Food Sterilization Research Articles

Computer-aided engineering: Quantification of the heating non-uniformity and distribution of the thermal load occurring during continuous ohmic and conventional thermal food sterilization

The characterization of continuous thermal processing (CTP) is a crucial aspect in the design and selection of technologies for the production of safe products with optimal quality retention after the thermal stress. Conventional methods for CTP characterization are constrained in their capacity to comprehensively capture the complex dynamics of fluid flow through pipelines and the different heating principles that contribute to local temperature variations. These methods rely on isolated local temperature measurements, which fail to account for the intricate interactions between temperature, heat transfer phenomena and fluid dynamics. In view of the aforementioned limitations, this study presents the implementation of a computational fluid dynamic digital model as a toolbox for the characterization and comparison of a conventional heating (CH) ultra-high temperature (UHT) sterilization process and ohmic heating (OH) UHT sterilization. This serves as a tool for an extensive and accurate comparison of the two processes. The model enabled the estimation of each technology's thermal load through the F0 value, thereby providing a more comprehensive assessment than local temperature measurements alone. Furthermore, this approach accounted for the flow behavior throughout the sterilization process. This strategy demonstrated that 2.5 % of the food product is exposed to an up to 75.4 times the average thermal load, whereas for OH treatments only 0.4 % of the product was exposed up to 5.1 times the average thermal load. This is due to the volumetric heating feature of OH, which leads to a 54.7 % reduction in the cooking grade of the product. Furthermore, the computer-aided comparison revealed no statistically significant difference (p-value of 0.6) between the two technologies in their capacity to inactivate Geobacillus stearothermophilus spores in terms of thermal load. This study highlights the importance of computer-aided engineering methodologies for the technological assessment of food sterilization processes prior to industrial transfer.

Food Preservation in the Industrial Revolution Epoch: Innovative High Pressure Processing (HPP, HPT) for the 21st-Century Sustainable Society.

The paper presents the 'progressive review' for high pressure preservation/processing (HPP) (cold pasteurization) of foods and the next-generation high-pressure and high temperature (HPHT, HPT) food sterilization technologies. It recalls the basics of HPP and HPT, showing their key features and advantages. It does not repeat detailed results regarding HPP and HPT implementations for specific foods, available in numerous excellent review papers. This report focuses on HPP and HPT-related issues that remain challenging and can hinder further progress. For HPP implementations, the reliable modeling of microorganisms' number decay after different times of high pressure treatment or product storage is essential. This report indicates significant problems with model equations standard nonlinear fitting paradigm and introduces the distortion-sensitive routine enabling the ultimate validation. An innovative concept based on the barocaloric effect is proposed for the new generation of HPT technology. The required high temperature appears only for a strictly defined short time period controlled by the maximal pressure value. Results of the feasibility test using neopentyl glycol as the barocaloric medium are presented. Attention is also paid to feedback interactions between socioeconomic and technological issues in the ongoing Industrial Revolution epoch. It indicates economic constraints for HPP and HPT developments and emerging business possibilities. The discussion recalls the inherent feedback interactions between technological and socioeconomic innovations as the driving force for the Industrial Revolution epoch.

Rational Design of Triboelectric Materials and Devices for Self‐Powered Food Sensing

AbstractAgainst the backdrop of rapid advancements in 5G and Internet of Things (IoT) technologies, there is an urgent need to upgrade food sensing systems to achieve automation, digitalization, and intelligence. However, this transformation process faces numerous challenges. Triboelectric nanogenerators (TENGs), as an emerging energy conversion and sensing technology, play a crucial role in this context. They not only provide power to functional devices but also serve as sensors in multifunctional self‐powered food sensing systems, capable of detecting various physical and chemical information. This review explores the development of TENGs in the field of food sensing, focusing on the working principles of their self‐powered sensing. The review also systematically organizes and classifies the material and device designs used for TENGs in various food applications. Based on the performance of TENGs, a detailed introduction is provided on the specific applications of self‐powered food sterilization, self‐powered food quality monitoring, and self‐powered taste sensing in the field of food safety. Finally, this paper discusses the challenges and corresponding strategies of TENGs in the food sensing field. The aim is to further promote unmanned and smart services and management in the food sector and to provide new research perspectives.

The viable but non-culturable (VBNC) status of Shewanella putrefaciens (S. putrefaciens) with thermosonication (TS) treatment

Although thermosonication (TS) treatment has been widely used in food sterilization, the viable but non‐culturable (VBNC) of bacteria with TS treatment has still concerned potential food safety and public health. The molecular mechanism of VBNC status of bacteria with TS treatment is not clearly known. Therefore, in this study, we used Shewanella putrefaciens, which was a common putrefactive bacteria in aquatic products, to study the VBNC state of bacteria with TS treatment. Firstly, our results revealed that S. putrefaciens still could enter the VBNC state after TS treatments: 50 kHz, 300 W, 30 min ultrasonic treatment and 70 °C heating; Subsequently, we found the VBNC state of S. putrefaciens can resist the damage of TS treatment, such as cell wall break, DNA degradation, etc; Finally, four-dimensional data-independent acquisition-based proteomics showed that under VBNC state, S. putrefaciens upregulated functional proteins to resist TS treatment, such as: ribosomal proteins to accelerate the synthesis of stress proteins to counteract TS treatments, ornithine decarboxylase SpeF and MraY to repair TS treatment-induced damage, etc. Meanwhile, S. putrefaciens downregulates metabolic and transport functional proteins such as dehydrogenase to reduce the metabolism. Importantly, among those proteins, the ribosomal transcriptional regulatory protein family, such as rpsB, etc, may be the key proteins for S. putrefaciens entering VBNC state. This finding can provide some new strategies for preventing VBNC status of bacteria with TS treatment, such as: inhibition of key proteins, etc.

Evaluation of antimicrobial photodynamic activity of CuminUP60®- A commercially-available high-soluble curcumin

Curcumin, a polyphenol extracted from Curcuma longa L. with a variety of biological and pharmacological activities, has been identified as a promising photosensitizer for food sterilization. However, its low aqueous solubility and bioavailability greatly restrict the practical application of curcumin. In the last decades, a number of approaches have been proposed to address this challenge, with several having already attained notable commercial viability. CuminUP60®, a patented curcumin complex consisting of curcumin extract and Poloxam407, has gathered attention in commercial realms for its enhanced solubility, bioavailability and therapeutic potential. However, the antimicrobial photodynamic activity of this novel curcumin complex has not been investigated. In the current study, we found that CuminUP60® showed a maximum absorption intensity at 434 nm with capability to produce Reactive Oxygen Species (ROS) upon blue light excitation. Furthermore, CuminUP60® showed desirable bactericidal activity against a range of typical foodborne bacteria including Staphylococcus aureus, Listeria monocytogenes Vibrio parahaemolyticus, Shewanella putrefaciens, Pseudomonas fluorescens (MIC = 83.33 μM) and Escherichia coli (MIC = 166.66 μM) upon blue light (5.3 mW/cm2) illumination for 30 min. Taken together, the results demonstrated that CuminUP60® possess desirable antibacterial photodynamic activity, which could provide crucial support for the development of industrially applicable photodynamic sterilization systems within the food industry.

Cold Atmospheric Pressure Plasma Solutions for Sustainable Food Packaging.

Increasing the number of resistant bacteria resistant to treatment is one of the leading causes of death worldwide. These bacteria are created in wounds and injuries and can be transferred through hospital equipment. Various attempts have been made to treat these bacteria in recent years, such as using different drugs and new sterilization methods. However, some bacteria resist drugs, and other traditional methods cannot destroy them. In the meantime, various studies have shown that cold atmospheric plasma can kill these bacteria through different mechanisms, making cold plasma a promising tool to deactivate bacteria. This new technology can be effectively used in the food industry because it has the potential to inactivate microorganisms such as spores and microbial toxins and increase the wettability and printability of polymers to pack fresh and dried food. It can also increase the shelf life of food without leaving any residue or chemical effluent. This paper investigates cold plasma's potential, advantages, and disadvantages in the food industry and sterilization.

Fitting Monte Carlo simulation results with an empirical model of megavoltage x-ray beams for rapid depth dose calculations in water

Objective. The purpose of this study was to assess a method of accelerating Monte Carlo simulations for modeling depth dose distributions from megavoltage x-ray beams by fitting them to an empirically-derived function. Approach. Using Geant4, multiple simulations of a typical medical linear accelerator beam in water and in water with an air cavity were conducted with varying numbers of initial electrons. The resulting percent depth dose curves were compared to published data from actual linear accelerator measurements. Two methods were employed to reduce computation time for this modeling process. First, an empirical function derived from measurements at a particular linear accelerator energy, source-to-surface distance, and field size was used to directly fit the simulated data. Second, a linear regression was performed to predict the empirical function’s parameters for simulations with more initial electrons. Main results. Fitting simulated depth dose curves with the empirical function yielded significant improvements in either accuracy or computation time, corresponding to the two methods described. When compared to published measurements, the maximum error for the largest simulation was 5.58%, which was reduced to 2.01% with the best fit of the function. Fitting the empirical function around the air cavity heterogeneity resulted in errors less than 2.5% at the interfaces. The linear regression prediction modestly improved the same simulation with a maximum error of 4.22%, while reducing the required computation time from 66.53 h to 43.75 h. Significance. This study demonstrates the effective use of empirical functions to expedite Monte Carlo simulations for a range of applications from radiation protection to food sterilization. These results are particularly impactful in radiation therapy treatment planning, where time and accuracy are especially valuable. Employing these methods may improve patient outcomes by ensuring that dose delivery more accurately matches the prescription or by shortening the preparation time before treatment in Monte Carlo-based treatment planning systems.

Inactivation effects of combined thermosonication and potassium sorbate treatments on Bacillus subtilis spores.

This study aimed to investigate the inactivation effect of combined TS (thermosonication) and PS (potassium sorbate) treatments on Bacillus subtilis spores. The inactivation effect and potential mechanisms were examined using plate counts, OD600 values, nucleic acid leakage, DPA (dipicolinic acid) leakage, flow cytometry, and FTIR (Fourier transform infrared spectroscopy). The results showed that, after TS + PS treatments, the integrity of the inner membrane was lost, the permeability of the inner membrane to water molecules was increased, and the intraspore substances leaked. Furthermore, the OD600 value was reduced, indicating that the spore core hydration was enhanced. Spores proportion with damaged inner membrane was significantly increased to 66%, the ordered secondary structure of the protein was changed into a disordered structure and nucleic acid was fragmented after TS + PS treatment. The results indicated that the combined TS and PS treatments may be a useful method for inactivating bacterial spores in food processing and sterilization.

Smart windows based on ultraviolet-B persistent luminescence phosphors for bacterial inhibition and food preservation

Herein, ultraviolet B (UVB) persistent luminescence phosphors containing SrAl12O19: Ce3+, Sc3+ nanoparticles were reported. Thermoluminescence (TL) spectrum analysis reveals that the shallow trap induced by Sc3+ co-doping plays an important role in photoluminescence persistent luminescence (PersL) development, while the deep trap dominates the generation of optical stimulated luminescence (OSL). Owing the appearance of deep trap, the OSL is observed under light (700 nm - 900 nm) excitation. UVB luminescence exerts good bactericidal effects on pathogenic bacteria involved in the process of food spoilage. Thus, the smart window with SrAl12O19: Ce3+, Sc3+/PDMS produces UVB PersL to efficiently inactivate Escherichia coli and Staphylococcus aureus. In addition, the presence of the smart window delays the critical point of pork decay, and greatly reduces the time of pork spoilage. It maximizes the convenience of eradicating bacteria and preserving food, thus offering a fresh perspective on the use of UV light for food sterilization and preservation.

Nonthermal Sterilization of Animal-based Foods by Intense Pulsed Light Treatment.

The consumption of meat has been increasing, leading to a dynamic meat and meat processing industry. To maintain the quality and safety of meat products, various technologies have been explored, including intense pulsed light (IPL) technology. Several factors affect the inactivation of microorganisms by IPL treatment, including light intensity (fluence), treatment duration, pulse frequency, and the distance between the lamp and the samples. Meat products have been studied for IPL treatment, resulting in microbial reductions of approximately 0.4-2.4 Log. There are also impacts on color, sensory attributes, and physico-chemical quality, depending on treatment conditions. Processed meat products like sausages and ham have shown microbial reductions of around 0.1-4 Log with IPL treatment. IPL treatment has minimal impact on color and lipid oxidation in these products. Egg products and dairy items can also benefit from IPL treatment, achieving microbial reductions of around 1-7.8 Log. The effect on product quality varies depending on the treatment conditions. IPL technology has shown promise in enhancing the safety and quality of various food products, including meat, processed meat, egg products, and dairy items. However, the research results on animal-based food are not diverse and fragmentary, this study discusses the future research direction and industrial application through a review of these researches.

Advancing sustainable seawater disinfection: Enhanced inactivation and mechanism of pulsed UV-LEDs irradiation on Tetraselmis sp.

Ultraviolet light-emitting diodes (UV-LEDs), as a novel ultraviolet light source with flexible pulse mode, has gained significant attention for applications in water disinfection and food sterilization. This study investigated the comparative inactivation efficiency of Tetraselmis sp. with continuous and pulsed UV-LEDs irradiation, exploring different wavelengths, duty rates and pulse frequencies. The results reveal a significant enhancement in inactivation efficiency (p < 0.05) under pulsed conditions even at the same UV dose, with inactivation efficiency increasing as duty rate or pulse frequency decreases. The optimal conditions for achieving peak inactivation efficacy are identified as a duty rate of 50% and a pulse frequency of 5 Hz. Within this parameter space, pulsed irradiation leads to a remarkable 1.7-fold increase in inactivation efficiency at UV265 nm and a 1.5-fold increase at UV285 nm compared to continuous irradiation, respectively. Additionally, the disruptive impacts on photosynthetic performance are more pronounced with pulsed irradiation, particularly at the 5 Hz pulse frequency. In shed of these findings, the application of pulsed UV-LEDs irradiation emerges as a promising alternative to the conventional continuous UV disinfection methods in the area of seawater disinfection, offering higher disinfection efficacy and energy consumption.

Allergenic risk assessment of enolase leaked from Saccharomyces cerevisiae under pressurization

High hydrostatic pressure (HHP) is widely employed in food sterilization and processing, but it can release the allergenic proteins into the food matrix, raising the risk of sensitization. In this research, the leaked allergen enolase from Saccharomyces cerevisiae after HHP-treatment was characterized and quantified by ELISA, Western-blot, and LC-MS/MS. MS2 results indicated that the amounts of leaked enolase following untreated, 300 MPa, and 600 MPa were respectively 0.0291, 0.0816, and 0.229 μg/mL. This illustrated a progressive release of the allergen under HHP. Furthermore, Molecular docking experiments demonstrated that enolase binds ARD1, GMP1 and TDH3 during the leakage process, affecting its allergenicity. The implications of these findings are noteworthy for comprehending the safety hazards of allergens in the context of HHP processing and for advocating the adoption of HHP technology in the food sector.

Release of anthocyanins encapsulated by high hydrostatic pressure-treated micellar casein: Effect of serum Ca2+ level during in vitro digestion

Anthocyanins (ACNs) possess the natural advantage of gastric stabilization and has the potential to be adopted for the delivery system design for prolonged gastric release to enhance its bioavailability. In this study, micellar casein treated with high hydrostatic pressure (100, 300, and 500 MPa) was applied to load ACNs, and exogenous serum Ca2+ (0.15, 2, and 5 mM) controlled the gastric aggregation behavior of casein during in vitro digestion. The results showed that the high level of pressure dissociated the micellar structure and provided more cross-linking possibilities for serum Ca2+. Furthermore, the high serum Ca2+ level enhanced gastric aggregation of casein subunits and submicelles leading to delayed gastric emptying, and controlled the slow release of ACNs, which contributed to prolong the ACN retention in the stomach. Industrial relevanceThe application of high hydrostatic pressure (HHP) in food sterilization has been relatively mature, and there is an urgent need to expand it toward the nutritional and health field in search of high added value. Herein, HHP was applied to solve the problem of low bioavailability of ACNs based on the ingenious relationship between HHP and casein micelles. The research data can help to develop nutraceuticals or high satiety foods with ACNs as the main functional component at low cost.

Calcined and Hydrated Shell Powder with Layered Porous Structures for Food Sterilization and Pesticide Residue Removal

Shell powder, a natural source product with excellent adsorption and antibacterial properties, has exhibited a broad application prospect in daily life. Herein, low-temperature calcined shell powder (LCSP) and high-temperature calcined and hydrated shell powder (HCSP) were prepared using shells as raw materials in different calcination processes. The surface structures and the chemical compositions were analyzed and the specific surface areas and pore size distributions were measured. The LCSP and HCSP reserved the unique layered porous structures of the shell. The main composition of LCSP is CaCO3, which also contains a small number of organisms. The main composition of HCSP is Ca (OH)2, which also contains CaO and a small amount of CaCO3. According to the better adsorption characteristic of the HCSP, the antibacterial activities and the removal abilities of pesticide residues of HCSP were systematically studied. The results indicated that HCSP exhibited excellent antibacterial activity (> 99.99%) and high efficiency in removing common pesticide residues (> 90%).

Bactericidal Efficacy and Mechanisms of Non-Electrolytic Slightly Acidic Hypochlorous Water on Pseudomonas fragi and Pseudomonas fluorescens.

Chilled pork is frequently contaminated with Pseudomonas fragi and Pseudomonas fluorescens. In this study, the bactericidal efficacy and mechanisms of non-electrolytic slightly acidic hypochlorous water (NE-SAHW) against two strains of these two species were evaluated. The results showed that the antibacterial efficacy of NE-SAHW was positively correlated with the concentration level of NE-SAHW and negatively correlated with the initial populations of the strains. The strains of small populations were completely inhibited when provided with each level of NE-SAHW. The killed cells of P. fragi were 0.94, 1.39, 4.02, and 5.60 log10 CFU/mL, respectively, and of P. fluorescens they were 1.21, 1.52, 4.14, and 5.74 log10 CFU/mL, respectively, when the initial populations of the strains were at high levels (about 7 log10 CFU/mL). Both strains were completely killed within 12 s with the available chlorine concentration (ACC) of 50 mg/L of NE-SAHW. Morphological changes in both cells were observed by using a Scanning Electron Microscope (SEM) and it was discovered that the cell membranes were damaged, which led to the leakage of the intracellular substances, including K+, nucleic acid, and protein. In terms of the Fourier Transform Infrared Spectroscopy (FTIR) results, NE-SAHW destroyed the structures of membrane proteins and cell structure proteins, and influenced the composition of polysaccharides. The bacteria were definitely dead after treatment by NE-SAHW compared to the control according to the results of flow cytometry. These results demonstrated the potential bactericidal property of NE-SAHW when applied to the meat and other food sterilization industries.

A novel antibacterial mechanism of atmospheric cold plasma against Staphylococcus aureus through degradation of cellular staphyloxanthin

Atmospheric cold plasma (ACP) is an emerging non-thermal food sterilization technology. This study investigated the effects of ACP on the antioxidant membrane-bound triterpenoid carotenoid pigment (staphyloxanthin, STX) in S. aureus. Results showed that the survival rate of S. aureus in water (1.3 × 107 CFU/mL) after ACP treatment for 5, 10, 15, 20 min significantly decreased to 55.0%, 18.5%, 9.7% and 4.1%, accompanied by a decrease of STX content from 448.8 to 276.7, 80.3, 45.1 and 19.7 μg/mL, respectively. Particularly, 20-min ACP-treated S. aureus became more susceptible (4.79 times) to hydrogen peroxide (0.1 M) attack most probably due to the decrease of STX. ACP also caused a decrease in the cell membrane potential (MP), accumulation of intracellular reactive oxygen species (ROS), and cell necrosis. Pearson correlation analysis indicated that the survival rate, MP, intracellular ROS, and cell necrosis were all highly correlated to STX content, indicating that STX contributed to ACP-induced physiological alterations in S. aureus. These results demonstrated that STX was an important attack target during ACP inactivation of S. aureus. Industrial relevanceThis study proposes a novel antibacterial mechanism of ACP against S. aureus from the perspective of STX, which would accelerate the development of ACP in food sterilization. Noting that pigmentation is a hallmark of multiple foodborne pathogenic microbes, this work shows the exciting potential of inactivating foodborne pathogens through destroying their intrinsic pigments.

Aseptic microwave sterilization and validation of food containing particles

Microwave and ohmic heating are becoming a more popular choice for heating in aseptic processing due to rapid heating for bacteriological destruction and better product quality. Due to regulatory constraints and the complexities of validation requirements, the food industry has been struggling to launch aseptic low-acid products containing particles into the market with confidence. This study aims to find an alternative approach to simulate and mimic processing conditions by modeling and validating the model process by using surrogate particles and microorganisms. A mathematical model was used to simulate the heat transfer in the carrier fluid and solid particles. For the validation of the process, a simulated particle was designed to create the worst-case conditions, being both the fastest moving and slowest heating compared to the real food particles. These particles with conservative thermal and physical properties were inoculated with Geobacillus stearothermophilus spores as a surrogate microorganism for the microbiological validation of the thermal process. Magnetic implants were embedded in simulated spherical particles (12.77 mm and 15.88 mm) to measure the residence time distribution. Total accumulated lethality using the surrogate system was estimated at F0 > 7.7 min. The microwave aseptic system was microbiologically validated to produce shelf-stable particulate food products.

Numerical study of the effects of pulsed electric field on β-casein

As a non-thermal microbial inactivation technology, pulsed electric field (PEF) treatment can be used in liquid food sterilization. It is necessary to investigate the effects and mechanisms of PEF on the important contents of liquid food. In this study, molecular dynamics (MD) simulation and multiple structural analyses were employed to investigate the effects of PEF on β-casein (BCN) molecule. The investigation focused on examining the impact of PEF on molecular conformation, flexibility, electrostatic properties, and solvent interactions. Results found that high-intensity pulsed electric fields can cause irreversibly complete unfolding of BCN molecule within a picosecond timeframe. The applied PEF changed the dipole moment of BCN molecules, leading to the reorientation of residues towards the direction of the applied electric field. Furthermore, the electric field-induced movement of hydrophobic and hydrophilic residues within the BCN molecules was observed, resulting in concomitant changes in the solvent accessible surface area (SASA) of BCN molecule.Industrial relevance: PEF is an emerging non-thermal processing technology in the food industry. MD simulations were employed to investigate the conformational changes of BCN under different pulse electric fields and exposure times. Our study elucidates the fundamental mechanism of PEF's interaction with protein molecules and may contribute to improving the functional properties of this protein. Analysis at the molecular level can be experimentally validated, providing a theoretical foundation for the widespread application of PEF technology in protein-containing food systems.

Investigation of 60Co Irradiation on the Volatile Organic Compounds from Finger Citron (Citri Sarcodactylis Fructus) Using GC-IMS.

In recent years, as the desire for a healthy lifestyle has become more widespread, consumers are gaining an increasing appreciation for safe, high-quality food. Researchers are constantly seeking new ways to protect foods from insect pests and fungi. This study used GC-IMS to analyze the volatile organic compounds and flavor characteristics of Finger Citron in response to different doses of 60Co irradiation. The principal component analysis method was used to explore the overall differences in flavor spectra, and a total of 60 compounds were identified. The fingerprints of volatile organic compounds in the samples showed that the volatile organic compounds with doses of 60Co irradiation in about 0 kGy and 5 kGy are similar, while the 10 kGy samples are quite different. The PCA results showed that the similarity between 0 kGy and 5 kGy was slightly higher, and the difference between 10 kGy and other samples was greater. Therefore, it was determined that 60Co irradiation with a 10 kGy intensity has a significant influence on the content of volatile oils components, while 60Co irradiation with a 5 kGy intensity has little effect. Irradiation technology is demonstrated as a promising method of food sterilization, but the irradiation dose and chemical composition must be taken into consideration.

The electron beam irradiation of collagen in the dry and gel states: The effect of the dose and water content from the primary to the quaternary levels

The aim of our study was to describe the impact of collagen in the gel and dry state to various doses of electron beam radiation (1, 10 and 25 kGy) which are using for food processing and sterilization. The changes in the chemical compositions (water, amino acids, lipids, glycosaminoglycans) were analyzed and the changes in the structure (triple-helix or β-sheet, the integrity of the collagen) were assessed. Subsequently, the impact of the applied doses on the mechanical properties, stability in the enzymatic environment, swelling and morphology were determined. The irradiated gels evinced enhanced degrees of cross-linking with only partial degradation. Nevertheless, an increase was observed in their stability manifested via a higher degree of resistance to the enzymatic environment, a reduction in swelling and, in terms of the mechanical behaviour, an approximation to the non-linear behavior of native tissues. In contrast, irradiation in the dry state exerted a somewhat negative impact on the observed properties and was manifested mainly via the scission of the collagen molecule and via a lower degree of stability in the aqueous and enzymatic environments. Neither the chemical composition nor the morphology was affected by irradiation.