A microfluidic approach for studying microcolonization of Escherichia coli O157:H7 on leaf trichome-mimicking surfaces under fluid shear stress.

Escherichia coli O157:H7 have previously been associated with disease outbreaks associated with leafy green vegetables. However, the physical mechanisms that determine the spatial organization of bacteria onto leafy greens are still not clear. Microfluidics with embedded trichome-mimicking microposts were employed to investigate the role of shear flow and configuration of trichomes on E.

Molecular dynamics evidence for nonthermal effects of electric fields on pectin methylesterase activity.

Experimental studies relevant to the nonthermal effects of electric fields on biological systems are emerging. However, these effects are poorly understood at the molecular level. The present study investigates pectin methylesterase, a cell wall modifying enzyme in plants, exposed to various electric field strengths.

Moderate Electric Field Treatment Enhances Enzymatic Hydrolysis of Cellulose at Below-Optimal Temperatures.

Saccharification of cellulosic biomass for the fermentation of transportation fuels faces several challenges. Cellulose is highly stable, and even with enzymatic assistance, decomposition of cellulose is slow. Additionally, the enzymes are expensive and sensitive to thermal and mechanical inactivation.

Novel Processing Technologies as Compared to Thermal Treatment on the Bioaccessibility and Caco-2 Cell Uptake of Carotenoids from Tomato and Kale-Based Juices.

This research aimed to measure the impact of novel food processing techniques, i.e., pulsed electric field (PEF) and ohmic heating (OH), on carotenoid bioaccessibility and Caco-2 cell uptake from tomato juice and high-pressure processing (HPP) and PEF on the same attributes from kale-based juices, as compared with raw (nonprocessed) and conventional thermally treated (TT) juices.

Mechanisms of enhanced bacterial endospore inactivation during sterilization by ohmic heating.

During ohmic heating, the electric field may additionally inactivate bacterial endospores. However, the exact mechanism of action is unclear. Thus, a mechanistic study was carried out, investigating the possible target of electric fields inside the spore.

Ohmic Heating Assisted Lye Peeling of Pears.

Unlabelled: Currently, high concentrations (15% to 18%) of lye (sodium hydroxide) are used in peeling pears, constituting a wastewater handling and disposal problem for fruit processors. In this study, the effect of ohmic heating on lye peeling of pears was investigated. Pears were peeled using 0.

Toward a Philosophy and Theory of Volumetric Nonthermal Processing.

Nonthermal processes for food preservation have been under intensive investigation for about the past quarter century, with varying degrees of success. We focus this discussion on two volumetrically acting nonthermal processes, high pressure processing (HPP) and pulsed electric fields (PEF), with emphasis on scientific understanding of each, and the research questions that need to be addressed for each to be more successful in the future. We discuss the character or "philosophy" of food preservation, with a question about the nature of the kill step(s), and the sensing challenges that need to be addressed.

Effects of controlled-frequency moderate electric fields on pectin methylesterase and polygalacturonase activities in tomato homogenate.

The effect of controlled-frequency moderate electric field treatments on pectin methylesterase and polygalcturonase activities in tomato homogenate was investigated by subjecting identically treated control and electrically-treated samples to the same temperature history. Additionally, a model was developed for the motion of the enzyme molecules subjected to an electric field. Results show that the application of electric fields at a low field strength (0.

Physics of Fresh Produce Safety: Role of Diffusion and Tissue Reaction in Sanitization of Leafy Green Vegetables with Liquid and Gaseous Ozone-Based Sanitizers.

Produce safety has received much recent attention, with the emphasis being largely on discovery of how microbes invade produce. However, the sanitization operation deserves more attention than it has received. The ability of a sanitizer to reach the site of pathogens is a fundamental prerequisite for efficacy.

Mathematical modeling and microbiological verification of ohmic heating of a multicomponent mixture of particles in a continuous flow ohmic heater system with electric field parallel to flow.

To accomplish continuous flow ohmic heating of a low-acid food product, sufficient heat treatment needs to be delivered to the slowest-heating particle at the outlet of the holding section. This research was aimed at developing mathematical models for sterilization of a multicomponent food in a pilot-scale ohmic heater with electric-field-oriented parallel to the flow and validating microbial inactivation by inoculated particle methods. The model involved 2 sets of simulations, one for determination of fluid temperatures, and a second for evaluating the worst-case scenario.

In situ measurement of reaction volume and calculation of pH of weak acid buffer solutions under high pressure.

Direct measurements of reaction volume, so far, have been limited to atmospheric pressure. This study describes a method for in situ reaction volume measurements under pressure using a variable volume piezometer. Reaction volumes for protonic ionization of weak acid buffering agents (MES, citric acid, sulfanilic acid, and phosphoric acid) were measured in situ under pressure up to 400 MPa at 25 °C.

Ohmic heating of peaches in the wide range of frequencies (50 Hz to 1 MHz).

Unlabelled: The ohmic heating (OH) rate of peaches was studied at fixed electric field strength of 60 V.cm⁻¹, square-shaped instant reversal bipolar pulses, and frequencies varying within 50 Hz to 1 MHz. Thermal damage of tissue was evaluated from electrical admittivity.

In situ measurement of pH under high pressure.

In situ measurement of pH under high pressure is complicated by the need to remain functional under extreme pressures, electrically noisy environments, and the difficulty in inferring chemical equilibrium conditions under pressure. We describe a pH sensor wherein the current flowing at a given input voltage is directly related to hydrogen ion concentration and can be operated within extreme environments. The sensor was tested at 25 °C for in situ pH measurement of several buffer solutions under high pressure up to 784.

Residence time distribution (RTD) of particulate foods in a continuous flow pilot-scale ohmic heater.

The residence time distribution (RTD) of a model particulate-fluid mixture (potato in starch solution) in the ohmic heater in a continuous sterilization process was measured using a radio frequency identification (RFID) methodology. The effect of solid concentration and the rotational speed of the agitators on the RTD were studied. The velocity of the fastest particle was 1.

Inactivation of Escherichia coli O157:H7 and natural microbiota on spinach leaves using gaseous ozone during vacuum cooling and simulated transportation.

The aim of this study was to integrate an ozone-based sanitization step into existing processing practices for fresh produce and to evaluate the efficacy of this step against Escherichia coli O157:H7. Baby spinach inoculated with E. coli O157:H7 (approximately 10(7) CFU/g) was treated in a pilot-scale system with combinations of vacuum cooling and sanitizing levels of ozone gas (SanVac).

Heating and sterilization technology for long-duration space missions: transport processes in a reusable package.

Long-duration space missions require a high-quality, shelf-stable food supply but must also contend with packaging waste after use. We have developed a package, adapted from a military pouch, that enables heating of foods to serving temperature. After the food is consumed, the package may be reused for containment and sterilization of waste, and, potentially, for packaging and sterilizing foods grown on a Mars base.

Effect of moderate electric field frequency and growth stage on the cell membrane permeability of Lactobacillus acidophilus.

Changes in growth kinetics and metabolic activity of microorganisms under the presence of a moderate electric field (MEF) have been hypothesized as being due to temporary permeabilization of cell membranes. We investigated herein the effects of frequency and growth stage on cell membrane permeabilization of Lactobacillus acidophilus OSU 133 during MEF fermentation. Cells were stained with two fluorescent nucleic acid stains: the green, nonselective, cell membrane permeable SYTO 9, and the red, cell membrane impermeable propidium iodide (PI).

Effect of moderate electric field frequency on growth kinetics and metabolic activity of Lactobacillus acidophilus.

Moderate electric fields (MEF) have been previously shown to alter the metabolic activity of microbial cells; thus, the effect of frequency and electric field would be of considerable interest. We investigated herein the effects of MEF frequency on microbial growth kinetics and bacteriocin (Lacidin A) production of Lactobacillus acidophilus OSU 133 during fermentation. The following fermentation treatments were compared: conventional (for 40 h), MEF (1 V cm(-1), for 40 h), combination of MEF (1 V cm(-1), for the first 5 h) and conventional (for 35 h) at various frequency levels (45, 60, and 90 Hz) all at 30 degrees C, and control (conventional) fermentation at 37 degrees C.

Influence of temperature, electrical conductivity, power and pH on ascorbic acid degradation kinetics during ohmic heating using stainless steel electrodes.

Degradation kinetics of ascorbic acid was determined in pH 5.7 buffer solution using an isothermal batch ohmic heater with stainless steel electrodes. Variables included in this study were temperature (40, 60 and 80 degrees C); power (0, 100,150 and 300 W); and electrical conductivity (varied using 0.