Combined Effect Of High Pressure Research Articles

Kinetic study of the combined effect of high pressure and pH-value on Arthrospira Platensis (Spirulina) proteins extraction

The combined effect of High pressure (HP) and pH-value on the extraction of proteins from Arthrospira (Spirulina) platensis was studied. Fresh Spirulina biomass (81% moisture, 60.2 g/100 g dm total soluble proteins-TSP, 16.1 g/100 g dm C-phycocyanin-C-pc) was suspended in phosphate buffer 0.1 M (1/20 w/v) (pH range 5.7–8.6). During a 24-h HP (100–600 MPa and 25 °C) post-processing period, the C-pc and TSP concentrations and C-pc purity were monitored. Chroma analysis and cells disruption through optical microscopy were also performed. Data were described by first order kinetics. Increased extraction rates of proteins were received for higher pressures and pH values. Pressures ≥400 MPa and pH-values ≥8.0 led to lower C-pc yield, due to denaturation process. Pressure 300 MPa and pH 7.1 resulted in highest purity in C-pc extracts (C-pc/other proteins = 1.14, reagent grade). The required extraction times for maximum TSP and C-pc extraction yield were estimated for all HP-pH combinations studied. Industrial relevanceAlternative proteins are among the trends of food research worldwide, targeting to partial replacement of meat-based proteins for human consumption, due in part to health and environmental concerns as well as animal welfare. Thus, plant-based food and alternative proteins (including proteins from algae) novel products are expected to significantly grow the coming years.Algae like spirulina are sources of proteins, nevertheless, some processes need to be applied for extracting them from the biomass. These processes are time-consuming and in most cases the yield of the extracted material is really poor, thus novel approaches are studied.Combination of High pressure (HP) technology along with different pH values of spirulina biomass are parameters that could result in high extractability of proteins (reaching a yield of even 99%) while simultaneously obtaining extracts of high-purity. In addition, appropriate combinations of HP and pH result in a fast and effective process for spirulina proteins extraction compared to conventional methods, thus reducing dramatically the needed time for extraction, allowing for integration of this approach into the microalgae production line.

An enhancement in diesel engine performance, combustion, and emission attributes fueled with Eichhornia crassipes oil and copper oxide nanoparticles at different injection pressures

ABSTRACT Current scenario of crude oil exhaustion and price rise has motivated researchers to opt and explore other forms of energy which are renewable and sustainable in nature. Waste plant oils have significant potential to become a viable alternative to petro-diesel fuel for transportation and manufacturing purposes. Esterification of unrefined waste oils has significantly addressed the issues mainly occurring due to highly viscous nature of the oil. This analysis aims to conduct a controlled study to examine the impact of injection pressure on the engine parameters amalgamated with copper (III) oxide composites as a nanofuel additive. Biofuel obtained from waste plants (Eichhornia Crassipes) is amalgamated with plain diesel in a 30:70 ratio and copper (III) oxide (Cu2O3) as nano-additive. It is essential to operate the engine over a wide range of injection pressures (180, 200, and 220 bar) for furnishing maximum efficiency when mixed with 90 ppm nano-additive volume fraction. The current analysis shows that the injection of nano-additives raises the injection pressure leads to enhanced engine combustion characteristics, including a maximum peak pressure and a faster heat release rate. At 220 bar, injection pressure with a 90-ppm volumetric fraction of nano-additives yielded superior results in comparison with its counterpart blends. The inclusion of nano-additives for increased injection pressures decreases emissions of hydrocarbon, oxides of nitrogen, and soot particles. Thus, biofuels engines benefit by enhanced injection pressure and decreased emission levels by successfully amalgamating copper (III) oxide as nano-additives. Combined effect of high pressure and nano-additive fuel furnishes a maximal progression of 3.5% in combustion efficacy and a 14% drop in BSEC with reduction of 14% in HC, 15% in NOx, and 15% in smoke.

Combined effect of nisin addition and high pressure processing on the stability of liquid micellar casein concentrates

The combined effect of high pressure (HP) processing and the addition of nisin on the microbial quality of liquid micellar casein concentrates (LMCCs) at two different concentrations (7 and 10%) were investigated. Two pressure levels were applied (300 and 450 MPa over 5 min) with three different nisin levels (0, 250, and 500 IU mL−1). Microbial and physicochemical quality were studied at day 0 and after 7 days at 10 °C. Results indicated that low-intensity HP treatment (300 MPa) alone or in combination with nisin was not effective enough to limit microbial growth after storage (10 °C, 7 days). However, 450 MPa HP treatment combined with nisin addition showed efficiency in bacterial control, without affecting physicochemical properties (acidity, pH, and colour). It has been proved that nisin has the potential to enhance the bacteriological effectiveness of HP processing and thus extend the self-life of LMCCs without altering their physicochemical properties.

Role of unusual moisture transport across Equatorial Indian Ocean on the extreme rainfall event during Kerala flood 2018

Southwestern Indian state, Kerala experienced extreme devastating statewide flood event of the century during 2018 monsoon season. In this study, an attempt has been made to bring out the salient dynamical factors contributed to the Kerala flood. There were 3 active spells over Kerala during 2018 Monsoon season. All the three spells were accustomed with the intrinsic factors of low frequency components of the active spells such as strength of monsoon Low Level Jet (LLJ), Monsoon depressions in the Bay of Bengal, favorable Madden-Julian oscillation (MJO) phases and Western Pacific systems. Though all the common ingredients remain same, the third spell is distinct with the less evaporation flux over Western and Central Arabian Sea and unusual moisture transport from maritime continent through South Equatorial Indian ocean (SEIO) towards the Kerala coast across Equator. Strong meridional pressure gradient force created by the combined effect of high pressure anomaly oriented Northwest-Southeast direction across tropical Indian ocean and anomalous low pressure along monsoon trough might have contributed to this unusual moisture transport across SEIO originating from west of Australia. The anomalous high pressure in South Indian ocean was greatly influenced by the position of the Mascarene high. Subtropical Indian ocean dipole (SIOD) also exhibits an influential role by altering tropical Southern Indian ocean dynamics in favor of the unusual moisture transport. The position of the monsoon depression and presence of typhoons in Western Pacific might have aided to this moisture transport. However, the normal moisture transport from Central Arabian sea towards Kerala coast by virtue of the strong LLJ along with additional moisture transport directly from South of maritime continent through SEIO across the Equator towards Kerala coast might have played a dominant role in the historical flood event over entire Kerala state.

High pressures increase \u03b1-chymotrypsin enzyme activity under perchlorate stress

Deep subsurface environments can harbour high concentrations of dissolved ions, yet we know little about how this shapes the conditions for life. We know even less about how the combined effects of high pressure influence the way in which ions constrain the possibilities for life. One such ion is perchlorate, which is found in extreme environments on Earth and pervasively on Mars. We investigated the interactions of high pressure and high perchlorate concentrations on enzymatic activity. We demonstrate that high pressures increase α-chymotrypsin enzyme activity even in the presence of high perchlorate concentrations. Perchlorate salts were shown to shift the folded α-chymotrypsin phase space to lower temperatures and pressures. The results presented here may suggest that high pressures increase the habitability of environments under perchlorate stress. Therefore, deep subsurface environments that combine these stressors, potentially including the subsurface of Mars, may be more habitable than previously thought.

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

Abstract The study aimed at extending shelf life without compromising quality of precooked chicken breast slices by various packaging and processing technologies. The slices were packaged in modified atmosphere packaging (MAP, 40% CO2, 60% N2), vacuum packaging (VAC, 93% vacuum), processed with high pressure (HPP, 600 MPa, 2 min), microwave volumetric heating (MVH, 1 kW, 3 × 15 s), soluble gas stabilization (SGS, 100% CO2, 18 h, 1 °C) followed by MAP (SGS-MAP), SGS followed by VAC (SGS-VAC), SGS followed by HPP (SGS-HPP), and SGS followed by MVH (SGS-MVH). The eight treatments were studied for their microbial and physicochemical quality during 4 °C storage for maximum 119 d. The results showed that MAP, the most common commercial packaging of ready-to-eat chicken, was slightly superior to VAC but much inferior to HPP, MVH, and SGS in microbial control. HPP, with/without SGS, was the most efficient method extending the shelf life of precooked chicken to more than three months. SGS improved microbial inhibition compared to non-SGS, but synergetic effects with HPP or MVH on microbial and physicochemical quality were insignificant. All treated chickens shared relatively comparable color, texture, pH and drip loss. These quality attributes changed marginally during storage while lipid oxidation increased markedly. HPP and MVH reduced lipid oxidation right after treatment and during storage. SGS suppressed the lipid oxidation but this effect did not last longer than two weeks of storage.

Mechanical Forces Alter Endothelin-1 Signaling: Comparative Ovine Models of Congenital Heart Disease

The risk and progression of pulmonary vascular disease (PVD) in patients with congenital heart disease (CHD) dependent on the hemodynamics associated with different lesions. However, the underlying mechanisms are not understood. Endothelin-1 (ET-1) is a potent vasoconstrictor known to play a role in the pathobiology of PVD. We investigate the hypothesis that the combined effect of high pressure (P) and flow shear stresses (FSS), but not FSS alone, upregulates ET-1 signaling. We used 2 ovine models of CHD: (1) Fetal aortopulmonary graft placement (shunt), resulting in increased FSS and P; and (2) Fetal ligation of the left pulmonary artery (LPA) resulting in increased FSS but normal P to the right lung. Pulmonary arterial endothelial cells (PAEC) and peripheral lung were harvested from control, shunt, and LPA lambs at 3-7 weeks of age. PAECs from control lambs were exposed to high FSS=20dyn/cm2, cyclic stretch CS=18%, and P from 20-50mmHg at constant shear conditions FSS=5dyn/cm2, utilizing a microfluidic device. Lung preproET-1 mRNA were increased in shunt lambs compared to controls. PreproET-1 mRNA expression was unchanged in LPA lambs. In both shunt and LPA lambs, Lung ECE-1 mRNA and protein expression were increased. These changes resulted in increased lung ET-1 levels in shunt lambs, while LPA levels were similar to controls. PAECs exposed to increased FSS decreased ET-1 by 5-fold, while CS increased levels by 1.5-fold. Under physiological FSS=5dyn/cm, the additive effects of P increased preproET-1 mRNA expression, while ECE-1 expression was unchanged. These data suggest that P or the additive effect of P+FSS, rather than increased FSS alone, is the principal driver of increased ET-1 in CHD. Defining the molecular drivers of the pathobiology of PVD resulting from the different mechanical stimuli will allow for a more targeted therapeutic approach.

Non-thermal approach to Listeria monocytogenes inactivation in milk: The combined effect of high pressure, pediocin PA-1 and bacteriophage P100

Non-thermal food processing and replacement of chemical additives by natural antimicrobials are promising trends in the food industry. The objective of the present work was to evaluate the effect of a process which combines mild high hydrostatic pressure – HHP (200 and 300 MPa, 5 min, 10 °C), phage Listex™ P100 and the bacteriocin pediocin PA-1 as a new non-thermal process for destruction of Listeria monocytogenes (104 CFU mL−1 or 107 CFU mL−1) in milk. For inoculum levels of 104 CFU mL−1, HHP combined with phage P100 eliminated L. monocytogenes immediately after pressurization. When L. monocytogenes was inoculated at levels of 107 CFU mL−1, a synergistic effect between phage P100, pediocin PA-1 and HHP (300 MPa) on the inactivation of L. monocytogenes was observed during storage of milk at 4 °C. For non-pressure treated samples inoculated with phage or pediocin or both, L. monocytogenes counts decreased immediately after biocontrol application, but regrowth was observed in a few samples during storage. Phage particles were stable during refrigerated storage for seven days while pediocin PA-1 remained stable only during three days. Further studies will have to be performed to validate the findings of this work in specific applications (e.g. production of raw milk cheese).

Combined effect of high pressure and vinegar addition on the control of Clostridium perfringens and quality in nitrite-free emulsion-type sausage

Abstract We evaluated the combined effect of high pressure (HP) and vinegar addition on control of Clostridium perfringens and quality in emulsion-type pork sausages. Sausages were manufactured with different levels of commercial white distilled vinegar made with jasmine tea extract (0, 1, and 2%) and sodium nitrite (0.02%, control). The sausages except for sodium nitrite treatment were subjected to HP at 500 MPa (four cycles and each for 3 min). After storage, the combined treatment of HP and vinegar showed the lowest number of C. perfringens vegetative cells (4.8-log CFU/g reduction) among the all treatments. The combined treatment also inhibited the growth of C. perfringens spores for five weeks (stored at 4 °C for two weeks followed by at 20 °C for three weeks). Among all treatment combinations, the best pH, water-holding capacity and chewiness, were found with the HP-vinegar sausage. In addition, vinegar treatment inhibited the lipid oxidation of sausage throughout the storage. Use of HP and vinegar addition inhibited growth of C. perfringens without observed adverse effects on quality of the emulsion-type sausage. Industrial relevance Currently, the use of natural additives and novel processing technologies for replacing sodium nitrite in meat products is gaining attention owing to increase in consumer demand for nitrite-free and safe meat products. The study showed that the addition of 1% (w/v) of vinegar and pressure treatment at 500 MPa (four cycles and each for 3 min) can replace sodium nitrite to inhibit growth of C. perfringens in emulsion-type sausages.

The effects of high pressure and superheating on the planar growth of Al3Ni phase in hypo-peritectic Al-30wt%Ni alloy

The constitutional undercooling criterion of the Al3Ni intermetallic compound with nil solubility was established, which reveals that there is no constitutional undercooling when the initial Al-Ni alloy concentration is lower than 43 wt%. Meanwhile, the interface stability growth criterion for the Al3Ni was also established by considering the effects of pressure and superheating on diffusion coefficient, interface growth rate, interface energy, and kinetic coefficient. The results demonstrate that when the pressure is greater than 4.2 GPa, the Al3Ni phase will move forward with a planar interface without superheating. Under the combined effects of high pressure and superheating the transition point of Al3Ni planar growth decreases. For example, with a superheat of 600 K, the pressure for stable planar growth decreases to 2.7 GPa. In addition, the microstructure of hypo-peritectic Al-30 wt%Ni alloy solidified at different conditions was investigated. It shows that the Al3Ni phase growth interface is unstable at 2 and 4 GPa with no superheating. The microstructure of the sample synthesized at 2 GPa with the superheat degree 600 K is typically hypereutectic microstructure. While the whole sample can be divided into there regions (high pressure solid solution region, mushy zone, and fully melted region which consists of planar growth single phase Al3Ni area and hypoeutectic zone) at 3 GPa/600 K.

Pressure-Inactivated Virus: A Promising Alternative for Vaccine Production.

In recent years, many applications in diverse scientific fields with various purposes have examined pressure as a thermodynamic parameter. Pressure studies on viruses have direct biotechnological applications. Currently, most studies that involve viral inactivation by HHP are found in the area of food engineering and focus on the inactivation of foodborne viruses. Nevertheless, studies of viral inactivation for other purposes have also been conducted. HHP has been shown to be efficient in the inactivation of many viruses of clinical importance and the use of HHP approach has been proposed for the development of animal and human vaccines. Several studies have demonstrated that pressure can result in virus inactivation while preserving immunogenic properties. Viruses contain several components that can be susceptible to the effects of pressure. HHP has been a valuable tool for assessing viral structure function relationships because the viral structure is highly dependent on protein-protein interactions. In the case of small icosahedral viruses, incremental increases in pressure produce a progressive decrease in the folding structure when moving from assembled capsids to ribonucleoprotein intermediates (in RNA viruses), free dissociated units (dimers and/or monomers) and denatured monomers. High pressure inactivates enveloped viruses by trapping their particles in a fusion-like intermediate state. The fusogenic state, which is characterized by a smaller viral volume, is the final conformation promoted by HHP, in contrast with the metastable native state, which is characterized by a larger volume. The combined effects of high pressure with other factors, such as low or subzero temperature, pH and agents in sub-denaturing conditions (urea), have been a formidable tool in the assessment of the component's structure, as well as pathogen inactivation. HHP is a technology for the production of inactivated vaccines that are free of chemicals, safe and capable of inducing strong humoral and cellular immune responses. Here we present a current overview about the pressure-induced viral inactivation and the production of inactivated viral vaccines.

Light‐Induced Catalyst and Solvent‐Free High Pressure Synthesis of High Density Polyethylene at Ambient Temperature

The combined effect of high pressure and electronic photo-excitation has been proven to be very efficient in activating extremely selective polymerisations of small unsaturated hydrocarbons in diamond anvil cells (DAC). Here we report an ambient temperature, large volume synthesis of high density polyethylene based only on high pressure (0.4-0.5 GPa) and photo-excitation (~350 nm), without any solvent, catalyst or radical initiator. The reaction conditions are accessible to the current industrial technology and the laboratory scale pilot reactor can be scaled up to much larger dimensions for practical applications. FTIR and Raman spectroscopy, and X-ray diffraction, indicate that the synthesised material is of comparable quality with respect to the outstanding crystalline material obtained in the DAC. The polydispersity index is comparable to that of IV generation Ziegler-Natta catalysts. Moreover the crystalline quality of the synthesised material can be further enhanced by a thermal annealing at 373 K and ambient pressure.

Combined effects of high pressure, moderate heat and pH on the inactivation kinetics of Bacillus licheniformis spores in carrot juice

The objective of this research was to evaluate the combined effect of high pressure processing (temperature, pressure and time) and product (pH) related variables on destruction kinetics of spores of Bacillus licheniformis in carrot juice. A 3-level factorial experimental design was used with the microbial spores inoculated into carrot juice at the natural pH (6.2) and acidified pH (4.5 and 5.5), pressure (400, 500 or 600MPa), temperature (40, 50, and 60°C) and time (0–40min) conditions. D values found varied from 0.6 to 14.1min based on the temperature, pressure and pH level combinations. The corresponding temperature and pressure dependency of D values were in the range 23.3 to 31°C and 241 to 465MPa, respectively. The destruction pattern was also dependent on pH, with lower pH contributing to higher destruction rate. Conventional log-linear model and Weibull model were used to describe the survivor curves and for predicting processing time to achieve a 5D spore reduction. The survivor curves exhibited slightly upward concavity and therefore better described by a Weibull than the log-linear model. Treatment combinations showed significant (p≤0.05) effects on D and z values of log-linear model and rate parameter (α) of Weibull model. The 5D spore count reduction times estimated using Weibull model parameters were longer than those from the log-linear model, generally demonstrating an over-treatment. Overall, the pH reduction of low acid foods showed a significant enhancement of rate of destruction of B. licheniformis spores.

Combined effects of high pressure processing and addition of soy sauce and olive oil on safety and quality characteristics of chicken breast meat.

This study was conducted to evaluate the combined effect of high pressure (HP) with the addition of soy sauce and/or olive oil on the quality and safety of chicken breast meats. Samples were cut into 100 g pieces and 10% (w/w) of soy sauce (SS), 10% (w/w) of olive oil (OO), and a mixture of both 5% of soy sauce and 5% olive oil (w/w) (SO) were pressurized into meat with high pressure at 300 or 600 MPa. Cooking loss was lower in OO samples than SS samples. With increased pressure to 600 MPa, the oleic acid content of OO samples increased. The total unsaturated fatty acids were the highest in SO and OO 600 MPa samples. Lipid oxidation was retarded by addition of olive oil combined with HP. The addition of olive oil and soy sauce followed by HP decreased the amount of volatile basic nitrogen during storage and reduced the population of pathogens. Sensory evaluation indicated that the addition of olive oil enhanced the overall acceptance and willingness to buy. In conclusion, the combination of HP with the addition of soy sauce and/or olive oil is an effective technology that can improve chemical, health, sensory qualities and safety of chicken breast.

Effects of High Pressure Treatments on Polymeric Films for Flexible Food Packaging

Effects of high pressure (HP) treatments on functional and morphological properties of commercial packaging films have been investigated, to assess their suitability for use in these processes. Experimental analyses have been performed on packaging films, used to make pouches containing four different types of food simulants, after HP pasteurization and sterilization treatments at 200, 500 and 700 MPa. The investigated polymeric flexible packaging structures were single layer as well as bilayer films. Effects of treatments on structural/morphological properties (i.e. crystallinity and density) and on thermodynamic and barrier properties were addressed. Quite all the investigated films were found to be suitable for HP pasteurization, which only determined a negligible effect on the glass transition temperatures and on density of the amorphous regions of some polymeric materials, without a significant effect on functional properties of the packaging. Only bilayer structures including metalized polyethyleneterephthalate were not able to withstand processing conditions because of an extensive delamination accompanied by loss of metallization layer. Conversely, in the case of HP sterilization, combined effects of HP and relatively high temperature caused significant modifications in some of the packaging materials, even those not including a metalized film. In particular, localized delamination occurred in the case of bilayer structures made by laminating polyethyleneterephtalate with linear low density polyethylene or with polypropylene. Films obtained by laminating cast polyamide and bioriented polyamide with polypropylene displayed no evidence of delamination. In the case of films not displaying delamination, only limited changes in gas and vapour barrier properties were detected. Copyright © 2014 John Wiley & Sons, Ltd.

Combined effects of high pressure and sodium hydrogen carbonate treatment on pork ham: improvement of texture and palatability

In this study, the combined effects of high pressure and sodium hydrogen carbonate (NaHCO3) treatment on the physical and chemical properties, and palatability of pork ham, a tough and under-utilized meat, were investigated. Assessment of meat properties with heat treatment, after exposure to NaHCO3 and high pressure treatment, revealed an increase in water content, and decreased weight reduction and rupture stress. The free amino acid content of meat samples increased with NaHCO3 and high pressure treatment. The effect of high pressure processing was especially notable at a pressure of 300 MPa. Sensory evaluation showed that meat subjected to high pressure processing after NaHCO3 treatment was tender and juicy. In addition, the sample produced minimal residue in the mouth and was characterized by a good taste.

Combined effects of high pressure and sodium hydrogen carbonate treatment on beef: improvement of texture and color

We investigated the effect of combined high pressure and sodium hydrogen carbonate (NaHCO3) treatment on the physical properties and color of silverside Australian beef. Meat samples were pressurized at 100–500 MPa and the water content, weight reduction, rupture stress, and meat color were determined. The water content of meat treated with NaHCO3 and high pressure (300 MPa) reached a maximum of 70.1%. Weight reduction tended to decrease with high pressure treatment at 300 MPa. Meats treated with NaHCO3 and high pressure at 400 MPa showed a>50% decrease in hardness. Whitening of the meat was reduced by the combined high pressure and NaHCO3 treatment. Therefore, the combined high pressure and NaHCO3 treatment is effective for improvement of beef quality.

Modeling the inactivation kinetics of Bacillus coagulans spores in tomato pulp from the combined effect of high pressure and moderate temperature

High hydrostatic pressure processing (HHP) have been widely studied as a means to reduce and/or eliminate microbial spoilage and the presence of pathogenic microorganism. The present study evaluated the combined effect of HHP and moderate temperature on inactivation kinetics of Bacillus coagulans spore in tomato pulp. Pressures from 300 to 600 MPa and temperatures of 50 and 60 °C were applied. Inactivation kinetic parameters were obtained through the application of a primary biphasic model and classical secondary models to describe the influence of pressure and temperature on spore inactivation. Processes of 300 MPa combined with temperatures of 50 and 60 °C showed 2 and 2.4log reductions, respectively, after 15 min of treatment. For processes at 600 MPa and 50 or 60 °C temperatures with the same holding time, the reductions were 3.1 and 5.7log reductions, respectively. These findings illustrate the improved efficiency of HHP with the application of moderate temperatures on the inactivation of B. coagulans spores, and how variations in pressure and temperature impact the effectiveness of the process. Results shown in this study may help in the design of processes for food preservation based on HHP technology.

Entropy and Volume Change of Dissociation in Tobacco Mosaic Virus Probed by High Pressure

Virus dissociation and inactivation by high pressure have been extensively studied in recent decades. Pressure-induced dissociation of viral particles involves a reduction in the Gibbs free energy of dissociation and a negative change in volume. In this work, we investigated the combined effect of high pressure and temperature on the dissociation of tobacco mosaic virus (TMV). We assumed the presence of two states of TMV with different tendencies to dissociate. Thus one form presents a low tendency (L) and the other a high tendency (H) to dissociate. Based on the model described here, the L-H transition was favored by an increase in pressure and a decrease in temperature. The volume change of dissociation was pressure- and temperature-dependent, with a highly negative value of -80 mL/mol being recorded at 0 °C and atmospheric pressure. The entropy and enthalpy of dissociation were very temperature- and pressure-dependent, with values of entropy of 450 to -1300 kJ/mol and values of enthalpy of 5.5 × 10(4) to 2.4 × 10(4) kJ/mol. The dissociation of TMV was enthalpy-driven at all temperatures and pressures investigated. Based on these findings, we conclude that the model presented allows accurate predictions of viral dissociation behavior in different experimental conditions.

Inactivation and Injury of Listeria monocytogenes under Combined Effect of Pressure and Temperature in UHT Whole Milk

AbstractInactivation and injury of Listeria monocytogenes was studied under the combined effect of high pressure and temperature. Three pressure levels (400, 500 and 600 MPa) and three temperature levels (27, 43 and 60C) were chosen. In total, seven combinations were tested: (1) 400 MPa at three temperature levels; and (2) 500 and 600 MPa at 27 and 43C, i.e., the treatment times at 60C were too short (<1 s) to obtain reliable data based on machine precision. Comparison of D‐values on both media showed that (1) the D‐values of treatment condition 400 MPa, 27C and 400 MPa, 43C were significantly different (P < 0.05), and from the rest of the five pressure and temperature combinations, (2) the remaining five combinations were not significantly different from each other (P > 0.05). Injury of L. monocytogenes was evaluated in terms of log reduction value, which was obtained from nonselective and selective media. Treatment temperature played an important role on injury of L. monocytogenes specifically at lower pressure level. At 400 MPa, the injured log reduction values obtained at 27 and 43C were 2.10 and 3.46, respectively, for 15‐min treatment time, whereas at 60C, it was 4.58 for 1 min. This study showed that 6 log10 reductions could be obtained in <2 min using low pressure (400 MPa) and high temperature (60C), which would have industrial relevance in reducing the cost related to high pressure processing of food.Practical ApplicationsListeria monocytogenes is responsible for many foodborne illnesses. Because of its psychrotrophic nature, L. monocytogenes is a potential threat to milk and dairy products as it has the ability to grow under refrigeration temperatures. Inactivation of L. monocytogenes in milk under high pressure has been studied widely. However, few studies have been done to evaluate the injury of the microorganisms, which were limited to low pressure and temperature. Quantification of injured population of L. monocytogenes is important; i.e., after high pressure treatment the sublethally injured cells can recover in the milk medium during the storage period. Hence, there is a great need of quantification of injured population of L. monocytogenes in addition to the inactivation over a wide range of pressure and temperature conditions. The kinetic data on both inactivation and injury of microorganisms will help to establish the safe processing conditions for milk during high pressure and temperature treatment.