Food Sterilization Research Articles

Inactivation mechanisms of electron beam irradiation on Listeria innocua through the integrity of cell membrane, genomic DNA and protein structures

SummaryAs a non‐thermal sterilisation technology, electron beam irradiation (EBI) has attracted great interest for microbial inactivation in food preservation. This study aims to investigate the effects of EBI on membrane permeability, physiological status, morphological structure, genome integrity and protein structures of Listeria innocua irradiated at doses of 0.75, 1.50, 2.25, 3.00, 3.75 and 5.00 kGy. The results showed that EBI noticeably reduced the total microbial counts of L. innocua by more than 7 log CFU mL−1 with 5.00 kGy treatment. The cell membrane permeability increased, resulting in the leakage of intracellular substances and changes in cell physiological status, which was proven by the cell staining and electron microscopy (EM) observations. Moreover, the integrity of genomic DNA and protein secondary structure, but not the protein primary structure were also disrupted. These findings provide the intrinsic mechanisms for the inactivation of L. innocua affected by EBI, which could serve as a theoretical basis for a better application of EBI in food sterilisation.

UV Resistance of bacteria from the Kenyan Marine cyanobacterium Moorea producens.

UV resistance of bacteria isolated from the marine cyanobacterium Moorea producens has not been observed previously, findings which highlight how unsafe germicidal UV irradiation for sterilization of air, food, and water could be. Further, UV resistance of Bacillus licheniformis is being observed for the first time. This study focused on bacteria isolated from the marine cyanobacterium M. producens collected off the Kenyan coast at Shimoni, Wasini, Kilifi, and Mida. UV irradiance of isolates (302 nm, 70 W/m2, 0–1 hr) established B. licheniformis as the most UV resistant strain, with the following order of taxon resistance: Bacilli> γ proteobacteria > Actinobacteria. UV resistance was independent of pigmentation. The maximum likelihood phylogenetic distance determined for both B. licheniformis and Bacillus aerius relative to M. producens CCAP 1446/4 was 2.0. Survival of B. licheniformis upon UV irradiance followed first‐order kinetics (k = 0.035/min, R 2 = 0.88). Addition of aqueous extracts (2, 10, 20 and 40 mg/ml) of this B. licheniformis strain on the less resistant Marinobacterium stanieri was not significant, however, the commercial sunscreen benzophenone‐3 (BP‐3) positive control and the time of irradiance were significant. Detection of bacteria on M. producens filaments stained with acridine orange confirmed its nonaxenic nature. Although the chemistry of UV resistance in cyanobacteria has been studied in depth revealing for example the role of mycosporine like amino acids (MAAs) in UV resistance less is known about how bacteria resist UV irradiation. This is of interest since cyanobacteria live in association with bacteria.

Quantitative microbial assessment for Escherichia coli after treatment by high voltage gas phase plasma

High voltage electrical discharge (gas and liquid) plasmas are new developing techniques used for food and water decontamination. This study investigates the influence of high voltage gas phase plasma treatment on several parameters: inactivation of Escherichia coli K12, recovery, proteomic analyses, cellular leakage and influence of pH and generated H2O2 species on inactivation of the E. coli cells. Samples were treated in a glass reactor with a point-to-plate electrode configuration. Electrical conductivity (100 and 800 μS/cm), polarity (+/−), time (5 and 10 min) and frequency (60, 90 and 120 Hz) were chosen in order to determine their influence on listed parameters. Statistical analyses were obtained to optimize conducted treatments. Treatment regime of 90 Hz, positive polarity, 100 μS/cm and 10 min resulted in the highest reduction (7.8 log10 CFU/mL) of E. coli. Recovery of cells after the treatment suggested oxidative stress overcome. Plasma processing is an energy effective process, comparing to traditional thermal processes like pasteurization and sterilization. Plasma treated liquid remains at low temperature, which lowers electrical energy consumption during industrial processes. The proposed study investigates the possible application of high voltage gas phase electrical discharge plasmas for inactivation of Escherichia coli K12 MG1655 in water. The main aim was to confirm effectiveness of plasma treatment conducted in argon (which is uninfected by plasma and can be recycled) on inactivation and cell recovery of E. coli K12. This research is a first step towards the development of the gas phase plasma technology for disinfection of liquids. However, future development, optimization and application of this technology for food sterilization will lead to acceptable ecological regulations like lowering greenhouse gas emissions.

Prediction of the electric discharge occurrence under repetitive bipolar rectangular pulsed electric field <20 kV/cm

Pulsed Electric Field (PEF) is a newly developed food sterilization technology applying repetitive electric pulses to inactivate microorganisms and enzymes in liquid food. The evolution of bubbles and consequent electrical breakdown of the liquid treatment chamber have been a bottleneck of its industrial applications. Traditional theory of impulse breakdown cannot be applied to the PEF treatment since its discharge is greatly determined by the size of bubbles. The aim of this study is to clarify the bubbles' evolution characteristics under different pulse parameters and their impact on discharges. A high-precision bubble monitoring system, including a high speed camera was developed to study the behavior of micron-scale bubbles in treated liquids. Quantitative formulas between the bubble cross-sectional area with electric field intensity, pulse duration, and pulse repetition rate were obtained, and the dependence of discharge probability on the bubble area was proposed. Prediction formulas were developed to predict the average discharge time, which makes it possible to find the proper PEF processing time without discharges under given parameters and offer theoretical support to optimize pulse parameters in the PEF food treatment process.

Inactivation of yeast in apple juice using gas-phase surface discharge plasma treatment with a spray reactor

Non-thermal plasma technology can inactivate microorganisms that maybe used in the food processing industry. This study mainly aims to evaluate the effect of a gas-phase surface discharge plasma system with a spray reactor on yeasts (Zygosaccharomyces rouxii LB and 1130) in apple juice. This method avoids the limitation of liquid penetration depths in plasma treatment, expanding the processing capacity. Owing to this advantage, this approach can be used to industrialize liquid food sterilization. Experimental results showed that the number of Z. rouxii LB and 1130 cells decreased by about 6.58 and 6.82 log reductions, respectively, in apple juice after discharge plasma treatment for 30 min. The treatment used a voltage of 21.3 kV and inactivation followed the downward concave Weibull kinetics. Longer plasma exposure times with higher discharge voltages and regulated volume flow rate for both gas and liquid phases resulted in greater inactivation rates. Scanning electron microscopy revealed that the structures of plasma-treated cells were severely damaged during the discharge plasma process. Plasma-generated compounds in liquid, such as hydrogen peroxide and ozone in the liquid phase, are generally responsible for the inactivation of microorganisms.

Evaluation of biological inactivation efficacy for in-duct pulsed xenon lamp

In-duct pulsed xenon lamp can destroy the bioaerosols in the flowing airstream as it passes through. Current researches mostly focus on the food sterilization and surface sterilization. In this work, an in-duct pulsed xenon lamp sterilization experimental system was developed with stainless steel duct to model use in the HVAC (Heating, Ventilation and Air Conditioning) system. To study the effect of power supply parameters on the inactivation efficacy, 42 experimental conditions were conducted with the variation of input voltage, capacitance capacity, flash frequency and airstream velocity. The results indicate that the one-pass inactivation efficiency ranges from 63.12% to 88.87%. Inactivation efficiency has positive correlation with input voltage, capacitor capacity and flash frequency of the device, and negative correlation with airstream velocity. The factors affecting the inactivation efficiency in descending order are input voltage, capacitor capacity, flash frequency and airstream velocity. As the power consumption indicator P/G (input power per airflow volume) increases, the inactivation efficiency shows a near linear increase. This study developed a comprehensive evaluation method on the inactivation efficacy by selecting higher ratio of efficiency to input power under the premise of ensuring inactivation efficiency. Optimal combinations of parameters could be obtained with the method in the applications.

Evaluation of environmental impact of two ready-to-eat canned meat products using Life Cycle Assessment

The main objective of this study was to assess the environmental impact of two ready-to-eat canned meat products through Life Cycle Assessment (LCA). The analysis of both products, pork lean and meatballs with peas, was performed under a cradle-to-grave approach and 5 stages of their life cycle were included: meat production, food processing, distribution, use and final disposal.The stages with the greatest environmental impact were meat production and food processing for both products. Both stages have a similar degree of contribution throughout the product life cycle. Within the food processing stage, canning and sterilization were the processes with higher impact. Three scenarios employing different canning material were evaluated. The results have shown that the replacement of tin by recycled aluminum can significantly reduce the impact of the products, reaching 94% in some impact categories. Although the type of canning material is a key aspect of the environmental impact, the efficiency of the containers (relationship between the amount of material and the amount of canned food) also shows an important influence on the impact of this process.The impacts of sterilization are mainly due to the consumption of steam and electricity and it is a phase with great possibilities for technological improvement, among which the reuse of the water used in the process could be considered.

Computational Fluid Dynamics (CFD) Modelling and Application for Sterilization of Foods: A Review

Computational fluid dynamics (CFD) is a powerful tool to model fluid flow motions for momentum, mass and energy transfer. CFD has been widely used to simulate the flow pattern and temperature distribution during the thermal processing of foods. This paper discusses the background of the thermal processing of food, and the fundamentals in developing CFD models. The constitution of simulation models is provided to enable the design of effective and efficient CFD modeling. An overview of the current CFD modeling studies of thermal processing in solid, liquid, and liquid-solid mixtures is also provided. Some limitations and unrealistic assumptions faced by CFD modelers are also discussed.

Continuous Versus Discontinuous Ultra-High-Pressure Systems for Food Sterilization with Focus on Ultra-High-Pressure Homogenization and High-Pressure Thermal Sterilization: A Review.

High-pressure thermal sterilization (HPTS) and ultra-high-pressure homogenization (UHPH) are two emerging sterilization techniques that have not been implemented in the food industry yet. The two technologies apply different acting principles as HPTS uses isostatic pressure in combination with heat whereas UHPH uses dynamic pressure in combination with shear stress, cavitation, impingement, and heat. Both technologies offer significant benefits in terms of spore inactivation in food production with reduced thermal intensity and minimized effects on sensory and nutritional profiles. These benefits have resulted in relevant research efforts on both technologies over the past few decades. This state of the art of the discontinuous HPTS-based and the continuous UHPH-based sterilization concepts are assessed within this review. Further, various basic principles and promising future preservation applications of HPTS and UHPH for food processing, that are also applicable in the pharmaceutical, biochemical, and biotechnological sectors, are summarized. In addition, the applications and limitations of these technologies in terms of optimizations needed to overcome the identified challenges are emphasized.

Development of Nonthermal Sterilization Treatment System without Impacting to Enzyme in Vegetable Drink by Pulsed Electric Field

SUMMARYFor the sterilization of food, heat sterilization, chemical sterilization, and similar methods are available. However, they cause the change of the quality and flavor of the food. As the solution, the intense pulsed high electric field (IPEF) sterilization method has been studied. IPEF sterilization is used for the nonthermal sterilization of the foods because it destroys the cell membrane of bacteria physically. In this study, we have attempted to apply the IPEF sterilization for green juice. The development of a circulation sterilization system for a practical test was carried out. It was confirmed that enzyme included in the green juice was not deactivated when IPEF was applied. As a result, at applying 20‐min pulse electric field in 30 kV/cm and 40 kV/cm, survival ratios of viable bacteria in the green juice were reduced to about 40% and 12%, respectively. Also, deactivation of superoxide dismutase did not occur when the bacteria were sterilized.

Cold Sterilization of Coconut Water Using Membrane Filtration: Effect of Membrane Property and Operating Condition

Coconut water has been considered as a nutritional, refreshing and highly isotonic beverage with delicate aroma and flavor. In food sterilization technique, thermal processing, however tends to reduce these beneficial properties especially estrogen hormone and flavor. To overcome this limitation, this study therefore aimed to clarified and sterilized coconut water using non–thermal processing, membrane filtration. Hollow fiber microfiltration (MF) membrane with pore size of 0.1 and 0.2 μm and ultrafiltration (UF) membrane with molecular weight cut–off (MWCO) of 100 and 30 kDa were used. The effect of membrane pore size and MWCO on quality of clarified juice, permeate flux and fouling were studied. It was found that fresh coconut water and clarified coconut water obtained from MF and UF did not show difference in pH, total soluble solid, reducing sugar, estrogen hormone and minerals including calcium, magnesium, phosphorus, potassium and sodium. The results from microbiological analysis of the clarified coconut water showed that sterilized of coconut water was obtained using either MF or UF membranes. This microbiological quality of clarified coconut water was met the Thai legislation for juice and drinks. The permeate flux of MF was much higher than those of UF while the fouling resistance of UF membrane was much higher than those of MF membrane. The permeate flux of membrane with pore size of 0.1 £gm was slightly lower than that of membrane with pore size of 0.2 μm. The results also indicated that the major fouling of both MF and UF membranes was reversible. The irreversible fouling resistance of 0.1 μm membrane was the lowest and most of this irreversible fouling was external irreversible fouling, formed on the membrane surface. According to these results, it could be concluded that 0.1 μm membrane was the most suitable membrane for clarification and sterilization of coconut water. In addition, the effects of TMP, cross flow velocity (CFV) and the % recovery on permeate flux in batch concentration mode were also studied. It was found that the permeate flux of 0.1 μm membrane was significantly increased with increasing CFV and decreased as % recovery increased. These results suggested that permeate flux during MF of coconut water was dependent on reversible fouling and could be improved by using hydrodynamic modification techniques.

Analytical models of Ohmic heating and conventional heating in food processing

Ohmic heating is a food processing operation in which an electric current is passed through a food and the electrical resistance of the food causes the electric power to be transformed directly into heat. The heat is not delivered through a surface as in conventional heat exchangers but it is internally generated by Joule effect. Therefore, no temperature gradient is required and it origins quicker and more uniform heating within the food. On the other hand, it is associated with high energy costs and its use is limited to a particular range of food products with an appropriate electrical conductivity. Sterilization of foods by Ohmic heating has gained growing interest in the last few years. The aim of this study is to evaluate the benefits of Ohmic heating with respect to conventional heat exchangers under uniform wall temperature, a condition that is often present in industrial plants. This comparison is carried out by means of analytical models. The two different heating conditions are simulated under typical circumstances for the food industry. Particular attention is paid to the uniformity of the heat treatment and to the heating section length required in the two different conditions.

Processing of baby food using pressure-assisted thermal sterilization (PATS) and comparison with thermal treatment

ABSTRACTCurrently baby food is sterilized using retort processing that gives an extended shelf life. However, this type of heat processing leads to reduction of organoleptic and nutrition value. Alternatively, the combination of pressure and heat could be used to achieve sterilization at reduced temperatures. This study investigates the potential of pressure-assisted thermal sterilization (PATS) technology for baby food sterilization. Here, baby food (apple puree), inoculated with Bacillus subtilis spores was treated using PATS at different operating temperatures, pressures and times and was compared with thermal only treatment. The results revealed that the decimal reduction time of B. subtilis in PATS treatment was lower than that of thermal only treatment. At a similar spore inactivation, the retention of ascorbic acid of PATS-treated sample was higher than that of thermally treated sample. The results indicated that PATS could be a potential technology for baby food processing while minimizing quality deterioration.

Monitoring chemical changes during food sterilisation using ultrahigh resolution mass spectrometry

Sterilised food products undergo chemical changes during processing that ultimately determine the product quality. To provide detailed information on the chemistry of each stage of a pet-food sterilisation process, a laboratory-scale system was developed, which allowed sampling under the high temperatures and pressures associated with sterilisation. Products from the laboratory-scale system were representative of the factory process. Sample extracts were analysed by Fourier Transform-Ion Cyclotron Resonance-Mass Spectrometry (FT-ICR-MS), which delivered the molecular formulae and ion intensities of the compounds present. Data were examined to determine the coverage of this method, the degree of chemical change occurring during pet food thermal processing, and the level of identification possible with FT-ICR-MS. Data visualisation and statistical analysis identified significant chemical changes in pet food as a result of processing, and allowed tentative identification of the compounds involved. Insights generated using FT-ICR-MS analysis can be confirmed and further explored using conventional, targeted analyses.

Influence of oven and microwave roasting on bioproperties, phenolic compounds, fatty acid composition, and mineral contents of nongerminated peanut and germinated peanut kernel and oils

While antioxidant activity values of nongerminated peanut kernel extracts change between 46.58% (raw peanut) and 49.63% (oven), this values of germinated kernel extracts varied between 38.67 (oven) and 44.83 mgGAE/100 g (germinated). In addition, total phenolic contents of both nongerminated and germinated peanut kernels changed between 12.68 (oven) and 19.73 mgGAE/100 g (raw) and 23.81 (oven) and 41.62 mgGAE/100 g (germinated), respectively. p-Hydroxybenzoic, vanillic, ferulic, quercetin, and p-coumaric and cinnamic acids were the dominant compounds of both germinated and nongerminated peanut kernels. It was observed statistically differences in fatty acid composition of peanut oils (p < .05). The highest oleic acid contents (62.74%) were determined in nongerminated kernel oil roasted in oven. The contents of α-tocopherol in nongerminated peanut ranged from 16.58 mg/100 g (oven roasted) to 18.64 mg/100 g (raw),while α-tocopherol contents of germinated kernel oils change between 14.72 mg/100 g (microwave roasted) and 16.49 mg/100 g (germinated). Mineral contents of germinated peanut kernels decreased partially compared to nongerminated peanut kernels. Practical applications Nut oils are receiving growing interest due to their high concentration of bioactive lipid components, which have shown various health benefits. Germination produced high phenolic content and antioxidant activities in lupin seeds. Phenolic compounds are generally secondary metabolite produced in plants, and they might be correlated to antioxidant activity, which has been shown to retain various biological benefits; microwave energy and conventional heating are currently being used for food processing operations, including cooking, drying, tempering, baking, pasteurization, and sterilization.

Benchmarking the minimum Electron Beam (eBeam) dose required for the sterilization of space foods

As manned space missions extend in length, the safety, nutrition, acceptability, and shelf life of space foods are of paramount importance to NASA. Since food and mealtimes play a key role in reducing stress and boredom of prolonged missions, the quality of food in terms of appearance, flavor, texture, and aroma can have significant psychological ramifications on astronaut performance. The FDA, which oversees space foods, currently requires a minimum dose of 44kGy for irradiated space foods. The underlying hypothesis was that commercial sterility of space foods could be achieved at a significantly lower dose, and this lowered dose would positively affect the shelf life of the product. Electron beam processed beef fajitas were used as an example NASA space food to benchmark the minimum eBeam dose required for sterility. A 15kGy dose was able to achieve an approximately 10log reduction in Shiga-toxin-producing Escherichia coli bacteria, and a 5log reduction in Clostridium sporogenes spores. Furthermore, accelerated shelf life testing (ASLT) to determine sensory and quality characteristics under various conditions was conducted. Using Multidimensional gas-chromatography–olfactometry–mass spectrometry (MDGC-O-MS), numerous volatiles were shown to be dependent on the dose applied to the product. Furthermore, concentrations of off –flavor aroma compounds such as dimethyl sulfide were decreased at the reduced 15kGy dose. The results suggest that the combination of conventional cooking combined with eBeam processing (15kGy) can achieve the safety and shelf-life objectives needed for long duration space-foods.

Piperidine-conjugated polyfunctional star-shaped PLLA as a novel bio-based antioxidant additive for bioplastics

Antioxidant-conjugated star-shaped PLLA (star-PLLA-PPD) were originally proposed as a novel polyfunctional free radical stabilizing additive for bioplastics. By a simple ring opening polymerization of l-lactide (L-LA) on a poly-functional core molecule (i.e., pentaerylthritol) using tin (II)-2-ethylhexanoate (SnOct2) as a catalyst, the 4-arms star-shaped PLLA was successfully prepared and confirmed by FT-IR and 1H-NMR. Percent conversion of L-LA to 4-arms star-PLLA was 78.50% and the weight and number average molecular weights determined by GPC were 34726 Da and 27286 Da, respectively (PDI = 1.27). Piperidine (PPD) was then conjugated onto 4-arms star-PLLA to obtain star-PLLA-PPD. As observed by SEM and DSC, the star-PLLA-PPD exhibited excellent compatibilizer as well as nucleating agent for PLA. A model study on free radical scavenging ability of the star-PLLA-PPD in PLA blends was carried out under radiation-induced free radical process. Irradiation doses of 10 kGy and 25 kGy were used because they are generally used for food and medical device sterilization, respectively. Free radical scavenging ability was demonstrated using EPR spectroscopy. The star-PLLA-PPD efficiently scavenges the free radicals in PLA matrix upon irradiation. The star-PLLA-PPD additive could retard the degradation of PLA under irradiation as observed by protecting molecular weight reduction when compared with the neat PLA. The migration of star-PLLA-PPD is significant lower than PPD. A novel star-PLLA-PPD additive would be a good model of polyfunctional bio-based antioxidant additive for bioplastics especially for food packaging and biomedical materials.

Plasma Technology in Food Industry: mini-review

Plasma treatment is an interesting technology with many potential applications in industry. At present, more and more often we encounter papers that deal with utilization of plasma technology in food industry. This mini-review provides an overview of the latest developments in this area. At the beginning the principles of plasma interaction with solid surfaces are shortly discussed. The next chapters are focused on sterilization of food from bacteria and fungi. The infl uence of plasma treatment on the food quality and nutritional parameters is discussed in last section.

A Novel Technique for Sterilization Using a Power Self-Regulated Single-Mode Microwave Cavity.

In this paper, a novel technique to achieve precise temperatures in food sterilization has been proposed. An accurate temperature profile is needed in order to reach a commitment between the total removal of pathogens inside the product and the preservation of nutritional and organoleptic characteristics. The minimal variation of the target temperature in the sample by means of a monitoring and control software platform, allowing temperature stabilization over 100 °C, is the main goal of this work. A cylindrical microwave oven, under pressure conditions and continuous control of the microwave supply power as function of the final temperature inside the sample, has been designed and developed with conditions of single-mode resonance. The uniform heating in the product is achieved by means of sample movement and the self-regulated power control using the measured temperature. Finally, for testing the sterilization of food with this technology, specific biological validation based on Bacillus cereus as a biosensor of heat inactivation has been incorporated as a distribution along the sample in the experimental process to measure the colony-forming units (CFUs) for different food samples (laboratory medium, soup, or fish-based animal by-products). The obtained results allow the validation of this new technology for food sterilization with precise control of the microwave system to ensure the uniform elimination of pathogens using high temperatures.

Non Thermal Pasteurization for Orange Juice Using Pulsed Electric Field

Pasteurization is an act or a process to minimize or eliminate all forms of life, particularly microorganisms in food products. Its aim is to reduce or eliminate the number of viable pathogens, which are likely to cause diseases. Pasteurization can be in the form of thermal and non-thermal methods. Thermal pasteurization typically uses high heat and temperature to reduce or eliminate microorganisms. Although this method has been practiced and proven effective, the process is associated with many side effects. Due to this problem, new approaches using a non-thermal pasteurization to generate pulsed electric field (PEF) is proposed. In this paper, non-thermal sterilization using Cascaded H-Bridge Multilevel Inverter (CHMI) pulse power generator was evaluated in order to produce pulsed electric field in inactivating of microorganisms such as Saccharomyces cerevisiae and Escherichia coli in orange juice. The experimental set-up was conducted where an orange juice was placed inside the treatment chamber. The electrodes between the treatment chamber were applied with pulsed electric field up to 15 kV/cm by using the CHMI. The hardware development was implemented using MOSFET 2K3748 power devices and the gate signal generator was controlled by using dSPACE DS 1104. The experimental results show that, an output voltage of 1.2 kVp−p was effective to inactivate Escherichia coli and Saccharomyces cerevisiae. Thus, power consumption was decreased and energy was saved. The pulsed width of 1000 μs with repetitive rate of 50 Hz was generated from the hardware implementation. The results proved that the specifications of the experimental set-up meet the requirements for liquid food sterilization, particularly to inactivate Escherichia coli and Saccharomyces cerevisiae microorganisms in orange juice by using streaking plate techniques.