Comparison of the inactivation kinetics of pectin methylesterases from carrot and peach by high-pressure carbon dioxide

The inactivation of pectin methylesterases (PMEs) from carrot and peach in buffer by high-pressure carbon dioxide (HPCD) at 55 °C was investigated. The two PMEs were effectively inactivated by HPCD, their residual activity (RA) decreasing with increasing pressures. The RA of the two PMEs exhibited a fast decrease firstly and reached a constant after a prolonged treatment time; their inactivation kinetics was adequately modelled by a fractional-conversion model. The non-zero RA(A_∞)of the two PMEs was 6–7%, with increasing pressures the kinetic rate constant, k, increased and the decimal reduction time, D, decreased for the HPCD-labile fraction of the two PMEs. The labile fraction of carrot PME was more susceptible to HPCD than that of peach PME; the activation volume, V_a, and Z_P (the temperature increase needed for a 90% reduction of D) was −1079.37 cm³/mol and 5.80 MPa for carrot PME, and −130.51 cm³/mol and 48.31 MPa for peach PME.     

Inactivation kinetics of Listeria monocytogenes, Salmonella enterica serovar Typhimurium, and Campylobacter jejuni in ready-to-eat sliced ham using UV-C irradiation

To investigate the applicability of UV-C irradiation on the inactivation of foodborne pathogenic bacteria in ready-to-eat sliced ham, UV-C treatment was evaluated. Irradiation dose required for 90% reduction of the populations of Listeria monocytogenes, Salmonella enterica serovar Typhimurium, and Campylobacter jejuni were determined to be 2.48, 2.39, and 2.18 J/m². Ready-to-eat sliced hams were inoculated with the pathogens and irradiated with UV-C light of 1000, 2000, 4000, 6000, and 8000 J/m². Microbiological data indicated that foodborne pathogen populations significantly (p < 0.05) decreased with increasing UV-C irradiation. In particular, UV-C irradiation at 8000 J/m² reduced the populations of L. monocytogenes, S. Typhimurium, and C. jejuni in the ham by 2.74, 2.02, and 1.72 log CFU/g. The results indicate that UV-C irradiation can be used as a microbial inactivation method for ready-to-eat sliced ham, and inactivation kinetics of the foodborne pathogens fit the Weibull model better than the first-order kinetics model.     

Recent Advances in the Use of High Pressure as an Effective Processing Technique in the Food Industry

High pressure processing is a food processing method which has shown great potential in the food industry. Similar to heat treatment, high pressure processing inactivates microorganisms, denatures proteins and extends the shelf life of food products. But in the meantime, unlike heat treatments, high pressure treatment can also maintain the quality of fresh foods, with little effects on flavour and nutritional value. Furthermore, the technique is independent of the size, shape or composition of products. In this paper, many aspects associated with applying high pressure as a processing method in the food industry are reviewed, including operating principles, effects on food quality and safety and most recent commercial and research applications. It is hoped that this review will promote more widespread applications of the technology to the food industry.     

High pressure/temperature treatments to inactivate highly infectious prion subpopulations

High hydrostatic pressure can be used for gentle pasteurization of food as well as a physical parameter to study the stability and energetics of biomolecules. High pressure has been recently postulated as a feasible technology to decontaminate scrapie infectious materials. Here we discuss the kinetic parameters driving the inactivation of the Transmissible Spongiform Encephalopathy agents and the perspectives of pressure as a thermodynamic parameter to obtain a deeper insight into the aggregation of the 263K strain of scrapie. At 60–80 °C an efficient pressure inactivation of infectious scrapie prions was observed during short pressure treatments at 800 MPa (3 × 5 min cycles). However, discrepancies between in vivo infectivity counts and the results of an enzyme immunoassay further revealed that the infectivity was inactivated faster and much more efficiently than PrP^res was degraded, indicating that pressure affects a highly infectious subpopulation of scrapie prions.

Industrial relevance

Conventional inactivation methods for the agents of the Transmissible Spongiform Encephalopathies are not compatible with food processing due to the required aggressive conditions. High pressure assisted thermal sterilization methods are nowadays attracting attention as a food preservation technology able to preserve quality attributes. Here the stark effects in the secondary prion structure of high pressure combined with heat below the usual denaturing conditions were investigated with specific tests. This technology was proven to be a feasible alternative to achieve the decontamination of TSE risk materials at milder conditions. Kinetic data provided here should be useful to establish criteria to inactivate prions under pressure.     

Effects of steam and lactic acid treatments on inactivation of Listeria innocua surface-inoculated on chicken skins

Effectiveness of combined steam (10 and 60 s, 70 degrees C and 98 degrees C) and chemical treatments, using concentrated solutions of lactic acid (1 and 30 min, 5% and 10% lactic acid), on the inactivation of Listeria innocua inoculated on the surface of chicken skins have been studied. Surviving bacteria on the skin were enumerated immediately after treatment, and after 7 days of storage at 4 degrees C. The most effective treatment was the combination of steam of 98 degrees C and 10% lactic acid with its immediate efficacy being mainly attributed to the applied heat treatment. However, after 7-day storage, the treatment's effectiveness was mainly due to the applied acid treatment, which prevented growth of the bacteria that survived the heat treatment. Milder treatments (70 degrees C steam, 5% lactic acid) revealed a genuine synergy between the heat and acid treatments, paving the way for an effective means of reducing bacterial load on the surface of poultry without affecting the product's "raw" appearance.     

三重组合瓦楞纸板压缩承载规律的实验研究

以重型商品包装中广为采用的三重组合瓦楞纸板为对象，通过静态平压、迫压和例向压缩实验，从应力应变关系、压缩失效形态上讨论了3B、X—PLY(B)型组合板材的强度特性与承压规律，为重型商品纸包装容器的优化设计提供参考。     

Static and Dynamic,but not Pulsed High‐Pressure Treatment Efficiently Inactivates Yeast

Static high‐pressure (HP) treatment has become a powerful tool for preserving foodstuffs, allowing high inactivation rates and minimal adverse effects on valuable components. Due to HP maxima and batch mode conditions, it is restricted to high‐grade products. To overcome these restrictions, dynamic HP offers the possibility of a quasi‐continuous mode of operation. The effects of three different HP treatments (static, pulsed, and dynamic) on yeast were investigated. The inactivation efficiency and membrane damage increase with increasing pressure or pressure holding time. The cells do not show higher sensitivity to fast and repeated depressurization, and the number of pressure pulses plays only a minor role in inducing membrane damage. A form of programmed cell death could not be detected.     

Inactivation of aflatoxigenic fungi (Aspergillus spp.) on granular food model,maize, in an atmospheric pressure fluidized bed plasma system

Atmospheric plasma provides the advantages of high microbial inactivation that can be performed under ambient conditions; therefore, it is regarded as a potential alternative to traditional food preservation methods. The present work presents the results of a critical study conducted on the efficiency of a non-thermal atmospheric pressure fluidized bed plasma (APFBP) system used for decontamination of maize. Maize grains that were artificially contaminated with Aspergillus flavus and Aspergillus parasiticus spores were treated in APFBP system for 1–5 min at two differently designed fluidized bed reactors with air and nitrogen. Results indicate maximum significant reductions of 5.48 and 5.20 log (cfu/g) in Aspergillus flavus and A. parasiticus after 5 min air plasma treatment. The native microbial flora of the maize grains decreased to more than 3 log after 3 min APFBP treatment, and no viable cells were counted. During the storage of plasma treated maize samples at 25 °C for 30 days, the Aspergillus spp. spores log reduction was maintained with no occurrence of re-growth. Overall, this study shows that plasma treatment has a fungicidal effect on A. flavus and A. parasiticus spores associated with alterations in spore surface morphology and loss of spore integrity. APFBP can inactivate aflatoxigenic spores on maize grains and could be optimized to improve the safety and quality of produce.     

Comparison of spore inactivation with novel agitating retort,static retort and combined high pressure-temperature treatments

Optimization of food preservation technologies is necessary for improved product quality and nutrition as well as energy and environmental sustainability. In the current study, inactivation of Bacillus subtilis spores in a model soup (pH 6.1) with agitating retort, static retort and combined high pressure-temperature treatments was investigated. With isothermal experiments, D_95° C and z values for B. subtilis spores in the soup were obtained as 4.67 min and 8.65 °C. Log-linear model performed well for describing isothermal spore inactivation kinetics with satisfactory R²_adj values (0.94–0.97). Agitating retort treatments caused a dramatic reduction in processing times, as 17 min processing in agitating mode was required for 7-log inactivation of B. subtilis spores, compared to 53 min in static mode at 110 °C. For agitating process, observed and predicted lethality values were similar. This implied a homogenous heat load distribution within the soup with the help of high frequency agitation. Combined HPP and mild temperature treatments were highly synergistic for elimination of B. subtilis spores in the same model soup used in heat treatments. HPP treatments combining 650 MPa and 55–65 °C for 10 min resulted in up to 4.5 log kill effect on spores. The findings from the current study can be utilized in selection of test conditions for similar products in future safety studies. Results clearly showed that using novel mechanisms in food processing provide an opportunity for milder processing which can lead to better food quality and sustainability.     

Microorganism Inactivation by Ozone Dissolved in Aqueous Solution: A Kinetic Study Based on Bacterial Culture Lipid Unsaturation

Physiological solutions ozonated are widely used in the medical field (dentistry and surgery) as an effective bactericide. In this investigation, the inactivation of Escherichia coli and Pseudomonas aeruginosa by ozone dissolved in physiological solution was studied. There is a poor knowledge of the inactivation efficiency of this solution for different bacteria. The efficiency of the microorganisms’ inactivation was evaluated by the total unsaturation of lipids measured by the so-called Double Bond Index (DB-index). This is a sensitive analysis to evaluate the quantity of carbon-carbon double bonds (>C=C<) available in organic and biological samples, with high efficiency and in a short time. DB-index results were compared with the quantity of colony forming units (CFU) available in the culture. Three experimental systems were evaluated to determine the relationship between the DB-index variable and the microorganism’s inactivation: 1) using BHI agar as a culture medium to evaluate the dynamic growing curve when the ozone dissolved was dosed over the strain’s surface; 2) using a glucose solution (5%) as culture media and keeping the ozone concentration constant, which was dissolved in different physiological solutions, to observe the effects of solvent type over the bacteria growth; and, 3) using a glucose solution (5%) as culture media, and physiological solution of NaCl (0.9%) as a dissolved media for ozone at different concentrations. From the experimental data, a model of the ozone inactivation of each pathogen was built to obtain the inactivation kinetics. The model obtained showed a correlation between the CFU behavior and DB-index to each bacteria, since Pseudomona aeruginosa was more resistant to being oxidized than Escherichia coli.