Effect of Low-Temperature-High-Pressure Treatment on the Reduction of Escherichia coli in Milk

Regulation of the Ice Ⅰ to Ice III high pressure phase transition meta-stability in milk and its bactericidal effects

This study was focused on a novel approach of creating perturbations under high pressure (HP) meta-stable Ice Ⅰ to Ice Ⅲ phase transition and its bactericidal effects. Experiments were carried out under subzero high pressure processing conditions using Escherichia coli suspended in milk, and the microbial inactivation before and after the meta-stable state regulation was compared. The phase transition position of unperturbed milk was 302 MPa/-37.5 °C. The volume change resulting from the phase transition was employed as the perturbation mechanism. Glucose (5 %, 20 %) and sodium chloride solutions (5 %, 20 %) were used as regulatory sources. Glucose solutions accelerated the phase change of the milk better than the sodium chloride solution and resulted in an optimum phase transition position of milk at 243 MPa/-30.6 °C. The induced perturbations accelerated meta-stable transformation and enhanced the microbial destruction. At 330 MPa/3s, compared to the unfrozen samples, the lethality of E. coli in the frozen-regulated samples significantly increased by 1.79 log. The relationship between the E. coli inactivation within the phase change pressure range and the pressure was not continuous, but a segmented one, both before and after meta-stable state regulation. A higher level of E. coli destruction was accomplished by a 5 min pressure-holding of frozen samples at 220 MPa and 280 MPa as compared to the one-pulse and two-pulses treatments without holding time. The maximum lethality of 6.73 log was achieved at 280 MPa/5 min in the frozen-regulated application.

Ultralow temperature high pressure processing enhances inactivation of norovirus surrogates

High pressure processing (HPP) is a powerful non-thermal method for inactivating pathogens. Human norovirus and genetically-related caliciviruses are moderately sensitive to temperatures above 0 °C with >400 MPa (MPa) or higher required to inactivate multiple logs of virus. Sensitivity of murine norovirus (MNV) and Tulane virus (TV) to ice phase transitions was evaluated using ultra low temperature HPP. Identical samples containing MNV or TV were either equilibrated to +1.5 °C (thawed) or -40 °C (frozen) 24 h prior to pressurization. All samples (thawed and frozen) were then placed in a pre-chilled chamber which was then rapidly filled with -40 °C chamber fluid. Samples were immediately pressurized for 5 min at 200, 250 or 300 MPa. Controls were not pressurized. For samples that were thawed and then pressurized in 40 °C chamber fluid, the MNV average log reduction at 200 MPa was 4.4, while >6.1 log reduction (non-detectable) was achieved at 250 and 300 MPa. TV samples averaged 2.3, 5 and 4.3 log reduction at 200, 250, and 300 MPa respectively. For samples that were frozen and then pressurized in 40 °C chamber fluid, the MNV average log reductions were 2.3, 3.2 and 4.2 at 200 MPa, 250 MPa and 300 MPa, respectively, while TV samples averaged 0.81, 2.3 and 1.7 log reductions at 200, 250, and 300 MPa, respectively. Inactivation of TV within oysters at these pressures was also demonstrated. Overall, results indicate that in addition to enhancing inactivation of norovirus surrogates compared to higher temperatures, ultra-cold HPP performed on thawed samples especially enhances inactivation.

Effect of high hydrostatic pressure treatment on the inactivation and sublethal injury of foodborne pathogens and quality of apple puree at different pH

The objectives of this study were to evaluate the survival of high hydrostatic pressure (HHP)-treated Salmonella Typhimurium, Escherichia coli O157:H7, and Listeria monocytogenes in apple puree, as well as to determine the levels of HHP-induced cell injury according to the pressure level, holding time, and pH of apple puree. Apple puree was inoculated with three foodborne pathogens and treated at pressures of 300-600 MPa for up to 7 min at 22 °C using HHP equipment. Increasing the pressure level and lowering the pH of apple puree led to larger microbial reductions, and E. coli O157:H7 showed higher resistance compared to S. Typhimurium and L. monocytogenes. Besides, approximately 5-log injured cells of E. coli O157:H7 were induced in apple puree at pH 3.5 and 3.8. HHP treatment at 500 MPa for 2 min effectively achieved complete inactivation of the three pathogens in apple puree at pH 3.5. For apple puree at pH 3.8, more than 2 min treatment of HHP at 600 MPa is seemingly needed to achieve complete inactivation of the three pathogens. Transmission electron microscopy analysis was conducted to identify ultrastructural changes in the injured or dead cells after HHP treatment. Plasmolysis and uneven cavities in the cytoplasm were observed in injured cells, and additional deformations, such as distorted and rough cell envelopes, and cell disruption occurred in dead cells. No changes in solid soluble content (SSC) and color of apple puree were observed after HHP treatment, and no differences were detected between control and HHP-treated samples during 10 d of storage at 5 °C. The results of this study could be useful in determining the acidity of apple purees or the treatment time at specific acidity levels when applying the HHP processing.

Facilitation of metastable ice Ⅰ - ice III phase transition of liquid foods at high-pressure sub-zero temperature by perturbation

In this study, the distribution of ice Ⅰ - ice III phase transition positions and its influencing factors on various fruit juices and food model solutions under high pressure (HP) were investigated. In addition, the effect of perturbation on induction of phase change in metastable apple juice was also explored. The phase transition positions of fruit juice samples deviated far from the theoretical value (210 MPa/ -21 °C), with pressure in range of 268 ∼ 305 MPa and temperature between -31.09 °C and -37.21 °C, with the most extreme phase transition position of 305 MPa/ -37.21 °C for apple juice. The phase change position was affected by the type of solution but not by the concentration of solutions. The cooling media namely, sodium chloride (5%, 20%) and glucose solution (5%, 20%) were used as perturbation sources to stimulate the metastable apple juice by using instantaneous volume reduction during the ice Ⅰ - ice III phase transition. They successfully promoted the phase transition of apple juice, where 20% sodium chloride solution significantly (p < 0.05) reduced the phase change pressure of apple juice to 239 MPa. The perturbation effect was influenced by the type and concentration of the perturbation source, the composition of the cavity area and the softness of the sample container.

The potential of antifungal peptide Sesquin as natural food preservative

Sesquin is a wide spectrum antimicrobial peptide displaying a remarkable activity on fungi. Contrarily to most antimicrobial peptides, it presents an overall negative charge. In the present study, we elucidate the molecular basis of its mode of action towards biomimetic membranes by NMR and MD experiments. While a specific recognition of phosphatidylethanolamine (PE) might explain its activity in a variety of different organisms (including bacteria), a further interaction with ergosterol accounts for its strong antifungal activity. NMR data reveal a charge gradient along its amide protons allowing the peptide to reach the membrane phosphate groups despite its negative charge. Subsequently, the peptide gets structured inside the bilayer, reducing its order. MD simulations predict that its activity is retained in conditions commonly used for food preservation: low temperatures, high pressure, or the presence of electric field pulses, making Sesquin a good candidate as food preservative.

Frozen-Phase High-Pressure Destruction Kinetics of Escherichia coli as Influenced by Application Mode, Substrate, and Enrichment Medium

The synergistic effect of frozen-phase high pressure (HP) on the inactivation of E. coli ATCC 25922 cultures in suspension medium, Chinese bayberry juice (pH 3.0), and carrot juice (pH 6.5) was evaluated. The survivor count of E. coli remained at 3.36 log CFU/mL on a nonselective brain heart infusion (BHIA) medium, while no survivor was detected on a selective violet red bile agar (VRBA) medium after a 5 min hold pressure at 250 MPa in a frozen culture suspension. BHIA was suitable for safe testing of the injured E coli cells after HP treatment in frozen state. Frozen Chinese bayberry juice showed higher sensitivity to HP treatment for its matrix property with high sterilizing efficiency at 170 MPa. Two pulses exhibited a significant inactivation effect in frozen samples compared with one pulse, especially for the Chinese bayberry juice with different pressure levels. The destruction kinetics of HP pulse mode followed the first-order rate kinetics with a Zp value of 267 MPa in frozen carrot juice. Our results evaluated the influenced factors of frozen HP destruction effects, including the medium, substrate, and application mode. The frozen HP destruction kinetics of pulses afford us better understanding of the technology application in the food industry.

Sensory Analysis for Cow Milk Product Development Using High Pressure Processing (HPP) in the Dairy Industry

High pressure processing (HPP) can be applied as an alternative thermal treatment of milk to maintain its natural and original sensory quality. Milk was processed at 600 MPa for 10 min or given thermal treatment at 125 °C for 4 s. Sensory evaluation of treated milk samples was conducted using the triangle and the acceptance and preference tests. The triangle test was used as a discriminative test to check whether there was a noticeable difference between both treated milk samples. The acceptance and preference test determined attributes of milk including colour, milkiness, creaminess, mouthfeel, and aftertaste based on the 5-point just-about-right (JAR) scale. In the triangle test, 89.5% of panellists were able to identify the odd sample and differentiate milk processed using high pressure from heat treatment. For the acceptance and preference test, 61% of panellists gave higher overall preference for the high pressure processed milk over heat-treated milk. The JAR evaluation showed no significant differences (p > 0.05) in all evaluated milk attributes which included milkiness, creaminess, mouthfeel, and aftertaste, with the exception of colour. Overall, high pressure processed milk scored better in terms of organoleptic properties as the penalty value for most attributes including colour, milkiness, mouthfeel, and aftertaste were lower than the penalty of heat-treated milk, except for creaminess. Therefore, to improve the acceptance and preference of high pressure processed milk, future development needs to focus on increasing creaminess of high pressure processed milk.

Demonstration of Escherichia coli Inactivation in Sterile Physiological Saline under High Pressure (HP) Phase Transition Conditions and Analysis of Probable Contribution of HP Metastable Positions Using Model Solutions and Apple Juice

It was demonstrated that the inactivation of high pressure (HP) treatment on Escherichia coli survival in sterile physiological saline (SPS) was influenced by the treatment conditions: unfrozen, frozen-thawed and fully frozen (phase transition). In order to probe the enhanced phase transition microbial destruction, vibration effects of phase transition position were created and discussed. Test samples were placed in HP chamber for treatment (150/240/330 MPa, no holding time) at room temperature and a special cooling device was used to maintain the phase transition conditions. Results showed that the phase transition from ice I to ice III of frozen SPS could be realized based on the cooling of a 20% sodium chloride solution. HP treatment under fully frozen conditions produced the best lethal effect compared to unfrozen and freeze-thaw samples. Vibration tests were carried out by using model solutions and apple juice to explore the behavior of phase transition. A synchronous and advance phase transition of internal apple juice was realized, respectively, by using pure water and 5% sodium chloride solution as external vibration sources, and the advance phase transitions of external pure water were realized by using 5% sodium chloride solution and 5% glucose solution as internal vibration sources.

Airborne pathogenic microorganisms and air cleaning technology development: A review

Transmission of pathogens through air is a critical pathway for the spread of airborne diseases, as airborne pathogenic microorganisms cause several harmful infections. This review summarizes the occurrence, transmission, and adverse impacts of airborne pathogenic microorganisms that spread over large distances via bioaerosols. Air cleaning technologies have demonstrated great potential to prevent and reduce the spread of airborne diseases. The recent advances in air cleaning technologies are summarized on the basis of their advantages, disadvantages, and adverse health effects with regard to the inactivation mechanisms. The application scope and energy consumption of different technologies are compared, and the characteristics of air cleaners in the market are discussed. The development of high-efficiency, low-cost, dynamic air cleaning technology is identified as the leading research direction of air cleaning. Furthermore, future research perspectives are discussed and further development of current air cleaning technologies is proposed.

Facilitating high pressure phase-transition research and kinetics studies at subzero temperatures using self-cooling laboratory units

Self-cooling phase-transition units were built and tested to successfully carryout pressure shift freezing, high pressure thawing and subzero temperature microbial destruction kinetics. The design of these equipment has been progressively improved over the years as highlighted in this paper. Phase transition data on grape & apple juices, and sodium chloride (20%) & glucose solutions (20%) in Ice I were gathered and modeled using Simon-like and polynomial equations. Factors influencing the Ice I and water to Ice III phase transition position were evaluated, and found to be mainly affected by the solute in the aqueous solution. For pressure shifting freezing and pressure assisting freezing to Ice III, water and 20% sodium chloride solution were successfully employed and verified as cooling media for creating the temperature change pathway of potato and carrot. Using sodium chloride solution (20%) as the cooling medium, the phase transition pathway of apple juice and grape juice under high pressure for the phase transition of Ice I and metastable water to Ice III was established. This could be used in kinetic studies. The developed cooling unit concepts can use in any commercial high pressure equipment for subzero temperature treatment of foods without externally supplied cooling.

Benefits and effectiveness of high pressure processing on cheese: a ricotta case study

Today High Pressure Processing (HPP) is receiving interest thanks to its ability to stabilize foods preserving nutritional and sensorial characteristics. This work applies HPP on nutrient ricottas created in the Parmigiano Reggiano area and demonstrates not only its benefits, but also disadvantages, testing different pressures and packaging. Moreover, the ability of HPP to prolong the lag phase and reduce the maximum growth rate of bacteria is illustrated with a mathematical model. Results show the influence of HPP parameters on microbial growth, volatile organic compounds, syneresis, softness and colour, and demonstrate that not all packaging are suitable for the treatment. Obtained data highlight the effectiveness of HPP, which results the best stabilization method to sell safe and nutritive ricottas on the market with a long shelf life. Of course, the work can be a starting point for food companies who want to test an innovative and promising non-thermal technology.