal treatment, nisin added at concentrations up to 0.1 mg liter(-1) did not reduce the viable counts of C. sporogenes when added to the recovery medium, but inactivation of more than 4 log cycles was achieved after only 3 s at 100°C. At 100°C, the time needed to reduce viable counts by more than 3 log cycles was nine times shorter when 0.01 mg liter(-1) nisin was added to the recovery medium than without it. The heat resistance values calculated under isothermal conditions were used to predict the survival in the nonisothermal experiments, and the predicted values accurately fit the experimental data. The combination of nisin with a thermal treatment can help control C. sporogenes.