Mild Thermal Treatment Research Articles

Effects of Pulsed Electric Field and Thermal Treatments on Microbial Reduction, Volatile Composition, and Sensory Properties of Orange Juice, and Their Characterization by a Principal Component Analysis

The effects of pulsed electric field (PEF) treatments on microbial reduction, volatile composition, and sensory characteristics of orange juice were investigated. Mild (Thermal-1) and intensive (Thermal-2) thermal treatments were applied for comparison. A pilot-scale PEF system, with a flow rate of 30 L/h and maximum field strength of 20 kV/cm, was used. PEF treatment at a specific energy of 150 kJ/L resulted in 9.0 and 8.0 decimal reductions of Escherichia coli and Saccharomyces cerevisiae, respectively. The PEF treatments preserved the characteristic compounds associated with a fresh flavor (e.g., dl-limonene, β-myrcene, α-pinene, and valencene) more effectively than an intensive thermal treatment. This was verified by descriptive analysis of sensory evaluations. Based on the principal component analyses (PCAs) and partial least-squares (PLS) regression analyses, PEF-treated orange juice showed higher similarity to untreated orange juice. Our results indicate that PEF may be an alternative processing technique that can preserve the fresh flavor and taste of freshly squeezed orange juice.

Facile mechanochemical synthesis of highly mesoporous γ-Al2O3 using boehmite

A facile ball milling process was used to obtain mesoporous crystalline γ-alumina with high specific surface area up to 389 m 2 g −1 and large pore volume up to 1.55 cm 3 g −1 from boehmite. First boehmite particles were efficiently dispersed into small nanocrystals, which was achieved by using ball milling with addition of a small amount of diluted nitric acid. Such pulverized alumina precursor showed the ability to self-assemble in the presence of block copolymer into mesostructures upon continued milling. Next, the direct mild thermal treatment was used to remove polymeric micelles and achieve the desired crystallinity. The as-obtained mesoporous crystalline γ-alumina is highly suitable for several applications such as catalysis and adsorption. • Research Highlights: • Mesoporous crystalline alumina with high surface area and uniform porosity. • A facile ball milling preparation of boehmite small nanocrystals. • Block copolymer-assisted assembly of boehmite into mesostructures upon milling.

Efficacy of mild thermal and pulsed light treatments, individually applied or in combination, for maintaining postharvest quality of strawberry cv. Albion

Fil: Contigiani, Eunice Valentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Industrias. Instituto de Tecnologia de Alimentos y Procesos Quimicos. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Tecnologia de Alimentos y Procesos Quimicos.; Argentina

Performance of combined technologies for the inactivation of Saccharomyces cerevisiae and Escherichia coli in pomegranate juice: The effects of a continuous‐flow UV‐Microwave system

AbstractDuring the past decade, the application of new technologies such as high pressure, ultrasound, pulsed electric fields, short‐wave ultraviolet C (UVC) light, and microwave (MW) has been thoroughly investigated for food processing. Combinations of UVC light with different technologies have been previously investigated, with promising results when combined with mild thermal treatments. The objective of this work was to study the inactivation of Saccharomyces cerevisiae and Escherichia coli inoculated in pomegranate juice within a unit of UVC‐coiled (254 nm) equipment and the continuous‐flow MW (876 W energy output). Individual and combined treatments were evaluated at two flow rates through the tested systems. The combined technologies notably improved the inactivation of the target microorganisms. Our findings indicated a synergistic effect between the systems, respectively yielding 6.1 and 5.5 log‐cycle reductions in the yeast and bacteria for the UVC–MW treatment with a flow rate of 400 ml/min. When increasing the flow rate, different results were observed, depending on the temperature pattern. A dynamic model was obtained for MW temperature profiles and residence time distributions for the studied systems to better explain the obtained results.Practical applicationsNowadays, alternative food‐processing technologies are under research to obtain safe, fresh‐tasting, and nutritive foods using mild temperatures or no heat. This work aimed to evaluate a configuration wherein a unit of UVC‐coiled equipment was coupled with a continuous‐flow MW system. Processing times for treating juices can be significantly reduced by combining a UVC coiled equipment with a continuous flow microwave system, because of the enhanced effect of UVC at mild temperatures and the faster heating due to the MW. Its potential implementation will allow the food industry to offer minimally processed products with clean labels and at an affordable cost.

Low Temperature Synthesis of Photocatalytic Mesoporous TiO2 Nanomaterials

We report the synthesis of mesoporous TiO2 nanostructures based on the decomposition of TiOSO4 in aqueous alkaline solution at room temperature, followed by mild thermal treatment (110 °C) in an oven and suitable to yield up to 40 g of product per batch. The duration of the thermal treatment was found to be crucial to control crystalline phase composition, specific surface area, surface chemistry and, accordingly, the photocatalytic properties of the obtained TiO2 nanocrystals. The thorough investigation of the prepared samples allowed us to explain the relationship between the structure of the obtained nanoparticles and their photocatalytic behavior, that was tested in a model reaction. In addition, the advantage of the mild treatment against a harsher calcination at 450 °C was illustrated. The proposed approach represents a facile and sustainable route to promptly access an effective photocatalyst, thus holding a significant promise for the development of solutions suitable to real technological application in environmental depollution.

New Analytical Tools for Unmasking Frauds in Raw Milk-Based Dairy Products: Assessment, Validation and Application to Fiore Sardo PDO Cheese of a RP-HPLC Method for the Evaluation of the α-l-Fucosidase Activity

The activity of α-l-fucosidase (FSC) has been measured for the first time in Fiore Sardo PDO (Protected Designation of Origin) raw milk cheese. To do this, a RP-HPLC method has been developed, validated and tested on a reliable sampling of cheese experimentally produced in laboratory batches. Three experimental factors have been considered in this work: the thermal treatment undergone by the milk, the lactation period and the ripening time of cheese. Results obtained have evidenced: (i) a meaningful reduction in the activity of FSC from cheeses produced using raw milk to those obtained by thermized milk; (ii) an increase in the activity of FSC during the first months of lactation period (from December to February), followed by a substantial constancy in the central and final months of lactation (from February to May); (iii) the enzyme activity is independent of the ripening time. This method might be useful in revealing frauds related to the use of mild thermal treatments of the milk when this is not allowed as for Fiore Sardo PDO cheese but also for several PDO cheeses for which the specifications establish that raw milk only must be used for their production.

Structural changes in lignin of thermally treated eucalyptus wood

Changes in the lignin structure of eight eucalypt species (E. botryoides, E. globulus, E. grandis, E. maculata, E. propinqua, E. rudis, E. saligna, and E. viminalis) upon mild thermal treatment, where the temperature was gradually raised from 160 to 230 °C over 3 h, were studied by solid-state carbon nuclear magnetic resonance (13C NMR) and after lignin isolation from the wood by acidolysis employing liquid-state 1D and 2D NMR techniques. The molecular weight of the isolated lignins was assessed by size exclusion chromatography (SEC) and their composition by analytic pyrolysis coupled with gas chromatography and mass spectrometry (Py-GC/MS). The thermal treatment induced in lignin partial demethylation (up to ca. 30% from total) and a remarkable reduction in β-O-4 structures (up to ca. 60%), in an extent depending on the ratio of syringyl and guaiacyl units of the specific lignins. The lignin molecular weight reduced only ca. 25% under the thermal treatment due to the likely occurrence of condensation reactions by homolytic and heterolytic mechanisms. The noticeable increase in phenylcoumaran (β-5) and pinoresinol/syringaresinol (β-β) structures in lignin after thermal treatment was tentatively explained by their relative thermal resistance and by newly formed structures as the result of radical coupling reactions occurred during homolytic dissociation of the β-O-4 linkages. Lignins in thermally treated wood contained more than twice phenolic hydroxyls and more aliphatic carboxyl groups than lignins in untreated wood.

Surface Modification of Cured Inorganic Foams with Cationic Cellulose Nanocrystals and Their Use as Reactive Filter Media for Anionic Dye Removal.

In this work, a surface cationized inorganic–organic hybrid foam was produced from porous geopolymer (GP) and cellulose nanocrystals (CNCs). GPs were synthesized from alkali-activated metakaolin using H2O2 as a blowing agent and hexadecyltrimethylammonium bromide (CTAB) as a surfactant. These highly porous GPs were combined at pH 7.5 with cationic CNCs that had been synthesized from dissolving pulp through periodate oxidation followed by cationization in a deep eutectic solvent. The GP-CNC hybrid foams were employed as reactive filters in the removal of the anionic dye, methyl orange (MO; 5–10 mg/L, pH 7). The effects of a mild acid wash and thermal treatments on the structure, properties, and adsorption capacity of the GPs with CNCs and MO were investigated. The CNCs aligned as films and filaments on the surfaces of the neutralized GPs and the addition of CNCs improved MO removal by up to 84% compared with the reference sample. In addition, CTAB was found to disrupt the attachment of CNCs on the pores and improve adsorption of MO in the GPs with and without CNCs.

Guanidinium‐Assisted Surface Matrix Engineering for Highly Efficient Perovskite Quantum Dot Photovoltaics

Metal halide perovskite quantum dots (Pe-QDs) are of great interest in new-generation photovoltaics (PVs). However, it remains challenging in the construction of conductive and intact Pe-QD films to maximize their functionality. Herein, a ligand-assisted surface matrix strategy to engineer the surface and packing states of Pe-QD solids is demonstrated by a mild thermal annealing treatment after ligand exchange processing (referred to as "LE-TA") triggered by guanidinium thiocyanate. The "LE-TA" method induces the formation of surface matrix on CsPbI3 QDs, which is dominated by the cationic guanidinium (GA+ ) rather than the SCN- , maintaining the intact cubic structure and facilitating interparticle electrical interaction of QD solids. Consequently, the GA-matrix-confined CsPbI3 QDs exhibit remarkably enhanced charge mobility and carrier diffusion length compared to control ones, leading to a champion power conversion efficiency of 15.21% when assembled in PVs, which is one of the highest among all Pe-QD solar cells. Additionally, the "LE-TA" method shows similar effects when applied to other Pe-QD PV systems like CsPbBr3 and FAPbI3 (FA = formamidinium), indicating its versatility in regulating the surfaces of various Pe-QDs. This work may afford new guidelines to construct electrically conductive and structurally intact Pe-QD solids for efficient optoelectronic devices.

Correction of defective textures in packaged dry-cured pork ham by applying conventional and ultrasonically-assisted mild thermal treatments

Pastiness is a textural defect characterized by an excessive softness and loss of elasticity which lacks corrective actions at industrial level. The objective of this study was to evaluate the textural and microstructural changes of dry-cured pork ham, with different pastiness levels, subjected to conventional and ultrasonically-assisted corrective mild thermal treatments. Pastiness was assessed by an expert sensory panel and hams were classified into three categories: high (HP), medium (MP) and no (NP) pastiness. Ham samples (n = 108) were heated (40 and 50 °C) with power ultrasound (PuS) and without (CV) PuS application. After heating, all of the textural parameters assessed were improved. Hardness increased by 102% and adhesiveness decreased by 55% and the ham became less viscoelastic. The largest modifications were found in the samples heated at 50 °C and no differences were found between CV and PuS treatments. The microstructure of pasty samples revealed that the treatment produced a shrinkage of the myofibrils, which could explain the increase in hardness and the improvement in texture of defective ham.

Engineering of colloidal nanocrystal thin films and their optoelectronic properties: A simple and effective route

This work investigates the effect of heat treatments on CdSe/CdS core–shell nanocrystals assemblies with different sizes and capping ligands. Nanostructured thin films, consisting of an array of CdSe quantum dots embedded in a continuous matrix of CdS, have been obtained by mild thermal treatments of CdSe/CdS core–shell nanocrystals deposited on glass substrates from colloidal solution. These materials are regarded as promising photon upconverters, or absorbers for high-efficiency photovoltaic devices. The treatments were conducted in the range 300–550 °C for up to 150 min. The nanoscale evolution during the heat treatment was investigated by monitoring optical properties of the films. Initially, the well-defined photoluminescence band, corresponding to the first quantum dots exciton state, rapidly shifts towards lower energy, indicating delocalization of the exciton and suggesting that nanocrystal CdS shells are merging by sintering mechanisms, thus forming a continuous matrix. Control over this phase of the heat treatment leads to the desired nanoscale morphology and properties. The kinetics of sintering has been characterized, and the procedure has been systemically applied to CdSe/CdS nanocrystals of different sizes and ligand types. This research provides novel values for the activation energy of the sintering process and strongly support the general applicability of such process to control and optimize optoelectronic properties of nanostructured thin films for applications like light-emitting diodes, tunable emitters and photoconductors among others.

Inactivation by osmotic dehydration and air drying of Salmonella, Shiga toxin-producing Escherichia coli, Listeria monocytogenes, hepatitis A virus and selected surrogates on blueberries

Osmotically dehydrated and air dried berry fruits are used as ingredients for the production of yoghurts, chocolates, cereal bars and mixes, ice creams and cakes and these fruits are often subjected to mild thermal treatments only, posing questions around their microbiological safety. As osmotic dehydration methods and parameters vary considerably within the industry and minimally processed high quality fruits are increasingly sought, the scope of this study was to determine which temperatures are required for the inactivation of relevant bacteria and viruses during osmotic dehydration of berries, using blueberries as a model berry in a thawed state to mimic common industrial practices. Additionally, we studied the inactivation of osmotic dehydration at 23 °C, sometimes referred to “cold infusion” followed by air drying at 100 °C to determine the microbiological safety achieved by this combined treatment. Four pathogens (Salmonella enterica, Escherichia coli O157:H7, Listeria monocytogenes and hepatitis A virus (HAV)) and five surrogates (Enterococcus faecium, Escherichia coli P1, Listeria innocua, murine Norovirus (MNV) and bacteriophage MS2) were inoculated on blueberries and reductions were measured after different treatment combinations. After osmotic dehydration of bacterial strains at 40 °C no survivors were detected on blueberries, with the exception of E. faecium. Inactivation of the viruses at 45 °C showed no survivors for MS2 and mean reductions of 1.5 and 3.4 log10 median tissue culture infectious dose (TCID50)/g for HAV and MNV, respectively. Similarly, in the sugar solution at 40 °C, no survivors were observed, with the exception of E. faecium and the three viruses. The combined process (osmotic dehydration at 23 °C followed by air-drying at 100 °C) achieved an >6 log reduction of all tested bacterial strains and MS2. For HAV and MNV, 2.6 and >3.4 log10 TCID50/g were measured. In summary, the present study shows that osmotic dehydration appears an efficient control measure for the control of L. monocytogenes, S. enterica and E. coli O157:H7 if carried out at 40 °C or at 23 °C and followed by air-drying at 100 °C. Based on the results generated with MNV, the combined treatment is also expected to reduce human Norovirus (NoV) but does not appear to be sufficient to fully control HAV. The results contribute to a better management of the microbial safety of osmotically dehydrated and dried berries and especially the results generated for the viruses emphasize that within a robust food safety management system, safety must be assured through the entire food supply chain and therefore must start at primary production with the implementation of Good Agricultural Practices (GAP).

Effects of pulsed electric fields and mild thermal treatment on antimicrobial efficacy of nisin-loaded pectin nanoparticles for food preservation

Pulsed electric field (PEF) treatment is a common and primarily non-thermal sterilization technique that is used in food processing, which can be improved when combined with food-compatible antimicrobial agents such as nisin. In this work, we have combined the nisin-loaded nanoparticles with mild thermal treatment (40 °C, 2 min) and pulsed electric fields (30 kV/cm; 200 ns – 500 μs protocols, 17.5–87.6 kJ/L) for potentiation of the antimicrobial effects against S. typhimurium and L. innocua. It was demonstrated that PEF treatment efficacy does not linearly depend on the energy delivered to the cells, which highlights the differences in polarization between the two bacteria in sub-microsecond range. The mild thermal treatment improved the efficacy of nisin nanoparticles and allowed to inactivate both bacteria in stationary growth phase, while limit the energy density of PEF in 50–90 kJ/L range. The synergistic effect of PEF and nisin-loaded pectin nanoparticles improved the sensitivity of gram-negative bacteria to nisin.

The role of palladium salt precursors in Pd-PdO/CeO2 catalysts prepared by dry milling for methane oxidation

Heterogeneous catalysts comprising palladium as active phase are widely used to promote a variety of reactions due to the easy tuning of Pd particle size and its oxidation state. When Pd is combined with CeO2, specific structural arrangements at the nanoscale level can strongly impact on activity and durability, especially in methane oxidation. In this work, the effect of different palladium salt precursors on the final state of a Pd/CeO2 catalyst prepared by dry milling was studied by coupling thermogravimetric characterization and temperature-programmed reaction methods. The combination of palladium acetate and a mild oxidative thermal treatment proved successful in generating an appropriate Pd0/Pd2+ mixture on the ceria surface with improved methane oxidation activity.

Upgrading of Venezuela extra-heavy oil vacuum residue by two-step thermal treatment

A two-step thermal treatment approach (TSTT), composed by mild thermal treatment and deep thermal cracking, is proposed to upgrade the Venezuela extra-heavy oil vacuum residue. In comparison to the conventional one-step thermal processing, the use of TSTT increased the liquid yield by 4.4 wt% and reduced the coke yield by 4.0 wt%. The cycle of light gas-oil as hydrogen donor significantly enhanced the percentage of diesel subfraction (200–350 °C) in the liquid product.

Correction to: Synthesis of fluorescent carbon quantum dots (CQDs) through the mild thermal treatment of agro-industrial residues assisted by γ-alumina

Carbon deposits are well known to cover the γ-alumina surface when exposed to high temperatures in the presence of carbonaceous feedstocks by means of coking and/or fouling mechanisms. Herein, it is demonstrated that this phenomenon, which is extremely undesirable when γ-alumina is used as a catalyst or an adsorbent material, can be successfully exploited for the production of fluorescent carbon-based quantum nanodots (CQDs) under mild conditions of temperatures (250–300 °C) and time (30 min) by using residual biomasses as a carbon source. Specifically, four agro-industrial residues including sugar beet pulp (SBP), grape marc, tomato peels and seeds, and olive pomace have been successfully tested for the synthesis of biomass-based CQDs. Different techniques including UV–vis spectroscopy, fluorescence spectroscopy (PL), X-ray photoelectron spectroscopy, Raman spectroscopy, and transmission electron microscopy (TEM) have been applied for the characterization of the as-prepared SBP-based CQDs. Results highlight that the obtained carbon dots exhibit excellent solubility in both water and organic media. In addition, TEM investigations show that such nanoparticles disclose a rather uniform spherical morphology and a narrow size distribution in the range of 2–4 nm. The typical excitation dependent PL emission behavior of carbon-based quantum dots was also observed by PL analysis. Unlike other currently available bottom-up synthesis routes, a high-value by-product is obtained during the synthesis of biomass-based CQDs assisted by γ-Al2O3, i.e., the residual thermally treated biomass, which can be further valorized as a high-quality solid biofuel exhibiting a lower oxygen-to-carbon ratio and, hence, a higher calorific value than the parent biomass. The innovative finding of the present work is that a catalyst can be used to produce CQDs from the volatile matter that is driven off the biomass by heating, which opens up new possibilities of valorization for the off-gas substream coming from other biomass conversion process, like for example slow pyrolysis and carbonization.

Unfolding and Inhibition of Polyphenoloxidase Induced by Acidic pH and Mild Thermal Treatment

The activity of polyphenoloxidase (PPO) treated by acidic pH and mild thermal processing was found to be closely related to the conformational changes. Weakly acidic environment (pH 4.0–6.0) resulted in reversible inhibition of activity and slight changes in the conformation, and refolding of PPO was observed after readjusting pH to 6.8. At pH lower than 4.0, PPO activity was strongly inhibited with great unfolding in conformation and all changes were irreversible. Acidic environment increased the susceptibility of PPO to thermal treatment, and greater changes in activity and conformation of PPO were observed under the combined treatment of acidic pH and mild thermal treatment. Besides, the inactivation of PPO induced by thermal treatment followed a biphasic kinetic model, and acidic pH increased the inactivation rate of labile and stable PPO. The combination of acidic pH and mild thermal processing expected to avoid the nutritional loss and sensory damage in fruits and vegetables caused by severe acid or temperature.

Analysis of polypeptide inter-chain entanglements using swelling dynamics of a spin coated protein layer

A study of swelling dynamics was applied to analyze the internal structure with regard to inter-chain entanglements of a bio-molecular film. Lysozyme – an enzyme protein was spun coated on silicon substrates to study swelling dynamics when exposed to water vapor. Two different samples were prepared with two different spinning speeds with 500 and 1000 rpm. The changes in the thickness of the films were progressively monitored using x-ray reflectivity technique as a function of time till the saturation of thickness. The swelling dynamics for protein layer were fitted with an existing polyelectrolyte chain swelling model. The fittings were used to obtain diffusion coefficient and charge fraction. It was found that the spinning speed strongly affects the swelling dynamics, charge fraction and saturation thickness. The slower dynamics in 1000 rpm film were attributed to inter-chain entanglements arising due to higher degree of compression during spinning. The enhanced degree of inter-chain entanglements leads to complete loss of swelling functionality on a mild thermal treatment. This study has stronger implication for the analysis of internal structure of homogeneous biomolecular films for inter-chain entanglements which are otherwise difficult to infer from direct space measurement techniques.

Mechanical and transport properties of fibrous amorphous silica meshes and membranes fabricated from compressed electrospun precursor fibers

Highly porous, 0.1–1.5 mm thick fibrous amorphous silica (FAS) meshes with 500 ± 200 nm fiber diameters were prepared from the precursor fibers made by a high-yield free-surface alternating field electrospinning (AFES) process. A combination of mild thermal and pressure treatment of the fibrous precursor material before the calcination step was used to tailor the mechanical and transport properties of the resulting FAS structures. Compression of the as-spun material determined the resulting porosity, effective fiber diameter, and microarchitecture of the FAS structures when calcined between 600 and 1000 °C. Flexible FAS meshes and membranes revealed the tensile strength and modulus up to 1.4 MPa and 580 MPa, respectively, and Darcy'S permeability coefficient in a range of 1.2 × 10−12–1.6 × 10−11 m2. Taking into consideration the compression-dependent effective fiber diameter, the permeability of compressed FAS membranes fitted the models developed for two-dimensional fibrous layer architectures with partial fiber alignment within the stacked layers.

Characterizing Lithiation/Delithiation of Thick Electrodes without Binders and Conductive Additives Using Neutron Imaging

The advantages of thick electrodes in improving energy density at the cell level has been reported in many lithium-ion battery papers. Thick electrodes increase energy density by reducing the fraction of the cell dedicated to inactive components, in particular current collectors and separators. However, thick electrodes increase electron and ion transport path lengths through the electrode which increases cell resistance and can result in limited current densities of battery operation. In this presentation the fabrication and characterization of cells with thick electrodes will be described. These electrodes are produced via hydraulic pressing and mild thermal treatment of active material powders as opposed to conventional casting of composite slurries. These electrodes thus have no binders or conductive additives, which would be expected to increase the diffusion of ions through the electrolyte-impregnated void regions within the electrode. However, these all active material electrodes can now have multiple processes that might limit their rate of charge/discharge, including transport of ions through the electrode microstructure, transport of ions through the solid active material particles, and transport of electrons through the all active material electrode matrix to the current collector. To provide insights into the processes that are limiting the current density in the high energy electrodes, we will describe the use of neutron imaging. Neutron imaging is highly sensitive to the lithium concentration within the battery cell, and thus regions undergoing lithiation/delithiation can be interrogated in operando during charge/discharge of the cell. The lithiation/delithiation profiles provide insights into what process limits the cell and opportunities to improve the performance of these thick electrodes fabricated with less common processing routes.