Aseptic Processing Of Foods Research Articles

Influence of Temperature, Light, and H2O2 Concentration on Microbial Spore Inactivation: In‐Situ Raman Spectroscopy Combined with Optical Trapping

To gain insight on chemical sterilization processes, the influence of temperature (up to 70 °C), intense green light, and hydrogen peroxide (H2O2) concentration (up to 30% in aqueous solution) on microbial spore inactivation is evaluated by in‐situ Raman spectroscopy with an optical trap. Bacillus atrophaeus is utilized as a model organism. Individual spores are isolated and their chemical makeup is monitored under dynamically changing conditions (temperature, light, and H2O2 concentration) to mimic industrially relevant process parameters for sterilization in the field of aseptic food processing. While isolated spores in water are highly stable, even at elevated temperatures of 70 °C, exposure to H2O2 leads to a loss of spore integrity characterized by the release of the key spore biomarker dipicolinic acid (DPA) in a concentration‐dependent manner, which indicates damage to the inner membrane of the spore. Intensive light or heat, both of which accelerate the decomposition of H2O2 into reactive oxygen species (ROS), drastically shorten the spore lifetime, suggesting the formation of ROS as a rate‐limiting step during sterilization. It is concluded that Raman spectroscopy can deliver mechanistic insight into the mode of action of H2O2‐based sterilization and reveal the individual contributions of different sterilization methods acting in tandem.

Heat transfer analysis in a heat exchanger with two coaxial tubes for sustainable aseptic processing of foods

Thermal-based approaches in food sterilization techniques principally utilize the heating process until the desired sterilization level of the food can achieved. More specifically, aseptic processing allows for a more cost-effective and time-efficient method for preserving food without degrading the food quality. In this work, we propose a heat transfer analysis of a scraped surface heat exchanger with two coaxial tubes that provides a simplified prototype of a sustainable aseptic processing system. The heat exchanger is installed with scraped blades to allow a stirring mechanism that can only oscillate back and forth at certain angles called oscillating angles. In this simulation, water and solid food particles are put in the system. Moreover, simple regression models are used to find the relation between the mechanical properties of the stirring process with the heat transfer properties. Therefore, experimental data of the temperature and heat transfer coefficient during the heating are used for model fitting. The model fit shows that the angle, frequency, and velocity of the stirring affect the temperature trend and the heat flow rate inside the system. Establishing a comprehensive heat transfer modelling can help to improve the traditional sterilization approach to focus on optimizing energy efficiency and reducing environmental impacts.

Real-Time Monitoring of H2O2 Sterilization on Individual Bacillus atrophaeus Spores by Optical Sensing with Trapping Raman Spectroscopy

Hydrogen peroxide (H2O2), a strong oxidizer, is a commonly used sterilization agent employed during aseptic food processing and medical applications. To assess the sterilization efficiency with H2O2, bacterial spores are common microbial systems due to their remarkable robustness against a wide variety of decontamination strategies. Despite their widespread use, there is, however, only little information about the detailed time-resolved mechanism underlying the oxidative spore death by H2O2. In this work, we investigate chemical and morphological changes of individual Bacillus atrophaeus spores undergoing oxidative damage using optical sensing with trapping Raman microscopy in real-time. The time-resolved experiments reveal that spore death involves two distinct phases: (i) an initial phase dominated by the fast release of dipicolinic acid (DPA), a major spore biomarker, which indicates the rupture of the spore’s core; and (ii) the oxidation of the remaining spore material resulting in the subsequent fragmentation of the spores’ coat. Simultaneous observation of the spore morphology by optical microscopy corroborates these mechanisms. The dependence of the onset of DPA release and the time constant of spore fragmentation on H2O2 shows that the formation of reactive oxygen species from H2O2 is the rate-limiting factor of oxidative spore death.

Direct Observation of the Sporicidal Action of Hydrogen Peroxide on Bacillus atrophaeus Spores By Optical Trapping Raman Microscopy

Hydrogen peroxide (H2O2), a strong oxidizer, is frequently used for chemical sterilization in aseptic food processing. Due to their inherent robustness, bacterial spores, i.e. spores of Bacillus atrophaeus, are commonly employed to evaluate the efficacy of the sterilization procedure [1]. Despite its widespread use, however, the details of the sporicidal action of H2O2 are not yet fully understood, with various mechanisms being discussed in the literature [2,3]. Here, we employ optical trapping Raman microscopy to elucidate the sporicidal mechanism of H2O2. Optical trapping Raman microscopy allows us to isolate, investigate, and manipulate individual spores from a sample (Fig. 1A). Combining optical microscopy with the real-time, label-free chemical information obtained from Raman spectroscopy directly reveals the sequence of steps that lead to oxidative spore death after H2O2 exposure (Fig. 1B).We find that spore degradation begins with the fast, cooperative release of dipicolinic acid (DPA), a key spore biomarker and a major component of spore’s core. This indicates a breach of the inner membrane surrounding the core. The onset of DPA release depends on the concentration of H2O2. DPA outflux is accompanied by the formation of oxidation products (mostly carbonyl compounds) and oxidation continues after exchange of DPA with the surrounding medium is complete. The remaining spore shell then slowly disintegrates and continues to shrink on a timescale of hundreds of seconds. Simultaneous observation of spore morphology and size by optical microscopy and particle tracking corroborates this three-step mechanism.The presented assay allows on-line monitoring of spore composition and morphology, which directly reveals the mechanism underlying the sporicidal action of H2O2. In addition, trapped spores can be exposed to different chemical or physical stimuli (temperature, light, chemical composition of the surrounding medium, etc.) to investigate a variety of industrially relevant sterilization conditions. Jildeh, Z. B., Wagner, P. H. & Schöning, M. J. Sterilization of Objects, Products, and Packaging Surfaces and Their Characterization in Different Fields of Industry: The Status in 2020. physica status solidi (a) 218, 2000732 (2021). Setlow, P. & Christie, G. What’s new and notable in bacterial spore killing. World J Microbiol Biotechnol 37, 144 (2021). Setlow, P. Spores of Bacillus subtilis: their resistance to and killing by radiation, heat and chemicals. J Appl Microbiol 101, 514-525 (2006). Figure 1

Simultaneous Online Monitoring and Sterility Assurance in Aseptic Food Processing Based on a Combined Calorimetric Gas- and Spore-Based Biosensor Array

Introduction Gaseous hydrogen peroxide is one of the most used sterilants for packaging in aseptic filling machines [1]. To validate a sterilization method under investigation, spores (resistant microorganisms against the sterilant) are exposed to the sterilant, the logarithmic kill rate is determined and at the end, the sterilization can be concluded. The main drawback of these methods is their tedious physical work and their slow response; the results can be obtained at the earliest after 24-48 hours. As a result, a novel sensing method has been previously introduced [2] to overcome these issues. In this work, such spore-based biosensor is combined with a calorimetric H2O2 sensor onto single chips to evaluate both the viability of spores and to determine gaseous hydrogen peroxide concentrations. Materials and Methods The calorimetric gas sensor was developed to measure gaseous hydrogen peroxide concentrations. Here, two meander structures were utilized as temperature sensors (see Fig. 1 a), at the bottom part of the sensor chip). One sensor was used as a reference (i.e., inert to H2O2 exposure), whereas the other one was employed as an active element (i.e., functionalized with MnO2 which catalyzes H2O2). As both structures were exposed to H2O2, a temperature increase occurred only at the active sensor. As a result, a temperature difference between both sensors could be correlated to the H2O2concentration. In addition, a spore-based biosensor was fabricated to evaluate the viability of spores. For this, interdigitated electrodes were operated as impedimetric sensors (see Fig. 1 a) at the top part of the sensor chip). A differential setup measurement was used similar like in the calorimetric gas sensor. In this case, spores were immobilized on the active part of the sensor chip. Upon H2O2 exposure, changes in the morphology of the spores aroused, which (by means of impedimetric changes) could be correlated to the viability of spores and hydrogen peroxide concentration. Results and Conclusions The calorimetric gas sensor responds to different concentrations of gaseous hydrogen peroxide (see Fig. 1 b)). The upper curves correspond to the temperature of the catallytically active sensor and the passive one. The temperature difference and accordingly, the actual H2O2 concentration is shown in the lower part curve. In the second experiment, biosensors were investigated with three different strains of bacteria measured at different stages. In the first stage, three biosensors’ impedances were measured after being cleaned. In the second step, B. atrophaeus DSM 675, B. subtilisDSM 402 and G. stearothermophilus DSM 5934 spores were immobilized on them. Finally, the spore-based biosensors were submitted to several concentrations of gaseous hydrogen peroxide. Signal responses (impedance) of the spore-based biosensors at different applied H2O2 concentrations are overviewed in Fig. 1 c).In conclusion, the synergy of these two sensor types as one combined sensor array allows a considerably more specific multi-parameter experience in aseptic filling machines in comparison to isolated microbiological state-of-the-art- or hydrogen peroxide methods.

Simultaneous Online Monitoring and Sterility Assurance in Aseptic Food Processing Based on a Combined Calorimetric Gas- and Spore-Based Biosensor Array

Introduction Gaseous hydrogen peroxide is one of the most used sterilants for packaging in aseptic filling machines [1]. To validate a sterilization method under investigation, spores (resistant microorganisms against the sterilant) are exposed to the sterilant, the logarithmic kill rate is determined and at the end, the sterilization can be concluded. The main drawback of these methods is their tedious physical work and their slow response; the results can be obtained at the earliest after 24-48 hours. As a result, a novel sensing method has been previously introduced [2] to overcome these issues. In this work, such spore-based biosensor is combined with a calorimetric H2O2 sensor onto single chips to evaluate both the viability of spores and to determine gaseous hydrogen peroxide concentrations. Materials and Methods The calorimetric gas sensor was developed to measure gaseous hydrogen peroxide concentrations. Here, two meander structures were utilized as temperature sensors (see Fig. 1 a), at the bottom part of the sensor chip). One sensor was used as a reference (i.e., inert to H2O2 exposure), whereas the other one was employed as an active element (i.e., functionalized with MnO2 which catalyzes H2O2). As both structures were exposed to H2O2, a temperature increase occurred only at the active sensor. As a result, a temperature difference between both sensors could be correlated to the H2O2concentration. In addition, a spore-based biosensor was fabricated to evaluate the viability of spores. For this, interdigitated electrodes were operated as impedimetric sensors (see Fig. 1 a) at the top part of the sensor chip). A differential setup measurement was used similar like in the calorimetric gas sensor. In this case, spores were immobilized on the active part of the sensor chip. Upon H2O2 exposure, changes in the morphology of the spores aroused, which (by means of impedimetric changes) could be correlated to the viability of spores and hydrogen peroxide concentration. Results and Conclusions The calorimetric gas sensor responds to different concentrations of gaseous hydrogen peroxide (see Fig. 1 b)). The upper curves correspond to the temperature of the catallytically active sensor and the passive one. The temperature difference and accordingly, the actual H2O2 concentration is shown in the lower part curve. In the second experiment, biosensors were investigated with three different strains of bacteria measured at different stages. In the first stage, three biosensors’ impedances were measured after being cleaned. In the second step, B. atrophaeus DSM 675, B. subtilisDSM 402 and G. stearothermophilus DSM 5934 spores were immobilized on them. Finally, the spore-based biosensors were submitted to several concentrations of gaseous hydrogen peroxide. Signal responses (impedance) of the spore-based biosensors at different applied H2O2 concentrations are overviewed in Fig. 1 c).In conclusion, the synergy of these two sensor types as one combined sensor array allows a considerably more specific multi-parameter experience in aseptic filling machines in comparison to isolated microbiological state-of-the-art- or hydrogen peroxide methods.Fig. 1. a) Combined sensor array consisting of a calorimetric H2O2 sensor and a spore-based biosensor with their respective sensor calorimetric and impedance responses in b) and c).

Effects of Particle Blockage and Eccentricity in Location on the Non-Newtonian Fluid Hydrodynamics around a Sphere

The flow of an incompressible non-Newtonian fluid over an eccentrically located sphere confined in a circular tube was investigated using three-dimensional steady state Computational Fluid Dynamics simulations. Pseudoplastic fluids with different power-law indices of 0.57, 0.76, and 0.94 were considered. The effects of ratio of particle diameter to tube diameter (blockage ratio, BR) and ratio of offset of the sphere position from the tube axis to the tube radius (eccentricity, Ec) on the hydrodynamic phenomena around the sphere are reported over a range of particle Reynolds numbers (Rep). The simulations were carried out in the range (0.1 ≤ Rep ≤ 40, 0.01 ≤ BR ≤ 0.5, and 0.0 ≤ Ec ≤ 0.6). The drag coefficient predictions for an unconfined sphere were found to be sensitive to the value of the consistency index parameter (K) in the viscous flow regime, especially at lower n values. At lower particle Reynolds numbers and centrally located sphere, the enhancement in drag coefficient due to blockage ratio was felt least by the fluid with the lowest n value. Even at higher Rep, higher blockage ratios still could cause significant enhancements in the drag coefficients (∼20%) for centrally located spheres. Irrespective of the power-law index, eccentric location of the sphere caused a decline in the overall drag coefficient due to the dominant influence of the lower hemisphere which was closer to the tube wall. At the highest particle Reynolds numbers, eccentricity, and blockage ratio, asymmetric fluid flow distribution caused opposing effects by decreasing the viscous drag coefficient and increasing the form drag coefficient relative to those obtained with the centrally confined sphere. Sharp variations in the shear rate dependent viscosity at the sphere surface could be associated with boundary layer separation. Wall effects at higher blockage ratio suppressed the boundary layer separation in the case of the fluid with the highest power-law index. Eccentricity also caused accelerated boundary layer separation at the upper hemisphere and absence of boundary layer separation along the lower hemisphere. At lower blockage ratios a maximum in the lift coefficient versus particle Reynolds number was usually observed. This study will be relevant in applications such as aseptic food processing, petroleum well drilling, fluidization, and particle transport in microfluidic devices.

Simulation of non-Newtonian fluid-food particle heat transfer in the holding tube used in aseptic processing operations

In aseptic food processing, a hot carrier fluid, usually non-Newtonian, is used to thermally sterilize the food particles suspended in a holding tube. The effects of a spherical food particle's diameter relative to the holding tube diameter on the heat transfer rates are investigated using Computational Fluid Dynamics (CFDs) simulations. As the particle to holding tube diameter ratio (blockage-ratio) increases, higher particle heating rates were usually observed when compared to the heating rates of an unconfined particle. Variations in the non-Newtonian fluid viscosities with shear rate and temperature played important roles in affecting the local Nusselt numbers. Significant effect of the blockage ratio was found on the integrated lethality of the thermal treatment at low particle Reynolds numbers (Rep). For such cases, conventional steady state fluid–particle heat transfer coefficient correlations, applicable when the particle is immersed in an unbounded stream of fluid, may lead to erroneous predictions of integrated lethality of treatment inside the holding tube. The thermal processing of the food particle was compared using two approaches. In the first rigorous approach, the transient and spatial fluid–particle heat flux variations around the sphere were accounted while in the second approach, a constant heat transfer coefficient value was specified as the boundary condition. Even at intermediate Biot number values (4–17), considerable differences between the two approaches could be observed in the conductive heating patterns inside the sphere as well as in the integrated lethalities.

Feasibility of Utilizing Bioindicators for Testing Microbial Inactivation in Sweetpotato Purees Processed with a Continuous‐Flow Microwave System

Continuous-flow microwave heating has potential in aseptic processing of various food products, including purees from sweetpotatoes and other vegetables. Establishing the feasibility of a new processing technology for achieving commercial sterility requires evaluating microbial inactivation. This study aimed to assess the feasibility of using commercially available plastic pouches of bioindicators containing spores of Geobacillius stearothermophilus ATCC 7953 and Bacillus subtilis ATCC 35021 for evaluating the degree of microbial inactivation achieved in vegetable purees processed in a continuous-flow microwave heating unit. Sweetpotato puree seeded with the bioindicators was subjected to 3 levels of processing based on the fastest particles: undertarget process (F(0) approximately 0.65), target process (F(0) approximately 2.8), and overtarget process (F(0) approximately 10.10). After initial experiments, we found it was necessary to engineer a setup with 2 removable tubes connected to the continuous-flow microwave system to facilitate the injection of indicators into the unit without interrupting the puree flow. Using this approach, 60% of the indicators injected into the system could be recovered postprocess. Spore survival after processing, as evaluated by use of growth indicator dyes and standard plating methods, verified inactivation of the spores in sweetpotato puree. The log reduction results for B. subtilis were equivalent to the predesigned degrees of sterilization (F(0)). This study presents the first report suggesting that bioindicators such as the flexible, food-grade plastic pouches can be used for microbial validation of commercial sterilization in aseptic processing of foods using a continuous-flow microwave system.

Radiation treatment for sterilization of packaging materials

Treatment with gamma and electron radiation is becoming a common process for the sterilization of packages, mostly made of natural or synthetic plastics, used in the aseptic processing of foods and pharmaceuticals. The effect of irradiation on these materials is crucial for packaging engineering to understand the effects of these new treatments. Packaging material may be irradiated either prior to or after filling. The irradiation prior to filling is usually chosen for dairy products, processed food, beverages, pharmaceutical, and medical device industries in the United States, Europe, and Canada. Radiation effects on packaging material properties still need further investigation. This paper summarizes the work done by different groups and discusses recent developments in regulations and testing procedures in the field of packaging technology.

Magnetic thermometry in the aseptic processing of foods containing particulates (abstract)

Aseptic processing of foods has many advantages over canning, including higher efficiency, lighter packaging, better taste, and higher nutritional value. Aseptic processing is different from canning where the food and container are sterilized together. Instead, a thin stream of food is heated and the packaging is independently sterilized before the food is placed in the package. However, no aseptic processes have been successfully filed with the FDA for foods containing sizable solid particles because of uncertainties in the thermal sterilization of the particles (e.g., soup). We have demonstrated that by inserting small paramagnetic particles in the interior of the simulated and real food particles, the local temperature can be measured. With this information, any questions about the adequate sterilization of the particles can be resolved. The measurements were done by directing the food stream through a magnetic field and sensing the voltages induced in a pickup coil by the motion of the magnetized particles. Details of the equipment design and data analysis will be discussed along with an introduction to the aseptic processing of foods.

Convective Heat Transfer at Particle‐Liquid Interface in Continuous Tube Flow at Elevated Fluid Temperatures

ABSTRACTLiquid‐to‐particle convective heat transfer coefficients are useful in developing aseptic food processing systems. They were determined for continuous flow through a holding tube at 115.5°C using liquid crystal and relative velocity methods with sodium carboxymethylcellulose solution to simulate non‐Newtonian fluid characteristics. An on‐line tube viscometer was used for in situ estimation of rheological characteristics. Minimum and maximum values of hfp determined from the liquid crystal method ranged from 986 W/m20K to 2270 W/m20K, (Nusselt numbers from 26.4 to 54.6). Values from the relative velocity method ranged from 1143 to 2270 W/m20K (Nusselt numbers from 33.2 to 63.1) when using the Ranz and Marshall relation, and from 598 to 1456 W/m20C (Nusselt numbers from 13.6 to 24.1) with a flat‐plate correlation. Heat transfer coefficients increased significantly with decreasing carrier medium viscosity and decreasing particle‐to‐tube diameter ratio and increased with flow rate.

The thermal-hydraulics of aseptic food processing

The temperature profile for an N- component mixture of particles in a fluid flowing through a heated tube has been evaluated using a numerical method for the fluid and an analytical solution for the particles. The results for the time-at-temperature of the particles depend on the drift-flux parameters, which quantify the local slip. In particular, the more slip the better the heat transfer and the shorter the heat exchanger required for aseptic food processing. Two diagrams are given, which cover all parameters of interest for laminar flow.

Determination of lethality and processing time in a continuous sterilization system containing particulates

A finite difference program was used to simulate an aseptic processing of foods containing particulates. The accumulated lethality at the center of the particle moving through the heat/hold/cool sections of the continuous sterilization system and the minimum processing time to destroy 6 D of Clostridium sp. PA3679 and 12 D of peroxidase necessary to prevent regeneration were calculated. Effect of operating conditions and change of thermal properties of particle and fluid on accumulated lethality and required minimum processing time is presented. Results indicated that size, shape, thermal properties, and residence time distributions of the particle within scraped-surface heat exchanger (SSHE) and holding tube greatly influenced the accumulated lethality and, subsequently, the minimum required processing time. In addition, effects of the overall heat transfer coefficient for both heater and holding tube and the particle surface heat transfer coefficient were found to be significant.