High Thermal Treatment Research Articles

Effects of TiCl<SUB>4</SUB> Post-Treatment on the Efficiency of Dye-Sensitized Solar Cells

The effects of compact TiO2 overlayers, deposited on TiO2 photoelectrodes through the hydrolysis of TiCl4, on the overall performance of dye-sensitized solar cells (DSSCs) were investigated. A thermal treatment at high-enough temperature was required for a more effective and higher dye-loading of the compact TiO2 overlayers. This led to improvements in the crystallinity and porosity of the layer, which contributed to higher power conversion efficiencies (PCE) of DSSCs compared with the electrodes prepared at relatively lower temperatures. Moreover, the existence of an additional secondary overlayer led to an increase in the net PCE of the cells by increasing the amount of dye-loading, even though this layer itself, in the absence of a first overlayer formed under high thermal treatment, did not enhance cell efficiency, because of the higher charge transport resistance over the layers and an increase in surface states.

Design of plurimetallic catalysts for solid biomass conversion: Batch versus continuous reactors

Catalysts composed of plurimetallic particles (Cu, Ni and Ru) supported on Keggin type polyanion salts (Cs2.5H0.5PW12O40) are synthesized and characterized by various physicochemical techniques. Several catalysts have been prepared in this view by varying the metal content. The organic yield obtained with CuNi2Ru1@CsPW catalyst (ca. 30wt.%) is two times higher than the one found for the bimetallic CuRu1@CsPW and close to the activity of CuRu2@CsPW material. In the batch reactor, a high yield of good quality biofuel is obtained. However, the catalyst reusability is compromised due to high thermal treatment required for the charcoal removal from the surface of the material which causes catalyst degradation and particles sintering. Moreover, the accumulation of ashes on the catalyst surface decreases the active species accessibility. To avoid the contamination of the catalyst with ashes and charcoal, hydrotreatment process is combined with slow pyrolysis of biomass. Indeed, the pyrolysis oil resulted from thermal decomposition of biomass is treated in a fixed bed reactor containing CuNi2Ru1@CsPW. In this case, the catalytic activity is low, only 15wt.% of biofuel is obtained, but the activity is stable even after four catalytic cycles.

Volatile profile of human milk subjected to high-pressure thermal processing

High pressure thermal (HPT) treatments consist of a combination of high pressure (500–900MPa) and temperature (70–120°C) over a short holding time. The rapid temperature increase during compression and temperature decrease in the product upon decompression could help to reduce the hardness of thermal effects encountered in conventional thermal technologies. The objective of this study was to evaluate the effect of HPT processing (300, 600 and 900MPa combined with 50, 65 and 80°C) on the profile of volatile compounds in breast milk. A total of 50 volatiles, belonging to 6 different chemical groups, were detected in milk samples. In general, HPT processing increased aldehydes, ketones, furans and pyrans, as well as alcohols, however, it did not modify the levels of carboxylic acids, and reduced the content of aliphatic hydrocarbons present in the non-treated human milk samples. HPT processing enhanced the total area content of volatile compounds derived from Maillard and lipid oxidation reactions, these changes being subjected to the intensity of pressure and temperature applied. Given that the levels of volatiles were significantly modified after the application of HPT processing, we can conclude that the range of the intensity of the treatments selected was not adequate to preserve the original profile of volatile compounds in breast milk.

Phase properties of carbon-supported platinum–gold nanoparticles for formic acid eletro-oxidation

The design of active and robust bimetallic nanocatalysts requires the control of the nanoscale alloying, phase-segregation and the correlation between nanoscale phase-segregation and catalytic properties. To enhance the performance and durability of formic acid oxidation reaction in fuel-cell applications, we prepared a platinum–gold (PtAu) nanocatalyst with controlled morphology and composition. The catalyst is further treated by calcination under controlled temperature and atmosphere. The morphology of the bimetallic nanoparticles is determined by transmission electron microscopy. The nanoscale phase properties and surface composition are carried out by X-ray diffraction and X-ray photoelectron spectroscopy. Cyclic voltammetry measurements demonstrated that the catalytic activity is highly dependent on the nanoscale evolution of alloying and phase segregation. The mass activity of as-prepared Pt50Au50/C with 600 °C treatment temperature is about 11 times higher than that of commercial Pt/C. Stability tests showed no obvious loss of activity after 500 potential cycles. The high activity and stability are attributed to lattice contraction effect as a result of the high thermal treatment condition. Our findings demonstrate the importance of phase segregation at the nanoscale in harnessing the true electrocatalytic potential of bimetallic nanoparticles.

Amaranth protein films prepared with high-pressure treated proteins

This work studies the effect of using high-pressure modified amaranth proteins in the preparation of edible film and compares the efficiency of high pressure and thermal treatment on the functionality of amaranth protein films. This films were prepared by casting using glycerol as plasticizer from protein dispersions submitted to high pressure treatments of different intensity (0.1, 200, 400 and 600MPa). Protein dispersions treated with high-pressure were able to form uniform films with better mechanical properties, lower water solubility and water vapor permeability than those prepared from non-treated protein dispersions without modifying its thickness, color and water content, but somewhat more opaque. This could be attributed to structural changes by high-pressure treatment, which favored protein unfolding, increasing protein surface hydrophobicity and the amount of free SH, that were re-associated during film formation producing a higher crosslinking of matrixes that was denoted in a better functionality of films. These films also showed better properties than those prepared with amaranth protein isolates thermally treated.

Effect of high pressure processing and thermal treatment on quality of hilsa (Tenualosa ilisha) fillets during refrigerated storage

Abstract The effect of high pressure processing (250 and 350 MPa for 10 min) and thermal treatment (75 °C for 5 min) on microbiological, physical and biochemical quality of hilsa fillets during refrigeration storage was studied. Thermally treated and the samples at 350 MPa showed higher L* and b* values with lower a* values compared to both control and samples treated at 250 MPa. Trimethylamine nitrogen levels rose over the storage period but did not exceed the critical limit for both pressure and thermally treated samples. High pressure treatments promoted texture improvement and reduced the samples susceptibility to oxidation Pressurization of 350 MPa effectively prevented lipid hydrolysis. The treated samples maintained lower viable counts throughout the storage, thus having better microbial quality than untreated sample. Pressure treatment of 350 MPa was found to be most effective in preserving the quality and extending the shelf life of hilsa fillets for > 25 days compared to 10 days in raw samples. Industrial relevance Hilsa is a high value commodity with persistent demand in seafood market. But it is highly perishable with limited shelf life. High pressure processed hilsa fillets showed better quality attributes (texture, FFA, lipid oxidation) and extended shelf life compared to thermal treatment. Thus, high pressure processing is potentially more suitable processing method than thermal treatment.

Storage Stability of Chinese Bayberry Juice after High Pressure or Thermal Treatment

The effect of high pressure (HP) and thermal (TP) treatments on storage stability of Chinese bayberry juice was investigated. Samples were treated for 5 min at 500 MPa (HP treatment) at room temperature or in a water bath (TP treatment) at 55C for an effective time of 8 min and stored at 4 and 25C. The soluble solids content of the HP- and TP-treated samples was stable at both temperatures, while it decreased at 25C in control samples. Color retention was better in the HP-treated samples than in TP-treated samples. Anthocyanin retention values in the HP- and TP-treated samples were 96.5 and 85.1%, respectively, while ascorbic acid retention values were 89.2 and 58.3%, respectively. Anthocyanin and ascorbic acid degradation during storage followed a first-order kinetics, and the rate constants were lowest for the HP-treated samples followed by TP treatment and were highest for the control samples. Practical Applications Chinese bayberries (Myrica rubra Sieb. et Zucc.) are highly susceptible to mechanical injury and microbiological spoilage, which limits their postharvest life even at refrigerated conditions. Extraction of bayberries to juice followed by thermal treatment is a practical process for shelf life extension. The juice has a strong antioxidant capacity because of its anthocyanin, phenolic and ascorbic acid contents. Consumption of fruit and vegetable juices containing anthocyanins and ascorbic acid can contribute to reducing the severity of various degenerative diseases. However, anthocyanins and ascorbic acid are very sensitive to heat. Thermal processing may cause detrimental quality changes. High pressure processing is one of the promising novel nonthermal techniques with potential for better retention of color, flavor and nutritional parameters of food. Our study showed that high pressure treatment was more efficient in preserving some physicochemical properties of Chinese bayberry juice as compared to thermal treatment. This work provides relevant information for further study of Chinese bayberry juice.

Effects of combined high pressure and thermal treatments on the allergenic potential of shrimp (Litopenaeus vannamei) tropomyosin in a mouse model of allergy

Abstract Crustacean allergy is a significant health problem worldwide, and tropomyosin (TM) is the major allergen found in crustaceans. Therefore, this study aimed to determine whether high pressure and thermal treatments could reduce the allergic properties of TM. Shrimp protein extracts were treated with high pressure and/or thermal treatment, and the allergenicity of TM was analyzed by competitive inhibition enzyme-linked immunosorbent assays using pooled sera from eight patients with shrimp specific IgE. Compared to the boiling treatment, a reduction with 73.59% in immunoglobulin E (IgE) binding was observed when the samples were treated at 55 °C, 500 MPa for 10 min. Furthermore, in a BALB/c mouse model of allergy, significant reductions in specific IgE titers were observed in mice fed with TM treated with high pressure and heat (TMH), accompanied by reduced histamine levels in serum. Similarly, real-time reverse transcription polymerase chain reaction revealed the decrease in mRNAs encoding interferon-γ, interleukin (IL)-4, and IL-10 in jejunum tissues. TMH had almost no allergenicity in the BALB/c mouse model of TM allergy. Industrial relevance High hydrostatic pressure (HHP) processing can inactivate microorganisms and enzymes, leaving sensory and nutritional quality almost unchanged. Furthermore, HHP could alter allergen conformation and hence decrease allergenic activity in rice, fish, milk and celery that were reported. As a health concern, shrimp allergies have been studied in this work. This study was conducted to determine whether high pressure and heat could reduce the allergic properties of shrimp allergen tropomyosin (TM). In addition, the effects on the allergenicity of TM treated with high pressure and heat (TMH) were characterized using a BALB/c mouse model of allergy. The results showed that TMH has great potential for industrialization to eliminate or decrease allergenicity of food protein.

Alteration of antioxidative properties of longan flower-honey after high pressure, ultra-sonic and thermal processing

Abstract This work evaluated the effect of high hydrostatic pressure (300–500 MPa/25 °C/5–20 min), ultra-sonic (20–60% amplitude/20 kHz/5–20 min) and thermal (50–100 °C/1–5 min) processing on phenolic contents and antioxidant capacities of honey from the longan flower. Total phenolic compounds, total flavonoids and antioxidant capacity (DPPH and FRAP assays) were determined. It was found that high pressure, ultra-sonic and thermal treatments had a significant effect on antioxidative properties of honey sample. After pressurization, the quantities of total phenols, flavonoids and antioxidant capacity in honey significantly increased with the increasing pressure levels and processing times, in particular samples pressurized at 500 MPa for 20 min. Similarly, these bioactive compounds in honey samples processed by ultra-sonication were also enhanced when the amplitude levels and treatment times increased. For thermal treatments at 50 and 70 °C, all antioxidative constituents had no significant differences when compared to the control, while the sample heated at 100 °C contained the lowest levels of phenols and antioxidant capacity. Therefore, both high pressure and ultra-sonic processing are an alternative technique to preserve the antioxidative qualities of longan flower-honey, while also not affecting the nutritional values.

Quality changes in high pressure processed ginger paste under refrigerated storage

Abstract This investigation was carried out to evaluate quality changes in ginger paste followed by high hydrostatic pressure and thermal treatment during 6 months of storage at 6±1 °C. Ginger samples were washed in water, peeled manually and pulverized in the form of smooth paste and were mixed with ascorbic (100 mg kg −1 ) and citric (100 mg kg −1 ) acids and subsequently packed in polyethylene pouches (25 μm thickness, 50 g pack size). The pastes were processed in an isostatic high pressure system at a pressure of 200, 400 and 600 MPa at 30 °C for 5 min. The high pressure and thermal treated samples were analyzed for various physico-chemical, enzymatic, sensory and microbiological parameters. The pH and titratable acidity were not significantly ( p E ), showed that there were significant differences ( p

Scaling of correlation length in lamellae forming PS-b-PMMA thin films upon high temperature rapid thermal treatments

Highly ordered lamellar grains were produced by thermal treatment of the samples in a rapid thermal processing machine. The processing parameters that maximize the lateral order avoiding any degradation of the macromolecules were identified.

Transient analysis of heat and mass transfer during heat treatment of wood including pressure equation

In the present paper, three-dimensional equations for coupled heat and mass conservation equations for wood are solved to study the transient heat and mass transfer during high thermal treatment of wood. The model is based on Luikov’s approach, including pressure. The model equations are solved numerically by the commercial package FEMLfor the temperature and moisture content histories under different treatment conditions. The simulation of the proposed conjugate problem allows the assessment of the effect of the heat and mass transfer within wood. A parametric study was also carried out to determine the effects of several parameters such as initial moisture content and the sample thickness on the temperature, pressure and moisture content distributions within the samples during heat treatment.

Effect of high pressure processing and thermal treatment on physicochemical parameters, antioxidant activity and volatile compounds of green asparagus juice

This study was conducted to investigate the effect of high pressure processing (HPP) at different pressures (200, 400 and 600 MPa) and treatment times (10 and 20 min) on microbial population, physicochemical parameters, bioactive compounds, total antioxidant activity and volatile compounds in green asparagus juice, in comparison with thermal processing (121 °C/3 min) and control (no treatment). The results indicated that HPP at 400 and 600 MPa for both treatment times decreased the total mesophilic bacteria to undetectable level as the thermal treatment did, thus ensuring the safety of asparagus juice. The pH value and soluble solids content of asparagus juice were not significantly affected by HPP treatments as compared to thermal processing and control. However, all HPP treatments retained significantly more ascorbic acid, rutin and total phenolic contents and higher total antioxidant activity than thermal treatment. The main volatile compounds in asparagus juice were aldehydes, alcohols and ketones. HPP treatments maintained significantly higher concentrations of aldehydes, alcohols and ketones than thermal treatment. These results suggest that HPP could be an effective alternative to conventional thermal processing for production of high quality green asparagus juice.

Comparison of volumetric and surface decontamination techniques for innovative processing of mealworm larvae (Tenebrio molitor)

Abstract For food and feed safety of edible insects, effective decontamination methods need to be evaluated and developed. Traditional decontamination and preparation methods were reviewed and thermal and innovative inactivation methods for the decontamination of mealworm larvae were evaluated and compared. The impact of the surface decontamination techniques direct and indirect plasma treatment, and of volumetric methods such as high hydrostatic pressure treatment (400, 500, and 600 MPa) and thermal treatments (45 °C and 90 °C) for up to 15 min on the surface microbial load and on the overall microbial count of mealworm larvae ( Tenebrio molitor ) have been investigated. It was found that the indirect plasma treatment was an effective means for the surface decontamination of mealworm larvae, whereas high hydrostatic pressure at 600 MPa and thermal treatments in a water bath at 90 °C in comparison resulted in the highest reduction of the overall count. It is thus concluded that volumetric methods are favorable for the inactivation of the gut microbiota of insects. Industrial relevance Edible insects represent a valuable alternative protein source that could contribute to food and feed security and are industrially mainly unexploited. For a successful marketing of edible insects food and feed safety has to be ensured and effective decontamination methods need to be developed.

Effect of a different high pressure thermal processing compared to a traditional thermal treatment on a red flesh and peel plum purée

Abstract The effect of the application of different high pressure thermal (HPT) treatments on the instrumental color, the activity of the polyphenoloxidase (PPO) enzyme, bioactive compounds (total polyphenols and anthocyanins) content and the antioxidant activity were was evaluated after processing a red flesh and peel plum puree and compared to an equivalent thermal treatment (TT). Different pressure levels (300, 600, and 900 MPa) at different initial processing temperatures (60, 70, and 80 °C) were applied. HPT treatments produced a similar inactivation of the PPO as the TT (~ 50%). In addition, HPT treatment was more effective than the TT in preserving the original colour, the anthocyanins content and the antioxidant activity of the processed purees. The application of pressures at 600 MPa combined with initial temperatures of 70 °C was the treatment which gave the highest inactivation of the PPO and best maintained the bioactive compounds of purees. Industrial relevance The exploration of new technologies, such as the combination of pressure and heating for short times (high pressure thermal or HPT treatments), could be a new way to extend the shelf-life of fruit-derived products. HPT treatments can better preserve bioactive compared to most traditional thermal treatment. While there are currently no HPT-processed shelf-stable foods commercially available, it's possible to provide a viable process for heat-sensitive products such as fruit-derived products that would suffer a severe loss of quality by the application of a traditional thermal process. A previous study (Gonzalez-Cebrino et al., 2013) showed that high pressure processing (HPP) did not inactivate polyphenoloxidase enzyme in plum puree. Results of this paper could allow production of a plum puree with an enzyme activity similar to a thermally treated puree.

(Ultra) high pressure homogenization for continuous high pressure sterilization of pumpable foods - a review.

Bacterial spores have a strong resistance to both chemical and physical hurdles and create a risk for the food industry, which has been tackled by applying high thermal intensity treatments to sterilize food. These strong thermal treatments lead to a reduction of the organoleptic and nutritional properties of food and alternatives are actively searched for. Innovative hurdles offer an alternative to inactivate bacterial spores. In particular, recent technological developments have enabled a new generation of high pressure homogenizer working at pressures up to 400 MPa and thus, opening new opportunities for high pressure sterilization of foods. In this short review, we summarize the work conducted on (ultra) high pressure homogenization (U)HPH to inactivate endospores in model and food systems. Specific attention is given to process parameters (pressure, inlet, and valve temperatures). This review gathers the current state of the art and underlines the potential of UHPH sterilization of pumpable foods while highlighting the needs for future work.

Physical and electrical characterization of TiO2 particles after high temperature processing and before and after ultraviolet irradiation

In this work, rutile-phase TiO2 particles (r-TiO2, about 360 nm in size) are embedded within a silicon oxide matrix using different concentration ratios of r-TiO2 with respect to SiO2:H2O, so that suspensions of mixed TiO2:SiO2 oxides were obtained and analyzed. These TiO2:SiO2 suspensions were deposited on previously-cleaned crystalline silicon and quartz substrates so that thin films of TiO2:SiO2 were obtained. All films were then exposed to relatively high-temperature thermal treatments in nitrogen and different characterization techniques were used to determine their physical and electrical properties before and after ultraviolet (UV) irradiation. Before high thermal treatment, X-ray diffraction patterns show that the main diffraction peaks for the obtained TiO2:SiO2 films correspond to the crystalline phase of rutile-TiO2. Infrared analyses before and after thermal treatment show significant changes in the chemical bonding of the final films relative to the temperatures used during annealing. Also, UV–visible spectra provide a constant optical band gap for the films, independent of different TiO2 concentrations as expected. On the other hand, atomic-force microscopy measurements before and after UV irradiation show an appreciable difference in the grain size and surface morphology of the resulting TiO2:SiO2 oxides annealed at 1000 °C. Finally, photoelectrical I–V properties were obtained for all TiO2:SiO2 films by depositing ultrathin titanium stripes on top of the photoactive material and then, measuring the total current flowing through the metal electrode before and after UV irradiation. From these last measurements, a detectable increase in the I–V slope (lower resistance of the titanium stripe) is found for all samples during UV exposure, thus making this device to act as a simple photoresistor based on r-TiO2 particles.

A Highly Stable and Active CaO/Al2O3 Base Catalyst in the Form of Calcium Aluminate Phase for Oxidation of Cyclohexanone to ε-Caprolactone

A series of CaO/Al2O3 base catalysts with different crystal phases is prepared via thermal treatment. The as-prepared base catalysts are tested through Baeyer–Villiger oxidation of cyclohexanone to e-caprolactone in liquid-phase using a mixture of aqueous hydrogen peroxide and benzonitrile as oxidant. The corresponding results show that the CaO/Al2O3 catalysts with high thermal treatment temperature (e.g. 900 °C) exhibit excellent activity as well as stability. Upon these, the catalysts are characterized by TG–DTG, XRD, N2-physisorption, SEM and CO2-TPD techniques. The characterization results clearly suggest that such a stable and efficient catalytic performance is beneficial from the formation of calcium aluminate phase, thus overcoming one of base catalyst application barriers, that Ca or CaO species loss (leach) from CaO-based catalysts during reactions. Correspondingly, it can be inferred that the treatment of the catalysts at different temperatures results in the diverse distribution of basic strength. Furthermore, it is also demonstrated that the suitable base strength (medium strength is good for the reaction selected in the work) plays a critically role in the improvement of catalytic performance. Finally, the effects of operation conditions on catalytic activity and product selectivity are also determined and discussed.

Optimisation of parameters for dynamic surface annealing of silicon wafers

Dynamic surface annealing for high temperature rapid thermal treatment of silicon wafer is an important technology in semiconductor industries. In this study, we proposed using a L9 orthogonal array to obtain the optimisation of parameters for dynamic surface annealing of silicon wafers. Base on the analysis of variance results, the optimisation of parameters for dynamic surface annealing were laser scanning speed of 250 mm s−1, energy output of 60%. Meanwhile temperature should be kept at 250°C heating and preheating time was 35 s. According on nominal-the-best analysis, this study calculated the expected resistance, which was 606·879 Ω/sq. After test and verification, the resistance was determined to be 611·057 Ω/sq and deviation of resistance was only less than 0·1%.

On the generation of bulk microdefects in phosphorus-diffused monocrystalline silicon solar wafers after a high-thermal treatment studied by X-ray topography

Oxygen is the most important impurity in free dislocation Czochralski silicon single crystals incorporated interstitially during the growth. The knowledge of oxygen behavior after thermal processes is of great technological importance, since different kinds of bulk microdefects such us SiO2 precipitates, dislocation loops and stacking faults can be generated. In monocrystalline silicon solar cell manufacturing fabrication, there are several high-thermal treatments. The first is the diffusion process at 850–900 °C. Three different kinds of phosphorus diffusion wafers, standard PO3Cl liquid, spray-on and screen printing, were comparatively studied by X-ray topography showing that phosphorus diffusion improves the crystal quality by a gettering process whose best efficiency is in PO3Cl-diffused wafers. Later, another fabrication high-thermal step is for instance the rear surface passivation taking place at temperatures from 800 to 1,050 °C. For this reason, it is important to study how a high-thermal treatment at 1,000 °C affects the different phosphorus-diffused wafers mentioned above. To evaluate and characterize the possible defects induced by the oxygen precipitation, X-ray topography has been employed. Results show that annealed wafers are not perfect crystals; the oxygen precipitation induces the generation of bulk microdefects whose kind, size and density depend on the diffusion method employed. In PO3Cl and spray-on diffused wafers, retardation in the oxygen precipitation process takes place after annealing, while in screen printing this process is recovered and a kind of mixed defects between dislocation loops and platelet precipitates is generated.