High Pressure Thermal Treatment Research Articles

Overcoming strength-ductility tradeoff with high pressure thermal treatment

Conventional material processing approaches often achieve strengthening of materials at the cost of reduced ductility. Here, we show that high-pressure and high-temperature (HPHT) treatment can help overcome the strength-ductility trade-off in structural materials. We report an initially strong-yet-brittle eutectic high entropy alloy simultaneously doubling its strength to 1150 MPa and its tensile ductility to 36% after the HPHT treatment. Such strength-ductility synergy is attributed to the HPHT-induced formation of a hierarchically patterned microstructure with coherent interfaces, which promotes multiple deformation mechanisms, including dislocations, stacking faults, microbands and deformation twins, at multiple length scales. More importantly, the HPHT-induced microstructure helps relieve stress concentration at the interfaces, thereby arresting interfacial cracking commonly observed in traditional eutectic high entropy alloys. These findings suggest a new direction of research in employing HPHT techniques to help develop next generation structural materials.

Inactivation of Bacillus subtilis spores by a combination of high-pressure thermal treatment and potassium sorbate

Combining High-pressure Thermal Treatment (HPTT) and Potassium Sorbate (PS) may have a stronger spore inactivation effect. Spores of Bacillus subtilis were subjected to HPTT at 600 MPa-65 °C/75 °C and a combination of HPTT and PS of 0.1% and 0.2% concentrations. After these treatments, different procedures and techniques were employed to investigate the spore's inactivation. The results revealed that 4.92 ± 0.05 log spores were inactivated after treatment at 600 MPa-75 °C, while 5.97 ± 0.09 log spores were inactivated when the HPTT treatment was combined with 0.2% PS. Changes in permeability of the spore's inner membrane were characterized by OD600 value and release rates of nucleic acids, protein, and dipicolinic acid (DPA). Compared with HPTT treatment at 600 MPa-75 °C, the OD600 value of spores decreased further by about 50% after treatment with a combination of HPTT and 0.2% PS. Additionally, the combined treatments resulted in a significant increase in the OD260 and OD280 values, as well as the DPA release. The spore size analysis indicated a significant decrease in the size of spores treated with a combination of HPTT at 600 MPa-75 °C and PS of 0.2% concentration. Furthermore, the flow cytometry analysis and confocal laser scanning microscopy (CLSM) analysis indicated that the inner membrane damage of spores was higher after combined treatments than that after HPTT treatment alone. A significant reduction was also found in the Na+/K+-ATPase activity after the combined treatments. Also, the FTIR analysis revealed that the combined treatments resulted in significant adverse changes in the spores' inner membrane, cell wall, cortex, and nucleic acid. Therefore, the combination of HPTT and PS has a stronger inactivation effect and can be suggested as a promising strategy for the inactivation of Bacillus subtilis spores.

Effect of oven roasting on major chemical components in cereals and its modulation on flour-based products quality.

Oven roasting (OR) could induce hierarchical structural changes in starch, which is fundamental for altering the pasting and hydration properties of cereal flour. OR makes proteins denatured and peptide chains unraveled or rearranged. OR could alter compositions of cereal lipids and minerals. Although OR may degrade phenolics, their release from bound forms is predominant when mild/moderate conditions are exerted. Hence, some OR-modified cereals even exhibit many physiological functions, such as anti-diabetic and anti-inflammatory activity. Furthermore, these minor components interplay with starch/protein via physical entrapment, non-covalent interactions, or cross-linking. The structural changes and interactions modulate functionalities of OR-modified cereal flour, its dough/batter property, and related staple food quality. Compared with hydrothermal or high-pressure thermal treatments, proper OR even induces greater enhancement in technological quality and bioactive compounds release. Given the simple operation and low cost, it is worth utilizing OR for the development of sensory-appealing healthy staple foods.

Effects of High Pressure Processing and Thermal Treatment on the Interaction between α-Lactalbumin and Pelargonium-3-Glucoside.

In this study, high pressure processing (HPP) and thermal treatment were comparatively evaluated by examining their impacts on the binding behavior and interaction between α-lactalbumin (α-La) and pelargonium-3-glucoside (P3G) under pH values of 6.0, 7.4, and 8.0. The methods of circular dichroism spectroscopy, fluorescence quenching, dynamic light scattering, and molecular simulation were used to characterize the effects of processing-induced changes in protein structure, size distribution, binding site conformation, and residue charges on their binding characteristics between them. The results indicated that the thermal treatments significantly increased the quenching constants of the complex at pH 7.4/8.0 and 60/80 °C, as well as the accessible fraction of protein at pH 8.0/80 °C. Both HPP and thermal treatments increased the random coil content and showed limited effects on the α-helix and β-sheet contents of α-La and caused the aggregation of the complex to varying degrees. Molecular dynamic simulation and docking analyses revealed that the binding site of the complex did not change under different processing conditions, but the solvent-accessible surface area varied under different conditions.

Influence of water activity and acidity on Bacillus cereus spore inactivation during combined high pressure-thermal treatment

Understanding the inactivation kinetics of bacterial spores during combined pressure-thermal processing is essential for process design. The knowledge on the influence of pH and water activity (aw) during combined pressure-thermal treatment is limited. Experiments were conducted using Bacillus cereus spores suspended in citrate-phosphate buffers, adjusted to different levels of pH (3.8–7.3) and aw (0.80–0.99). Spores were then treated with a pressure-heat combination (600 MPa, 70 °C) using a laboratory-scale high-pressure kinetic tester. Linear regression and Weibull models were used to fit the experimental data. The kinetic parameters of the spores inactivation estimated from the models were plotted as a function of pH and aw. Results showed that the inactivation kinetic curves were characterized by tailing, particularly at low aw levels. The log reduction of B. cereus spores decreased with the decrease of aw. During pressure-thermal treatment, the changes in acidity values for a given water activity have limited influence on decimal reduction values of the spores. Study findings will be helpful for designing pressure-thermal processes to produce microbially safe products with varying water activity and acidity levels.

Effect of high pressure processing and heat treatment on the gelation properties of blue crab meat proteins

This study was carried out to evaluate the effect of high pressure processing (HPP) and thermal treatments on the gelling properties of proteins from blue crab meat. Crabmeat was pressurized at 100, 300, and 500 MPa (10 °C/5 min) with and without heating (90 °C/20 min) after the HPP treatment. Treated samples were analyzed by protein interactions, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and dynamic rheometry. Protein gelation after pressurization was based on physical interactions which were modified after HPP treatment; meanwhile, thermal gelation was based mainly on the formation of covalent bonds. DSC showed that pressure levels over 300 MPa reduced myosin denaturation temperature indicating protein unfolding. HPP treatment at 100 MPa led to a partial protein denaturation effect. FTIR results showed a reduction in the fraction of α-helix structure along with a development of β-sheet portion as a result of protein denaturation promoted by the application of pressure. The sweep temperature analysis indicated that the combination of treatments stabilized the protein network in the gels from blue crab meat. The combination of pressure (100 MPa) and heat (90 °C) treatments allowed obtaining gels from crabmeat proteins with optimal rheological properties.

High pressure processing (HPP) improved safety and quality of emerging aronia berry juice: a pilot scale shelf-life study.

The effect of high pressure processing (HPP, 600MPa, 5min) and thermal treatment (85°C, 15min) on aronia berry juice in a pilot scale was studied. The maximal shelf-life of treated samples at room temperature (RT, approximately 25°C) or refrigerated storage (RS, 4°C) was also investigated. Microbial counts, physicochemical properties, enzymes activities, phenolic compounds, and antioxidant activities of these juices were determined and compared. Results indicated that HPP treatment improved the microbial shelf-life of the aronia juice by at least 10-times at RT and 5-times at RS. Although thermal treatment was equally effective in extending the shelf-life, the high temperature resulted in a quicker degradation of polyphenols in aronia juice, which was decreased by 36.6% during RT storage (5weeks) and 43.3% at RS storage (24weeks). Therefore, HPP was more efficient in maintaining the safety and quality of aronia juice. The study also indicated HPP treated aronia juice could be stored at RT for at least one month that could be of benefit to the non-cold chain process which is targeting for a low-energy input while still retaining a minimal effect on the nutritional properties of food products.

Immunological components and antioxidant activity in human milk processed by different high pressure-thermal treatments at low initial temperature and flash holding times

The effect of high pressure thermal (HPT) processing on the immunoglobulin (IgM, IgA and IgG), and cytokine content (IL-6, IL-8, IL-10, and TNF-α), and antioxidant activity of human milk was analyzed after the application of different treatments between 200, and 800 MPa at low initial temperatures (between −15, and 50 °C) and for 1 s (flash treatments). Low pressures intensities did not induce changes in Igs while at 800 MPa, all combinations reduced the control levels. IL-6 and IL-10 were not affected by any of the treatments applied while IL-8 and TNF-α were reduced at treatments which combined temperatures at 50 °C. In general antioxidant activity was not affected at the processing conditions chosen. The flash HPT treatment applied at 600 MPa and at 0 °C could be the best choice to preserve immunological parameters and the antioxidant activity of human milk.

Thyme Antimicrobial Effect in Edible Films with High Pressure Thermally Treated Whey Protein Concentrate.

Application of high pressure-thermal treatment (600 MPa and 70 °C, 20 min) for obtaining edible films functionalized with thyme extracts have been studied in order to evaluate the antimicrobial capacity of films structure to retain and release the bioactive compounds. The high pressure-thermally treated films (HPT) were compared with the thermally treated (TT) ones (80 ± 0.5 °C, 35 min). The film structures were analyzed and the sorption isotherms, water vapor permeability, antimicrobial activity and the volatile fingerprints by GC/MS were performed. The HPT film presented more binding sites for water chemi-sorption than TT films and displayed significantly lower WVP than TT films (p < 0.05). TT films displayed slightly, but significant higher, antimicrobial activity (p < 0.05) against Geotrichum candidum in the first day and against Bacillus subtilis in the 10th day of storage. The HPT film structure had ~1.5-fold higher capacity to retain volatiles after drying compared to TT films. From the HPT films higher amount of p-cymene and α-terpinene was volatilized during 10 days of storage at 25 °C, 50% RH while from the TT films higher amount of caryophyllene and carvacrol were released. During storage HPT films had a 2-fold lower capacity to retain monoterpenes compared to TT films.

Preference-based multi-objectivization applied to decision support for High-Pressure Thermal processes in food treatment

Food industry aims to provide healthy products that must satisfy the quality requirements of the considered legislation. To do so, food is treated by using some processing techniques, such as High-Pressure Thermal (HPT) treatments. In this work, we propose a preference-based multi-objectivization methodology to design HPT processes for food treatment. This approach is based on formulating a multi-objective optimization problem, instead of a constrained mono-objective problem, where the constraints are reformulated as separate objective functions. The multi-objective problem is then solved by using preference-based evolutionary optimization algorithms (PMOEAs). PMOEAs focus the search of a numerical solution inside a region of interest defined by the food engineer, avoiding exploring HPT designs that are out of interest. The proposed methodology is validated by considering several particular mono-objective and multi-objective optimization problems related to HPT processing. In particular, we compare the results obtained by two competitive state-of-the-art PMOEAs, called WASF-GA and R-NSGA-II, with the ones returned by a mono-objective algorithm called MLS-GA. As part of this study, the influence of the optimization algorithm parameters on the solutions, their quality and the computing time are discussed. Finally, the best solutions returned by the algorithm that shows a better performance for our problems, which is WASF-GA, are analyzed from a food engineering point of view and a sensitivity analysis regarding the impact of design parameters on the performances of those solutions is carried out.

Physicochemical properties and bioactive compounds of fermented pomegranate juice as affected by high-pressure processing and thermal treatment

ABSTRACT High-pressure processing (HPP) is a novel non-thermal processing technology, ensuring the safety of food products, as well as preserving their nutritional and functional characteristics, and avoiding the harmful effects of traditional thermal technologies. This study examined the inactivation of microorganisms and the HPP kinetic model in fermented pomegranate juice (FPJ) at different pressures (400 MPa, 500 MPa, and 600 MPa), and different treatment times (3 min, 5 min, 7 min, and 10 min). Moreover, HPP and thermal processing (TP) (65 °C/20 min) treatment responsible for a similar microbial inactivation activity, were compared by examining their impact on bioactive compounds, volatile compounds, and various quality attributes to provide a theoretical basis for FPJ processing. The inactivation curves of the microorganisms as a result of HPP were fitted using the Weibull model. Furthermore, HPP at or over 600 MPa/3 min inactivated the microorganisms and sufficiently retained the microbial populations investigated in this study below the detection limit. Following HPP and TP treatment, the total color difference (ΔE) values, total soluble solids (TSS), pH and titratable acidity (TA) had not significantly (p>0.05) changed. For total flavonoids, total phenols, anthocyanins, and antioxidant activity, the maximal retention of 91.18%, 97.52%, 95.69%, and 95.89% was achieved at 600 MPa/3 min, which was 4.62%, 24.61%, 26.83%, and 7.08% higher than in the TP-treated sample. The main volatile compounds in FPJ were esters and alcohols, and the FPJ treated at 600 MPa/3 min exhibited the highest alcohol content, while the esters were 2.27% higher than in the control. Considering the pasteurization effect and quality maintenance abilities of HPP and TP treatment, 600 MPa/3 min could be considered as an optimal condition in facilitating FPJ processing.

Inactivation of non-proteolytic Clostridium botulinum type E in low-acid foods and phosphate buffer by heat and pressure.

The effect of high pressure thermal (HPT) treatments on the inactivation of spores of non-proteolytic type E Clostridium botulinum TMW 2.990 was investigated at high pressures (300 to 600 MPa) and elevated temperatures (80 to 100 °C) in four low-acid foods (steamed sole, green peas with ham, vegetable soup, braised veal) and imidazole phosphate buffer (IPB). In addition, corresponding conventional thermal treatments at ambient pressure were performed to expose possible synergisms of pressure and temperature on spore inactivation. In general, spore count reduction was more efficient by combining pressure and temperatures < 100 °C and the overall process duration could be shortened due to accelerated heating rates (adiabatic effect). Processing at 90 °C and 600 MPa resulted in inactivation below the detection limit after 5 min in all foods except steamed sole. Traditional thermal processing of spores at 90 °C for 10 min, on the other hand, did not result in an estimated 6-log reduction. Additional HPT treatments in steamed sole and IPB did not reveal pronounced food matrix dependent protective effects. Here, varying pressure levels did not appear to be the driving force for spore count reduction in steamed sole at any temperature. By applying a Weibull distribution on destruction kinetics of isobaric/isothermal holding times, 6D-values were calculated. Compression and decompression phase (1 s pressure holding time) had a considerable impact on spore count reduction (max. -2.9 log units) in both, foods and buffer. Hence, compression and decompression phases should directly be included into the total lethal effect of HPT treatments to avoid prolonged holding times and overprocessing.

Characterization of thermal, mechanical and hydration properties of novel films based on Saccharomyces cerevisiae biomass

Abstract Characterization of films made of Saccharomyces cerevisiae biomass was performed so as to better understand their properties. The treated yeast biomass, named HTH, was prepared by subsequent steps including a first homogenization, heat treatment and final homogenization. Glycerol was added as plasticizer and films were evaluated using different techniques to measure mechanical behaviour, thermal properties and water sorption. Temperature of maximum decomposition rate was found near 300 °C, while the gradually disappearance of amide II band (1543 cm−1) occurred from 225 °C, identified by FTIR spectra of residues of thermally treated films by TGA. A glass transition at 64.5 ± 3.0 °C and two low energy endotherms at 61.2 ± 2.3 and 106.1 ± 0.7 °C were determined in completely dehydrated films without glycerol. When glycerol content was increased the glass transition temperature was shifted to lower values, a maximum elongation of 12% was reached, Young's modulus decreased from 88 to 9 MPa and the water uptake of films raised from 0.49 to 0.79 g H2O/g of dry matter. The characterization of yeast biodegradable films provided evidence of their properties for a potential future use in packaging industry. Industrial relevance The development of biodegradable films based on yeast biomass carries many advantages to the food industry, such as, the possibility of using commercial pressed baker's yeast or an industrial residue from brewing industry, the use of a low-cost sources and the application of environmentally friendly procedures. The methodologies applied for the development of the film forming dispersion, high pressure homogenization and thermal treatment, are able to be scaled-up to an industrial level.

High-performance computing for the optimization of high-pressure thermal treatments in food industry

In food industry, the combined treatments based on high-pressure and temperature (HPT) are frequently used to increase the durability of the products without damaging their organoleptic and nutritional properties. However, achieving a reasonable compromise between conservation and quality is usually a challenging task. In a previous work, we proposed a decision tool which solves a multi-objective optimization problem providing a set of pressure and temperature configurations for the HPT equipment in order to adapt the final product to different quality scenarios. The considered optimizer is a population-based evolutionary algorithm that takes the decision maker preferences into account. Nevertheless, when the number of solutions demanded by the decision maker is very large or a high precision is required, the computational time needed by such an algorithm may not be negligible at all. In this work, a parallel version of the optimizer has been designed. This parallel algorithm allows obtaining a greater number of solutions by working with more individuals in the population due to the significant reduction in the total execution time (up to 95.6%). Additionally, using it, we can consider more iterations in the optimization process that lead us to better distributed and more accurate solutions. The computational experiments show that the performance of the proposed method is scalable and its speedup is almost linear.

Optical investigations of europium ion implanted in nitride-based diode structures

AlGaN/GaN-superlattice based diode structures under study were grown by metal organic chemical vapour deposition, then implanted with two different Eu ion beam fluences, and further submitted to high temperature and high pressure thermal annealing treatments. The effects of Eu implantation and annealing on the diode structure emission characteristics were investigated at 14 K and room temperature. Eu3+ luminescence was observed in both Eu-implanted and annealed samples, being the most intense emission assigned to the 5D0 → 7F2 transition in the red spectral region (~621 nm), in line with the main observed behaviour of Eu3+ ions implanted in GaN layers. The combined excitation/emission spectra revealed that the measured intraionic emission corresponds to an overlap of two principal emitting centres which can be excited through above and below GaN bandgap. In addition, a considerable reduction of the non-radiative channels was observed for the diode structure implanted with the highest Eu fluence, inducing a higher thermal stability of the intra-4f6 lines intensity. In contrast to GaN layers, the perceived Eu3+ red emission observed at room temperature was found to be strongly sensitive to the GaN above bandgap excitation (out of the resonance conditions) suggesting that additional energy transfer between the AlGaN/GaN superlattice excitons and the Eu3+ ions occurs, therefore widening the excitation pathways for the red luminescence.

Differences in the resistance of microbial spores to thermosonication, high pressure thermal processing and thermal treatment alone

Bacterial and fungal spores can survive pasteurization treatments, and germinate/grow after food processing, causing food spoilage and/or outbreaks. High pressure processing (HPP) and power ultrasound technologies can be combined with heat (HPP-thermal or HPTP, TS) to increase the rate of spore inactivation. In this study, the differences in the resistance of bacterial and mould spores of several microbial species to thermal, 600 MPa HPP-thermal, and TS (0.33 W/mL or g) treatments were investigated. Thermal processes in the range of 70–78 °C almost did not affect the five microbial species’ spores tested (<1 log after 40 min). On the contrary, 600 MPa-75 °C HPP treatment reduced all microbial spores (2.8 to >5.8 log after 40 min): C. perfringens presented the highest resistance, followed by B. nivea and N. fischeri moulds, and lastly B. cereus. TS treatments (70–75 °C) up to 60 min had almost no effect on A. acidoterrestris and C. perfringens, while B. cereus in beef slurry was readily inactivated (6 log after 2 min). Activation shoulders were registered for both moulds. As opposed to HPP-thermal and thermal treatments, the type of food had a significant effect in the spore inactivation by TS.

Non-linear pressure/temperature-dependence of high pressure thermal inactivation of proteolytic Clostridium botulinum type B in foods.

The effect of high pressure thermal (HPT) processing on the inactivation of spores of proteolytic type B Clostridium botulinum TMW 2.357 in four differently composed low-acid foods (green peas with ham, steamed sole, vegetable soup, braised veal) was studied in an industrially feasible pressure range and temperatures between 100 and 120°C. Inactivation curves exhibited rapid inactivation during compression and decompression followed by strong tailing effects. The highest inactivation (approx. 6-log cycle reduction) was obtained in braised veal at 600 MPa and 110°C after 300 s pressure-holding time. In general, inactivation curves exhibited similar negative exponential shapes, but maximum achievable inactivation levels were lower in foods with higher fat contents. At high treatment temperatures, spore inactivation was more effective at lower pressure levels (300 vs. 600 MPa), which indicates a non-linear pressure/temperature-dependence of the HPT spore inactivation efficiency. A comparison of spore inactivation levels achievable using HPT treatments versus a conventional heat sterilization treatment (121.1°C, 3 min) illustrates the potential of combining high pressures and temperatures to replace conventional retorting with the possibility to reduce the process temperature or shorten the processing time. Finally, experiments using varying spore inoculation levels suggested the presence of a resistant fraction comprising approximately 0.01% of a spore population as reason for the pronounced tailing effects in survivor curves. The loss of the high resistance properties upon cultivation indicates that those differences develop during sporulation and are not linked to permanent modifications at the genetic level.

Application of innovative technologies, moderate-intensity pulsed electric fields and high-pressure thermal treatment, to preserve and/or improve the bioactive compounds content of pumpkin

Abstract The application of novel technologies such as moderate-intensity pulsed electric fields (MIPEF) and/or high pressure thermal (HPT) treatments improved the quality of processed pumpkin. MIPEF was applied to whole pumpkin in order to increase the bioactive compounds content, in contrast, HPT treatment was applied in order to preserve the purees. Traditional thermal treatment (TT) of pasteurization and sterilization was compared with equivalent HPT treatments. The effect of processing (TT vs. HPT) in purees made from pumpkin pretreated with MIPEF was evaluated. Microbiological counts, enzyme inactivation (polyphenol oxidase, PPO) and bioactive compounds content (carotenoids, phenolic compounds and antioxidant activity) were analyzed in all processed purees. Regarding the pretreatment of the pumpkin, the application of MIPEF increased the content of some bioactive compounds of interest, such as carotenoids. The HPT treatment equivalent to sterilization preserved high levels of carotene compounds and antioxidant activity of pumpkin puree although this treatment importantly modified the original color of puree. However, the HPT treatment equivalent to pasteurization did not inactivate PPO enzyme in contrast to the effect reached by the equivalent TT. The bioactive compounds levels in HPT treated puree were similar or lower than those treated by TT. Industrial relevance Pulsed electric fields and high pressure thermal processing are emerging non-thermal food processing technologies. Moderate-intensity pulsed electric fields (MIPEF) were applied to increase the generation of bioactive compounds in vegetables. This treatment enhanced the carotenoids content in pumpkin. High pressure thermal treatment (applied at conditions equivalent to sterilization) was the method that best preserved pumpkin purees. The application of MIPEF to pumpkin and HPT treatment to the resulting purees could be proposed as a strategy for producing and preserving vegetable products with high bioactive compounds content.

Effect of processing on the bioaccessibility of bioactive compounds – A review focusing on carotenoids, minerals, ascorbic acid, tocopherols and polyphenols

Health benefits of bioactive compounds depend not only on the intake levels but also on their bioavailability (BAv). In vitro methods to simulate gastro-intestinal digestion allow to determine the bioaccessibility (BAcs) of these compounds, as a first step of BAv, and can be used to evaluate the effect of processing on them to design functional foods with increased health-promoting effects. The impact of traditional processing technologies such as thermal treatment and novel emerging non-thermal technologies such as high pressure processing, high-intensity pulsed electric fields and ultrasound on BAcs of bioactive compounds as carotenoids, minerals, ascorbic acid, tocopherols, polyphenols and total antioxidant capacity is described in this review article. In general, combination of high pressure processing and thermal treatment in the presence of oil for carotenoids, thermal treatment for ascorbic acid and polyphenols, and high pressure processing for minerals, tocopherols and total antioxidant capacity would increase BAcs of these bioactive compounds. Ultrasound processing is likely to improve polyphenol compound BAcs and high-intensity pulsed electric fields could improve carotenoid, vitamin C and phenolic compounds BAcs, as well as antioxidant activity. However, general guidelines seem not to be applicable for every case study and more research in this field is needed.

The kinetics study on 5- formyltetrahydrofolic acid degradation and 5,10- methenyltetrahydrofolic acid formation during thermal and combined high pressure thermal treatments

The kinetics study on 5- formyltetrahydrofolic acid degradation and 5,10- methenyltetrahydrofolic acid formation during thermal and combined high pressure thermal treatments